personal-finance/backend-api/src/services/DebtAccountService.ts

import {DebtAccount} from '@prisma/client';
import {DebtAccountRepository} from '../repositories/DebtAccountRepository';
import {DebtCategoryRepository} from '../repositories/DebtCategoryRepository';
import {NotFoundError, ValidationError, ForbiddenError} from '../utils/errors';

export interface CreateDebtAccountDTO {
  categoryId: string;
  name: string;
  creditor: string;
  accountNumber?: string;
  originalBalance: number;
  currentBalance: number;
  interestRate?: number;
  minimumPayment?: number;
  dueDate?: Date;
  notes?: string;
}

export interface UpdateDebtAccountDTO {
  name?: string;
  creditor?: string;
  accountNumber?: string;
  currentBalance?: number;
  interestRate?: number;
  minimumPayment?: number;
  dueDate?: Date;
  notes?: string;
}

/**
 * Service for DebtAccount business logic
 * Implements Single Responsibility Principle - handles only business logic
 * Implements Dependency Inversion - depends on repository abstractions
 */
export class DebtAccountService {
  constructor(
    private accountRepository: DebtAccountRepository,
    private categoryRepository: DebtCategoryRepository
  ) {}

  /**
   * Create a new debt account
   */
  async create(userId: string, data: CreateDebtAccountDTO): Promise<DebtAccount> {
    this.validateAccountData(data);

    // Verify category ownership
    const category = await this.categoryRepository.findById(data.categoryId);
    if (!category) {
      throw new NotFoundError('Debt category not found');
    }
    if (category.userId !== userId) {
      throw new ForbiddenError('Access denied');
    }

    return this.accountRepository.create({
      name: data.name,
      creditor: data.creditor,
      accountNumber: data.accountNumber,
      originalBalance: data.originalBalance,
      currentBalance: data.currentBalance,
      interestRate: data.interestRate,
      minimumPayment: data.minimumPayment,
      dueDate: data.dueDate,
      notes: data.notes,
      category: {
        connect: {id: data.categoryId},
      },
    });
  }

  /**
   * Get all debt accounts for a user
   */
  async getAllByUser(userId: string): Promise<DebtAccount[]> {
    return this.accountRepository.findAllByUser(userId);
  }

  /**
   * Get debt accounts with statistics
   */
  async getWithStats(userId: string): Promise<any[]> {
    return this.accountRepository.getWithStats(userId);
  }

  /**
   * Get debt accounts by category
   */
  async getByCategory(categoryId: string, userId: string): Promise<DebtAccount[]> {
    // Verify category ownership
    const category = await this.categoryRepository.findById(categoryId);
    if (!category) {
      throw new NotFoundError('Debt category not found');
    }
    if (category.userId !== userId) {
      throw new ForbiddenError('Access denied');
    }

    return this.accountRepository.findByCategory(categoryId);
  }

  /**
   * Get a single debt account by ID
   */
  async getById(id: string, userId: string): Promise<DebtAccount> {
    const account = await this.accountRepository.findById(id);

    if (!account) {
      throw new NotFoundError('Debt account not found');
    }

    // Verify ownership through category
    if (account.category.userId !== userId) {
      throw new ForbiddenError('Access denied');
    }

    return account;
  }

  /**
   * Update a debt account
   */
  async update(id: string, userId: string, data: UpdateDebtAccountDTO): Promise<DebtAccount> {
    await this.getById(id, userId);

    if (data.currentBalance !== undefined || data.interestRate !== undefined || data.minimumPayment !== undefined) {
      this.validateAccountData(data as CreateDebtAccountDTO);
    }

    return this.accountRepository.update(id, data);
  }

  /**
   * Delete a debt account
   */
  async delete(id: string, userId: string): Promise<void> {
    await this.getById(id, userId);
    await this.accountRepository.delete(id);
  }

  /**
   * Get total debt for a user
   */
  async getTotalDebt(userId: string): Promise<number> {
    return this.accountRepository.getTotalDebt(userId);
  }

  /**
   * Validate account data
   */
  private validateAccountData(data: CreateDebtAccountDTO | UpdateDebtAccountDTO): void {
    if ('originalBalance' in data && data.originalBalance < 0) {
      throw new ValidationError('Original balance cannot be negative');
    }

    if (data.currentBalance !== undefined && data.currentBalance < 0) {
      throw new ValidationError('Current balance cannot be negative');
    }

    if (data.interestRate !== undefined && (data.interestRate < 0 || data.interestRate > 100)) {
      throw new ValidationError('Interest rate must be between 0 and 100');
    }

    if (data.minimumPayment !== undefined && data.minimumPayment < 0) {
      throw new ValidationError('Minimum payment cannot be negative');
    }
  }
}