"""

 This module houses the error-checking routines used by the GDAL

 ctypes prototypes.

"""

from ctypes import c_void_p, string_at

from django.contrib.gis.gdal.error import check_err, OGRException, SRSException

from django.contrib.gis.gdal.libgdal import lgdal

# Helper routines for retrieving pointers and/or values from 

# arguments passed in by reference. 

def arg_byref(args, offset=-1):

    "Returns the pointer argument's by-refernece value."

    return args[offset]._obj.value

def ptr_byref(args, offset=-1):

    "Returns the pointer argument passed in by-reference."

    return args[offset]._obj

def check_bool(result, func, cargs):

    "Returns the boolean evaluation of the value."

    if bool(result): return True

    else: return False

### String checking Routines ###

def check_const_string(result, func, cargs, offset=None):

    """

    Similar functionality to `check_string`, but does not free the pointer.

    """

    if offset:

        check_err(result)

        ptr = ptr_byref(cargs, offset)

        return ptr.value

    else:

        return result

def check_string(result, func, cargs, offset=-1, str_result=False):

    """

    Checks the string output returned from the given function, and frees

    the string pointer allocated by OGR.  The `str_result` keyword

    may be used when the result is the string pointer, otherwise

    the OGR error code is assumed.  The `offset` keyword may be used

    to extract the string pointer passed in by-reference at the given

    slice offset in the function arguments.

    """

    if str_result:

        # For routines that return a string.

        ptr = result

        if not ptr: s = None

        else: s = string_at(result)

    else:

        # Error-code return specified.

        check_err(result)

        ptr = ptr_byref(cargs, offset)

        # Getting the string value

        s = ptr.value

    # Correctly freeing the allocated memory beind GDAL pointer 

    # w/the VSIFree routine.

    if ptr: lgdal.VSIFree(ptr)

    return s

### DataSource, Layer error-checking ###

### Envelope checking ###

def check_envelope(result, func, cargs, offset=-1):

    "Checks a function that returns an OGR Envelope by reference."

    env = ptr_byref(cargs, offset)

    return env

### Geometry error-checking routines ###

def check_geom(result, func, cargs):

    "Checks a function that returns a geometry."

    # OGR_G_Clone may return an integer, even though the

    # restype is set to c_void_p

    if isinstance(result, int):

        result = c_void_p(result)

    if not result: 

        raise OGRException('Invalid geometry pointer returned from "%s".' % func.__name__)

    return result

def check_geom_offset(result, func, cargs, offset=-1):

    "Chcks the geometry at the given offset in the C parameter list."

    check_err(result)

    geom = ptr_byref(cargs, offset=offset)

    return check_geom(geom, func, cargs)

### Spatial Reference error-checking routines ###

def check_srs(result, func, cargs):

    if isinstance(result, int):

        result = c_void_p(result)

    if not result:

        raise SRSException('Invalid spatial reference pointer returned from "%s".' % func.__name__)

    return result

### Other error-checking routines ###

def check_arg_errcode(result, func, cargs):

    """

    The error code is returned in the last argument, by reference.

    Check its value with `check_err` before returning the result.

    """

    check_err(arg_byref(cargs))

    return result

def check_errcode(result, func, cargs):

    """

    Check the error code returned (c_int).

    """

    check_err(result)

    return

def check_pointer(result, func, cargs):

    "Makes sure the result pointer is valid."

    if bool(result): 

        return result

    else: 

        raise OGRException('Invalid pointer returned from "%s"' % func.__name__)

def check_str_arg(result, func, cargs):

    """

    This is for the OSRGet[Angular|Linear]Units functions, which

    require that the returned string pointer not be freed.  This

    returns both the double and tring values.

    """

    dbl = result

    ptr = cargs[-1]._obj

    return dbl, ptr.value