import { BaseApprovalService } from "src/common/shared/base-approval.service";
import { Expenses, Prisma }    from "@prisma/client";
import { PrismaService }       from "src/prisma/prisma.service";
import { UpsertExpenseDto }    from "../dtos/upsert-expense.dto";
import { BankCodesRepo }       from "../repos/bank-codes.repo";
import { TimesheetsRepo }      from "../repos/timesheets.repo";
import { EmployeesRepo }       from "../repos/employee.repo";
import { toDateOnlyUTC }       from "src/modules/shifts/helpers/shifts-date-time-helpers";
import { 
  BadRequestException, 
  Injectable, 
  NotFoundException 
} from "@nestjs/common";
import { ExpenseResponse, UpsertAction } from "../types and interfaces/expenses.types.interfaces";
import { 
  assertAndTrimComment, 
  computeMileageAmount, 
  mapDbExpenseToDayResponse, 
  normalizeType as normalizeTypeUtil 
} from "../utils/expenses.utils";

@Injectable()
export class ExpensesCommandService extends BaseApprovalService<Expenses> {
  constructor(
    prisma: PrismaService,
    private readonly bankCodesRepo:  BankCodesRepo,
    private readonly timesheetsRepo: TimesheetsRepo,
    private readonly employeesRepo:  EmployeesRepo,  
  ) { super(prisma); }

  protected get delegate() {
    return this.prisma.expenses;
  }

  protected delegateFor(transaction: Prisma.TransactionClient){
    return transaction.expenses;
  }

  async updateApproval(id: number, isApproved: boolean): Promise<Expenses> {
    return this.prisma.$transaction((transaction) =>
    this.updateApprovalWithTransaction(transaction, id, isApproved),
    );
  }

  //-------------------- Master CRUD function --------------------
  readonly upsertExpensesByDate = async (email: string, date: string, dto: UpsertExpenseDto,
  ): Promise<{ action:UpsertAction; day: ExpenseResponse[] }> => {

    //validates if there is an existing expense, at least 1 old or new
    const { old_expense, new_expense } = dto ?? {};
    if(!old_expense && !new_expense) {
      throw new BadRequestException('At least one expense must be provided');
    }

    //validate date format
    const date_only = toDateOnlyUTC(date);
    if(Number.isNaN(date_only.getTime())) {
      throw new BadRequestException('Invalid date format (expected: YYYY-MM-DD)');
    }

    //resolve employee_id by email
    const employee_id = await this.resolveEmployeeIdByEmail(email);

    //make sure a timesheet existes
    const timesheet_id = await this.ensureTimesheetForDate(employee_id, date_only);

    return this.prisma.$transaction(async (tx) => {
      const loadDay = async (): Promise<ExpenseResponse[]> => {
        const rows = await tx.expenses.findMany({
          where: {
            timesheet_id: timesheet_id,
            date: date_only,
          },
          include: {
            bank_code: { 
              select: { 
                type: true,
              },
            },
          },
          orderBy: [{ date: 'asc' }, { id: 'asc' }],
        });

        return rows.map((r) =>
          this.mapDbToDayResponse({
          date:        r.date,
          amount:      r.amount ?? 0,
          mileage:     r.mileage ?? 0,
          comment:     r.comment,
          is_approved: r.is_approved,
          bank_code:   r.bank_code,
        }));
      };

      const normalizePayload = async (payload: {
        type:        string;
        amount?:     number;
        mileage?:    number;
        comment:     string;
        attachment?: string | number;
      }): Promise<{
        type:         string;
        bank_code_id: number;
        amount:       Prisma.Decimal;
        mileage:      number | null;
        comment:      string;
        attachment:   number | null;
      }> => {
        const type       = this.normalizeType(payload.type);
        const comment    = this.assertAndTrimComment(payload.comment);
        const attachment = this.parseAttachmentId(payload.attachment);
        
        const { id: bank_code_id, modifier } = await this.lookupBankCodeOrThrow(tx, type);
        let amount = this.computeAmountDecimal(type, payload, modifier);
        let mileage: number | null = null;

        if (type === 'MILEAGE') {
          mileage = Number(payload.mileage ?? 0);
          if (!(mileage > 0)) {
            throw new BadRequestException('Mileage required and must be > 0 for type MILEAGE');
          }

          const amountNumber = computeMileageAmount(mileage, modifier);
          amount = new Prisma.Decimal(amountNumber);

        } else {
          if (!(typeof payload.amount === 'number' && payload.amount >= 0)) {
            throw new BadRequestException('Amount required for non-MILEAGE expense');
          }
          amount = new Prisma.Decimal(payload.amount);
        }

        if (attachment !== null) {
          const attachmentRow = await tx.attachments.findUnique({
            where: { id: attachment },
            select: { status: true },
          });
          if (!attachmentRow || attachmentRow.status !== 'ACTIVE') {
            throw new BadRequestException('Attachment not found or inactive');
          }
        }

        return { 
          type, 
          bank_code_id, 
          amount,
          mileage,
          comment, 
          attachment 
        };
      };

      const findExactOld = async (norm: {
        bank_code_id: number;
        amount:       Prisma.Decimal;
        mileage:      number | null;
        comment:      string;
        attachment:   number | null;
      }) => {
        return tx.expenses.findFirst({
          where: {
            timesheet_id: timesheet_id,
            date:         date_only,
            bank_code_id: norm.bank_code_id,
            amount:       norm.amount,
            comment:      norm.comment,
            attachment:   norm.attachment,
            ...(norm.mileage !== null ? { mileage: norm.mileage } : { mileage: null }),
          },
          select: { id: true },
        });
      };

      let action : UpsertAction;
      //-------------------- DELETE --------------------
      if(old_expense && !new_expense) {
        const oldNorm = await normalizePayload(old_expense);
        const existing = await findExactOld(oldNorm);
        if(!existing) {
          throw new NotFoundException({
            error_code: 'EXPENSE_STALE',
            message: 'The expense was modified or deleted by someone else',
          });
        }
        await tx.expenses.delete({where: { id: existing.id } });
        action = 'delete';
      }
      //-------------------- CREATE --------------------
      else if (!old_expense && new_expense) {
        const new_exp = await normalizePayload(new_expense);
        await tx.expenses.create({
          data: {
            timesheet_id: timesheet_id,
            date:         date_only,
            bank_code_id: new_exp.bank_code_id,
            amount:       new_exp.amount,
            mileage:      new_exp.mileage,
            comment:      new_exp.comment,
            attachment:   new_exp.attachment,
            is_approved:  false,
          },
        });
        action = 'create';
      }
      //-------------------- UPDATE --------------------
      else if(old_expense && new_expense) {
        const oldNorm = await normalizePayload(old_expense);
        const existing = await findExactOld(oldNorm);
        if(!existing) {
          throw new NotFoundException({
            error_code: 'EXPENSE_STALE',
            message: 'The expense was modified or deleted by someone else',
          });
        }

        const new_exp = await normalizePayload(new_expense);
        await tx.expenses.update({
          where: { id: existing.id },
          data: {
            bank_code_id: new_exp.bank_code_id,
            amount:       new_exp.amount,
            mileage:      new_exp.mileage,
            comment:      new_exp.comment,
            attachment:   new_exp.attachment,
          },
        });
        action = 'update';
      }
      else {
        throw new BadRequestException('Invalid upsert combination');
      }

      const day = await loadDay();

      return { action, day };
    });
  }


  //-------------------- helpers --------------------
  private readonly normalizeType = (type: string): string => 
    normalizeTypeUtil(type);

  private readonly assertAndTrimComment = (comment: string): string => 
    assertAndTrimComment(comment);

  private readonly parseAttachmentId = (value: unknown): number | null => {
    if (value == null) {
      return null;
    }

    if (typeof value === 'number') {
      if (!Number.isInteger(value) || value <= 0) {
        throw new BadRequestException('Invalid attachment id');
      }
      return value;
    }

    if (typeof value === 'string') {

      const trimmed = value.trim();
      if (!trimmed.length) return null;      
      if (!/^\d+$/.test(trimmed)) throw new BadRequestException('Invalid attachment id');
      
      const parsed = Number(trimmed);
      if (parsed <= 0) throw new BadRequestException('Invalid attachment id');

      return parsed;
    }
    throw new BadRequestException('Invalid attachment id');
  };


  private readonly resolveEmployeeIdByEmail = async (email: string): Promise<number> => 
    this.employeesRepo.findIdByEmail(email);

  private readonly ensureTimesheetForDate = async ( employee_id: number, date: Date 
  ): Promise<number> => {
    const { id } = await this.timesheetsRepo.ensureForDate(employee_id, date);
    return id;
  };

  private readonly lookupBankCodeOrThrow = async ( transaction: Prisma.TransactionClient, type: string 
  ): Promise<{id: number; modifier: number}> => 
    this.bankCodesRepo.findByType(type, transaction);
  
  private readonly computeAmountDecimal = ( 
    type: string, 
    payload: { 
      amount?:  number; 
      mileage?: number;
    },
    modifier: number,    
  ): Prisma.Decimal => {
    if(type === 'MILEAGE') {
      const km = payload.mileage ?? 0;
      const amountNumber = computeMileageAmount(km, modifier);
      return new Prisma.Decimal(amountNumber);
    }
    return new Prisma.Decimal(payload.amount!);
  };

  private readonly mapDbToDayResponse = (row: {
    date:        Date;
    amount:      Prisma.Decimal | number | string;
    mileage:     Prisma.Decimal | number | string;
    comment:     string;
    is_approved: boolean;
    bank_code:   { type: string } | null;
  }): ExpenseResponse => mapDbExpenseToDayResponse(row);


}