import { Injectable, NotFoundException } from '@nestjs/common';
import { PrismaService } from 'src/prisma/prisma.service';
import { CreateEmployeeDto } from '../dtos/create-employee.dto';
import { UpdateEmployeeDto } from '../dtos/update-employee.dto';
import { Employees, Users } from '@prisma/client';

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

  async create(dto: CreateEmployeeDto): Promise<Employees> {
    const {
      first_name,
      last_name,
      email,
      phone_number,
      residence,
      external_payroll_id,
      company_code,
      first_work_day,
      last_work_day,
    } = dto;

    return this.prisma.$transaction(async (tx) => {
      const user: Users = await tx.users.create({
        data: {
          first_name,
          last_name,
          email,
          phone_number,
          residence,
        },
      });
      return tx.employees.create({
        data: {
          user_id: user.id,
          external_payroll_id,
          company_code,
          first_work_day,
          last_work_day,
        },
      });
    });
  }

  findAll(): Promise<Employees[]> {
    return this.prisma.employees.findMany({
      include: { user: true },
    });
  }

  async findOne(id: number): Promise<Employees> {
    const emp = await this.prisma.employees.findUnique({
      where: { id },
      include: { user: true },
    });
    if (!emp) {
      throw new NotFoundException(`Employee #${id} not found`);
    }
    return emp;
  }

async update(
    id: number,
    dto: UpdateEmployeeDto,
  ): Promise<Employees> {
    const emp = await this.findOne(id);

    const {
      first_name,
      last_name,
      email,
      phone_number,
      residence,
      external_payroll_id,
      company_code,
      first_work_day,
      last_work_day,
    } = dto;

    return this.prisma.$transaction(async (tx) => {
      await tx.users.update({
        where: { id: emp.user_id },
        data: {
          ...(first_name    !== undefined && { first_name }),
          ...(last_name     !== undefined && { last_name }),
          ...(email         !== undefined && { email }),
          ...(phone_number  !== undefined && { phone_number }),
          ...(residence     !== undefined && { residence }),
        },
      });

      return tx.employees.update({
        where: { id },
        data: {
          ...(external_payroll_id !== undefined && { external_payroll_id }),
          ...(company_code        !== undefined && { company_code }),
          ...(first_work_day      !== undefined && { first_work_day }),
          ...(last_work_day       !== undefined && { last_work_day }),
        },
      });
    });
  }


  async remove(id: number): Promise<Employees> {
    await this.findOne(id);
    return this.prisma.employees.delete({ where: { id } });
  }


  //archivation function
  async patchEmployee(id: number, dto: UpdateEmployeeDto): Promise<any> {
    //fetching existing employee
    const existing = await this.prisma.employees.findUnique({
      where: { id },
      include: { user: true, archive: true },
    });
    if (existing) {
      //verify last_work_day is not null => trigger archivation
      if(dto.last_work_day != undefined && existing.last_work_day == null) {
        return this.archiveOnTermination(existing, dto);
      }
      //if null => regular update
      return this.prisma.employees.update({
        where: { id },
        data: dto,
      });
    }
    //if not found => fetch archives side for restoration
    const archived = await this.prisma.employeesArchive.findFirst({
      where: { employee_id: id },
      include: { employee: true, user: true },
    });
    if (archived) {
      //conditions for restoration
      const restore = dto.last_work_day === null || dto.first_work_day != null;
      if(restore) {
        return this.restoreEmployee(archived, dto);
      }
    }
    //if neither activated nor archivated => 404
    return null;
  }

  //transfers the employee to archive and then delete from employees table
  private async archiveOnTermination(existing: any, dto: UpdateEmployeeDto): Promise<any> {
    return this.prisma.$transaction(async transaction => {
      //archive insertion
      const archived = await transaction.employeesArchive.create({
        data: {
          employee_id: existing.id,
          user_id: existing.user_id,
          first_name: existing.first_name,
          last_name: existing.last_name,
          external_payroll_id: existing.external_payroll_id,
          company_code: existing.company_code,
          first_Work_Day: existing.first_Work_Day,
          last_work_day: existing.last_work_day,
          supervisor_id: existing.supervisor_id ?? null,
        },
      });
      //delete from employees table
      await transaction.employees.delete({ where: { id: existing.id } });
      //return archived employee
      return archived
    });
  }
  
  //transfers the employee from archive to the employees table
  private async restoreEmployee(archived: any, dto: UpdateEmployeeDto): Promise<any> {
    return this.prisma.$transaction(async transaction => {
      //restores the archived employee into the employees table
      const restored = await transaction.employees.create({
        data: {
          id: archived.employee_id,
          user_id: archived.user_id,
          external_payroll_id: dto.external_payroll_id ?? archived.external_payroll_id,
          company_code: dto.company_code ?? archived.company_code,
          first_work_day: dto.first_work_day ?? archived.first_Work_Day,
          last_work_day: null,
          supervisor_id: dto.supervisor_id ?? archived.supervisor_id,
        },
      });
      //deleting archived entry by id
      await transaction.employeesArchive.delete({  where: { id: archived.id } });

      //return restored employee
      return restored;
    });
  }
}