package main

import (
	"bytes"
	"image"
	"image/color"
	"image/jpeg"
	"math/rand"
	"testing"
	"tweetdistributor/output"
)

// noiseJPEG returns a JPEG image of random noise, which compresses poorly
// and reliably exceeds maxImageBytes at large dimensions.
func noiseJPEG(t *testing.T, width, height int) []byte {
	t.Helper()
	rng := rand.New(rand.NewSource(1))
	img := image.NewRGBA(image.Rect(0, 0, width, height))
	for y := 0; y < height; y++ {
		for x := 0; x < width; x++ {
			img.Set(x, y, color.RGBA{uint8(rng.Intn(256)), uint8(rng.Intn(256)), uint8(rng.Intn(256)), 255})
		}
	}
	var buf bytes.Buffer
	if err := jpeg.Encode(&buf, img, &jpeg.Options{Quality: 95}); err != nil {
		t.Fatal(err)
	}
	return buf.Bytes()
}

func TestShrinkImageLarge(t *testing.T) {
	data := noiseJPEG(t, 3000, 3000)
	if len(data) <= maxImageBytes {
		t.Fatalf("test image should exceed maxImageBytes, got %d", len(data))
	}

	shrunk, err := shrinkImage(output.Image{Data: data, ContentType: "image/jpeg", Filename: "DSC_7277.jpg"})
	if err != nil {
		t.Fatal(err)
	}
	if len(shrunk.Data) > maxImageBytes {
		t.Errorf("shrunk image is %d bytes, want <= %d", len(shrunk.Data), maxImageBytes)
	}
	if shrunk.ContentType != "image/jpeg" {
		t.Errorf("ContentType = %q, want image/jpeg", shrunk.ContentType)
	}
	if shrunk.Filename != "DSC_7277.jpg" {
		t.Errorf("Filename = %q, want DSC_7277.jpg", shrunk.Filename)
	}
	if _, _, err := image.Decode(bytes.NewReader(shrunk.Data)); err != nil {
		t.Errorf("shrunk image is not decodable: %s", err)
	}
}

func TestShrinkImageSmallPassthrough(t *testing.T) {
	data := noiseJPEG(t, 100, 100)
	img := output.Image{Data: data, ContentType: "image/png", Filename: "small.png"}
	shrunk, err := shrinkImage(img)
	if err != nil {
		t.Fatal(err)
	}
	if !bytes.Equal(shrunk.Data, img.Data) || shrunk.ContentType != img.ContentType || shrunk.Filename != img.Filename {
		t.Error("small image should pass through unchanged")
	}
}