// icocheck：校验生成的 .ico 结构，并把它内嵌的每个尺寸导出成 PNG，
// 方便肉眼确认缩放质量、以及圆角有没有被 premultiplied alpha 处理对。
//
// 用法：
//
//	go run ./tools/icocheck build/windows/icon.ico <导出目录>
package main

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"image"
	"image/png"
	"os"
	"path/filepath"
)

func main() {
	if len(os.Args) < 2 {
		fmt.Fprintln(os.Stderr, "用法: go run ./tools/icocheck <icon.ico> [导出目录]")
		os.Exit(1)
	}
	icoPath := os.Args[1]
	outDir := ""
	if len(os.Args) > 2 {
		outDir = os.Args[2]
	}

	raw, err := os.ReadFile(icoPath)
	if err != nil {
		fail(err)
	}
	fmt.Printf("文件: %s  (%d 字节)\n", icoPath, len(raw))
	if len(raw) < 6 {
		fail(fmt.Errorf("文件太短，不是 ICO"))
	}

	reserved := binary.LittleEndian.Uint16(raw[0:2])
	typ := binary.LittleEndian.Uint16(raw[2:4])
	count := int(binary.LittleEndian.Uint16(raw[4:6]))
	fmt.Printf("ICONDIR: reserved=%d type=%d (1=icon) count=%d\n", reserved, typ, count)
	if reserved != 0 || typ != 1 {
		fail(fmt.Errorf("头部不对：reserved=%d type=%d", reserved, typ))
	}
	if 6+16*count > len(raw) {
		fail(fmt.Errorf("目录表超出文件长度"))
	}

	if outDir != "" {
		if err := os.MkdirAll(outDir, 0o755); err != nil {
			fail(err)
		}
	}

	fmt.Println()
	fmt.Printf("%-10s %-6s %-9s %-9s %-7s %s\n", "尺寸", "编码", "数据长度", "偏移", "实际", "四角alpha(应≈0=圆角透明)")
	for i := 0; i < count; i++ {
		o := 6 + 16*i
		w := int(raw[o])
		h := int(raw[o+1])
		dim := fmt.Sprintf("%dx%d", w, h)
		if w == 0 && h == 0 {
			dim = "256x256"
		}
		size := int(binary.LittleEndian.Uint32(raw[o+8 : o+12]))
		off := int(binary.LittleEndian.Uint32(raw[o+12 : o+16]))
		if off < 0 || size < 0 || off+size > len(raw) {
			fail(fmt.Errorf("第 %d 项越界: off=%d size=%d 文件=%d", i, off, size, len(raw)))
		}

		body := raw[off : off+size]
		var kind string
		var img image.Image
		switch {
		case bytes.HasPrefix(body, []byte{0x89, 'P', 'N', 'G'}):
			kind = "PNG"
			im, err := png.Decode(bytes.NewReader(body))
			if err != nil {
				fail(fmt.Errorf("第 %d 项 PNG 解不开: %v", i, err))
			}
			img = im
		case binary.LittleEndian.Uint32(body[0:4]) == 40:
			kind = "DIB"
			im, err := decodeDIB(body)
			if err != nil {
				fail(fmt.Errorf("第 %d 项 DIB 解不开: %v", i, err))
			}
			img = im
		default:
			fail(fmt.Errorf("第 %d 项既不是 PNG 也不是 DIB: % x", i, body[:min(4, len(body))]))
		}

		b := img.Bounds()
		if b.Dx() != b.Dy() {
			fail(fmt.Errorf("第 %d 项不是正方形: %dx%d", i, b.Dx(), b.Dy()))
		}

		if outDir != "" {
			name := filepath.Join(outDir, fmt.Sprintf("ico-%03d-%s.png", b.Dx(), kind))
			f, err := os.Create(name)
			if err != nil {
				fail(err)
			}
			if err := png.Encode(f, img); err != nil {
				fail(err)
			}
			f.Close()
		}

		fmt.Printf("%-10s %-6s %-9d %-9d %-7s %v\n",
			dim, kind, size, off,
			fmt.Sprintf("%dx%d", b.Dx(), b.Dy()),
			cornerAlpha(img))
	}
	fmt.Println()
	fmt.Println("✓ 全部条目校验通过")
}

func cornerAlpha(im image.Image) [4]uint32 {
	var out [4]uint32
	b := im.Bounds()
	pts := [][2]int{{b.Min.X, b.Min.Y}, {b.Max.X - 1, b.Min.Y}, {b.Min.X, b.Max.Y - 1}, {b.Max.X - 1, b.Max.Y - 1}}
	for i, p := range pts {
		_, _, _, a := im.At(p[0], p[1]).RGBA()
		out[i] = a >> 8
	}
	return out
}

// decodeDIB 解 BITMAPINFOHEADER + 自下而上 BGRA + AND 掩码
func decodeDIB(b []byte) (image.Image, error) {
	if len(b) < 40 {
		return nil, fmt.Errorf("DIB 太短")
	}
	w := int(int32(binary.LittleEndian.Uint32(b[4:8])))
	hFull := int(int32(binary.LittleEndian.Uint32(b[8:12])))
	bits := binary.LittleEndian.Uint16(b[14:16])
	h := hFull / 2 // biHeight 含 AND 掩码那一半
	if w <= 0 || h <= 0 {
		return nil, fmt.Errorf("DIB 尺寸非法 w=%d h=%d", w, h)
	}
	if bits != 32 {
		return nil, fmt.Errorf("只支持 32bpp，实际 %d", bits)
	}

	img := image.NewNRGBA(image.Rect(0, 0, w, h))
	xor := b[40:]
	stride := w * 4
	for row := 0; row < h; row++ {
		srcRow := h - 1 - row // DIB 自下而上
		for x := 0; x < w; x++ {
			i := srcRow*stride + x*4
			if i+4 > len(xor) {
				return nil, fmt.Errorf("像素数据不足")
			}
			o := row*img.Stride + x*4
			img.Pix[o+0] = xor[i+2] // R
			img.Pix[o+1] = xor[i+1] // G
			img.Pix[o+2] = xor[i+0] // B
			img.Pix[o+3] = xor[i+3] // A
		}
	}
	return img, nil
}

func fail(err error) {
	fmt.Fprintln(os.Stderr, "✗ "+err.Error())
	os.Exit(1)
}