import {
  BadRequestException,
  Injectable,
  Logger,
  NotFoundException,
} from '@nestjs/common';
import { InjectDataSource } from '@nestjs/typeorm';
import { DataSource } from 'typeorm';

import { Booking } from '../bookings/entities/booking.entity';
import { RouteMilestone } from '../routes/entities/route-milestone.entity';
import { TrainSchedule } from '../train-schedules/entities/train-schedule.entity';
import { BookingBatchService, type Capacity } from './booking-batch.service';
import { TrainCheckpointEvent } from './entities/train-checkpoint-event.entity';

/**
 * Intercity (DOMESTIC) ride-along: intercity bookings never get their own
 * train — they ride a passing import/export schedule whose route milestones
 * contain the booking's origin strictly before its destination.
 *
 * Flow: the customer books a corridor with no date; at finalize time staff see
 * every waiting intercity booking whose corridor lies on the schedule's route,
 * with its wagon/weight/length need against the train's remaining capacity;
 * accepting reserves it (pay window → payment → allocation, same lifecycle as
 * a batch reservation). Cargo is loaded manually when the train reaches the
 * booking's origin yard and unloaded at its destination yard.
 */
@Injectable()
export class IntercityService {
  private readonly logger = new Logger(IntercityService.name);

  constructor(
    @InjectDataSource() private readonly dataSource: DataSource,
    private readonly bookingBatchService: BookingBatchService,
  ) {}

  /**
   * Waiting intercity bookings this schedule could carry, with the train's
   * remaining capacity along all three axes (wagons, weight, length) and each
   * booking's need, so staff can pick what fits.
   */
  async listCandidates(scheduleId: string) {
    const schedule = await this.getSchedule(scheduleId);
    const milestoneSeq = await this.routeMilestoneSequence(schedule);
    const capacity = await this.bookingBatchService.intercityCapacity(scheduleId);

    const waiting = milestoneSeq
      ? await this.findWaitingIntercityBookings(milestoneSeq)
      : [];
    const accepted = await this.findAcceptedIntercityBookings(scheduleId);

    return {
      scheduleId,
      routeId: schedule.routeId ?? null,
      remaining: capacity?.budget ?? null,
      candidates: waiting.map((booking) => {
        const need = capacity?.needFor(booking) ?? null;
        return {
          ...this.mapBooking(booking),
          need,
          fits: need && capacity ? fits(need, capacity.budget) : false,
        };
      }),
      accepted: accepted.map((booking) => ({
        ...this.mapBooking(booking),
        need: capacity?.needFor(booking) ?? null,
      })),
    };
  }

  /**
   * Accept selected waiting intercity bookings onto this train, in the given
   * order, each re-checked against the shrinking capacity budget. Commercial
   * bookings open a pay window (payment → allocation runs on the existing
   * settle lifecycle); government bookings allocate immediately.
   */
  async acceptBookings(scheduleId: string, bookingIds: string[]) {
    if (bookingIds.length === 0) {
      throw new BadRequestException('Select at least one intercity booking');
    }
    const schedule = await this.getSchedule(scheduleId);
    const milestoneSeq = await this.routeMilestoneSequence(schedule);
    if (!milestoneSeq) {
      throw new BadRequestException(
        'Schedule has no route milestones — cannot serve intercity corridors',
      );
    }
    const capacity = await this.bookingBatchService.intercityCapacity(scheduleId);
    if (!capacity) {
      throw new BadRequestException(
        'Schedule has no locomotive/train set — capacity unknown',
      );
    }

    const accepted: string[] = [];
    const rejected: Array<{ bookingId: string; reason: string }> = [];
    let budget = capacity.budget;

    for (const bookingId of bookingIds) {
      const booking = await this.dataSource
        .getRepository(Booking)
        .findOne({ where: { id: bookingId }, relations: { bookingContainers: true } });
      if (!booking) {
        rejected.push({ bookingId, reason: 'Booking not found' });
        continue;
      }
      const notWaiting = this.whyNotWaiting(booking, milestoneSeq);
      if (notWaiting) {
        rejected.push({ bookingId, reason: notWaiting });
        continue;
      }
      const need = capacity.needFor(booking);
      if (!fits(need, budget)) {
        rejected.push({
          bookingId,
          reason: 'Does not fit the remaining wagon/weight/length capacity',
        });
        continue;
      }
      await this.bookingBatchService.acceptIntercity(booking, scheduleId);
      budget = subtract(budget, need);
      accepted.push(bookingId);
      this.logger.log(
        `Intercity booking ${booking.reference ?? bookingId} accepted onto schedule ${scheduleId}`,
      );
    }

    return { accepted, rejected, remaining: budget };
  }

  /**
   * Mark an accepted intercity booking's cargo as loaded. Only allowed while
   * the train is physically at the booking's origin yard: either it has not
   * departed yet and the booking boards at the train's own origin, or the
   * latest recorded checkpoint is at the booking's origin yard.
   */
  async loadBooking(scheduleId: string, bookingId: string) {
    const { schedule, booking } = await this.getAcceptedBooking(
      scheduleId,
      bookingId,
    );
    if (booking.status !== 'PAID') {
      throw new BadRequestException(
        `Booking must be paid before loading (currently ${booking.status})`,
      );
    }
    await this.assertTrainAtYard(schedule, booking.originYardId, 'origin');
    await this.dataSource
      .getRepository(Booking)
      .update(bookingId, { status: 'IN_TRANSIT' });
    return { bookingId, status: 'IN_TRANSIT' as const };
  }

  /**
   * Mark an intercity booking's cargo as unloaded at its destination yard —
   * requires the latest checkpoint to be at that yard. Completes the booking.
   */
  async unloadBooking(scheduleId: string, bookingId: string) {
    const { schedule, booking } = await this.getAcceptedBooking(
      scheduleId,
      bookingId,
    );
    if (booking.status !== 'IN_TRANSIT') {
      throw new BadRequestException(
        `Booking must be loaded/in transit before unloading (currently ${booking.status})`,
      );
    }
    await this.assertTrainAtYard(schedule, booking.destinationYardId, 'destination');
    await this.dataSource
      .getRepository(Booking)
      .update(bookingId, { status: 'COMPLETED' });
    return { bookingId, status: 'COMPLETED' as const };
  }

  // ---- helpers ---------------------------------------------------------------

  private async getSchedule(scheduleId: string): Promise<TrainSchedule> {
    const schedule = await this.dataSource
      .getRepository(TrainSchedule)
      .findOne({ where: { id: scheduleId } });
    if (!schedule) {
      throw new NotFoundException(`Train schedule ${scheduleId} not found`);
    }
    return schedule;
  }

  /**
   * yardId → sequenceNo for the schedule's route. Falls back to a two-stop
   * origin/destination pseudo-route for legacy schedules without a routeId,
   * so an intercity booking exactly matching the train's own corridor still
   * qualifies.
   */
  private async routeMilestoneSequence(
    schedule: TrainSchedule,
  ): Promise<Map<string, number> | null> {
    if (schedule.routeId) {
      const milestones = await this.dataSource
        .getRepository(RouteMilestone)
        .find({ where: { routeId: schedule.routeId }, order: { sequenceNo: 'ASC' } });
      if (milestones.length >= 2) {
        return new Map(milestones.map((m) => [m.yardId, m.sequenceNo]));
      }
    }
    if (schedule.originStationId && schedule.destinationStationId) {
      return new Map([
        [schedule.originStationId, 1],
        [schedule.destinationStationId, 2],
      ]);
    }
    return null;
  }

  /** Waiting = ready intercity bookings not yet on any train, corridor on this route. */
  private async findWaitingIntercityBookings(
    milestoneSeq: Map<string, number>,
  ): Promise<Booking[]> {
    const pool = await this.dataSource
      .getRepository(Booking)
      .createQueryBuilder('booking')
      .leftJoinAndSelect('booking.company', 'company')
      .leftJoinAndSelect('booking.bookingContainers', 'bookingContainer')
      .leftJoinAndSelect('booking.originYard', 'originYard')
      .leftJoinAndSelect('booking.destinationYard', 'destinationYard')
      .where(`booking.trade_direction = 'DOMESTIC'`)
      .andWhere('booking.train_schedule_id IS NULL')
      .andWhere(
        `((booking.is_government = false AND booking.status = 'FULLY_EXECUTED')
          OR (booking.is_government = true AND booking.status = 'APPROVED'))`,
      )
      .orderBy('booking.is_government', 'DESC')
      .addOrderBy('booking.priority_score', 'DESC')
      .addOrderBy('booking.created_at', 'ASC')
      .getMany();

    return pool.filter((b) => this.corridorOnRoute(b, milestoneSeq));
  }

  /** Intercity bookings already reserved/allocated on this schedule. */
  private async findAcceptedIntercityBookings(
    scheduleId: string,
  ): Promise<Booking[]> {
    return this.dataSource
      .getRepository(Booking)
      .createQueryBuilder('booking')
      .leftJoinAndSelect('booking.company', 'company')
      .leftJoinAndSelect('booking.bookingContainers', 'bookingContainer')
      .leftJoinAndSelect('booking.originYard', 'originYard')
      .leftJoinAndSelect('booking.destinationYard', 'destinationYard')
      .where(`booking.trade_direction = 'DOMESTIC'`)
      .andWhere('booking.train_schedule_id = :scheduleId', { scheduleId })
      .orderBy('booking.created_at', 'ASC')
      .getMany();
  }

  private corridorOnRoute(
    booking: Booking,
    milestoneSeq: Map<string, number>,
  ): boolean {
    const originSeq = milestoneSeq.get(booking.originYardId);
    const destinationSeq = milestoneSeq.get(booking.destinationYardId);
    return (
      originSeq != null && destinationSeq != null && originSeq < destinationSeq
    );
  }

  private whyNotWaiting(
    booking: Booking,
    milestoneSeq: Map<string, number>,
  ): string | null {
    if (booking.tradeDirection !== 'DOMESTIC') {
      return 'Not an intercity booking';
    }
    if (booking.trainScheduleId) {
      return 'Already assigned to a train';
    }
    const readyStatus = booking.isGovernment ? 'APPROVED' : 'FULLY_EXECUTED';
    if (booking.status !== readyStatus) {
      return `Not ready to board (status ${booking.status})`;
    }
    if (!this.corridorOnRoute(booking, milestoneSeq)) {
      return "Corridor is not on this schedule's route";
    }
    return null;
  }

  private async getAcceptedBooking(scheduleId: string, bookingId: string) {
    const schedule = await this.getSchedule(scheduleId);
    const booking = await this.dataSource
      .getRepository(Booking)
      .findOne({ where: { id: bookingId } });
    if (!booking) throw new NotFoundException(`Booking ${bookingId} not found`);
    if (booking.trainScheduleId !== scheduleId) {
      throw new BadRequestException('Booking is not assigned to this schedule');
    }
    if (booking.tradeDirection !== 'DOMESTIC') {
      throw new BadRequestException('Not an intercity booking');
    }
    return { schedule, booking };
  }

  /**
   * The train is "at" a yard when the latest recorded checkpoint is that yard,
   * or — for a booking boarding at the train's own origin — when the train has
   * not recorded any checkpoint yet (still sitting at its origin).
   */
  private async assertTrainAtYard(
    schedule: TrainSchedule,
    yardId: string,
    side: 'origin' | 'destination',
  ): Promise<void> {
    const latest = await this.dataSource
      .getRepository(TrainCheckpointEvent)
      .findOne({
        where: { trainScheduleId: schedule.id },
        order: { occurredAt: 'DESC', createdAt: 'DESC' },
      });

    if (!latest) {
      if (side === 'origin' && schedule.originStationId === yardId) return;
      throw new BadRequestException(
        'Train has not reached this yard yet — record its checkpoint first',
      );
    }
    if (latest.yardId !== yardId) {
      throw new BadRequestException(
        `Train's last recorded position is not at the booking's ${side} yard`,
      );
    }
  }

  private mapBooking(booking: Booking) {
    return {
      id: booking.id,
      reference: booking.reference,
      status: booking.status,
      freightType: booking.freightType,
      isGovernment: booking.isGovernment,
      customer: booking.company?.name ?? 'Unknown customer',
      originYardId: booking.originYardId,
      destinationYardId: booking.destinationYardId,
      origin:
        booking.originYard?.label ?? booking.originYard?.code ?? 'Unknown origin',
      destination:
        booking.destinationYard?.label ??
        booking.destinationYard?.code ??
        'Unknown destination',
      weightTons: Number(booking.cargoTotalWeightVgm ?? 0),
      paymentDeadline: booking.paymentDeadline?.toISOString() ?? null,
    };
  }
}

function fits(need: Capacity, budget: Capacity): boolean {
  return (
    need.wagons <= budget.wagons &&
    need.weightTons <= budget.weightTons &&
    need.lengthMeters <= budget.lengthMeters
  );
}

function subtract(budget: Capacity, need: Capacity): Capacity {
  return {
    wagons: budget.wagons - need.wagons,
    weightTons: budget.weightTons - need.weightTons,
    lengthMeters: budget.lengthMeters - need.lengthMeters,
  };
}