import { Injectable, Logger } from '@nestjs/common'
import {
  TimeSlotStatus,
  TimeSlotSource,
  MembershipStatus,
  BookingStatus,
  SLOT_GENERATION_DAYS,
  DEFAULT_SLOT_CAPACITY,
  getDefaultTimeSlots,
} from '@mp-pilates/shared'
import { PrismaService } from '../prisma/prisma.service'

/** Build a UTC Date for midnight of a local calendar date */
function toUtcMidnight(date: Date): Date {
  const d = new Date(date)
  d.setUTCHours(0, 0, 0, 0)
  return d
}

@Injectable()
export class SlotGeneratorService {
  private readonly logger = new Logger(SlotGeneratorService.name)

  constructor(private readonly prisma: PrismaService) {}

  /**
   * Generate time slots for the next `daysAhead` days based on the fixed
   * default schedule (Mon-Sun: 08:00-09:00, then 09:30-21:30 hourly).
   * Uses `createMany` with `skipDuplicates` so re-runs are safe.
   *
   * @returns Number of newly created slots
   */
  async generateSlots(daysAhead: number = SLOT_GENERATION_DAYS): Promise<number> {
    const defaultSlots = getDefaultTimeSlots()

    const tomorrow = new Date()
    tomorrow.setDate(tomorrow.getDate() + 1)
    tomorrow.setUTCHours(0, 0, 0, 0)

    const slotsToCreate: Array<{
      date: Date
      startTime: string
      endTime: string
      capacity: number
      source: TimeSlotSource
    }> = []

    for (let offset = 0; offset < daysAhead; offset++) {
      const target = new Date(tomorrow)
      target.setDate(target.getDate() + offset)

      for (const slot of defaultSlots) {
        slotsToCreate.push({
          date: toUtcMidnight(target),
          startTime: slot.startTime,
          endTime: slot.endTime,
          capacity: DEFAULT_SLOT_CAPACITY,
          source: TimeSlotSource.TEMPLATE,
        })
      }
    }

    if (slotsToCreate.length === 0) {
      return 0
    }

    const result = await this.prisma.timeSlot.createMany({
      data: slotsToCreate,
      skipDuplicates: true,
    })

    this.logger.log(`Generated ${result.count} new time slots`)
    return result.count
  }

  /**
   * Mark all OPEN slots whose date is strictly before today as CLOSED.
   *
   * @returns Number of slots updated
   */
  async cleanupExpiredSlots(): Promise<number> {
    const today = new Date()
    today.setUTCHours(0, 0, 0, 0)

    const result = await this.prisma.timeSlot.updateMany({
      where: {
        status: TimeSlotStatus.OPEN,
        date: { lt: today },
      },
      data: { status: TimeSlotStatus.CLOSED },
    })

    this.logger.log(`Closed ${result.count} expired time slots`)
    return result.count
  }

  /**
   * Expire memberships whose end date has passed or whose remaining sessions
   * have been exhausted.
   *
   * @returns Total number of memberships updated
   */
  async checkExpiredMemberships(): Promise<number> {
    const now = new Date()

    const [expired, usedUp] = await Promise.all([
      this.prisma.membership.updateMany({
        where: {
          status: MembershipStatus.ACTIVE,
          expireDate: { lt: now },
        },
        data: { status: MembershipStatus.EXPIRED },
      }),
      this.prisma.membership.updateMany({
        where: {
          status: MembershipStatus.ACTIVE,
          remainingTimes: 0,
        },
        data: { status: MembershipStatus.USED_UP },
      }),
    ])

    const total = expired.count + usedUp.count
    this.logger.log(
      `Expired ${expired.count} memberships by date, ${usedUp.count} by sessions`,
    )
    return total
  }

  /**
   * Mark CONFIRMED bookings whose associated time slot is in the past as
   * COMPLETED.
   *
   * @returns Number of bookings updated
   */
  async completeBookings(): Promise<number> {
    const today = new Date()
    today.setUTCHours(0, 0, 0, 0)

    const result = await this.prisma.booking.updateMany({
      where: {
        status: BookingStatus.CONFIRMED,
        timeSlot: {
          date: { lt: today },
        },
      },
      data: { status: BookingStatus.COMPLETED, completedAt: new Date(), reviewReminderDueAt: new Date(Date.now() + 24 * 3600000) },
    })

    this.logger.log(`Completed ${result.count} past bookings`)
    return result.count
  }
}