//
//  RouteOptimizer.swift
//  SportsTime
//

import Foundation
import CoreLocation

/// Optimization strategy for ranking itinerary options.
enum OptimizationStrategy {
    case balanced       // Balance games vs driving
    case maximizeGames  // Prioritize seeing more games
    case minimizeDriving // Prioritize shorter routes
    case scenic         // Prioritize scenic routes
}

/// Route optimizer for ranking and scoring itinerary options.
///
/// The TSP-solving logic has been moved to scenario-specific candidate
/// generation in TripPlanningEngine. This optimizer now focuses on:
/// - Ranking multiple route options
/// - Scoring routes based on optimization strategy
/// - Reordering games within constraints
struct RouteOptimizer {

    // MARK: - Route Ranking

    /// Ranks a list of itinerary options based on the optimization strategy.
    ///
    /// - Parameters:
    ///   - options: Unranked itinerary options
    ///   - strategy: Optimization strategy for scoring
    ///   - request: Planning request for context
    /// - Returns: Options sorted by score (best first) with rank assigned
    func rankOptions(
        _ options: [ItineraryOption],
        strategy: OptimizationStrategy = .balanced,
        request: PlanningRequest
    ) -> [ItineraryOption] {
        // Score each option
        let scoredOptions = options.map { option -> (ItineraryOption, Double) in
            let score = scoreOption(option, strategy: strategy, request: request)
            return (option, score)
        }

        // Sort by score (lower is better for our scoring system)
        let sorted = scoredOptions.sorted { $0.1 < $1.1 }

        // Assign ranks
        return sorted.enumerated().map { index, scored in
            ItineraryOption(
                rank: index + 1,
                stops: scored.0.stops,
                travelSegments: scored.0.travelSegments,
                totalDrivingHours: scored.0.totalDrivingHours,
                totalDistanceMiles: scored.0.totalDistanceMiles,
                geographicRationale: scored.0.geographicRationale
            )
        }
    }

    // MARK: - Scoring

    /// Scores an itinerary option based on the optimization strategy.
    /// Lower scores are better.
    ///
    /// - Parameters:
    ///   - option: Itinerary option to score
    ///   - strategy: Optimization strategy
    ///   - request: Planning request for context
    /// - Returns: Score value (lower is better)
    func scoreOption(
        _ option: ItineraryOption,
        strategy: OptimizationStrategy,
        request: PlanningRequest
    ) -> Double {
        switch strategy {
        case .balanced:
            return scoreBalanced(option, request: request)
        case .maximizeGames:
            return scoreMaximizeGames(option, request: request)
        case .minimizeDriving:
            return scoreMinimizeDriving(option, request: request)
        case .scenic:
            return scoreScenic(option, request: request)
        }
    }

    /// Balanced scoring: trade-off between games and driving.
    private func scoreBalanced(_ option: ItineraryOption, request: PlanningRequest) -> Double {
        // Each game "saves" 2 hours of driving in value
        let gameValue = Double(option.totalGames) * 2.0
        let drivingPenalty = option.totalDrivingHours

        // Also factor in must-see games coverage
        let mustSeeCoverage = calculateMustSeeCoverage(option, request: request)
        let mustSeeBonus = mustSeeCoverage * 10.0  // Strong bonus for must-see coverage

        return drivingPenalty - gameValue - mustSeeBonus
    }

    /// Maximize games scoring: prioritize number of games.
    private func scoreMaximizeGames(_ option: ItineraryOption, request: PlanningRequest) -> Double {
        // Heavily weight game count
        let gameScore = -Double(option.totalGames) * 100.0
        let drivingPenalty = option.totalDrivingHours * 0.1  // Minimal driving penalty

        return gameScore + drivingPenalty
    }

    /// Minimize driving scoring: prioritize shorter routes.
    private func scoreMinimizeDriving(_ option: ItineraryOption, request: PlanningRequest) -> Double {
        // Primarily driving time
        let drivingScore = option.totalDrivingHours
        let gameBonus = Double(option.totalGames) * 0.5  // Small bonus for games

        return drivingScore - gameBonus
    }

    /// Scenic scoring: balance games with route pleasantness.
    private func scoreScenic(_ option: ItineraryOption, request: PlanningRequest) -> Double {
        // More relaxed pacing is better
        let gamesPerDay = Double(option.totalGames) / Double(max(1, option.stops.count))
        let pacingScore = abs(gamesPerDay - 1.5) * 5.0  // Ideal is ~1.5 games per day

        let drivingScore = option.totalDrivingHours * 0.3
        let gameBonus = Double(option.totalGames) * 2.0

        return pacingScore + drivingScore - gameBonus
    }

    /// Calculates what percentage of must-see games are covered.
    private func calculateMustSeeCoverage(
        _ option: ItineraryOption,
        request: PlanningRequest
    ) -> Double {
        let mustSeeIds = request.preferences.mustSeeGameIds
        if mustSeeIds.isEmpty { return 1.0 }

        let coveredGames = option.stops.flatMap { $0.games }
        let coveredMustSee = Set(coveredGames).intersection(mustSeeIds)

        return Double(coveredMustSee.count) / Double(mustSeeIds.count)
    }

    // MARK: - Route Improvement

    /// Attempts to improve a route by swapping non-essential stops.
    /// Only applies to stops without must-see games.
    ///
    /// - Parameters:
    ///   - option: Itinerary option to improve
    ///   - request: Planning request for context
    /// - Returns: Improved itinerary option, or original if no improvement found
    func improveRoute(
        _ option: ItineraryOption,
        request: PlanningRequest
    ) -> ItineraryOption {
        // For now, return as-is since games must remain in chronological order
        // Future: implement swap logic for same-day games in different cities
        return option
    }

    // MARK: - Validation Helpers

    /// Checks if all must-see games are included in the option.
    func includesAllMustSeeGames(
        _ option: ItineraryOption,
        request: PlanningRequest
    ) -> Bool {
        let includedGames = Set(option.stops.flatMap { $0.games })
        return request.preferences.mustSeeGameIds.isSubset(of: includedGames)
    }

    /// Returns must-see games that are missing from the option.
    func missingMustSeeGames(
        _ option: ItineraryOption,
        request: PlanningRequest
    ) -> Set<UUID> {
        let includedGames = Set(option.stops.flatMap { $0.games })
        return request.preferences.mustSeeGameIds.subtracting(includedGames)
    }

    // MARK: - Distance Calculations

    /// Calculates total route distance for a sequence of coordinates.
    func totalDistance(for coordinates: [CLLocationCoordinate2D]) -> Double {
        guard coordinates.count >= 2 else { return 0 }

        var total: Double = 0
        for i in 0..<(coordinates.count - 1) {
            total += distance(from: coordinates[i], to: coordinates[i + 1])
        }
        return total
    }

    /// Calculates distance between two coordinates in meters.
    private func distance(
        from: CLLocationCoordinate2D,
        to: CLLocationCoordinate2D
    ) -> Double {
        let fromLoc = CLLocation(latitude: from.latitude, longitude: from.longitude)
        let toLoc = CLLocation(latitude: to.latitude, longitude: to.longitude)
        return fromLoc.distance(from: toLoc)
    }

    // MARK: - Legacy Support

    /// Legacy optimization method for backward compatibility.
    /// Delegates to the new TripPlanningEngine for actual routing.
    func optimize(
        graph: RouteGraph,
        request: PlanningRequest,
        candidates: [GameCandidate],
        strategy: OptimizationStrategy = .balanced
    ) -> CandidateRoute {
        // Build a simple chronological route from candidates
        let sortedCandidates = candidates.sorted { $0.game.dateTime < $1.game.dateTime }

        var route = CandidateRoute()

        // Add start node
        if let startNode = graph.nodes.first(where: { $0.type == .start }) {
            route.nodeSequence.append(startNode.id)
        }

        // Add stadium nodes in chronological order
        var visitedStadiums = Set<UUID>()
        for candidate in sortedCandidates {
            // Find the node for this stadium
            for node in graph.nodes {
                if case .stadium(let stadiumId) = node.type,
                   stadiumId == candidate.stadium.id,
                   !visitedStadiums.contains(stadiumId) {
                    route.nodeSequence.append(node.id)
                    route.games.append(candidate.game.id)
                    visitedStadiums.insert(stadiumId)
                    break
                }
            }
        }

        // Add end node
        if let endNode = graph.nodes.first(where: { $0.type == .end }) {
            route.nodeSequence.append(endNode.id)
        }

        // Calculate totals
        for i in 0..<(route.nodeSequence.count - 1) {
            if let edge = graph.edges(from: route.nodeSequence[i])
                .first(where: { $0.toNodeId == route.nodeSequence[i + 1] }) {
                route.totalDistance += edge.distanceMeters
                route.totalDuration += edge.durationSeconds
            }
        }

        // Score the route
        route.score = scoreRoute(route, strategy: strategy, graph: graph)

        return route
    }

    /// Legacy route scoring for CandidateRoute.
    private func scoreRoute(
        _ route: CandidateRoute,
        strategy: OptimizationStrategy,
        graph: RouteGraph
    ) -> Double {
        switch strategy {
        case .balanced:
            return route.totalDuration - Double(route.games.count) * 3600 * 2

        case .maximizeGames:
            return -Double(route.games.count) * 10000 + route.totalDuration

        case .minimizeDriving:
            return route.totalDuration

        case .scenic:
            return route.totalDuration * 0.5 - Double(route.games.count) * 3600
        }
    }
}