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

@Injectable()
export class OvertimeService {
    
    private logger = new Logger(OvertimeService.name);
    private daily_max = 8; // maximum for regular hours per day
    private weekly_max = 40; //maximum for regular hours per week
    private INCLUDED_TYPES = ['EMERGENCY', 'EVENING','OVERTIME','REGULAR'] as const; // included types for weekly overtime calculation

    constructor(private prisma: PrismaService) {}

    //calculate daily overtime
    async getDailyOvertimeHoursForDay(employee_id: number, date: Date): Promise<number> {
        const shifts = await this.prisma.shifts.findMany({
            where: { date: date, timesheet: { employee_id: employee_id } },
            select: { start_time: true, end_time: true },
        });
        const total = shifts.map((shift)=> 
            computeHours(shift.start_time, shift.end_time, 5)).reduce((sum, hours)=> sum + hours, 0);
        const overtime = Math.max(0, total - this.daily_max);

        this.logger.debug(`[OVERTIME]-[DAILY] total=${total.toFixed(2)}h, overtime= ${overtime.toFixed(2)}h`);
        return overtime;    
    }

    //calculate Weekly overtime
    async getWeeklyOvertimeHours(employee_id: number, ref_date: Date): Promise<number> {
        const week_start = getWeekStart(ref_date);
        const week_end   = getWeekEnd(week_start);

        //fetches all shifts from INCLUDED_TYPES array
        const included_shifts = await this.prisma.shifts.findMany({
            where: { 
                date: { gte:week_start, lte: week_end },
                timesheet: { employee_id },
                bank_code: { type: { in: this.INCLUDED_TYPES as unknown as string[] } },
                },
                select: { start_time: true, end_time: true },
                orderBy: [{date: 'asc'}, {start_time:'asc'}],
        });

        //calculate total hours of those shifts minus weekly Max to find total overtime hours
        const total = included_shifts.map(shift => computeHours(shift.start_time, shift.end_time, 5))
                                              .reduce((sum, hours)=> sum+hours, 0);
        const overtime = Math.max(0, total - this.weekly_max);

        this.logger.debug(`[OVERTIME]-[WEEKLY] total=${total.toFixed(2)}h, overtime= ${overtime.toFixed(2)}h`);
        return overtime;
    }

    //transform REGULAR shifts to OVERTIME when exceed 40hrs of included_types of shift
    async transformRegularHoursToWeeklyOvertime(
        employee_id: number,
        ref_date: Date,
        tx?: Prisma.TransactionClient,
    ): Promise<void> {
        //ensures the use of the transaction if needed. fallback to this.prisma if no transaction is detected.
        const db = tx ?? this.prisma;

        //calculate weekly overtime
        const overtime_hours = await this.getWeeklyOvertimeHours(employee_id, ref_date);
        if(overtime_hours <= 0) return;

        const convert_to_minutes = Math.round(overtime_hours * 60);

        const [regular, overtime] = await Promise.all([
            db.bankCodes.findFirst({where: { type: 'REGULAR' }, select: { id: true } }),
            db.bankCodes.findFirst({where: { type: 'OVERTIME'}, select: { id: true } }),
        ]);
        if(!regular || !overtime) return;
        
        const week_start = getWeekStart(ref_date);
        const week_end   = getWeekEnd(week_start);

        //gets all regular shifts and order them by desc
        const regular_shifts_desc = await db.shifts.findMany({
            where: {
                date: { gte:week_start, lte: week_end },
                timesheet: { employee_id },
                bank_code_id: regular.id,
            },
            select: {
                id: true,
                timesheet_id: true,
                date: true,
                start_time: true,
                end_time: true,
                is_remote: true,
                comment: true,
            },
            orderBy: [{date: 'desc'}, {start_time:'desc'}],
        });

        let remaining_minutes = convert_to_minutes;

        for(const shift of regular_shifts_desc) {
            if(remaining_minutes <= 0) break;

            const start = shift.start_time;
            const end = shift.end_time;
            const duration_in_minutes = Math.max(0, Math.round((end.getTime() - start.getTime())/60000));
            if(duration_in_minutes === 0) continue;

            if(duration_in_minutes <= remaining_minutes) {
                await db.shifts.update({
                    where: { id: shift.id },
                    data: { bank_code_id: overtime.id },
                });
                remaining_minutes -= duration_in_minutes;
                continue;
            }
            //sets the start_time of the new overtime shift
            const new_overtime_start = new Date(end.getTime() - remaining_minutes * 60000);

            //shorten the regular shift
            await db.shifts.update({
                where: { id: shift.id },
                data: { end_time: new_overtime_start },
            });

            //creates the new overtime shift to replace the shorten regular shift
            await db.shifts.create({
                data: {
                    timesheet_id: shift.timesheet_id,
                    date: shift.date,
                    start_time: new_overtime_start,
                    end_time: end,
                    is_remote: shift.is_remote,
                    comment: shift.comment,
                    bank_code_id: overtime.id,
                },
            });
            remaining_minutes = 0;
        }
        this.logger.debug(`[OVERTIME]-[WEEKLY]-[TRANSFORM] emp=${employee_id} 
            week: ${week_start.toISOString().slice(0,10)}..${week_end.toISOString().slice(0,10)}
            converted= ${(convert_to_minutes-remaining_minutes)/60}h`);
    }

    //apply modifier to overtime hours
    // calculateOvertimePay(overtime_hours: number, modifier: number): number {
    //     const pay = overtime_hours * modifier;
    //     this.logger.debug(`Overtime payable hours = ${pay.toFixed(2)} (hours ${overtime_hours}, modifier ${modifier})`);

    //     return pay;
    // }

}