import { Injectable, NotFoundException, BadRequestException } from '@nestjs/common';
import { EntityManager } from '@mikro-orm/postgresql';
import { CreateInvoiceDto } from './dto/create-invoice.dto';
import { UpdateInvoiceDto } from './dto/update-invoice.dto';
import { FindInvoicesDto } from './dto/find-invoices.dto';
import { Invoice } from './entities/invoice.entity';
import { InvoiceItem } from './entities/invoice-item.entity';
import { Request } from '../request/entities/request.entity';
import { User } from '../user/entities/user.entity';
import { ProductService } from '../product/providers/product.service';
import { InvoiceRepository } from './repositories/invoice.repository';

const TAX_RATE = 0.1;

@Injectable()
export class InvoiceService {
  constructor(
    private readonly em: EntityManager,
    private readonly productService: ProductService,
    private readonly invoiceRepository: InvoiceRepository,
  ) { }


  async create(dto: CreateInvoiceDto) {
    let user: User;
    let request: Request | undefined;

    if (dto.requestId) {
      const requestEntity = await this.em.findOne(
        Request,
        { id: dto.requestId },
        { populate: ['user'] },
      );
      if (!requestEntity) {
        throw new NotFoundException('Request not found');
      }
      user = requestEntity.user;
      request = requestEntity;
    } else if (dto.userId) {
      user = await this.em.findOneOrFail(User, { id: dto.userId });
    } else {
      throw new BadRequestException('Either requestId or userId must be provided');
    }

    const enableTax = dto.enableTax ?? false;
    const approvalDeadline = dto.approvalDeadline
      ? new Date(dto.approvalDeadline)
      : undefined;

    const discount = dto.items.reduce((acc, item) => acc + (item.discount ?? 0), 0);

    return this.em.transactional(async (em) => {
      const invoice = em.create(Invoice, {
        user,
        ...(request && { request }),
        enableTax,
        approvalDeadline,
        discount,
        paidAmount: 0,
        balance: 0,
      });
      em.persist(invoice);

      let subTotal = 0;

      for (const item of dto.items) {
        const product = await this.productService.findOneOrFail(item.productId);
        const unitPrice = item.unitPrice;
        const itemDiscount = item.discount ?? 0;
        const itemTotal = Math.max(0, unitPrice * item.quantity - itemDiscount);
        subTotal += itemTotal;

        const invoiceItem = em.create(InvoiceItem, {
          invoice,
          product,
          quantity: item.quantity,
          unitPrice: unitPrice,
          discount: itemDiscount || undefined,
          description: item.description,
        });
        invoice.items.add(invoiceItem);
      }

      const taxAmount = enableTax
        ? Math.round((subTotal - discount) * TAX_RATE)
        : 0;
      const total = Math.max(0, subTotal - discount + taxAmount);

      invoice.subTotal = subTotal;
      invoice.taxAmount = taxAmount;
      invoice.total = total;
      invoice.balance = total - invoice.paidAmount;

      await em.flush();
      return invoice;
    });
  }

  findAll(userId: string, dto: FindInvoicesDto) {
    return this.invoiceRepository.findAllPaginated({ userId, ...dto });
  }

  findAllAsAdmin(dto: FindInvoicesDto) {
    return this.invoiceRepository.findAllPaginated(dto);
  }

  async findOne(id: string, userId: string) {
    const invoice = await this.em.findOne(
      Invoice,
      { id, user: { id: userId } },
      { populate: ['user', 'request', 'items', 'items.product'] },
    );
    if (!invoice) {
      throw new NotFoundException('Invoice not found');
    }
    return invoice;
  }

  async confirmInvoiceItem(id: string, userId: string) {
    const item = await this.em.findOne(
      InvoiceItem,
      { id, invoice: { user: { id: userId } } },
      { populate: ['invoice', 'product'] },
    );
    if (!item) {
      throw new NotFoundException('Invoice item not found');
    }
    if(item.confirmedAt){
      throw new BadRequestException('Invoice item already confirmed');
    }
    item.confirmedAt = new Date();
    await this.em.persistAndFlush(item);
    return item;
  }

  async update(id: string, updateInvoiceDto: UpdateInvoiceDto) {
    const invoice = await this.findOneOrFail(id);
    if (updateInvoiceDto.enableTax !== undefined) invoice.enableTax = updateInvoiceDto.enableTax;
    if (updateInvoiceDto.approvalDeadline !== undefined) {
      invoice.approvalDeadline = new Date(updateInvoiceDto.approvalDeadline);
    }
    if (updateInvoiceDto.items !== undefined && updateInvoiceDto.items.length > 0) {
      for (const item of updateInvoiceDto.items) {
        if (item.id) {
          const existingItem = await this.em.findOne(InvoiceItem, {
            id: item.id,
            invoice: { id: invoice.id },
          });
          if (!existingItem) {
            throw new NotFoundException(`Invoice item ${item.id} not found`);
          }
          if (item.productId !== undefined) {
            existingItem.product = await this.productService.findOneOrFail(
              item.productId,
            );
          }
          if (item.quantity !== undefined) existingItem.quantity = item.quantity;
          if (item.unitPrice !== undefined)
            existingItem.unitPrice = item.unitPrice;
          if (item.discount !== undefined) existingItem.discount = item.discount;
          if (item.description !== undefined)
            existingItem.description = item.description;
        } else {
          if (
            item.productId === undefined ||
            item.quantity === undefined ||
            item.unitPrice === undefined
          ) {
            throw new BadRequestException(
              'New invoice items must have productId, quantity and unitPrice',
            );
          }
          const product = await this.productService.findOneOrFail(item.productId);
          const itemDiscount = item.discount ?? 0;
          const invoiceItem = this.em.create(InvoiceItem, {
            invoice,
            product,
            quantity: item.quantity,
            unitPrice: item.unitPrice,
            discount: itemDiscount || undefined,
            description: item.description,
          });
          invoice.items.add(invoiceItem);
        }
      }

      const allItems = invoice.items.getItems();
      let subTotal = 0;
      let discount = 0;
      for (const item of allItems) {
        const itemTotal = Math.max(
          0,
          item.unitPrice * item.quantity - (item.discount ?? 0),
        );
        subTotal += itemTotal;
        discount += item.discount ?? 0;
      }
      invoice.discount = discount;
      const taxAmount = invoice.enableTax
        ? Math.round((subTotal - discount) * TAX_RATE)
        : 0;
      const total = Math.max(0, subTotal - discount + taxAmount);
      invoice.subTotal = subTotal;
      invoice.taxAmount = taxAmount;
      invoice.total = total;
      invoice.balance = total - invoice.paidAmount;
    }
    await this.em.flush();
    return invoice;
  }

  async remove(id: string) {
    const invoice = await this.findOneOrFail(id);
    this.em.remove(invoice);
    await this.em.flush();
    return invoice;
  }

  async findOneOrFail(id: string) {
    const invoice = await this.em.findOne(
      Invoice,
      { id },
      { populate: ['user', 'request', 'items', 'items.product'] },
    );
    if (!invoice) {
      throw new NotFoundException('Invoice not found');
    }
    return invoice;
  }
}