import { Injectable, NotFoundException } from "@nestjs/common";
import { EmployeePeriodOverviewDto } from "../dtos/overview-employee-period.dto";
import { PayPeriodOverviewDto } from "../dtos/overview-pay-period.dto";
import { PrismaService } from "src/prisma/prisma.service";

@Injectable()
export class PayPeriodsOverviewService {
    constructor(private readonly prisma: PrismaService) {}
        //function to get a full overview of a selected period filtered by employee ID
    async getOverview(periodNumber: number): Promise<PayPeriodOverviewDto> {
        //fetch the period
        const period = await this.prisma.payPeriods.findUnique({
            where: { period_number: periodNumber },
        });
        if(!period) {
            throw new NotFoundException(`Period #${periodNumber} not found`);
        }

        //fetch all included shifts for that period
        const shifts = await this.prisma.shifts.findMany({
            where: {
                date: {
                    gte: period.start_date,
                    lte: period.end_date,
                },
            },
            include: {
                timesheet: {
                    include: {
                        employee: { include: { user: true }},
                    },
                },
            },
        });

        //regroup by employee
        const map = new Map<string, EmployeePeriodOverviewDto>();
        for (const shift of shifts) {
            const employee_record = shift.timesheet.employee;
            const user = employee_record.user;
            const employee_id = employee_record.user_id;
            const employee_name = `${user.first_name} ${user.last_name}`;
            const hours = (shift.end_time.getTime() - shift.start_time.getTime() / 3600000);

            //check if employee had prior shifts and adds hours of found shift to the total hours
            if (map.has(employee_id)) {
                const summary = map.get(employee_id)!;
                summary.total_hours += hours;
                //keeps is_approved false as long as a single shift is left un-validated
                summary.is_approved = summary.is_approved && shift.timesheet.is_approved;
            } else {
                //if first shift of an employee is found, it adds a new entry
                map.set(employee_id, {
                    employee_id: employee_id,
                    employee_name: employee_name,
                    total_hours: hours,
                    is_approved: shift.timesheet.is_approved,
                });
            }
        }

        return {
            period_number: period.period_number,
            start_date: period.start_date,
            end_date: period.end_date,
            label: period.label,
            employees_overview: Array.from(map.values()),
        };
    }
}