package library

import (
	"bytes"
	"encoding/binary"
	"strings"
	"testing"

	"github.com/dhowden/tag"
)

// rawFrame is a frame with a byte-exact payload, so tests can express encoding
// bytes and embedded nulls that a string-keyed helper can't.
type rawFrame struct {
	id      string
	payload []byte
}

// buildID3v2 assembles a tag for the given major version. Frame size encoding
// differs per version (2.4 is synchsafe, 2.2/2.3 are plain), which is exactly
// the kind of detail a parser gets subtly wrong, so tests build all three.
func buildID3v2(t *testing.T, major byte, frames ...rawFrame) []byte {
	t.Helper()
	var body bytes.Buffer
	for _, f := range frames {
		switch major {
		case 2:
			if len(f.id) != 3 {
				t.Fatalf("v2.2 frame id %q must be 3 bytes", f.id)
			}
			body.WriteString(f.id)
			n := len(f.payload)
			body.Write([]byte{byte(n >> 16), byte(n >> 8), byte(n)})
		case 3:
			body.WriteString(f.id)
			_ = binary.Write(&body, binary.BigEndian, uint32(len(f.payload)))
			body.Write([]byte{0x00, 0x00})
		case 4:
			body.WriteString(f.id)
			body.Write(synchsafeBytes(len(f.payload)))
			body.Write([]byte{0x00, 0x00})
		}
		body.Write(f.payload)
	}
	var out bytes.Buffer
	out.WriteString("ID3")
	out.Write([]byte{major, 0x00, 0x00})
	out.Write(synchsafeBytes(body.Len()))
	out.Write(body.Bytes())
	// A few bytes of MPEG sync so dhowden/tag accepts the file shape.
	out.Write([]byte{0xFF, 0xFB, 0x90, 0x00})
	return out.Bytes()
}

func synchsafeBytes(n int) []byte {
	return []byte{
		byte((n >> 21) & 0x7F),
		byte((n >> 14) & 0x7F),
		byte((n >> 7) & 0x7F),
		byte(n & 0x7F),
	}
}

// utf8Frame builds a text-frame payload: encoding byte 3 (UTF-8) followed by
// values joined with the null separator ID3v2 uses for multiple values.
func utf8Frame(values ...string) []byte {
	return append([]byte{0x03}, []byte(strings.Join(values, "\x00"))...)
}

// TestReadID3v2GenreValues_MultiValue is the #2499 regression. dhowden/tag
// rejoins these values with the empty string, producing "Alternative RockRock";
// the whole point of our own reader is that they stay separate.
func TestReadID3v2GenreValues_MultiValue(t *testing.T) {
	for _, major := range []byte{2, 3, 4} {
		id := "TCON"
		if major == 2 {
			id = "TCO"
		}
		data := buildID3v2(t, major, rawFrame{id, utf8Frame("Alternative Rock", "Rock")})
		got, err := readID3v2GenreValues(bytes.NewReader(data))
		if err != nil {
			t.Fatalf("v2.%d: %v", major, err)
		}
		want := []string{"Alternative Rock", "Rock"}
		if !equalStrings(got, want) {
			t.Errorf("v2.%d genres = %q, want %q", major, got, want)
		}
	}
}

// The operator's worst case: eight values welded into one 70-character token.
func TestReadID3v2GenreValues_ManyValues(t *testing.T) {
	values := []string{
		"Boom Bap", "Downtempo", "Hip Hop", "Instrumental",
		"Lo-Fi", "Lo-Fi Hip Hop", "Chillwave", "Instrumental Hip Hop",
	}
	data := buildID3v2(t, 4, rawFrame{"TCON", utf8Frame(values...)})
	got, err := readID3v2GenreValues(bytes.NewReader(data))
	if err != nil {
		t.Fatal(err)
	}
	if !equalStrings(got, values) {
		t.Errorf("genres = %q, want %q", got, values)
	}
}

// A trailing null terminator is legal and must not produce an empty value.
func TestReadID3v2GenreValues_TrailingTerminator(t *testing.T) {
	data := buildID3v2(t, 4, rawFrame{"TCON", append(utf8Frame("Jazz"), 0x00)})
	got, err := readID3v2GenreValues(bytes.NewReader(data))
	if err != nil {
		t.Fatal(err)
	}
	if !equalStrings(got, []string{"Jazz"}) {
		t.Errorf("genres = %q, want [Jazz]", got)
	}
}

// UTF-16 uses a TWO-byte separator. Splitting it on single nulls would cut
// every ASCII character in half, so this guards the width handling.
func TestReadID3v2GenreValues_UTF16(t *testing.T) {
	tests := []struct {
		name    string
		payload []byte
	}{
		{
			// Spec-correct: encoding 1 with a BOM on every value.
			name: "utf16le, BOM on each value",
			payload: concat([]byte{0x01},
				[]byte{0xFF, 0xFE}, utf16LE("Rock"),
				[]byte{0x00, 0x00},
				[]byte{0xFF, 0xFE}, utf16LE("Pop")),
		},
		{
			// Sloppy but common: BOM only on the first value. Without carrying
			// the byte order forward, "Pop" decodes byte-swapped to CJK.
			name: "utf16le, BOM only on the first value",
			payload: concat([]byte{0x01},
				[]byte{0xFF, 0xFE}, utf16LE("Rock"),
				[]byte{0x00, 0x00}, utf16LE("Pop")),
		},
		{
			// Encoding 2: big-endian, no BOM anywhere.
			name: "utf16be no BOM",
			payload: concat([]byte{0x02},
				utf16BE("Rock"), []byte{0x00, 0x00}, utf16BE("Pop")),
		},
	}
	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			data := buildID3v2(t, 4, rawFrame{"TCON", tc.payload})
			got, err := readID3v2GenreValues(bytes.NewReader(data))
			if err != nil {
				t.Fatal(err)
			}
			if !equalStrings(got, []string{"Rock", "Pop"}) {
				t.Errorf("genres = %q, want [Rock Pop]", got)
			}
		})
	}
}

// ISO-8859-1 must be widened, not reinterpreted as UTF-8 — "Bj\xf6rk" would
// otherwise come back as invalid bytes.
func TestReadID3v2GenreValues_Latin1(t *testing.T) {
	payload := append([]byte{0x00}, []byte("Chanson Fran\xe7aise")...)
	data := buildID3v2(t, 3, rawFrame{"TCON", payload})
	got, err := readID3v2GenreValues(bytes.NewReader(data))
	if err != nil {
		t.Fatal(err)
	}
	if !equalStrings(got, []string{"Chanson Française"}) {
		t.Errorf("genres = %q, want [Chanson Française]", got)
	}
}

// Frames before TCON must be walked over correctly. If the size field were
// decoded with the wrong scheme the walk lands mid-frame and TCON is missed.
func TestReadID3v2GenreValues_SkipsPrecedingFrames(t *testing.T) {
	for _, major := range []byte{3, 4} {
		data := buildID3v2(t, major,
			rawFrame{"TIT2", utf8Frame("Some Title")},
			rawFrame{"TPE1", utf8Frame("Some Artist")},
			rawFrame{"TCON", utf8Frame("Shoegaze", "Dream Pop")},
		)
		got, err := readID3v2GenreValues(bytes.NewReader(data))
		if err != nil {
			t.Fatalf("v2.%d: %v", major, err)
		}
		if !equalStrings(got, []string{"Shoegaze", "Dream Pop"}) {
			t.Errorf("v2.%d genres = %q, want [Shoegaze Dream Pop]", major, got)
		}
	}
}

func TestReadID3v2GenreValues_NoGenreFrame(t *testing.T) {
	data := buildID3v2(t, 4, rawFrame{"TIT2", utf8Frame("Only A Title")})
	if _, err := readID3v2GenreValues(bytes.NewReader(data)); err == nil {
		t.Fatal("expected an error when no genre frame is present")
	}
}

func TestReadID3v2GenreValues_NotAnID3File(t *testing.T) {
	if _, err := readID3v2GenreValues(bytes.NewReader([]byte("not a tag at all"))); err == nil {
		t.Fatal("expected an error for a file with no ID3v2 tag")
	}
}

// Padding after the last frame is zero bytes; the walk must stop rather than
// read a frame id of "\x00\x00\x00\x00".
func TestReadID3v2GenreValues_StopsAtPadding(t *testing.T) {
	tagged := buildID3v2(t, 4, rawFrame{"TCON", utf8Frame("Rock")})
	// Splice 32 padding bytes in before the MPEG sync trailer, growing the
	// declared tag size to match.
	body := tagged[10 : len(tagged)-4]
	padded := append(append([]byte{}, body...), make([]byte, 32)...)
	var out bytes.Buffer
	out.WriteString("ID3")
	out.Write([]byte{4, 0x00, 0x00})
	out.Write(synchsafeBytes(len(padded)))
	out.Write(padded)
	got, err := readID3v2GenreValues(bytes.NewReader(out.Bytes()))
	if err != nil {
		t.Fatal(err)
	}
	if !equalStrings(got, []string{"Rock"}) {
		t.Errorf("genres = %q, want [Rock]", got)
	}
}

// Unsynchronisation inserts 0xFF 0x00 pairs that must be collapsed before the
// frame list is walked, or every offset past the first pair is wrong.
func TestReadID3v2GenreValues_TagUnsynchronisation(t *testing.T) {
	// Latin-1 so a genre can legitimately contain the byte 0xFF ("ÿ"). Once
	// unsynchronised that becomes 0xFF 0x00 — which is indistinguishable from a
	// value separator until the collapse runs, so this fails loudly if
	// undoUnsynchronisation is skipped.
	payload := concat([]byte{0x00}, []byte("Ro\xffck"), []byte{0x00}, []byte("Pop"))
	inner := buildID3v2(t, 3, rawFrame{"TCON", payload})
	body := inner[10 : len(inner)-4]
	encoded := bytes.ReplaceAll(body, []byte{0xFF}, []byte{0xFF, 0x00})
	if bytes.Equal(encoded, body) {
		t.Fatal("test is vacuous: nothing was unsynchronised")
	}
	var out bytes.Buffer
	out.WriteString("ID3")
	out.Write([]byte{3, 0x00, 0x80}) // 0x80 = unsynchronisation
	out.Write(synchsafeBytes(len(encoded)))
	out.Write(encoded)

	got, err := readID3v2GenreValues(bytes.NewReader(out.Bytes()))
	if err != nil {
		t.Fatal(err)
	}
	if !equalStrings(got, []string{"Roÿck", "Pop"}) {
		t.Errorf("genres = %q, want [Roÿck Pop]", got)
	}
}

func TestNormaliseGenreValue(t *testing.T) {
	tests := []struct {
		name string
		in   string
		want []string
	}{
		{"plain text", "Alternative Rock", []string{"Alternative Rock"}},
		{"trims whitespace", "  Jazz  ", []string{"Jazz"}},
		{"empty", "", nil},
		{"whitespace only", "   ", nil},

		// The operator's digit soup, one value at a time.
		{"bare numeric", "17", []string{"Rock"}},
		{"bare numeric pop", "13", []string{"Pop"}},
		{"bare numeric electronic", "52", []string{"Electronic"}},
		{"winamp extension range", "187", []string{"Indie Rock"}},
		{"numeric out of range", "9999", nil},
		{"negative", "-1", nil},

		// ID3v2.3 refinement syntax.
		{"parenthesised", "(17)", []string{"Rock"}},
		{"parenthesised repeated", "(51)(39)", []string{"Techno-Industrial", "Noise"}},
		{"parenthesised with refinement", "(17)Hard Rock", []string{"Rock", "Hard Rock"}},
		{"remix", "(RX)", []string{"Remix"}},
		{"cover", "(CR)", []string{"Cover"}},
		{"escaped open paren", "((Weird", []string{"(Weird"}},
		{"parenthesised non-numeric", "(Live)", []string{"(Live)"}},

		// A label that merely starts with digits is text, not a reference.
		{"digits in a name", "1980s", []string{"1980s"}},
		{"hyphenated", "Lo-Fi Hip Hop", []string{"Lo-Fi Hip Hop"}},
	}
	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			got := normaliseGenreValue(tc.in)
			if !equalStrings(got, tc.want) {
				t.Errorf("normaliseGenreValue(%q) = %q, want %q", tc.in, got, tc.want)
			}
		})
	}
}

func TestNormaliseGenres_DedupesCaseInsensitively(t *testing.T) {
	got := normaliseGenres([]string{"Rock", "rock", "ROCK", "Pop"})
	// First spelling wins — we are not imposing a canonical case here, only
	// removing values that repeat within a single file.
	if !equalStrings(got, []string{"Rock", "Pop"}) {
		t.Errorf("genres = %q, want [Rock Pop]", got)
	}
}

// "(40)AlternRock" declares the same genre twice — numerically and in text.
func TestNormaliseGenres_DedupesResolvedNumeric(t *testing.T) {
	got := normaliseGenres([]string{"(40)AlternRock"})
	if !equalStrings(got, []string{"AlternRock"}) {
		t.Errorf("genres = %q, want [AlternRock]", got)
	}
}

func TestNormaliseGenres_AllJunkYieldsNil(t *testing.T) {
	if got := normaliseGenres([]string{"", "  ", "9999"}); got != nil {
		t.Errorf("genres = %q, want nil", got)
	}
}

// End-to-end through dhowden/tag, which is what the scanner actually calls.
// Proves the welded value never reaches the caller.
func TestExtractGenres_EndToEnd(t *testing.T) {
	data := buildID3v2(t, 4,
		rawFrame{"TIT2", utf8Frame("A Song")},
		rawFrame{"TCON", utf8Frame("Alternative Rock", "Rock")},
	)
	rs := bytes.NewReader(data)
	meta, err := tag.ReadFrom(rs)
	if err != nil {
		t.Fatalf("tag.ReadFrom: %v", err)
	}
	// Confirm the upstream behaviour this fix exists for is still present —
	// if dhowden ever fixes it, this test tells us the workaround can go.
	if welded := meta.Genre(); welded != "Alternative RockRock" {
		t.Logf("note: dhowden/tag no longer welds multi-values (got %q)", welded)
	}

	genres, fellBack := extractGenres(meta, rs)
	if fellBack {
		t.Error("fellBack = true, want false — the TCON frame is parseable")
	}
	if !equalStrings(genres, []string{"Alternative Rock", "Rock"}) {
		t.Errorf("genres = %q, want [Alternative Rock Rock]", genres)
	}
	if joined := strings.Join(genres, genreDelimiter); joined != "Alternative Rock;Rock" {
		t.Errorf("stored value = %q, want %q", joined, "Alternative Rock;Rock")
	}
}

// The digit-soup case, end to end: numeric references resolve to names.
func TestExtractGenres_ResolvesNumericReferences(t *testing.T) {
	data := buildID3v2(t, 4, rawFrame{"TCON", utf8Frame("40", "17")})
	rs := bytes.NewReader(data)
	meta, err := tag.ReadFrom(rs)
	if err != nil {
		t.Fatalf("tag.ReadFrom: %v", err)
	}
	genres, _ := extractGenres(meta, rs)
	if !equalStrings(genres, []string{"AlternRock", "Rock"}) {
		t.Errorf("genres = %q, want [AlternRock Rock]", genres)
	}
}

// A file with no genre at all must yield nothing and must NOT be reported as a
// fallback — that would log a warning for every untagged file in the library.
func TestExtractGenres_NoGenreIsNotAFallback(t *testing.T) {
	data := buildID3v2(t, 4, rawFrame{"TIT2", utf8Frame("A Song")})
	rs := bytes.NewReader(data)
	meta, err := tag.ReadFrom(rs)
	if err != nil {
		t.Fatalf("tag.ReadFrom: %v", err)
	}
	genres, fellBack := extractGenres(meta, rs)
	if len(genres) != 0 {
		t.Errorf("genres = %q, want none", genres)
	}
	if fellBack {
		t.Error("fellBack = true for an untagged file; would log on every such file")
	}
}

func concat(parts ...[]byte) []byte {
	var out []byte
	for _, p := range parts {
		out = append(out, p...)
	}
	return out
}

func utf16LE(s string) []byte {
	out := make([]byte, 0, len(s)*2)
	for _, r := range s {
		out = append(out, byte(r), byte(r>>8))
	}
	return out
}

func utf16BE(s string) []byte {
	out := make([]byte, 0, len(s)*2)
	for _, r := range s {
		out = append(out, byte(r>>8), byte(r))
	}
	return out
}

func equalStrings(a, b []string) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}