# walk.py -- General implementation of walking commits and their contents.
# Copyright (C) 2010 Google, Inc.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; version 2
# or (at your option) any later version of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA  02110-1301, USA.

"""General implementation of walking commits and their contents."""


from collections import defaultdict

import collections
import heapq
from itertools import chain

from dulwich.diff_tree import (
    RENAME_CHANGE_TYPES,
    tree_changes,
    tree_changes_for_merge,
    RenameDetector,
    )
from dulwich.errors import (
    MissingCommitError,
    )

ORDER_DATE = 'date'
ORDER_TOPO = 'topo'

ALL_ORDERS = (ORDER_DATE, ORDER_TOPO)

# Maximum number of commits to walk past a commit time boundary.
_MAX_EXTRA_COMMITS = 5


class WalkEntry(object):
    """Object encapsulating a single result from a walk."""

    def __init__(self, walker, commit):
        self.commit = commit
        self._store = walker.store
        self._get_parents = walker.get_parents
        self._changes = None
        self._rename_detector = walker.rename_detector

    def changes(self):
        """Get the tree changes for this entry.

        :return: For commits with up to one parent, a list of TreeChange
            objects; if the commit has no parents, these will be relative to the
            empty tree. For merge commits, a list of lists of TreeChange
            objects; see dulwich.diff.tree_changes_for_merge.
        """
        if self._changes is None:
            commit = self.commit
            if not self._get_parents(commit):
                changes_func = tree_changes
                parent = None
            elif len(self._get_parents(commit)) == 1:
                changes_func = tree_changes
                parent = self._store[self._get_parents(commit)[0]].tree
            else:
                changes_func = tree_changes_for_merge
                parent = [self._store[p].tree for p in self._get_parents(commit)]
            self._changes = list(changes_func(
              self._store, parent, commit.tree,
              rename_detector=self._rename_detector))
        return self._changes

    def __repr__(self):
        return '<WalkEntry commit=%s, changes=%r>' % (
          self.commit.id, self.changes())


class _CommitTimeQueue(object):
    """Priority queue of WalkEntry objects by commit time."""

    def __init__(self, walker):
        self._walker = walker
        self._store = walker.store
        self._get_parents = walker.get_parents
        self._excluded = walker.excluded
        self._pq = []
        self._pq_set = set()
        self._seen = set()
        self._done = set()
        self._min_time = walker.since
        self._last = None
        self._extra_commits_left = _MAX_EXTRA_COMMITS
        self._is_finished = False

        for commit_id in chain(walker.include, walker.excluded):
            self._push(commit_id)

    def _push(self, commit_id):
        try:
            commit = self._store[commit_id]
        except KeyError:
            raise MissingCommitError(commit_id)
        if commit_id not in self._pq_set and commit_id not in self._done:
            heapq.heappush(self._pq, (-commit.commit_time, commit))
            self._pq_set.add(commit_id)
            self._seen.add(commit_id)

    def _exclude_parents(self, commit):
        excluded = self._excluded
        seen = self._seen
        todo = [commit]
        while todo:
            commit = todo.pop()
            for parent in self._get_parents(commit):
                if parent not in excluded and parent in seen:
                    # TODO: This is inefficient unless the object store does
                    # some caching (which DiskObjectStore currently does not).
                    # We could either add caching in this class or pass around
                    # parsed queue entry objects instead of commits.
                    todo.append(self._store[parent])
                excluded.add(parent)

    def next(self):
        if self._is_finished:
            return None
        while self._pq:
            _, commit = heapq.heappop(self._pq)
            sha = commit.id
            self._pq_set.remove(sha)
            if sha in self._done:
                continue
            self._done.add(sha)

            for parent_id in self._get_parents(commit):
                self._push(parent_id)

            reset_extra_commits = True
            is_excluded = sha in self._excluded
            if is_excluded:
                self._exclude_parents(commit)
                if self._pq and all(c.id in self._excluded
                                    for _, c in self._pq):
                    _, n = self._pq[0]
                    if self._last and n.commit_time >= self._last.commit_time:
                        # If the next commit is newer than the last one, we need
                        # to keep walking in case its parents (which we may not
                        # have seen yet) are excluded. This gives the excluded
                        # set a chance to "catch up" while the commit is still
                        # in the Walker's output queue.
                        reset_extra_commits = True
                    else:
                        reset_extra_commits = False

            if (self._min_time is not None and
                commit.commit_time < self._min_time):
                # We want to stop walking at min_time, but commits at the
                # boundary may be out of order with respect to their parents. So
                # we walk _MAX_EXTRA_COMMITS more commits once we hit this
                # boundary.
                reset_extra_commits = False

            if reset_extra_commits:
                # We're not at a boundary, so reset the counter.
                self._extra_commits_left = _MAX_EXTRA_COMMITS
            else:
                self._extra_commits_left -= 1
                if not self._extra_commits_left:
                    break

            if not is_excluded:
                self._last = commit
                return WalkEntry(self._walker, commit)
        self._is_finished = True
        return None

    __next__ = next


class Walker(object):
    """Object for performing a walk of commits in a store.

    Walker objects are initialized with a store and other options and can then
    be treated as iterators of Commit objects.
    """

    def __init__(self, store, include, exclude=None, order=ORDER_DATE,
                 reverse=False, max_entries=None, paths=None,
                 rename_detector=None, follow=False, since=None, until=None,
                 get_parents=lambda commit: commit.parents,
                 queue_cls=_CommitTimeQueue):
        """Constructor.

        :param store: ObjectStore instance for looking up objects.
        :param include: Iterable of SHAs of commits to include along with their
            ancestors.
        :param exclude: Iterable of SHAs of commits to exclude along with their
            ancestors, overriding includes.
        :param order: ORDER_* constant specifying the order of results. Anything
            other than ORDER_DATE may result in O(n) memory usage.
        :param reverse: If True, reverse the order of output, requiring O(n)
            memory.
        :param max_entries: The maximum number of entries to yield, or None for
            no limit.
        :param paths: Iterable of file or subtree paths to show entries for.
        :param rename_detector: diff.RenameDetector object for detecting
            renames.
        :param follow: If True, follow path across renames/copies. Forces a
            default rename_detector.
        :param since: Timestamp to list commits after.
        :param until: Timestamp to list commits before.
        :param get_parents: Method to retrieve the parents of a commit
        :param queue_cls: A class to use for a queue of commits, supporting the
            iterator protocol. The constructor takes a single argument, the
            Walker.
        """
        # Note: when adding arguments to this method, please also update
        # dulwich.repo.BaseRepo.get_walker
        if order not in ALL_ORDERS:
            raise ValueError('Unknown walk order %s' % order)
        self.store = store
        if not isinstance(include, list):
            include = [include]
        self.include = include
        self.excluded = set(exclude or [])
        self.order = order
        self.reverse = reverse
        self.max_entries = max_entries
        self.paths = paths and set(paths) or None
        if follow and not rename_detector:
            rename_detector = RenameDetector(store)
        self.rename_detector = rename_detector
        self.get_parents = get_parents
        self.follow = follow
        self.since = since
        self.until = until

        self._num_entries = 0
        self._queue = queue_cls(self)
        self._out_queue = collections.deque()

    def _path_matches(self, changed_path):
        if changed_path is None:
            return False
        for followed_path in self.paths:
            if changed_path == followed_path:
                return True
            if (changed_path.startswith(followed_path) and
                    changed_path[len(followed_path)] == b'/'[0]):
                return True
        return False

    def _change_matches(self, change):
        if not change:
            return False

        old_path = change.old.path
        new_path = change.new.path
        if self._path_matches(new_path):
            if self.follow and change.type in RENAME_CHANGE_TYPES:
                self.paths.add(old_path)
                self.paths.remove(new_path)
            return True
        elif self._path_matches(old_path):
            return True
        return False

    def _should_return(self, entry):
        """Determine if a walk entry should be returned..

        :param entry: The WalkEntry to consider.
        :return: True if the WalkEntry should be returned by this walk, or False
            otherwise (e.g. if it doesn't match any requested paths).
        """
        commit = entry.commit
        if self.since is not None and commit.commit_time < self.since:
            return False
        if self.until is not None and commit.commit_time > self.until:
            return False
        if commit.id in self.excluded:
            return False

        if self.paths is None:
            return True

        if len(self.get_parents(commit)) > 1:
            for path_changes in entry.changes():
                # For merge commits, only include changes with conflicts for
                # this path. Since a rename conflict may include different
                # old.paths, we have to check all of them.
                for change in path_changes:
                    if self._change_matches(change):
                        return True
        else:
            for change in entry.changes():
                if self._change_matches(change):
                    return True
        return None

    def _next(self):
        max_entries = self.max_entries
        while max_entries is None or self._num_entries < max_entries:
            entry = next(self._queue)
            if entry is not None:
                self._out_queue.append(entry)
            if entry is None or len(self._out_queue) > _MAX_EXTRA_COMMITS:
                if not self._out_queue:
                    return None
                entry = self._out_queue.popleft()
                if self._should_return(entry):
                    self._num_entries += 1
                    return entry
        return None

    def _reorder(self, results):
        """Possibly reorder a results iterator.

        :param results: An iterator of WalkEntry objects, in the order returned
            from the queue_cls.
        :return: An iterator or list of WalkEntry objects, in the order required
            by the Walker.
        """
        if self.order == ORDER_TOPO:
            results = _topo_reorder(results, self.get_parents)
        if self.reverse:
            results = reversed(list(results))
        return results

    def __iter__(self):
        return iter(self._reorder(iter(self._next, None)))


def _topo_reorder(entries, get_parents=lambda commit: commit.parents):
    """Reorder an iterable of entries topologically.

    This works best assuming the entries are already in almost-topological
    order, e.g. in commit time order.

    :param entries: An iterable of WalkEntry objects.
    :param get_parents: Optional function for getting the parents of a commit.
    :return: iterator over WalkEntry objects from entries in FIFO order, except
        where a parent would be yielded before any of its children.
    """
    todo = collections.deque()
    pending = {}
    num_children = defaultdict(int)
    for entry in entries:
        todo.append(entry)
        for p in get_parents(entry.commit):
            num_children[p] += 1

    while todo:
        entry = todo.popleft()
        commit = entry.commit
        commit_id = commit.id
        if num_children[commit_id]:
            pending[commit_id] = entry
            continue
        for parent_id in get_parents(commit):
            num_children[parent_id] -= 1
            if not num_children[parent_id]:
                parent_entry = pending.pop(parent_id, None)
                if parent_entry:
                    todo.appendleft(parent_entry)
        yield entry
