# Use _psycopg directly to avoid overhead.
try:
    # If possible, you should copy the _psycopg.pyd file into a top level
    # so this SM can avoid importing the entire package.
    import _psycopg
except ImportError:
    from psycopg2 import _psycopg

from geniusql import conns, errors
from geniusql.providers import postgres

#-------------------------------------------------------------------------------
def safe_connection_close(conn):
    """If you call close on an already closed connection, psycopg raises an error.

    Normally - this is fine - but we try to close our connections/cursors in the case
    of connection errors so that we can properly re-connect - so we catch and ignore
    ONLY those errors right now.
    """
    try:
        conn.close()
    except _psycopg.InterfaceError, exc:
        msg = exc.args[0]
        if msg.startswith('connection already closed'):
            return
        else:
            raise

#-------------------------------------------------------------------------------
def safe_cursor_close(cursor):
    """If you call close on an already closed cursor, psycopg raises an error.

    Normally - this is fine - but we try to close our connections/cursors in the case
    of connection errors so that we can properly re-connect - so we catch and ignore
    ONLY those errors right now.
    """
    try:
        cursor.close()
    except _psycopg.InterfaceError, exc:
        msg = exc.args[0]
        if msg.startswith('cursor already closed'):
            return
        else:
            raise

class PsycoPgConnectionManager(conns.ConnectionManager):

    default_isolation = "READ COMMITTED"

    def _get_conn(self, master=False):
        if master:
            # Commit any pending transaction in the current thread.
            if self.in_transaction():
                self.commit()

            # Must shut down all connections to avoid
            # "being accessed by other users" error.
            self.shutdown()

            connstr = ""
            for atom in self.Connect.split(" "):
                k, v = atom.split("=", 1)
                if k == 'dbname':
                    v = 'template1'
                connstr += "%s=%s " % (k, v)
        else:
            connstr = self.Connect

        try:
            c = _psycopg.connect(connstr)
            # Allow statements like CREATE DATABASE to run outside a transaction.
            c.set_isolation_level(0)
            if self.initial_sql:
                cursor.execute(self.initial_sql)
            return c
        except _psycopg.DatabaseError, x:
            if x.args[0].startswith('could not connect'):
                raise errors.OutOfConnectionsError(*x.args)
            raise

    def _del_conn(self, conn):
        safe_connection_close(conn)


class PsycoPgSchema(postgres.PgSchema):

    def _get_dbinfo(self, conn=None):
        dbinfo = {}
        try:
            data, _ = self.db.fetch("SELECT pg_encoding_to_char(encoding) "
                                    "FROM pg_database;", conn=conn)
            dbinfo['encoding'] = data[0][0]
        except _psycopg.DatabaseError, x:
            if "does not exist" not in x.args[0]:
                raise
        return dbinfo


class PsycoPgDatabase(postgres.PgDatabase):

    connectionmanager = PsycoPgConnectionManager
    schemaclass = PsycoPgSchema

    def version(self):
        c = self.connections._get_conn(master=True)
        data, _ = self.fetch("SELECT version();", c)
        v, = data[0]
        c.close()
        return "%s\npsycopg version: %s" % (v, _psycopg.__version__)

    def is_connection_error(self, exc):
        """If the given exception instance is a connection error, return True.

        This should return True for errors which arise from broken connections;
        for example, if the database server has dropped the connection socket,
        or is unreachable.
        """
        if isinstance(exc, _psycopg.OperationalError):
            # OperationalError: connection not open
            msg = exc.args[0]
            return msg.startswith('connection not open') or msg.startswith("terminating connection due")
        if isinstance(exc, _psycopg.InterfaceError):
            # InterfaceError: connection already closed
            msg = exc.args[0]
            return msg.startswith('connection already closed')
        return False

    def execute(self, sql, conn=None):
        """Return a native response for the given SQL."""
        if conn is None:
            conn = self.connections.get()
        if isinstance(sql, unicode):
            sql = sql.encode(self.encoding)
        self.log(sql)

        def _execute_implementation(sql):
            cursor = conn.cursor()
            try:
                return cursor.execute(sql)
            finally:
                safe_cursor_close(cursor)

        try:
            return _execute_implementation(sql)
        except Exception, x:
            if self.is_connection_error(x):
                self.connections.reset(conn)
                return _execute_implementation(sql)
            raise

    def fetch(self, sql, conn=None):
        """Return rowdata, columns(name, type) for the given sql.

        sql should be a SQL string.

        rowdata will be an iterable of iterables containing the result values.
        columns will be an iterable of (column name, data type) pairs.
        """
        if conn is None:
            conn = self.connections.get()
        if isinstance(sql, unicode):
            sql = sql.encode(self.encoding)
        self.log(sql)

        def _fetch_implementation(sql):
            cursor = conn.cursor()
            try:
                cursor.execute(sql)
                data = cursor.fetchall()
                coldefs = cursor.description
            finally:
                safe_cursor_close(cursor)
            return data, coldefs

        try:
            return _fetch_implementation(sql)
        except Exception, x:
            if self.is_connection_error(x):
                self.connections.reset(conn)
                return _fetch_implementation(sql)
            else:
                raise

        return data, coldefs