"""
A Pillow loader for .dds files (S3TC-compressed aka DXTC)
Jerome Leclanche <jerome@leclan.ch>

Documentation:
  http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt

The contents of this file are hereby released in the public domain (CC0)
Full text of the CC0 license:
  https://creativecommons.org/publicdomain/zero/1.0/
"""

import struct
from io import BytesIO
from PIL import Image, ImageFile


# Magic ("DDS ")
DDS_MAGIC = 0x20534444

# DDS flags
DDSD_CAPS = 0x1
DDSD_HEIGHT = 0x2
DDSD_WIDTH = 0x4
DDSD_PITCH = 0x8
DDSD_PIXELFORMAT = 0x1000
DDSD_MIPMAPCOUNT = 0x20000
DDSD_LINEARSIZE = 0x80000
DDSD_DEPTH = 0x800000

# DDS caps
DDSCAPS_COMPLEX = 0x8
DDSCAPS_TEXTURE = 0x1000
DDSCAPS_MIPMAP = 0x400000

DDSCAPS2_CUBEMAP = 0x200
DDSCAPS2_CUBEMAP_POSITIVEX = 0x400
DDSCAPS2_CUBEMAP_NEGATIVEX = 0x800
DDSCAPS2_CUBEMAP_POSITIVEY = 0x1000
DDSCAPS2_CUBEMAP_NEGATIVEY = 0x2000
DDSCAPS2_CUBEMAP_POSITIVEZ = 0x4000
DDSCAPS2_CUBEMAP_NEGATIVEZ = 0x8000
DDSCAPS2_VOLUME = 0x200000

# Pixel Format
DDPF_ALPHAPIXELS = 0x1
DDPF_ALPHA = 0x2
DDPF_FOURCC = 0x4
DDPF_PALETTEINDEXED8 = 0x20
DDPF_RGB = 0x40
DDPF_LUMINANCE = 0x20000


# dds.h

DDS_FOURCC = DDPF_FOURCC
DDS_RGB = DDPF_RGB
DDS_RGBA = DDPF_RGB | DDPF_ALPHAPIXELS
DDS_LUMINANCE = DDPF_LUMINANCE
DDS_LUMINANCEA = DDPF_LUMINANCE | DDPF_ALPHAPIXELS
DDS_ALPHA = DDPF_ALPHA
DDS_PAL8 = DDPF_PALETTEINDEXED8

DDS_HEADER_FLAGS_TEXTURE = (DDSD_CAPS | DDSD_HEIGHT | DDSD_WIDTH |
                            DDSD_PIXELFORMAT)
DDS_HEADER_FLAGS_MIPMAP = DDSD_MIPMAPCOUNT
DDS_HEADER_FLAGS_VOLUME = DDSD_DEPTH
DDS_HEADER_FLAGS_PITCH = DDSD_PITCH
DDS_HEADER_FLAGS_LINEARSIZE = DDSD_LINEARSIZE

DDS_HEIGHT = DDSD_HEIGHT
DDS_WIDTH = DDSD_WIDTH

DDS_SURFACE_FLAGS_TEXTURE = DDSCAPS_TEXTURE
DDS_SURFACE_FLAGS_MIPMAP = DDSCAPS_COMPLEX | DDSCAPS_MIPMAP
DDS_SURFACE_FLAGS_CUBEMAP = DDSCAPS_COMPLEX

DDS_CUBEMAP_POSITIVEX = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_POSITIVEX
DDS_CUBEMAP_NEGATIVEX = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_NEGATIVEX
DDS_CUBEMAP_POSITIVEY = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_POSITIVEY
DDS_CUBEMAP_NEGATIVEY = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_NEGATIVEY
DDS_CUBEMAP_POSITIVEZ = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_POSITIVEZ
DDS_CUBEMAP_NEGATIVEZ = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_NEGATIVEZ


# DXT1
DXT1_FOURCC = 0x31545844

# DXT3
DXT3_FOURCC = 0x33545844

# DXT5
DXT5_FOURCC = 0x35545844


# dxgiformat.h

DXGI_FORMAT_BC7_TYPELESS = 97
DXGI_FORMAT_BC7_UNORM = 98
DXGI_FORMAT_BC7_UNORM_SRGB = 99


class DdsImageFile(ImageFile.ImageFile):
    format = "DDS"
    format_description = "DirectDraw Surface"

    def _open(self):
        magic, header_size = struct.unpack("<II", self.fp.read(8))
        if header_size != 124:
            raise IOError("Unsupported header size %r" % (header_size))
        header_bytes = self.fp.read(header_size - 4)
        if len(header_bytes) != 120:
            raise IOError("Incomplete header: %s bytes" % len(header_bytes))
        header = BytesIO(header_bytes)

        flags, height, width = struct.unpack("<3I", header.read(12))
        self.size = (width, height)
        self.mode = "RGBA"

        pitch, depth, mipmaps = struct.unpack("<3I", header.read(12))
        reserved = struct.unpack("<11I", header.read(44))

        # pixel format
        pfsize, pfflags = struct.unpack("<2I", header.read(8))
        fourcc = header.read(4)
        bitcount, rmask, gmask, bmask, amask = struct.unpack("<5I",
                                                             header.read(20))

        data_start = header_size + 4
        n = 0
        if fourcc == b"DXT1":
            self.pixel_format = "DXT1"
            n = 1
        elif fourcc == b"DXT3":
            self.pixel_format = "DXT3"
            n = 2
        elif fourcc == b"DXT5":
            self.pixel_format = "DXT5"
            n = 3
        elif fourcc == b"DX10":
            data_start += 20
            # ignoring flags which pertain to volume textures and cubemaps
            dxt10 = BytesIO(self.fp.read(20))
            dxgi_format, dimension = struct.unpack("<II", dxt10.read(8))
            if dxgi_format in (DXGI_FORMAT_BC7_TYPELESS, DXGI_FORMAT_BC7_UNORM):
                self.pixel_format = "BC7"
                n = 7
            elif dxgi_format == DXGI_FORMAT_BC7_UNORM_SRGB:
                self.pixel_format = "BC7"
                self.im_info["gamma"] = 1/2.2
                n = 7
            else:
                raise NotImplementedError("Unimplemented DXGI format %d" %
                                          (dxgi_format))
        else:
            raise NotImplementedError("Unimplemented pixel format %r" %
                                      (fourcc))

        self.tile = [
            ("bcn", (0, 0) + self.size, data_start, (n))
        ]

    def load_seek(self, pos):
        pass


def _validate(prefix):
    return prefix[:4] == b"DDS "


Image.register_open(DdsImageFile.format, DdsImageFile, _validate)
Image.register_extension(DdsImageFile.format, ".dds")
