package main

import (
	"bytes"
	"image"
	"image/jpeg"
	"testing"
)

// testPhoto returns a JPEG-decoded (so *image.YCbCr, 4:2:0) image with an odd
// size and a non-zero origin to exercise the plane offset arithmetic.
func testPhoto(t testing.TB, w, h int) *image.YCbCr {
	t.Helper()
	src := image.NewRGBA(image.Rect(0, 0, w, h))
	for i := range src.Pix {
		src.Pix[i] = uint8(i*7 + i/w)
	}
	var buf bytes.Buffer
	if err := jpeg.Encode(&buf, src, &jpeg.Options{Quality: 90}); err != nil {
		t.Fatal(err)
	}
	img, err := jpeg.Decode(&buf)
	if err != nil {
		t.Fatal(err)
	}
	return img.(*image.YCbCr).SubImage(image.Rect(3, 5, w, h)).(*image.YCbCr)
}

func TestResizeBoxYCbCrMatchesGeneric(t *testing.T) {
	src := testPhoto(t, 1001, 667)
	fast := resizeBox(src, 120).(*image.RGBA)
	// Hide the concrete type so resizeBox takes the generic At() path.
	slow := resizeBox(struct{ image.Image }{src}, 120).(*image.RGBA)
	if fast.Bounds() != slow.Bounds() {
		t.Fatalf("bounds %v != %v", fast.Bounds(), slow.Bounds())
	}
	for i := range fast.Pix {
		if fast.Pix[i] != slow.Pix[i] {
			t.Fatalf("pixel byte %d: fast %d, generic %d", i, fast.Pix[i], slow.Pix[i])
		}
	}
}

func BenchmarkResizeBox(b *testing.B) {
	src := testPhoto(b, 4000, 3000)
	b.Run("ycbcr", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			resizeBox(src, 300)
		}
	})
	b.Run("generic", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			resizeBox(struct{ image.Image }{src}, 300)
		}
	})
}