import { Injectable, Logger } from "@nestjs/common";
import { PrismaService } from "../../../prisma/prisma.service";
import { computeHours, getWeekStart } from "src/common/utils/date-utils";

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

    constructor(private readonly prisma: PrismaService) {}

    private async computeHoursPrevious4Weeks(employeeId: number, holidayDate: Date): Promise<number> {
        //sets the end of the window to 1ms before the week with the holiday
        const holidayWeekStart = getWeekStart(holidayDate);
        const windowEnd = new Date(holidayWeekStart.getTime() - 1);
        //sets the start of the window to 28 days ( 4 completed weeks ) before the week with the holiday
        const windowStart = new Date(windowEnd.getTime() - 28 * 24 * 60 * 60000 + 1 )

        const validCodes = ['G1', 'G45', 'G56', 'G104', 'G105', 'G700'];
        //fetches all shift of the employee in said window ( 4 previous completed weeks )
        const shifts = await this.prisma.shifts.findMany({
            where: { timesheet: { employee_id: employeeId } ,
            date:  { gte: windowStart, lte: windowEnd },
            bank_code: { bank_code: { in: validCodes } },
            },
            select: { date: true, start_time: true, end_time: true },
        });

        const totalHours = shifts.map(s => computeHours(s.start_time, s.end_time)).reduce((sum, h)=> sum + h, 0);
        const dailyHours = totalHours / 20;

        return dailyHours;
    }

    async calculateHolidayPay( employeeId: number, holidayDate: Date, modifier: number): Promise<number> {
        const hours = await this.computeHoursPrevious4Weeks(employeeId, holidayDate);
        const dailyRate = Math.min(hours, 8);
        this.logger.debug(`Holiday pay calculation: hours= ${hours.toFixed(2)}`);
        return dailyRate * modifier;
    }
}