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

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

JSON 格式:
{
    "tile_size": 32,
    "columns": 4,
    "tiles": [
        { "id": 0, "file": "empty.png" },
        { "id": 1, "file": "ground_top.png" },
        ...
    ]
}

- tile_size: 每个 tile 的像素尺寸（正方形）
- columns: atlas 每行放几个 tile
- tiles: 按 tile_id 排序的列表，id 从 0 开始连续
- file: 相对于 config.json 所在目录的 PNG 路径
- 未指定的 tile_id 自动填充透明
"""

import json
import os
import sys
import math

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)

    tile_size = cfg["tile_size"]
    columns = cfg["columns"]
    tiles = cfg["tiles"]

    max_id = max(t["id"] for t in tiles)
    tile_count = max_id + 1
    rows = (tile_count + columns - 1) // columns

    atlas_w = columns * tile_size
    atlas_h = rows * tile_size

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

    tile_map = {t["id"]: t for t in tiles}

    for tid in range(tile_count):
        col = tid % columns
        row = tid // columns
        x = col * tile_size
        y = row * tile_size

        if tid in tile_map:
            png_path = os.path.join(config_dir, tile_map[tid]["file"])
            img = Image.open(png_path).convert("RGBA")
            if img.size != (tile_size, tile_size):
                img = img.resize((tile_size, tile_size), Image.NEAREST)
            atlas.paste(img, (x, y))

    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_tile_atlas.py\n")
        f.write(f"#pragma once\n#include <cstdint>\n#include \"Image.h\"\n\n")
        f.write(f"static const int32_t {var_name}_width = {atlas_w};\n")
        f.write(f"static const int32_t {var_name}_height = {atlas_h};\n")
        f.write(f"static const int32_t {var_name}_tile_size = {tile_size};\n")
        f.write(f"static const int32_t {var_name}_columns = {columns};\n\n")
        f.write(f"static const uint16_t {var_name}_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 {var_name}_image({var_name}_pixels, {var_name}_width, {var_name}_height);\n")

    print(f"已生成: {output_path}")
    print(f"  atlas: {atlas_w}x{atlas_h}, {tile_count} tiles ({columns}x{rows})")
    print(f"  var: {var_name}")


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()