#!/usr/bin/python


# Copyright (c) 2015 - Mathieu Bridon <bochecha@daitauha.fr>
#
# This script 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 3 of the License, or
# (at your option) any later version.
#
# This script 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 script.  If not, see <http://www.gnu.org/licenses/>.


import argparse
import errno
from grp import getgrnam
import hashlib
import os
from pwd import getpwnam
import sys


def get_args():
    parser = argparse.ArgumentParser()

    parser.add_argument('--perform', action='store_true', default=False,
                        help="Actually do the hardlinking (default is to "
                             "report only)")
    parser.add_argument('--link-hashtype', default='md5',
                        choices=('md5', 'sha512'),
                        help='The hash type to use in the new path of the'
                             'hardlink. (default: "md5")')
    parser.add_argument('lookasideroot',
                        help="The full path to the root of the lookaside "
                             "cache")

    return parser.parse_args()


def info(msg):
    sys.stdout.write("%s\n" % msg)


def error(msg):
    sys.stderr.write("ERROR: %s\n" % msg)


def die(msg):
    sys.stderr.write("FATAL: %s\n" % msg)
    sys.exit(1)


def get_file_hash(full_path, hashtype):
    hash = hashlib.new(hashtype)

    with open(full_path, 'rb') as f:
        chunk = f.read(4096)

        while chunk:
            hash.update(chunk)
            chunk = f.read(4096)

    return hash.hexdigest()


def verify_source(dir, expected_name, expected_hash, hashtype):
    sources = list(listdir(dir))

    if len(sources) == 0:
        raise Exception("No source file in %s" % dir)

    if len(sources) > 1:
        raise Exception("Multiple source files in %s: %s" % (dir, sources))

    if sources[0] != expected_name:
        raise Exception("Badly named source file in %s: %s"
                        % (dir, sources[0]))

    source_path = os.path.join(dir, expected_name)
    hash = get_file_hash(source_path, hashtype)

    if hash != expected_hash:
        die("Invalid %s for %s: %s" % (hashtype.upper(), source_path, hash))

    return source_path


def listdir(dir):
    try:
        for f in os.listdir(dir):
            yield f

    except OSError as e:
        if e.errno == errno.ENOTDIR:
            error("%s is not a directory" % dir)

        else:
            raise


def makedirs(dir):
    try:
        os.makedirs(dir)

    except OSError as e:
        if e.errno != errno.EEXIST:
            raise e


def hardlink(src, dst):
    makedirs(os.path.dirname(dst))

    try:
        os.link(src, dst)

    except OSError as e:
        if e.errno != errno.EEXIST:
            raise e

        # The file already exists at the new-style path?
        # Overwrite it with a hardlink.
        os.unlink(dst)
        os.link(src, dst)


def main(root, link_hashtype, perform=False):
    ownerid = getpwnam('apache').pw_uid
    groupid = getgrnam('apache').gr_gid

    try:
        os.chdir(root)
        info("All future paths relative to %s" % root)

    except OSError as e:
        die(e)

    for pkg_name in listdir(root):
        for source_name in listdir(pkg_name):
            source_dir = os.path.join(pkg_name, source_name)

            for hash in listdir(source_dir):
                if hash in ('md5', 'sha512'):
                    # This is not a hash, but a new-style path containing the
                    # hashtype. Let's just verify what it contains
                    hashtype = hash
                    hashtype_dir = os.path.join(source_dir, hash)

                    for hash in listdir(hashtype_dir):
                        try:
                            verify_source(os.path.join(hashtype_dir, hash),
                                          source_name, hash, hashtype)
                        except Exception as e:
                            error(e)
                            continue

                    continue

                else:
                    # This is what is used for hashes which are not under a
                    # hashtype folder
                    hashtype = 'md5'

                try:
                    source_path = verify_source(
                        os.path.join(source_dir, hash), source_name, hash,
                        hashtype)
                except Exception as e:
                    error(e)
                    continue

                if link_hashtype != hashtype:
                    new_hash = get_file_hash(source_path, link_hashtype)

                else:
                    new_hash = hash

                new_path = os.path.join(source_dir, link_hashtype, new_hash,
                                        source_name)
                info("Hardlinking: %s to %s" % (source_path, new_path))

                if perform:
                    hardlink(source_path, new_path)
                    segments = new_path.split('/')

                    for i in range(1, len(segments) + 1):
                        os.chown('/'.join(segments[:i], ownerid, groupid)


if __name__ == '__main__':
    args = get_args()

    main(args.lookasideroot, args.link_hashtype, perform=args.perform)
    sys.exit(0)