import { Injectable, NotFoundException } from '@nestjs/common';
import { PrismaService } from '../../common/prisma.service';
import { SearchTripsDto, FareQuoteDto, FareBreakdownRequestDto, FareBreakdownPassengerDto } from './search.dto';
import { CurrencyService } from '../currency/currency.service';
import { FareEngineService } from '../fare-engine/fare-engine.service';
import { SegmentsService } from '../segments/segments.service';
import { resolveCurrencyFromNationality } from '../fare-engine/fare-engine.dto';
import { Currency } from '@prisma/client';
import { SystemConfigService, CONFIG_KEYS } from '../system-config/system-config.service';

const POINTS_TO_MINOR = 10;

// Shape returned by the heavy schedule include used throughout this service
type ScheduleWithIncludes = {
  id: string;
  routeId: string | null;
  departureAt: Date;
  arrivalAt: Date;
  status: string;
  train: any;
  originStation: any;
  destinationStation: any;
  stopTimes: Array<{ stationId: string; sequence: number; plannedArrivalAt: Date | null; plannedDepartureAt: Date | null; station: any }>;
  coachAssignments: Array<{ coach: { id: string; seats: any[]; coachType: { id: string; name: string; code: string; seatClasses: any[] } | null } }>;
};

const SCHEDULE_INCLUDE = {
  train: true,
  originStation: true,
  destinationStation: true,
  stopTimes: { include: { station: true }, orderBy: { sequence: 'asc' } },
  coachAssignments: {
    include: { coach: { include: { seats: true, coachType: { include: { seatClasses: true } } } } },
  },
} as const;

@Injectable()
export class SearchService {
  constructor(
    private prisma: PrismaService,
    private currencyService: CurrencyService,
    private fareEngine: FareEngineService,
    private segmentsService: SegmentsService,
    private systemConfig: SystemConfigService,
  ) {}

  private async getCutoffHours(): Promise<number> {
    return this.systemConfig.getNumber(CONFIG_KEYS.HOLD_CUTOFF_HOURS_BEFORE_DEPARTURE);
  }

  async searchTrips(dto: SearchTripsDto) {
    const [direct, transit] = await Promise.all([
      this.searchSchedules(
        dto.originStationId,
        dto.destinationStationId,
        dto.date,
        dto.adultCount,
        dto.childCount,
        dto.nationality,
      ),
      this.searchTransitOptions(
        dto.originStationId,
        dto.destinationStationId,
        dto.date,
        dto.adultCount,
        dto.childCount,
        dto.nationality,
      ),
    ]);

    const outbound = [...direct, ...transit];

    if (outbound.length === 0 && dto.journeyType !== 'ROUND_TRIP') {
      const alternativesOutbound = await this.searchAlternatives(
        dto.originStationId,
        dto.destinationStationId,
        dto.date,
        dto.adultCount,
        dto.childCount,
        dto.nationality,
      );
      return {
        journeyType: 'ONE_WAY',
        outbound: [],
        alternativeOutbound: alternativesOutbound,
        requestedDate: dto.date,
      };
    }

    if (dto.journeyType === 'ROUND_TRIP') {
      const [returnDirect, returnTransit] = await Promise.all([
        this.searchSchedules(
          dto.destinationStationId,
          dto.originStationId,
          dto.returnDate ?? dto.date,
          dto.adultCount,
          dto.childCount,
          dto.nationality,
        ),
        this.searchTransitOptions(
          dto.destinationStationId,
          dto.originStationId,
          dto.returnDate ?? dto.date,
          dto.adultCount,
          dto.childCount,
          dto.nationality,
        ),
      ]);

      const allReturn = [...returnDirect, ...returnTransit];
      const latestOutboundArrival = outbound.length > 0
        ? Math.max(...outbound.map((s: any) => new Date(s.arrivalAt ?? s.leg2?.arrivalAt).getTime()))
        : Date.now();

      const inbound = allReturn.filter((s: any) =>
        new Date(s.departureAt ?? s.leg1?.departureAt).getTime() > latestOutboundArrival
      );

      const returnDate = dto.returnDate ?? dto.date;

      if (outbound.length === 0 || inbound.length === 0) {
        const [alternativeOutbound, alternativeInbound] = await Promise.all([
          outbound.length === 0
            ? this.searchAlternatives(dto.originStationId, dto.destinationStationId, dto.date, dto.adultCount, dto.childCount, dto.nationality)
            : Promise.resolve([]),
          inbound.length === 0
            ? this.searchAlternatives(dto.destinationStationId, dto.originStationId, returnDate, dto.adultCount, dto.childCount, dto.nationality)
            : Promise.resolve([]),
        ]);
        return {
          journeyType: 'ROUND_TRIP',
          outbound,
          inbound,
          alternativeOutbound,
          alternativeInbound,
          requestedDate: dto.date,
          requestedReturnDate: returnDate,
        };
      }

      return { journeyType: 'ROUND_TRIP', outbound, inbound, requestedDate: dto.date, requestedReturnDate: returnDate };
    }

    return { journeyType: 'ONE_WAY', outbound };
  }

  private async searchAlternatives(
    originStationId: string,
    destinationStationId: string,
    dateStr: string,
    adultCount: number,
    childCount?: number,
    nationality?: string,
  ) {
    const [y, m, d] = dateStr.split('-').map(Number);
    const requestedDate = new Date(y, m - 1, d, 0, 0, 0, 0);
    const requestedNextDay = new Date(y, m - 1, d + 1, 0, 0, 0, 0);
    const now = new Date();
    const totalPassengers = adultCount + (childCount ?? 0);
    const NEEDED = 3;

    const baseWhere = {
      status: 'SCHEDULED',
      isPackageOnly: false,
      stopTimes: { some: { stationId: originStationId } },
      coachAssignments: { some: {} },
    } as const;

    // Fetch candidates before and after in parallel; take more than needed to
    // account for routes that don't serve the destination or have no availability.
    const FETCH_LIMIT = NEEDED * 5;

    const [beforeCandidates, afterCandidates] = await Promise.all([
      this.prisma.trainSchedule.findMany({
        where: { ...baseWhere, departureAt: { gte: now < requestedDate ? now : new Date(0), lt: requestedDate } },
        include: SCHEDULE_INCLUDE,
        orderBy: { departureAt: 'desc' },
        take: FETCH_LIMIT,
      }),
      this.prisma.trainSchedule.findMany({
        where: { ...baseWhere, departureAt: { gte: requestedNextDay > now ? requestedNextDay : now } },
        include: SCHEDULE_INCLUDE,
        orderBy: { departureAt: 'asc' },
        take: FETCH_LIMIT,
      }),
    ]);

    const pickN = async (candidates: typeof beforeCandidates, limit: number) => {
      const out: NonNullable<Awaited<ReturnType<typeof this.buildScheduleResult>>>[] = [];
      for (const schedule of candidates) {
        if (out.length >= limit) break;
        const r = await this.buildScheduleResult(schedule as any, originStationId, destinationStationId, totalPassengers, nationality);
        if (r?.hasAvailability) out.push(r);
      }
      return out;
    };

    const [before, after] = await Promise.all([
      pickN(beforeCandidates, NEEDED),
      pickN(afterCandidates, NEEDED),
    ]);

    // before was fetched desc (closest first); reverse so result is chronological
    return [...before.reverse(), ...after];
  }

  private async searchSchedules(
    originStationId: string,
    destinationStationId: string,
    dateStr: string,
    adultCount: number,
    childCount?: number,
    nationality?: string,
  ) {
    const [y, m, d] = dateStr.split('-').map(Number);
    const date    = new Date(y, m - 1, d, 0, 0, 0, 0);
    const nextDay = new Date(y, m - 1, d + 1, 0, 0, 0, 0);
    const now = new Date();
    const totalPassengers = adultCount + (childCount ?? 0);

    const cutoffHours = await this.getCutoffHours();
    const cutoffThreshold = new Date(now.getTime() + cutoffHours * 60 * 60 * 1000);
    const isToday = now.getFullYear() === y && now.getMonth() === m - 1 && now.getDate() === d;
    const earliest = isToday ? cutoffThreshold : date;

    const schedules = await this.prisma.trainSchedule.findMany({
      where: {
        status: 'SCHEDULED',
        isPackageOnly: false,
        departureAt: { gte: earliest, lt: nextDay },
        stopTimes: { some: { stationId: originStationId } },
        coachAssignments: { some: {} },
      },
      include: SCHEDULE_INCLUDE,
    });

    const results = await Promise.all(
      schedules.map(schedule =>
        this.buildScheduleResult(schedule as any, originStationId, destinationStationId, totalPassengers, nationality)
      )
    );
    return results.filter((r): r is NonNullable<typeof r> => !!r && r.hasAvailability);
  }

  // ── Transit search ─────────────────────────────────────────────────────────
  private readonly MIN_CONNECTION_MINUTES = 30;
  private readonly MAX_CONNECTION_MINUTES = 360;

  private async searchTransitOptions(
    originStationId: string,
    destinationStationId: string,
    dateStr: string,
    adultCount: number,
    childCount?: number,
    nationality?: string,
  ) {
    const [y, m, d] = dateStr.split('-').map(Number);
    const dayStart = new Date(y, m - 1, d, 0, 0, 0, 0);
    const dayEnd   = new Date(y, m - 1, d + 1, 0, 0, 0, 0);
    const leg2WindowEnd = new Date(dayEnd.getTime() + this.MAX_CONNECTION_MINUTES * 60_000);
    const totalPassengers = adultCount + (childCount ?? 0);

    // Load leg1 and all potential leg2 candidates in one parallel round-trip
    // instead of firing a separate DB query per transit stop.
    const [leg1Schedules, allCandidates] = await Promise.all([
      this.prisma.trainSchedule.findMany({
        where: {
          status: 'SCHEDULED',
          isPackageOnly: false,
          departureAt: { gte: dayStart, lt: dayEnd },
          stopTimes: { some: { stationId: originStationId } },
          coachAssignments: { some: {} },
        },
        include: SCHEDULE_INCLUDE,
      }),
      this.prisma.trainSchedule.findMany({
        where: {
          status: 'SCHEDULED',
          isPackageOnly: false,
          departureAt: { gte: dayStart, lt: leg2WindowEnd },
          coachAssignments: { some: {} },
        },
        include: SCHEDULE_INCLUDE,
      }),
    ]);

    const cutoffHours = await this.getCutoffHours();
    const cutoffThreshold = new Date(Date.now() + cutoffHours * 60 * 60 * 1000);

    const results: any[] = [];

    for (const leg1 of (leg1Schedules as ScheduleWithIncludes[]).filter(s => new Date(s.departureAt) > cutoffThreshold)) {
      const originStop = leg1.stopTimes.find(s => s.stationId === originStationId);
      if (!originStop) continue;

      const candidateTransitStops = leg1.stopTimes.filter(
        s => s.sequence > originStop.sequence,
      );

      for (const transitStop of candidateTransitStops) {
        const leg1HasDest = leg1.stopTimes.some(s => s.stationId === destinationStationId);
        if (leg1HasDest) continue;

        const transitStationId = transitStop.stationId;
        const leg1ArrivalAt = transitStop.plannedArrivalAt ?? transitStop.plannedDepartureAt ?? leg1.arrivalAt;

        const connWindowStart = new Date(new Date(leg1ArrivalAt).getTime() + this.MIN_CONNECTION_MINUTES * 60_000);
        const connWindowEnd   = new Date(new Date(leg1ArrivalAt).getTime() + this.MAX_CONNECTION_MINUTES * 60_000);

        // Filter from pre-loaded candidates in memory — no extra DB query
        const leg2Schedules = (allCandidates as ScheduleWithIncludes[]).filter(s => {
          const dep = new Date(s.departureAt).getTime();
          return dep >= connWindowStart.getTime()
            && dep <= connWindowEnd.getTime()
            && s.stopTimes.some(st => st.stationId === transitStationId);
        });

        for (const leg2 of leg2Schedules) {
          const leg2TransitStop = leg2.stopTimes.find(s => s.stationId === transitStationId);
          const leg2DestStop    = leg2.stopTimes.find(s => s.stationId === destinationStationId);

          if (!leg2TransitStop || !leg2DestStop) continue;
          if (leg2TransitStop.sequence >= leg2DestStop.sequence) continue;

          const [leg1Result, leg2Result] = await Promise.all([
            this.buildScheduleResult(leg1, originStationId, transitStationId, totalPassengers, nationality),
            this.buildScheduleResult(leg2, transitStationId, destinationStationId, totalPassengers, nationality),
          ]);

          if (!leg1Result || !leg2Result) continue;
          if (!leg1Result.hasAvailability || !leg2Result.hasAvailability) continue;

          const leg2DepartureAt = leg2TransitStop.plannedDepartureAt ?? leg2.departureAt;
          const connectionMinutes = Math.round(
            (new Date(leg2DepartureAt).getTime() - new Date(leg1ArrivalAt).getTime()) / 60_000,
          );

          const leg1MinFare        = Math.min(...(leg1Result.faresByClass as any[]).map((f: any) => f.baseFareMinor).filter((n: number) => n > 0), Infinity);
          const leg2MinFare        = Math.min(...(leg2Result.faresByClass as any[]).map((f: any) => f.baseFareMinor).filter((n: number) => n > 0), Infinity);
          const leg1MinDisplay     = Math.min(...(leg1Result.faresByClass as any[]).map((f: any) => f.displayAmountMinor).filter((n: number) => n > 0), Infinity);
          const leg2MinDisplay     = Math.min(...(leg2Result.faresByClass as any[]).map((f: any) => f.displayAmountMinor).filter((n: number) => n > 0), Infinity);
          const combinedMinFareMinor   = (isFinite(leg1MinFare)    ? leg1MinFare    : 0) + (isFinite(leg2MinFare)    ? leg2MinFare    : 0);
          const combinedMinFareDisplay = (isFinite(leg1MinDisplay) ? leg1MinDisplay : 0) + (isFinite(leg2MinDisplay) ? leg2MinDisplay : 0);
          const displayCurrency = leg1Result.displayCurrency ?? leg2Result.displayCurrency ?? Currency.ETB;

          results.push({
            type: 'TRANSIT',
            transitStationId,
            transitStationName: transitStop.station.name,
            connectionMinutes,
            leg1: leg1Result,
            leg2: leg2Result,
            displayCurrency,
            combinedMinFareMinor,
            combinedMinFareDisplay,
            departureAt: leg1Result.departureAt,
            arrivalAt:   leg2Result.arrivalAt,
            totalDurationMinutes:
              leg1Result.durationMinutes + connectionMinutes + leg2Result.durationMinutes,
          });
        }
      }
    }

    return results;
  }

  private async buildScheduleResult(
    schedule: ScheduleWithIncludes,
    originStationId: string,
    destinationStationId: string,
    totalPassengers: number,
    nationality?: string,
  ) {
    const originStop = schedule.stopTimes.find(s => s.stationId === originStationId);
    const destStop   = schedule.stopTimes.find(s => s.stationId === destinationStationId);
    if (!originStop || !destStop || originStop.sequence >= destStop.sequence) return null;

    // Collect all valid seat IDs upfront for a single batch availability check
    const allValidSeatIds = schedule.coachAssignments.flatMap(a =>
      a.coach.seats
        .filter((s: any) => s.status !== 'BLOCKED' && s.seatNumber?.trim())
        .map((s: any) => s.id as string)
    );

    // Exclude schedules with no seats at all
    if (allValidSeatIds.length === 0) return null;

    // Run availability batch and fare calculation in parallel
    const [freeSeats, faresByClass] = await Promise.all([
      this.segmentsService.getFreeSeatIds(
        schedule.id,
        allValidSeatIds,
        schedule.stopTimes,
        originStop.sequence,
        destStop.sequence,
      ),
      this.calculateFaresForSegment(schedule, originStationId, destinationStationId, nationality),
    ]);

    // Compute per-class availability using the pre-computed free seat set. A coach type
    // has separate seat classes per nationality tier (e.g. "VIP Bed Upper (Local)" AND
    // "VIP Bed Upper (Intl)" on the same coach) — filter to the searching passenger's own
    // nationality first, otherwise a name-based `.find()` across both tiers would credit
    // all availability to whichever tier happens to come first in the query result,
    // leaving the other tier's class permanently at 0 ("Fully booked") even when seats
    // are actually free. Matched via the class's own bedPosition field (case-insensitive:
    // Seat.bedPosition is lowercase, SeatClass.bedPosition is uppercase) rather than a
    // name substring, since that's an exact, unambiguous signal.
    const nationalityUpper = (nationality ?? '').toUpperCase();
    const resolvedNationalityType = (nationalityUpper === 'ETHIOPIAN' || nationalityUpper === 'DJIBOUTIAN')
      ? 'LOCAL' : 'INTERNATIONAL';

    const availabilityByClass: Record<string, number> = {};
    for (const assignment of schedule.coachAssignments) {
      const seatClasses = (assignment.coach.coachType?.seatClasses ?? []).filter(
        (sc: any) => !sc.nationalityType || sc.nationalityType === resolvedNationalityType,
      );
      const isBedCoach = assignment.coach.seats.some((s: any) => s.bedPosition);

      if (isBedCoach) {
        for (const bedPosition of ['upper', 'middle', 'lower']) {
          let count = 0;
          for (const seat of assignment.coach.seats) {
            if (seat.bedPosition !== bedPosition || seat.status === 'BLOCKED' || !seat.seatNumber?.trim()) continue;
            if (freeSeats.has(seat.id)) count++;
          }
          if (count > 0) {
            const matchingClass = seatClasses.find((sc: any) => sc.bedPosition?.toLowerCase() === bedPosition);
            if (matchingClass) availabilityByClass[matchingClass.name] = (availabilityByClass[matchingClass.name] ?? 0) + count;
          }
        }
      } else {
        let available = 0;
        for (const seat of assignment.coach.seats) {
          if (seat.status === 'BLOCKED' || !seat.seatNumber?.trim()) continue;
          if (freeSeats.has(seat.id)) available++;
        }
        const names = seatClasses.length > 0 ? seatClasses.map((sc: any) => sc.name) : ['Standard'];
        for (const name of names) availabilityByClass[name] = (availabilityByClass[name] ?? 0) + available;
      }
    }

    const coachTypes   = this.buildCoachTypeDetails(schedule, faresByClass, nationality, availabilityByClass);
    const legDepartureAt = originStop.plannedDepartureAt ?? schedule.departureAt;
    const legArrivalAt   = destStop.plannedArrivalAt   ?? schedule.arrivalAt;

    const displayCurrency = faresByClass[0]?.displayCurrency ?? resolveCurrencyFromNationality(nationality);

    return {
      type: 'DIRECT',
      scheduleId: schedule.id,
      trainNumber: schedule.train.number,
      trainName:   schedule.train.name,
      origin: { id: originStop.stationId, code: originStop.station.code, name: originStop.station.name, city: originStop.station.city, sequence: originStop.sequence },
      destination: { id: destStop.stationId, code: destStop.station.code, name: destStop.station.name, city: destStop.station.city, sequence: destStop.sequence },
      departureAt: legDepartureAt,
      arrivalAt:   legArrivalAt,
      durationMinutes: Math.round((new Date(legArrivalAt).getTime() - new Date(legDepartureAt).getTime()) / 60_000),
      status: schedule.status,
      stops: schedule.stopTimes
        .filter(st => st.sequence >= originStop.sequence && st.sequence <= destStop.sequence)
        .map(st => ({ stationId: st.stationId, stationName: st.station.name, sequence: st.sequence, plannedArrivalAt: st.plannedArrivalAt, plannedDepartureAt: st.plannedDepartureAt })),
      availabilityByClass,
      hasAvailability: Object.values(availabilityByClass).some(n => n >= totalPassengers),
      displayCurrency,
      faresByClass,
      coachTypes,
    };
  }

  async getFareQuote(dto: FareQuoteDto) {
    const schedule = await this.prisma.trainSchedule.findUnique({
      where: { id: dto.scheduleId },
      include: {
        originStation: true,
        destinationStation: true,
        stopTimes: { include: { station: true }, orderBy: { sequence: 'asc' } },
      },
    });
    if (!schedule) throw new NotFoundException('Schedule not found');
    if (!schedule.routeId) throw new NotFoundException('Schedule has no route configured for fare calculation');

    const originStop = schedule.stopTimes.find((s: any) => s.stationId === dto.originStationId);
    const destStop = schedule.stopTimes.find((s: any) => s.stationId === dto.destinationStationId);
    if (!originStop || !destStop || originStop.sequence >= destStop.sequence) {
      throw new NotFoundException('Origin or destination not found on this schedule');
    }

    const seatClass = await this.prisma.seatClass.findFirst({ where: { name: dto.seatClassName } });
    if (!seatClass) throw new NotFoundException(`Seat class '${dto.seatClassName}' not found`);

    const fare = await this.fareEngine.calculate({
      routeId: schedule.routeId,
      originStationId: dto.originStationId,
      destinationStationId: dto.destinationStationId,
      seatClassId: seatClass.id,
      nationality: dto.nationality,
      scheduleId: dto.scheduleId,
      adultCount: dto.adultCount,
      childCount: dto.childCount ?? 0,
      promoCode: dto.promoCode,
    });

    const loyaltyMinor = (dto.loyaltyRedemptionPoints ?? 0) * POINTS_TO_MINOR;
    const totalMinor = Math.max(0, fare.totalMinor - loyaltyMinor);

    const segmentRoute = `${originStop.station.code}-${destStop.station.code}`;
    const displayCurrency = dto.displayCurrency ?? resolveCurrencyFromNationality(dto.nationality);
    const displayTotalMinor = displayCurrency !== Currency.ETB
      ? await this.currencyService.convertAmount(totalMinor, Currency.ETB, displayCurrency)
      : totalMinor;

    return {
      scheduleId: dto.scheduleId,
      originStationId: dto.originStationId,
      destinationStationId: dto.destinationStationId,
      segmentRoute,
      seatClassName: dto.seatClassName,
      nationality: dto.nationality,
      adultCount: fare.adultCount,
      childCount: fare.childCount,
      baseFareMinor: fare.baseFarePerPassengerMinor,
      adultFareMinor: fare.adultCount * fare.farePerPassengerMinor,
      childFareMinor: fare.paidChildrenCount * fare.farePerPassengerMinor,
      freeChildrenCount: fare.freeChildrenCount,
      paidChildrenCount: fare.paidChildrenCount,
      premiumMinor: fare.premiumPerPassenger,
      insuranceFeeMinor: fare.insurancePerPassenger,
      totalBaseFareMinor: fare.subtotalMinor,
      discountMinor: fare.discountMinor,
      taxesFeesMinor: 0,
      loyaltyRedemptionMinor: loyaltyMinor,
      totalMinor,
      currency: 'ETB',
      displayCurrency,
      displayTotalMinor,
    };
  }

  async getFareBreakdown(dto: FareBreakdownRequestDto) {
    const schedule = await this.prisma.trainSchedule.findUnique({
      where: { id: dto.scheduleId },
      select: { routeId: true, originStationId: true, destinationStationId: true },
    });
    if (!schedule) throw new NotFoundException('Schedule not found');
    if (!schedule.routeId) throw new NotFoundException('Schedule has no route configured for fare calculation');

    const now = new Date();
    const displayCurrency = dto.displayCurrency ?? Currency.ETB;

    let parsedPassengers: FareBreakdownPassengerDto[];
    try {
      parsedPassengers = JSON.parse(dto.passengers as unknown as string);
    } catch {
      throw new NotFoundException('passengers must be a valid JSON array');
    }

    // Categorise passengers by age
    const categorised = parsedPassengers.map(p => {
      const ageMs = now.getTime() - new Date(p.dateOfBirth).getTime();
      const ageYears = ageMs / (1000 * 60 * 60 * 24 * 365.25);
      return { ...p, category: (ageYears >= 5 ? 'ADULT' : 'CHILD') as 'ADULT' | 'CHILD', ageYears };
    });

    const adultCount = categorised.filter(p => p.category === 'ADULT').length;
    const childCount = categorised.filter(p => p.category === 'CHILD').length;

    // Ask the fare engine for the authoritative free-child count using the full group
    // Use the first passenger's seatClassId as a representative — freeChildrenCount
    // depends only on adultCount/childCount, not on seat class.
    const groupFare = await this.fareEngine.calculate({
      routeId: schedule.routeId!,
      originStationId: dto.originStationId,
      destinationStationId: dto.destinationStationId,
      seatClassId: categorised[0].seatClassId,
      nationality: categorised[0].nationality,
      scheduleId: dto.scheduleId,
      adultCount,
      childCount,
    });
    const freeChildrenAllowed = groupFare.freeChildrenCount;

    // Calculate per-passenger fare rate (engine called with 1 adult, 0 children — pure rate lookup)
    let freeChildrenUsed = 0;
    const passengerLines = await Promise.all(
      categorised.map(async (p) => {
        const fare = await this.fareEngine.calculate({
          routeId: schedule.routeId!,
          originStationId: dto.originStationId,
          destinationStationId: dto.destinationStationId,
          seatClassId: p.seatClassId,
          nationality: p.nationality,
          scheduleId: dto.scheduleId,
          adultCount: 1,
          childCount: 0,
        });

        const isFree = p.category === 'CHILD' && freeChildrenUsed < freeChildrenAllowed;
        if (isFree) freeChildrenUsed++;

        const fareMinor = isFree
          ? fare.premiumPerPassenger + fare.insurancePerPassenger
          : fare.farePerPassengerMinor;
        const displayFareMinor = displayCurrency !== Currency.ETB
          ? await this.currencyService.convertAmount(fareMinor, Currency.ETB, displayCurrency)
          : fareMinor;

        return {
          passengerName: p.passengerName,
          dateOfBirth: p.dateOfBirth,
          category: p.category,
          ageYears: Math.floor(p.ageYears),
          seatClassId: fare.seatClassId,
          seatClassName: fare.seatClassName,
          nationality: p.nationality ?? null,
          baseFareMinor: fare.baseFarePerPassengerMinor,
          premiumMinor: fare.premiumPerPassenger,
          insuranceFeeMinor: fare.insurancePerPassenger,
          fareMinor,
          isFree,
          displayCurrency,
          displayFareMinor,
        };
      }),
    );

    let subtotalMinor = passengerLines.reduce((sum, l) => sum + l.fareMinor, 0);

    let discountMinor = 0;
    if (dto.promoCode) {
      const promo = await this.prisma.promotion.findUnique({ where: { code: dto.promoCode } });
      if (promo?.active && promo.validUntil > now) {
        discountMinor = promo.percentOff
          ? Math.round(subtotalMinor * promo.percentOff / 100)
          : (promo.amountOffMinor ?? 0);
      }
    }

    const totalMinor = subtotalMinor - discountMinor;
    const displayTotalMinor = displayCurrency !== Currency.ETB
      ? await this.currencyService.convertAmount(totalMinor, Currency.ETB, displayCurrency)
      : totalMinor;

    return {
      scheduleId: dto.scheduleId,
      originStationId: dto.originStationId,
      destinationStationId: dto.destinationStationId,
      passengers: passengerLines,
      subtotalMinor,
      discountMinor,
      totalMinor,
      currency: 'ETB',
      displayCurrency,
      displayTotalMinor,
    };
  }

  private async calculateFaresForSegment(
    schedule: ScheduleWithIncludes,
    originStationId: string,
    destinationStationId: string,
    nationality?: string,
  ): Promise<Array<{ seatClassName: string; baseFareMinor: number; displayCurrency: Currency; displayAmountMinor: number }>> {
    const displayCurrency = resolveCurrencyFromNationality(nationality);

    const nationalityUpper = (nationality ?? '').toUpperCase();
    const nationalityType = (nationalityUpper === 'ETHIOPIAN' || nationalityUpper === 'DJIBOUTIAN')
      ? 'LOCAL' : 'INTERNATIONAL';

    // Collect seat class IDs from the schedule include for the ID set,
    // but fetch fresh records from DB so updated baseFareMinor is always current
    const seatClassIdSet = new Set<string>();
    for (const a of schedule.coachAssignments) {
      for (const sc of (a.coach.coachType?.seatClasses ?? [])) {
        if (sc.isActive) seatClassIdSet.add(sc.id);
      }
    }
    const freshSeatClasses = await this.prisma.seatClass.findMany({
      where: {
        id: { in: Array.from(seatClassIdSet) },
        isActive: true,
        OR: [
          { nationalityType: null },
          { nationalityType: nationalityType },
        ],
      },
    });
    const seatClassMap = new Map(freshSeatClasses.map(sc => [sc.id, sc]));
    const seatClasses = freshSeatClasses.sort((a, b) => a.baseFareMinor - b.baseFareMinor);

    if (seatClasses.length === 0) return [];

    if (schedule.routeId) {
      const results = await Promise.all(
        seatClasses.map(async (sc) => {
          try {
            const fare = await this.fareEngine.calculate({
              routeId: schedule.routeId!,
              originStationId,
              destinationStationId,
              seatClassId: sc.id,
              nationality,
              scheduleId: schedule.id,
            });
            return {
              // Use the input seat class name (sc.name) so it always matches what
              // buildCoachTypeDetails looks up via coachType.seatClasses. The fare
              // engine may resolve a nationality-specific variant (nationalitySeatClass)
              // whose name differs from sc.name, which would cause the class to be
              // silently dropped from coachTypes and show N/A on the results page.
              seatClassName:      sc.name,
              baseFareMinor:      fare.totalMinor,
              displayCurrency:    fare.billingCurrency as Currency,
              displayAmountMinor: fare.totalInBillingCurrency,
            };
          } catch {
            return null;
          }
        }),
      );

      const validResults = results.filter(
        (r): r is { seatClassName: string; baseFareMinor: number; displayCurrency: Currency; displayAmountMinor: number } => r !== null,
      );
      if (validResults.length > 0) return validResults;
    }

    // Fallback: use station codes from already-loaded stopTimes when available
    const originStop = schedule.stopTimes.find(st => st.stationId === originStationId);
    const destStop   = schedule.stopTimes.find(st => st.stationId === destinationStationId);
    const originCode = originStop?.station?.code;
    const destCode   = destStop?.station?.code;

    if (originCode && destCode) {
      const segmentRoute = `${originCode}-${destCode}`;
      const now = new Date();

      const fareRules = await this.prisma.fareRule.findMany({
        where: {
          route: segmentRoute,
          seatClassId: { in: seatClasses.map((sc: any) => sc.id) },
          validFrom: { lte: now },
          OR: [{ validUntil: null }, { validUntil: { gte: now } }],
        },
      });

      if (fareRules.length > 0) {
        const exchangeRate = await this.currencyService.getExchangeRate(Currency.ETB, displayCurrency);
        const TAX_RATE = 0.05;
        return fareRules.map(rule => {
          const totalMinor = rule.baseFareMinor + Math.round(rule.baseFareMinor * TAX_RATE);
          return {
            seatClassName:      seatClassMap.get(rule.seatClassId)?.name ?? 'Unknown',
            baseFareMinor:      totalMinor,
            displayCurrency,
            displayAmountMinor: Math.round(totalMinor * exchangeRate),
          };
        });
      }
    }

    return [];
  }

  // buildCoachTypeDetails is pure in-memory — no async needed
  private buildCoachTypeDetails(
    schedule: ScheduleWithIncludes,
    faresByClass: Array<{ seatClassName: string; baseFareMinor: number; displayCurrency: Currency; displayAmountMinor: number }>,
    nationality?: string,
    availabilityByClass: Record<string, number> = {},
  ): Array<{
    coachTypeId: string;
    coachTypeName: string;
    coachTypeCode: string;
    coachId: string;
    classes: Array<{ name: string; baseFareMinor: number; displayCurrency: Currency; displayAmountMinor: number; available: number }>;
  }> {
    const coachTypeMap = new Map<
      string,
      { coachType: any; classNames: Set<string>; coachId: string }
    >();

    for (const assignment of schedule.coachAssignments) {
      const coachType = assignment.coach.coachType;
      if (!coachType) continue;

      if (!coachTypeMap.has(coachType.id)) {
        coachTypeMap.set(coachType.id, {
          coachType,
          classNames: new Set(),
          coachId: assignment.coach.id,
        });
      }

      const nationalityUpper = (nationality ?? '').toUpperCase();
      const resolvedNationalityType = (nationalityUpper === 'ETHIOPIAN' || nationalityUpper === 'DJIBOUTIAN')
        ? 'LOCAL' : 'INTERNATIONAL';

      const entry = coachTypeMap.get(coachType.id)!;
      coachType.seatClasses?.forEach((sc: any) => {
        // Exclude classes that belong to the wrong nationality type
        if (sc.nationalityType && sc.nationalityType !== resolvedNationalityType) return;
        if (faresByClass.some(f => f.seatClassName === sc.name)) entry.classNames.add(sc.name);
      });
    }

    const result = [];
    for (const [, { coachType, classNames, coachId }] of coachTypeMap) {
      const classes = Array.from(classNames)
        .map((className) => {
          const fareInfo = faresByClass.find((f) => f.seatClassName === className);
          if (!fareInfo) return null;
          return {
            name:               className,
            baseFareMinor:      fareInfo.baseFareMinor,
            displayCurrency:    fareInfo.displayCurrency,
            displayAmountMinor: fareInfo.displayAmountMinor,
            available:          availabilityByClass[className] ?? 0,
          };
        })
        .filter((c): c is { name: string; baseFareMinor: number; displayCurrency: Currency; displayAmountMinor: number; available: number } => c !== null)
        .sort((a, b) => a.baseFareMinor - b.baseFareMinor);

      if (classes.length === 0) continue;
      result.push({
        coachTypeId: coachType.id,
        coachTypeName: coachType.name,
        coachTypeCode: coachType.code,
        coachId,
        classes,
      });
    }

    return result.sort((a, b) => {
      const minPriceA = Math.min(...a.classes.map((c) => c.baseFareMinor));
      const minPriceB = Math.min(...b.classes.map((c) => c.baseFareMinor));
      return minPriceA - minPriceB;
    });
  }

}