"""

 Error checking functions for GEOS ctypes prototype functions.

"""

import os

from ctypes import string_at, CDLL

from ctypes.util import find_library

from django.contrib.gis.geos.error import GEOSException

# Getting the C library, needed to free the string pointers

# returned from GEOS.

if os.name == 'nt':

    libc_name = 'msvcrt'

else:

    libc_name = 'libc'

libc = CDLL(find_library(libc_name))

### ctypes error checking routines ###

def last_arg_byref(args):

    "Returns the last C argument's by reference value."

    return args[-1]._obj.value

def check_dbl(result, func, cargs):

    "Checks the status code and returns the double value passed in by reference."

    # Checking the status code

    if result != 1: return None

    # Double passed in by reference, return its value.

    return last_arg_byref(cargs)

def check_geom(result, func, cargs):

    "Error checking on routines that return Geometries."

    if not result: 

        raise GEOSException('Error encountered checking Geometry returned from GEOS C function "%s".' % func.__name__)

    return result

def check_minus_one(result, func, cargs):

    "Error checking on routines that should not return -1."

    if result == -1:

        raise GEOSException('Error encountered in GEOS C function "%s".' % func.__name__)

    else:

        return result

def check_predicate(result, func, cargs):

    "Error checking for unary/binary predicate functions."

    val = ord(result) # getting the ordinal from the character

    if val == 1: return True

    elif val == 0: return False

    else:

        raise GEOSException('Error encountered on GEOS C predicate function "%s".' % func.__name__)

def check_sized_string(result, func, cargs):

    "Error checking for routines that return explicitly sized strings."

    if not result:

        raise GEOSException('Invalid string pointer returned by GEOS C function "%s"' % func.__name__)

    # A c_size_t object is passed in by reference for the second

    # argument on these routines, and its needed to determine the

    # correct size.

    s = string_at(result, last_arg_byref(cargs))

    libc.free(result)

    return s

def check_string(result, func, cargs):

    "Error checking for routines that return strings."

    if not result: raise GEOSException('Error encountered checking string return value in GEOS C function "%s".' % func.__name__)

    # Getting the string value at the pointer address.

    s = string_at(result)

    # Freeing the memory allocated by the GEOS library.

    libc.free(result)

    return s

def check_zero(result, func, cargs):

    "Error checking on routines that should not return 0."

    if result == 0:

        raise GEOSException('Error encountered in GEOS C function "%s".' % func.__name__)

    else:

        return result