package validator

import (
	"fmt"

	"github.com/damirmukimov/city_resource_graph/models/cost"
	"github.com/damirmukimov/city_resource_graph/models/customer"
	"github.com/damirmukimov/city_resource_graph/models/impact"
	"github.com/damirmukimov/city_resource_graph/models/revenue"
)

// ValidationError represents a validation failure.
type ValidationError struct {
	Year    int
	Rule    string
	Message string
	Value   interface{}
}

func (ve ValidationError) Error() string {
	return fmt.Sprintf("validation failed [Year %d, Rule: %s]: %s (value: %v)", ve.Year, ve.Rule, ve.Message, ve.Value)
}

// ValidationResult contains all validation errors found.
type ValidationResult struct {
	Errors []ValidationError
}

// IsValid returns true if no validation errors were found.
func (vr ValidationResult) IsValid() bool {
	return len(vr.Errors) == 0
}

// Validate performs all sanity checks on the model outputs for a given year.
func Validate(
	year int,
	custMetrics customer.CustomerMetrics,
	revBreakdown revenue.RevenueBreakdown,
	costBreakdown cost.CostBreakdown,
	impactMetrics impact.ImpactMetrics,
) ValidationResult {
	var errors []ValidationError

	// 1. ARPU sanity check
	// ARPU should be within typical B2B SaaS range: €300-€6,000/year
	if custMetrics.PayingOrgs > 0 {
		arpu := revBreakdown.Total / float64(custMetrics.PayingOrgs)
		if arpu < 300 || arpu > 6000 {
			errors = append(errors, ValidationError{
				Year:    year,
				Rule:    "ARPU_SANITY",
				Message: fmt.Sprintf("ARPU (€%.2f) outside typical B2B SaaS range (€300-€6,000)", arpu),
				Value:   arpu,
			})
		}
	}

	// 2. Implementation density check
	// Matches per organization should not exceed 1.5 (unrealistic for 3-year horizon)
	if impactMetrics.CO2Avoided > 0 || custMetrics.TotalOrgs > 0 {
		// Estimate matches from implementation revenue
		// This is approximate - ideally should come from model directly
		implRev := revBreakdown.Implementation.Total
		if implRev > 0 && revBreakdown.Implementation.PaidImpls > 0 {
			matchesPerOrg := revBreakdown.Implementation.Matches / float64(custMetrics.TotalOrgs)
			if matchesPerOrg > 1.5 {
				errors = append(errors, ValidationError{
					Year:    year,
					Rule:    "IMPLEMENTATION_DENSITY",
					Message: fmt.Sprintf("Matches per org (%.2f) exceeds realistic limit (1.5)", matchesPerOrg),
					Value:   matchesPerOrg,
				})
			}
		}
	}

	// 3. CO₂ / revenue ratio check
	// Catches unit mistakes (e.g., if CO₂ is in wrong units)
	if revBreakdown.Total > 0 {
		co2PerEur := impactMetrics.CO2Avoided / revBreakdown.Total
		if co2PerEur > 10 {
			errors = append(errors, ValidationError{
				Year:    year,
				Rule:    "CO2_REVENUE_RATIO",
				Message: fmt.Sprintf("CO₂ per EUR (%.2f t CO₂/€) exceeds sanity limit (10)", co2PerEur),
				Value:   co2PerEur,
			})
		}
	}

	// 4. Heat MWh sanity check
	// If heat exceeds 5,000,000 MWh/year, likely multiplied by 12 (monthly mistake)
	if impactMetrics.CO2Avoided > 0 {
		// Reconstruct heat from CO₂ to check
		// This is approximate - ideally should validate input directly
		estimatedHeat := impactMetrics.CO2Avoided / (0.3 * 0.9 * 0.7) // Reverse calculation
		if estimatedHeat > 5_000_000 {
			errors = append(errors, ValidationError{
				Year:    year,
				Rule:    "HEAT_MWH_SANITY",
				Message: fmt.Sprintf("Estimated heat (%.0f MWh) exceeds sanity limit (5M MWh/year) - possible monthly multiplier error", estimatedHeat),
				Value:   estimatedHeat,
			})
		}
	}

	// 5. Profitability check (warning only)
	if revBreakdown.Total > 0 && costBreakdown.Total > 0 {
		profit := revBreakdown.Total - costBreakdown.Total
		margin := (profit / revBreakdown.Total) * 100
		if margin < -100 {
			// Losses exceed revenue - suspicious
			errors = append(errors, ValidationError{
				Year:    year,
				Rule:    "PROFITABILITY_WARNING",
				Message: fmt.Sprintf("Margin (%.1f%%) indicates losses exceeding revenue - verify cost inputs", margin),
				Value:   margin,
			})
		}
	}

	return ValidationResult{Errors: errors}
}

// ValidateMunicipalPenetration checks if municipal city count is reasonable.
// This requires external context (total cities in target region).
func ValidateMunicipalPenetration(year int, cities int, maxCities int) ValidationError {
	if cities > maxCities {
		return ValidationError{
			Year:    year,
			Rule:    "MUNICIPAL_PENETRATION",
			Message: fmt.Sprintf("Municipal cities (%d) exceeds maximum expected (%d)", cities, maxCities),
			Value:   cities,
		}
	}
	return ValidationError{} // No error
}