"""
将多个独立 sprite PNG 按 JSON 配置打包为 sprite atlas，生成 C++ header。

用法:
    python tools/pack_sprite_atlas.py config.json output.h

JSON 格式:
{
    "atlas_width": 512,
    "atlas_height": 512,
    "sprites": [
        { "name": "player_idle_0", "file": "player_idle_0.png" },
        { "name": "player_idle_1", "file": "player_idle_1.png" },
        ...
    ]
}

- atlas_width / atlas_height: 输出 atlas 尺寸
- sprites: 按顺序排列的 sprite 列表
- 每个 sprite 保持原始尺寸，从左到右、从上到下排列
- 生成的 header 包含每个 sprite 的子矩形信息
"""

import json
import os
import sys

from PIL import Image


def pack(config_path: str, output_path: str):
    config_dir = os.path.dirname(os.path.abspath(config_path))

    with open(config_path, "r", encoding="utf-8") as f:
        cfg = json.load(f)

    atlas_w = cfg["atlas_width"]
    atlas_h = cfg["atlas_height"]
    sprites = cfg["sprites"]

    atlas = Image.new("RGBA", (atlas_w, atlas_h), (0, 0, 0, 0))

    regions = []
    cursor_x = 0
    cursor_y = 0
    row_height = 0

    for s in sprites:
        png_path = os.path.join(config_dir, s["file"])
        img = Image.open(png_path).convert("RGBA")
        w, h = img.size

        if cursor_x + w > atlas_w:
            cursor_x = 0
            cursor_y += row_height
            row_height = 0

        if cursor_y + h > atlas_h:
            print(f"错误: atlas 空间不足，sprite '{s['name']}' 放不下")
            sys.exit(1)

        atlas.paste(img, (cursor_x, cursor_y))
        regions.append({
            "name": s["name"],
            "x": cursor_x,
            "y": cursor_y,
            "w": w,
            "h": h,
        })

        cursor_x += w
        row_height = max(row_height, h)

    var_name = os.path.splitext(os.path.basename(output_path))[0]

    pixels = list(atlas.getdata())
    packed = []
    for r, g, b, a in pixels:
        packed.append(
            ((r >> 3) << 11)
            | ((g >> 3) << 6)
            | ((b >> 3) << 1)
            | (1 if a else 0)
        )

    with open(output_path, "w", encoding="utf-8") as f:
        f.write("// Auto-generated by tools/pack_sprite_atlas.py\n")
        f.write(f"#pragma once\n#include <cstdint>\n#include \"Image.h\"\n#include \"Sprite.h\"\n\n")
        f.write(f"namespace {var_name} {{\n\n")
        f.write(f"static const int32_t atlas_width = {atlas_w};\n")
        f.write(f"static const int32_t atlas_height = {atlas_h};\n\n")
        f.write(f"static const uint16_t atlas_pixels[] = {{\n")

        for i in range(0, len(packed), 16):
            chunk = packed[i : i + 16]
            line = ", ".join(f"0x{p:04X}" for p in chunk)
            f.write(f"    {line},\n")

        f.write("};\n\n")
        f.write(f"static const RenderData::Image atlas_image(atlas_pixels, atlas_width, atlas_height);\n\n")

        for r in regions:
            f.write(f"static const RenderData::Sprite spr_{r['name']}("
                    f"&atlas_image, {r['x']}, {r['y']}, {r['w']}, {r['h']});\n")

        f.write(f"\n}} // namespace {var_name}\n")

    print(f"已生成: {output_path}")
    print(f"  atlas: {atlas_w}x{atlas_h}, {len(regions)} sprites")
    for r in regions:
        print(f"    {r['name']}: ({r['x']},{r['y']}) {r['w']}x{r['h']}")


def main():
    if len(sys.argv) < 3:
        print(f"用法: {sys.argv[0]} config.json output.h")
        sys.exit(1)

    pack(sys.argv[1], sys.argv[2])


if __name__ == "__main__":
    main()