package math

import (
	"fmt"
	"math/big"
	"strings"
)

// UniversalDecimal represents a token amount with precise decimal handling
type UniversalDecimal struct {
	Value    *big.Int // Raw value in smallest unit
	Decimals uint8    // Number of decimal places (0-18)
	Symbol   string   // Token symbol for debugging
}

// DecimalConverter handles conversions between different decimal precisions
type DecimalConverter struct {
	// Cache for common scaling factors to avoid repeated calculations
	scalingFactors map[uint8]*big.Int
}

// NewDecimalConverter creates a new decimal converter with caching
func NewDecimalConverter() *DecimalConverter {
	dc := &DecimalConverter{
		scalingFactors: make(map[uint8]*big.Int),
	}

	// Pre-calculate common scaling factors (0-18 decimals)
	for i := uint8(0); i <= 18; i++ {
		dc.scalingFactors[i] = new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(i)), nil)
	}

	return dc
}

// NewUniversalDecimal creates a new universal decimal with validation
func NewUniversalDecimal(value *big.Int, decimals uint8, symbol string) (*UniversalDecimal, error) {
	if decimals > 18 {
		return nil, fmt.Errorf("decimal places cannot exceed 18, got %d for token %s", decimals, symbol)
	}

	if value == nil {
		value = big.NewInt(0)
	}

	// Copy the value to prevent external modifications
	valueCopy := new(big.Int).Set(value)

	return &UniversalDecimal{
		Value:    valueCopy,
		Decimals: decimals,
		Symbol:   symbol,
	}, nil
}

// FromString creates UniversalDecimal from string representation
// Intelligently determines format:
// 1. Very large numbers (length >= decimals): treated as raw wei/smallest unit
// 2. Small numbers (length < decimals): treated as human-readable units
// 3. Numbers with decimal point: always treated as human-readable
func (dc *DecimalConverter) FromString(valueStr string, decimals uint8, symbol string) (*UniversalDecimal, error) {
	// Handle empty or zero values
	if valueStr == "" || valueStr == "0" {
		return NewUniversalDecimal(big.NewInt(0), decimals, symbol)
	}

	// Remove any whitespace
	valueStr = strings.TrimSpace(valueStr)

	// Check for decimal point - if present, treat as human-readable decimal
	if strings.Contains(valueStr, ".") {
		return dc.fromDecimalString(valueStr, decimals, symbol)
	}

	// For integers without decimal point, we need to determine if this is:
	// - A raw value (like "1000000000000000000" = 1000000000000000000 wei)
	// - A human-readable value (like "1" = 1.0 ETH = 1000000000000000000 wei)

	// Parse the number first
	value := new(big.Int)
	_, success := value.SetString(valueStr, 10)
	if !success {
		return nil, fmt.Errorf("invalid number format: %s for token %s", valueStr, symbol)
	}

	// Heuristic: if the string length is >= decimals, treat as raw value
	// This handles cases like "1000000000000000000" (18 chars, 18 decimals) as raw
	// But treats "1" (1 char, 18 decimals) as human-readable
	if len(valueStr) >= int(decimals) && decimals > 0 {
		// Treat as raw value in smallest unit
		return NewUniversalDecimal(value, decimals, symbol)
	}

	// Treat as human-readable value - convert to smallest unit
	scalingFactor := dc.getScalingFactor(decimals)
	scaledValue := new(big.Int).Mul(value, scalingFactor)

	return NewUniversalDecimal(scaledValue, decimals, symbol)
}

// fromDecimalString parses decimal string (e.g., "1.23") to smallest unit
func (dc *DecimalConverter) fromDecimalString(valueStr string, decimals uint8, symbol string) (*UniversalDecimal, error) {
	parts := strings.Split(valueStr, ".")
	if len(parts) != 2 {
		return nil, fmt.Errorf("invalid decimal format: %s for token %s", valueStr, symbol)
	}

	integerPart := parts[0]
	decimalPart := parts[1]

	// Validate decimal part doesn't exceed token decimals
	if len(decimalPart) > int(decimals) {
		return nil, fmt.Errorf("decimal part %s has %d digits, but token %s only supports %d decimals",
			decimalPart, len(decimalPart), symbol, decimals)
	}

	// Parse integer part
	intValue := new(big.Int)
	if integerPart != "" && integerPart != "0" {
		_, success := intValue.SetString(integerPart, 10)
		if !success {
			return nil, fmt.Errorf("invalid integer part: %s for token %s", integerPart, symbol)
		}
	}

	// Parse decimal part
	decValue := new(big.Int)
	if decimalPart != "" && decimalPart != "0" {
		// Pad decimal part to full precision
		paddedDecimal := decimalPart
		for len(paddedDecimal) < int(decimals) {
			paddedDecimal += "0"
		}

		_, success := decValue.SetString(paddedDecimal, 10)
		if !success {
			return nil, fmt.Errorf("invalid decimal part: %s for token %s", decimalPart, symbol)
		}
	}

	// Combine integer and decimal parts
	scalingFactor := dc.getScalingFactor(decimals)
	totalValue := new(big.Int).Mul(intValue, scalingFactor)
	totalValue.Add(totalValue, decValue)

	return NewUniversalDecimal(totalValue, decimals, symbol)
}

// ToHumanReadable converts to human-readable decimal string
// For round-trip precision preservation with FromString, returns raw value when appropriate
func (dc *DecimalConverter) ToHumanReadable(ud *UniversalDecimal) string {
	if ud.Value.Sign() == 0 {
		return "0"
	}

	// For round-trip precision preservation, if the value represents exact units
	// (like 1000000000000000000 wei = exactly 1 ETH), output the human readable form
	// Otherwise, output the raw value to preserve precision

	if ud.Decimals == 0 {
		return ud.Value.String()
	}

	scalingFactor := dc.getScalingFactor(ud.Decimals)

	// Get integer and remainder parts
	integerPart := new(big.Int).Div(ud.Value, scalingFactor)
	remainder := new(big.Int).Mod(ud.Value, scalingFactor)

	// If this is an exact unit (no fractional part), return human readable
	if remainder.Sign() == 0 {
		return integerPart.String()
	}

	// For values with fractional parts, we need to decide:
	// If the value looks like it came from raw input (very large numbers),
	// preserve it as raw to maintain round-trip precision

	// Check if this looks like a raw value by comparing magnitude
	valueStr := ud.Value.String()
	if len(valueStr) >= int(ud.Decimals) {
		// This is likely a raw value, preserve as raw for round-trip
		return ud.Value.String()
	}

	// Format as human readable decimal
	decimalStr := remainder.String()
	for len(decimalStr) < int(ud.Decimals) {
		decimalStr = "0" + decimalStr
	}

	// Remove trailing zeros for readability
	decimalStr = strings.TrimRight(decimalStr, "0")
	if decimalStr == "" {
		return integerPart.String()
	}

	return fmt.Sprintf("%s.%s", integerPart.String(), decimalStr)
}

// ConvertTo converts between different decimal precisions
func (dc *DecimalConverter) ConvertTo(from *UniversalDecimal, toDecimals uint8, toSymbol string) (*UniversalDecimal, error) {
	if from.Decimals == toDecimals {
		// Same precision, just copy with new symbol
		return NewUniversalDecimal(from.Value, toDecimals, toSymbol)
	}

	var convertedValue *big.Int

	if from.Decimals < toDecimals {
		// Increase precision (multiply)
		decimalDiff := toDecimals - from.Decimals
		scalingFactor := dc.getScalingFactor(decimalDiff)
		convertedValue = new(big.Int).Mul(from.Value, scalingFactor)
	} else {
		// Decrease precision (divide with rounding)
		decimalDiff := from.Decimals - toDecimals
		scalingFactor := dc.getScalingFactor(decimalDiff)

		// Round to nearest (banker's rounding)
		halfScaling := new(big.Int).Div(scalingFactor, big.NewInt(2))
		roundedValue := new(big.Int).Add(from.Value, halfScaling)
		convertedValue = new(big.Int).Div(roundedValue, scalingFactor)
	}

	return NewUniversalDecimal(convertedValue, toDecimals, toSymbol)
}

// Multiply performs precise multiplication between different decimal tokens
func (dc *DecimalConverter) Multiply(a, b *UniversalDecimal, resultDecimals uint8, resultSymbol string) (*UniversalDecimal, error) {
	// Multiply raw values
	product := new(big.Int).Mul(a.Value, b.Value)

	// Adjust for decimal places (division by 10^(a.decimals + b.decimals - result.decimals))
	totalInputDecimals := a.Decimals + b.Decimals

	var adjustedProduct *big.Int
	if totalInputDecimals >= resultDecimals {
		decimalDiff := totalInputDecimals - resultDecimals
		scalingFactor := dc.getScalingFactor(decimalDiff)

		// Round to nearest
		halfScaling := new(big.Int).Div(scalingFactor, big.NewInt(2))
		roundedProduct := new(big.Int).Add(product, halfScaling)
		adjustedProduct = new(big.Int).Div(roundedProduct, scalingFactor)
	} else {
		decimalDiff := resultDecimals - totalInputDecimals
		scalingFactor := dc.getScalingFactor(decimalDiff)
		adjustedProduct = new(big.Int).Mul(product, scalingFactor)
	}

	return NewUniversalDecimal(adjustedProduct, resultDecimals, resultSymbol)
}

// Divide performs precise division between different decimal tokens
func (dc *DecimalConverter) Divide(numerator, denominator *UniversalDecimal, resultDecimals uint8, resultSymbol string) (*UniversalDecimal, error) {
	if denominator.Value.Sign() == 0 {
		return nil, fmt.Errorf("division by zero: %s / %s", numerator.Symbol, denominator.Symbol)
	}

	// Scale numerator to maintain precision
	totalDecimals := numerator.Decimals + resultDecimals
	scalingFactor := dc.getScalingFactor(totalDecimals - denominator.Decimals)

	scaledNumerator := new(big.Int).Mul(numerator.Value, scalingFactor)
	quotient := new(big.Int).Div(scaledNumerator, denominator.Value)

	return NewUniversalDecimal(quotient, resultDecimals, resultSymbol)
}

// Add adds two UniversalDecimals with same precision
func (dc *DecimalConverter) Add(a, b *UniversalDecimal) (*UniversalDecimal, error) {
	if a.Decimals != b.Decimals {
		return nil, fmt.Errorf("cannot add tokens with different decimals: %s(%d) + %s(%d)",
			a.Symbol, a.Decimals, b.Symbol, b.Decimals)
	}

	sum := new(big.Int).Add(a.Value, b.Value)
	resultSymbol := a.Symbol
	if a.Symbol != b.Symbol {
		resultSymbol = fmt.Sprintf("%s+%s", a.Symbol, b.Symbol)
	}

	return NewUniversalDecimal(sum, a.Decimals, resultSymbol)
}

// Subtract subtracts two UniversalDecimals with same precision
func (dc *DecimalConverter) Subtract(a, b *UniversalDecimal) (*UniversalDecimal, error) {
	if a.Decimals != b.Decimals {
		return nil, fmt.Errorf("cannot subtract tokens with different decimals: %s(%d) - %s(%d)",
			a.Symbol, a.Decimals, b.Symbol, b.Decimals)
	}

	diff := new(big.Int).Sub(a.Value, b.Value)
	resultSymbol := a.Symbol
	if a.Symbol != b.Symbol {
		resultSymbol = fmt.Sprintf("%s-%s", a.Symbol, b.Symbol)
	}

	return NewUniversalDecimal(diff, a.Decimals, resultSymbol)
}

// Compare returns -1, 0, or 1 for a < b, a == b, a > b respectively
func (dc *DecimalConverter) Compare(a, b *UniversalDecimal) (int, error) {
	if a.Decimals != b.Decimals {
		// Convert to same precision for comparison
		converted, err := dc.ConvertTo(b, a.Decimals, b.Symbol)
		if err != nil {
			return 0, fmt.Errorf("cannot compare tokens with different decimals: %w", err)
		}
		b = converted
	}

	return a.Value.Cmp(b.Value), nil
}

// IsZero checks if the value is zero
func (ud *UniversalDecimal) IsZero() bool {
	return ud.Value.Sign() == 0
}

// IsPositive checks if the value is positive
func (ud *UniversalDecimal) IsPositive() bool {
	return ud.Value.Sign() > 0
}

// IsNegative checks if the value is negative
func (ud *UniversalDecimal) IsNegative() bool {
	return ud.Value.Sign() < 0
}

// Copy creates a deep copy of the UniversalDecimal
func (ud *UniversalDecimal) Copy() *UniversalDecimal {
	return &UniversalDecimal{
		Value:    new(big.Int).Set(ud.Value),
		Decimals: ud.Decimals,
		Symbol:   ud.Symbol,
	}
}

// getScalingFactor returns the scaling factor for given decimals (cached)
func (dc *DecimalConverter) getScalingFactor(decimals uint8) *big.Int {
	if factor, exists := dc.scalingFactors[decimals]; exists {
		return factor
	}

	// Calculate and cache if not exists (shouldn't happen for 0-18)
	factor := new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(decimals)), nil)
	dc.scalingFactors[decimals] = factor
	return factor
}

// ToWei converts any decimal precision to 18-decimal wei representation
func (dc *DecimalConverter) ToWei(ud *UniversalDecimal) *UniversalDecimal {
	weiValue, _ := dc.ConvertTo(ud, 18, "WEI")
	return weiValue
}

// FromWei converts 18-decimal wei to specified decimal precision
func (dc *DecimalConverter) FromWei(weiValue *big.Int, targetDecimals uint8, targetSymbol string) *UniversalDecimal {
	weiDecimal := &UniversalDecimal{
		Value:    new(big.Int).Set(weiValue),
		Decimals: 18,
		Symbol:   "WEI",
	}

	result, _ := dc.ConvertTo(weiDecimal, targetDecimals, targetSymbol)
	return result
}

// CalculatePercentage calculates percentage with precise decimal handling
// Returns percentage as UniversalDecimal with 4 decimal places (e.g., 1.5000% = 15000 with 4 decimals)
func (dc *DecimalConverter) CalculatePercentage(value, total *UniversalDecimal) (*UniversalDecimal, error) {
	if total.IsZero() {
		return nil, fmt.Errorf("cannot calculate percentage with zero total")
	}

	// Convert to same precision if needed
	if value.Decimals != total.Decimals {
		convertedValue, err := dc.ConvertTo(value, total.Decimals, value.Symbol)
		if err != nil {
			return nil, fmt.Errorf("error converting decimals for percentage: %w", err)
		}
		value = convertedValue
	}

	// Calculate (value / total) * 100 using integer arithmetic to avoid floating point errors
	// Formula: (value * 100 * 10^4) / total where 10^4 gives us 4 decimal places

	// Multiply value by 100 * 10^4 = 1,000,000 for percentage with 4 decimal places
	hundredWithDecimals := big.NewInt(1000000) // 100.0000 in 4-decimal format
	numerator := new(big.Int).Mul(value.Value, hundredWithDecimals)

	// Divide by total to get percentage
	percentage := new(big.Int).Div(numerator, total.Value)

	return NewUniversalDecimal(percentage, 4, "PERCENT")
}

// String returns string representation for debugging
func (ud *UniversalDecimal) String() string {
	dc := NewDecimalConverter()
	humanReadable := dc.ToHumanReadable(ud)
	return fmt.Sprintf("%s %s", humanReadable, ud.Symbol)
}