import { Injectable } from '@nestjs/common';
import { DataSource } from 'typeorm';

/**
 * READ-ONLY view into the train-scheduling / wagons domain for the warehouse module.
 *
 * IMPORTANT: this facade only ever runs SELECTs. The warehouse must never modify
 * wagon assignment, rescheduling, import_ready/export_ready, or locomotive flow.
 * It is intentionally decoupled (raw SQL) so it does not import the scheduling
 * services/entities and cannot accidentally write to them.
 */
export interface WagonView {
  id: string;
  wagonNumber: string;
  status: string;
  trainId: string | null;
}

export interface BookingScheduleView {
  schedule: {
    id: string;
    status: string;
    scheduledDepartureDate: string | null;
    scheduledArrivalDate: string | null;
    originStationId: string | null;
    destinationStationId: string | null;
  } | null;
  wagon: {
    wagonId: string | null;
    wagonNumber: string | null;
    sequenceNo: number | null;
    allocatedWeightTons: number | null;
  } | null;
  /** Mirror of schedule.status — the headline "where is the train" indicator. */
  departureStatus: string | null;
}

@Injectable()
export class SchedulingReadFacade {
  constructor(private readonly dataSource: DataSource) {}

  /** Look up a single physical wagon. Returns null if it does not exist. */
  async findWagon(wagonId: string): Promise<WagonView | null> {
    const rows = await this.dataSource.query(
      `SELECT id, wagon_number AS "wagonNumber", status, train_id AS "trainId"
       FROM freight.wagons
       WHERE id = $1 AND deleted_at IS NULL
       LIMIT 1`,
      [wagonId],
    );
    return rows?.[0] ?? null;
  }

  /** True when the wagon is already part of a train set (selected by an existing schedule). */
  async isWagonScheduled(wagonId: string): Promise<boolean> {
    const rows = await this.dataSource.query(
      `SELECT 1 FROM freight.train_set_wagons
       WHERE physical_wagon_id = $1 AND deleted_at IS NULL
       LIMIT 1`,
      [wagonId],
    );
    return (rows?.length ?? 0) > 0;
  }

  /** List wagons usable for loading (available, or already assigned to a schedule). */
  listLoadableWagons(): Promise<WagonView[]> {
    return this.dataSource.query(
      `SELECT id, wagon_number AS "wagonNumber", status, train_id AS "trainId"
       FROM freight.wagons
       WHERE deleted_at IS NULL
         AND status NOT IN ('RETIRED', 'MAINTENANCE')
       ORDER BY wagon_number ASC`,
    );
  }

  /**
   * Given a booking, return its related schedule, wagon assignment and departure status.
   * All fields are read straight from the scheduling tables — nothing is written.
   */
  async getBookingSchedule(bookingId: string): Promise<BookingScheduleView> {
    const scheduleRows = await this.dataSource.query(
      `SELECT ts.id,
              ts.status,
              ts.scheduled_departure_date AS "scheduledDepartureDate",
              ts.scheduled_arrival_date   AS "scheduledArrivalDate",
              ts.origin_station_id        AS "originStationId",
              ts.destination_station_id   AS "destinationStationId"
       FROM freight.train_schedule_bookings tsb
       INNER JOIN freight.train_schedules ts ON ts.id = tsb.train_schedule_id
       WHERE tsb.booking_id = $1 AND ts.deleted_at IS NULL
       ORDER BY ts.scheduled_departure_date DESC NULLS LAST
       LIMIT 1`,
      [bookingId],
    );
    const schedule = scheduleRows?.[0] ?? null;

    const wagonRows = await this.dataSource.query(
      `SELECT w.id          AS "wagonId",
              w.wagon_number AS "wagonNumber",
              tsw.sequence_no AS "sequenceNo",
              wba.allocated_weight_tons AS "allocatedWeightTons"
       FROM freight.wagon_booking_allocations wba
       INNER JOIN freight.train_set_wagons tsw ON tsw.id = wba.train_set_wagon_id
       LEFT JOIN freight.wagons w ON w.id = tsw.physical_wagon_id
       WHERE wba.booking_id = $1
       ORDER BY tsw.sequence_no ASC NULLS LAST
       LIMIT 1`,
      [bookingId],
    );
    const wagon = wagonRows?.[0] ?? null;

    return {
      schedule,
      wagon,
      departureStatus: schedule?.status ?? null,
    };
  }
}