import sqlite3
import logging
import os.path
from time import strftime

class SqliteCache:
    def __init__(self, database_name='cache.sqlite3', logger=None):
        self._logger = logger or logging.getLogger(__name__)
        self._database_name = database_name
        self._ensure_db_exists()

    def _ensure_db_exists(self):
        if not os.path.exists(self._database_name):
            with Cursor(self._database_name) as cursor:
                cursor.execute('''CREATE TABLE cache (key TEXT PRIMARY KEY, value TEXT, date TEXT)''')

    def exists(self, key):
        with Cursor(self._database_name) as cursor:
            cursor.execute("""SELECT key FROM cache WHERE key=?""", (key,))
            return cursor.fetchone() is not None

    def get(self, key):
        self._logger.debug("Fetching value '{0}' from cache".format(key))
        with Cursor(self._database_name) as cursor:
            cursor.execute("""SELECT value FROM cache WHERE key=?""", (key,))
            c = cursor.fetchone()
            return None if not c else c[0]

    def cache(self, key, value):
        if self.exists(key):
            self._logger.debug("The key '{0}' already exists in the cache".format(key))
            return

        self._logger.debug("Caching value with key {0}".format(key))
        with Cursor(self._database_name) as cursor:
            date = strftime("%Y-%m-%d %H:%M:%S")
            cursor.execute('''INSERT INTO cache VALUES (?, ?, ?)''', (key, value, date))

class Cursor:
    def __init__(self, database_name):
        self._database_name = database_name

    def __enter__(self):
        self.conn = sqlite3.connect(self._database_name)
        cursor = self.conn.cursor()
        return cursor

    def __exit__(self, type, value, traceback):
        self.conn.commit()
        self.conn.close()