// Package validation provides comprehensive Ethereum address validation and corruption detection.
// This package is critical for the MEV bot's security and reliability, preventing costly errors
// from malformed or corrupted addresses that could cause transaction failures or security issues.
//
// Key features:
// - Multi-layer address validation (format, length, corruption detection)
// - Contract type classification and prevention of ERC-20/pool confusion
// - Corruption scoring system to identify suspicious addresses
// - Known contract registry for instant validation of major protocols
package validation

import (
	"fmt"
	"regexp"
	"strings"

	"github.com/ethereum/go-ethereum/common"
)

// AddressValidator provides comprehensive Ethereum address validation with advanced
// corruption detection and contract type classification. This validator is designed
// to prevent the costly errors that can occur when malformed addresses are used
// in contract calls, particularly in high-frequency MEV operations.
//
// The validator implements multiple validation layers:
// 1. Basic format validation (hex format, length, prefix)
// 2. Corruption pattern detection (repetitive patterns, suspicious zeros)
// 3. Contract type classification to prevent misuse
// 4. Known contract registry for instant validation
type AddressValidator struct {
	// Known corrupted patterns that should be immediately rejected
	// These patterns are derived from observed corruption incidents in production
	corruptedPatterns []string
	// Precompiled regex equivalents for efficient matching
	corruptedPatternRegex []*regexp.Regexp

	// Registry of known contract addresses and their verified types
	// This enables instant validation without requiring RPC calls
	knownContracts map[common.Address]ContractType

	// Enhanced known contract registry for detailed validation
	knownContractsRegistry *KnownContractRegistry
}

// ContractType represents the classification of an Ethereum contract.
// This classification is critical for preventing the ERC-20/pool confusion
// that was causing massive log spam and transaction failures in production.
type ContractType int

const (
	// ContractTypeUnknown indicates the contract type could not be determined
	// This is the default for addresses not in the known contracts registry
	ContractTypeUnknown ContractType = iota

	// ContractTypeERC20Token indicates a standard ERC-20 token contract
	// These contracts should never be used in pool-specific operations
	ContractTypeERC20Token

	// ContractTypeUniswapV2Pool indicates a Uniswap V2 compatible pool contract
	// These support token0(), token1(), and getReserves() functions
	ContractTypeUniswapV2Pool

	// ContractTypeUniswapV3Pool indicates a Uniswap V3 compatible pool contract
	// These support token0(), token1(), and slot0() functions
	ContractTypeUniswapV3Pool

	// ContractTypeRouter indicates a DEX router contract
	// These should not be used directly as token or pool addresses
	ContractTypeRouter

	// ContractTypeFactory indicates a pool factory contract
	// These create pools but are not pools themselves
	ContractTypeFactory
)

// String returns a human-readable representation of the contract type.
func (ct ContractType) String() string {
	switch ct {
	case ContractTypeERC20Token:
		return "ERC20_TOKEN"
	case ContractTypeUniswapV2Pool:
		return "UNISWAP_V2_POOL"
	case ContractTypeUniswapV3Pool:
		return "UNISWAP_V3_POOL"
	case ContractTypeRouter:
		return "ROUTER"
	case ContractTypeFactory:
		return "FACTORY"
	case ContractTypeUnknown:
		fallthrough
	default:
		return "UNKNOWN"
	}
}

// ValidationError represents a structured validation failure for an address.
type ValidationError struct {
	Code    string
	Message string
	Context map[string]interface{}
}

// Error implements the error interface.
func (e *ValidationError) Error() string {
	if e == nil {
		return ""
	}
	if e.Code != "" {
		return fmt.Sprintf("%s: %s", e.Code, e.Message)
	}
	return e.Message
}

// AddressValidationResult contains comprehensive validation results and metadata
// for an Ethereum address. This structure provides detailed information about
// the validation process, including any issues found and confidence metrics.
type AddressValidationResult struct {
	// IsValid indicates whether the address passed all validation checks
	// A false value means the address should not be used in transactions
	IsValid bool

	// Address contains the parsed Ethereum address (only valid if IsValid is true)
	Address common.Address

	// ContractType indicates the classification of the contract (if known)
	ContractType ContractType

	// ErrorMessages contains detailed descriptions of validation failures
	// These are critical issues that prevent the address from being used
	ErrorMessages []string

	// WarningMessages contains non-critical issues or concerns
	// These don't prevent usage but should be logged for monitoring
	WarningMessages []string

	// CorruptionScore is a 0-100 metric indicating likelihood of corruption
	// Higher scores indicate more suspicious patterns (0=clean, 100=definitely corrupted)
	// Addresses with scores >30 are typically rejected in critical operations
	CorruptionScore int
}

// NewAddressValidator creates a new address validator
func NewAddressValidator() *AddressValidator {
	patterns := []string{
		// Patterns indicating clear corruption
		"0000000000000000000000000000000000000000",  // All zeros
		"000000000000000000000000000000000000000",   // Missing one zero
		"00000000000000000000000000000000000000000", // Extra zero
		// Patterns with trailing zeros indicating truncation
		"00000000000000000000000000$",
		"000000000000000000000000$",
		"0000000000000000000000$",
		// Patterns with leading non-hex after 0x
		"^0x[^0-9a-fA-F]",
	}

	compiled := make([]*regexp.Regexp, 0, len(patterns))
	for _, pattern := range patterns {
		compiled = append(compiled, regexp.MustCompile(pattern))
	}

	return &AddressValidator{
		corruptedPatterns:      patterns,
		corruptedPatternRegex:  compiled,
		knownContracts:         make(map[common.Address]ContractType),
		knownContractsRegistry: NewKnownContractRegistry(),
	}
}

// InitializeKnownContracts populates the validator with known Arbitrum contracts
func (av *AddressValidator) InitializeKnownContracts() {
	// Known Arbitrum tokens
	av.knownContracts[common.HexToAddress("0xFF970A61A04b1cA14834A43f5dE4533eBDDB5CC8")] = ContractTypeERC20Token // USDC
	av.knownContracts[common.HexToAddress("0x82aF49447D8a07e3bd95BD0d56f35241523fBab1")] = ContractTypeERC20Token // WETH
	av.knownContracts[common.HexToAddress("0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9")] = ContractTypeERC20Token // USDT
	av.knownContracts[common.HexToAddress("0x2f2a2543B76A4166549F7aaB2e75Bef0aefC5B0f")] = ContractTypeERC20Token // WBTC
	av.knownContracts[common.HexToAddress("0x912CE59144191C1204E64559FE8253a0e49E6548")] = ContractTypeERC20Token // ARB

	// Known Arbitrum routers
	av.knownContracts[common.HexToAddress("0xE592427A0AEce92De3Edee1F18E0157C05861564")] = ContractTypeRouter // Uniswap V3 Router
	av.knownContracts[common.HexToAddress("0x4752ba5dbc23f44d87826276bf6fd6b1c372ad24")] = ContractTypeRouter // Uniswap V2 Router02
	av.knownContracts[common.HexToAddress("0xA51afAFe0263b40EdaEf0Df8781eA9aa03E381a3")] = ContractTypeRouter // Universal Router
	av.knownContracts[common.HexToAddress("0xC36442b4a4522E871399CD717aBDD847Ab11FE88")] = ContractTypeRouter // Position Manager

	// Known Arbitrum factories
	av.knownContracts[common.HexToAddress("0x1F98431c8aD98523631AE4a59f267346ea31F984")] = ContractTypeFactory // Uniswap V3 Factory
	av.knownContracts[common.HexToAddress("0xf1D7CC64Fb4452F05c498126312eBE29f30Fbcf9")] = ContractTypeFactory // Uniswap V2 Factory

	// Known high-volume pools
	av.knownContracts[common.HexToAddress("0xC6962004f452bE9203591991D15f6b388e09E8D0")] = ContractTypeUniswapV3Pool // USDC/WETH 0.05%
	av.knownContracts[common.HexToAddress("0x17c14D2c404D167802b16C450d3c99F88F2c4F4d")] = ContractTypeUniswapV3Pool // USDC/WETH 0.3%
	av.knownContracts[common.HexToAddress("0x2f5e87C9312fa29aed5c179E456625D79015299c")] = ContractTypeUniswapV3Pool // WBTC/WETH 0.05%
}

// ValidateAddress performs comprehensive validation of an Ethereum address string.
// This is the primary validation function that applies all validation layers
// in sequence to determine if an address is safe to use in transactions.
//
// The validation process includes:
// 1. Basic format validation (hex format, 0x prefix)
// 2. Length validation (must be exactly 42 characters)
// 3. Corruption pattern detection
// 4. Contract type classification
// 5. Corruption scoring
//
// Parameters:
//   - addressStr: The address string to validate (should include 0x prefix)
//
// Returns:
//   - *AddressValidationResult: Comprehensive validation results
func (av *AddressValidator) ValidateAddress(addressStr string) *AddressValidationResult {
	// Initialize the result structure with safe defaults
	result := &AddressValidationResult{
		IsValid:         false, // Default to invalid until all checks pass
		ErrorMessages:   make([]string, 0),
		WarningMessages: make([]string, 0),
		CorruptionScore: 0, // Start with zero corruption score
	}

	// Basic format validation
	if !av.isValidHexFormat(addressStr) {
		result.ErrorMessages = append(result.ErrorMessages, "invalid hex format")
		result.CorruptionScore += 50
		return result
	}

	// Length validation
	if !av.isValidLength(addressStr) {
		result.ErrorMessages = append(result.ErrorMessages, "invalid address length")
		result.CorruptionScore += 50
		return result
	}

	// Corruption pattern detection
	corruptionDetected, patterns := av.detectCorruption(addressStr)
	if corruptionDetected {
		result.ErrorMessages = append(result.ErrorMessages, fmt.Sprintf("corruption detected: %v", patterns))
		result.CorruptionScore += 70
		return result
	}

	// Convert to common.Address for further validation
	if !common.IsHexAddress(addressStr) {
		result.ErrorMessages = append(result.ErrorMessages, "not a valid Ethereum address")
		result.CorruptionScore += 30
		return result
	}

	address := common.HexToAddress(addressStr)
	result.Address = address

	// Check for zero address
	if address == (common.Address{}) {
		result.ErrorMessages = append(result.ErrorMessages, "zero address")
		result.CorruptionScore += 40
		return result
	}

	// Check known contract types
	if contractType, exists := av.knownContracts[address]; exists {
		result.ContractType = contractType
	} else {
		result.ContractType = ContractTypeUnknown
		result.WarningMessages = append(result.WarningMessages, "unknown contract type")
	}

	// Additional pattern-based corruption detection
	result.CorruptionScore += av.calculateCorruptionScore(addressStr)

	// Mark as valid if corruption score is low enough
	if result.CorruptionScore < 30 {
		result.IsValid = true
	}

	return result
}

// isValidHexFormat checks if the string is a valid hex format
func (av *AddressValidator) isValidHexFormat(addressStr string) bool {
	if len(addressStr) < 3 {
		return false
	}

	if !strings.HasPrefix(addressStr, "0x") && !strings.HasPrefix(addressStr, "0X") {
		return false
	}

	// Check if all characters after 0x are valid hex
	hexPart := addressStr[2:]
	if len(hexPart) == 0 {
		return false
	}

	for i := 0; i < len(hexPart); i++ {
		switch {
		case hexPart[i] >= '0' && hexPart[i] <= '9':
		case hexPart[i] >= 'a' && hexPart[i] <= 'f':
		case hexPart[i] >= 'A' && hexPart[i] <= 'F':
		default:
			return false
		}
	}

	return true
}

// isValidLength checks if the address has the correct length
func (av *AddressValidator) isValidLength(addressStr string) bool {
	// Ethereum addresses should be 42 characters (0x + 40 hex chars)
	return len(addressStr) == 42
}

// detectCorruption checks for known corruption patterns
func (av *AddressValidator) detectCorruption(addressStr string) (bool, []string) {
	var detectedPatterns []string

	for idx, re := range av.corruptedPatternRegex {
		if re.MatchString(addressStr) {
			detectedPatterns = append(detectedPatterns, av.corruptedPatterns[idx])
		}
	}

	return len(detectedPatterns) > 0, detectedPatterns
}

// calculateCorruptionScore calculates a 0-100 score indicating the likelihood
// that an address has been corrupted or malformed. This scoring system is based
// on patterns observed in production corruption incidents.
//
// Scoring factors:
// - Trailing zeros (indicates truncation): +1 per excess zero
// - Leading zeros in middle (unusual pattern): +0.5 per zero
// - Repetitive patterns (indicates generation errors): +10
// - Other suspicious patterns: variable points
//
// Parameters:
//   - addressStr: The address string to analyze (with 0x prefix)
//
// Returns:
//   - int: Corruption score (0=clean, 100=definitely corrupted)
func (av *AddressValidator) calculateCorruptionScore(addressStr string) int {
	score := 0
	// Extract the hex part (remove 0x prefix)
	hexPart := addressStr[2:]

	// Count trailing zeros (sign of truncation)
	trailingZeros := 0
	for i := len(hexPart) - 1; i >= 0; i-- {
		if hexPart[i] == '0' {
			trailingZeros++
		} else {
			break
		}
	}

	// More than 10 trailing zeros is suspicious
	if trailingZeros > 10 {
		score += trailingZeros
	}

	// Count leading zeros after first non-zero
	leadingZeros := 0
	foundNonZero := false
	for _, char := range hexPart {
		if char != '0' {
			foundNonZero = true
		} else if foundNonZero {
			leadingZeros++
		}
	}

	// Large blocks of zeros in the middle are suspicious
	if leadingZeros > 8 {
		score += leadingZeros / 2
	}

	// Check for repetitive patterns
	if av.hasRepetitivePattern(hexPart) {
		score += 10
	}

	// Overall zero density check for leading-zero patterns (common corruption)
	zeroCount := strings.Count(hexPart, "0")
	if strings.HasPrefix(hexPart, "0000") && float64(zeroCount)/float64(len(hexPart)) > 0.7 {
		score += 30
	}

	// Leading zero prefix (common corruption pattern from truncated data)
	if strings.HasPrefix(hexPart, "000000") {
		score += 20
	}

	return score
}

// hasRepetitivePattern detects repetitive patterns in hex strings that indicate
// corruption or artificial generation. These patterns are rarely seen in legitimate
// Ethereum addresses and often indicate data corruption or malicious generation.
//
// Detected patterns include:
// - Long sequences of the same character (000000000000, ffffffffffff)
// - Addresses where all characters are identical
// - Other suspicious repetitive patterns
//
// Parameters:
//   - hexStr: The hex string to analyze (without 0x prefix)
//
// Returns:
//   - bool: true if repetitive patterns are detected
func (av *AddressValidator) hasRepetitivePattern(hexStr string) bool {
	// Define patterns that indicate corruption or artificial generation
	// These patterns are extremely rare in legitimate Ethereum addresses
	patterns := []string{"000000000000", "ffffffffffff", "aaaaaaaaaaaa", "bbbbbbbbbbbb",
		"1111111111", "2222222222", "3333333333", "4444444444", "5555555555",
		"6666666666", "7777777777", "8888888888", "9999999999"}

	for _, pattern := range patterns {
		if strings.Contains(hexStr, pattern) {
			return true
		}
	}

	// Additional check for address with same character repeated throughout
	if len(hexStr) >= 10 {
		firstChar := hexStr[0]
		allSame := true
		for i := 1; i < len(hexStr); i++ {
			if hexStr[i] != firstChar {
				allSame = false
				break
			}
		}
		if allSame {
			return true
		}
	}

	return false
}

// IsValidPoolAddress checks if an address is valid for pool operations
func (av *AddressValidator) IsValidPoolAddress(address common.Address) bool {
	result := av.ValidateAddress(address.Hex())

	if !result.IsValid {
		return false
	}

	// Must not be a token, router, or factory for pool operations
	switch result.ContractType {
	case ContractTypeERC20Token, ContractTypeRouter, ContractTypeFactory:
		return false
	case ContractTypeUniswapV2Pool, ContractTypeUniswapV3Pool:
		return true
	case ContractTypeUnknown:
		// Allow unknown contracts but warn
		return result.CorruptionScore < 20
	}

	return false
}

// IsValidTokenAddress checks if an address is valid for token operations
func (av *AddressValidator) IsValidTokenAddress(address common.Address) bool {
	result := av.ValidateAddress(address.Hex())

	if !result.IsValid {
		return false
	}

	// Prefer known tokens, but allow unknown contracts with low corruption scores
	switch result.ContractType {
	case ContractTypeERC20Token:
		return true
	case ContractTypeRouter, ContractTypeFactory, ContractTypeUniswapV2Pool, ContractTypeUniswapV3Pool:
		return false
	case ContractTypeUnknown:
		return result.CorruptionScore < 15
	}

	return false
}

// GetContractType returns the contract type for a given address
func (av *AddressValidator) GetContractType(address common.Address) ContractType {
	if contractType, exists := av.knownContracts[address]; exists {
		return contractType
	}
	return ContractTypeUnknown
}

// ValidateContractTypeConsistency validates that addresses don't have conflicting contract types
func (av *AddressValidator) ValidateContractTypeConsistency(tokenAddresses []common.Address, poolAddresses []common.Address) error {
	// CRITICAL: Ensure no address appears in both token and pool lists
	for _, token := range tokenAddresses {
		for _, pool := range poolAddresses {
			if token == pool {
				return fmt.Errorf("address %s cannot be both a token and a pool", token.Hex())
			}
		}
	}

	// CRITICAL: Validate each token address is actually a token
	for _, token := range tokenAddresses {
		if !av.IsValidTokenAddress(token) {
			return fmt.Errorf("address %s is not a valid token address", token.Hex())
		}

		// Additional check: ensure it's not marked as a pool in known contracts
		if contractType := av.GetContractType(token); contractType == ContractTypeUniswapV2Pool || contractType == ContractTypeUniswapV3Pool {
			return fmt.Errorf("address %s is marked as a pool but being used as a token", token.Hex())
		}
	}

	// CRITICAL: Validate each pool address is actually a pool
	for _, pool := range poolAddresses {
		if !av.IsValidPoolAddress(pool) {
			return fmt.Errorf("address %s is not a valid pool address", pool.Hex())
		}

		// Additional check: ensure it's not marked as a token in known contracts
		if contractType := av.GetContractType(pool); contractType == ContractTypeERC20Token {
			return fmt.Errorf("address %s is marked as a token but being used as a pool", pool.Hex())
		}
	}

	return nil
}

// PreventERC20PoolConfusion is a critical safety function that prevents the costly
// error where ERC-20 token contracts are incorrectly used as pool contracts.
// This was the root cause of the 535K+ log spam incident in production.
//
// The function performs a type safety check to ensure that:
// - ERC-20 tokens are not used in pool operations
// - Pool contracts are not used in token operations
// - Unknown contracts meet safety thresholds
//
// This is a mandatory check for all contract address usage in critical operations.
//
// Parameters:
//   - address: The contract address to validate
//   - expectedType: The contract type expected by the calling code
//
// Returns:
//   - error: nil if the address is safe to use, error describing the issue otherwise
func (av *AddressValidator) PreventERC20PoolConfusion(address common.Address, expectedType ContractType) error {
	// Check if we have prior knowledge about this contract
	knownType := av.GetContractType(address)

	// If we have knowledge about this contract, use it
	if knownType != ContractTypeUnknown {
		if knownType != expectedType {
			return fmt.Errorf("contract type mismatch for %s: expected %s but known as %s",
				address.Hex(), contractTypeToString(expectedType), contractTypeToString(knownType))
		}
		return nil
	}

	// For unknown contracts, perform basic validation
	result := av.ValidateAddress(address.Hex())
	if !result.IsValid {
		return fmt.Errorf("invalid address %s: %v", address.Hex(), result.ErrorMessages)
	}

	// High corruption score indicates potential misclassification
	if result.CorruptionScore > 25 {
		return fmt.Errorf("high corruption score (%d) for address %s, refusing to use as %s",
			result.CorruptionScore, address.Hex(), contractTypeToString(expectedType))
	}

	return nil
}

// contractTypeToString converts ContractType to string representation
func contractTypeToString(ct ContractType) string {
	switch ct {
	case ContractTypeERC20Token:
		return "ERC-20 Token"
	case ContractTypeUniswapV2Pool:
		return "Uniswap V2 Pool"
	case ContractTypeUniswapV3Pool:
		return "Uniswap V3 Pool"
	case ContractTypeRouter:
		return "Router"
	case ContractTypeFactory:
		return "Factory"
	default:
		return "Unknown"
	}
}

// IsKnownContract checks if we have specific knowledge about a contract
func (av *AddressValidator) IsKnownContract(address common.Address) bool {
	_, exists := av.knownContracts[address]
	return exists
}

// GetValidationStats returns statistics about validation results
func (av *AddressValidator) GetValidationStats() map[string]interface{} {
	return map[string]interface{}{
		"known_contracts":     len(av.knownContracts),
		"corruption_patterns": len(av.corruptedPatterns),
	}
}

// SanitizeAddress attempts to clean up a potentially corrupted address
func (av *AddressValidator) SanitizeAddress(addressStr string) (string, error) {
	// Remove common prefixes that might be corrupted
	cleaned := strings.TrimSpace(addressStr)

	// Ensure 0x prefix
	if !strings.HasPrefix(cleaned, "0x") && !strings.HasPrefix(cleaned, "0X") {
		if len(cleaned) == 40 && av.isValidHexFormat("0x"+cleaned) {
			cleaned = "0x" + cleaned
		} else {
			return "", fmt.Errorf("cannot sanitize address without 0x prefix")
		}
	}

	// Normalize to lowercase
	cleaned = strings.ToLower(cleaned)

	// Validate the sanitized address
	result := av.ValidateAddress(cleaned)
	if !result.IsValid {
		return "", fmt.Errorf("sanitized address is still invalid: %v", result.ErrorMessages)
	}

	return cleaned, nil
}

// ValidatePoolOperation validates if a pool-specific operation should be allowed on an address
// This prevents the critical error where ERC-20 tokens are treated as pools
func (av *AddressValidator) ValidatePoolOperation(address common.Address, operation string) error {
	// Check if this is a known ERC-20 token
	if av.knownContractsRegistry != nil {
		if err := av.knownContractsRegistry.ValidatePoolCall(address, operation); err != nil {
			return err
		}
	}

	// Additional validation for suspicious addresses
	addressStr := address.Hex()

	// Check for zero address (common corruption)
	if address == (common.Address{}) {
		return fmt.Errorf("pool operation '%s' attempted on zero address (likely corruption)", operation)
	}

	// Check for addresses with excessive zeros (likely corruption)
	if strings.Count(addressStr, "0") > 30 {
		return fmt.Errorf("pool operation '%s' attempted on suspicious address %s (excessive zeros)", operation, addressStr)
	}

	// Fallback to general validation
	result := av.ValidateAddress(addressStr)
	if !result.IsValid {
		return fmt.Errorf("pool operation '%s' attempted on invalid address %s: %v", operation, addressStr, result.ErrorMessages)
	}

	if result.CorruptionScore > 25 {
		return fmt.Errorf("pool operation '%s' blocked due to corruption score %d on address %s", operation, result.CorruptionScore, addressStr)
	}

	return nil
}

// GetDetailedAddressAnalysis provides comprehensive analysis of an address including corruption patterns
func (av *AddressValidator) GetDetailedAddressAnalysis(address common.Address) map[string]interface{} {
	analysis := make(map[string]interface{})
	addressStr := address.Hex()

	// Basic validation
	result := av.ValidateAddress(addressStr)
	analysis["is_valid"] = result.IsValid
	analysis["corruption_score"] = result.CorruptionScore
	analysis["contract_type"] = result.ContractType.String()
	analysis["error_messages"] = result.ErrorMessages

	// Known contract information
	if av.knownContractsRegistry != nil {
		contractType, name := av.knownContractsRegistry.GetContractType(address)
		analysis["known_contract_type"] = contractType.String()
		analysis["known_contract_name"] = name

		isERC20, tokenName := av.knownContractsRegistry.IsKnownERC20(address)
		analysis["is_known_erc20"] = isERC20
		if isERC20 {
			analysis["token_name"] = tokenName
		}

		// Corruption pattern analysis
		corruptionPattern := av.knownContractsRegistry.GetCorruptionPattern(address)
		analysis["corruption_pattern"] = corruptionPattern
	}

	// Address characteristics
	analysis["is_zero_address"] = address == (common.Address{})
	analysis["zero_count"] = strings.Count(addressStr, "0")
	analysis["hex_length"] = len(addressStr)

	return analysis
}