mercurial/crecord.py

wireproto: add streams to frame-based protocol

Previously, the frame-based protocol was just a series of frames,
with each frame associated with a request ID.

In order to scale the protocol, we'll want to enable the use of
compression. While it is possible to enable compression at the
socket/pipe level, this has its disadvantages. The big one is it
undermines the point of frames being standalone, atomic units that
can be read and written: if you add compression above the framing
protocol, you are back to having a stream-based protocol as opposed
to something frame-based.

So in order to preserve frames, compression needs to occur at
the frame payload level.

Compressing each frame's payload individually will limit compression
ratios because the window size of the compressor will be limited
by the max frame size, which is 32-64kb as currently defined. It
will also add CPU overhead, as it is more efficient for compressors
to operate on fewer, larger blocks of data than more, smaller blocks.

So compressing each frame independently is out.

This means we need to compress each frame's payload as if it is part
of a larger stream.

The simplest approach is to have 1 stream per connection. This
could certainly work. However, it has disadvantages (documented below).

We could also have 1 stream per RPC/command invocation. (This is the
model HTTP/2 goes with.) This also has disadvantages.

The main disadvantage to one global stream is that it has the very
real potential to create CPU bottlenecks doing compression. Networks
are only getting faster and the performance of single CPU cores has
been relatively flat. Newer compression formats like zstandard offer
better CPU cycle efficiency than predecessors like zlib. But it still
all too common to saturate your CPU with compression overhead long
before you saturate the network pipe.

The main disadvantage with streams per request is that you can't
reap the benefits of the compression context for multiple requests.
For example, if you send 1000 RPC requests (or HTTP/2 requests for
that matter), the response to each would have its own compression
context. The overall size of the raw responses would be larger because
compression contexts wouldn't be able to reference data from another
request or response.

The approach for streams as implemented in this commit is to support
N streams per connection and for streams to potentially span requests
and responses. As explained by the added internals docs, this
facilitates servers and clients delegating independent streams and
compression to independent threads / CPU cores. This helps alleviate
the CPU bottleneck of compression. This design also allows compression
contexts to be reused across requests/responses. This can result in
improved compression ratios and less overhead for compressors and
decompressors having to build new contexts.

Another feature that was defined was the ability for individual frames
within a stream to declare whether that individual frame's payload
uses the content encoding (read: compression) defined by the stream.
The idea here is that some servers may serve data from a combination
of caches and dynamic resolution. Data coming from caches may be
pre-compressed. We want to facilitate servers being able to essentially
stream bytes from caches to the wire with minimal overhead. Being
able to mix and match with frames are compressed within a stream
enables these types of advanced server functionality.

This commit defines the new streams mechanism. Basic code for
supporting streams in frames has been added. But that code is
seriously lacking and doesn't fully conform to the defined protocol.
For example, we don't close any streams. And support for content
encoding within streams is not yet implemented. The change was
rather invasive and I didn't think it would be reasonable to implement
the entire feature in a single commit.

For the record, I would have loved to reuse an existing multiplexing
protocol to build the new wire protocol on top of. However, I couldn't
find a protocol that offers the performance and scaling characteristics
that I desired. Namely, it should support multiple compression
contexts to facilitate scaling out to multiple CPU cores and
compression contexts should be able to live longer than single RPC
requests. HTTP/2 *almost* fits the bill. But the semantics of HTTP
message exchange state that streams can only live for a single
request-response. We /could/ tunnel on top of HTTP/2 streams and
frames with HEADER and DATA frames. But there's no guarantee that
HTTP/2 libraries and proxies would allow us to use HTTP/2 streams
and frames without the HTTP message exchange semantics defined in
RFC 7540 Section 8. Other RPC protocols like gRPC tunnel are built
on top of HTTP/2 and thus preserve its semantics of stream per
RPC invocation. Even QUIC does this. We could attempt to invent a
higher-level stream that spans HTTP/2 streams. But this would be
violating HTTP/2 because there is no guarantee that HTTP/2 streams
are routed to the same server. The best we can do - which is what
this protocol does - is shoehorn all request and response data into
a single HTTP message and create streams within. At that point, we've
defined a Content-Type in HTTP parlance. It just so happens our
media type can also work as a standalone, stream-based protocol,
without leaning on HTTP or similar protocol.

Differential Revision: https://phab.mercurial-scm.org/D2907

# stuff related specifically to patch manipulation / parsing
#
# Copyright 2008 Mark Edgington <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
#
# This code is based on the Mark Edgington's crecord extension.
# (Itself based on Bryan O'Sullivan's record extension.)

from __future__ import absolute_import

import locale
import os
import re
import signal

from .i18n import _
from . import (
    encoding,
    error,
    patch as patchmod,
    scmutil,
    util,
)
from .utils import (
    stringutil,
)
stringio = util.stringio

# This is required for ncurses to display non-ASCII characters in default user
# locale encoding correctly.  --immerrr
locale.setlocale(locale.LC_ALL, u'')

# patch comments based on the git one
diffhelptext = _("""# To remove '-' lines, make them ' ' lines (context).
# To remove '+' lines, delete them.
# Lines starting with # will be removed from the patch.
""")

hunkhelptext = _("""#
# If the patch applies cleanly, the edited hunk will immediately be
# added to the record list. If it does not apply cleanly, a rejects file
# will be generated. You can use that when you try again. If all lines
# of the hunk are removed, then the edit is aborted and the hunk is left
# unchanged.
""")

patchhelptext = _("""#
# If the patch applies cleanly, the edited patch will immediately
# be finalised. If it does not apply cleanly, rejects files will be
# generated. You can use those when you try again.
""")

try:
    import curses
    curses.error
except ImportError:
    # I have no idea if wcurses works with crecord...
    try:
        import wcurses as curses
        curses.error
    except ImportError:
        # wcurses is not shipped on Windows by default, or python is not
        # compiled with curses
        curses = False

def checkcurses(ui):
    """Return True if the user wants to use curses

    This method returns True if curses is found (and that python is built with
    it) and that the user has the correct flag for the ui.
    """
    return curses and ui.interface("chunkselector") == "curses"

class patchnode(object):
    """abstract class for patch graph nodes
    (i.e. patchroot, header, hunk, hunkline)
    """

    def firstchild(self):
        raise NotImplementedError("method must be implemented by subclass")

    def lastchild(self):
        raise NotImplementedError("method must be implemented by subclass")

    def allchildren(self):
        "Return a list of all of the direct children of this node"
        raise NotImplementedError("method must be implemented by subclass")

    def nextsibling(self):
        """
        Return the closest next item of the same type where there are no items
        of different types between the current item and this closest item.
        If no such item exists, return None.
        """
        raise NotImplementedError("method must be implemented by subclass")

    def prevsibling(self):
        """
        Return the closest previous item of the same type where there are no
        items of different types between the current item and this closest item.
        If no such item exists, return None.
        """
        raise NotImplementedError("method must be implemented by subclass")

    def parentitem(self):
        raise NotImplementedError("method must be implemented by subclass")

    def nextitem(self, skipfolded=True):
        """
        Try to return the next item closest to this item, regardless of item's
        type (header, hunk, or hunkline).

        If skipfolded == True, and the current item is folded, then the child
        items that are hidden due to folding will be skipped when determining
        the next item.

        If it is not possible to get the next item, return None.
        """
        try:
            itemfolded = self.folded
        except AttributeError:
            itemfolded = False
        if skipfolded and itemfolded:
            nextitem = self.nextsibling()
            if nextitem is None:
                try:
                    nextitem = self.parentitem().nextsibling()
                except AttributeError:
                    nextitem = None
            return nextitem
        else:
            # try child
            item = self.firstchild()
            if item is not None:
                return item

            # else try next sibling
            item = self.nextsibling()
            if item is not None:
                return item

            try:
                # else try parent's next sibling
                item = self.parentitem().nextsibling()
                if item is not None:
                    return item

                # else return grandparent's next sibling (or None)
                return self.parentitem().parentitem().nextsibling()

            except AttributeError: # parent and/or grandparent was None
                return None

    def previtem(self):
        """
        Try to return the previous item closest to this item, regardless of
        item's type (header, hunk, or hunkline).

        If it is not possible to get the previous item, return None.
        """
        # try previous sibling's last child's last child,
        # else try previous sibling's last child, else try previous sibling
        prevsibling = self.prevsibling()
        if prevsibling is not None:
            prevsiblinglastchild = prevsibling.lastchild()
            if ((prevsiblinglastchild is not None) and
                not prevsibling.folded):
                prevsiblinglclc = prevsiblinglastchild.lastchild()
                if ((prevsiblinglclc is not None) and
                    not prevsiblinglastchild.folded):
                    return prevsiblinglclc
                else:
                    return prevsiblinglastchild
            else:
                return prevsibling

        # try parent (or None)
        return self.parentitem()

class patch(patchnode, list): # todo: rename patchroot
    """
    list of header objects representing the patch.
    """
    def __init__(self, headerlist):
        self.extend(headerlist)
        # add parent patch object reference to each header
        for header in self:
            header.patch = self

class uiheader(patchnode):
    """patch header

    xxx shouldn't we move this to mercurial/patch.py ?
    """

    def __init__(self, header):
        self.nonuiheader = header
        # flag to indicate whether to apply this chunk
        self.applied = True
        # flag which only affects the status display indicating if a node's
        # children are partially applied (i.e. some applied, some not).
        self.partial = False

        # flag to indicate whether to display as folded/unfolded to user
        self.folded = True

        # list of all headers in patch
        self.patch = None

        # flag is False if this header was ever unfolded from initial state
        self.neverunfolded = True
        self.hunks = [uihunk(h, self) for h in self.hunks]

    def prettystr(self):
        x = stringio()
        self.pretty(x)
        return x.getvalue()

    def nextsibling(self):
        numheadersinpatch = len(self.patch)
        indexofthisheader = self.patch.index(self)

        if indexofthisheader < numheadersinpatch - 1:
            nextheader = self.patch[indexofthisheader + 1]
            return nextheader
        else:
            return None

    def prevsibling(self):
        indexofthisheader = self.patch.index(self)
        if indexofthisheader > 0:
            previousheader = self.patch[indexofthisheader - 1]
            return previousheader
        else:
            return None

    def parentitem(self):
        """
        there is no 'real' parent item of a header that can be selected,
        so return None.
        """
        return None

    def firstchild(self):
        "return the first child of this item, if one exists.  otherwise None."
        if len(self.hunks) > 0:
            return self.hunks[0]
        else:
            return None

    def lastchild(self):
        "return the last child of this item, if one exists.  otherwise None."
        if len(self.hunks) > 0:
            return self.hunks[-1]
        else:
            return None

    def allchildren(self):
        "return a list of all of the direct children of this node"
        return self.hunks

    def __getattr__(self, name):
        return getattr(self.nonuiheader, name)

class uihunkline(patchnode):
    "represents a changed line in a hunk"
    def __init__(self, linetext, hunk):
        self.linetext = linetext
        self.applied = True
        # the parent hunk to which this line belongs
        self.hunk = hunk
        # folding lines currently is not used/needed, but this flag is needed
        # in the previtem method.
        self.folded = False

    def prettystr(self):
        return self.linetext

    def nextsibling(self):
        numlinesinhunk = len(self.hunk.changedlines)
        indexofthisline = self.hunk.changedlines.index(self)

        if (indexofthisline < numlinesinhunk - 1):
            nextline = self.hunk.changedlines[indexofthisline + 1]
            return nextline
        else:
            return None

    def prevsibling(self):
        indexofthisline = self.hunk.changedlines.index(self)
        if indexofthisline > 0:
            previousline = self.hunk.changedlines[indexofthisline - 1]
            return previousline
        else:
            return None

    def parentitem(self):
        "return the parent to the current item"
        return self.hunk

    def firstchild(self):
        "return the first child of this item, if one exists.  otherwise None."
        # hunk-lines don't have children
        return None

    def lastchild(self):
        "return the last child of this item, if one exists.  otherwise None."
        # hunk-lines don't have children
        return None

class uihunk(patchnode):
    """ui patch hunk, wraps a hunk and keep track of ui behavior """
    maxcontext = 3

    def __init__(self, hunk, header):
        self._hunk = hunk
        self.changedlines = [uihunkline(line, self) for line in hunk.hunk]
        self.header = header
        # used at end for detecting how many removed lines were un-applied
        self.originalremoved = self.removed

        # flag to indicate whether to display as folded/unfolded to user
        self.folded = True
        # flag to indicate whether to apply this chunk
        self.applied = True
        # flag which only affects the status display indicating if a node's
        # children are partially applied (i.e. some applied, some not).
        self.partial = False

    def nextsibling(self):
        numhunksinheader = len(self.header.hunks)
        indexofthishunk = self.header.hunks.index(self)

        if (indexofthishunk < numhunksinheader - 1):
            nexthunk = self.header.hunks[indexofthishunk + 1]
            return nexthunk
        else:
            return None

    def prevsibling(self):
        indexofthishunk = self.header.hunks.index(self)
        if indexofthishunk > 0:
            previoushunk = self.header.hunks[indexofthishunk - 1]
            return previoushunk
        else:
            return None

    def parentitem(self):
        "return the parent to the current item"
        return self.header

    def firstchild(self):
        "return the first child of this item, if one exists.  otherwise None."
        if len(self.changedlines) > 0:
            return self.changedlines[0]
        else:
            return None

    def lastchild(self):
        "return the last child of this item, if one exists.  otherwise None."
        if len(self.changedlines) > 0:
            return self.changedlines[-1]
        else:
            return None

    def allchildren(self):
        "return a list of all of the direct children of this node"
        return self.changedlines

    def countchanges(self):
        """changedlines -> (n+,n-)"""
        add = len([l for l in self.changedlines if l.applied
                   and l.prettystr()[0] == '+'])
        rem = len([l for l in self.changedlines if l.applied
                   and l.prettystr()[0] == '-'])
        return add, rem

    def getfromtoline(self):
        # calculate the number of removed lines converted to context lines
        removedconvertedtocontext = self.originalremoved - self.removed

        contextlen = (len(self.before) + len(self.after) +
                      removedconvertedtocontext)
        if self.after and self.after[-1] == '\\ No newline at end of file\n':
            contextlen -= 1
        fromlen = contextlen + self.removed
        tolen = contextlen + self.added

        # diffutils manual, section "2.2.2.2 detailed description of unified
        # format": "an empty hunk is considered to end at the line that
        # precedes the hunk."
        #
        # so, if either of hunks is empty, decrease its line start. --immerrr
        # but only do this if fromline > 0, to avoid having, e.g fromline=-1.
        fromline, toline = self.fromline, self.toline
        if fromline != 0:
            if fromlen == 0:
                fromline -= 1
            if tolen == 0:
                toline -= 1

        fromtoline = '@@ -%d,%d +%d,%d @@%s\n' % (
            fromline, fromlen, toline, tolen,
            self.proc and (' ' + self.proc))
        return fromtoline

    def write(self, fp):
        # updated self.added/removed, which are used by getfromtoline()
        self.added, self.removed = self.countchanges()
        fp.write(self.getfromtoline())

        hunklinelist = []
        # add the following to the list: (1) all applied lines, and
        # (2) all unapplied removal lines (convert these to context lines)
        for changedline in self.changedlines:
            changedlinestr = changedline.prettystr()
            if changedline.applied:
                hunklinelist.append(changedlinestr)
            elif changedlinestr[0] == "-":
                hunklinelist.append(" " + changedlinestr[1:])

        fp.write(''.join(self.before + hunklinelist + self.after))

    pretty = write

    def prettystr(self):
        x = stringio()
        self.pretty(x)
        return x.getvalue()

    def reversehunk(self):
        """return a recordhunk which is the reverse of the hunk

        Assuming the displayed patch is diff(A, B) result. The returned hunk is
        intended to be applied to B, instead of A.

        For example, when A is "0\n1\n2\n6\n" and B is "0\n3\n4\n5\n6\n", and
        the user made the following selection:

                 0
            [x] -1           [x]: selected
            [ ] -2           [ ]: not selected
            [x] +3
            [ ] +4
            [x] +5
                 6

        This function returns a hunk like:

                 0
                -3
                -4
                -5
                +1
                +4
                 6

        Note "4" was first deleted then added. That's because "4" exists in B
        side and "-4" must exist between "-3" and "-5" to make the patch
        applicable to B.
        """
        dels = []
        adds = []
        for line in self.changedlines:
            text = line.linetext
            if line.applied:
                if text[0] == '+':
                    dels.append(text[1:])
                elif text[0] == '-':
                    adds.append(text[1:])
            elif text[0] == '+':
                dels.append(text[1:])
                adds.append(text[1:])
        hunk = ['-%s' % l for l in dels] + ['+%s' % l for l in adds]
        h = self._hunk
        return patchmod.recordhunk(h.header, h.toline, h.fromline, h.proc,
                                   h.before, hunk, h.after)

    def __getattr__(self, name):
        return getattr(self._hunk, name)

    def __repr__(self):
        return '<hunk %r@%d>' % (self.filename(), self.fromline)

def filterpatch(ui, chunks, chunkselector, operation=None):
    """interactively filter patch chunks into applied-only chunks"""
    chunks = list(chunks)
    # convert chunks list into structure suitable for displaying/modifying
    # with curses.  create a list of headers only.
    headers = [c for c in chunks if isinstance(c, patchmod.header)]

    # if there are no changed files
    if len(headers) == 0:
        return [], {}
    uiheaders = [uiheader(h) for h in headers]
    # let user choose headers/hunks/lines, and mark their applied flags
    # accordingly
    ret = chunkselector(ui, uiheaders, operation=operation)
    appliedhunklist = []
    for hdr in uiheaders:
        if (hdr.applied and
            (hdr.special() or len([h for h in hdr.hunks if h.applied]) > 0)):
            appliedhunklist.append(hdr)
            fixoffset = 0
            for hnk in hdr.hunks:
                if hnk.applied:
                    appliedhunklist.append(hnk)
                    # adjust the 'to'-line offset of the hunk to be correct
                    # after de-activating some of the other hunks for this file
                    if fixoffset:
                        #hnk = copy.copy(hnk) # necessary??
                        hnk.toline += fixoffset
                else:
                    fixoffset += hnk.removed - hnk.added

    return (appliedhunklist, ret)

def chunkselector(ui, headerlist, operation=None):
    """
    curses interface to get selection of chunks, and mark the applied flags
    of the chosen chunks.
    """
    ui.write(_('starting interactive selection\n'))
    chunkselector = curseschunkselector(headerlist, ui, operation)
    origsigtstp = sentinel = object()
    if util.safehasattr(signal, 'SIGTSTP'):
        origsigtstp = signal.getsignal(signal.SIGTSTP)
    try:
        curses.wrapper(chunkselector.main)
        if chunkselector.initerr is not None:
            raise error.Abort(chunkselector.initerr)
        # ncurses does not restore signal handler for SIGTSTP
    finally:
        if origsigtstp is not sentinel:
            signal.signal(signal.SIGTSTP, origsigtstp)
    return chunkselector.opts

def testdecorator(testfn, f):
    def u(*args, **kwargs):
        return f(testfn, *args, **kwargs)
    return u

def testchunkselector(testfn, ui, headerlist, operation=None):
    """
    test interface to get selection of chunks, and mark the applied flags
    of the chosen chunks.
    """
    chunkselector = curseschunkselector(headerlist, ui, operation)
    if testfn and os.path.exists(testfn):
        testf = open(testfn)
        testcommands = [x.rstrip('\n') for x in testf.readlines()]
        testf.close()
        while True:
            if chunkselector.handlekeypressed(testcommands.pop(0), test=True):
                break
    return chunkselector.opts

_headermessages = { # {operation: text}
    'apply': _('Select hunks to apply'),
    'discard': _('Select hunks to discard'),
    None: _('Select hunks to record'),
}

class curseschunkselector(object):
    def __init__(self, headerlist, ui, operation=None):
        # put the headers into a patch object
        self.headerlist = patch(headerlist)

        self.ui = ui
        self.opts = {}

        self.errorstr = None
        # list of all chunks
        self.chunklist = []
        for h in headerlist:
            self.chunklist.append(h)
            self.chunklist.extend(h.hunks)

        # dictionary mapping (fgcolor, bgcolor) pairs to the
        # corresponding curses color-pair value.
        self.colorpairs = {}
        # maps custom nicknames of color-pairs to curses color-pair values
        self.colorpairnames = {}

        # Honor color setting of ui section. Keep colored setup as
        # long as not explicitly set to a falsy value - especially,
        # when not set at all. This is to stay most compatible with
        # previous (color only) behaviour.
        uicolor = stringutil.parsebool(self.ui.config('ui', 'color'))
        self.usecolor = uicolor is not False

        # the currently selected header, hunk, or hunk-line
        self.currentselecteditem = self.headerlist[0]

        # updated when printing out patch-display -- the 'lines' here are the
        # line positions *in the pad*, not on the screen.
        self.selecteditemstartline = 0
        self.selecteditemendline = None

        # define indentation levels
        self.headerindentnumchars = 0
        self.hunkindentnumchars = 3
        self.hunklineindentnumchars = 6

        # the first line of the pad to print to the screen
        self.firstlineofpadtoprint = 0

        # keeps track of the number of lines in the pad
        self.numpadlines = None

        self.numstatuslines = 1

        # keep a running count of the number of lines printed to the pad
        # (used for determining when the selected item begins/ends)
        self.linesprintedtopadsofar = 0

        # the first line of the pad which is visible on the screen
        self.firstlineofpadtoprint = 0

        # stores optional text for a commit comment provided by the user
        self.commenttext = ""

        # if the last 'toggle all' command caused all changes to be applied
        self.waslasttoggleallapplied = True

        # affects some ui text
        if operation not in _headermessages:
            raise error.ProgrammingError('unexpected operation: %s' % operation)
        self.operation = operation

    def uparrowevent(self):
        """
        try to select the previous item to the current item that has the
        most-indented level.  for example, if a hunk is selected, try to select
        the last hunkline of the hunk prior to the selected hunk.  or, if
        the first hunkline of a hunk is currently selected, then select the
        hunk itself.
        """
        currentitem = self.currentselecteditem

        nextitem = currentitem.previtem()

        if nextitem is None:
            # if no parent item (i.e. currentitem is the first header), then
            # no change...
            nextitem = currentitem

        self.currentselecteditem = nextitem

    def uparrowshiftevent(self):
        """
        select (if possible) the previous item on the same level as the
        currently selected item.  otherwise, select (if possible) the
        parent-item of the currently selected item.
        """
        currentitem = self.currentselecteditem
        nextitem = currentitem.prevsibling()
        # if there's no previous sibling, try choosing the parent
        if nextitem is None:
            nextitem = currentitem.parentitem()
        if nextitem is None:
            # if no parent item (i.e. currentitem is the first header), then
            # no change...
            nextitem = currentitem

        self.currentselecteditem = nextitem

    def downarrowevent(self):
        """
        try to select the next item to the current item that has the
        most-indented level.  for example, if a hunk is selected, select
        the first hunkline of the selected hunk.  or, if the last hunkline of
        a hunk is currently selected, then select the next hunk, if one exists,
        or if not, the next header if one exists.
        """
        #self.startprintline += 1 #debug
        currentitem = self.currentselecteditem

        nextitem = currentitem.nextitem()
        # if there's no next item, keep the selection as-is
        if nextitem is None:
            nextitem = currentitem

        self.currentselecteditem = nextitem

    def downarrowshiftevent(self):
        """
        select (if possible) the next item on the same level as the currently
        selected item.  otherwise, select (if possible) the next item on the
        same level as the parent item of the currently selected item.
        """
        currentitem = self.currentselecteditem
        nextitem = currentitem.nextsibling()
        # if there's no next sibling, try choosing the parent's nextsibling
        if nextitem is None:
            try:
                nextitem = currentitem.parentitem().nextsibling()
            except AttributeError:
                # parentitem returned None, so nextsibling() can't be called
                nextitem = None
        if nextitem is None:
            # if parent has no next sibling, then no change...
            nextitem = currentitem

        self.currentselecteditem = nextitem

    def rightarrowevent(self):
        """
        select (if possible) the first of this item's child-items.
        """
        currentitem = self.currentselecteditem
        nextitem = currentitem.firstchild()

        # turn off folding if we want to show a child-item
        if currentitem.folded:
            self.togglefolded(currentitem)

        if nextitem is None:
            # if no next item on parent-level, then no change...
            nextitem = currentitem

        self.currentselecteditem = nextitem

    def leftarrowevent(self):
        """
        if the current item can be folded (i.e. it is an unfolded header or
        hunk), then fold it.  otherwise try select (if possible) the parent
        of this item.
        """
        currentitem = self.currentselecteditem

        # try to fold the item
        if not isinstance(currentitem, uihunkline):
            if not currentitem.folded:
                self.togglefolded(item=currentitem)
                return

        # if it can't be folded, try to select the parent item
        nextitem = currentitem.parentitem()

        if nextitem is None:
            # if no item on parent-level, then no change...
            nextitem = currentitem
            if not nextitem.folded:
                self.togglefolded(item=nextitem)

        self.currentselecteditem = nextitem

    def leftarrowshiftevent(self):
        """
        select the header of the current item (or fold current item if the
        current item is already a header).
        """
        currentitem = self.currentselecteditem

        if isinstance(currentitem, uiheader):
            if not currentitem.folded:
                self.togglefolded(item=currentitem)
                return

        # select the parent item recursively until we're at a header
        while True:
            nextitem = currentitem.parentitem()
            if nextitem is None:
                break
            else:
                currentitem = nextitem

        self.currentselecteditem = currentitem

    def updatescroll(self):
        "scroll the screen to fully show the currently-selected"
        selstart = self.selecteditemstartline
        selend = self.selecteditemendline

        padstart = self.firstlineofpadtoprint
        padend = padstart + self.yscreensize - self.numstatuslines - 1
        # 'buffered' pad start/end values which scroll with a certain
        # top/bottom context margin
        padstartbuffered = padstart + 3
        padendbuffered = padend - 3

        if selend > padendbuffered:
            self.scrolllines(selend - padendbuffered)
        elif selstart < padstartbuffered:
            # negative values scroll in pgup direction
            self.scrolllines(selstart - padstartbuffered)

    def scrolllines(self, numlines):
        "scroll the screen up (down) by numlines when numlines >0 (<0)."
        self.firstlineofpadtoprint += numlines
        if self.firstlineofpadtoprint < 0:
            self.firstlineofpadtoprint = 0
        if self.firstlineofpadtoprint > self.numpadlines - 1:
            self.firstlineofpadtoprint = self.numpadlines - 1

    def toggleapply(self, item=None):
        """
        toggle the applied flag of the specified item.  if no item is specified,
        toggle the flag of the currently selected item.
        """
        if item is None:
            item = self.currentselecteditem

        item.applied = not item.applied

        if isinstance(item, uiheader):
            item.partial = False
            if item.applied:
                # apply all its hunks
                for hnk in item.hunks:
                    hnk.applied = True
                    # apply all their hunklines
                    for hunkline in hnk.changedlines:
                        hunkline.applied = True
            else:
                # un-apply all its hunks
                for hnk in item.hunks:
                    hnk.applied = False
                    hnk.partial = False
                    # un-apply all their hunklines
                    for hunkline in hnk.changedlines:
                        hunkline.applied = False
        elif isinstance(item, uihunk):
            item.partial = False
            # apply all it's hunklines
            for hunkline in item.changedlines:
                hunkline.applied = item.applied

            siblingappliedstatus = [hnk.applied for hnk in item.header.hunks]
            allsiblingsapplied = not (False in siblingappliedstatus)
            nosiblingsapplied = not (True in siblingappliedstatus)

            siblingspartialstatus = [hnk.partial for hnk in item.header.hunks]
            somesiblingspartial = (True in siblingspartialstatus)

            #cases where applied or partial should be removed from header

            # if no 'sibling' hunks are applied (including this hunk)
            if nosiblingsapplied:
                if not item.header.special():
                    item.header.applied = False
                    item.header.partial = False
            else: # some/all parent siblings are applied
                item.header.applied = True
                item.header.partial = (somesiblingspartial or
                                        not allsiblingsapplied)

        elif isinstance(item, uihunkline):
            siblingappliedstatus = [ln.applied for ln in item.hunk.changedlines]
            allsiblingsapplied = not (False in siblingappliedstatus)
            nosiblingsapplied = not (True in siblingappliedstatus)

            # if no 'sibling' lines are applied
            if nosiblingsapplied:
                item.hunk.applied = False
                item.hunk.partial = False
            elif allsiblingsapplied:
                item.hunk.applied = True
                item.hunk.partial = False
            else: # some siblings applied
                item.hunk.applied = True
                item.hunk.partial = True

            parentsiblingsapplied = [hnk.applied for hnk
                                     in item.hunk.header.hunks]
            noparentsiblingsapplied = not (True in parentsiblingsapplied)
            allparentsiblingsapplied = not (False in parentsiblingsapplied)

            parentsiblingspartial = [hnk.partial for hnk
                                     in item.hunk.header.hunks]
            someparentsiblingspartial = (True in parentsiblingspartial)

            # if all parent hunks are not applied, un-apply header
            if noparentsiblingsapplied:
                if not item.hunk.header.special():
                    item.hunk.header.applied = False
                    item.hunk.header.partial = False
            # set the applied and partial status of the header if needed
            else: # some/all parent siblings are applied
                item.hunk.header.applied = True
                item.hunk.header.partial = (someparentsiblingspartial or
                                            not allparentsiblingsapplied)

    def toggleall(self):
        "toggle the applied flag of all items."
        if self.waslasttoggleallapplied: # then unapply them this time
            for item in self.headerlist:
                if item.applied:
                    self.toggleapply(item)
        else:
            for item in self.headerlist:
                if not item.applied:
                    self.toggleapply(item)
        self.waslasttoggleallapplied = not self.waslasttoggleallapplied

    def togglefolded(self, item=None, foldparent=False):
        "toggle folded flag of specified item (defaults to currently selected)"
        if item is None:
            item = self.currentselecteditem
        if foldparent or (isinstance(item, uiheader) and item.neverunfolded):
            if not isinstance(item, uiheader):
                # we need to select the parent item in this case
                self.currentselecteditem = item = item.parentitem()
            elif item.neverunfolded:
                item.neverunfolded = False

            # also fold any foldable children of the parent/current item
            if isinstance(item, uiheader): # the original or 'new' item
                for child in item.allchildren():
                    child.folded = not item.folded

        if isinstance(item, (uiheader, uihunk)):
            item.folded = not item.folded

    def alignstring(self, instr, window):
        """
        add whitespace to the end of a string in order to make it fill
        the screen in the x direction.  the current cursor position is
        taken into account when making this calculation.  the string can span
        multiple lines.
        """
        y, xstart = window.getyx()
        width = self.xscreensize
        # turn tabs into spaces
        instr = instr.expandtabs(4)
        strwidth = encoding.colwidth(instr)
        numspaces = (width - ((strwidth + xstart) % width) - 1)
        return instr + " " * numspaces + "\n"

    def printstring(self, window, text, fgcolor=None, bgcolor=None, pair=None,
        pairname=None, attrlist=None, towin=True, align=True, showwhtspc=False):
        """
        print the string, text, with the specified colors and attributes, to
        the specified curses window object.

        the foreground and background colors are of the form
        curses.color_xxxx, where xxxx is one of: [black, blue, cyan, green,
        magenta, red, white, yellow].  if pairname is provided, a color
        pair will be looked up in the self.colorpairnames dictionary.

        attrlist is a list containing text attributes in the form of
        curses.a_xxxx, where xxxx can be: [bold, dim, normal, standout,
        underline].

        if align == True, whitespace is added to the printed string such that
        the string stretches to the right border of the window.

        if showwhtspc == True, trailing whitespace of a string is highlighted.
        """
        # preprocess the text, converting tabs to spaces
        text = text.expandtabs(4)
        # strip \n, and convert control characters to ^[char] representation
        text = re.sub(br'[\x00-\x08\x0a-\x1f]',
                lambda m:'^' + chr(ord(m.group()) + 64), text.strip('\n'))

        if pair is not None:
            colorpair = pair
        elif pairname is not None:
            colorpair = self.colorpairnames[pairname]
        else:
            if fgcolor is None:
                fgcolor = -1
            if bgcolor is None:
                bgcolor = -1
            if (fgcolor, bgcolor) in self.colorpairs:
                colorpair = self.colorpairs[(fgcolor, bgcolor)]
            else:
                colorpair = self.getcolorpair(fgcolor, bgcolor)
        # add attributes if possible
        if attrlist is None:
            attrlist = []
        if colorpair < 256:
            # then it is safe to apply all attributes
            for textattr in attrlist:
                colorpair |= textattr
        else:
            # just apply a select few (safe?) attributes
            for textattr in (curses.A_UNDERLINE, curses.A_BOLD):
                if textattr in attrlist:
                    colorpair |= textattr

        y, xstart = self.chunkpad.getyx()
        t = "" # variable for counting lines printed
        # if requested, show trailing whitespace
        if showwhtspc:
            origlen = len(text)
            text = text.rstrip(' \n') # tabs have already been expanded
            strippedlen = len(text)
            numtrailingspaces = origlen - strippedlen

        if towin:
            window.addstr(text, colorpair)
        t += text

        if showwhtspc:
                wscolorpair = colorpair | curses.A_REVERSE
                if towin:
                    for i in range(numtrailingspaces):
                        window.addch(curses.ACS_CKBOARD, wscolorpair)
                t += " " * numtrailingspaces

        if align:
            if towin:
                extrawhitespace = self.alignstring("", window)
                window.addstr(extrawhitespace, colorpair)
            else:
                # need to use t, since the x position hasn't incremented
                extrawhitespace = self.alignstring(t, window)
            t += extrawhitespace

        # is reset to 0 at the beginning of printitem()

        linesprinted = (xstart + len(t)) / self.xscreensize
        self.linesprintedtopadsofar += linesprinted
        return t

    def _getstatuslinesegments(self):
        """-> [str]. return segments"""
        selected = self.currentselecteditem.applied
        spaceselect = _('space: select')
        spacedeselect = _('space: deselect')
        # Format the selected label into a place as long as the longer of the
        # two possible labels.  This may vary by language.
        spacelen = max(len(spaceselect), len(spacedeselect))
        selectedlabel = '%-*s' % (spacelen,
                                  spacedeselect if selected else spaceselect)
        segments = [
            _headermessages[self.operation],
            '-',
            _('[x]=selected **=collapsed'),
            _('c: confirm'),
            _('q: abort'),
            _('arrow keys: move/expand/collapse'),
            selectedlabel,
            _('?: help'),
        ]
        return segments

    def _getstatuslines(self):
        """() -> [str]. return short help used in the top status window"""
        if self.errorstr is not None:
            lines = [self.errorstr, _('Press any key to continue')]
        else:
            # wrap segments to lines
            segments = self._getstatuslinesegments()
            width = self.xscreensize
            lines = []
            lastwidth = width
            for s in segments:
                w = encoding.colwidth(s)
                sep = ' ' * (1 + (s and s[0] not in '-['))
                if lastwidth + w + len(sep) >= width:
                    lines.append(s)
                    lastwidth = w
                else:
                    lines[-1] += sep + s
                    lastwidth += w + len(sep)
        if len(lines) != self.numstatuslines:
            self.numstatuslines = len(lines)
            self.statuswin.resize(self.numstatuslines, self.xscreensize)
        return [stringutil.ellipsis(l, self.xscreensize - 1) for l in lines]

    def updatescreen(self):
        self.statuswin.erase()
        self.chunkpad.erase()

        printstring = self.printstring

        # print out the status lines at the top
        try:
            for line in self._getstatuslines():
                printstring(self.statuswin, line, pairname="legend")
            self.statuswin.refresh()
        except curses.error:
            pass
        if self.errorstr is not None:
            return

        # print out the patch in the remaining part of the window
        try:
            self.printitem()
            self.updatescroll()
            self.chunkpad.refresh(self.firstlineofpadtoprint, 0,
                                  self.numstatuslines, 0,
                                  self.yscreensize - self.numstatuslines,
                                  self.xscreensize)
        except curses.error:
            pass

    def getstatusprefixstring(self, item):
        """
        create a string to prefix a line with which indicates whether 'item'
        is applied and/or folded.
        """

        # create checkbox string
        if item.applied:
            if not isinstance(item, uihunkline) and item.partial:
                checkbox = "[~]"
            else:
                checkbox = "[x]"
        else:
            checkbox = "[ ]"

        try:
            if item.folded:
                checkbox += "**"
                if isinstance(item, uiheader):
                    # one of "m", "a", or "d" (modified, added, deleted)
                    filestatus = item.changetype

                    checkbox += filestatus + " "
            else:
                checkbox += "  "
                if isinstance(item, uiheader):
                    # add two more spaces for headers
                    checkbox += "  "
        except AttributeError: # not foldable
            checkbox += "  "

        return checkbox

    def printheader(self, header, selected=False, towin=True,
                    ignorefolding=False):
        """
        print the header to the pad.  if countlines is True, don't print
        anything, but just count the number of lines which would be printed.
        """

        outstr = ""
        text = header.prettystr()
        chunkindex = self.chunklist.index(header)

        if chunkindex != 0 and not header.folded:
            # add separating line before headers
            outstr += self.printstring(self.chunkpad, '_' * self.xscreensize,
                                       towin=towin, align=False)
        # select color-pair based on if the header is selected
        colorpair = self.getcolorpair(name=selected and "selected" or "normal",
                                      attrlist=[curses.A_BOLD])

        # print out each line of the chunk, expanding it to screen width

        # number of characters to indent lines on this level by
        indentnumchars = 0
        checkbox = self.getstatusprefixstring(header)
        if not header.folded or ignorefolding:
            textlist = text.split("\n")
            linestr = checkbox + textlist[0]
        else:
            linestr = checkbox + header.filename()
        outstr += self.printstring(self.chunkpad, linestr, pair=colorpair,
                                   towin=towin)
        if not header.folded or ignorefolding:
            if len(textlist) > 1:
                for line in textlist[1:]:
                    linestr = " "*(indentnumchars + len(checkbox)) + line
                    outstr += self.printstring(self.chunkpad, linestr,
                                               pair=colorpair, towin=towin)

        return outstr

    def printhunklinesbefore(self, hunk, selected=False, towin=True,
                             ignorefolding=False):
        "includes start/end line indicator"
        outstr = ""
        # where hunk is in list of siblings
        hunkindex = hunk.header.hunks.index(hunk)

        if hunkindex != 0:
            # add separating line before headers
            outstr += self.printstring(self.chunkpad, ' '*self.xscreensize,
                                       towin=towin, align=False)

        colorpair = self.getcolorpair(name=selected and "selected" or "normal",
                                      attrlist=[curses.A_BOLD])

        # print out from-to line with checkbox
        checkbox = self.getstatusprefixstring(hunk)

        lineprefix = " "*self.hunkindentnumchars + checkbox
        frtoline = "   " + hunk.getfromtoline().strip("\n")

        outstr += self.printstring(self.chunkpad, lineprefix, towin=towin,
                                   align=False) # add uncolored checkbox/indent
        outstr += self.printstring(self.chunkpad, frtoline, pair=colorpair,
                                   towin=towin)

        if hunk.folded and not ignorefolding:
            # skip remainder of output
            return outstr

        # print out lines of the chunk preceeding changed-lines
        for line in hunk.before:
            linestr = " "*(self.hunklineindentnumchars + len(checkbox)) + line
            outstr += self.printstring(self.chunkpad, linestr, towin=towin)

        return outstr

    def printhunklinesafter(self, hunk, towin=True, ignorefolding=False):
        outstr = ""
        if hunk.folded and not ignorefolding:
            return outstr

        # a bit superfluous, but to avoid hard-coding indent amount
        checkbox = self.getstatusprefixstring(hunk)
        for line in hunk.after:
            linestr = " "*(self.hunklineindentnumchars + len(checkbox)) + line
            outstr += self.printstring(self.chunkpad, linestr, towin=towin)

        return outstr

    def printhunkchangedline(self, hunkline, selected=False, towin=True):
        outstr = ""
        checkbox = self.getstatusprefixstring(hunkline)

        linestr = hunkline.prettystr().strip("\n")

        # select color-pair based on whether line is an addition/removal
        if selected:
            colorpair = self.getcolorpair(name="selected")
        elif linestr.startswith("+"):
            colorpair = self.getcolorpair(name="addition")
        elif linestr.startswith("-"):
            colorpair = self.getcolorpair(name="deletion")
        elif linestr.startswith("\\"):
            colorpair = self.getcolorpair(name="normal")

        lineprefix = " "*self.hunklineindentnumchars + checkbox
        outstr += self.printstring(self.chunkpad, lineprefix, towin=towin,
                                   align=False) # add uncolored checkbox/indent
        outstr += self.printstring(self.chunkpad, linestr, pair=colorpair,
                                   towin=towin, showwhtspc=True)
        return outstr

    def printitem(self, item=None, ignorefolding=False, recursechildren=True,
                  towin=True):
        """
        use __printitem() to print the the specified item.applied.
        if item is not specified, then print the entire patch.
        (hiding folded elements, etc. -- see __printitem() docstring)
        """

        if item is None:
            item = self.headerlist
        if recursechildren:
            self.linesprintedtopadsofar = 0

        outstr = []
        self.__printitem(item, ignorefolding, recursechildren, outstr,
                                  towin=towin)
        return ''.join(outstr)

    def outofdisplayedarea(self):
        y, _ = self.chunkpad.getyx() # cursor location
        # * 2 here works but an optimization would be the max number of
        # consecutive non selectable lines
        # i.e the max number of context line for any hunk in the patch
        miny = min(0, self.firstlineofpadtoprint - self.yscreensize)
        maxy = self.firstlineofpadtoprint + self.yscreensize * 2
        return y < miny or y > maxy

    def handleselection(self, item, recursechildren):
        selected = (item is self.currentselecteditem)
        if selected and recursechildren:
            # assumes line numbering starting from line 0
            self.selecteditemstartline = self.linesprintedtopadsofar
            selecteditemlines = self.getnumlinesdisplayed(item,
                                                          recursechildren=False)
            self.selecteditemendline = (self.selecteditemstartline +
                                        selecteditemlines - 1)
        return selected

    def __printitem(self, item, ignorefolding, recursechildren, outstr,
                    towin=True):
        """
        recursive method for printing out patch/header/hunk/hunk-line data to
        screen.  also returns a string with all of the content of the displayed
        patch (not including coloring, etc.).

        if ignorefolding is True, then folded items are printed out.

        if recursechildren is False, then only print the item without its
        child items.
        """

        if towin and self.outofdisplayedarea():
            return

        selected = self.handleselection(item, recursechildren)

        # patch object is a list of headers
        if isinstance(item, patch):
            if recursechildren:
                for hdr in item:
                    self.__printitem(hdr, ignorefolding,
                            recursechildren, outstr, towin)
        # todo: eliminate all isinstance() calls
        if isinstance(item, uiheader):
            outstr.append(self.printheader(item, selected, towin=towin,
                                       ignorefolding=ignorefolding))
            if recursechildren:
                for hnk in item.hunks:
                    self.__printitem(hnk, ignorefolding,
                            recursechildren, outstr, towin)
        elif (isinstance(item, uihunk) and
              ((not item.header.folded) or ignorefolding)):
            # print the hunk data which comes before the changed-lines
            outstr.append(self.printhunklinesbefore(item, selected, towin=towin,
                                                ignorefolding=ignorefolding))
            if recursechildren:
                for l in item.changedlines:
                    self.__printitem(l, ignorefolding,
                            recursechildren, outstr, towin)
                outstr.append(self.printhunklinesafter(item, towin=towin,
                                                ignorefolding=ignorefolding))
        elif (isinstance(item, uihunkline) and
              ((not item.hunk.folded) or ignorefolding)):
            outstr.append(self.printhunkchangedline(item, selected,
                towin=towin))

        return outstr

    def getnumlinesdisplayed(self, item=None, ignorefolding=False,
                             recursechildren=True):
        """
        return the number of lines which would be displayed if the item were
        to be printed to the display.  the item will not be printed to the
        display (pad).
        if no item is given, assume the entire patch.
        if ignorefolding is True, folded items will be unfolded when counting
        the number of lines.
        """

        # temporarily disable printing to windows by printstring
        patchdisplaystring = self.printitem(item, ignorefolding,
                                            recursechildren, towin=False)
        numlines = len(patchdisplaystring) // self.xscreensize
        return numlines

    def sigwinchhandler(self, n, frame):
        "handle window resizing"
        try:
            curses.endwin()
            self.xscreensize, self.yscreensize = scmutil.termsize(self.ui)
            self.statuswin.resize(self.numstatuslines, self.xscreensize)
            self.numpadlines = self.getnumlinesdisplayed(ignorefolding=True) + 1
            self.chunkpad = curses.newpad(self.numpadlines, self.xscreensize)
        except curses.error:
            pass

    def getcolorpair(self, fgcolor=None, bgcolor=None, name=None,
                     attrlist=None):
        """
        get a curses color pair, adding it to self.colorpairs if it is not
        already defined.  an optional string, name, can be passed as a shortcut
        for referring to the color-pair.  by default, if no arguments are
        specified, the white foreground / black background color-pair is
        returned.

        it is expected that this function will be used exclusively for
        initializing color pairs, and not curses.init_pair().

        attrlist is used to 'flavor' the returned color-pair.  this information
        is not stored in self.colorpairs.  it contains attribute values like
        curses.A_BOLD.
        """

        if (name is not None) and name in self.colorpairnames:
            # then get the associated color pair and return it
            colorpair = self.colorpairnames[name]
        else:
            if fgcolor is None:
                fgcolor = -1
            if bgcolor is None:
                bgcolor = -1
            if (fgcolor, bgcolor) in self.colorpairs:
                colorpair = self.colorpairs[(fgcolor, bgcolor)]
            else:
                pairindex = len(self.colorpairs) + 1
                if self.usecolor:
                    curses.init_pair(pairindex, fgcolor, bgcolor)
                    colorpair = self.colorpairs[(fgcolor, bgcolor)] = (
                        curses.color_pair(pairindex))
                    if name is not None:
                        self.colorpairnames[name] = curses.color_pair(pairindex)
                else:
                    cval = 0
                    if name is not None:
                        if name == 'selected':
                            cval = curses.A_REVERSE
                        self.colorpairnames[name] = cval
                    colorpair = self.colorpairs[(fgcolor, bgcolor)] = cval

        # add attributes if possible
        if attrlist is None:
            attrlist = []
        if colorpair < 256:
            # then it is safe to apply all attributes
            for textattr in attrlist:
                colorpair |= textattr
        else:
            # just apply a select few (safe?) attributes
            for textattrib in (curses.A_UNDERLINE, curses.A_BOLD):
                if textattrib in attrlist:
                    colorpair |= textattrib
        return colorpair

    def initcolorpair(self, *args, **kwargs):
        "same as getcolorpair."
        self.getcolorpair(*args, **kwargs)

    def helpwindow(self):
        "print a help window to the screen.  exit after any keypress."
        helptext = _(
            """            [press any key to return to the patch-display]

crecord allows you to interactively choose among the changes you have made,
and confirm only those changes you select for further processing by the command
you are running (commit/shelve/revert), after confirming the selected
changes, the unselected changes are still present in your working copy, so you
can use crecord multiple times to split large changes into smaller changesets.
the following are valid keystrokes:

                [space] : (un-)select item ([~]/[x] = partly/fully applied)
                      A : (un-)select all items
    up/down-arrow [k/j] : go to previous/next unfolded item
        pgup/pgdn [K/J] : go to previous/next item of same type
 right/left-arrow [l/h] : go to child item / parent item
 shift-left-arrow   [H] : go to parent header / fold selected header
                      f : fold / unfold item, hiding/revealing its children
                      F : fold / unfold parent item and all of its ancestors
                 ctrl-l : scroll the selected line to the top of the screen
                      m : edit / resume editing the commit message
                      e : edit the currently selected hunk
                      a : toggle amend mode, only with commit -i
                      c : confirm selected changes
                      r : review/edit and confirm selected changes
                      q : quit without confirming (no changes will be made)
                      ? : help (what you're currently reading)""")

        helpwin = curses.newwin(self.yscreensize, 0, 0, 0)
        helplines = helptext.split("\n")
        helplines = helplines + [" "]*(
            self.yscreensize - self.numstatuslines - len(helplines) - 1)
        try:
            for line in helplines:
                self.printstring(helpwin, line, pairname="legend")
        except curses.error:
            pass
        helpwin.refresh()
        try:
            with self.ui.timeblockedsection('crecord'):
                helpwin.getkey()
        except curses.error:
            pass

    def commitMessageWindow(self):
        "Create a temporary commit message editing window on the screen."

        curses.raw()
        curses.def_prog_mode()
        curses.endwin()
        self.commenttext = self.ui.edit(self.commenttext, self.ui.username())
        curses.cbreak()
        self.stdscr.refresh()
        self.stdscr.keypad(1) # allow arrow-keys to continue to function

    def confirmationwindow(self, windowtext):
        "display an informational window, then wait for and return a keypress."

        confirmwin = curses.newwin(self.yscreensize, 0, 0, 0)
        try:
            lines = windowtext.split("\n")
            for line in lines:
                self.printstring(confirmwin, line, pairname="selected")
        except curses.error:
            pass
        self.stdscr.refresh()
        confirmwin.refresh()
        try:
            with self.ui.timeblockedsection('crecord'):
                response = chr(self.stdscr.getch())
        except ValueError:
            response = None

        return response

    def reviewcommit(self):
        """ask for 'y' to be pressed to confirm selected. return True if
        confirmed."""
        confirmtext = _(
"""if you answer yes to the following, the your currently chosen patch chunks
will be loaded into an editor.  you may modify the patch from the editor, and
save the changes if you wish to change the patch.  otherwise, you can just
close the editor without saving to accept the current patch as-is.

note: don't add/remove lines unless you also modify the range information.
      failing to follow this rule will result in the commit aborting.

are you sure you want to review/edit and confirm the selected changes [yn]?
""")
        with self.ui.timeblockedsection('crecord'):
            response = self.confirmationwindow(confirmtext)
        if response is None:
            response = "n"
        if response.lower().startswith("y"):
            return True
        else:
            return False

    def toggleamend(self, opts, test):
        """Toggle the amend flag.

        When the amend flag is set, a commit will modify the most recently
        committed changeset, instead of creating a new changeset.  Otherwise, a
        new changeset will be created (the normal commit behavior).
        """

        try:
            ver = float(util.version()[:3])
        except ValueError:
            ver = 1
        if ver < 2.19:
            msg = _("The amend option is unavailable with hg versions < 2.2\n\n"
                    "Press any key to continue.")
        elif opts.get('amend') is None:
            opts['amend'] = True
            msg = _("Amend option is turned on -- committing the currently "
                    "selected changes will not create a new changeset, but "
                    "instead update the most recently committed changeset.\n\n"
                    "Press any key to continue.")
        elif opts.get('amend') is True:
            opts['amend'] = None
            msg = _("Amend option is turned off -- committing the currently "
                    "selected changes will create a new changeset.\n\n"
                    "Press any key to continue.")
        if not test:
            self.confirmationwindow(msg)

    def recenterdisplayedarea(self):
        """
        once we scrolled with pg up pg down we can be pointing outside of the
        display zone. we print the patch with towin=False to compute the
        location of the selected item even though it is outside of the displayed
        zone and then update the scroll.
        """
        self.printitem(towin=False)
        self.updatescroll()

    def toggleedit(self, item=None, test=False):
        """
        edit the currently selected chunk
        """
        def updateui(self):
            self.numpadlines = self.getnumlinesdisplayed(ignorefolding=True) + 1
            self.chunkpad = curses.newpad(self.numpadlines, self.xscreensize)
            self.updatescroll()
            self.stdscr.refresh()
            self.statuswin.refresh()
            self.stdscr.keypad(1)

        def editpatchwitheditor(self, chunk):
            if chunk is None:
                self.ui.write(_('cannot edit patch for whole file'))
                self.ui.write("\n")
                return None
            if chunk.header.binary():
                self.ui.write(_('cannot edit patch for binary file'))
                self.ui.write("\n")
                return None

            # write the initial patch
            patch = stringio()
            patch.write(diffhelptext + hunkhelptext)
            chunk.header.write(patch)
            chunk.write(patch)

            # start the editor and wait for it to complete
            try:
                patch = self.ui.edit(patch.getvalue(), "", action="diff")
            except error.Abort as exc:
                self.errorstr = str(exc)
                return None

            # remove comment lines
            patch = [line + '\n' for line in patch.splitlines()
                     if not line.startswith('#')]
            return patchmod.parsepatch(patch)

        if item is None:
            item = self.currentselecteditem
        if isinstance(item, uiheader):
            return
        if isinstance(item, uihunkline):
            item = item.parentitem()
        if not isinstance(item, uihunk):
            return

        # To go back to that hunk or its replacement at the end of the edit
        itemindex = item.parentitem().hunks.index(item)

        beforeadded, beforeremoved = item.added, item.removed
        newpatches = editpatchwitheditor(self, item)
        if newpatches is None:
            if not test:
                updateui(self)
            return
        header = item.header
        editedhunkindex = header.hunks.index(item)
        hunksbefore = header.hunks[:editedhunkindex]
        hunksafter = header.hunks[editedhunkindex + 1:]
        newpatchheader = newpatches[0]
        newhunks = [uihunk(h, header) for h in newpatchheader.hunks]
        newadded = sum([h.added for h in newhunks])
        newremoved = sum([h.removed for h in newhunks])
        offset = (newadded - beforeadded) - (newremoved - beforeremoved)

        for h in hunksafter:
            h.toline += offset
        for h in newhunks:
            h.folded = False
        header.hunks = hunksbefore + newhunks + hunksafter
        if self.emptypatch():
            header.hunks = hunksbefore + [item] + hunksafter
        self.currentselecteditem = header
        if len(header.hunks) > itemindex:
            self.currentselecteditem = header.hunks[itemindex]

        if not test:
            updateui(self)

    def emptypatch(self):
        item = self.headerlist
        if not item:
            return True
        for header in item:
            if header.hunks:
                return False
        return True

    def handlekeypressed(self, keypressed, test=False):
        """
        Perform actions based on pressed keys.

        Return true to exit the main loop.
        """
        if keypressed in ["k", "KEY_UP"]:
            self.uparrowevent()
        if keypressed in ["K", "KEY_PPAGE"]:
            self.uparrowshiftevent()
        elif keypressed in ["j", "KEY_DOWN"]:
            self.downarrowevent()
        elif keypressed in ["J", "KEY_NPAGE"]:
            self.downarrowshiftevent()
        elif keypressed in ["l", "KEY_RIGHT"]:
            self.rightarrowevent()
        elif keypressed in ["h", "KEY_LEFT"]:
            self.leftarrowevent()
        elif keypressed in ["H", "KEY_SLEFT"]:
            self.leftarrowshiftevent()
        elif keypressed in ["q"]:
            raise error.Abort(_('user quit'))
        elif keypressed in ['a']:
            self.toggleamend(self.opts, test)
        elif keypressed in ["c"]:
            return True
        elif test and keypressed in ['X']:
            return True
        elif keypressed in ["r"]:
            if self.reviewcommit():
                self.opts['review'] = True
                return True
        elif test and keypressed in ['R']:
            self.opts['review'] = True
            return True
        elif keypressed in [' '] or (test and keypressed in ["TOGGLE"]):
            self.toggleapply()
            if self.ui.configbool('experimental', 'spacemovesdown'):
                self.downarrowevent()
        elif keypressed in ['A']:
            self.toggleall()
        elif keypressed in ['e']:
            self.toggleedit(test=test)
        elif keypressed in ["f"]:
            self.togglefolded()
        elif keypressed in ["F"]:
            self.togglefolded(foldparent=True)
        elif keypressed in ["m"]:
            self.commitMessageWindow()
        elif keypressed in ["?"]:
            self.helpwindow()
            self.stdscr.clear()
            self.stdscr.refresh()
        elif curses.unctrl(keypressed) in ["^L"]:
            # scroll the current line to the top of the screen
            self.scrolllines(self.selecteditemstartline)

    def main(self, stdscr):
        """
        method to be wrapped by curses.wrapper() for selecting chunks.
        """

        origsigwinch = sentinel = object()
        if util.safehasattr(signal, 'SIGWINCH'):
            origsigwinch = signal.signal(signal.SIGWINCH,
                                         self.sigwinchhandler)
        try:
            return self._main(stdscr)
        finally:
            if origsigwinch is not sentinel:
                signal.signal(signal.SIGWINCH, origsigwinch)

    def _main(self, stdscr):
        self.stdscr = stdscr
        # error during initialization, cannot be printed in the curses
        # interface, it should be printed by the calling code
        self.initerr = None
        self.yscreensize, self.xscreensize = self.stdscr.getmaxyx()

        curses.start_color()
        try:
            curses.use_default_colors()
        except curses.error:
            self.usecolor = False

        # available colors: black, blue, cyan, green, magenta, white, yellow
        # init_pair(color_id, foreground_color, background_color)
        self.initcolorpair(None, None, name="normal")
        self.initcolorpair(curses.COLOR_WHITE, curses.COLOR_MAGENTA,
                           name="selected")
        self.initcolorpair(curses.COLOR_RED, None, name="deletion")
        self.initcolorpair(curses.COLOR_GREEN, None, name="addition")
        self.initcolorpair(curses.COLOR_WHITE, curses.COLOR_BLUE, name="legend")
        # newwin([height, width,] begin_y, begin_x)
        self.statuswin = curses.newwin(self.numstatuslines, 0, 0, 0)
        self.statuswin.keypad(1) # interpret arrow-key, etc. esc sequences

        # figure out how much space to allocate for the chunk-pad which is
        # used for displaying the patch

        # stupid hack to prevent getnumlinesdisplayed from failing
        self.chunkpad = curses.newpad(1, self.xscreensize)

        # add 1 so to account for last line text reaching end of line
        self.numpadlines = self.getnumlinesdisplayed(ignorefolding=True) + 1

        try:
            self.chunkpad = curses.newpad(self.numpadlines, self.xscreensize)
        except curses.error:
            self.initerr = _('this diff is too large to be displayed')
            return
        # initialize selecteditemendline (initial start-line is 0)
        self.selecteditemendline = self.getnumlinesdisplayed(
            self.currentselecteditem, recursechildren=False)

        while True:
            self.updatescreen()
            try:
                with self.ui.timeblockedsection('crecord'):
                    keypressed = self.statuswin.getkey()
                if self.errorstr is not None:
                    self.errorstr = None
                    continue
            except curses.error:
                keypressed = "foobar"
            if self.handlekeypressed(keypressed):
                break

        if self.commenttext != "":
            whitespaceremoved = re.sub("(?m)^\s.*(\n|$)", "", self.commenttext)
            if whitespaceremoved != "":
                self.opts['message'] = self.commenttext