package rating

import (
	"bytes"
	"encoding/binary"
	"os"
	"testing"
)

// buildTaggedMP3 builds a synthetic MP3 with a real ID3v2 tag.
//   - ver: 3 or 4 (ID3v2 minor version)
//   - frames: pre-built frame bytes (full frame including 10-byte frame header)
//   - paddingLen: bytes of zero padding inside the tag
//   - audio: payload after the tag
//
// The returned bytes are: 10-byte ID3 header | frames | padding | audio.
func buildTaggedMP3(ver byte, frames []byte, paddingLen int, audio []byte) []byte {
	tagSize := len(frames) + paddingLen
	var hdr [10]byte
	hdr[0], hdr[1], hdr[2] = 'I', 'D', '3'
	hdr[3] = ver
	hdr[4] = 0
	hdr[5] = 0 // no flags
	s := uint32(tagSize)
	hdr[6] = byte((s >> 21) & 0x7F)
	hdr[7] = byte((s >> 14) & 0x7F)
	hdr[8] = byte((s >> 7) & 0x7F)
	hdr[9] = byte(s & 0x7F)

	out := make([]byte, 0, 10+tagSize+len(audio))
	out = append(out, hdr[:]...)
	out = append(out, frames...)
	out = append(out, make([]byte, paddingLen)...)
	out = append(out, audio...)
	return out
}

// makePOPMFrame builds a POPM frame matching ver's size encoding.
func makePOPMFrame(ver byte, email string, rating byte, counter []byte) []byte {
	dataLen := len(email) + 1 + 1 + len(counter)
	out := make([]byte, 10+dataLen)
	copy(out[0:4], "POPM")
	switch ver {
	case 3:
		binary.BigEndian.PutUint32(out[4:8], uint32(dataLen))
	case 4:
		s := uint32(dataLen)
		out[4] = byte((s >> 21) & 0x7F)
		out[5] = byte((s >> 14) & 0x7F)
		out[6] = byte((s >> 7) & 0x7F)
		out[7] = byte(s & 0x7F)
	}
	copy(out[10:], email)
	out[10+len(email)] = 0
	out[10+len(email)+1] = rating
	copy(out[10+len(email)+2:], counter)
	return out
}

func fakeAudio(n int) []byte {
	a := make([]byte, n)
	for i := range a {
		a[i] = byte((i * 7) & 0xFF)
	}
	return a
}

// --- TESTS: patch path with existing POPM (1-byte write) ---------------------

func TestPatch_existingPOPM_v23(t *testing.T) {
	for _, stars := range []int{1, 2, 3, 4, 5, 0} {
		t.Run("", func(t *testing.T) {
			// Use a starting rating (200) that doesn't match any starsToPOPM value
			// so we always observe a 1-byte change regardless of target stars.
			frame := makePOPMFrame(3, "rating@winamp.com", 200, []byte{0, 0, 0, 0})
			audio := fakeAudio(2048)
			data := buildTaggedMP3(3, frame, 512, audio)
			path := writeTempMP3(t, data)
			before, _ := os.ReadFile(path)

			if err := tryPatchPOPM(path, stars); err != nil {
				t.Fatalf("tryPatchPOPM: %v", err)
			}

			after, _ := os.ReadFile(path)
			if len(before) != len(after) {
				t.Fatalf("file size changed: %d → %d", len(before), len(after))
			}

			// Exactly ONE byte should differ — the rating byte.
			diffCount := 0
			diffOff := -1
			for i := range before {
				if before[i] != after[i] {
					diffCount++
					diffOff = i
				}
			}
			if diffCount != 1 {
				t.Fatalf("expected exactly 1 byte changed, got %d", diffCount)
			}
			// The rating byte sits at: 10 (header) + 10 (frame hdr) + len(email)+1
			wantOff := 10 + 10 + len("rating@winamp.com") + 1
			if diffOff != wantOff {
				t.Errorf("changed byte at %d, expected at %d", diffOff, wantOff)
			}
			if after[diffOff] != starsToPOPM(stars) {
				t.Errorf("rating byte = %d, want %d", after[diffOff], starsToPOPM(stars))
			}

			// Audio region untouched.
			audioStart := 10 + 10 + 23 + 512 // hdr + frame + padding
			if !bytes.Equal(after[audioStart:], audio) {
				t.Error("audio data corrupted")
			}

			// Get() should reflect the new rating
			got, _ := Get(path)
			if got != stars {
				t.Errorf("Get() = %d, want %d", got, stars)
			}
		})
	}
}

func TestPatch_existingPOPM_v24(t *testing.T) {
	frame := makePOPMFrame(4, "rating@winamp.com", 1, []byte{0, 0, 0, 0})
	audio := fakeAudio(1024)
	data := buildTaggedMP3(4, frame, 256, audio)
	path := writeTempMP3(t, data)

	if err := tryPatchPOPM(path, 5); err != nil {
		t.Fatalf("tryPatchPOPM: %v", err)
	}
	got, _ := Get(path)
	if got != 5 {
		t.Errorf("Get() = %d, want 5", got)
	}
}

// --- TESTS: patch path inserts new POPM into padding -------------------------

func TestPatch_insertIntoPadding(t *testing.T) {
	audio := fakeAudio(1024)
	data := buildTaggedMP3(3, nil, 1024, audio) // empty tag body, all padding
	path := writeTempMP3(t, data)
	beforeSize := int64(len(data))

	if err := tryPatchPOPM(path, 4); err != nil {
		t.Fatalf("tryPatchPOPM: %v", err)
	}

	st, _ := os.Stat(path)
	if st.Size() != beforeSize {
		t.Fatalf("file size changed: %d → %d", beforeSize, st.Size())
	}

	got, err := Get(path)
	if err != nil {
		t.Fatalf("Get: %v", err)
	}
	if got != 4 {
		t.Errorf("Get() = %d, want 4", got)
	}

	// Audio untouched.
	after, _ := os.ReadFile(path)
	audioStart := 10 + 1024
	if !bytes.Equal(after[audioStart:], audio) {
		t.Error("audio data corrupted")
	}
}

// --- TESTS: patch path refuses safely on unsupported inputs ------------------

func TestPatch_refusesNoID3(t *testing.T) {
	path := writeTempMP3(t, fakeAudio(2048))
	if err := tryPatchPOPM(path, 3); err != errPatchRefused {
		t.Errorf("got %v, want errPatchRefused", err)
	}
}

func TestPatch_refusesUnsyncFlag(t *testing.T) {
	data := buildTaggedMP3(3, nil, 1024, fakeAudio(512))
	data[5] = 0x80 // set unsync flag
	path := writeTempMP3(t, data)
	if err := tryPatchPOPM(path, 3); err != errPatchRefused {
		t.Errorf("got %v, want errPatchRefused", err)
	}
}

func TestPatch_refusesUnknownVersion(t *testing.T) {
	data := buildTaggedMP3(2, nil, 1024, fakeAudio(512))
	path := writeTempMP3(t, data)
	if err := tryPatchPOPM(path, 3); err != errPatchRefused {
		t.Errorf("got %v, want errPatchRefused", err)
	}
}

func TestPatch_refusesPaddingTooSmall(t *testing.T) {
	// No POPM, only 5 bytes padding — new frame needs ~33 bytes.
	data := buildTaggedMP3(3, nil, 5, fakeAudio(512))
	path := writeTempMP3(t, data)
	if err := tryPatchPOPM(path, 3); err != errPatchRefused {
		t.Errorf("got %v, want errPatchRefused", err)
	}
}

func TestPatch_refusesPOPMWithFlags(t *testing.T) {
	frame := makePOPMFrame(3, "rating@winamp.com", 128, []byte{0, 0, 0, 0})
	frame[9] = 0x01 // set a frame flag
	data := buildTaggedMP3(3, frame, 256, fakeAudio(512))
	path := writeTempMP3(t, data)
	if err := tryPatchPOPM(path, 3); err != errPatchRefused {
		t.Errorf("got %v, want errPatchRefused", err)
	}
}

func TestPatch_refusesInvalidFrameID(t *testing.T) {
	// Garbage frame ID (lowercase invalid).
	bad := []byte{'a', 'b', 'c', 'd', 0, 0, 0, 4, 0, 0, 0, 0, 0, 0}
	data := buildTaggedMP3(3, bad, 256, fakeAudio(512))
	path := writeTempMP3(t, data)
	if err := tryPatchPOPM(path, 3); err != errPatchRefused {
		t.Errorf("got %v, want errPatchRefused", err)
	}
}

func TestPatch_refusesPOPMOversizedSize(t *testing.T) {
	// POPM with size larger than what fits in the tag — must refuse, not panic.
	frame := makePOPMFrame(3, "rating@winamp.com", 128, []byte{0, 0, 0, 0})
	binary.BigEndian.PutUint32(frame[4:8], 999999) // lie about size
	data := buildTaggedMP3(3, frame, 256, fakeAudio(512))
	path := writeTempMP3(t, data)
	if err := tryPatchPOPM(path, 3); err != errPatchRefused {
		t.Errorf("got %v, want errPatchRefused", err)
	}
}

// --- TESTS: stars=0 semantics in patch path ----------------------------------

func TestPatch_starsZeroWithNoFrame_noWrite(t *testing.T) {
	data := buildTaggedMP3(3, nil, 1024, fakeAudio(512))
	path := writeTempMP3(t, data)
	before, _ := os.ReadFile(path)

	if err := tryPatchPOPM(path, 0); err != nil {
		t.Fatalf("unexpected: %v", err)
	}
	after, _ := os.ReadFile(path)
	if !bytes.Equal(before, after) {
		t.Error("file changed even though stars=0 and no existing frame")
	}
}

// --- TESTS: walks past non-POPM frames correctly ----------------------------

func TestPatch_skipsOtherFrames(t *testing.T) {
	// TIT2 (title) frame first, then POPM. Encoding byte 0x00 = ISO-8859-1.
	tit2Data := append([]byte{0x00}, "Test Title"...)
	tit2 := make([]byte, 10+len(tit2Data))
	copy(tit2[0:4], "TIT2")
	binary.BigEndian.PutUint32(tit2[4:8], uint32(len(tit2Data)))
	copy(tit2[10:], tit2Data)

	popm := makePOPMFrame(3, "rating@winamp.com", 1, []byte{0, 0, 0, 0})
	frames := append(tit2, popm...)

	audio := fakeAudio(1024)
	data := buildTaggedMP3(3, frames, 512, audio)
	path := writeTempMP3(t, data)

	if err := tryPatchPOPM(path, 5); err != nil {
		t.Fatalf("tryPatchPOPM: %v", err)
	}
	got, _ := Get(path)
	if got != 5 {
		t.Errorf("Get() = %d, want 5", got)
	}

	// Audio untouched.
	after, _ := os.ReadFile(path)
	audioStart := 10 + len(frames) + 512
	if !bytes.Equal(after[audioStart:], audio) {
		t.Error("audio data corrupted")
	}
}

// --- TESTS: Set() integration uses patch when it can ------------------------

func TestSet_usesPatchPathWhenPossible(t *testing.T) {
	// File has padding → patch should succeed → audio MUST remain byte-identical.
	audio := fakeAudio(4096)
	data := buildTaggedMP3(3, nil, 2048, audio)
	path := writeTempMP3(t, data)
	beforeSize := int64(len(data))

	if err := Set(path, 3); err != nil {
		t.Fatalf("Set: %v", err)
	}

	st, _ := os.Stat(path)
	if st.Size() != beforeSize {
		t.Errorf("Set() with available padding changed file size: %d → %d (patch path should be used)",
			beforeSize, st.Size())
	}

	got, _ := Get(path)
	if got != 3 {
		t.Errorf("Get() = %d, want 3", got)
	}
}