# dagop.py - graph ancestry and topology algorithm for revset
#
# Copyright 2010 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import heapq

from . import (
    error,
    mdiff,
    node,
    patch,
    smartset,
)

baseset = smartset.baseset
generatorset = smartset.generatorset

def _genrevancestors(repo, revs, followfirst):
    if followfirst:
        cut = 1
    else:
        cut = None
    cl = repo.changelog

    # load input revs lazily to heap so earlier revisions can be yielded
    # without fully computing the input revs
    revs.sort(reverse=True)
    irevs = iter(revs)
    pendingheap = []

    inputrev = next(irevs, None)
    if inputrev is not None:
        heapq.heappush(pendingheap, -inputrev)

    lastrev = None
    while pendingheap:
        currev = -heapq.heappop(pendingheap)
        if currev == inputrev:
            inputrev = next(irevs, None)
            if inputrev is not None:
                heapq.heappush(pendingheap, -inputrev)
        if currev != lastrev:
            lastrev = currev
            yield currev
            try:
                for prev in cl.parentrevs(currev)[:cut]:
                    if prev != node.nullrev:
                        heapq.heappush(pendingheap, -prev)
            except error.WdirUnsupported:
                for pctx in repo[currev].parents()[:cut]:
                    if pctx.rev() != node.nullrev:
                        heapq.heappush(pendingheap, -pctx.rev())

def revancestors(repo, revs, followfirst):
    """Like revlog.ancestors(), but supports followfirst."""
    gen = _genrevancestors(repo, revs, followfirst)
    return generatorset(gen, iterasc=False)

def revdescendants(repo, revs, followfirst):
    """Like revlog.descendants() but supports followfirst."""
    if followfirst:
        cut = 1
    else:
        cut = None

    def iterate():
        cl = repo.changelog
        # XXX this should be 'parentset.min()' assuming 'parentset' is a
        # smartset (and if it is not, it should.)
        first = min(revs)
        nullrev = node.nullrev
        if first == nullrev:
            # Are there nodes with a null first parent and a non-null
            # second one? Maybe. Do we care? Probably not.
            for i in cl:
                yield i
        else:
            seen = set(revs)
            for i in cl.revs(first + 1):
                for x in cl.parentrevs(i)[:cut]:
                    if x != nullrev and x in seen:
                        seen.add(i)
                        yield i
                        break

    return generatorset(iterate(), iterasc=True)

def _reachablerootspure(repo, minroot, roots, heads, includepath):
    """return (heads(::<roots> and ::<heads>))

    If includepath is True, return (<roots>::<heads>)."""
    if not roots:
        return []
    parentrevs = repo.changelog.parentrevs
    roots = set(roots)
    visit = list(heads)
    reachable = set()
    seen = {}
    # prefetch all the things! (because python is slow)
    reached = reachable.add
    dovisit = visit.append
    nextvisit = visit.pop
    # open-code the post-order traversal due to the tiny size of
    # sys.getrecursionlimit()
    while visit:
        rev = nextvisit()
        if rev in roots:
            reached(rev)
            if not includepath:
                continue
        parents = parentrevs(rev)
        seen[rev] = parents
        for parent in parents:
            if parent >= minroot and parent not in seen:
                dovisit(parent)
    if not reachable:
        return baseset()
    if not includepath:
        return reachable
    for rev in sorted(seen):
        for parent in seen[rev]:
            if parent in reachable:
                reached(rev)
    return reachable

def reachableroots(repo, roots, heads, includepath=False):
    """return (heads(::<roots> and ::<heads>))

    If includepath is True, return (<roots>::<heads>)."""
    if not roots:
        return baseset()
    minroot = roots.min()
    roots = list(roots)
    heads = list(heads)
    try:
        revs = repo.changelog.reachableroots(minroot, heads, roots, includepath)
    except AttributeError:
        revs = _reachablerootspure(repo, minroot, roots, heads, includepath)
    revs = baseset(revs)
    revs.sort()
    return revs

def _changesrange(fctx1, fctx2, linerange2, diffopts):
    """Return `(diffinrange, linerange1)` where `diffinrange` is True
    if diff from fctx2 to fctx1 has changes in linerange2 and
    `linerange1` is the new line range for fctx1.
    """
    blocks = mdiff.allblocks(fctx1.data(), fctx2.data(), diffopts)
    filteredblocks, linerange1 = mdiff.blocksinrange(blocks, linerange2)
    diffinrange = any(stype == '!' for _, stype in filteredblocks)
    return diffinrange, linerange1

def blockancestors(fctx, fromline, toline, followfirst=False):
    """Yield ancestors of `fctx` with respect to the block of lines within
    `fromline`-`toline` range.
    """
    diffopts = patch.diffopts(fctx._repo.ui)
    introrev = fctx.introrev()
    if fctx.rev() != introrev:
        fctx = fctx.filectx(fctx.filenode(), changeid=introrev)
    visit = {(fctx.linkrev(), fctx.filenode()): (fctx, (fromline, toline))}
    while visit:
        c, linerange2 = visit.pop(max(visit))
        pl = c.parents()
        if followfirst:
            pl = pl[:1]
        if not pl:
            # The block originates from the initial revision.
            yield c, linerange2
            continue
        inrange = False
        for p in pl:
            inrangep, linerange1 = _changesrange(p, c, linerange2, diffopts)
            inrange = inrange or inrangep
            if linerange1[0] == linerange1[1]:
                # Parent's linerange is empty, meaning that the block got
                # introduced in this revision; no need to go futher in this
                # branch.
                continue
            # Set _descendantrev with 'c' (a known descendant) so that, when
            # _adjustlinkrev is called for 'p', it receives this descendant
            # (as srcrev) instead possibly topmost introrev.
            p._descendantrev = c.rev()
            visit[p.linkrev(), p.filenode()] = p, linerange1
        if inrange:
            yield c, linerange2

def blockdescendants(fctx, fromline, toline):
    """Yield descendants of `fctx` with respect to the block of lines within
    `fromline`-`toline` range.
    """
    # First possibly yield 'fctx' if it has changes in range with respect to
    # its parents.
    try:
        c, linerange1 = next(blockancestors(fctx, fromline, toline))
    except StopIteration:
        pass
    else:
        if c == fctx:
            yield c, linerange1

    diffopts = patch.diffopts(fctx._repo.ui)
    fl = fctx.filelog()
    seen = {fctx.filerev(): (fctx, (fromline, toline))}
    for i in fl.descendants([fctx.filerev()]):
        c = fctx.filectx(i)
        inrange = False
        for x in fl.parentrevs(i):
            try:
                p, linerange2 = seen[x]
            except KeyError:
                # nullrev or other branch
                continue
            inrangep, linerange1 = _changesrange(c, p, linerange2, diffopts)
            inrange = inrange or inrangep
            # If revision 'i' has been seen (it's a merge), we assume that its
            # line range is the same independently of which parents was used
            # to compute it.
            assert i not in seen or seen[i][1] == linerange1, (
                'computed line range for %s is not consistent between '
                'ancestor branches' % c)
            seen[i] = c, linerange1
        if inrange:
            yield c, linerange1

def toposort(revs, parentsfunc, firstbranch=()):
    """Yield revisions from heads to roots one (topo) branch at a time.

    This function aims to be used by a graph generator that wishes to minimize
    the number of parallel branches and their interleaving.

    Example iteration order (numbers show the "true" order in a changelog):

      o  4
      |
      o  1
      |
      | o  3
      | |
      | o  2
      |/
      o  0

    Note that the ancestors of merges are understood by the current
    algorithm to be on the same branch. This means no reordering will
    occur behind a merge.
    """

    ### Quick summary of the algorithm
    #
    # This function is based around a "retention" principle. We keep revisions
    # in memory until we are ready to emit a whole branch that immediately
    # "merges" into an existing one. This reduces the number of parallel
    # branches with interleaved revisions.
    #
    # During iteration revs are split into two groups:
    # A) revision already emitted
    # B) revision in "retention". They are stored as different subgroups.
    #
    # for each REV, we do the following logic:
    #
    #   1) if REV is a parent of (A), we will emit it. If there is a
    #   retention group ((B) above) that is blocked on REV being
    #   available, we emit all the revisions out of that retention
    #   group first.
    #
    #   2) else, we'll search for a subgroup in (B) awaiting for REV to be
    #   available, if such subgroup exist, we add REV to it and the subgroup is
    #   now awaiting for REV.parents() to be available.
    #
    #   3) finally if no such group existed in (B), we create a new subgroup.
    #
    #
    # To bootstrap the algorithm, we emit the tipmost revision (which
    # puts it in group (A) from above).

    revs.sort(reverse=True)

    # Set of parents of revision that have been emitted. They can be considered
    # unblocked as the graph generator is already aware of them so there is no
    # need to delay the revisions that reference them.
    #
    # If someone wants to prioritize a branch over the others, pre-filling this
    # set will force all other branches to wait until this branch is ready to be
    # emitted.
    unblocked = set(firstbranch)

    # list of groups waiting to be displayed, each group is defined by:
    #
    #   (revs:    lists of revs waiting to be displayed,
    #    blocked: set of that cannot be displayed before those in 'revs')
    #
    # The second value ('blocked') correspond to parents of any revision in the
    # group ('revs') that is not itself contained in the group. The main idea
    # of this algorithm is to delay as much as possible the emission of any
    # revision.  This means waiting for the moment we are about to display
    # these parents to display the revs in a group.
    #
    # This first implementation is smart until it encounters a merge: it will
    # emit revs as soon as any parent is about to be emitted and can grow an
    # arbitrary number of revs in 'blocked'. In practice this mean we properly
    # retains new branches but gives up on any special ordering for ancestors
    # of merges. The implementation can be improved to handle this better.
    #
    # The first subgroup is special. It corresponds to all the revision that
    # were already emitted. The 'revs' lists is expected to be empty and the
    # 'blocked' set contains the parents revisions of already emitted revision.
    #
    # You could pre-seed the <parents> set of groups[0] to a specific
    # changesets to select what the first emitted branch should be.
    groups = [([], unblocked)]
    pendingheap = []
    pendingset = set()

    heapq.heapify(pendingheap)
    heappop = heapq.heappop
    heappush = heapq.heappush
    for currentrev in revs:
        # Heap works with smallest element, we want highest so we invert
        if currentrev not in pendingset:
            heappush(pendingheap, -currentrev)
            pendingset.add(currentrev)
        # iterates on pending rev until after the current rev have been
        # processed.
        rev = None
        while rev != currentrev:
            rev = -heappop(pendingheap)
            pendingset.remove(rev)

            # Seek for a subgroup blocked, waiting for the current revision.
            matching = [i for i, g in enumerate(groups) if rev in g[1]]

            if matching:
                # The main idea is to gather together all sets that are blocked
                # on the same revision.
                #
                # Groups are merged when a common blocking ancestor is
                # observed. For example, given two groups:
                #
                # revs [5, 4] waiting for 1
                # revs [3, 2] waiting for 1
                #
                # These two groups will be merged when we process
                # 1. In theory, we could have merged the groups when
                # we added 2 to the group it is now in (we could have
                # noticed the groups were both blocked on 1 then), but
                # the way it works now makes the algorithm simpler.
                #
                # We also always keep the oldest subgroup first. We can
                # probably improve the behavior by having the longest set
                # first. That way, graph algorithms could minimise the length
                # of parallel lines their drawing. This is currently not done.
                targetidx = matching.pop(0)
                trevs, tparents = groups[targetidx]
                for i in matching:
                    gr = groups[i]
                    trevs.extend(gr[0])
                    tparents |= gr[1]
                # delete all merged subgroups (except the one we kept)
                # (starting from the last subgroup for performance and
                # sanity reasons)
                for i in reversed(matching):
                    del groups[i]
            else:
                # This is a new head. We create a new subgroup for it.
                targetidx = len(groups)
                groups.append(([], {rev}))

            gr = groups[targetidx]

            # We now add the current nodes to this subgroups. This is done
            # after the subgroup merging because all elements from a subgroup
            # that relied on this rev must precede it.
            #
            # we also update the <parents> set to include the parents of the
            # new nodes.
            if rev == currentrev: # only display stuff in rev
                gr[0].append(rev)
            gr[1].remove(rev)
            parents = [p for p in parentsfunc(rev) if p > node.nullrev]
            gr[1].update(parents)
            for p in parents:
                if p not in pendingset:
                    pendingset.add(p)
                    heappush(pendingheap, -p)

            # Look for a subgroup to display
            #
            # When unblocked is empty (if clause), we were not waiting for any
            # revisions during the first iteration (if no priority was given) or
            # if we emitted a whole disconnected set of the graph (reached a
            # root).  In that case we arbitrarily take the oldest known
            # subgroup. The heuristic could probably be better.
            #
            # Otherwise (elif clause) if the subgroup is blocked on
            # a revision we just emitted, we can safely emit it as
            # well.
            if not unblocked:
                if len(groups) > 1:  # display other subset
                    targetidx = 1
                    gr = groups[1]
            elif not gr[1] & unblocked:
                gr = None

            if gr is not None:
                # update the set of awaited revisions with the one from the
                # subgroup
                unblocked |= gr[1]
                # output all revisions in the subgroup
                for r in gr[0]:
                    yield r
                # delete the subgroup that you just output
                # unless it is groups[0] in which case you just empty it.
                if targetidx:
                    del groups[targetidx]
                else:
                    gr[0][:] = []
    # Check if we have some subgroup waiting for revisions we are not going to
    # iterate over
    for g in groups:
        for r in g[0]:
            yield r