package security

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"io"
	"os"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// SecureConfig manages all security-sensitive configuration
type SecureConfig struct {
	// Network endpoints - never hardcoded
	RPCEndpoints []string
	WSEndpoints  []string
	BackupRPCs   []string

	// Security settings
	MaxGasPriceGwei     int64
	MaxTransactionValue string // In ETH
	MaxSlippageBps      uint64
	MinProfitThreshold  string // In ETH

	// Rate limiting
	MaxRequestsPerSecond int
	BurstSize            int

	// Timeouts
	RPCTimeout         time.Duration
	WebSocketTimeout   time.Duration
	TransactionTimeout time.Duration

	// Encryption
	encryptionKey []byte
}

// SecurityLimits defines operational security limits
type SecurityLimits struct {
	MaxGasPrice         int64  // Gwei
	MaxTransactionValue string // ETH
	MaxDailyVolume      string // ETH
	MaxSlippage         uint64 // basis points
	MinProfit           string // ETH
	MaxOrderSize        string // ETH
}

// EndpointConfig stores RPC endpoint configuration securely
type EndpointConfig struct {
	URL            string
	Priority       int
	Timeout        time.Duration
	MaxConnections int
	HealthCheckURL string
	RequiresAuth   bool
	AuthToken      string // Encrypted when stored
}

// NewSecureConfig creates a new secure configuration from environment
func NewSecureConfig() (*SecureConfig, error) {
	config := &SecureConfig{}

	// Load encryption key from environment
	keyStr := os.Getenv("MEV_BOT_ENCRYPTION_KEY")
	if keyStr == "" {
		return nil, fmt.Errorf("MEV_BOT_ENCRYPTION_KEY environment variable is required")
	}

	key, err := base64.StdEncoding.DecodeString(keyStr)
	if err != nil {
		return nil, fmt.Errorf("invalid encryption key format: %w", err)
	}

	if len(key) != 32 {
		return nil, fmt.Errorf("encryption key must be 32 bytes (256 bits)")
	}

	config.encryptionKey = key

	// Load RPC endpoints
	if err := config.loadRPCEndpoints(); err != nil {
		return nil, fmt.Errorf("failed to load RPC endpoints: %w", err)
	}

	// Load security limits
	if err := config.loadSecurityLimits(); err != nil {
		return nil, fmt.Errorf("failed to load security limits: %w", err)
	}

	// Load rate limiting config
	if err := config.loadRateLimits(); err != nil {
		return nil, fmt.Errorf("failed to load rate limits: %w", err)
	}

	// Load timeouts
	if err := config.loadTimeouts(); err != nil {
		return nil, fmt.Errorf("failed to load timeouts: %w", err)
	}

	return config, nil
}

// loadRPCEndpoints loads and validates RPC endpoints from environment
func (sc *SecureConfig) loadRPCEndpoints() error {
	// Primary RPC endpoints
	rpcEndpoints := os.Getenv("ARBITRUM_RPC_ENDPOINTS")
	if rpcEndpoints == "" {
		return fmt.Errorf("ARBITRUM_RPC_ENDPOINTS environment variable is required")
	}

	sc.RPCEndpoints = strings.Split(rpcEndpoints, ",")
	for i, endpoint := range sc.RPCEndpoints {
		sc.RPCEndpoints[i] = strings.TrimSpace(endpoint)
		if err := validateEndpoint(sc.RPCEndpoints[i]); err != nil {
			return fmt.Errorf("invalid RPC endpoint %s: %w", sc.RPCEndpoints[i], err)
		}
	}

	// WebSocket endpoints
	wsEndpoints := os.Getenv("ARBITRUM_WS_ENDPOINTS")
	if wsEndpoints != "" {
		sc.WSEndpoints = strings.Split(wsEndpoints, ",")
		for i, endpoint := range sc.WSEndpoints {
			sc.WSEndpoints[i] = strings.TrimSpace(endpoint)
			if err := validateWebSocketEndpoint(sc.WSEndpoints[i]); err != nil {
				return fmt.Errorf("invalid WebSocket endpoint %s: %w", sc.WSEndpoints[i], err)
			}
		}
	}

	// Backup RPC endpoints
	backupRPCs := os.Getenv("BACKUP_RPC_ENDPOINTS")
	if backupRPCs != "" {
		sc.BackupRPCs = strings.Split(backupRPCs, ",")
		for i, endpoint := range sc.BackupRPCs {
			sc.BackupRPCs[i] = strings.TrimSpace(endpoint)
			if err := validateEndpoint(sc.BackupRPCs[i]); err != nil {
				return fmt.Errorf("invalid backup RPC endpoint %s: %w", sc.BackupRPCs[i], err)
			}
		}
	}

	return nil
}

// loadSecurityLimits loads security limits from environment with safe defaults
func (sc *SecureConfig) loadSecurityLimits() error {
	// Max gas price in Gwei (default: 1000 Gwei)
	maxGasPriceStr := getEnvWithDefault("MAX_GAS_PRICE_GWEI", "1000")
	maxGasPrice, err := strconv.ParseInt(maxGasPriceStr, 10, 64)
	if err != nil || maxGasPrice <= 0 || maxGasPrice > 100000 {
		return fmt.Errorf("invalid MAX_GAS_PRICE_GWEI: must be between 1 and 100000")
	}
	sc.MaxGasPriceGwei = maxGasPrice

	// Max transaction value in ETH (default: 100 ETH)
	sc.MaxTransactionValue = getEnvWithDefault("MAX_TRANSACTION_VALUE_ETH", "100")
	if err := validateETHAmount(sc.MaxTransactionValue); err != nil {
		return fmt.Errorf("invalid MAX_TRANSACTION_VALUE_ETH: %w", err)
	}

	// Max slippage in basis points (default: 500 = 5%)
	maxSlippageStr := getEnvWithDefault("MAX_SLIPPAGE_BPS", "500")
	maxSlippage, err := strconv.ParseUint(maxSlippageStr, 10, 64)
	if err != nil || maxSlippage > 10000 {
		return fmt.Errorf("invalid MAX_SLIPPAGE_BPS: must be between 0 and 10000")
	}
	sc.MaxSlippageBps = maxSlippage

	// Min profit threshold in ETH (default: 0.01 ETH)
	sc.MinProfitThreshold = getEnvWithDefault("MIN_PROFIT_THRESHOLD_ETH", "0.01")
	if err := validateETHAmount(sc.MinProfitThreshold); err != nil {
		return fmt.Errorf("invalid MIN_PROFIT_THRESHOLD_ETH: %w", err)
	}

	return nil
}

// loadRateLimits loads rate limiting configuration
func (sc *SecureConfig) loadRateLimits() error {
	// Max requests per second (default: 100)
	maxRPSStr := getEnvWithDefault("MAX_REQUESTS_PER_SECOND", "100")
	maxRPS, err := strconv.Atoi(maxRPSStr)
	if err != nil || maxRPS <= 0 || maxRPS > 10000 {
		return fmt.Errorf("invalid MAX_REQUESTS_PER_SECOND: must be between 1 and 10000")
	}
	sc.MaxRequestsPerSecond = maxRPS

	// Burst size (default: 200)
	burstSizeStr := getEnvWithDefault("RATE_LIMIT_BURST_SIZE", "200")
	burstSize, err := strconv.Atoi(burstSizeStr)
	if err != nil || burstSize <= 0 || burstSize > 20000 {
		return fmt.Errorf("invalid RATE_LIMIT_BURST_SIZE: must be between 1 and 20000")
	}
	sc.BurstSize = burstSize

	return nil
}

// loadTimeouts loads timeout configuration
func (sc *SecureConfig) loadTimeouts() error {
	// RPC timeout (default: 30s)
	rpcTimeoutStr := getEnvWithDefault("RPC_TIMEOUT_SECONDS", "30")
	rpcTimeout, err := strconv.Atoi(rpcTimeoutStr)
	if err != nil || rpcTimeout <= 0 || rpcTimeout > 300 {
		return fmt.Errorf("invalid RPC_TIMEOUT_SECONDS: must be between 1 and 300")
	}
	sc.RPCTimeout = time.Duration(rpcTimeout) * time.Second

	// WebSocket timeout (default: 60s)
	wsTimeoutStr := getEnvWithDefault("WEBSOCKET_TIMEOUT_SECONDS", "60")
	wsTimeout, err := strconv.Atoi(wsTimeoutStr)
	if err != nil || wsTimeout <= 0 || wsTimeout > 600 {
		return fmt.Errorf("invalid WEBSOCKET_TIMEOUT_SECONDS: must be between 1 and 600")
	}
	sc.WebSocketTimeout = time.Duration(wsTimeout) * time.Second

	// Transaction timeout (default: 300s)
	txTimeoutStr := getEnvWithDefault("TRANSACTION_TIMEOUT_SECONDS", "300")
	txTimeout, err := strconv.Atoi(txTimeoutStr)
	if err != nil || txTimeout <= 0 || txTimeout > 3600 {
		return fmt.Errorf("invalid TRANSACTION_TIMEOUT_SECONDS: must be between 1 and 3600")
	}
	sc.TransactionTimeout = time.Duration(txTimeout) * time.Second

	return nil
}

// GetPrimaryRPCEndpoint returns the first healthy RPC endpoint
func (sc *SecureConfig) GetPrimaryRPCEndpoint() string {
	if len(sc.RPCEndpoints) == 0 {
		return ""
	}
	return sc.RPCEndpoints[0]
}

// GetAllRPCEndpoints returns all configured RPC endpoints
func (sc *SecureConfig) GetAllRPCEndpoints() []string {
	return append(sc.RPCEndpoints, sc.BackupRPCs...)
}

// Encrypt encrypts sensitive data using AES-256-GCM
func (sc *SecureConfig) Encrypt(plaintext string) (string, error) {
	if sc.encryptionKey == nil {
		return "", fmt.Errorf("encryption key not initialized")
	}

	block, err := aes.NewCipher(sc.encryptionKey)
	if err != nil {
		return "", fmt.Errorf("failed to create cipher: %w", err)
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("failed to create GCM: %w", err)
	}

	nonce := make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", fmt.Errorf("failed to generate nonce: %w", err)
	}

	ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// Decrypt decrypts data encrypted with Encrypt
func (sc *SecureConfig) Decrypt(ciphertext string) (string, error) {
	if sc.encryptionKey == nil {
		return "", fmt.Errorf("encryption key not initialized")
	}

	data, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return "", fmt.Errorf("failed to decode ciphertext: %w", err)
	}

	block, err := aes.NewCipher(sc.encryptionKey)
	if err != nil {
		return "", fmt.Errorf("failed to create cipher: %w", err)
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("failed to create GCM: %w", err)
	}

	nonceSize := gcm.NonceSize()
	if len(data) < nonceSize {
		return "", fmt.Errorf("ciphertext too short")
	}

	nonce, ciphertextBytes := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertextBytes, nil)
	if err != nil {
		return "", fmt.Errorf("failed to decrypt: %w", err)
	}

	return string(plaintext), nil
}

// GenerateEncryptionKey generates a new 256-bit encryption key
func GenerateEncryptionKey() (string, error) {
	key := make([]byte, 32) // 256 bits
	if _, err := rand.Read(key); err != nil {
		return "", fmt.Errorf("failed to generate encryption key: %w", err)
	}
	return base64.StdEncoding.EncodeToString(key), nil
}

// validateEndpoint validates RPC endpoint URL format
func validateEndpoint(endpoint string) error {
	if endpoint == "" {
		return fmt.Errorf("endpoint cannot be empty")
	}

	// Check for required protocols
	if !strings.HasPrefix(endpoint, "https://") && !strings.HasPrefix(endpoint, "wss://") {
		return fmt.Errorf("endpoint must use HTTPS or WSS protocol")
	}

	// Check for suspicious patterns that might indicate hardcoded keys
	suspiciousPatterns := []string{
		"localhost",
		"127.0.0.1",
		"demo",
		"test",
		"example",
	}

	lowerEndpoint := strings.ToLower(endpoint)
	for _, pattern := range suspiciousPatterns {
		if strings.Contains(lowerEndpoint, pattern) {
			return fmt.Errorf("endpoint contains suspicious pattern: %s", pattern)
		}
	}

	return nil
}

// validateWebSocketEndpoint validates WebSocket endpoint
func validateWebSocketEndpoint(endpoint string) error {
	if !strings.HasPrefix(endpoint, "wss://") {
		return fmt.Errorf("WebSocket endpoint must use WSS protocol")
	}
	return validateEndpoint(endpoint)
}

// validateETHAmount validates ETH amount string
func validateETHAmount(amount string) error {
	// Use regex to validate ETH amount format
	ethPattern := `^(\d+\.?\d*|\.\d+)$`
	matched, err := regexp.MatchString(ethPattern, amount)
	if err != nil {
		return fmt.Errorf("regex error: %w", err)
	}
	if !matched {
		return fmt.Errorf("invalid ETH amount format")
	}

	return nil
}

// getEnvWithDefault gets environment variable with fallback default
func getEnvWithDefault(key, defaultValue string) string {
	if value := os.Getenv(key); value != "" {
		return value
	}
	return defaultValue
}

// CreateConfigHash creates a SHA256 hash of configuration for integrity checking
func (sc *SecureConfig) CreateConfigHash() string {
	hasher := sha256.New()
	hasher.Write([]byte(fmt.Sprintf("%v", sc.RPCEndpoints)))
	hasher.Write([]byte(fmt.Sprintf("%d", sc.MaxGasPriceGwei)))
	hasher.Write([]byte(sc.MaxTransactionValue))
	hasher.Write([]byte(fmt.Sprintf("%d", sc.MaxSlippageBps)))
	return fmt.Sprintf("%x", hasher.Sum(nil))
}

// SecurityProfile returns current security configuration summary
func (sc *SecureConfig) SecurityProfile() map[string]interface{} {
	return map[string]interface{}{
		"max_gas_price_gwei":      sc.MaxGasPriceGwei,
		"max_transaction_value":   sc.MaxTransactionValue,
		"max_slippage_bps":        sc.MaxSlippageBps,
		"min_profit_threshold":    sc.MinProfitThreshold,
		"max_requests_per_second": sc.MaxRequestsPerSecond,
		"rpc_timeout":             sc.RPCTimeout.String(),
		"websocket_timeout":       sc.WebSocketTimeout.String(),
		"transaction_timeout":     sc.TransactionTimeout.String(),
		"rpc_endpoints_count":     len(sc.RPCEndpoints),
		"backup_rpcs_count":       len(sc.BackupRPCs),
		"config_hash":             sc.CreateConfigHash(),
	}
}