import os
import itertools
import cStringIO
import subprocess

import dulwich, dulwich.patch
from diff import prepare_udiff

def pairwise(iterable):
    """
    Yields the items in `iterable` pairwise:

    >>> list(pairwise(['a', 'b', 'c', 'd']))
    [('a', 'b'), ('b', 'c'), ('c', 'd')]
    """
    prev = None
    for item in iterable:
        if prev is not None:
            yield prev, item
        prev = item

class RepoWrapper(dulwich.repo.Repo):
    def get_branch_or_commit(self, id):
        """
        Returns a `(commit_object, is_branch)` tuple for the commit or branch
        identified by `id`.
        """
        try:
            return self[id], False
        except KeyError:
            return self.get_branch(id), True

    def get_branch(self, name):
        """ Returns the commit object pointed to by the branch `name`. """
        return self['refs/heads/'+name]

    def get_default_branch(self):
        return self.get_branch('master')

    def get_branch_names(self, exclude=()):
        """ Returns a sorted list of branch names. """
        branches = []
        for ref in self.get_refs():
            if ref.startswith('refs/heads/'):
                name = ref[len('refs/heads/'):]
                if name not in exclude:
                    branches.append(name)
        branches.sort()
        return branches

    def get_tag_names(self):
        """ Returns a sorted list of tag names. """
        tags = []
        for ref in self.get_refs():
            if ref.startswith('refs/tags/'):
                tags.append(ref[len('refs/tags/'):])
        tags.sort()
        return tags

    def history(self, commit, path=None, max_commits=None, skip=0):
        """
        Returns a list of all commits that infected `path`, starting at branch
        or commit `commit`. `skip` can be used for pagination, `max_commits`
        to limit the number of commits returned.

        Similar to `git log [branch/commit] [--skip skip] [-n max_commits]`.
        """
    # XXX The pure-Python/dulwich code is very slow compared to `git log`
    #     at the time of this writing (Oct 2011).
    #     For instance, try `git log .tx` in the Django root directory takes
    #     about 0.15s on my machine whereas the history() method needs 5s.
    #     Therefore we use `git log` here unless dulwich gets faster.

        cmd = ['git', 'log', '--format=%H']
        if skip:
            cmd.append('--skip=%d' % skip)
        if max_commits:
            cmd.append('--max-count=%d' % max_commits)
        cmd.append(commit)
        path = path.strip('/')
        if path:
            cmd.extend(['--', path])

        # sha1_sums = subprocess.check_output(cmd, cwd=os.path.abspath(self.path))
        # Can't use 'check_output' for Python 2.6 compatibility reasons
        sha1_sums = subprocess.Popen(cmd, cwd=os.path.abspath(self.path),
                                     stdout=subprocess.PIPE).communicate()[0]
        return [self[sha1] for sha1 in sha1_sums.strip().split('\n')]
    #
    #     if not isinstance(commit, dulwich.objects.Commit):
    #         commit, _ = self.get_branch_or_commit(commit)
    #     commits = self._history(commit)
    #     path = path.strip('/')
    #     if path:
    #         commits = (c1 for c1, c2 in pairwise(commits)
    #                    if self._path_changed_between(path, c1, c2))
    #     return list(itertools.islice(commits, skip, skip+max_commits))

    # def _history(self, commit):
    #     """ Yields all commits that lead to `commit`. """
    #     if commit is None:
    #         commit = self.get_default_branch()
    #     while commit.parents:
    #         yield commit
    #         commit = self[commit.parents[0]]
    #     yield commit

    # def _path_changed_between(self, path, commit1, commit2):
    #     """
    #     Returns `True` if `path` changed between `commit1` and `commit2`,
    #     including the case that the file was added or deleted in `commit2`.
    #     """
    #     path, filename = os.path.split(path)
    #     try:
    #         blob1 = self.get_tree(commit1, path)
    #         if not isinstance(blob1, dulwich.objects.Tree):
    #             return True
    #         blob1 = blob1[filename]
    #     except KeyError:
    #         blob1 = None
    #     try:
    #         blob2 = self.get_tree(commit2, path)
    #         if not isinstance(blob2, dulwich.objects.Tree):
    #             return True
    #         blob2 = blob2[filename]
    #     except KeyError:
    #         blob2 = None
    #     if blob1 is None and blob2 is None:
    #         # file present in neither tree
    #         return False
    #     return blob1 != blob2

    def get_tree(self, commit, path, noblobs=False):
        """ Returns the Git tree object for `path` at `commit`. """
        tree = self[commit.tree]
        if path:
            for directory in path.strip('/').split('/'):
                if directory:
                    tree = self[tree[directory][1]]
        return tree

    def commit_diff(self, commit):
        from klaus import guess_is_binary, force_unicode

        if commit.parents:
            parent_tree = self[commit.parents[0]].tree
        else:
            parent_tree = None

        changes = self.object_store.tree_changes(parent_tree, commit.tree)
        for (oldpath, newpath), (oldmode, newmode), (oldsha, newsha) in changes:
            try:
                if newsha and guess_is_binary(self[newsha].chunked) or \
                   oldsha and guess_is_binary(self[oldsha].chunked):
                    yield {
                        'is_binary': True,
                        'old_filename': oldpath or '/dev/null',
                        'new_filename': newpath or '/dev/null',
                        'chunks': [[{'line' : 'Binary diff not shown'}]]
                    }
                    continue
            except KeyError:
                # newsha/oldsha are probably related to submodules.
                # Dulwich will handle that.
                pass

            stringio = cStringIO.StringIO()
            dulwich.patch.write_object_diff(stringio, self.object_store,
                                            (oldpath, oldmode, oldsha),
                                            (newpath, newmode, newsha))
            files = prepare_udiff(force_unicode(stringio.getvalue()),
                                  want_header=False)
            if not files:
                # the diff module doesn't handle deletions/additions
                # of empty files correctly.
                yield {
                    'old_filename': oldpath or '/dev/null',
                    'new_filename': newpath or '/dev/null',
                    'chunks': []
                }
            else:
                yield files[0]


def Repo(name, path, _cache={}):
    repo = _cache.get(path)
    if repo is None:
        repo = _cache[path] = RepoWrapper(path)
        repo.name = name
    return repo