"""
A Pillow loader for .ftc and .ftu files (FTEX)
Jerome Leclanche <jerome@leclan.ch>

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/

Independence War 2: Edge Of Chaos - Texture File Format - 16 October 2001

The textures used for 3D objects in Independence War 2: Edge Of Chaos are in a
packed custom format called FTEX. This file format uses file extensions FTC
and FTU.
* FTC files are compressed textures (using standard texture compression).
* FTU files are not compressed.
Texture File Format
The FTC and FTU texture files both use the same format. This
has the following structure:
{header}
{format_directory}
{data}
Where:
{header} = {
    u32:magic,
    u32:version,
    u32:width,
    u32:height,
    u32:mipmap_count,
    u32:format_count
}

* The "magic" number is "FTEX".
* "width" and "height" are the dimensions of the texture.
* "mipmap_count" is the number of mipmaps in the texture.
* "format_count" is the number of texture formats (different versions of the
same texture) in this file.

{format_directory} = format_count * { u32:format, u32:where }

The format value is 0 for DXT1 compressed textures and 1 for 24-bit RGB
uncompressed textures.
The texture data for a format starts at the position "where" in the file.

Each set of texture data in the file has the following structure:
{data} = format_count * { u32:mipmap_size, mipmap_size * { u8 } }
* "mipmap_size" is the number of bytes in that mip level. For compressed
textures this is the size of the texture data compressed with DXT1. For 24 bit
uncompressed textures, this is 3 * width * height. Following this are the image
bytes for that mipmap level.

Note: All data is stored in little-Endian (Intel) byte order.
"""

from __future__ import annotations

import struct
from enum import IntEnum
from io import BytesIO

from . import Image, ImageFile

MAGIC = b"FTEX"


class Format(IntEnum):
    DXT1 = 0
    UNCOMPRESSED = 1


class FtexImageFile(ImageFile.ImageFile):
    format = "FTEX"
    format_description = "Texture File Format (IW2:EOC)"

    def _open(self) -> None:
        assert self.fp is not None
        if not _accept(self.fp.read(4)):
            msg = "not an FTEX file"
            raise SyntaxError(msg)
        struct.unpack("<i", self.fp.read(4))  # version
        self._size = struct.unpack("<2i", self.fp.read(8))
        mipmap_count, format_count = struct.unpack("<2i", self.fp.read(8))

        # Only support single-format files.
        # I don't know of any multi-format file.
        assert format_count == 1

        format, where = struct.unpack("<2i", self.fp.read(8))
        self.fp.seek(where)
        (mipmap_size,) = struct.unpack("<i", self.fp.read(4))

        data = self.fp.read(mipmap_size)

        if format == Format.DXT1:
            self._mode = "RGBA"
            self.tile = [ImageFile._Tile("bcn", (0, 0) + self.size, 0, (1,))]
        elif format == Format.UNCOMPRESSED:
            self._mode = "RGB"
            self.tile = [ImageFile._Tile("raw", (0, 0) + self.size, 0, "RGB")]
        else:
            msg = f"Invalid texture compression format: {repr(format)}"
            raise ValueError(msg)

        self.fp.close()
        self.fp = BytesIO(data)

    def load_seek(self, pos: int) -> None:
        pass


def _accept(prefix: bytes) -> bool:
    return prefix.startswith(MAGIC)


Image.register_open(FtexImageFile.format, FtexImageFile, _accept)
Image.register_extensions(FtexImageFile.format, [".ftc", ".ftu"])
