#!/usr/bin/env python
# -*- coding: utf-8 -*-

# Copyright (C) 2013 by Łukasz Langa

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import argparse
import atexit
import datetime
import errno
import hashlib
import os
import shutil
import sqlite3
import stat
import sys
import tempfile
import time


DEFAULT_CHUNK_SIZE = 16384
DOT_THRESHOLD = 200
VERSION = (0, 9, 0)
IGNORED_FILE_SYSTEM_ERRORS = {errno.ENOENT, errno.EACCES}
FSENCODING = sys.getfilesystemencoding()


if sys.version[0] == '2':
    str = type(u'text')
    # use `bytes` for bytestrings


def sha1(path, chunk_size):
    digest = hashlib.sha1()
    with open(path, 'rb') as f:
        d = f.read(chunk_size)
        while d:
            digest.update(d)
            d = f.read(chunk_size)
    return digest.hexdigest()


def ts():
    return datetime.datetime.utcnow().strftime('%Y-%m-%d %H:%M:%S%z')


def get_sqlite3_cursor(path, copy=False):
    path = path.decode(FSENCODING)
    if copy:
        if not os.path.exists(path):
            raise ValueError("error: bitrot database at {} does not exist."
                             "".format(path))
        db_copy = tempfile.NamedTemporaryFile(prefix='bitrot_', suffix='.db',
                                              delete=False)
        with open(path, 'rb') as db_orig:
            try:
                shutil.copyfileobj(db_orig, db_copy)
            finally:
                db_copy.close()
        path = db_copy.name
        atexit.register(os.unlink, path)
    conn = sqlite3.connect(path)
    atexit.register(conn.close)
    cur = conn.cursor()
    tables = set(t for t, in cur.execute('SELECT name FROM sqlite_master'))
    if 'bitrot' not in tables:
        cur.execute('CREATE TABLE bitrot (path TEXT PRIMARY KEY, '
                    'mtime INTEGER, hash TEXT, timestamp TEXT)')
    if 'bitrot_hash_idx' not in tables:
        cur.execute('CREATE INDEX bitrot_hash_idx ON bitrot (hash)')
    atexit.register(conn.commit)
    return conn


def list_existing_paths(directory, expected=(), ignored=(), follow_links=False):
    """list_existing_paths('/dir') -> ([path1, path2, ...], total_size)

    Returns a tuple with a list with existing files in `directory` and their
    `total_size`.

    Doesn't add entries listed in `ignored`.  Doesn't add symlinks if
    `follow_links` is False (the default).  All entries present in `expected`
    must be files (can't be directories or symlinks).
    """
    paths = []
    total_size = 0
    for path, _, files in os.walk(directory):
        for f in files:
            p = os.path.join(path, f)
            try:
                p_uni = p.decode(FSENCODING)
            except UnicodeDecodeError:
                try:
                    print(
                        "warning: cannot decode file name:",
                        path,
                        file=sys.stderr,
                    )
                except UnicodeDecodeError:
                    # yup, even printing the filename might fail in certain
                    # occasions
                    pass

                continue

            try:
                if follow_links or p_uni in expected:
                    st = os.stat(p)
                else:
                    st = os.lstat(p)
            except OSError as ex:
                if ex.errno not in IGNORED_FILE_SYSTEM_ERRORS:
                    raise
            else:
                if not stat.S_ISREG(st.st_mode) or p in ignored:
                    continue
                paths.append(p)
                total_size += st.st_size
    paths.sort()
    return paths, total_size


class BitrotException(Exception):
    pass


class Bitrot(object):
    def __init__(
        self, verbosity=1, test=False, follow_links=False, commit_interval=300,
        chunk_size=DEFAULT_CHUNK_SIZE,
    ):
        self.verbosity = verbosity
        self.test = test
        self.follow_links = follow_links
        self.commit_interval = commit_interval
        self.chunk_size = chunk_size
        self._last_reported_size = ''
        self._last_commit_ts = 0

    def maybe_commit(self, conn):
        if time.time() < self._last_commit_ts + self.commit_interval:
            # no time for commit yet!
            return

        conn.commit()
        self._last_commit_ts = time.time()

    def run(self):
        check_sha512_integrity(verbosity=self.verbosity)

        bitrot_db = get_path()
        bitrot_sha512 = get_path(ext=b'sha512')
        try:
            conn = get_sqlite3_cursor(bitrot_db, copy=self.test)
        except ValueError:
            raise BitrotException(
                2,
                'No database exists so cannot test. Run the tool once first.',
            )

        cur = conn.cursor()
        new_paths = []
        updated_paths = []
        renamed_paths = []
        errors = []
        current_size = 0
        missing_paths = self.select_all_paths(cur)
        paths, total_size = list_existing_paths(
            b'.', expected=missing_paths, ignored={bitrot_db, bitrot_sha512},
            follow_links=self.follow_links,
        )

        for p in paths:
            p_uni = p.decode('utf8')
            try:
                st = os.stat(p)
            except OSError as ex:
                if ex.errno in IGNORED_FILE_SYSTEM_ERRORS:
                    # The file disappeared between listing existing paths and
                    # this run or is (temporarily?) locked with different
                    # permissions. We'll just skip it for now.
                    print(
                        '\rwarning: `{}` is currently unavailable for '
                        'reading: {}'.format(
                            p_uni, ex,
                        ),
                        file=sys.stderr,
                    )
                    continue

                raise   # Not expected? https://github.com/ambv/bitrot/issues/

            new_mtime = int(st.st_mtime)
            current_size += st.st_size
            if self.verbosity:
                self.report_progress(current_size, total_size)

            missing_paths.discard(p_uni)
            try:
                new_sha1 = sha1(p, self.chunk_size)
            except (IOError, OSError) as e:
                if self.verbosity:
                    print(
                        '\rwarning: cannot compute hash of {} [{}]'.format(
                            p, errno.errorcode[e.args[0]],
                        ),
                        file=sys.stderr,
                    )
                continue

            cur.execute('SELECT mtime, hash, timestamp FROM bitrot WHERE '
                        'path=?', (p_uni,))
            row = cur.fetchone()
            if not row:
                stored_path = self.handle_unknown_path(
                    cur, p_uni, new_mtime, new_sha1,
                )
                self.maybe_commit(conn)

                if p_uni == stored_path:
                    new_paths.append(p)   # FIXME: shouldn't that be p_uni?
                else:
                    renamed_paths.append((stored_path, p_uni))
                    missing_paths.discard(stored_path)
                continue

            stored_mtime, stored_sha1, stored_ts = row
            if int(stored_mtime) != new_mtime:
                updated_paths.append(p)
                cur.execute('UPDATE bitrot SET mtime=?, hash=?, timestamp=? '
                            'WHERE path=?',
                            (new_mtime, new_sha1, ts(), p_uni))
                self.maybe_commit(conn)
                continue

            if stored_sha1 != new_sha1:
                errors.append(p)
                print(
                    '\rerror: SHA1 mismatch for {}: expected {}, got {}.'
                    ' Last good hash checked on {}.'.format(
                        p, stored_sha1, new_sha1, stored_ts
                    ),
                    file=sys.stderr,
                )

        for path in missing_paths:
            cur.execute('DELETE FROM bitrot WHERE path=?', (path,))

        conn.commit()

        if self.verbosity:
            cur.execute('SELECT COUNT(path) FROM bitrot')
            all_count = cur.fetchone()[0]
            self.report_done(
                total_size,
                all_count,
                len(errors),
                new_paths,
                updated_paths,
                renamed_paths,
                missing_paths,
            )

        update_sha512_integrity(verbosity=self.verbosity)

        if errors:
            raise BitrotException(
                1, 'There were {} errors found.'.format(len(errors)), errors,
            )

    def select_all_paths(self, cur):
        result = set()
        cur.execute('SELECT path FROM bitrot')
        row = cur.fetchone()
        while row:
            result.add(row[0])
            row = cur.fetchone()
        return result

    def report_progress(self, current_size, total_size):
        size_fmt = '\r{:>6.1%}'.format(current_size/(total_size or 1))
        if size_fmt == self._last_reported_size:
            return

        sys.stdout.write(size_fmt)
        sys.stdout.flush()
        self._last_reported_size = size_fmt

    def report_done(
        self, total_size, all_count, error_count, new_paths, updated_paths,
        renamed_paths, missing_paths):
        print('\rFinished. {:.2f} MiB of data read. {} errors found.'
            ''.format(total_size/1024/1024, error_count))
        if self.verbosity == 1:
            print(
                '{} entries in the database, {} new, {} updated, '
                '{} renamed, {} missing.'.format(
                    all_count, len(new_paths), len(updated_paths),
                    len(renamed_paths), len(missing_paths),
                ),
            )
        elif self.verbosity > 1:
            print('{} entries in the database.'.format(all_count), end=' ')
            if new_paths:
                print('{} entries new:'.format(len(new_paths)))
                new_paths.sort()
                for path in new_paths:
                    print(' ', path)
            if updated_paths:
                print('{} entries updated:'.format(len(updated_paths)))
                updated_paths.sort()
                for path in updated_paths:
                    print(' ', path)
            if renamed_paths:
                print('{} entries renamed:'.format(len(renamed_paths)))
                renamed_paths.sort()
                for path in renamed_paths:
                    print(' from', path[0], 'to', path[1])
            if missing_paths:
                print('{} entries missing:'.format(len(missing_paths)))
                missing_paths = sorted(missing_paths)
                for path in missing_paths:
                    print(' ', path)
            if not any((new_paths, updated_paths, missing_paths)):
                print()
        if self.test and self.verbosity:
            print('warning: database file not updated on disk (test mode).')

    def handle_unknown_path(self, cur, new_path, new_mtime, new_sha1):
        """Either add a new entry to the database or update the existing entry
        on rename.

        Returns `new_path` if the entry was indeed new or the `stored_path` (e.g.
        outdated path) if there was a rename.
        """
        cur.execute('SELECT mtime, path, timestamp FROM bitrot WHERE hash=?',
                    (new_sha1,))
        rows = cur.fetchall()
        for row in rows:
            stored_mtime, stored_path, stored_ts = row
            if os.path.exists(stored_path):
                # file still exists, move on
                continue

            # update the path in the database
            cur.execute(
                'UPDATE bitrot SET mtime=?, path=?, timestamp=? WHERE path=?',
                (new_mtime, new_path, ts(), stored_path),
            )

            return stored_path

        # no rename, just a new file with the same hash
        cur.execute(
            'INSERT INTO bitrot VALUES (?, ?, ?, ?)',
            (new_path, new_mtime, new_sha1, ts()),
        )
        return new_path


def get_path(directory=b'.', ext=b'db'):
    """Compose the path to the selected bitrot file."""
    return os.path.join(directory, b'.bitrot.' + ext)


def stable_sum(bitrot_db):
    """Calculates a stable SHA512 of all entries in the database.

    Useful for comparing if two directories hold the same data, as it ignores
    timing information."""
    digest = hashlib.sha512()
    conn = get_sqlite3_cursor(bitrot_db)
    cur = conn.cursor()
    cur.execute('SELECT hash FROM bitrot ORDER BY path')
    row = cur.fetchone()
    while row:
        digest.update(row[0])
        row = cur.fetchone()
    return digest.hexdigest()


def check_sha512_integrity(verbosity=1):
    sha512_path = get_path(ext=b'sha512')
    if not os.path.exists(sha512_path):
        return

    if verbosity:
        print('Checking bitrot.db integrity... ', end='')
        sys.stdout.flush()
    with open(sha512_path, 'rb') as f:
        old_sha512 = f.read().strip()
    bitrot_db = get_path()
    digest = hashlib.sha512()
    with open(bitrot_db, 'rb') as f:
        digest.update(f.read())
    new_sha512 = digest.hexdigest().encode('ascii')
    if new_sha512 != old_sha512:
        if verbosity:
            if len(old_sha512) == 128:
                print(
                    "error: SHA512 of the file is different, bitrot.db might "
                    "be corrupt.",
                )
            else:
                print(
                    "error: SHA512 of the file is different but bitrot.sha512 "
                    "has a suspicious length. It might be corrupt.",
                )
            print(
                "If you'd like to continue anyway, delete the .bitrot.sha512 "
                "file and try again.",
                file=sys.stderr,
            )
        raise BitrotException(
            3, 'bitrot.db integrity check failed, cannot continue.',
        )

    if verbosity:
        print('ok.')

def update_sha512_integrity(verbosity=1):
    old_sha512 = 0
    sha512_path = get_path(ext=b'sha512')
    if os.path.exists(sha512_path):
        with open(sha512_path, 'rb') as f:
            old_sha512 = f.read().strip()
    bitrot_db = get_path()
    digest = hashlib.sha512()
    with open(bitrot_db, 'rb') as f:
        digest.update(f.read())
    new_sha512 = digest.hexdigest().encode('ascii')
    if new_sha512 != old_sha512:
        if verbosity:
            print('Updating bitrot.sha512... ', end='')
            sys.stdout.flush()
        with open(sha512_path, 'wb') as f:
            f.write(new_sha512)
        if verbosity:
            print('done.')

def run_from_command_line():
    global FSENCODING

    parser = argparse.ArgumentParser(prog='bitrot')
    parser.add_argument(
        '-l', '--follow-links', action='store_true',
        help='follow symbolic links and store target files\' hashes. Once '
             'a path is present in the database, it will be checked against '
             'changes in content even if it becomes a symbolic link. In '
             'other words, if you run `bitrot -l`, on subsequent runs '
             'symbolic links registered during the first run will be '
             'properly followed and checked even if you run without `-l`.')
    parser.add_argument(
        '-q', '--quiet', action='store_true',
        help='don\'t print anything besides checksum errors')
    parser.add_argument(
        '-s', '--sum', action='store_true',
        help='using only the data already gathered, return a SHA-512 sum '
             'of hashes of all the entries in the database. No timestamps '
             'are used in calculation.')
    parser.add_argument(
        '-v', '--verbose', action='store_true',
        help='list new, updated and missing entries')
    parser.add_argument(
        '-t', '--test', action='store_true',
        help='just test against an existing database, don\'t update anything')
    parser.add_argument(
        '--version', action='version',
        version='%(prog)s {}.{}.{}'.format(*VERSION))
    parser.add_argument(
        '--commit-interval', type=float, default=300,
        help='min time in seconds between commits '
             '(0 commits on every operation)')
    parser.add_argument(
        '--chunk-size', type=int, default=DEFAULT_CHUNK_SIZE,
        help='read files this many bytes at a time')
    parser.add_argument(
        '--fsencoding', default='',
        help='override the codec to decode filenames, otherwise taken from '
             'the LANG environment variables')
    args = parser.parse_args()
    if args.sum:
        try:
            print(stable_sum())
        except RuntimeError as e:
            print(str(e).encode('utf8'), file=sys.stderr)
    else:
        verbosity = 1
        if args.quiet:
            verbosity = 0
        elif args.verbose:
            verbosity = 2
        bt = Bitrot(
            verbosity=verbosity,
            test=args.test,
            follow_links=args.follow_links,
            commit_interval=args.commit_interval,
            chunk_size=args.chunk_size,
        )
        if args.fsencoding:
            FSENCODING = args.fsencoding
        try:
            bt.run()
        except BitrotException as bre:
            print('error:', bre.args[1], file=sys.stderr)
            sys.exit(bre.args[0])


if __name__ == '__main__':
    run_from_command_line()