package media

import (
	"bytes"
	"context"
	"image"
	"image/color"
	"image/jpeg"
	"image/png"
	"testing"
)

func testPNG(t *testing.T, w, h int) []byte {
	t.Helper()
	img := image.NewRGBA(image.Rect(0, 0, w, h))
	for x := 0; x < w; x++ {
		for y := 0; y < h; y++ {
			img.Set(x, y, color.RGBA{R: uint8(x % 256), G: uint8(y % 256), B: 120, A: 255})
		}
	}
	var buf bytes.Buffer
	if err := png.Encode(&buf, img); err != nil {
		t.Fatalf("png.Encode: %v", err)
	}
	return buf.Bytes()
}

func TestGenerateSkipsSmallImage(t *testing.T) {
	data := testPNG(t, 64, 64)
	out, err := Generate(context.Background(), bytes.NewReader(data), "image/png", 256)
	if err != nil {
		t.Fatalf("Generate: %v", err)
	}
	if out != nil {
		t.Fatalf("small image produced thumbnail, want nil")
	}
}

func TestGenerateResizesLargeImage(t *testing.T) {
	data := testPNG(t, 512, 512)
	out, err := Generate(context.Background(), bytes.NewReader(data), "image/png", 256)
	if err != nil {
		t.Fatalf("Generate: %v", err)
	}
	if out == nil {
		t.Fatal("large image produced nil thumbnail")
	}
	img, err := jpeg.Decode(bytes.NewReader(out))
	if err != nil {
		t.Fatalf("thumbnail is not valid JPEG: %v", err)
	}
	b := img.Bounds()
	if b.Dx() > 256 || b.Dy() > 256 {
		t.Fatalf("thumbnail size = %dx%d, want <= 256x256", b.Dx(), b.Dy())
	}
}

func TestGenerateNonImageReturnsNil(t *testing.T) {
	out, err := Generate(context.Background(), bytes.NewReader([]byte("plain")), "text/plain", 256)
	if err != nil {
		t.Fatalf("Generate: %v", err)
	}
	if out != nil {
		t.Fatal("non-image produced thumbnail, want nil")
	}
}

func TestGenerateCorruptImageFails(t *testing.T) {
	_, err := Generate(context.Background(), bytes.NewReader([]byte("not an image")), "image/png", 256)
	if err == nil {
		t.Fatal("corrupt image: Generate = nil error, want error")
	}
}