package editor

import (
	"bytes"
	"fmt"
	"testing"
	"time"

	"pad/internal/io/pool/mock"
)

// withState runs fn on the logic goroutine (the sole state owner) and fails
// the test on timeout. Test-only helper (architecture.md §1): tests must
// never touch l.state directly while Run() is active.
func withState(t *testing.T, l *Logic, fn func(*State)) {
	t.Helper()
	_, ok := l.Inspect(func(st *State) any {
		fn(st)
		return nil
	})
	if !ok {
		t.Fatalf("withState: inspect timed out")
	}
}

func TestAutoSaveE2E(t *testing.T) {
	// 1. Setup
	mockFS := mock.NewFileSystem()
	filename := "/test.txt"
	initialContent := "Hello"
	mockFS.AddFile(filename, []byte(initialContent), time.Now())

	l := NewLogic(mockFS, "/", func(string) {})
	go l.Run()
	defer l.Shutdown()

	// Drain frameChan to prevent deadlocks
	go func() {
		for range l.FrameChan() {
		}
	}()

	withState(t, l, func(st *State) {
		TheState = st
	})

	// 2. Open File (OpenFile also sets Editor.Filename on the owner)
	withState(t, l, func(st *State) {
		TheState = st
		OpenFile(filename)
	})

	// Wait for the file to be loaded by checking if ChunkedBuffer is populated
	success := false
	for i := 0; i < 20; i++ {
		v, ok := l.Inspect(func(st *State) any {
			cb := st.Editor.ChunkedBuffer
			return cb != nil && cb.FileLen() > 0
		})
		if ok && v.(bool) {
			success = true
			break
		}
		time.Sleep(100 * time.Millisecond)
	}
	if !success {
		t.Fatal("Timed out waiting for file to load")
	}

	// 3. Edit (owner-side)
	withState(t, l, func(st *State) {
		st.Editor.CursorPosition = len(initialContent)
		HandleInsert(" World")
	})

	// 4. Trigger auto-save (owner-side)
	withState(t, l, func(st *State) {
		l.markDirty()
	})

	// 5. Wait for the write to complete
	success = false
	for i := 0; i < 20; i++ {
		content, _ := mockFS.ReadFile(filename)
		if string(content) == "Hello World" {
			success = true
			break
		}
		time.Sleep(200 * time.Millisecond)
	}

	// 6. Assert
	if !success {
		t.Errorf("Timed out waiting for file to save")
	}
}

// TestLargeFileChunkBoundary verifies that edits near and at chunk boundaries
// are correctly persisted through the full editor pipeline (open → edit → save →
// re-open → verify). It creates a 256 KB file (4 × 64 KB chunks) and performs
// three edits:
//
//  1. Near the end of chunk 1  (position 65000)
//  2. Right at the chunk 0 / chunk 1 boundary (position 65535)
//  3. Near the end of chunk 3 (position 262000)
//
// After saving, the file is re-opened and the full content is compared
// byte-for-byte against the expected result.
func TestLargeFileChunkBoundary(t *testing.T) {
	const fileSize = 256 * 1024 // 4 chunks

	// --- 1. Setup: create a 256 KB file with a predictable pattern ---
	mockFS := mock.NewFileSystem()
	filename := "/large.txt"
	initialContent := make([]byte, fileSize)
	for i := range initialContent {
		initialContent[i] = byte(i % 256)
	}
	mockFS.AddFile(filename, initialContent, time.Now())

	l := NewLogic(mockFS, "/", func(string) {})
	go l.Run()
	defer l.Shutdown()

	// Drain frameChan to prevent deadlocks
	go func() {
		for range l.FrameChan() {
		}
	}()

	withState(t, l, func(st *State) {
		TheState = st
	})

	// --- 2. Open File ---
	withState(t, l, func(st *State) {
		TheState = st
		OpenFile(filename)
	})

	success := false
	for i := 0; i < 20; i++ {
		v, ok := l.Inspect(func(st *State) any {
			cb := st.Editor.ChunkedBuffer
			return cb != nil && cb.FileLen() > 0
		})
		if ok && v.(bool) {
			success = true
			break
		}
		time.Sleep(100 * time.Millisecond)
	}
	if !success {
		t.Fatal("Timed out waiting for large file to load")
	}

	// --- 3. Edit near the end of chunk 1 (position 65000, inside chunk 1) ---
	withState(t, l, func(st *State) {
		st.Editor.CursorPosition = 65000
		HandleInsert("CHUNK1")
	})

	// --- 4. Edit right at the chunk 0 / chunk 1 boundary (position 65535) ---
	withState(t, l, func(st *State) {
		st.Editor.CursorPosition = 65535
		HandleInsert("BOUNDARY")
	})

	// --- 5. Edit near the end of chunk 3 (position 262000) ---
	withState(t, l, func(st *State) {
		st.Editor.CursorPosition = 262000
		HandleInsert("CHUNK3")
	})

	// --- 6. Trigger save (owner-side) ---
	withState(t, l, func(st *State) {
		l.FlushAll()
	})

	// --- 7. Read back from mockFS and verify byte-for-byte ---
	savedContent, err := mockFS.ReadFile(filename)
	if err != nil {
		t.Fatalf("Failed to read saved file from mockFS: %v", err)
	}

	// Build the expected content by applying the same three inserts to the
	// original content as a whole, in order. This is the shift-correct ground
	// truth: each insert at an absolute position pushes all later bytes right.
	// (The old fixed-slot model treated each chunk as an independent buffer and
	// did NOT shift later chunks; that was the bug this design replaces.)
	expectedStr := string(initialContent)
	expectedStr = expectedStr[:65000] + "CHUNK1" + expectedStr[65000:]     // insert 1 @65000
	expectedStr = expectedStr[:65535] + "BOUNDARY" + expectedStr[65535:]   // insert 2 @65535
	expectedStr = expectedStr[:262000] + "CHUNK3" + expectedStr[262000:]   // insert 3 @262000
	expected := []byte(expectedStr)

	if len(savedContent) != len(expected) {
		t.Errorf("Saved file length %d != expected %d (too long by %d, too short by %d)",
			len(savedContent), len(expected),
			len(savedContent)-len(expected), len(expected)-len(savedContent))
	}

	// Byte-for-byte comparison
	if !bytes.Equal(savedContent, expected) {
		// Find the first differing byte
		minLen := len(savedContent)
		if len(expected) < minLen {
			minLen = len(expected)
		}
		diffPos := -1
		for i := 0; i < minLen; i++ {
			if savedContent[i] != expected[i] {
				diffPos = i
				break
			}
		}
		if diffPos == -1 {
			t.Errorf("Saved content differs in length: got %d bytes, expected %d bytes", len(savedContent), len(expected))
		} else {
			t.Errorf("Saved content differs at byte %d: got %d (%q), expected %d (%q)",
				diffPos, savedContent[diffPos], safeByte(savedContent[diffPos]),
				expected[diffPos], safeByte(expected[diffPos]))
		}
	}
}

// safeByte converts a byte to a printable representation for error messages.
func safeByte(b byte) string {
	if b >= 32 && b < 127 {
		return string(b)
	}
	return fmt.Sprintf("\\x%02x", b)
}

func TestFlushOnExitE2E(t *testing.T) {
	// 1. Setup
	mockFS := mock.NewFileSystem()
	filename := "/test.txt"
	initialContent := "Hello"
	mockFS.AddFile(filename, []byte(initialContent), time.Now())

	l := NewLogic(mockFS, "/", func(string) {})
	go l.Run()
	defer l.Shutdown()

	// Drain frameChan to prevent deadlocks
	go func() {
		for range l.FrameChan() {
		}
	}()

	withState(t, l, func(st *State) {
		st.Editor.Filename = filename
		st.Editor.Buffer = initialContent
		TheState = st
	})

	// 2. Edit (owner-side)
	withState(t, l, func(st *State) {
		st.Editor.CursorPosition = len(initialContent)
		HandleInsert(" World")
	})

	// 3. Trigger Flush (owner-side)
	withState(t, l, func(st *State) {
		l.FlushAll()
	})

	// 4. Assert
	content, _ := mockFS.ReadFile(filename)
	if string(content) != "Hello World" {
		t.Errorf("Expected 'Hello World', got %q", string(content))
	}
}