import tempfile
import pandas.io.sql

class PgSQLDatabase(pandas.io.sql.SQLDatabase):
    # FIXME Schema is pulled from Meta object, shouldn't actually be part of signature!
    def to_sql(self, frame, name, if_exists='fail', index=True,
               index_label=None, schema=None, chunksize=None, dtype=None, pk=None):
        """
        Write records stored in a DataFrame to a SQL database.

        Parameters
        ----------
        frame : DataFrame
        name : string
            Name of SQL table
        if_exists : {'fail', 'replace', 'append'}, default 'fail'
            - fail: If table exists, do nothing.
            - replace: If table exists, drop it, recreate it, and insert data.
            - append: If table exists, insert data. Create if does not exist.
        index : boolean, default True
            Write DataFrame index as a column
        index_label : string or sequence, default None
            Column label for index column(s). If None is given (default) and
            `index` is True, then the index names are used.
            A sequence should be given if the DataFrame uses MultiIndex.
        schema : string, default None
            Name of SQL schema in database to write to (if database flavor
            supports this). If specified, this overwrites the default
            schema of the SQLDatabase object.
        chunksize : int, default None
            If not None, then rows will be written in batches of this size at a
            time.  If None, all rows will be written at once.
        dtype : dict of column name to SQL type, default None
            Optional specifying the datatype for columns. The SQL type should
            be a SQLAlchemy type.
        pk: name of column(s) to set as primary keys
        """
        if dtype is not None:
            import sqlalchemy.sql.type_api as type_api

            for col, my_type in dtype.items():
                if not issubclass(my_type, type_api.TypeEngine):
                    raise ValueError('The type of %s is not a SQLAlchemy '
                                     'type ' % col)

        table = pandas.io.sql.SQLTable(name, self, frame=frame, index=index,
                                       if_exists=if_exists, index_label=index_label,
                                       schema=self.meta.schema, dtype=dtype)
        table.create()
        if pk is not None:
            if isinstance(pk, str):
                pks = pk
            else:
                pks = ", ".join(pk)
            sql = "ALTER TABLE {schema_name}.{table_name} ADD PRIMARY KEY ({pks})".format(schema_name=self.meta.schema, table_name=name, pks=pks)
            self.execute(sql)

        # Some tricks needed here:
        # Need to explicitly keep reference to connection
        # Need to "open" temp file seperately in write and read mode
        # Otherwise data does not get loaded
        conn = self.engine.raw_connection()
        with conn.cursor() as cur, tempfile.NamedTemporaryFile(mode='w') as temp_file:
            frame.to_csv(temp_file, index=index)

            with open(temp_file.name, 'r') as f:
                sql = "COPY {schema_name}.{table_name} FROM STDIN WITH (FORMAT CSV, HEADER TRUE)".format(
                    schema_name=self.meta.schema, table_name=name)
                cur.copy_expert(sql, f)
        conn.commit()

        # check for potentially case sensitivity issues (GH7815)
        self.meta.reflect()
        if name not in self.engine.table_names(schema=schema or self.meta.schema):
            warnings.warn("The provided table name '{0}' is not found exactly "
                          "as such in the database after writing the table, "
                          "possibly due to case sensitivity issues. Consider "
                          "using lower case table names.".format(name), UserWarning)