from .cinterface import CTaosInterface
from .error import *

class TDengineCursor(object):
    """Database cursor which is used to manage the context of a fetch operation.

    Attributes:
        .description: Read-only attribute consists of 7-item sequences:

            > name (mondatory)
            > type_code (mondatory)
            > display_size
            > internal_size
            > precision
            > scale
            > null_ok

            This attribute will be None for operations that do not return rows or
            if the cursor has not had an operation invoked via the .execute*() method yet.

        .rowcount:This read-only attribute specifies the number of rows that the last
            .execute*() produced (for DQL statements like SELECT) or affected 
    """

    def __init__(self, connection=None):
        self._description = None
        self._rowcount = -1
        self._connection = None
        self._result = None
        self._fields = None
        self._block = None
        self._block_rows = -1
        self._block_iter = 0

        if connection is not None:
            self._connection = connection

    def __iter__(self):
        return self

    def next(self):
        if self._result is None or self._fields is None:
            raise OperationalError("Invalid use of fetch iterator")

        if self._block_rows <= self._block_iter:
            block, self._block_rows = CTaosInterface.fetchBlock(self._result, self._fields)
            if self._block_rows == 0:
                raise StopIteration
            self._block = list(map(tuple, zip(*block)))
            self._block_iter = 0

        data =  self._block[self._block_iter]
        self._block_iter += 1

        return data

    @property
    def description(self):
        """Return the description of the object.
        """
        return self._description

    @property
    def rowcount(self):
        """Return the rowcount of the object
        """
        return self._rowcount

    def callproc(self, procname, *args):
        """Call a stored database procedure with the given name.

        Void functionality since no stored procedures.
        """
        pass

    def close(self):
        """Close the cursor.
        """
        if self._connection is None:
            return False
        
        self._connection.clear_result_set()
        self._reset_result()
        self._connection = None

        return True

    def execute(self, operation, params=None):
        """Prepare and execute a database operation (query or command).
        """
        if not operation:
            return None

        if not self._connection:
            # TODO : change the exception raised here
            raise ProgrammingError("Cursor is not connected")
        
        self._connection.clear_result_set()
        self._reset_result()

        stmt = operation
        if params is not None:
            pass
        
        res = CTaosInterface.query(self._connection._conn, stmt)
        if res == 0:
            if CTaosInterface.fieldsCount(self._connection._conn) == 0:
                return CTaosInterface.affectedRows(self._connection._conn)
            else:
                self._result, self._fields = CTaosInterface.useResult(self._connection._conn)
                return self._handle_result()
        else:
            raise ProgrammingError(CTaosInterface.errStr(self._connection._conn))

    def executemany(self, operation, seq_of_parameters):
        """Prepare a database operation (query or command) and then execute it against all parameter sequences or mappings found in the sequence seq_of_parameters.
        """
        pass

    def fetchone(self):
        """Fetch the next row of a query result set, returning a single sequence, or None when no more data is available.
        """
        pass

    def fetchmany(self):
        pass

    def fetchall(self):
        """Fetch all (remaining) rows of a query result, returning them as a sequence of sequences (e.g. a list of tuples). Note that the cursor's arraysize attribute can affect the performance of this operation.
        """
        if self._result is None or self._fields is None:
            raise OperationalError("Invalid use of fetchall")
        
        buffer = [[] for i in range(len(self._fields))]
        self._rowcount = 0
        while True:
            block, num_of_fields = CTaosInterface.fetchBlock(self._result, self._fields)
            if num_of_fields == 0: break
            self._rowcount += num_of_fields
            for i in range(len(self._fields)):
                buffer[i].extend(block[i])

        self._connection.clear_result_set()
        
        return list(map(tuple, zip(*buffer)))



    def nextset(self):
        """
        """
        pass

    def setinputsize(self, sizes):
        pass

    def setutputsize(self, size, column=None):
        pass

    def _reset_result(self):
        """Reset the result to unused version.
        """
        self._description = None
        self._rowcount = -1
        self._result = None
        self._fields = None
        self._block = None
        self._block_rows = -1
        self._block_iter = 0
    
    def _handle_result(self):
        """Handle the return result from query.
        """
        self._description = []
        for ele in self._fields:
            self._description.append((ele['name'], ele['type'], None, None, None, None, False))
        
        return self._result