package match

import (
	"fmt"
	"math"

	"github.com/damirmukimov/city_resource_graph/models/transport"
)

// EconomicCalculation represents the economic viability calculations for a match
// Based on economic_calculation.json schema
type EconomicCalculation struct {
	MatchID        string                 `json:"match_id"`
	SourceResource ResourceFlowSummary    `json:"source_resource"`
	TargetResource ResourceFlowSummary    `json:"target_resource"`
	Calculations   MatchCalculations      `json:"calculations"`
	Assumptions    CalculationAssumptions `json:"assumptions"`
}

// ResourceFlowSummary represents a simplified resource flow for matching
type ResourceFlowSummary struct {
	ID          string  `json:"id"`
	Type        string  `json:"type"`
	Direction   string  `json:"direction"`
	Quantity    float64 `json:"quantity"`
	Unit        string  `json:"unit"`
	CostPerUnit float64 `json:"cost_per_unit"`
}

// MatchCalculations contains all economic calculations for a match
type MatchCalculations struct {
	AnnualSavings            float64                `json:"annual_savings"`
	PaybackPeriodYears       float64                `json:"payback_period_years"`
	NPV10Years               float64                `json:"npv_10_years"`
	IRRPercent               float64                `json:"irr_percent"`
	TransportationCosts      TransportationEstimate `json:"transportation_costs"`
	CO2ReductionTonnes       float64                `json:"co2_reduction_tonnes"`
	ImplementationComplexity string                 `json:"implementation_complexity"`
	RegulatoryRequirements   []string               `json:"regulatory_requirements"`
}

// TransportationEstimate represents transportation cost estimates for a match
type TransportationEstimate struct {
	AnnualCost  float64 `json:"annual_cost"`
	DistanceKm  float64 `json:"distance_km"`
	Method      string  `json:"method"`
	Feasibility float64 `json:"feasibility_score"` // 0-1 scale
}

// CalculationAssumptions contains the assumptions used in calculations
type CalculationAssumptions struct {
	DiscountRate          float64 `json:"discount_rate"`
	OperatingHoursYear    int     `json:"operating_hours_year"`
	MaintenanceCostFactor float64 `json:"maintenance_cost_factor"`
	EnergyCostInflation   float64 `json:"energy_cost_inflation"`
}

// MatchEconomicsParams contains parameters for match economic calculations
type MatchEconomicsParams struct {
	SourceResource     ResourceFlowSummary
	TargetResource     ResourceFlowSummary
	DistanceKm         float64
	InitialInvestment  float64 // One-time setup costs
	SymbiosisType      transport.SymbiosisType
	Complexity         string
	RiskLevel          string
	AnnualQuantity     float64 // Units exchanged per year
	UnitValue          float64 // € per unit exchanged
	CO2ReductionFactor float64 // tonnes CO2 per unit exchanged
}

// DefaultCalculationAssumptions returns standard assumptions for calculations
func DefaultCalculationAssumptions() CalculationAssumptions {
	return CalculationAssumptions{
		DiscountRate:          0.08, // 8% discount rate
		OperatingHoursYear:    8000, // 8000 hours/year
		MaintenanceCostFactor: 0.05, // 5% of capital annually
		EnergyCostInflation:   0.02, // 2% annual inflation
	}
}

// CalculateMatchEconomics computes all economic metrics for a potential match
func CalculateMatchEconomics(params MatchEconomicsParams, assumptions CalculationAssumptions) (*EconomicCalculation, error) {
	if params.SourceResource.ID == "" || params.TargetResource.ID == "" {
		return nil, fmt.Errorf("source and target resource IDs are required")
	}

	// Calculate annual savings (cost reduction for source, value creation for target)
	annualSavings := calculateAnnualSavings(params)

	// Calculate transportation costs using the exchange cost calculator
	transportCost, err := calculateTransportationCost(params)
	if err != nil {
		return nil, fmt.Errorf("failed to calculate transportation cost: %w", err)
	}

	// Calculate CO2 reduction
	co2Reduction := params.AnnualQuantity * params.CO2ReductionFactor

	// Calculate implementation complexity
	complexity := assessImplementationComplexity(params)

	// Identify regulatory requirements
	regulatoryReqs := identifyRegulatoryRequirements(params)

	// Calculate NPV over 10 years
	npv10Years := calculateMatchNPV(params, assumptions, annualSavings, transportCost.AnnualCost)

	// Calculate IRR
	irrPercent := calculateMatchIRR(params, assumptions, annualSavings, transportCost.AnnualCost)

	// Calculate payback period
	paybackYears := calculatePaybackPeriod(params.InitialInvestment, annualSavings-transportCost.AnnualCost)

	calculations := MatchCalculations{
		AnnualSavings:            annualSavings,
		PaybackPeriodYears:       paybackYears,
		NPV10Years:               npv10Years,
		IRRPercent:               irrPercent * 100, // Convert to percentage
		TransportationCosts:      *transportCost,
		CO2ReductionTonnes:       co2Reduction,
		ImplementationComplexity: complexity,
		RegulatoryRequirements:   regulatoryReqs,
	}

	result := &EconomicCalculation{
		MatchID:        generateMatchID(params.SourceResource.ID, params.TargetResource.ID),
		SourceResource: params.SourceResource,
		TargetResource: params.TargetResource,
		Calculations:   calculations,
		Assumptions:    assumptions,
	}

	return result, nil
}

// calculateAnnualSavings calculates the annual cost savings or value creation from the match
func calculateAnnualSavings(params MatchEconomicsParams) float64 {
	// For waste-to-resource matches, savings = source disposal cost reduction + target value creation
	sourceSavings := params.SourceResource.CostPerUnit * params.AnnualQuantity // Avoid disposal costs
	targetValue := params.TargetResource.CostPerUnit * params.AnnualQuantity   // Value of resource to target

	return sourceSavings + targetValue
}

// calculateTransportationCost uses the exchange cost calculator to determine transport costs
func calculateTransportationCost(params MatchEconomicsParams) (*TransportationEstimate, error) {
	exchangeParams := transport.ExchangeParams{
		DistanceKm:    params.DistanceKm,
		Value:         params.UnitValue * params.AnnualQuantity, // Annual exchange value
		Volume:        params.AnnualQuantity,
		SymbiosisType: params.SymbiosisType,
		Complexity:    params.Complexity,
		RiskLevel:     params.RiskLevel,
	}

	cost, err := transport.CalculateExchangeCost(exchangeParams)
	if err != nil {
		return nil, err
	}

	estimate := &TransportationEstimate{
		AnnualCost:  cost.TotalAnnualCost,
		DistanceKm:  params.DistanceKm,
		Method:      determineTransportMethod(params.SymbiosisType),
		Feasibility: feasibilityToScore(cost.Feasibility),
	}

	return estimate, nil
}

// calculateMatchNPV calculates Net Present Value for the match over 10 years
func calculateMatchNPV(params MatchEconomicsParams, assumptions CalculationAssumptions,
	annualSavings, annualTransportCost float64) float64 {

	npv := -params.InitialInvestment // Initial investment (negative cash flow)

	annualNetBenefit := annualSavings - annualTransportCost
	maintenanceCost := params.InitialInvestment * assumptions.MaintenanceCostFactor

	for year := 1; year <= 10; year++ {
		// Apply energy cost inflation to benefits
		inflatedBenefit := annualNetBenefit * math.Pow(1+assumptions.EnergyCostInflation, float64(year-1))
		annualMaintenance := maintenanceCost * math.Pow(1+assumptions.EnergyCostInflation, float64(year-1))

		cashFlow := inflatedBenefit - annualMaintenance
		npv += cashFlow / math.Pow(1+assumptions.DiscountRate, float64(year))
	}

	return npv
}

// calculateMatchIRR calculates Internal Rate of Return for the match
func calculateMatchIRR(params MatchEconomicsParams, assumptions CalculationAssumptions,
	annualSavings, annualTransportCost float64) float64 {

	// Create cash flow array
	cashFlows := make([]float64, 11) // Year 0 to 10
	cashFlows[0] = -params.InitialInvestment

	annualNetBenefit := annualSavings - annualTransportCost
	maintenanceCost := params.InitialInvestment * assumptions.MaintenanceCostFactor

	for year := 1; year <= 10; year++ {
		inflatedBenefit := annualNetBenefit * math.Pow(1+assumptions.EnergyCostInflation, float64(year-1))
		annualMaintenance := maintenanceCost * math.Pow(1+assumptions.EnergyCostInflation, float64(year-1))
		cashFlows[year] = inflatedBenefit - annualMaintenance
	}

	// Use Newton's method to find IRR
	return calculateIRR(cashFlows)
}

// calculateIRR implements Newton's method to find IRR
func calculateIRR(cashFlows []float64) float64 {
	irr := 0.1 // Initial guess: 10%

	maxIterations := 1000
	tolerance := 0.00001

	for i := 0; i < maxIterations; i++ {
		npv := 0.0
		derivative := 0.0

		for t, cf := range cashFlows {
			if t == 0 {
				npv += cf
				derivative -= float64(t+1) * cf / math.Pow(1+irr, float64(t+2))
			} else {
				npv += cf / math.Pow(1+irr, float64(t))
				derivative -= float64(t) * cf / math.Pow(1+irr, float64(t+1))
			}
		}

		if math.Abs(npv) < tolerance {
			return irr
		}

		if derivative == 0 {
			return 0.0 // Cannot converge
		}

		irr = irr - npv/derivative
	}

	return irr // Return best approximation
}

// calculatePaybackPeriod calculates the payback period in years
func calculatePaybackPeriod(initialInvestment, annualNetCashFlow float64) float64 {
	if annualNetCashFlow <= 0 {
		return 999 // Never pays back
	}

	years := initialInvestment / annualNetCashFlow

	// Cap at 10 years for practicality
	if years > 10 {
		return 999
	}

	return years
}

// assessImplementationComplexity determines implementation complexity
func assessImplementationComplexity(params MatchEconomicsParams) string {
	score := 0.0

	// Distance factor
	if params.DistanceKm > 25 {
		score += 2.0
	} else if params.DistanceKm > 5 {
		score += 1.0
	}

	// Resource type complexity
	switch params.SymbiosisType {
	case transport.SymbiosisWasteToResource, transport.SymbiosisMaterialRecycling:
		score += 1.5 // Complex regulatory requirements
	case transport.SymbiosisEnergyCascading, transport.SymbiosisUtilitySharing:
		score += 1.0 // Moderate technical complexity
	}

	// Investment size
	if params.InitialInvestment > 50000 {
		score += 1.0
	}

	if score >= 3.0 {
		return "high"
	} else if score >= 1.5 {
		return "medium"
	}
	return "low"
}

// identifyRegulatoryRequirements determines required permits and approvals
func identifyRegulatoryRequirements(params MatchEconomicsParams) []string {
	requirements := []string{}

	// Waste and material handling always requires permits
	if params.SymbiosisType == transport.SymbiosisWasteToResource ||
		params.SymbiosisType == transport.SymbiosisMaterialRecycling {
		requirements = append(requirements, "waste_disposal_permit")
		requirements = append(requirements, "environmental_impact_assessment")
	}

	// Energy transfers may require grid connection permits
	if params.SymbiosisType == transport.SymbiosisEnergyCascading ||
		params.SymbiosisType == transport.SymbiosisUtilitySharing {
		requirements = append(requirements, "energy_distribution_license")
	}

	// Long distance transport may require additional permits
	if params.DistanceKm > 50 {
		requirements = append(requirements, "transport_license")
	}

	// High value exchanges may require insurance
	if params.UnitValue*params.AnnualQuantity > 100000 {
		requirements = append(requirements, "liability_insurance")
	}

	return requirements
}

// determineTransportMethod suggests the appropriate transport method
func determineTransportMethod(symbiosisType transport.SymbiosisType) string {
	switch symbiosisType {
	case transport.SymbiosisWasteToResource, transport.SymbiosisMaterialRecycling:
		return "truck"
	case transport.SymbiosisEnergyCascading, transport.SymbiosisUtilitySharing:
		if symbiosisType == transport.SymbiosisEnergyCascading {
			return "heat_pipe"
		}
		return "pipeline"
	case transport.SymbiosisDataSharing, transport.SymbiosisIoTNetwork, transport.SymbiosisSoftwareLicenses:
		return "network"
	default:
		return "truck"
	}
}

// feasibilityToScore converts feasibility string to numeric score
func feasibilityToScore(feasibility string) float64 {
	switch feasibility {
	case "high":
		return 0.9
	case "medium":
		return 0.6
	case "low":
		return 0.3
	default:
		return 0.5
	}
}

// generateMatchID creates a unique match identifier
func generateMatchID(sourceID, targetID string) string {
	return fmt.Sprintf("match_%s_%s", sourceID, targetID)
}

// ValidateEconomicCalculation validates the calculation results
func ValidateEconomicCalculation(calc *EconomicCalculation) error {
	if calc.MatchID == "" {
		return fmt.Errorf("match ID is required")
	}
	if calc.Calculations.AnnualSavings < 0 {
		return fmt.Errorf("annual savings cannot be negative")
	}
	if calc.Calculations.PaybackPeriodYears < 0 {
		return fmt.Errorf("payback period cannot be negative")
	}
	if calc.Calculations.IRRPercent < -100 || calc.Calculations.IRRPercent > 1000 {
		return fmt.Errorf("IRR percentage out of reasonable range")
	}
	return nil
}