package contracts

import (
	"context"
	"fmt"

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

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

// FunctionSignature represents a known function signature
type FunctionSignature struct {
	Name         string
	Selector     []byte
	AllowedTypes []ContractType
}

// SignatureValidator validates function calls against contract types
type SignatureValidator struct {
	detector   *ContractDetector
	logger     *logger.Logger
	signatures map[string]*FunctionSignature
}

// NewSignatureValidator creates a new function signature validator
func NewSignatureValidator(detector *ContractDetector, logger *logger.Logger) *SignatureValidator {
	sv := &SignatureValidator{
		detector:   detector,
		logger:     logger,
		signatures: make(map[string]*FunctionSignature),
	}

	// Initialize known function signatures
	sv.initializeSignatures()
	return sv
}

// initializeSignatures initializes the known function signatures and their allowed contract types
func (sv *SignatureValidator) initializeSignatures() {
	// ERC-20 token functions
	sv.signatures["name()"] = &FunctionSignature{
		Name:         "name()",
		Selector:     []byte{0x06, 0xfd, 0xde, 0x03},
		AllowedTypes: []ContractType{ContractTypeERC20Token},
	}
	sv.signatures["symbol()"] = &FunctionSignature{
		Name:         "symbol()",
		Selector:     []byte{0x95, 0xd8, 0x9b, 0x41},
		AllowedTypes: []ContractType{ContractTypeERC20Token},
	}
	sv.signatures["decimals()"] = &FunctionSignature{
		Name:         "decimals()",
		Selector:     []byte{0x31, 0x3c, 0xe5, 0x67},
		AllowedTypes: []ContractType{ContractTypeERC20Token},
	}
	sv.signatures["totalSupply()"] = &FunctionSignature{
		Name:         "totalSupply()",
		Selector:     []byte{0x18, 0x16, 0x0d, 0xdd},
		AllowedTypes: []ContractType{ContractTypeERC20Token},
	}
	sv.signatures["balanceOf()"] = &FunctionSignature{
		Name:         "balanceOf()",
		Selector:     []byte{0x70, 0xa0, 0x82, 0x31},
		AllowedTypes: []ContractType{ContractTypeERC20Token},
	}

	// Uniswap V2 Pool functions
	sv.signatures["token0()"] = &FunctionSignature{
		Name:     "token0()",
		Selector: []byte{0x0d, 0xfe, 0x16, 0x81},
		AllowedTypes: []ContractType{
			ContractTypeUniswapV2Pool,
			ContractTypeUniswapV3Pool,
		},
	}
	sv.signatures["token1()"] = &FunctionSignature{
		Name:     "token1()",
		Selector: []byte{0xd2, 0x12, 0x20, 0xa7},
		AllowedTypes: []ContractType{
			ContractTypeUniswapV2Pool,
			ContractTypeUniswapV3Pool,
		},
	}
	sv.signatures["getReserves()"] = &FunctionSignature{
		Name:         "getReserves()",
		Selector:     []byte{0x09, 0x02, 0xf1, 0xac},
		AllowedTypes: []ContractType{ContractTypeUniswapV2Pool},
	}

	// Uniswap V3 Pool specific functions
	sv.signatures["slot0()"] = &FunctionSignature{
		Name:         "slot0()",
		Selector:     []byte{0x38, 0x50, 0xc7, 0xbd},
		AllowedTypes: []ContractType{ContractTypeUniswapV3Pool},
	}
	sv.signatures["fee()"] = &FunctionSignature{
		Name:         "fee()",
		Selector:     []byte{0xdd, 0xca, 0x3f, 0x43},
		AllowedTypes: []ContractType{ContractTypeUniswapV3Pool},
	}
	sv.signatures["liquidity()"] = &FunctionSignature{
		Name:         "liquidity()",
		Selector:     []byte{0x1a, 0x68, 0x65, 0x0f},
		AllowedTypes: []ContractType{ContractTypeUniswapV3Pool},
	}
	sv.signatures["tickSpacing()"] = &FunctionSignature{
		Name:         "tickSpacing()",
		Selector:     []byte{0xd0, 0xc9, 0x32, 0x07},
		AllowedTypes: []ContractType{ContractTypeUniswapV3Pool},
	}

	// Router functions
	sv.signatures["WETH()"] = &FunctionSignature{
		Name:     "WETH()",
		Selector: []byte{0xad, 0x5c, 0x46, 0x48},
		AllowedTypes: []ContractType{
			ContractTypeUniswapV2Router,
			ContractTypeUniswapV3Router,
		},
	}
	sv.signatures["factory()"] = &FunctionSignature{
		Name:     "factory()",
		Selector: []byte{0xc4, 0x5a, 0x01, 0x55},
		AllowedTypes: []ContractType{
			ContractTypeUniswapV2Router,
			ContractTypeUniswapV3Router,
		},
	}
}

// ValidationResult contains the result of function signature validation
type ValidationResult struct {
	IsValid      bool
	FunctionName string
	ContractType ContractType
	Error        error
	Warnings     []string
}

// ValidateFunctionCall validates if a function can be called on a contract
func (sv *SignatureValidator) ValidateFunctionCall(ctx context.Context, contractAddress common.Address, functionSelector []byte) *ValidationResult {
	result := &ValidationResult{
		IsValid:  false,
		Warnings: []string{},
	}

	// Detect contract type
	detection := sv.detector.DetectContractType(ctx, contractAddress)
	result.ContractType = detection.ContractType

	if detection.Error != nil {
		result.Error = fmt.Errorf("contract type detection failed: %w", detection.Error)
		return result
	}

	// Find matching function signature
	var matchedSignature *FunctionSignature
	for _, sig := range sv.signatures {
		if len(sig.Selector) >= 4 && len(functionSelector) >= 4 {
			if sig.Selector[0] == functionSelector[0] &&
				sig.Selector[1] == functionSelector[1] &&
				sig.Selector[2] == functionSelector[2] &&
				sig.Selector[3] == functionSelector[3] {
				matchedSignature = sig
				result.FunctionName = sig.Name
				break
			}
		}
	}

	// If no signature match found, warn but allow (could be unknown function)
	if matchedSignature == nil {
		result.IsValid = true
		result.Warnings = append(result.Warnings, fmt.Sprintf("unknown function selector: %x", functionSelector))
		return result
	}

	// Check if the detected contract type is allowed for this function
	allowed := false
	for _, allowedType := range matchedSignature.AllowedTypes {
		if detection.ContractType == allowedType {
			allowed = true
			break
		}
	}

	if !allowed {
		result.Error = fmt.Errorf("function %s cannot be called on contract type %s (allowed types: %v)",
			matchedSignature.Name, detection.ContractType.String(), matchedSignature.AllowedTypes)
		return result
	}

	// Check confidence level
	if detection.Confidence < 0.7 {
		result.Warnings = append(result.Warnings, fmt.Sprintf("low confidence in contract type detection: %.2f", detection.Confidence))
	}

	result.IsValid = true
	return result
}

// ValidateToken0Call specifically validates token0() function calls
func (sv *SignatureValidator) ValidateToken0Call(ctx context.Context, contractAddress common.Address) *ValidationResult {
	token0Selector := []byte{0x0d, 0xfe, 0x16, 0x81}
	return sv.ValidateFunctionCall(ctx, contractAddress, token0Selector)
}

// ValidateToken1Call specifically validates token1() function calls
func (sv *SignatureValidator) ValidateToken1Call(ctx context.Context, contractAddress common.Address) *ValidationResult {
	token1Selector := []byte{0xd2, 0x12, 0x20, 0xa7}
	return sv.ValidateFunctionCall(ctx, contractAddress, token1Selector)
}

// ValidateGetReservesCall specifically validates getReserves() function calls
func (sv *SignatureValidator) ValidateGetReservesCall(ctx context.Context, contractAddress common.Address) *ValidationResult {
	getReservesSelector := []byte{0x09, 0x02, 0xf1, 0xac}
	return sv.ValidateFunctionCall(ctx, contractAddress, getReservesSelector)
}

// ValidateSlot0Call specifically validates slot0() function calls for Uniswap V3
func (sv *SignatureValidator) ValidateSlot0Call(ctx context.Context, contractAddress common.Address) *ValidationResult {
	slot0Selector := []byte{0x38, 0x50, 0xc7, 0xbd}
	return sv.ValidateFunctionCall(ctx, contractAddress, slot0Selector)
}

// GetSupportedFunctions returns the functions supported by a contract type
func (sv *SignatureValidator) GetSupportedFunctions(contractType ContractType) []string {
	var functions []string
	for _, sig := range sv.signatures {
		for _, allowedType := range sig.AllowedTypes {
			if allowedType == contractType {
				functions = append(functions, sig.Name)
				break
			}
		}
	}
	return functions
}