package transport

import (
	"bytes"
	"compress/gzip"
	"encoding/json"
	"fmt"
	"io"
	"sync"
)

// SerializationFormat defines supported serialization formats
type SerializationFormat string

const (
	SerializationJSON     SerializationFormat = "json"
	SerializationMsgPack  SerializationFormat = "msgpack"
	SerializationProtobuf SerializationFormat = "protobuf"
	SerializationAvro     SerializationFormat = "avro"
)

// CompressionType defines supported compression algorithms
type CompressionType string

const (
	CompressionNone   CompressionType = "none"
	CompressionGZip   CompressionType = "gzip"
	CompressionLZ4    CompressionType = "lz4"
	CompressionSnappy CompressionType = "snappy"
)

// SerializationConfig configures serialization behavior
type SerializationConfig struct {
	Format      SerializationFormat
	Compression CompressionType
	Encryption  bool
	Validation  bool
}

// SerializedMessage represents a serialized message with metadata
type SerializedMessage struct {
	Format      SerializationFormat `json:"format"`
	Compression CompressionType     `json:"compression"`
	Encrypted   bool                `json:"encrypted"`
	Checksum    string              `json:"checksum"`
	Data        []byte              `json:"data"`
	Size        int                 `json:"size"`
	Timestamp   int64               `json:"timestamp"`
}

// Serializer interface defines serialization operations
type Serializer interface {
	Serialize(msg *Message) (*SerializedMessage, error)
	Deserialize(serialized *SerializedMessage) (*Message, error)
	GetFormat() SerializationFormat
	GetConfig() SerializationConfig
}

// SerializationLayer manages multiple serializers and format selection
type SerializationLayer struct {
	serializers   map[SerializationFormat]Serializer
	defaultFormat SerializationFormat
	compressor    Compressor
	encryptor     Encryptor
	validator     Validator
	mu            sync.RWMutex
}

// Compressor interface for data compression
type Compressor interface {
	Compress(data []byte, algorithm CompressionType) ([]byte, error)
	Decompress(data []byte, algorithm CompressionType) ([]byte, error)
	GetSupportedAlgorithms() []CompressionType
}

// Encryptor interface for data encryption
type Encryptor interface {
	Encrypt(data []byte) ([]byte, error)
	Decrypt(data []byte) ([]byte, error)
	IsEnabled() bool
}

// Validator interface for data validation
type Validator interface {
	Validate(msg *Message) error
	GenerateChecksum(data []byte) string
	VerifyChecksum(data []byte, checksum string) bool
}

// NewSerializationLayer creates a new serialization layer
func NewSerializationLayer() *SerializationLayer {
	sl := &SerializationLayer{
		serializers:   make(map[SerializationFormat]Serializer),
		defaultFormat: SerializationJSON,
		compressor:    NewDefaultCompressor(),
		validator:     NewDefaultValidator(),
	}

	// Register default serializers
	sl.RegisterSerializer(NewJSONSerializer())

	return sl
}

// RegisterSerializer registers a new serializer
func (sl *SerializationLayer) RegisterSerializer(serializer Serializer) {
	sl.mu.Lock()
	defer sl.mu.Unlock()
	sl.serializers[serializer.GetFormat()] = serializer
}

// SetDefaultFormat sets the default serialization format
func (sl *SerializationLayer) SetDefaultFormat(format SerializationFormat) {
	sl.mu.Lock()
	defer sl.mu.Unlock()
	sl.defaultFormat = format
}

// SetCompressor sets the compression handler
func (sl *SerializationLayer) SetCompressor(compressor Compressor) {
	sl.mu.Lock()
	defer sl.mu.Unlock()
	sl.compressor = compressor
}

// SetEncryptor sets the encryption handler
func (sl *SerializationLayer) SetEncryptor(encryptor Encryptor) {
	sl.mu.Lock()
	defer sl.mu.Unlock()
	sl.encryptor = encryptor
}

// SetValidator sets the validation handler
func (sl *SerializationLayer) SetValidator(validator Validator) {
	sl.mu.Lock()
	defer sl.mu.Unlock()
	sl.validator = validator
}

// Serialize serializes a message using the specified or default format
func (sl *SerializationLayer) Serialize(msg *Message, format ...SerializationFormat) (*SerializedMessage, error) {
	sl.mu.RLock()
	defer sl.mu.RUnlock()

	// Determine format to use
	selectedFormat := sl.defaultFormat
	if len(format) > 0 {
		selectedFormat = format[0]
	}

	// Get serializer
	serializer, exists := sl.serializers[selectedFormat]
	if !exists {
		return nil, fmt.Errorf("unsupported serialization format: %s", selectedFormat)
	}

	// Validate message if validator is configured
	if sl.validator != nil {
		if err := sl.validator.Validate(msg); err != nil {
			return nil, fmt.Errorf("message validation failed: %w", err)
		}
	}

	// Serialize message
	serialized, err := serializer.Serialize(msg)
	if err != nil {
		return nil, fmt.Errorf("serialization failed: %w", err)
	}

	// Apply compression if configured
	config := serializer.GetConfig()
	if config.Compression != CompressionNone && sl.compressor != nil {
		compressed, err := sl.compressor.Compress(serialized.Data, config.Compression)
		if err != nil {
			return nil, fmt.Errorf("compression failed: %w", err)
		}
		serialized.Data = compressed
		serialized.Compression = config.Compression
	}

	// Apply encryption if configured
	if config.Encryption && sl.encryptor != nil && sl.encryptor.IsEnabled() {
		encrypted, err := sl.encryptor.Encrypt(serialized.Data)
		if err != nil {
			return nil, fmt.Errorf("encryption failed: %w", err)
		}
		serialized.Data = encrypted
		serialized.Encrypted = true
	}

	// Generate checksum
	if sl.validator != nil {
		serialized.Checksum = sl.validator.GenerateChecksum(serialized.Data)
	}

	// Update metadata
	serialized.Size = len(serialized.Data)
	serialized.Timestamp = msg.Timestamp.UnixNano()

	return serialized, nil
}

// Deserialize deserializes a message
func (sl *SerializationLayer) Deserialize(serialized *SerializedMessage) (*Message, error) {
	sl.mu.RLock()
	defer sl.mu.RUnlock()

	// Verify checksum if available
	if sl.validator != nil && serialized.Checksum != "" {
		if !sl.validator.VerifyChecksum(serialized.Data, serialized.Checksum) {
			return nil, fmt.Errorf("checksum verification failed")
		}
	}

	data := serialized.Data

	// Apply decryption if needed
	if serialized.Encrypted && sl.encryptor != nil && sl.encryptor.IsEnabled() {
		decrypted, err := sl.encryptor.Decrypt(data)
		if err != nil {
			return nil, fmt.Errorf("decryption failed: %w", err)
		}
		data = decrypted
	}

	// Apply decompression if needed
	if serialized.Compression != CompressionNone && sl.compressor != nil {
		decompressed, err := sl.compressor.Decompress(data, serialized.Compression)
		if err != nil {
			return nil, fmt.Errorf("decompression failed: %w", err)
		}
		data = decompressed
	}

	// Get serializer
	serializer, exists := sl.serializers[serialized.Format]
	if !exists {
		return nil, fmt.Errorf("unsupported serialization format: %s", serialized.Format)
	}

	// Create temporary serialized message for deserializer
	tempSerialized := &SerializedMessage{
		Format: serialized.Format,
		Data:   data,
	}

	// Deserialize message
	msg, err := serializer.Deserialize(tempSerialized)
	if err != nil {
		return nil, fmt.Errorf("deserialization failed: %w", err)
	}

	// Validate deserialized message if validator is configured
	if sl.validator != nil {
		if err := sl.validator.Validate(msg); err != nil {
			return nil, fmt.Errorf("deserialized message validation failed: %w", err)
		}
	}

	return msg, nil
}

// GetSupportedFormats returns all supported serialization formats
func (sl *SerializationLayer) GetSupportedFormats() []SerializationFormat {
	sl.mu.RLock()
	defer sl.mu.RUnlock()

	formats := make([]SerializationFormat, 0, len(sl.serializers))
	for format := range sl.serializers {
		formats = append(formats, format)
	}
	return formats
}

// JSONSerializer implements JSON serialization
type JSONSerializer struct {
	config SerializationConfig
}

// NewJSONSerializer creates a new JSON serializer
func NewJSONSerializer() *JSONSerializer {
	return &JSONSerializer{
		config: SerializationConfig{
			Format:      SerializationJSON,
			Compression: CompressionNone,
			Encryption:  false,
			Validation:  true,
		},
	}
}

// SetConfig updates the serializer configuration
func (js *JSONSerializer) SetConfig(config SerializationConfig) {
	js.config = config
	js.config.Format = SerializationJSON // Ensure format is correct
}

// Serialize serializes a message to JSON
func (js *JSONSerializer) Serialize(msg *Message) (*SerializedMessage, error) {
	data, err := json.Marshal(msg)
	if err != nil {
		return nil, fmt.Errorf("JSON marshal failed: %w", err)
	}

	return &SerializedMessage{
		Format:      SerializationJSON,
		Compression: CompressionNone,
		Encrypted:   false,
		Data:        data,
		Size:        len(data),
	}, nil
}

// Deserialize deserializes a message from JSON
func (js *JSONSerializer) Deserialize(serialized *SerializedMessage) (*Message, error) {
	var msg Message
	if err := json.Unmarshal(serialized.Data, &msg); err != nil {
		return nil, fmt.Errorf("JSON unmarshal failed: %w", err)
	}
	return &msg, nil
}

// GetFormat returns the serialization format
func (js *JSONSerializer) GetFormat() SerializationFormat {
	return SerializationJSON
}

// GetConfig returns the serializer configuration
func (js *JSONSerializer) GetConfig() SerializationConfig {
	return js.config
}

// DefaultCompressor implements basic compression operations
type DefaultCompressor struct {
	supportedAlgorithms []CompressionType
}

// NewDefaultCompressor creates a new default compressor
func NewDefaultCompressor() *DefaultCompressor {
	return &DefaultCompressor{
		supportedAlgorithms: []CompressionType{
			CompressionNone,
			CompressionGZip,
		},
	}
}

// Compress compresses data using the specified algorithm
func (dc *DefaultCompressor) Compress(data []byte, algorithm CompressionType) ([]byte, error) {
	switch algorithm {
	case CompressionNone:
		return data, nil

	case CompressionGZip:
		var buf bytes.Buffer
		writer := gzip.NewWriter(&buf)

		if _, err := writer.Write(data); err != nil {
			return nil, fmt.Errorf("gzip write failed: %w", err)
		}

		if err := writer.Close(); err != nil {
			return nil, fmt.Errorf("gzip close failed: %w", err)
		}

		return buf.Bytes(), nil

	default:
		return nil, fmt.Errorf("unsupported compression algorithm: %s", algorithm)
	}
}

// Decompress decompresses data using the specified algorithm
func (dc *DefaultCompressor) Decompress(data []byte, algorithm CompressionType) ([]byte, error) {
	switch algorithm {
	case CompressionNone:
		return data, nil

	case CompressionGZip:
		reader, err := gzip.NewReader(bytes.NewReader(data))
		if err != nil {
			return nil, fmt.Errorf("gzip reader creation failed: %w", err)
		}
		defer reader.Close()

		decompressed, err := io.ReadAll(reader)
		if err != nil {
			return nil, fmt.Errorf("gzip read failed: %w", err)
		}

		return decompressed, nil

	default:
		return nil, fmt.Errorf("unsupported compression algorithm: %s", algorithm)
	}
}

// GetSupportedAlgorithms returns supported compression algorithms
func (dc *DefaultCompressor) GetSupportedAlgorithms() []CompressionType {
	return dc.supportedAlgorithms
}

// DefaultValidator implements basic message validation
type DefaultValidator struct {
	strictMode bool
}

// NewDefaultValidator creates a new default validator
func NewDefaultValidator() *DefaultValidator {
	return &DefaultValidator{
		strictMode: false,
	}
}

// SetStrictMode enables/disables strict validation
func (dv *DefaultValidator) SetStrictMode(enabled bool) {
	dv.strictMode = enabled
}

// Validate validates a message
func (dv *DefaultValidator) Validate(msg *Message) error {
	if msg == nil {
		return fmt.Errorf("message is nil")
	}

	if msg.ID == "" {
		return fmt.Errorf("message ID is empty")
	}

	if msg.Topic == "" {
		return fmt.Errorf("message topic is empty")
	}

	if msg.Source == "" {
		return fmt.Errorf("message source is empty")
	}

	if msg.Type == "" {
		return fmt.Errorf("message type is empty")
	}

	if dv.strictMode {
		if msg.Data == nil {
			return fmt.Errorf("message data is nil")
		}

		if msg.Timestamp.IsZero() {
			return fmt.Errorf("message timestamp is zero")
		}
	}

	return nil
}

// GenerateChecksum generates a simple checksum for data
func (dv *DefaultValidator) GenerateChecksum(data []byte) string {
	// Simple checksum implementation
	// In production, use a proper hash function like SHA-256
	var sum uint32
	for _, b := range data {
		sum += uint32(b)
	}
	return fmt.Sprintf("%08x", sum)
}

// VerifyChecksum verifies a checksum
func (dv *DefaultValidator) VerifyChecksum(data []byte, checksum string) bool {
	return dv.GenerateChecksum(data) == checksum
}

// NoOpEncryptor implements a no-operation encryptor for testing
type NoOpEncryptor struct {
	enabled bool
}

// NewNoOpEncryptor creates a new no-op encryptor
func NewNoOpEncryptor() *NoOpEncryptor {
	return &NoOpEncryptor{enabled: false}
}

// SetEnabled enables/disables the encryptor
func (noe *NoOpEncryptor) SetEnabled(enabled bool) {
	noe.enabled = enabled
}

// Encrypt returns data unchanged
func (noe *NoOpEncryptor) Encrypt(data []byte) ([]byte, error) {
	return data, nil
}

// Decrypt returns data unchanged
func (noe *NoOpEncryptor) Decrypt(data []byte) ([]byte, error) {
	return data, nil
}

// IsEnabled returns whether encryption is enabled
func (noe *NoOpEncryptor) IsEnabled() bool {
	return noe.enabled
}

// SerializationMetrics tracks serialization performance
type SerializationMetrics struct {
	SerializedMessages   int64
	DeserializedMessages int64
	SerializationErrors  int64
	CompressionRatio     float64
	AverageMessageSize   int64
	TotalDataProcessed   int64
}

// MetricsCollector collects serialization metrics
type MetricsCollector struct {
	metrics SerializationMetrics
	mu      sync.RWMutex
}

// NewMetricsCollector creates a new metrics collector
func NewMetricsCollector() *MetricsCollector {
	return &MetricsCollector{}
}

// RecordSerialization records a serialization operation
func (mc *MetricsCollector) RecordSerialization(originalSize, serializedSize int) {
	mc.mu.Lock()
	defer mc.mu.Unlock()

	mc.metrics.SerializedMessages++
	mc.metrics.TotalDataProcessed += int64(originalSize)

	// Update compression ratio
	if originalSize > 0 {
		ratio := float64(serializedSize) / float64(originalSize)
		mc.metrics.CompressionRatio = (mc.metrics.CompressionRatio + ratio) / 2
	}

	// Update average message size
	mc.metrics.AverageMessageSize = mc.metrics.TotalDataProcessed / mc.metrics.SerializedMessages
}

// RecordDeserialization records a deserialization operation
func (mc *MetricsCollector) RecordDeserialization() {
	mc.mu.Lock()
	defer mc.mu.Unlock()
	mc.metrics.DeserializedMessages++
}

// RecordError records a serialization error
func (mc *MetricsCollector) RecordError() {
	mc.mu.Lock()
	defer mc.mu.Unlock()
	mc.metrics.SerializationErrors++
}

// GetMetrics returns current metrics
func (mc *MetricsCollector) GetMetrics() SerializationMetrics {
	mc.mu.RLock()
	defer mc.mu.RUnlock()
	return mc.metrics
}

// Reset resets all metrics
func (mc *MetricsCollector) Reset() {
	mc.mu.Lock()
	defer mc.mu.Unlock()
	mc.metrics = SerializationMetrics{}
}