package shortcodes

import (
	"bytes"
	"image"
	"image/color"
	"image/jpeg"
	"image/png"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"testing"
	"testing/fstest"
	"time"

	"khosra/internal/render"
)

// wide builds a real encoded picture of a given width, so the tests exercise decoding rather than a stub.
func wide(t *testing.T, width int, asPNG bool) []byte {
	t.Helper()
	img := image.NewRGBA(image.Rect(0, 0, width, width/2))
	for x := range width {
		for y := range width / 2 {
			img.Set(x, y, color.RGBA{uint8(x % 256), uint8(y % 256), 128, 255})
		}
	}
	var out bytes.Buffer
	var err error
	if asPNG {
		err = png.Encode(&out, img)
	} else {
		err = jpeg.Encode(&out, img, nil)
	}
	if err != nil {
		t.Fatal(err)
	}
	return out.Bytes()
}

func TestDeriveMakesEachMissingWidthAndIsIdempotent(t *testing.T) {
	cache := t.TempDir()
	big := wide(t, 2000, false)
	fsys := fstest.MapFS{
		"content/art/set/index.md":  {Data: []byte("---\ntitle: Set\n---\n")},
		"content/art/set/big.jpg":   {Data: big},
		"content/art/set/small.png": {Data: wide(t, 300, true)}, // narrower than every target
		"content/art/set/notes.md":  {Data: []byte("not a picture")},
	}
	made, err := Derive(fsys, cache)
	if err != nil {
		t.Fatal(err)
	}
	if made != len(widths) {
		t.Errorf("made %d derivatives, want %d — one per width below the original's", made, len(widths))
	}
	// Never upscale: nothing is made for a picture already narrower than the targets.
	entries, err := os.ReadDir(cache)
	if err != nil {
		t.Fatal(err)
	}
	if len(entries) != len(widths) {
		t.Errorf("cache holds %d files, want %d", len(entries), len(widths))
	}
	// Each is a real image of the width it claims.
	for _, e := range entries {
		data, err := os.ReadFile(filepath.Join(cache, e.Name()))
		if err != nil {
			t.Fatal(err)
		}
		cfg, _, err := image.DecodeConfig(bytes.NewReader(data))
		if err != nil {
			t.Fatalf("%s is not a decodable image: %v", e.Name(), err)
		}
		if !strings.Contains(e.Name(), "-w"+strconv.Itoa(cfg.Width)) {
			t.Errorf("%s decodes to width %d, which its name does not claim", e.Name(), cfg.Width)
		}
		if cfg.Height != cfg.Width/2 {
			t.Errorf("%s is %dx%d — the aspect ratio was not kept", e.Name(), cfg.Width, cfg.Height)
		}
	}
	// A second pass writes nothing: the name is the source's content, so there is nothing new to make.
	again, err := Derive(fsys, cache)
	if err != nil {
		t.Fatal(err)
	}
	if again != 0 {
		t.Errorf("second pass made %d, want 0 — the pass must be idempotent (ADR-0042)", again)
	}
}

func TestAnEditedPictureGetsADifferentName(t *testing.T) {
	// Content-addressed, so a stale derivative can never be served under a name that now means something else.
	first := derivedName(wide(t, 1000, false), "content/a/x.jpg", 480)
	second := derivedName(wide(t, 1200, false), "content/a/x.jpg", 480)
	if first == second {
		t.Error("two different pictures must not share a derivative name")
	}
	if derivedName([]byte("same"), "a.png", 480) == derivedName([]byte("same"), "a.png", 960) {
		t.Error("two widths of one picture must not share a name either")
	}
	if !strings.HasSuffix(derivedName([]byte("x"), "a.png", 480), ".png") {
		t.Error("a source that may carry transparency keeps a lossless derivative")
	}
}

func TestOriginalsAreNeverTouched(t *testing.T) {
	cache := t.TempDir()
	big := wide(t, 2000, false)
	original := append([]byte(nil), big...)
	fsys := fstest.MapFS{"content/art/set/big.jpg": {Data: big}}
	if _, err := Derive(fsys, cache); err != nil {
		t.Fatal(err)
	}
	after, err := fsys.ReadFile("content/art/set/big.jpg")
	if err != nil {
		t.Fatal(err)
	}
	if !bytes.Equal(original, after) {
		t.Error("the author's own file was modified")
	}
}

func TestAnEditedPictureIsInspectedAgain(t *testing.T) {
	// The whole risk of remembering: serving yesterday's size or srcset. The key carries size and modification
	// time, so an edit is a different key rather than a stale hit.
	fsys := fstest.MapFS{
		"content/art/set/index.md": {Data: []byte("---\ntitle: Set\n---\n")},
		"content/art/set/one.jpg":  {Data: wide(t, 1200, false), ModTime: time.Unix(1000, 0)},
	}
	origin := render.Origin{Dir: "content/art/set", Files: fsys}
	first, ok := picture(origin, "one.jpg")
	if !ok || first.Width != 1200 {
		t.Fatalf("first inspection = %+v", first)
	}
	if again, _ := picture(origin, "one.jpg"); again != first {
		t.Errorf("a second look at the same file should be identical, got %+v", again)
	}

	fsys["content/art/set/one.jpg"] = &fstest.MapFile{Data: wide(t, 800, false), ModTime: time.Unix(2000, 0)}
	edited, ok := picture(origin, "one.jpg")
	if !ok {
		t.Fatal("still a picture")
	}
	if edited.Width != 800 {
		t.Errorf("width = %d, want 800 — the edit was not noticed", edited.Width)
	}
	if edited.Srcset == first.Srcset {
		t.Error("the srcset should name different derivatives after an edit")
	}
}