import MySQLdb
import secrets

class Database:

    def __init__(self, hostname, dbname):
        self.hostname = hostname
        self.schema = dbname
        self.conn = None
        self.cur = None
        self.dcur = None
        self.error = None

    def connect(self, dbuser, dbpass):
        if self.conn:
            return True
        MySQLdb.paramstyle = 'pyformat'
        try:
            self.conn = MySQLdb.connect(host=self.hostname, db=self.schema,
                user=dbuser, passwd=dbpass, charset='utf8')
        except MySQLdb.Error as e:
            self.error = e
            return False
        self.conn.autocommit(False)
        self.cur = self.conn.cursor()
        self.dcur = self.conn.cursor(MySQLdb.cursors.DictCursor)
        return True

    def connect_local(self):
        # connection via local unix socket
        if self.conn:
            return True
        MySQLdb.paramstyle = 'pyformat'
        try:
            self.conn = MySQLdb.connect(host='localhost', db=self.schema,
                unix_socket='/run/mysqld/mysqld.sock', charset='utf8')
        except MySQLdb.Error as e:
            self.error = e
            return False
        self.cur = self.conn.cursor()
        self.dcur = self.conn.cursor(MySQLdb.cursors.DictCursor)
        return True
        
    def disconnect(self):
        self.cur.close()
        self.dcur.close()
        self.conn.close()

    def is_connected(self):
        return self.conn.open

    def get_timestamp(self):
        self.cur.execute("SELECT CURRENT_TIMESTAMP")
        return self.cur.fetchone()[0]

    def last_error(self):
        if not self.error:
            return(0, '')
        code = self.error.args[0]
        text = self.error.args[1]
        self.error = None
        return(code, text)

    def load_enum(self, table, column):
        """
        TODO this is only an example! perhaps other keys needed
        Load an enum directly from a database table and provide it as a
        dictionary for use in, for example, selection lists.
        """
        sql = (
            "SELECT TRIM(TRAILING ')' FROM SUBSTRING(column_type,6)) "
            "FROM information_schema.columns "
            "WHERE table_schema=DATABASE() AND table_name=%s AND column_name=%s AND data_type='enum'"
            )
        self.cur.execute(sql, (table, column))
        row = self.cur.fetchone()
        if not row:
            return {}
        return {
            i: _(value.strip("'"))
            for i, value in enumerate(row[0].split(','), 1)
        }

    def lock_acquire(self, table, key, userid):
        token = secrets.token_hex(8)
        # first try new lock
        sql = (
            "INSERT INTO recordlock (lock_table, lock_key, token, userid)"
            "VALUES (%s, %s, %s, %s)"
            )
        try:
            self.cur.execute(sql, (table, key, token, userid))
            self.conn.commit()
            return token
        except self.conn.IntegrityError as e:
            self.conn.rollback()
            if e.errno != 1062:
                raise
        # lazy locking: lock exists but is old, so we use it
        sql = (
            "UPDATE recordlock "
            "SET token=%s, userid=%s,"
            "    created_at=CURRENT_TIMESTAMP, last_seen=CURRENT_TIMESTAMP "
            "WHERE lock_table=%s AND lock_key=%s AND last_seen<CURRENT_TIMESTAMP-INTERVAL 5 MINUTE"
            )
        self.cur.execute(sql, (token, userid, table, key))
        self.conn.commit()
        if self.cur.rowcount == 1:
            return token
        return None

    def lock_refresh(self, token):
        sql = (
            "UPDATE recordlock "
            "SET last_seen=current_timestamp() "
            "WHERE token=%s"
            )
        self.cur.execute(sql, (token,))
        self.conn.commit()
        return self.cur.rowcount == 1

    def lock_release(self, token):
        sql = "DELETE FROM recordlock WHERE token=%s"
        self.cur.execute(sql, (token,))
        self.conn.commit()
        return self.cur.rowcount == 1

    def execute_write(self, sql, values=(), expected_rows=None):
        """
        Execute an INSERT, UPDATE, or DELETE statement.
        expected_rows:
            None = do not check the number of affected rows
            1    = expect exactly one affected row
            0    = expect no affected rows
        """
        try:
            self.cur.execute(sql, values)
        except MySQLdb.Error as e:
            self.rollback()
            self.error = e
            return False
        if (expected_rows is not None and self.cur.rowcount != expected_rows):
            self.rollback()
            self.error = RuntimeError(
                "Expected {} affected rows, got {}".format(
                    expected_rows,
                    self.cur.rowcount
                )
            )
            return False
        self.error = None
        return True