delta-find: stop using heuristic to determine if we are creating a snapshot This avoid assuming a changeset is a snapshot when it is actually something simpler.

delta-find: explicitly track stage of the search Being more explicit about what we are doing is going to be useful. We actually start making use of it in later changesets.

delta-find: drop some dead debug code Seems like it was never put to use, so lets simply remove it for now.

delta-find: introduce and use specialized _DeltaSearch class For now, we introduce some very simple variant, but they are still useful to display how having the class can helps keeping the simple case simple and their special case out of more advanced logic.

delta-find: introduce a base class for _DeltaSearch This prepare the introduction of specialized the class in the next changesets.

delta-find: simplify the delta checking function for snapshot Since the function is all about snapshot, we can safely use an early return and make the result simpler.

delta-find: move good delta code earlier in the class Nothing change except the code location. This greatly helps readability of the next future diff,

delta-find: split is_good_delta_info into more thematic function Same logic as for candidate filtering, we group code into related sub method. This will help clarifying later patches as some logic is pre-splitted

delta-find: clarify some comment and code in is_good_delta_info We move the comment closer to the code it describ and we compute an intermediate value without using the `textlen` variable, as it will stop being defined in a future patch. This will clarify future patches.

delta-find: move delta size check earlier in is_good_delta_info This will clarify future patches by regrouping related logic before larger movement.

delta-find: split the delta-chain part of `_pre_filter_rev` in a method Since `_pre_filter_rev` contains logic from various sources of constraint, we start splitting is in subfunction to clarify and document the grouping.

delta-find: split the "sparse" part of `_pre_filter_rev` in a method Since `_pre_filter_rev` contains logic from various sources of constraint, we start splitting is in subfunction to clarify and document the grouping.

delta-find: split the generic part of `_pre_filter_rev` in a method Since `_pre_filter_rev` contains logic from various sources of constraint, we start splitting is in subfunction to clarify and document the grouping.

delta-find: drop the temporary indent Now that the complicated change is made, we can do the noisy one.

delta-find: move pre-filtering of individual revision in its own function This goes one step further than the previous change by making the pre-filtering of individual candicates revision in its own function. This will allow subclass to easily configure this filtering with their own constrains. The `if True:` part help the readability of this diff a lot and will be drop in to the next changesets.

delta-find: move pre-filtering of candidates in its own function This organise the code further and open the way to specialization via sub-classing. Something important for the coming changes.

delta-find: move away from the generator API for _DeltaSearch We use more explicit function call. This make operations more explicit and will make future refactoring simpler.

delta-find: use "-1" as depth snapshot-dept for non snapshot in debug This will help do distinct full snapshot (level 0) and normal delta (not a snapshot, no snapshot level)

delta-find: fix the computation of the `prev` value The previous computation was "wrong" it always used the tiprev, even when computing a delta in a non-append case (mostly benchmark). This never produced wrong delta on disk, but would misled debug or performance command. Since it does not have any actual user impact, I did not put this on stable. With the code fixed we can now use revisions in some search and it makes the test display more interesting behavior since the algorithm has more to work with.

delta-find: move is_good_delta_info on the _DeltaSearch class There is a lot of format specific code in `is_good_delta_info`, moving it on _DeltaSearch will allow to split this into subclass soon.

delta-find: feed revinfo to _DeltaSearch The revinfo has more information and will allow for even more function to be turned into method.

delta-find: clarify that revisioninfo.p1/p2 constains nodeid This clarify the content of these attributes.

delta-find: move filing of some debug data in `_one_dbg_data` Since the `_one_dbg_data` method is meant to create a valid debug dictionnary. We can as well prefill the relevant value to reduce the amount of debug code in the main code.

delta-find: add more explanation to the the deltas_limit < length check More explanations is always good.

delta-find: move tested in the _DeltaSearch.__init__ Now that we have an object we can initialize that attribute at initialization time. This will make it available for more method in the future, allowing to split the code.

delta-find: check DELTA_BASE_REUSE_FORCE in the _DeltaSearch.__init__ Now that we have an object we can check that DELTA_BASE_REUSE_FORCE cases does not reach this code at in a more suitable location.

delta-find: move target_rev in the _DeltaSearch.__init__ Now that we have an object we can initialize that attribute at initialization time.

delta-find: move snapshot_cache in the _DeltaSearch.__init__ Now that we have an object we can initialize that attribute at initialization time.

delta-find: move `_rawgroups` on the `_DeltaSearch` object Moving more code before doing more logic changes.

delta-find: move `_refinedgroups` on the `_DeltaSearch` object Moving more code before doing more logic changes.

delta-find: introduce a _DeltaSearch object That object represent the search of a good delta for one revision. It will replace the interleaved generator currently in use. It will make the logic more explicit and easier to split into different subclass for the algorithm variant. We will move content gradually before doing deeper rework. For now, we only move the `_candidategroups` function here. More will follow in the same series.

delta-find: add a small docstring to deltacomputer As we are about to introduce another object related to finding delta. So lets have a minimal docstring to the existing one.