# dagutil.py - dag utilities for mercurial

#

# Copyright 2010 Benoit Boissinot <bboissin@gmail.com>

# and Peter Arrenbrecht <peter@arrenbrecht.ch>

#

# 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

from .node import nullrev

class basedag(object):

    '''generic interface for DAGs

    terms:

    "ix" (short for index) identifies a nodes internally,

    "id" identifies one externally.

    All params are ixs unless explicitly suffixed otherwise.

    Pluralized params are lists or sets.

    '''

    def __init__(self):

        self._inverse = None

    def heads(self):

        '''list of head ixs'''

        raise NotImplementedError

    def parents(self, ix):

        '''list of parents ixs of ix'''

        raise NotImplementedError

    def inverse(self):

        '''inverse DAG, where parents becomes children, etc.'''

        raise NotImplementedError

    def headsetofconnecteds(self, ixs):

        '''

        subset of connected list of ixs so that no node has a descendant in it

        By "connected list" we mean that if an ancestor and a descendant are in

        the list, then so is at least one path connecting them.

        '''

        raise NotImplementedError

class genericdag(basedag):

    '''generic implementations for DAGs'''

    def headsetofconnecteds(self, ixs):

        hds = set(ixs)

        if not hds:

            return hds

        for n in ixs:

            for p in self.parents(n):

                hds.discard(p)

        assert hds

        return hds

class revlogbaseddag(basedag):

    '''generic dag interface to a revlog'''

    def __init__(self, revlog):

        basedag.__init__(self)

        self._revlog = revlog

        self._heads = None

    def heads(self):

        if self._heads is None:

            self._heads = self._getheads()

        return self._heads

class revlogdag(revlogbaseddag):

    '''dag interface to a revlog'''

    def __init__(self, revlog, localsubset=None):

        revlogbaseddag.__init__(self, revlog)

        self._heads = localsubset

    def _getheads(self):

        return [r for r in self._revlog.headrevs() if r != nullrev]

    def parents(self, ix):

        rlog = self._revlog

        idx = rlog.index

        revdata = idx[ix]

        prev = revdata[5]

        if prev != nullrev:

            prev2 = revdata[6]

            if prev2 == nullrev:

                return [prev]

            return [prev, prev2]

        prev2 = revdata[6]

        if prev2 != nullrev:

            return [prev2]

        return []

    def inverse(self):

        if self._inverse is None:

            self._inverse = inverserevlogdag(self)

        return self._inverse

    def headsetofconnecteds(self, ixs):

        if not ixs:

            return set()

        rlog = self._revlog

        idx = rlog.index

        headrevs = set(ixs)

        for rev in ixs:

            revdata = idx[rev]

            for i in [5, 6]:

                prev = revdata[i]

                if prev != nullrev:

                    headrevs.discard(prev)

        assert headrevs

        return headrevs

    def linearize(self, ixs):

        '''linearize and topologically sort a list of revisions

        The linearization process tries to create long runs of revs where

        a child rev comes immediately after its first parent. This is done by

        visiting the heads of the given revs in inverse topological order,

        and for each visited rev, visiting its second parent, then its first

        parent, then adding the rev itself to the output list.

        '''

        sorted = []

        visit = list(self.headsetofconnecteds(ixs))

        visit.sort(reverse=True)

        finished = set()

        while visit:

            cur = visit.pop()

            if cur < 0:

                cur = -cur - 1

                if cur not in finished:

                    sorted.append(cur)

                    finished.add(cur)

            else:

                visit.append(-cur - 1)

                visit += [p for p in self.parents(cur)

                          if p in ixs and p not in finished]

        assert len(sorted) == len(ixs)

        return sorted

class inverserevlogdag(revlogbaseddag, genericdag):

    '''inverse of an existing revlog dag; see revlogdag.inverse()'''

    def __init__(self, orig):

        revlogbaseddag.__init__(self, orig._revlog)

        self._orig = orig

        self._children = {}

        self._roots = []

        self._walkfrom = len(self._revlog) - 1

    def _walkto(self, walkto):

        rev = self._walkfrom

        cs = self._children

        roots = self._roots

        idx = self._revlog.index

        while rev >= walkto:

            data = idx[rev]

            isroot = True

            for prev in [data[5], data[6]]: # parent revs

                if prev != nullrev:

                    cs.setdefault(prev, []).append(rev)

                    isroot = False

            if isroot:

                roots.append(rev)

            rev -= 1

        self._walkfrom = rev

    def _getheads(self):

        self._walkto(nullrev)

        return self._roots

    def parents(self, ix):

        if ix is None:

            return []

        if ix <= self._walkfrom:

            self._walkto(ix)

        return self._children.get(ix, [])

    def inverse(self):

        return self._orig