# Copyright (C) 2005 by Aaron Bentley

# 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; either version 2 of the License, or
# (at your option) any later version.
#
# 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

import contextlib

from .branch import Branch
from .trace import note
from .errors import NoSuchRevision, CommandError


class GhostFetcher(object):

    @classmethod
    def from_cmdline(cls, other):
        this_branch = Branch.open_containing('.')[0]
        if other is None:
            other = this_branch.get_parent()
            if other is None:
                raise CommandError('No branch specified and no location'
                                      ' saved.')
            else:
                note("Using saved location %s.", other)
        other_branch = Branch.open_containing(other)[0]
        return cls(this_branch, other_branch)

    def __init__(self, this_branch, other_branch):
        self.this_branch = this_branch
        self.other_branch = other_branch

    def run(self):
        lock_other = self.this_branch.base != self.other_branch.base
        with contextlib.ExitStack() as exit_stack:
            exit_stack.enter_context(self.this_branch.lock_write())
            if lock_other:
                exit_stack.enter_context(self.other_branch.lock_read())
            return self._run_locked()

    def iter_ghosts(self):
        """Find all ancestors that aren't stored in this branch."""
        seen = set()
        lines = [self.this_branch.last_revision()]
        if lines[0] is None:
            return
        while len(lines) > 0:
            new_lines = []
            for line in lines:
                if line in seen:
                    continue
                seen.add(line)
                try:
                    revision = self.this_branch.repository.get_revision(line)
                    new_lines.extend(revision.parent_ids)
                except NoSuchRevision:
                    yield line
            lines = new_lines

    def _run_locked(self):
        installed = []
        failed = []
        if self.this_branch.last_revision() is None:
            print("No revisions in branch.")
            return
        # Because iter_ghosts tests for existence after our last fetch
        # is complete, it won't falsely report an ancestor as a ghost.
        # Yay iterators!
        ghosts = self.iter_ghosts()
        for revision in ghosts:
            try:
                self.this_branch.fetch(self.other_branch, revision)
                installed.append(revision)
            except NoSuchRevision:
                failed.append(revision)
        return installed, failed