#!/usr/bin/python3

# pylint: disable=fixme,invalid-name
# pylint: disable=too-many-branches,too-many-locals,too-many-statements

"""Repack git repos fully the way I like them."""

from __future__ import print_function

import argparse
import os
from pathlib import Path
import shutil
import subprocess
import sys
import tempfile
from typing import Dict, List, Optional


def mount_settings() -> Dict[str, str]:
    """Return dict mapping path to its type"""
    ret = {}
    with Path('/proc/mounts').open(encoding='utf-8') as fp:
        for line in fp:
            ele = line.split()
            ret[ele[1]] = ele[2]
    return ret


def is_git_dir(path: Path) -> bool:
    """Whether |path| is a .git dir"""
    return ((path / 'refs').is_dir() and
            (path / 'objects').is_dir() and
            (path / 'config').is_file())


def find_git_dir(path: Path) -> Path:
    """Try to find the .git dir to operate on"""
    orig_path = path
    real_path = path = path.resolve()
    while True:
        curr_path = path
        if (path / '.git').is_dir():
            curr_path = path / '.git'

        if is_git_dir(curr_path):
            return curr_path

        parent = path.parent
        if path == parent:
            raise ValueError('could not locate .git dir: %s (%s)' %
                             (orig_path, real_path))
        path = parent


def find_temp_dir() -> Optional[Path]:
    """Find a good temp dir (one backed by tmpfs)"""
    SEARCH_PATHS = (
        '/var/tmp/portage',
        '/var/tmp',
        '/tmp',
        tempfile.gettempdir(),
    )
    mounts = mount_settings()
    for path in SEARCH_PATHS:
        if mounts.get(path) == 'tmpfs':
            return Path(path)
    return None


def readfile(path: Path) -> str:
    """Read |path| and return its data"""
    if path.is_file():
        return path.read_text(encoding='utf-8')
    return ''


def clean_hooks(path):
    """Strip out sample files from hooks/"""
    for hook in (path / 'hooks').glob('*.sample'):
        print('Trimming hook:', hook)
        hook.unlink()


def clean_packs(path):
    """Strip out temp files from objects/packs/"""
    for pack in (path / 'objects' / 'packs').glob('tmp_pack_*'):
        print('Trimming pack:', pack)
        pack.unlink()


def is_packed(path):
    """See if the git repo is already packed"""
    obj_path = path / 'objects'
    paths = {x.name for x in obj_path.iterdir()}
    if paths not in ({'info', 'pack'}, {'pack'}):
        return False
    packs = tuple((obj_path / 'pack').iterdir())
    if len(packs) != 2:
        return False
    return True


def repack(path: Path):
    """Clean up and trim cruft and repack |path|"""
    path = find_git_dir(path)
    print('Repacking', path)

    # Repack any submodules this project might use.
    modules_path = path / 'modules'
    if modules_path.is_dir():
        for root, dirs, _ in os.walk(modules_path):
            root = Path(root)
            dirs.sort()
            for d in dirs:
                mod_path = root / d
                if is_git_dir(mod_path):
                    repack(mod_path)

    tmpdir = find_temp_dir()
    if tmpdir:
        tmpdir = Path(tempfile.mkdtemp(prefix='git-repack.', dir=tmpdir))
        print('Using tempdir:', tmpdir)
        tmpdir.rmdir()
        # Doesn't matter for these needs.
        os.environ['GIT_WORK_TREE'] = str(tmpdir)

    grafts = alts = None
    try:
        # Push/pop the graft & alternate paths so we don't read them.
        # XXX: In some cases, this is bad, but I don't use them that way ...
        graft_file = path / 'info' / 'grafts'
        grafts = readfile(graft_file)
        graft_file.unlink(missing_ok=True)

        alt_file = path / 'objects' / 'info' / 'alternates'
        alts = readfile(alt_file)
        alt_file.unlink(missing_ok=True)

        clean_hooks(path)

        # XXX: Should do this for all remotes?
        origin_path = path / 'refs' / 'remotes' / 'origin'
        # Delete remote HEAD as we don't need it, and it might be stale.
        head = origin_path / 'HEAD'
        head.unlink(missing_ok=True)
        packed_refs = readfile(path / 'packed-refs')
        if origin_path.exists() or 'refs/remotes/origin/' in packed_refs:
            cmd = ['git', '--git-dir', str(path), 'remote', 'prune', 'origin']
            subprocess.run(cmd, cwd='/', check=True)

        clean_packs(path)

        if is_packed(path):
            print('Git repo is already packed; nothing to do')
            return

        if tmpdir:
            print('Syncing git repo to tempdir')
            shutil.copytree(path, tmpdir, symlinks=True)
            rundir = tmpdir
        else:
            rundir = path

        cmd = ['git', '--git-dir', str(rundir), 'reflog', 'expire', '--all', '--stale-fix']
        print('Cleaning reflog:', ' '.join(cmd))
        subprocess.run(cmd, cwd='/', check=True)

        # This also packs refs/tags for us.
        cmd = ['git', '--git-dir', str(rundir), 'gc', '--aggressive', '--prune=all']
        print('Repacking git repo:', ' '.join(cmd))
        subprocess.run(cmd, cwd='/', check=True)

        # Clean empty dirs.
        cmd = ['find', str(rundir), '-depth', '-type', 'd', '-exec', 'rmdir', '{}', '+']
        subprocess.run(cmd, stderr=subprocess.DEVNULL, check=False)

        # There's a few dirs we need to exist even if they're empty.
        refdir = rundir / 'refs'
        refdir.mkdir(exist_ok=True)

        if tmpdir:
            cmd = ['rsync', '-a', '--delete', str(tmpdir) + '/', str(path) + '/']
            print('Syncing back git repo:', ' '.join(cmd))
            subprocess.run(cmd, cwd='/', check=True)
            cmd = ['find', str(path) + '/', '-exec', 'chmod', 'u+rw', '{}', '+']
            subprocess.run(cmd, cwd='/', check=True)

    finally:
        if grafts:
            graft_file.write_text(grafts, encoding='utf-8')
        if alts:
            alt_file.write_text(alts, encoding='utf-8')
        if tmpdir:
            shutil.rmtree(tmpdir, ignore_errors=True)


def get_parser():
    """Get the command line parser"""
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('dir', type=Path, help='The git repo to process')
    return parser


def main(argv: List[str]):
    """The main script entry point"""
    parser = get_parser()
    opts = parser.parse_args(argv)
    repack(opts.dir)


if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))