//
//  DrivingFeasibilityValidator.swift
//  SportsTime
//

import Foundation

/// Validates driving feasibility based on daily hour limits.
/// Priority 4 in the rule hierarchy.
///
/// A route is valid ONLY IF:
/// - Daily driving time ≤ maxDailyDrivingHours for EVERY day
/// - Games are reachable between scheduled times
struct DrivingFeasibilityValidator {

    // MARK: - Validation Result

    struct ValidationResult {
        let isValid: Bool
        let violations: [ConstraintViolation]
        let failedSegment: SegmentFailure?

        static let valid = ValidationResult(isValid: true, violations: [], failedSegment: nil)

        static func drivingExceeded(
            segment: String,
            requiredHours: Double,
            limitHours: Double
        ) -> ValidationResult {
            let violation = ConstraintViolation(
                type: .drivingTime,
                description: "\(segment) requires \(String(format: "%.1f", requiredHours)) hours driving (limit: \(String(format: "%.1f", limitHours)) hours)",
                severity: .error
            )
            let failure = SegmentFailure(
                segmentDescription: segment,
                requiredHours: requiredHours,
                limitHours: limitHours
            )
            return ValidationResult(isValid: false, violations: [violation], failedSegment: failure)
        }

        static func gameUnreachable(
            gameId: UUID,
            arrivalTime: Date,
            gameTime: Date
        ) -> ValidationResult {
            let formatter = DateFormatter()
            formatter.dateStyle = .short
            formatter.timeStyle = .short
            let violation = ConstraintViolation(
                type: .gameReachability,
                description: "Cannot arrive (\(formatter.string(from: arrivalTime))) before game starts (\(formatter.string(from: gameTime)))",
                severity: .error
            )
            return ValidationResult(isValid: false, violations: [violation], failedSegment: nil)
        }
    }

    struct SegmentFailure {
        let segmentDescription: String
        let requiredHours: Double
        let limitHours: Double
    }

    // MARK: - Properties

    let constraints: DrivingConstraints

    // MARK: - Initialization

    init(constraints: DrivingConstraints = .default) {
        self.constraints = constraints
    }

    init(from preferences: TripPreferences) {
        self.constraints = DrivingConstraints(from: preferences)
    }

    // MARK: - Validation

    /// Validates that a single travel segment is feasible within daily driving limits.
    ///
    /// - Parameters:
    ///   - drivingHours: Required driving hours for this segment
    ///   - origin: Description of the origin location
    ///   - destination: Description of the destination location
    /// - Returns: ValidationResult indicating if the segment is feasible
    func validateSegment(
        drivingHours: Double,
        origin: String,
        destination: String
    ) -> ValidationResult {
        let maxDaily = constraints.maxDailyDrivingHours

        // A segment is valid if it can be completed in one day OR
        // can be split across multiple days with overnight stops
        if drivingHours <= maxDaily {
            return .valid
        }

        // Check if it can be reasonably split across multiple days
        // We allow up to 2 driving days for a single segment
        let maxTwoDayDriving = maxDaily * 2
        if drivingHours <= maxTwoDayDriving {
            return .valid
        }

        // Segment requires more than 2 days of driving - too long
        return .drivingExceeded(
            segment: "\(origin) → \(destination)",
            requiredHours: drivingHours,
            limitHours: maxDaily
        )
    }

    /// Validates that a game can be reached in time given departure time and driving duration.
    ///
    /// - Parameters:
    ///   - gameId: ID of the game to reach
    ///   - gameTime: When the game starts
    ///   - departureTime: When we leave the previous stop
    ///   - drivingHours: Hours of driving required
    ///   - bufferHours: Buffer time needed before game (default 1 hour for parking, etc.)
    /// - Returns: ValidationResult indicating if we can reach the game in time
    func validateGameReachability(
        gameId: UUID,
        gameTime: Date,
        departureTime: Date,
        drivingHours: Double,
        bufferHours: Double = 1.0
    ) -> ValidationResult {
        // Calculate arrival time
        let drivingSeconds = drivingHours * 3600
        let bufferSeconds = bufferHours * 3600
        let arrivalTime = departureTime.addingTimeInterval(drivingSeconds)
        let requiredArrivalTime = gameTime.addingTimeInterval(-bufferSeconds)

        if arrivalTime <= requiredArrivalTime {
            return .valid
        } else {
            return .gameUnreachable(
                gameId: gameId,
                arrivalTime: arrivalTime,
                gameTime: gameTime
            )
        }
    }

    /// Validates an entire itinerary's travel segments for driving feasibility.
    ///
    /// - Parameter segments: Array of travel segments to validate
    /// - Returns: ValidationResult with first failure found, or valid if all pass
    func validateItinerary(segments: [TravelSegment]) -> ValidationResult {
        for segment in segments {
            let result = validateSegment(
                drivingHours: segment.estimatedDrivingHours,
                origin: segment.fromLocation.name,
                destination: segment.toLocation.name
            )
            if !result.isValid {
                return result
            }
        }
        return .valid
    }

    /// Calculates how many travel days are needed for a given driving distance.
    ///
    /// - Parameter drivingHours: Total hours of driving required
    /// - Returns: Number of calendar days the travel will span
    func travelDaysRequired(for drivingHours: Double) -> Int {
        let maxDaily = constraints.maxDailyDrivingHours
        if drivingHours <= maxDaily {
            return 1
        }
        return Int(ceil(drivingHours / maxDaily))
    }

    /// Determines if an overnight stop is needed between two points.
    ///
    /// - Parameters:
    ///   - drivingHours: Hours of driving between points
    ///   - departureTime: When we plan to leave
    /// - Returns: True if an overnight stop is recommended
    func needsOvernightStop(drivingHours: Double, departureTime: Date) -> Bool {
        // If driving exceeds daily limit, we need an overnight
        if drivingHours > constraints.maxDailyDrivingHours {
            return true
        }

        // Also check if arrival would be unreasonably late
        let arrivalTime = departureTime.addingTimeInterval(drivingHours * 3600)
        let calendar = Calendar.current
        let arrivalHour = calendar.component(.hour, from: arrivalTime)

        // Arriving after 11 PM suggests we should have stopped
        return arrivalHour >= 23
    }
}