import { toDateFromString, toStringFromDate } from "../helpers/expenses-date-time-helpers";
import { Injectable, NotFoundException } from "@nestjs/common";
import { updateExpenseDto } from "../dtos/update-expense.dto";
import { GetExpenseDto } from "../dtos/get-expense.dto";
import { PrismaService } from "src/prisma/prisma.service";
import { ExpenseDto } from "../dtos/expense.dto";

type Normalized = { date: Date; comment: string; supervisor_comment?: string; };

export type CreateResult = { ok: true; data: GetExpenseDto } | { ok: false; error: any };
export type UpdatePayload = { id: number; dto: updateExpenseDto };
export type UpdateResult = { ok: true; id: number; data: GetExpenseDto } | { ok: false; id: number; error: any };
export type DeleteResult = { ok: true; id: number; } | { ok: false; id: number; error: any };

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

    //_________________________________________________________________
    //                              CREATE
    //_________________________________________________________________
    async createExpense(timesheet_id: number, dto: ExpenseDto): Promise<CreateResult> {
        try {
            //normalize strings and dates
            const normed_expense = this.normalizeExpenseDto(dto);

            //parse numbers
            const parsed_amount = this.parseOptionalNumber(dto.amount, "amount");
            const parsed_mileage = this.parseOptionalNumber(dto.mileage, "mileage");
            const parsed_attachment = this.parseOptionalNumber(dto.attachment, "attachment");

            //create a new expense
            const expense = await this.prisma.expenses.create({
                data: {
                    timesheet_id,
                    bank_code_id: dto.bank_code_id,
                    attachment: parsed_attachment,
                    date: normed_expense.date,
                    amount: parsed_amount,
                    mileage: parsed_mileage,
                    comment: normed_expense.comment,
                    supervisor_comment: normed_expense.supervisor_comment,
                    is_approved: dto.is_approved,
                },
                //return the newly created expense with id
                select: {
                    id: true,
                    timesheet_id: true,
                    bank_code_id: true,
                    attachment: true,
                    date: true,
                    amount: true,
                    mileage: true,
                    comment: true,
                    supervisor_comment: true,
                    is_approved: true,
                },
            });

            //build an object to return to the frontend to display
            const created: GetExpenseDto = {
                id: expense.id,
                timesheet_id: expense.timesheet_id,
                bank_code_id: expense.bank_code_id,
                attachment: expense.attachment ?? undefined,
                date: toStringFromDate(expense.date),
                amount: expense.amount?.toNumber(),
                mileage: expense.mileage?.toNumber(),
                comment: expense.comment,
                supervisor_comment: expense.supervisor_comment ?? undefined,
                is_approved: expense.is_approved,
            };
            return { ok: true, data: created }

        } catch (error) {
            return { ok: false, error: error }
        }
    }

    //_________________________________________________________________
    //                              UPDATE
    //_________________________________________________________________
    async updateExpense({id, dto}: UpdatePayload): Promise<UpdateResult> {
        try {
            //checks for modifications
            const data: Record<string, unknown> = {};
            if (dto.date         !== undefined) data.date         = toDateFromString(dto.date);
            if (dto.comment      !== undefined) data.comment      = this.truncate280(dto.comment);
            if (dto.attachment   !== undefined) data.attachment   = this.parseOptionalNumber(dto.attachment, "attachment");
            if (dto.amount       !== undefined) data.amount       = this.parseOptionalNumber(dto.amount, "amount");
            if (dto.mileage      !== undefined) data.mileage      = this.parseOptionalNumber(dto.mileage, "mileage");
            if (dto.bank_code_id !== undefined) data.bank_code_id = dto.bank_code_id;
            if (dto.supervisor_comment !== undefined) {
                data.supervisor_comment = dto.supervisor_comment?.trim()
                    ? this.truncate280(dto.supervisor_comment.trim())
                    : null;
            }
            //return an error if no fields needs an update
            if(!Object.keys(data).length) {
                return { ok: false, id, error: new Error("Nothing to update")};
            }

            const expense = await this.prisma.expenses.update({
                where: { id },
                data,
                select: {
                    id: true,
                    timesheet_id: true,
                    bank_code_id: true,
                    attachment: true,
                    date: true,
                    amount: true,
                    mileage: true,
                    comment: true,
                    supervisor_comment: true,
                    is_approved: true,
                },
            });

            const updated: GetExpenseDto = {
                id: expense.id,
                timesheet_id: expense.timesheet_id,
                bank_code_id: expense.bank_code_id,
                attachment: expense.attachment ?? undefined,
                date: toStringFromDate(expense.date),
                amount: expense.amount?.toNumber(),
                mileage: expense.mileage?.toNumber(),
                comment: expense.comment,
                supervisor_comment: expense.supervisor_comment ?? undefined,
                is_approved: expense.is_approved,
            };
            return { ok: true, id: expense.id, data: updated };
        } catch (error) {
            return { ok: false, id: id, error: error}
        }
    }
    //_________________________________________________________________
    //                              DELETE
    //_________________________________________________________________
    async deleteExpense(expense_id: number): Promise<DeleteResult> {
        try {
            await this.prisma.$transaction(async (tx) => {
                const expense = await tx.expenses.findUnique({
                    where: { id: expense_id },
                    select: { id: true },
                });
                if(!expense) throw new NotFoundException(`Expense with id: ${expense_id} not found`);
                
                await tx.expenses.delete({ where: { id: expense_id }});
                return { success: true };
            });
            return { ok: true, id: expense_id };
        } catch (error) {
            return { ok: false, id: expense_id, error };
        }
    }

    //_________________________________________________________________
    //                         LOCAL HELPERS
    //_________________________________________________________________
    //makes sure that comments are the right length the date is of Date type
    private normalizeExpenseDto(dto: ExpenseDto): Normalized {
        const date = toDateFromString(dto.date);
        const comment = this.truncate280(dto.comment);
        const supervisor_comment =
            dto.supervisor_comment && dto.supervisor_comment.trim()
                ? this.truncate280(dto.supervisor_comment.trim())
                : undefined;
        return { date, comment, supervisor_comment };
    }

    //makes sure that a string cannot exceed 280 chars
    private truncate280 = (input: string): string => {
        return input.length > 280 ? input.slice(0, 280) : input;
    }

    //makes sure that the type of data of numeric values is valid
    private parseOptionalNumber = (value: unknown, field: string) => {
        if (value == null) return undefined;
        const parsed = Number(value);
        if (Number.isNaN(parsed)) throw new Error(`Invalid value : ${value} for ${field}`);
        return parsed;
    };
}