package tools

import (
	"bytes"
	"image"
	"image/color"
	"image/png"
	"os"
	"path/filepath"
	"testing"
)

// makePNG 生成 w×h 的纯色 PNG 文件（可压缩性差的真实体积）。
func makePNG(t *testing.T, w, h int, noise bool) string {
	t.Helper()
	img := image.NewRGBA(image.Rect(0, 0, w, h))
	seed := uint32(1)
	next := func() uint8 {
		seed = seed*1664525 + 1013904223 // LCG 伪随机
		return uint8(seed >> 24)
	}
	for y := 0; y < h; y++ {
		for x := 0; x < w; x++ {
			if noise {
				// 逐像素伪随机：PNG 压不动，接近真实截图体积
				img.SetRGBA(x, y, color.RGBA{next(), next(), next(), 255})
			} else {
				img.SetRGBA(x, y, color.RGBA{200, 100, 50, 255})
			}
		}
	}
	p := filepath.Join(t.TempDir(), "big.png")
	f, err := os.Create(p)
	if err != nil {
		t.Fatal(err)
	}
	defer f.Close()
	if err := png.Encode(f, img); err != nil {
		t.Fatal(err)
	}
	return p
}

// TestShrinkForVision：大 PNG 降采样转 JPEG；小图原样返回。
func TestShrinkForVision(t *testing.T) {
	big := makePNG(t, 2400, 1600, true)
	st, _ := os.Stat(big)
	if st.Size() <= shrinkThresholdBytes {
		t.Skipf("test png too small (%d bytes), raise noise complexity", st.Size())
	}
	out, err := ShrinkForVision(big)
	if err != nil {
		t.Fatal(err)
	}
	if out == big {
		t.Fatal("big png should be shrunk")
	}
	if filepath.Ext(out) != ".jpg" {
		t.Fatalf("expect jpg output, got %s", out)
	}
	ost, err := os.Stat(out)
	if err != nil {
		t.Fatal(err)
	}
	if ost.Size() >= st.Size() {
		t.Fatalf("shrunk %d should be smaller than original %d", ost.Size(), st.Size())
	}
	// 宽度不超过上限
	f, _ := os.Open(out)
	defer f.Close()
	img, _, err := image.Decode(f)
	if err != nil {
		t.Fatal(err)
	}
	if w := img.Bounds().Dx(); w > maxVisionWidth {
		t.Fatalf("width %d exceeds %d", w, maxVisionWidth)
	}
	os.Remove(out)

	// 小图：原样返回
	small := makePNG(t, 64, 64, false)
	out2, err := ShrinkForVision(small)
	if err != nil || out2 != small {
		t.Fatalf("small image passthrough: %q %v", out2, err)
	}

	// 非图片文件：原样返回
	txt := filepath.Join(t.TempDir(), "x.png")
	os.WriteFile(txt, []byte("not an image"), 0o644)
	out3, err := ShrinkForVision(txt)
	if err != nil || out3 != txt {
		t.Fatalf("non-image passthrough: %q %v", out3, err)
	}
}

// TestVisionJPEGDecodable：压缩产物可被 image/jpeg 解码且尺寸正确。
func TestVisionJPEGDecodable(t *testing.T) {
	big := makePNG(t, 2000, 1000, true)
	out, err := ShrinkForVision(big)
	if err != nil || out == big {
		t.Fatalf("expected shrink: %q %v", out, err)
	}
	data, err := os.ReadFile(out)
	if err != nil {
		t.Fatal(err)
	}
	if !bytes.HasPrefix(data, []byte{0xFF, 0xD8}) {
		t.Fatal("output is not JPEG (missing SOI marker)")
	}
}