dupeguru/core/pe/cache_sqlite.py

# Copyright 2016 Virgil Dupras
#
# This software is licensed under the "GPLv3" License as described in the "LICENSE" file,
# which should be included with this package. The terms are also available at
# http://www.gnu.org/licenses/gpl-3.0.html

import os
import os.path as op
import logging
import sqlite3 as sqlite

from .cache import string_to_colors, colors_to_string

class SqliteCache:
    """A class to cache picture blocks in a sqlite backend.
    """
    def __init__(self, db=':memory:', readonly=False):
        # readonly is not used in the sqlite version of the cache
        self.dbname = db
        self.con = None
        self._create_con()

    def __contains__(self, key):
        sql = "select count(*) from pictures where path = ?"
        result = self.con.execute(sql, [key]).fetchall()
        return result[0][0] > 0

    def __delitem__(self, key):
        if key not in self:
            raise KeyError(key)
        sql = "delete from pictures where path = ?"
        self.con.execute(sql, [key])

    # Optimized
    def __getitem__(self, key):
        if isinstance(key, int):
            sql = "select blocks from pictures where rowid = ?"
        else:
            sql = "select blocks from pictures where path = ?"
        result = self.con.execute(sql, [key]).fetchone()
        if result:
            result = string_to_colors(result[0])
            return result
        else:
            raise KeyError(key)

    def __iter__(self):
        sql = "select path from pictures"
        result = self.con.execute(sql)
        return (row[0] for row in result)

    def __len__(self):
        sql = "select count(*) from pictures"
        result = self.con.execute(sql).fetchall()
        return result[0][0]

    def __setitem__(self, path_str, blocks):
        blocks = colors_to_string(blocks)
        if op.exists(path_str):
            mtime = int(os.stat(path_str).st_mtime)
        else:
            mtime = 0
        if path_str in self:
            sql = "update pictures set blocks = ?, mtime = ? where path = ?"
        else:
            sql = "insert into pictures(blocks,mtime,path) values(?,?,?)"
        try:
            self.con.execute(sql, [blocks, mtime, path_str])
        except sqlite.OperationalError:
            logging.warning('Picture cache could not set value for key %r', path_str)
        except sqlite.DatabaseError as e:
            logging.warning('DatabaseError while setting value for key %r: %s', path_str, str(e))

    def _create_con(self, second_try=False):
        def create_tables():
            logging.debug("Creating picture cache tables.")
            self.con.execute("drop table if exists pictures")
            self.con.execute("drop index if exists idx_path")
            self.con.execute("create table pictures(path TEXT, mtime INTEGER, blocks TEXT)")
            self.con.execute("create index idx_path on pictures (path)")

        self.con = sqlite.connect(self.dbname, isolation_level=None)
        try:
            self.con.execute("select path, mtime, blocks from pictures where 1=2")
        except sqlite.OperationalError: # new db
            create_tables()
        except sqlite.DatabaseError as e: # corrupted db
            if second_try:
                raise # Something really strange is happening
            logging.warning('Could not create picture cache because of an error: %s', str(e))
            self.con.close()
            os.remove(self.dbname)
            self._create_con(second_try=True)

    def clear(self):
        self.close()
        if self.dbname != ':memory:':
            os.remove(self.dbname)
        self._create_con()

    def close(self):
        if self.con is not None:
            self.con.close()
        self.con = None

    def filter(self, func):
        to_delete = [key for key in self if not func(key)]
        for key in to_delete:
            del self[key]

    def get_id(self, path):
        sql = "select rowid from pictures where path = ?"
        result = self.con.execute(sql, [path]).fetchone()
        if result:
            return result[0]
        else:
            raise ValueError(path)

    def get_multiple(self, rowids):
        sql = "select rowid, blocks from pictures where rowid in (%s)" % ','.join(map(str, rowids))
        cur = self.con.execute(sql)
        return ((rowid, string_to_colors(blocks)) for rowid, blocks in cur)

    def purge_outdated(self):
        """Go through the cache and purge outdated records.

        A record is outdated if the picture doesn't exist or if its mtime is greater than the one in
        the db.
        """
        todelete = []
        sql = "select rowid, path, mtime from pictures"
        cur = self.con.execute(sql)
        for rowid, path_str, mtime in cur:
            if mtime and op.exists(path_str):
                picture_mtime = os.stat(path_str).st_mtime
                if int(picture_mtime) <= mtime:
                    # not outdated
                    continue
            todelete.append(rowid)
        if todelete:
            sql = "delete from pictures where rowid in (%s)" % ','.join(map(str, todelete))
            self.con.execute(sql)