import { Injectable } from "@nestjs/common";
import { Weekday, Prisma } from "@prisma/client";
import { DATE_ISO_FORMAT, WEEKDAY } from "src/common/utils/constants.utils";
import { PrismaService } from "src/prisma/prisma.service";
import { ApplyResult } from "src/time-and-attendance/utils/type.utils";
import { EmailToIdResolver } from "src/common/mappers/email-id.mapper";
import { Result } from "src/common/errors/result-error.factory";


@Injectable()
export class SchedulePresetsApplyService {
    constructor(
        private readonly prisma: PrismaService,
        private readonly emailResolver: EmailToIdResolver
    ) { }

    async applyToTimesheet(email: string, id: number, start_date_iso: string): Promise<Result<ApplyResult, string>> {
        if (!DATE_ISO_FORMAT.test(start_date_iso)) return { success: false, error: 'INVALID_PRESET' };

        const employee_id = await this.emailResolver.findIdByEmail(email);
        if (!employee_id.success) return { success: false, error: employee_id.error }

        const preset = await this.prisma.schedulePresets.findFirst({
            where: { employee_id: employee_id.data, id },
            include: {
                shifts: {
                    orderBy: [{ week_day: 'asc' }, { sort_order: 'asc' }],
                    select: {
                        id: true,
                        week_day: true,
                        sort_order: true,
                        start_time: true,
                        end_time: true,
                        is_remote: true,
                        bank_code_id: true,
                    },
                },
            },
        });
        if (!preset) return { success: false, error: `PRESET_NOT_FOUND` };


        const start_date = new Date(`${start_date_iso}T00:00:00.000Z`);
        const timesheet = await this.prisma.timesheets.upsert({
            where: { employee_id_start_date: { employee_id: employee_id.data, start_date: start_date } },
            update: {},
            create: { employee_id: employee_id.data, start_date: start_date },
            select: { id: true },
        });

        //index shifts by weekday
        const index_by_day = new Map<Weekday, typeof preset.shifts>();
        for (const shift of preset.shifts) {
            const list = index_by_day.get(shift.week_day) ?? [];
            list.push(shift);
            index_by_day.set(shift.week_day, list);
        }

        const addDays = (date: Date, days: number) =>
            new Date(Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate() + days));

        const overlaps = (aStart: Date, aEnd: Date, bStart: Date, bEnd: Date) =>
            aStart.getTime() < bEnd.getTime() && aEnd.getTime() > bStart.getTime();

        let created = 0;
        let skipped = 0;

        await this.prisma.$transaction(async (tx) => {
            for (let i = 0; i < 7; i++) {
                const date = addDays(start_date, i);
                const week_day = WEEKDAY[date.getUTCDay()];
                const shifts = index_by_day.get(week_day) ?? [];

                if (shifts.length === 0) continue;

                const existing = await tx.shifts.findMany({
                    where: { timesheet_id: timesheet.id, date: date },
                    orderBy: { start_time: 'asc' },
                    select: {
                        start_time: true,
                        end_time: true,
                        bank_code_id: true,
                        is_remote: true,
                        comment: true,
                    },
                });

                const payload: Prisma.ShiftsCreateManyInput[] = [];

                for (const shift of shifts) {
                    if (shift.end_time.getTime() <= shift.start_time.getTime()) {
                        return {
                            success: false,
                            error: `INVALID_PRESET_SHIFT`
                        };
                    }
                    const conflict = existing.find((existe) => overlaps(
                        shift.start_time, shift.end_time,
                        existe.start_time, existe.end_time,
                    ));
                    if (conflict)
                        return {
                            success: false,
                            error: `OVERLAPING_SHIFT`
                        };

                    payload.push({
                        timesheet_id: timesheet.id,
                        date: date,
                        start_time: shift.start_time,
                        end_time: shift.end_time,
                        is_remote: shift.is_remote,
                        comment: null,
                        bank_code_id: shift.bank_code_id,
                    });
                }
                if (payload.length) {
                    const response = await tx.shifts.createMany({ data: payload, skipDuplicates: true });
                    created += response.count;
                    skipped += payload.length - response.count;
                }
            }
        });
        return { success: true, data: { timesheet_id: timesheet.id, created, skipped } };
    }
}