// 把多張 PNG 打包成 Windows .ico（PNG-in-ICO 格式，Vista+ 支援）
// 用法：go run gen_ico.go <output.ico> <png-dir> <sizes-csv>
// 範例：go run gen_ico.go icon.ico ../ 16,24,32,48,64,96,128,256
//go:build ignore

package main

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

type iconDir struct {
	Reserved uint16
	Type     uint16
	Count    uint16
}

type iconDirEntry struct {
	Width      uint8
	Height     uint8
	ColorCount uint8
	Reserved   uint8
	Planes     uint16
	BitCount   uint16
	SizeBytes  uint32
	Offset     uint32
}

func main() {
	if len(os.Args) < 4 {
		fmt.Fprintln(os.Stderr, "usage: gen_ico <output.ico> <png-dir> <sizes-csv>")
		os.Exit(1)
	}
	outPath := os.Args[1]
	pngDir := os.Args[2]
	sizesCSV := os.Args[3]

	var sizes []int
	for _, s := range strings.Split(sizesCSV, ",") {
		n, err := strconv.Atoi(strings.TrimSpace(s))
		if err != nil {
			fmt.Fprintln(os.Stderr, "bad size:", s)
			os.Exit(1)
		}
		sizes = append(sizes, n)
	}

	pngs := make([][]byte, len(sizes))
	for i, s := range sizes {
		data, err := os.ReadFile(filepath.Join(pngDir, "icon-"+strconv.Itoa(s)+".png"))
		if err != nil {
			fmt.Fprintln(os.Stderr, "read", s, err)
			os.Exit(1)
		}
		pngs[i] = data
	}

	var buf bytes.Buffer
	binary.Write(&buf, binary.LittleEndian, iconDir{Reserved: 0, Type: 1, Count: uint16(len(sizes))})
	headerSize := 6 + 16*len(sizes)
	offset := uint32(headerSize)
	for i, s := range sizes {
		w := uint8(s)
		h := uint8(s)
		if s >= 256 {
			w = 0
			h = 0
		}
		entry := iconDirEntry{
			Width:     w,
			Height:    h,
			Planes:    1,
			BitCount:  32,
			SizeBytes: uint32(len(pngs[i])),
			Offset:    offset,
		}
		binary.Write(&buf, binary.LittleEndian, entry)
		offset += uint32(len(pngs[i]))
	}
	for _, p := range pngs {
		buf.Write(p)
	}

	if err := os.WriteFile(outPath, buf.Bytes(), 0644); err != nil {
		fmt.Fprintln(os.Stderr, "write", err)
		os.Exit(1)
	}
	fmt.Println("wrote", outPath, "containing", len(sizes), "images")
}