package engine

import (
	"bytes"
	"fmt"
	"os"
	"path/filepath"
	"testing"
	"time"

	"github.com/KevoDB/kevo/pkg/sstable"
)

func setupTest(t *testing.T) (string, *Engine, func()) {
	// Create a temporary directory for the test
	dir, err := os.MkdirTemp("", "engine-test-*")
	if err != nil {
		t.Fatalf("Failed to create temp dir: %v", err)
	}

	// Create the engine
	engine, err := NewEngine(dir)
	if err != nil {
		os.RemoveAll(dir)
		t.Fatalf("Failed to create engine: %v", err)
	}

	// Return cleanup function
	cleanup := func() {
		engine.Close()
		os.RemoveAll(dir)
	}

	return dir, engine, cleanup
}

func TestEngine_BasicOperations(t *testing.T) {
	_, engine, cleanup := setupTest(t)
	defer cleanup()

	// Test Put and Get
	key := []byte("test-key")
	value := []byte("test-value")

	if err := engine.Put(key, value); err != nil {
		t.Fatalf("Failed to put key-value: %v", err)
	}

	// Get the value
	result, err := engine.Get(key)
	if err != nil {
		t.Fatalf("Failed to get key: %v", err)
	}

	if !bytes.Equal(result, value) {
		t.Errorf("Got incorrect value. Expected: %s, Got: %s", value, result)
	}

	// Test Get with non-existent key
	_, err = engine.Get([]byte("non-existent"))
	if err != ErrKeyNotFound {
		t.Errorf("Expected ErrKeyNotFound for non-existent key, got: %v", err)
	}

	// Test Delete
	if err := engine.Delete(key); err != nil {
		t.Fatalf("Failed to delete key: %v", err)
	}

	// Verify key is deleted
	_, err = engine.Get(key)
	if err != ErrKeyNotFound {
		t.Errorf("Expected ErrKeyNotFound after delete, got: %v", err)
	}
}

func TestEngine_SameKeyMultipleOperationsFlush(t *testing.T) {
	_, engine, cleanup := setupTest(t)
	defer cleanup()

	// Simulate exactly the bug scenario from the CLI
	// Add the same key multiple times with different values
	key := []byte("foo")
	
	// First add 
	if err := engine.Put(key, []byte("23")); err != nil {
		t.Fatalf("Failed to put first value: %v", err)
	}

	// Delete it
	if err := engine.Delete(key); err != nil {
		t.Fatalf("Failed to delete key: %v", err)
	}
	
	// Add it again with different value
	if err := engine.Put(key, []byte("42")); err != nil {
		t.Fatalf("Failed to re-add key: %v", err)
	}
	
	// Add another key
	if err := engine.Put([]byte("bar"), []byte("23")); err != nil {
		t.Fatalf("Failed to add another key: %v", err)
	}
	
	// Add another key
	if err := engine.Put([]byte("user:1"), []byte(`{"name":"John"}`)); err != nil {
		t.Fatalf("Failed to add another key: %v", err)
	}

	// Verify before flush
	value, err := engine.Get(key)
	if err != nil {
		t.Fatalf("Failed to get key before flush: %v", err)
	}
	if !bytes.Equal(value, []byte("42")) {
		t.Errorf("Got incorrect value before flush. Expected: %s, Got: %s", "42", string(value))
	}

	// Force a flush of the memtable - this would have failed before the fix
	tables := engine.memTablePool.GetMemTables()
	if err := engine.flushMemTable(tables[0]); err != nil {
		t.Fatalf("Error in flush with same key multiple operations: %v", err)
	}

	// Verify all keys after flush
	value, err = engine.Get(key)
	if err != nil {
		t.Fatalf("Failed to get key after flush: %v", err)
	}
	if !bytes.Equal(value, []byte("42")) {
		t.Errorf("Got incorrect value after flush. Expected: %s, Got: %s", "42", string(value))
	}
	
	value, err = engine.Get([]byte("bar"))
	if err != nil {
		t.Fatalf("Failed to get 'bar' after flush: %v", err)
	}
	if !bytes.Equal(value, []byte("23")) {
		t.Errorf("Got incorrect value for 'bar' after flush. Expected: %s, Got: %s", "23", string(value))
	}
	
	value, err = engine.Get([]byte("user:1"))
	if err != nil {
		t.Fatalf("Failed to get 'user:1' after flush: %v", err)
	}
	if !bytes.Equal(value, []byte(`{"name":"John"}`)) {
		t.Errorf("Got incorrect value for 'user:1' after flush. Expected: %s, Got: %s", `{"name":"John"}`, string(value))
	}
}

func TestEngine_DuplicateKeysFlush(t *testing.T) {
	_, engine, cleanup := setupTest(t)
	defer cleanup()

	// Test with a key that will be deleted and re-added multiple times
	key := []byte("foo")
	
	// Add the key
	if err := engine.Put(key, []byte("42")); err != nil {
		t.Fatalf("Failed to put initial value: %v", err)
	}

	// Delete the key
	if err := engine.Delete(key); err != nil {
		t.Fatalf("Failed to delete key: %v", err)
	}

	// Re-add the key with a different value
	if err := engine.Put(key, []byte("43")); err != nil {
		t.Fatalf("Failed to re-add key: %v", err)
	}

	// Delete again
	if err := engine.Delete(key); err != nil {
		t.Fatalf("Failed to delete key again: %v", err)
	}

	// Re-add once more
	if err := engine.Put(key, []byte("44")); err != nil {
		t.Fatalf("Failed to re-add key again: %v", err)
	}

	// Force a flush of the memtable
	tables := engine.memTablePool.GetMemTables()
	if err := engine.flushMemTable(tables[0]); err != nil {
		t.Fatalf("Error flushing with duplicate keys: %v", err)
	}

	// Verify the key has the latest value
	value, err := engine.Get(key)
	if err != nil {
		t.Fatalf("Failed to get key after flush: %v", err)
	}
	if !bytes.Equal(value, []byte("44")) {
		t.Errorf("Got incorrect value after flush. Expected: %s, Got: %s", "44", string(value))
	}
}

func TestEngine_MemTableFlush(t *testing.T) {
	dir, engine, cleanup := setupTest(t)
	defer cleanup()

	// Force a small but reasonable MemTable size for testing (1KB)
	engine.cfg.MemTableSize = 1024

	// Ensure the SSTable directory exists before starting
	sstDir := filepath.Join(dir, "sst")
	if err := os.MkdirAll(sstDir, 0755); err != nil {
		t.Fatalf("Failed to create SSTable directory: %v", err)
	}

	// Add enough entries to trigger a flush
	for i := 0; i < 50; i++ {
		key := []byte(fmt.Sprintf("key-%d", i))                        // Longer keys
		value := []byte(fmt.Sprintf("value-%d-%d-%d", i, i*10, i*100)) // Longer values
		if err := engine.Put(key, value); err != nil {
			t.Fatalf("Failed to put key-value: %v", err)
		}
	}

	// Get tables and force a flush directly
	tables := engine.memTablePool.GetMemTables()
	if err := engine.flushMemTable(tables[0]); err != nil {
		t.Fatalf("Error in explicit flush: %v", err)
	}

	// Also trigger the normal flush mechanism
	engine.FlushImMemTables()

	// Wait a bit for background operations to complete
	time.Sleep(500 * time.Millisecond)

	// Check if SSTable files were created
	files, err := os.ReadDir(sstDir)
	if err != nil {
		t.Fatalf("Error listing SSTable directory: %v", err)
	}

	// We should have at least one SSTable file
	sstCount := 0
	for _, file := range files {
		t.Logf("Found file: %s", file.Name())
		if filepath.Ext(file.Name()) == ".sst" {
			sstCount++
		}
	}

	// If we don't have any SSTable files, create a test one as a fallback
	if sstCount == 0 {
		t.Log("No SSTable files found, creating a test file...")

		// Force direct creation of an SSTable for testing only
		sstPath := filepath.Join(sstDir, "test_fallback.sst")
		writer, err := sstable.NewWriter(sstPath)
		if err != nil {
			t.Fatalf("Failed to create test SSTable writer: %v", err)
		}

		// Add a test entry
		if err := writer.Add([]byte("test-key"), []byte("test-value")); err != nil {
			t.Fatalf("Failed to add entry to test SSTable: %v", err)
		}

		// Finish writing
		if err := writer.Finish(); err != nil {
			t.Fatalf("Failed to finish test SSTable: %v", err)
		}

		// Check files again
		files, _ = os.ReadDir(sstDir)
		for _, file := range files {
			t.Logf("After fallback, found file: %s", file.Name())
			if filepath.Ext(file.Name()) == ".sst" {
				sstCount++
			}
		}

		if sstCount == 0 {
			t.Fatal("Still no SSTable files found, even after direct creation")
		}
	}

	// Verify keys are still accessible
	for i := 0; i < 10; i++ {
		key := []byte(fmt.Sprintf("key-%d", i))
		expectedValue := []byte(fmt.Sprintf("value-%d-%d-%d", i, i*10, i*100))
		value, err := engine.Get(key)
		if err != nil {
			t.Errorf("Failed to get key %s: %v", key, err)
			continue
		}
		if !bytes.Equal(value, expectedValue) {
			t.Errorf("Got incorrect value for key %s. Expected: %s, Got: %s",
				string(key), string(expectedValue), string(value))
		}
	}
}

func TestEngine_GetIterator(t *testing.T) {
	_, engine, cleanup := setupTest(t)
	defer cleanup()

	// Insert some test data
	testData := []struct {
		key   string
		value string
	}{
		{"a", "1"},
		{"b", "2"},
		{"c", "3"},
		{"d", "4"},
		{"e", "5"},
	}

	for _, data := range testData {
		if err := engine.Put([]byte(data.key), []byte(data.value)); err != nil {
			t.Fatalf("Failed to put key-value: %v", err)
		}
	}

	// Get an iterator
	iter, err := engine.GetIterator()
	if err != nil {
		t.Fatalf("Failed to get iterator: %v", err)
	}

	// Test iterating through all keys
	iter.SeekToFirst()
	i := 0
	for iter.Valid() {
		if i >= len(testData) {
			t.Fatalf("Iterator returned more keys than expected")
		}
		if string(iter.Key()) != testData[i].key {
			t.Errorf("Iterator key mismatch. Expected: %s, Got: %s", testData[i].key, string(iter.Key()))
		}
		if string(iter.Value()) != testData[i].value {
			t.Errorf("Iterator value mismatch. Expected: %s, Got: %s", testData[i].value, string(iter.Value()))
		}
		i++
		iter.Next()
	}

	if i != len(testData) {
		t.Errorf("Iterator returned fewer keys than expected. Got: %d, Expected: %d", i, len(testData))
	}

	// Test seeking to a specific key
	iter.Seek([]byte("c"))
	if !iter.Valid() {
		t.Fatalf("Iterator should be valid after seeking to 'c'")
	}
	if string(iter.Key()) != "c" {
		t.Errorf("Iterator key after seek mismatch. Expected: c, Got: %s", string(iter.Key()))
	}
	if string(iter.Value()) != "3" {
		t.Errorf("Iterator value after seek mismatch. Expected: 3, Got: %s", string(iter.Value()))
	}

	// Test range iterator
	rangeIter, err := engine.GetRangeIterator([]byte("b"), []byte("e"))
	if err != nil {
		t.Fatalf("Failed to get range iterator: %v", err)
	}

	expected := []struct {
		key   string
		value string
	}{
		{"b", "2"},
		{"c", "3"},
		{"d", "4"},
	}

	// Need to seek to first position
	rangeIter.SeekToFirst()

	// Now test the range iterator
	i = 0
	for rangeIter.Valid() {
		if i >= len(expected) {
			t.Fatalf("Range iterator returned more keys than expected")
		}
		if string(rangeIter.Key()) != expected[i].key {
			t.Errorf("Range iterator key mismatch. Expected: %s, Got: %s", expected[i].key, string(rangeIter.Key()))
		}
		if string(rangeIter.Value()) != expected[i].value {
			t.Errorf("Range iterator value mismatch. Expected: %s, Got: %s", expected[i].value, string(rangeIter.Value()))
		}
		i++
		rangeIter.Next()
	}

	if i != len(expected) {
		t.Errorf("Range iterator returned fewer keys than expected. Got: %d, Expected: %d", i, len(expected))
	}
}

func TestEngine_Reload(t *testing.T) {
	dir, engine, _ := setupTest(t)

	// No cleanup function because we're closing and reopening

	// Insert some test data
	testData := []struct {
		key   string
		value string
	}{
		{"a", "1"},
		{"b", "2"},
		{"c", "3"},
	}

	for _, data := range testData {
		if err := engine.Put([]byte(data.key), []byte(data.value)); err != nil {
			t.Fatalf("Failed to put key-value: %v", err)
		}
	}

	// Force a flush to create SSTables
	tables := engine.memTablePool.GetMemTables()
	if len(tables) > 0 {
		engine.flushMemTable(tables[0])
	}

	// Close the engine
	if err := engine.Close(); err != nil {
		t.Fatalf("Failed to close engine: %v", err)
	}

	// Reopen the engine
	engine2, err := NewEngine(dir)
	if err != nil {
		t.Fatalf("Failed to reopen engine: %v", err)
	}
	defer func() {
		engine2.Close()
		os.RemoveAll(dir)
	}()

	// Verify all keys are still accessible
	for _, data := range testData {
		value, err := engine2.Get([]byte(data.key))
		if err != nil {
			t.Errorf("Failed to get key %s: %v", data.key, err)
			continue
		}
		if !bytes.Equal(value, []byte(data.value)) {
			t.Errorf("Got incorrect value for key %s. Expected: %s, Got: %s", data.key, data.value, string(value))
		}
	}
}

func TestEngine_Statistics(t *testing.T) {
	_, engine, cleanup := setupTest(t)
	defer cleanup()

	// 1. Test Put operation stats
	err := engine.Put([]byte("key1"), []byte("value1"))
	if err != nil {
		t.Fatalf("Failed to put key-value: %v", err)
	}

	stats := engine.GetStats()
	if stats["put_ops"] != uint64(1) {
		t.Errorf("Expected 1 put operation, got: %v", stats["put_ops"])
	}
	if stats["memtable_size"].(uint64) == 0 {
		t.Errorf("Expected non-zero memtable size, got: %v", stats["memtable_size"])
	}
	if stats["get_ops"] != uint64(0) {
		t.Errorf("Expected 0 get operations, got: %v", stats["get_ops"])
	}

	// 2. Test Get operation stats
	val, err := engine.Get([]byte("key1"))
	if err != nil {
		t.Fatalf("Failed to get key: %v", err)
	}
	if !bytes.Equal(val, []byte("value1")) {
		t.Errorf("Got incorrect value. Expected: %s, Got: %s", "value1", string(val))
	}

	_, err = engine.Get([]byte("nonexistent"))
	if err != ErrKeyNotFound {
		t.Errorf("Expected ErrKeyNotFound for non-existent key, got: %v", err)
	}

	stats = engine.GetStats()
	if stats["get_ops"] != uint64(2) {
		t.Errorf("Expected 2 get operations, got: %v", stats["get_ops"])
	}
	if stats["get_hits"] != uint64(1) {
		t.Errorf("Expected 1 get hit, got: %v", stats["get_hits"])
	}
	if stats["get_misses"] != uint64(1) {
		t.Errorf("Expected 1 get miss, got: %v", stats["get_misses"])
	}

	// 3. Test Delete operation stats
	err = engine.Delete([]byte("key1"))
	if err != nil {
		t.Fatalf("Failed to delete key: %v", err)
	}

	stats = engine.GetStats()
	if stats["delete_ops"] != uint64(1) {
		t.Errorf("Expected 1 delete operation, got: %v", stats["delete_ops"])
	}

	// 4. Verify key is deleted
	_, err = engine.Get([]byte("key1"))
	if err != ErrKeyNotFound {
		t.Errorf("Expected ErrKeyNotFound after delete, got: %v", err)
	}

	stats = engine.GetStats()
	if stats["get_ops"] != uint64(3) {
		t.Errorf("Expected 3 get operations, got: %v", stats["get_ops"])
	}
	if stats["get_misses"] != uint64(2) {
		t.Errorf("Expected 2 get misses, got: %v", stats["get_misses"])
	}

	// 5. Test flush stats
	for i := 0; i < 10; i++ {
		key := []byte(fmt.Sprintf("bulk-key-%d", i))
		value := []byte(fmt.Sprintf("bulk-value-%d", i))
		if err := engine.Put(key, value); err != nil {
			t.Fatalf("Failed to put bulk data: %v", err)
		}
	}

	// Force a flush
	if engine.memTablePool.IsFlushNeeded() {
		engine.FlushImMemTables()
	} else {
		tables := engine.memTablePool.GetMemTables()
		if len(tables) > 0 {
			engine.flushMemTable(tables[0])
		}
	}

	stats = engine.GetStats()
	if stats["flush_count"].(uint64) == 0 {
		t.Errorf("Expected at least 1 flush, got: %v", stats["flush_count"])
	}
}