#! /usr/bin/env python
"""Python 3.x buffer-handling (currently just for bytes/bytearray types)
"""
import ctypes, sys

if sys.version_info[:2] < (2, 6):
    raise ImportError('Buffer interface only usable on Python 2.6+')
from ._arrayconstants import *

PyBUF_SIMPLE = 0
PyBUF_WRITABLE = PyBUF_WRITEABLE = 0x0001
PyBUF_ND = 0x0008
PyBUF_STRIDES = 0x0010 | PyBUF_ND
PyBUF_CONTIG = PyBUF_ND | PyBUF_WRITABLE
PyBUF_CONTIG_RO = PyBUF_ND
PyBUF_C_CONTIGUOUS = 0x0020 | PyBUF_STRIDES
PyBUF_FORMAT = 0x0004

# Python 2.6 doesn't define this...
c_ssize_t = getattr(ctypes, 'c_ssize_t', ctypes.c_ulong)

_fields_ = [
    ('buf', ctypes.c_void_p),
    ('obj', ctypes.c_void_p),
    ('len', c_ssize_t),
    ('itemsize', c_ssize_t),
    ('readonly', ctypes.c_int),
    ('ndim', ctypes.c_int),
    ('format', ctypes.c_char_p),
    ('shape', ctypes.POINTER(c_ssize_t)),
    ('strides', ctypes.POINTER(c_ssize_t)),
    ('suboffsets', ctypes.POINTER(c_ssize_t)),
]


if sys.version_info[:2] <= (2, 6) or sys.version_info[:2] >= (3, 3):
    # Original structure was eventually restored in 3.3, so just
    # 2.7 through 3.2 uses the "enhanced" structure below
    _fields_.extend(
        [
            ('internal', ctypes.c_void_p),
        ]
    )
else:
    # Sigh, this structure seems to have changed with Python 3.x...
    _fields_.extend(
        [
            ('smalltable', ctypes.c_size_t * 2),
            ('internal', ctypes.c_void_p),
        ]
    )


class Py_buffer(ctypes.Structure):
    """Wrapper around the Python buffer structure..."""

    @classmethod
    def from_object(
        cls, object, flags=PyBUF_STRIDES | PyBUF_FORMAT | PyBUF_C_CONTIGUOUS
    ):
        """Create a new Py_buffer referencing ram of object"""
        if not CheckBuffer(object):
            raise TypeError(
                "%s type does not support Buffer Protocol" % (object.__class__,)
            )
        buf = cls()
        # deallocation of the buf causes glibc abort :(
        result = GetBuffer(object, buf, flags)
        if result != 0:
            raise ValueError("Unable to retrieve Buffer from %s" % (object,))
        if not buf.buf:
            raise ValueError("Null pointer result from %s" % (object,))
        return buf

    _fields_ = _fields_

    @property
    def dims(self):
        return self.shape[: self.ndim]

    def __len__(self):
        return self.shape[0]

    @property
    def dim_strides(self):
        if self.strides:
            return self.strides[: self.ndim]
        return None

    def __enter__(self):
        pass

    def __exit__(self, exc_type=None, exc_value=None, traceback=None):
        if self.obj:
            ReleaseBuffer(self)

    def __del__(self):
        if self.obj:
            ReleaseBuffer(self)


BUFFER_POINTER = ctypes.POINTER(Py_buffer)


try:
    CheckBuffer = ctypes.pythonapi.PyObject_CheckBuffer
    CheckBuffer.argtypes = [ctypes.py_object]
    CheckBuffer.restype = ctypes.c_int
except AttributeError as err:
    # Python 2.6 doesn't appear to have CheckBuffer support...
    def CheckBuffer(x):
        True


IncRef = ctypes.pythonapi.Py_IncRef
IncRef.argtypes = [ctypes.py_object]

GetBuffer = ctypes.pythonapi.PyObject_GetBuffer
GetBuffer.argtypes = [ctypes.py_object, BUFFER_POINTER, ctypes.c_int]
GetBuffer.restype = ctypes.c_int

ReleaseBuffer = ctypes.pythonapi.PyBuffer_Release
ReleaseBuffer.argtypes = [BUFFER_POINTER]
ReleaseBuffer.restype = None