package main

import (
	"bytes"
	"image"
	"image/color"
	"image/jpeg"
	"math/rand"
	"strings"
	"testing"
	"tweetdistributor/output"
	"unicode/utf8"
)

// 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 TestFindLinks(t *testing.T) {
	tests := []struct {
		name    string
		content string
		want    []output.Link
	}{
		{
			// The offsets are byte offsets, so the multibyte prefix counts
			// for more than the three characters it looks like.
			"after multibyte text",
			"みてね https://example.com/article",
			[]output.Link{{URL: "https://example.com/article", ByteStart: 10, ByteEnd: 37}},
		},
		{
			"trailing punctuation is outside the link",
			"これ→https://example.com/x。",
			[]output.Link{{URL: "https://example.com/x", ByteStart: 9, ByteEnd: 30}},
		},
		{
			"several",
			"https://one.example https://two.example",
			[]output.Link{
				{URL: "https://one.example", ByteStart: 0, ByteEnd: 19},
				{URL: "https://two.example", ByteStart: 20, ByteEnd: 39},
			},
		},
		{"no link", "ただのつぶやき", nil},
		{"scheme only", "http:// と書いただけ", nil},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got := findLinks(tt.content)
			if len(got) != len(tt.want) {
				t.Fatalf("findLinks(%q) returned %d links, want %d", tt.content, len(got), len(tt.want))
			}
			for i, link := range got {
				if link != tt.want[i] {
					t.Errorf("link %d = %+v, want %+v", i, link, tt.want[i])
				}
				// A facet pointing at the wrong bytes marks up the wrong text.
				if slice := tt.content[link.ByteStart:link.ByteEnd]; slice != link.URL {
					t.Errorf("bytes [%d:%d] are %q, want %q", link.ByteStart, link.ByteEnd, slice, link.URL)
				}
			}
		})
	}
}

func TestTweetLength(t *testing.T) {
	tests := []struct {
		name    string
		content string
		want    int
	}{
		{"no link", "こんにちは", 5},
		{"long link", "https://www.youtube.com/watch?v=dQw4w9WgXcQ&list=PLabcdefghijklmnop", urlLength},
		{"short link", "https://a.jp", urlLength},
		{"link with text", "みてね " + strings.Repeat("x", 10) + " https://youtu.be/dQw4w9WgXcQ", 4 + 10 + 1 + urlLength},
		{"two links", "https://a.jp https://b.jp", urlLength*2 + 1},
		{"trailing punctuation still counts", "https://a.jp。", urlLength + 1},
		{"multibyte path", "https://ja.wikipedia.org/wiki/日本語", urlLength},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			if got := tweetLength(tt.content); got != tt.want {
				t.Errorf("tweetLength(%q) = %d, want %d", tt.content, got, tt.want)
			}
		})
	}
}

func TestTweetLengthAcceptsMessageOnlyLinksMakeTooLong(t *testing.T) {
	// A message that the raw rune count would reject but Twitter accepts.
	content := strings.Repeat("あ", 100) + " https://www.youtube.com/watch?v=dQw4w9WgXcQ&t=120s"

	if raw := utf8.RuneCountInString(content); raw <= maxTweetLength {
		t.Fatalf("test message should be %d raw characters, got %d", maxTweetLength+1, raw)
	}
	if got := tweetLength(content); got > maxTweetLength {
		t.Errorf("tweetLength = %d, want it to fit within %d", got, maxTweetLength)
	}
}

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")
	}
}