# Code dedicated to the computation and properties of "stable ranges"

#

# These stable ranges are use for obsolescence markers discovery

#

# Copyright 2017 Pierre-Yves David <pierre-yves.david@ens-lyon.org>

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

import collections

import math

from mercurial import (

    commands,

    cmdutil,

    localrepo,

    node as nodemod,

    scmutil,

)

from mercurial.i18n import _

from . import (

    exthelper,

)

eh = exthelper.exthelper()

##################################

### Stable topological sorting ###

##################################

@eh.command(

    'debugstablesort',

    [

        ('', 'rev', [], 'heads to start from'),

    ] + commands.formatteropts,

    _(''))

def debugstablesort(ui, repo, **opts):

    """display the ::REVS set topologically sorted in a stable way

    """

    revs = scmutil.revrange(repo, opts['rev'])

    displayer = cmdutil.show_changeset(ui, repo, opts, buffered=True)

    for r in stablesort(repo, revs):

        ctx = repo[r]

        displayer.show(ctx)

        displayer.flush(ctx)

    displayer.close()

def stablesort(repo, revs):

    """return '::revs' topologically sorted in "stable" order

    This is a depth first traversal starting from 'nullrev', using node as a

    tie breaker.

    """

    # Various notes:

    #

    # * Bitbucket is used dates as tie breaker, that might be a good idea.

    #

    # * It seemds we can traverse in the same order from (one) head to bottom,

    #   if we the following record data for each merge:

    #

    #  - highest (stablesort-wise) common ancestors,

    #  - order of parents (tablesort-wise)

    cl = repo.changelog

    parents = cl.parentrevs

    nullrev = nodemod.nullrev

    n = cl.node

    # step 1: We need a parents -> children mapping for 2 reasons.

    #

    # * we build the order from nullrev to tip

    #

    # * we need to detect branching

    children = collections.defaultdict(list)

    for r in cl.ancestors(revs, inclusive=True):

        p1, p2 = parents(r)

        children[p1].append(r)

        if p2 != nullrev:

            children[p2].append(r)

    # step two: walk back up

    # * pick lowest node in case of branching

    # * stack disregarded part of the branching

    # * process merge when both parents are yielded

    # track what changeset has been

    seen = [0] * (max(revs) + 2)

    seen[-1] = True # nullrev is known

    # starts from repository roots

    # reuse the list form the mapping as we won't need it again anyway

    stack = children[nullrev]

    if not stack:

        return []

    if 1 < len(stack):

        stack.sort(key=n, reverse=True)

    # list of rev, maybe we should yield, but since we built a children mapping we are 'O(N)' already

    result = []

    current = stack.pop()

    while current is not None or stack:

        if current is None:

            # previous iteration reached a merge or an unready merge,

            current = stack.pop()

            if seen[current]:

                current = None

                continue

        p1, p2 = parents(current)

        if not (seen[p1] and seen[p2]):

            # we can't iterate on this merge yet because other child is not

            # yielded yet (and we are topo sorting) we can discard it for now

            # because it will be reached from the other child.

            current = None

            continue

        assert not seen[current]

        seen[current] = True

        result.append(current) # could be yield, cf earlier comment

        cs = children[current]

        if not cs:

            current = None

        elif 1 == len(cs):

            current = cs[0]

        else:

            cs.sort(key=n, reverse=True)

            current = cs.pop() # proceed on smallest

            stack.extend(cs)   # stack the rest for later

    assert len(result) == len(set(result))

    return result

#################################

### Stable Range computation  ###

#################################

def _hlp2(i):

    """return highest power of two lower than 'i'"""

    return 2 ** int(math.log(i - 1, 2))

def subrangesclosure(repo, heads):

    """set of all standard subrange under heads

    This is intended for debug purposes. Range are returned from largest to

    smallest in terms of number of revision it contains."""

    subranges = repo.stablerange.subranges

    toproceed = [(r, 0, ) for r in heads]

    ranges = set(toproceed)

    while toproceed:

        entry = toproceed.pop()

        for r in subranges(repo, entry):

            if r not in ranges:

                ranges.add(r)

                toproceed.append(r)

    ranges = list(ranges)

    n = repo.changelog.node

    rangelength = repo.stablerange.rangelength

    ranges.sort(key=lambda r: (-rangelength(repo, r), n(r[0])))

    return ranges

    def __init__(self):

        self._depthcache = {}

        self._subrangescache = {}

        # To slices merge, we need to walk their descendant in reverse stable

        # sort order. For now we perform a full stable sort their descendant

        # and then use the relevant top most part. This order is going to be

        # the same for all ranges headed at the same merge. So we cache these

        # value to reuse them accross the same invocation.

        self._stablesortcache = {}

        # if we already know all the revision that belong to a range, it is

        # quite trivial to have the subrange "inherit" that knowledge. This

        # cache is dedicated to hold the full list of revs inside a subrange

        # when we happens to know it.

        #

        # For example. if we are slicing a range headed by a merge so will have

        # the revision computed anyway, and passing that knowledge around might

        # help to slice one of its subranges also containings a merge.

        self._revsinrangecache = {}

    def warmup(self, repo, heads):

        """warm the cache up to 'heads'"""

        for r in repo.revs("::%ld", heads):

            self.depthrev(repo, r)

    def depthrev(self, repo, rev):

        repo = repo.unfiltered()

        cl = repo.changelog

        cache = self._depthcache

        nullrev = nodemod.nullrev

        stack = [rev]

        while stack:

            revdepth = None

            current = stack[-1]

            revdepth = cache.get(current)

            if revdepth is not None:

                stack.pop()

                continue

            p1, p2 = cl.parentrevs(current)

            if p1 == nullrev:

                # root case

                revdepth = 1

            elif p2 == nullrev:

                # linear commit case

                parentdepth = cache.get(p1)

                if parentdepth is None:

                    stack.append(p1)

                else:

                    revdepth = parentdepth + 1

            else:

                # merge case

                revdepth = self._depthmerge(cl, current, p1, p2, stack, cache)

            if revdepth is not None:

                cache[current] = revdepth

                stack.pop()

        # actual_depth = len(list(cl.ancestors([rev], inclusive=True)))

        # assert revdepth == actual_depth, (rev, revdepth, actual_depth)

        return revdepth

    def rangelength(self, repo, rangeid):

        headrev, index = rangeid[0], rangeid[1]

        return self.depthrev(repo, headrev) - index

    def subranges(self, repo, rangeid):

        cached = self._subrangescache.get(rangeid)

        if cached is not None:

            return cached

        if self.rangelength(repo, rangeid) == 1:

            value = []

        else:

            slicepoint = self._slicepoint(repo, rangeid)

            value = self._slicesrangeat(repo, rangeid, slicepoint)

        self._subrangescache[rangeid] = value

        return value

    def revsfromrange(self, repo, rangeid):

        revs = self._revsinrangecache.get(rangeid)

        if revs is None:

            if self.rangelength(repo, rangeid) == 1:

                revs = [rangeid[0]]

            else:

                # get all revs under heads in stable order

                #

                # note: In the general case we can just walk down and then request

                # data about the merge. But I'm not sure this function will be even

                # call for the general case.

                allrevs = self._stablesortcache.get(rangeid[0])

                if allrevs is None:

                    allrevs = stablesort(repo, [rangeid[0]])

                    self._stablesortcache[rangeid[0]] = allrevs

                # takes from index

                revs = allrevs[rangeid[1]:]

            self._revsinrangecache[rangeid] = revs

        # sanity checks

        assert len(revs) == self.rangelength(repo, rangeid)

        return revs

    @staticmethod

    def _depthmerge(cl, rev, p1, p2, stack, cache):

        # sub method to simplify the main 'depthrev' one

        revdepth = None

        depth_p1 = cache.get(p1)

        depth_p2 = cache.get(p2)

        missingparent = False

        if depth_p1 is None:

            stack.append(p1)

            missingparent = True

        if depth_p2 is None:

            stack.append(p2)

            missingparent = True

        if missingparent:

            return None

        # computin depth of a merge

        # XXX the common ancestors heads could be cached

        ancnodes = cl.commonancestorsheads(cl.node(p1), cl.node(p2))

        ancrevs = [cl.rev(a) for a in ancnodes]

        anyunkown = False

        ancdepth = []

        for r in ancrevs:

            d = cache.get(r)

            if d is None:

                anyunkown = True

                stack.append(r)

            ancdepth.append((r, d))

        if anyunkown:

            return None

        if not ancrevs:

            # unrelated branch, (no common root)

            revdepth = depth_p1 + depth_p2 + 1

        elif len(ancrevs) == 1:

            # one unique branch point:

            # we can compute depth without any walk

            depth_anc = ancdepth[0][1]

            revdepth = depth_p1 + (depth_p2 - depth_anc) + 1

        else:

            # multiple ancestors, we pick one that is

            # * the deepest (less changeset outside of it),

            # * lowest revs because more chance to have descendant of other "above"

            anc, revdepth = max(ancdepth, key=lambda x: (x[1], -x[0]))

            revdepth += len(cl.findmissingrevs(common=[anc], heads=[rev]))

        return revdepth

    def _slicepoint(self, repo, rangeid):

        rangedepth = self.depthrev(repo, rangeid[0])

        step = _hlp2(rangedepth)

        standard_start = 0

        while standard_start < rangeid[1] and 0 < step:

            if standard_start + step < rangedepth:

                standard_start += step

            step //= 2

        if rangeid[1] == standard_start:

            slicesize = _hlp2(self.rangelength(repo, rangeid))

            slicepoint = rangeid[1] + slicesize

        else:

            assert standard_start < rangedepth

            slicepoint = standard_start

        return slicepoint

    def _slicesrangeat(self, repo, rangeid, globalindex):

        p1, p2 = repo.changelog.parentrevs(rangeid[0])

        if p2 != nodemod.nullrev:

            return self._slicesrangeatmerge(repo, rangeid, globalindex)

        assert p1 != nodemod.nullrev

        rangedepth = self.depthrev(repo, rangeid[0])

        topsize = rangedepth - globalindex

        parentrange = (p1, rangeid[1])

        # if we have an entry for the current range, lets update the cache

        if rangeid in self._revsinrangecache:

            parentrevs = self._revsinrangecache[rangeid][:-1]

            self._revsinrangecache[parentrange] = parentrevs

        if topsize == 1:

            top = (rangeid[0], globalindex)

            return [parentrange, top]

        else:

            # XXX recursive call, python have issue with them

            # The best way to break it would be directly 'self.subranges'

            # In that other method we could make sure subrangess for

            # (p1(rev), idx) are available before slicing (rev, idx). But the

            # heavy object approach makes it a bit inconvenient so that will

            # wait for that heavy object to be gone.

            parentsubranges = self.subranges(repo, parentrange)

            slices = parentsubranges[:-1] # pop the top

            top = (rangeid[0], globalindex)

            # if we have an entry for the current range, lets update the cache

            if rangeid in self._revsinrangecache:

                parentrevs = self._revsinrangecache[rangeid][-topsize:]

                self._revsinrangecache[top] = parentrevs

            slices.append(top)

            return slices

    def _slicesrangeatmerge(self, repo, rangeid, globalindex):

        localindex = globalindex - rangeid[1]

        cl = repo.changelog

        result = []

        allrevs = self.revsfromrange(repo, rangeid)

        toprevs = allrevs[localindex:]

        bottomrevs = allrevs[:localindex]

        top = (rangeid[0], globalindex)

        self._revsinrangecache[top] = toprevs # update cache

        #

        rangedepth = self.depthrev(repo, rangeid[0])

        toprootdepth = self.depthrev(repo, toprevs[0])

        if toprootdepth + self.rangelength(repo, top) == rangedepth + 1:

            bheads = [bottomrevs[-1]]

        else:

            bheads = set(bottomrevs)

            parentrevs = cl.parentrevs

            du = bheads.difference_update

            for r in bottomrevs:

                du(parentrevs(r))

            # if len(bheads) == 1:

            #     assert 1 == len(repo.revs('roots(%ld)', top._revs))

        if len(bheads) == 1:

            newhead = bottomrevs[-1]

            bottomdepth = self.depthrev(repo, newhead)

            newstart = bottomdepth - len(bottomrevs)

            bottom = (newhead, newstart)

            self._revsinrangecache[bottom] = bottomrevs # update cache

            result.append(bottom)

        else:

            # assert 1 < len(bheads), (toprootdepth, len(top), len(rangeid))