# Code dedicated to the computation of stable sorting

#

# These stable sorting are used stable ranges

#

# 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

from mercurial import (

    commands,

    cmdutil,

    error,

    node as nodemod,

    scmutil,

)

from mercurial.i18n import _

from . import (

    depthcache,

    exthelper,

)

eh = exthelper.exthelper()

eh.merge(depthcache.eh)

def _mergepoint_tie_breaker(repo):

    """the key use to tie break merge parent

    Exists as a function to help playing with different approaches.

    Possible other factor are:

        * depth of node,

        * number of exclusive merges,

        * number of jump points.

        * <insert-your-idea>

    """

    return repo.changelog.node

@eh.command(

    'debugstablesort',

    [

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

        ('', 'method', 'branchpoint', "method used for sorting, one of: "

         "branchpoint, basic-mergepoint and basic-headstart"),

        ('l', 'limit', '', 'number of revision display (default to all)')

    ] + commands.formatteropts,

    _(''))

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

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

    """

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

    method = opts['method']

    sorting = _methodmap.get(method)

    if sorting is None:

        valid_method = ', '.join(sorted(_methodmap))

        raise error.Abort('unknown sorting method: "%s"' % method,

                          hint='pick one of: %s' % valid_method)

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

    kwargs = {}

    if opts['limit']:

        kwargs['limit'] = int(opts['limit'])

    for r in sorting(repo, revs, **kwargs):

        ctx = repo[r]

        displayer.show(ctx)

        displayer.flush(ctx)

    displayer.close()

def stablesort_branchpoint(repo, revs, mergecallback=None):

    """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

        if mergecallback is not None and p2 != nullrev:

            mergecallback(result, current)

        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

def stablesort_mergepoint_multirevs(repo, revs):

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

    This is a depth first traversal starting from 'revs' (toward root), using node as a

    tie breaker.

    """

    cl = repo.changelog

    tiebreaker = _mergepoint_tie_breaker(repo)

    if not revs:

        return []

    elif len(revs) == 1:

        heads = list(revs)

    else:

        # keeps heads only

        heads = sorted(repo.revs('heads(%ld::%ld)', revs, revs), key=tiebreaker)

    results = []

    while heads:

        h = heads.pop()

        if revs:

            bound = cl.findmissingrevs(common=heads, heads=[h])

        else:

            bound = cl.ancestors([h], inclusive=True)

        results.append(stablesort_mergepoint_bounded(repo, h, bound))

    if len(results) == 1:

        return results[0]

    finalresults = []

    for r in results[::-1]:

        finalresults.extend(r)

    return finalresults

def stablesort_mergepoint_bounded(repo, head, revs):

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

    The 'revs' set MUST have 'head' as its one and unique head.

    """

    # Various notes:

    #

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

    cl = repo.changelog

    parents = cl.parentrevs

    nullrev = nodemod.nullrev

    tiebreaker = _mergepoint_tie_breaker(repo)

    # step 1: We need a parents -> children mapping to detect dependencies

    children = collections.defaultdict(set)

    parentmap = {}

    for r in revs:

        p1, p2 = parents(r)

        children[p1].add(r)

        if p2 != nullrev:

            children[p2].add(r)

            parentmap[r] = tuple(sorted((p1, p2), key=tiebreaker))

        elif p1 != nullrev:

            parentmap[r] = (p1,)

        else:

            parentmap[r] = ()

    # step two: walk again,

    stack = [head]

    resultset = set()

    result = []

    def add(current):

        resultset.add(current)

        result.append(current)

    while stack:

        current = stack.pop()

        add(current)

        parents = parentmap[current]

        for p in parents:

            if 1 < len(children[p]) and not children[p].issubset(resultset):

                # we need other children to be yield first

                continue

            if p in revs:

                stack.append(p)

    result.reverse()

    assert len(result) == len(resultset)

    return result

def stablesort_mergepoint_head_basic(repo, revs, limit=None):

    heads = repo.revs('heads(%ld)', revs)

    if not heads:

        return []

    elif 2 < len(heads):

        raise error.Abort('cannot use head based merging, %d heads found'

                          % len(heads))

    head = heads.first()

    revs = stablesort_mergepoint_bounded(repo, head, repo.revs('::%d', head))

    if limit is None:

        return revs

    return revs[-limit:]

_methodmap = {

    'branchpoint': stablesort_branchpoint,

    'basic-mergepoint': stablesort_mergepoint_multirevs,

    'basic-headstart': stablesort_mergepoint_head_basic,

}