//
//  ItinerarySectionBuilder.swift
//  SportsTime
//
//  Pure static builder for itinerary sections.
//  Extracted from TripDetailView to enable caching and testability.
//

import Foundation

enum ItinerarySectionBuilder {

    /// Build itinerary sections from trip data.
    ///
    /// This is a pure function: same inputs always produce the same output.
    /// Callers should cache the result and recompute only when inputs change.
    static func build(
        trip: Trip,
        tripDays: [Date],
        games: [String: RichGame],
        travelOverrides: [String: TravelOverride],
        itineraryItems: [ItineraryItem],
        allowCustomItems: Bool
    ) -> [ItinerarySection] {
        var sections: [ItinerarySection] = []

        // Use TravelPlacement for consistent day calculation (shared with tests).
        var travelByDay = TravelPlacement.computeTravelByDay(trip: trip, tripDays: tripDays)

        // Apply user overrides on top of computed defaults.
        for (segmentIndex, segment) in trip.travelSegments.enumerated() {
            let travelId = stableTravelAnchorId(segment, at: segmentIndex)
            guard let override = travelOverrides[travelId] else { continue }

            // Validate override is within valid day range
            if let validRange = validDayRange(for: travelId, trip: trip, tripDays: tripDays),
               validRange.contains(override.day) {
                // Remove from computed position (search all days)
                for key in travelByDay.keys {
                    travelByDay[key]?.removeAll { $0.id == segment.id }
                }
                travelByDay.keys.forEach { key in
                    if travelByDay[key]?.isEmpty == true { travelByDay[key] = nil }
                }
                // Place at overridden position
                travelByDay[override.day, default: []].append(segment)
            }
        }

        // Process ALL days
        for (index, dayDate) in tripDays.enumerated() {
            let dayNum = index + 1
            let gamesOnDay = gamesOn(date: dayDate, trip: trip, games: games)

            // Travel for this day (if any) - appears before day header
            for travelSegment in (travelByDay[dayNum] ?? []) {
                let segIdx = trip.travelSegments.firstIndex(where: { $0.id == travelSegment.id }) ?? 0
                sections.append(.travel(travelSegment, segmentIndex: segIdx))
            }

            // Day section - shows games or minimal rest day display
            sections.append(.day(dayNumber: dayNum, date: dayDate, games: gamesOnDay))

            // Custom items for this day (sorted by sortOrder)
            if allowCustomItems {
                // Add button first - always right after day header
                sections.append(.addButton(day: dayNum))

                let dayItems = itineraryItems
                    .filter { $0.day == dayNum && $0.isCustom }
                    .sorted { $0.sortOrder < $1.sortOrder }
                for item in dayItems {
                    sections.append(.customItem(item))
                }
            }
        }

        return sections
    }

    // MARK: - Helpers

    static func stableTravelAnchorId(_ segment: TravelSegment, at index: Int) -> String {
        let from = TravelInfo.normalizeCityName(segment.fromLocation.name)
        let to = TravelInfo.normalizeCityName(segment.toLocation.name)
        return "travel:\(index):\(from)->\(to)"
    }

    static func gamesOn(date: Date, trip: Trip, games: [String: RichGame]) -> [RichGame] {
        let calendar = Calendar.current
        let dayStart = calendar.startOfDay(for: date)
        let allGameIds = trip.stops.flatMap { $0.games }

        let foundGames = allGameIds.compactMap { games[$0] }

        return foundGames.filter { richGame in
            calendar.startOfDay(for: richGame.game.dateTime) == dayStart
        }.sorted { $0.game.dateTime < $1.game.dateTime }
    }

    /// Parse the segment index from a travel anchor ID.
    /// Format: "travel:INDEX:from->to" → INDEX
    private static func parseSegmentIndex(from travelId: String) -> Int? {
        let stripped = travelId.replacingOccurrences(of: "travel:", with: "")
        let parts = stripped.components(separatedBy: ":")
        guard parts.count >= 2, let index = Int(parts[0]) else { return nil }
        return index
    }

    private static func validDayRange(for travelId: String, trip: Trip, tripDays: [Date]) -> ClosedRange<Int>? {
        guard let segmentIndex = parseSegmentIndex(from: travelId),
              segmentIndex < trip.stops.count - 1 else {
            return nil
        }

        let fromStop = trip.stops[segmentIndex]
        let toStop = trip.stops[segmentIndex + 1]

        let fromDayNum = dayNumber(for: fromStop.departureDate, tripDays: tripDays)
        let toDayNum = dayNumber(for: toStop.arrivalDate, tripDays: tripDays)

        let minDay = max(fromDayNum + 1, 1)
        let maxDay = min(toDayNum, tripDays.count)

        if minDay > maxDay {
            return nil
        }

        return minDay...maxDay
    }

    private static func dayNumber(for date: Date, tripDays: [Date]) -> Int {
        let calendar = Calendar.current
        let target = calendar.startOfDay(for: date)

        for (index, tripDay) in tripDays.enumerated() {
            if calendar.startOfDay(for: tripDay) == target {
                return index + 1
            }
        }

        // If date is before trip, return 0; if after, return count + 1
        if let first = tripDays.first, target < calendar.startOfDay(for: first) {
            return 0
        }
        return tripDays.count + 1
    }
}