# repo.py - functions for repository handling
#
# Copyright (C) 2015 Arthur de Jong
#
# 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 St, Fifth Floor, Boston, MA  02110-1301 USA
#
# The files produced as output from the software do not automatically fall
# under the copyright of the software, unless explicitly stated otherwise.

import datetime
import json
import math
import os.path
import random
import re
import stat
import string
import time


# umask used for files created in the repository
# TODO: UMASK = 0077

def base36(i):
    """Return a BASE36 encoded string of the integer value."""
    alphabet = '0123456789abcdefghijklmnopqrstuvwxyz'
    result = []
    while i != 0:
        i, d = divmod(i, 36)
        result.append(alphabet[d])
    result.reverse()
    return ''.join(result)


def generate_passphrase(bits, alphabet=string.ascii_letters + string.digits):
    l = int(math.ceil(math.log(math.pow(2, bits)) / math.log(len(alphabet))))
    r = random.SystemRandom()
    return ''.join(r.choice(alphabet) for i in xrange(l + 1))


def generate_archive_name():
    """Generate a name based on a timestamp and random value."""
    name = '%8s-%8s' % (
        base36(int(time.time() * 10)),
        base36(random.randrange(int('zzzzzzzz', 36) + 1)))
    return name.replace(' ', '0')


def generate_backup_name():
    """Create a new backup in the repository."""
    return datetime.datetime.now().strftime('%Y%m%d-%H%M%S')


def clean_meta(meta):
    """Migrate metadata from previous formats."""
    meta.pop('ctime', None)  # ctime is no longer used
    if meta.pop('is_dir', None):
        meta['type'] = 'D'  # replace is_dir with type
    mode = meta['mode']
    if mode != stat.S_IMODE(mode):
        meta['mode'] = stat.S_IMODE(mode)
        if stat.S_ISDIR(mode):
            meta['type'] = 'D'
            meta['size'] = 0
        elif stat.S_ISCHR(mode):
            meta['type'] = 'C'
            meta['size'] = 0
        elif stat.S_ISBLK(mode):
            meta['type'] = 'B'
            meta['size'] = 0
        elif stat.S_ISFIFO(mode):
            meta['type'] = 'F'
            meta['size'] = 0
        elif stat.S_ISLNK(mode):
            meta['type'] = 'L'
            meta['size'] = 0
        elif stat.S_ISSOCK(mode):
            meta['type'] = 'S'
            meta['size'] = 0
        elif stat.S_ISREG(mode):
            meta['type'] = 'R'
        else:
            meta['type'] = '?'
    return meta


class Repository(object):

    def __init__(self, repository):
        self._passphrase = None
        self._uuid = None
        from backends.file import FileBackend
        self.backend = FileBackend(repository)

    def list_archives(self):
        """Return archives that are found in the repository."""
        filelist = set()
        for filename in self.backend.listdir('archives'):
            m = re.match(r'archives/([0-9a-zA-Z]{8}-[0-9a-zA-Z]{8})\.tar',
                         filename)
            if m:
                yield m.group(1)

    def remove_archive(self, archive):
        # remove archive files that start with `archive`
        if getattr(self, 'archive_files', None) is None:
            self.archive_files = list(self.backend.listdir('archives'))
        for archive_file in self.archive_files:
            if os.path.basename(archive_file).startswith(archive + '.'):
                try:
                    self.backend.remove(archive_file)
                except EnvironmentError:
                    import traceback
                    print(traceback.format_exc())

    def list_backups(self):
        """Return backups that are found in the repository."""
        filelist = list()
        for filename in self.backend.listdir('backups'):
            filelist.append(os.path.basename(filename))
        filelist.sort()
        return filelist

    def remove_backup(self, backup):
        try:
            self.backend.remove('backups/%s' % backup, recurse=True)
        except EnvironmentError:
            import traceback
            print(traceback.format_exc())

    def write_file(self, filename, executable=False,
                   encryption=None, compression=None):
        """Return an open file handle that can be used to write a file
        contents to."""
        if compression:
            filename = compression.rename(filename)
        if encryption:
            filename = encryption.rename(filename)
        f = self.backend.put(filename, executable)
        if encryption:
            f = encryption.writer(f)
        if compression:
            f = compression.writer(f)
        return f

    def get_filters(self, filename, encryption=None):
        from filters import (
            GzipCompression, Bzip2Compression, XZCompression, GnuPGEncryption)
        filters = []
        while True:
            if encryption and filename.endswith('.' + encryption.extension):
                filename = filename[:-(len(encryption.extension) + 1)]
                filters.append(encryption)
            elif filename.endswith('.' + GnuPGEncryption.extension):
                filename = filename[:-(len(GnuPGEncryption.extension) + 1)]
                filters.append(GnuPGEncryption(self))
            elif filename.endswith('.' + GzipCompression.extension):
                filename = filename[:-(len(GzipCompression.extension) + 1)]
                filters.append(GzipCompression())
            elif filename.endswith('.' + Bzip2Compression.extension):
                filename = filename[:-(len(Bzip2Compression.extension) + 1)]
                filters.append(Bzip2Compression())
            elif filename.endswith('.' + XZCompression.extension):
                filename = filename[:-(len(XZCompression.extension) + 1)]
                filters.append(XZCompression())
            else:
                break
        return filename, filters

    def expand(self, filename, encryption=None):
        path = os.path.dirname(filename)
        for f in self.backend.listdir(path):
            if f.startswith(filename):
                name, filters = self.get_filters(f, encryption)
                if name == filename:
                    return f, filters
        return filename, []

    def read_file(self, filename, encryption=None):
        """Returns an open file handle that can be used to read from."""
        filename, filters = self.expand(filename, encryption)
        f = self.backend.get(filename)
        for fltr in filters:
            f = fltr.reader(f)
        return f

    def read_fileslist(self, filename):
        """Read a file list from the repository and return information one
        line at a time."""
        # we take advantage of the fact that the JSON file contains a single
        # path per line (otherwise we would have to load the whole file in
        # memory)
        with self.read_file(filename) as f:
            line = f.next()
            if line != '[\n':
                raise ValueError('error on first line')
            for line in f:
                if line != ']\n':
                    yield clean_meta(json.loads(line.rstrip('\n,')))
            if line != ']\n':
                raise ValueError('error on last line')

    def get_passphrase(self):
        if not self._passphrase:
            # TODO: we should be able to use multiple passphrases for
            # different parts of the repository
            from filters import GnuPGKeyEncryption
            with self.read_file(
                    'keys/passphrase', encryption=GnuPGKeyEncryption()) as f:
                self._passphrase = str(f.read()).strip()
        return self._passphrase

    def get_or_create_passphrase(self):
        try:
            return self.get_passphrase()
        except EnvironmentError:
            # generate a passphrase with about 256 bits entropy
            return generate_passphrase(256)

    def write_passphrase(self, passphrase, keys):
        from filters import GnuPGKeyEncryption
        filename = 'keys/passphrase'
        # remove any existing new files
        newfile, filters = self.expand(filename + '.new')
        if self.backend.exists(newfile):
            self.backend.remove(newfile)
        # write out the new encrypted file
        with self.write_file(
                filename + '.new', encryption=GnuPGKeyEncryption(keys)) as f:
            f.write(('%s\n' % passphrase).encode('utf-8'))
        # check that we can actually read the file
        with self.read_file(
                filename + '.new', encryption=GnuPGKeyEncryption()) as f:
            assert str(f.read()).strip() == passphrase
        # figure out the file names
        newfile, filters = self.expand(filename + '.new')
        curfile, filters = self.expand(filename)
        oldfile, filters = self.expand(filename + '.old')
        # remove the old backup
        if self.backend.exists(oldfile):
            self.remove(oldfile)
        # backup the old passphrase
        if self.backend.exists(curfile):
            oldfile = (curfile + '.').replace('.', '.old.', 1).rstrip('.')
            self.backend.rename(curfile, oldfile)
        # put new passphrase file in place
        self.backend.rename(newfile, newfile.replace('.new', '', 1))

    @property
    def uuid(self):
        if self._uuid:
            return self._uuid
        # try to read the uuid file
        try:
            with self.read_file('uuid') as f:
                uuid = str(f.read()).strip()
            if re.match(r'^[0-9a-z]{8,16}$', uuid):
                self._uuid = uuid
                return uuid
        except EnvironmentError:
            pass  # ignore reading uuid, generate one instead
        # generate a new uuid
        uuid = '%16s' % base36(random.randrange(int(16 * 'z', 36) + 1))
        uuid.replace(' ', '0')
        self._uuid = uuid
        # save the uuid in the repository
        with self.write_file('uuid') as f:
            f.write(('%s\n' % uuid).encode('utf-8'))
        return uuid