import { Injectable, BadRequestException, NotFoundException, ConflictException } from "@nestjs/common";
import { Weekday, Prisma } from "@prisma/client";
import { DATE_ISO_FORMAT } from "src/time-and-attendance/utils/constants.utils";
import { PrismaService } from "src/prisma/prisma.service";
import { ApplyResult } from "src/time-and-attendance/utils/type.utils";
import { WEEKDAY } from "src/time-and-attendance/utils/mappers.utils";


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

    async applyToTimesheet(
        employee_id: number,
        preset_name: string,
        start_date_iso:  string,
    ): Promise<ApplyResult> {
        if(!preset_name?.trim()) throw new BadRequestException('A preset_name is required');
        if(!DATE_ISO_FORMAT.test(start_date_iso)) throw new BadRequestException('start_date must be of format :YYYY-MM-DD');

        const preset = await this.prisma.schedulePresets.findFirst({
            where: { employee_id, name: preset_name },
            include: { 
                shifts: {
                    orderBy: [{ week_day: 'asc'}, { sort_order: 'asc'}],
                    select: {
                        week_day: true,
                        sort_order: true,
                        start_time: true,
                        end_time: true,
                        is_remote: true,
                        bank_code_id: true,
                    },
                },
            },
        });
        if(!preset) throw new NotFoundException(`Preset ${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, start_date: start_date} },
            update: {},
            create: { employee_id, 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()) {
                        throw new ConflictException(`Invalid time range in preset day: ${week_day}, order: ${shift.sort_order}`);
                    }
                    const conflict = existing.find((existe)=> overlaps(
                        shift.start_time,  shift.end_time , 
                        existe.start_time, existe.end_time,
                    ));
                    if(conflict) {
                        throw new ConflictException({
                            error_code: 'SHIFT_OVERLAP_WITH_EXISTING',
                            mesage: `Preset shift overlaps existing shift on ${start_date} + ${i}(week day ${week_day})`,
                            conflict: {
                                existing_start: conflict.start_time.toISOString().slice(11,16),
                                existing_end: conflict.end_time.toISOString().slice(11,16),
                            },
                        });
                    }
                    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 { timesheet_id: timesheet.id, created, skipped };
    }
}