database: switching from mysql to sqlite

Currently we only need the db to keep track of the files that were
already downloaded, thus we only use one database and only one table.
A complete sql database is a bit too bulky for this purpose.
By using sqlite we can minimize and embed the db.

src/database.py

@@ -0,0 +1,69 @@
+import time
+import logging as log
+import os
+
+import pysqlite3
+
+
+class Database:
+
+    def __init__(self, reset_dl):
+        self.RESET_DL = reset_dl
+        self.TABLE_FILE = 'files'
+        self.DB_DIR = os.path.dirname(os.path.realpath(__file__))
+        self.setup_db()
+
+    def connect(self):
+        """Connect to an existing database instance based on the object
+        attributes.
+        """
+        path = os.path.join(self.DB_DIR, "data.db")
+        return pysqlite3.connect(path)
+
+    def setup_db(self):
+        """Creates a database with tables."""
+        log.info("check database")
+        db = self.connect()
+        crs = db.cursor()
+        query = "CREATE TABLE IF NOT EXISTS " + self.TABLE_FILE + \
+            "(id CHAR(32) NOT NULL," + \
+            "ch_date INT(11) NOT NULL," + \
+            "PRIMARY KEY(id))"
+        crs.execute(query)
+        log.debug(db)
+
+    def set_last_file_dl(self, file_id, time):
+        """Insert a downloaded file to the database.
+
+        Parameters:
+        file_id (string): id of the file downloaded
+        time(int): time the file was downloaded
+        """
+        db = self.connect()
+        crs = db.cursor()
+        log.debug('file: ' + file_id + ' time: ' + time)
+        query = "INSERT INTO " + self.TABLE_FILE + "(`id`,`ch_date`)" + \
+                "VALUES ('" + file_id + "','" + time + "')" + \
+                "ON CONFLICT(`id`) DO UPDATE SET `ch_date` = '" + time + "'"
+        crs.execute(query)
+        db.commit()
+
+    def get_last_file_dl(self, file_id):
+        """Check when a file was downloaded.
+
+        Parameters:
+        file_id(string): id of the file to check
+
+        Returns:
+        int: time when the file was downloaded last. None if it wasnt downloaded.
+        """
+        if self.RESET_DL:
+            return None
+        db = self.connect()
+        crs = db.cursor()
+        query = "SELECT ch_date FROM files WHERE id ='" + file_id + "'"
+        crs.execute(query)
+        res = crs.fetchone()
+        if res != None:
+            return res[0]
+        return None