#!/usr/bin/python2.6
import os, re, subprocess, sys

class GitError(EnvironmentError):
    def __init__(self, err, out, returncode):
        EnvironmentError.__init__(self, err)
        self.stdout = out
        self.returncode = returncode

def git(*args, **kw):
    p = subprocess.Popen(('git',) + args, **kw)
    out, err = p.communicate()
    if p.returncode:
        raise GitError(err, out, p.returncode)
    return out

def main():
    svn_id_re = re.compile('\n+git-svn-id: .*\n*$')
    grafts = []
    key = None
    skip = False
    try:
        for log in git('log', '-z', '--pretty=format:%H %P %an %B',
                       stdout=subprocess.PIPE, *sys.argv[1:]).split('\0'):
            # If there is more than 1 parent, 'k' will start
            # with their hash and will always differ from 'key'.
            # Thus, we never squash merge commits.
            h, p, k = log.split(' ', 2)
            k = svn_id_re.sub('', k)
            if k == key:
                skip = True
            else:
                if skip:
                    grafts.append((parent, h))
                key = k
                parent = h
                skip = False
        if skip:
            grafts.append((parent,))
        if grafts:
            git_dir = git('rev-parse', '--git-dir',
                          stdout=subprocess.PIPE).strip()
            with open(os.path.join(git_dir, 'info', 'grafts'), 'a') as f:
                for graft in grafts:
                    f.write(' '.join(graft) + '\n')
    except GitError, e:
        err = str(e)
        if err:
            sys.stderr.write(err)
        return e.returncode

if __name__ == '__main__':
    sys.exit(main())


# #!/bin/sh -e
# tmp=`mktemp -d`
# trap "rm -r $tmp" 0
# if git log --pretty=format:'%H %an %s' |uniq -cds 41 |while read n h line
#    do git rev-parse -q --verify $h^2 >/dev/null || git rev-list $h~$n..$h~
#    done | (cd "$tmp"; xargs touch 2>/dev/null)
# then git filter-branch --commit-filter "if rm $tmp/\$GIT_COMMIT 2>/dev/null
#        then skip_commit "\$@"
#        else git commit-tree "\$@"
#      fi" --tag-name-filter cat "$@"
# fi