package security

import (
	"context"
	"encoding/hex"
	"fmt"
	"math/big"
	"sync"
	"time"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethclient"

	"github.com/fraktal/mev-beta/internal/logger"
)

// ContractInfo represents information about a verified contract
type ContractInfo struct {
	Address        common.Address      `json:"address"`
	BytecodeHash   string              `json:"bytecode_hash"`
	Name           string              `json:"name"`
	Version        string              `json:"version"`
	DeployedAt     *big.Int            `json:"deployed_at"`
	Deployer       common.Address      `json:"deployer"`
	VerifiedAt     time.Time           `json:"verified_at"`
	IsWhitelisted  bool                `json:"is_whitelisted"`
	RiskLevel      RiskLevel           `json:"risk_level"`
	Permissions    ContractPermissions `json:"permissions"`
	ABIHash        string              `json:"abi_hash,omitempty"`
	SourceCodeHash string              `json:"source_code_hash,omitempty"`
}

// ContractPermissions defines what operations are allowed with a contract
type ContractPermissions struct {
	CanInteract    bool     `json:"can_interact"`
	CanSendValue   bool     `json:"can_send_value"`
	MaxValueWei    *big.Int `json:"max_value_wei,omitempty"`
	AllowedMethods []string `json:"allowed_methods,omitempty"`
	RequireConfirm bool     `json:"require_confirmation"`
	DailyLimit     *big.Int `json:"daily_limit,omitempty"`
}

// RiskLevel represents the risk assessment of a contract
type RiskLevel int

const (
	RiskLevelLow RiskLevel = iota
	RiskLevelMedium
	RiskLevelHigh
	RiskLevelCritical
	RiskLevelBlocked
)

func (r RiskLevel) String() string {
	switch r {
	case RiskLevelLow:
		return "Low"
	case RiskLevelMedium:
		return "Medium"
	case RiskLevelHigh:
		return "High"
	case RiskLevelCritical:
		return "Critical"
	case RiskLevelBlocked:
		return "Blocked"
	default:
		return "Unknown"
	}
}

// ContractValidationResult contains the result of contract validation
type ContractValidationResult struct {
	IsValid         bool              `json:"is_valid"`
	ContractInfo    *ContractInfo     `json:"contract_info"`
	ValidationError string            `json:"validation_error,omitempty"`
	Warnings        []string          `json:"warnings"`
	ChecksPerformed []ValidationCheck `json:"checks_performed"`
	RiskScore       int               `json:"risk_score"` // 1-10
}

// ValidationCheck represents a single validation check
type ValidationCheck struct {
	Name        string    `json:"name"`
	Passed      bool      `json:"passed"`
	Description string    `json:"description"`
	Error       string    `json:"error,omitempty"`
	Timestamp   time.Time `json:"timestamp"`
}

// ContractValidator provides secure contract validation and verification
type ContractValidator struct {
	client           *ethclient.Client
	logger           *logger.Logger
	trustedContracts map[common.Address]*ContractInfo
	contractCache    map[common.Address]*ContractInfo
	cacheMutex       sync.RWMutex
	config           *ContractValidatorConfig

	// Security tracking
	interactionCounts map[common.Address]int64
	dailyLimits       map[common.Address]*big.Int
	lastResetTime     time.Time
	limitsMutex       sync.RWMutex
}

// ContractValidatorConfig provides configuration for the contract validator
type ContractValidatorConfig struct {
	EnableBytecodeVerification bool          `json:"enable_bytecode_verification"`
	EnableABIValidation        bool          `json:"enable_abi_validation"`
	RequireWhitelist           bool          `json:"require_whitelist"`
	MaxBytecodeSize            int           `json:"max_bytecode_size"`
	CacheTimeout               time.Duration `json:"cache_timeout"`
	MaxRiskScore               int           `json:"max_risk_score"`
	BlockUnverifiedContracts   bool          `json:"block_unverified_contracts"`
	RequireSourceCode          bool          `json:"require_source_code"`
	EnableRealTimeValidation   bool          `json:"enable_realtime_validation"`
}

// NewContractValidator creates a new contract validator
func NewContractValidator(client *ethclient.Client, logger *logger.Logger, config *ContractValidatorConfig) *ContractValidator {
	if config == nil {
		config = getDefaultValidatorConfig()
	}

	return &ContractValidator{
		client:            client,
		logger:            logger,
		config:            config,
		trustedContracts:  make(map[common.Address]*ContractInfo),
		contractCache:     make(map[common.Address]*ContractInfo),
		interactionCounts: make(map[common.Address]int64),
		dailyLimits:       make(map[common.Address]*big.Int),
		lastResetTime:     time.Now(),
	}
}

// AddTrustedContract adds a contract to the trusted list
func (cv *ContractValidator) AddTrustedContract(info *ContractInfo) error {
	cv.cacheMutex.Lock()
	defer cv.cacheMutex.Unlock()

	// Validate the contract info
	if info.Address == (common.Address{}) {
		return fmt.Errorf("invalid contract address")
	}

	if info.BytecodeHash == "" {
		return fmt.Errorf("bytecode hash is required")
	}

	// Mark as whitelisted and set low risk
	info.IsWhitelisted = true
	if info.RiskLevel == 0 {
		info.RiskLevel = RiskLevelLow
	}
	info.VerifiedAt = time.Now()

	cv.trustedContracts[info.Address] = info
	cv.contractCache[info.Address] = info

	cv.logger.Info(fmt.Sprintf("Added trusted contract: %s (%s)", info.Address.Hex(), info.Name))
	return nil
}

// ValidateContract performs comprehensive contract validation
func (cv *ContractValidator) ValidateContract(ctx context.Context, address common.Address) (*ContractValidationResult, error) {
	result := &ContractValidationResult{
		IsValid:         false,
		Warnings:        make([]string, 0),
		ChecksPerformed: make([]ValidationCheck, 0),
	}

	// Check if contract is in trusted list first
	cv.cacheMutex.RLock()
	if trusted, exists := cv.trustedContracts[address]; exists {
		cv.cacheMutex.RUnlock()
		result.IsValid = true
		result.ContractInfo = trusted
		result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
			Name:        "Trusted Contract Check",
			Passed:      true,
			Description: "Contract found in trusted whitelist",
			Timestamp:   time.Now(),
		})
		return result, nil
	}

	// Check cache
	if cached, exists := cv.contractCache[address]; exists {
		if time.Since(cached.VerifiedAt) < cv.config.CacheTimeout {
			cv.cacheMutex.RUnlock()
			result.IsValid = true
			result.ContractInfo = cached
			result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
				Name:        "Cache Check",
				Passed:      true,
				Description: "Contract found in validation cache",
				Timestamp:   time.Now(),
			})
			return result, nil
		}
	}
	cv.cacheMutex.RUnlock()

	// Perform real-time validation
	contractInfo, err := cv.validateContractOnChain(ctx, address, result)
	if err != nil {
		result.ValidationError = err.Error()
		return result, err
	}

	result.ContractInfo = contractInfo
	result.RiskScore = cv.calculateRiskScore(contractInfo, result)

	// Check if contract meets security requirements
	if cv.config.RequireWhitelist && !contractInfo.IsWhitelisted {
		result.ValidationError = "Contract not whitelisted"
		result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
			Name:        "Whitelist Check",
			Passed:      false,
			Description: "Contract not found in whitelist",
			Error:       "Contract not whitelisted",
			Timestamp:   time.Now(),
		})
		return result, fmt.Errorf("contract not whitelisted: %s", address.Hex())
	}

	if result.RiskScore > cv.config.MaxRiskScore {
		result.ValidationError = fmt.Sprintf("Risk score too high: %d > %d", result.RiskScore, cv.config.MaxRiskScore)
		return result, fmt.Errorf("contract risk score too high: %d", result.RiskScore)
	}

	// Cache the validation result
	cv.cacheMutex.Lock()
	cv.contractCache[address] = contractInfo
	cv.cacheMutex.Unlock()

	result.IsValid = true
	return result, nil
}

// validateContractOnChain performs on-chain validation of a contract
func (cv *ContractValidator) validateContractOnChain(ctx context.Context, address common.Address, result *ContractValidationResult) (*ContractInfo, error) {
	// Check if address is a contract
	bytecode, err := cv.client.CodeAt(ctx, address, nil)
	if err != nil {
		result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
			Name:        "Bytecode Retrieval",
			Passed:      false,
			Description: "Failed to retrieve contract bytecode",
			Error:       err.Error(),
			Timestamp:   time.Now(),
		})
		return nil, fmt.Errorf("failed to get contract bytecode: %w", err)
	}

	if len(bytecode) == 0 {
		result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
			Name:        "Contract Existence",
			Passed:      false,
			Description: "Address is not a contract (no bytecode)",
			Error:       "No bytecode found",
			Timestamp:   time.Now(),
		})
		return nil, fmt.Errorf("address is not a contract: %s", address.Hex())
	}

	result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
		Name:        "Contract Existence",
		Passed:      true,
		Description: fmt.Sprintf("Contract bytecode found (%d bytes)", len(bytecode)),
		Timestamp:   time.Now(),
	})

	// Validate bytecode size
	if cv.config.MaxBytecodeSize > 0 && len(bytecode) > cv.config.MaxBytecodeSize {
		result.Warnings = append(result.Warnings, fmt.Sprintf("Large bytecode size: %d bytes", len(bytecode)))
	}

	// Create bytecode hash
	bytecodeHash := crypto.Keccak256Hash(bytecode).Hex()

	// Get deployment transaction info
	deployedAt, deployer, err := cv.getDeploymentInfo(ctx, address)
	if err != nil {
		cv.logger.Warn(fmt.Sprintf("Could not retrieve deployment info for %s: %v", address.Hex(), err))
		deployedAt = big.NewInt(0)
		deployer = common.Address{}
	}

	// Create contract info
	contractInfo := &ContractInfo{
		Address:       address,
		BytecodeHash:  bytecodeHash,
		Name:          "Unknown Contract",
		Version:       "unknown",
		DeployedAt:    deployedAt,
		Deployer:      deployer,
		VerifiedAt:    time.Now(),
		IsWhitelisted: false,
		RiskLevel:     cv.assessRiskLevel(bytecode, result),
		Permissions:   cv.getDefaultPermissions(),
	}

	// Verify bytecode against known contracts if enabled
	if cv.config.EnableBytecodeVerification {
		cv.verifyBytecodeSignature(bytecode, contractInfo, result)
	}

	result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
		Name:        "Bytecode Validation",
		Passed:      true,
		Description: "Bytecode hash calculated and verified",
		Timestamp:   time.Now(),
	})

	return contractInfo, nil
}

// getDeploymentInfo retrieves deployment information for a contract
func (cv *ContractValidator) getDeploymentInfo(ctx context.Context, address common.Address) (*big.Int, common.Address, error) {
	// This is a simplified implementation
	// In production, you would need to scan blocks or use an indexer
	return big.NewInt(0), common.Address{}, fmt.Errorf("deployment info not available")
}

// assessRiskLevel assesses the risk level of a contract based on its bytecode
func (cv *ContractValidator) assessRiskLevel(bytecode []byte, result *ContractValidationResult) RiskLevel {
	riskFactors := 0

	// Check for suspicious patterns in bytecode
	bytecodeStr := hex.EncodeToString(bytecode)

	// Look for dangerous opcodes
	dangerousOpcodes := []string{
		"ff", // SELFDESTRUCT
		"f4", // DELEGATECALL
		"3d", // RETURNDATASIZE (often used in proxy patterns)
	}

	for _, opcode := range dangerousOpcodes {
		if contains := func(haystack, needle string) bool {
			return len(haystack) >= len(needle) && haystack[:len(needle)] == needle ||
				len(haystack) > len(needle) && haystack[len(haystack)-len(needle):] == needle
		}; contains(bytecodeStr, opcode) {
			riskFactors++
		}
	}

	// Check bytecode size (larger contracts may be more complex/risky)
	if len(bytecode) > 20000 { // 20KB
		riskFactors++
		result.Warnings = append(result.Warnings, "Large contract size detected")
	}

	// Assess risk level based on factors
	switch {
	case riskFactors == 0:
		return RiskLevelLow
	case riskFactors <= 2:
		return RiskLevelMedium
	case riskFactors <= 4:
		return RiskLevelHigh
	default:
		return RiskLevelCritical
	}
}

// verifyBytecodeSignature verifies bytecode against known contract signatures
func (cv *ContractValidator) verifyBytecodeSignature(bytecode []byte, info *ContractInfo, result *ContractValidationResult) {
	// Known contract bytecode hashes for common contracts
	knownContracts := map[string]string{
		// Uniswap V3 Factory
		"0x1f98431c8ad98523631ae4a59f267346ea31f984": "uniswap_v3_factory",
		// Uniswap V3 Router
		"0xe592427a0aece92de3edee1f18e0157c05861564": "uniswap_v3_router",
		// Add more known contracts...
	}

	addressStr := info.Address.Hex()
	if name, exists := knownContracts[addressStr]; exists {
		info.Name = name
		info.IsWhitelisted = true
		info.RiskLevel = RiskLevelLow
		result.ChecksPerformed = append(result.ChecksPerformed, ValidationCheck{
			Name:        "Known Contract Verification",
			Passed:      true,
			Description: fmt.Sprintf("Verified as known contract: %s", name),
			Timestamp:   time.Now(),
		})
	}
}

// calculateRiskScore calculates a numerical risk score (1-10)
func (cv *ContractValidator) calculateRiskScore(info *ContractInfo, result *ContractValidationResult) int {
	score := 1 // Base score

	// Adjust based on risk level
	switch info.RiskLevel {
	case RiskLevelLow:
		score += 0
	case RiskLevelMedium:
		score += 2
	case RiskLevelHigh:
		score += 5
	case RiskLevelCritical:
		score += 8
	case RiskLevelBlocked:
		score = 10
	}

	// Adjust based on whitelist status
	if !info.IsWhitelisted {
		score += 2
	}

	// Adjust based on warnings
	score += len(result.Warnings)

	// Cap at 10
	if score > 10 {
		score = 10
	}

	return score
}

// getDefaultPermissions returns default permissions for unverified contracts
func (cv *ContractValidator) getDefaultPermissions() ContractPermissions {
	return ContractPermissions{
		CanInteract:    true,
		CanSendValue:   false,
		MaxValueWei:    big.NewInt(0),
		AllowedMethods: []string{}, // Empty means all methods allowed
		RequireConfirm: true,
		DailyLimit:     big.NewInt(1000000000000000000), // 1 ETH
	}
}

// ValidateTransaction validates a transaction against contract permissions
func (cv *ContractValidator) ValidateTransaction(ctx context.Context, tx *types.Transaction) error {
	if tx.To() == nil {
		return nil // Contract creation, allow
	}

	// Validate the contract
	result, err := cv.ValidateContract(ctx, *tx.To())
	if err != nil {
		return fmt.Errorf("contract validation failed: %w", err)
	}

	if !result.IsValid {
		return fmt.Errorf("transaction to invalid contract: %s", tx.To().Hex())
	}

	// Check permissions
	permissions := result.ContractInfo.Permissions

	// Check value transfer permission
	if tx.Value().Sign() > 0 && !permissions.CanSendValue {
		return fmt.Errorf("contract does not allow value transfers: %s", tx.To().Hex())
	}

	// Check value limits
	if permissions.MaxValueWei != nil && tx.Value().Cmp(permissions.MaxValueWei) > 0 {
		return fmt.Errorf("transaction value exceeds limit: %s > %s",
			tx.Value().String(), permissions.MaxValueWei.String())
	}

	// Check daily limits
	if err := cv.checkDailyLimit(*tx.To(), tx.Value()); err != nil {
		return err
	}

	cv.logger.Debug(fmt.Sprintf("Transaction validated for contract %s", tx.To().Hex()))
	return nil
}

// checkDailyLimit checks if transaction exceeds daily interaction limit
func (cv *ContractValidator) checkDailyLimit(contractAddr common.Address, value *big.Int) error {
	cv.limitsMutex.Lock()
	defer cv.limitsMutex.Unlock()

	// Reset daily counters if needed
	if time.Since(cv.lastResetTime) > 24*time.Hour {
		cv.dailyLimits = make(map[common.Address]*big.Int)
		cv.lastResetTime = time.Now()
	}

	// Get current daily usage
	currentUsage, exists := cv.dailyLimits[contractAddr]
	if !exists {
		currentUsage = big.NewInt(0)
		cv.dailyLimits[contractAddr] = currentUsage
	}

	// Get contract info for daily limit
	cv.cacheMutex.RLock()
	contractInfo, exists := cv.contractCache[contractAddr]
	cv.cacheMutex.RUnlock()

	if !exists {
		return nil // No limit if contract not cached
	}

	if contractInfo.Permissions.DailyLimit == nil {
		return nil // No daily limit set
	}

	// Check if adding this transaction would exceed limit
	newUsage := new(big.Int).Add(currentUsage, value)
	if newUsage.Cmp(contractInfo.Permissions.DailyLimit) > 0 {
		return fmt.Errorf("daily limit exceeded for contract %s: %s + %s > %s",
			contractAddr.Hex(),
			currentUsage.String(),
			value.String(),
			contractInfo.Permissions.DailyLimit.String())
	}

	// Update usage
	cv.dailyLimits[contractAddr] = newUsage
	return nil
}

// getDefaultValidatorConfig returns default configuration
func getDefaultValidatorConfig() *ContractValidatorConfig {
	return &ContractValidatorConfig{
		EnableBytecodeVerification: true,
		EnableABIValidation:        false, // Requires additional infrastructure
		RequireWhitelist:           false, // Start permissive, can be tightened
		MaxBytecodeSize:            50000, // 50KB
		CacheTimeout:               1 * time.Hour,
		MaxRiskScore:               7, // Allow medium-high risk
		BlockUnverifiedContracts:   false,
		RequireSourceCode:          false,
		EnableRealTimeValidation:   true,
	}
}

// GetContractInfo returns information about a validated contract
func (cv *ContractValidator) GetContractInfo(address common.Address) (*ContractInfo, bool) {
	cv.cacheMutex.RLock()
	defer cv.cacheMutex.RUnlock()

	if info, exists := cv.contractCache[address]; exists {
		return info, true
	}
	return nil, false
}

// ListTrustedContracts returns all trusted contracts
func (cv *ContractValidator) ListTrustedContracts() map[common.Address]*ContractInfo {
	cv.cacheMutex.RLock()
	defer cv.cacheMutex.RUnlock()

	// Create a copy to avoid race conditions
	trusted := make(map[common.Address]*ContractInfo)
	for addr, info := range cv.trustedContracts {
		trusted[addr] = info
	}
	return trusted
}