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

import {DebtCategory} from '@prisma/client';
import {DebtCategoryRepository, DebtCategoryWithStats} from '../repositories/DebtCategoryRepository';
import {NotFoundError, ValidationError, ForbiddenError, ConflictError} from '../utils/errors';

export interface CreateDebtCategoryDTO {
  name: string;
  description?: string;
  color?: string;
}

export interface UpdateDebtCategoryDTO {
  name?: string;
  description?: string;
  color?: string;
}

/**
 * Service for DebtCategory business logic
 * Implements Single Responsibility Principle - handles only business logic
 * Implements Dependency Inversion - depends on repository abstraction
 */
export class DebtCategoryService {
  constructor(private categoryRepository: DebtCategoryRepository) {}

  /**
   * Create default debt categories for a new user
   */
  async createDefaultCategories(userId: string): Promise<DebtCategory[]> {
    const defaultCategories = [
      {name: 'Credit Cards', description: 'Credit card debts', color: '#ef4444'},
      {name: 'Student Loans', description: 'Student loan debts', color: '#3b82f6'},
      {name: 'Auto Loans', description: 'Car and vehicle loans', color: '#10b981'},
      {name: 'Mortgages', description: 'Home mortgages', color: '#f59e0b'},
      {name: 'Personal Loans', description: 'Personal loan debts', color: '#8b5cf6'},
      {name: 'Other', description: 'Other debt types', color: '#6b7280'}
    ];

    const categories: DebtCategory[] = [];

    for (const category of defaultCategories) {
      const created = await this.categoryRepository.create({
        name: category.name,
        description: category.description,
        color: category.color,
        user: {
          connect: {id: userId}
        }
      });
      categories.push(created);
    }

    return categories;
  }

  /**
   * Create a new debt category
   */
  async create(userId: string, data: CreateDebtCategoryDTO): Promise<DebtCategory> {
    this.validateCategoryData(data);

    // Check for duplicate name
    const existing = await this.categoryRepository.findByName(userId, data.name);
    if (existing) {
      throw new ConflictError('A category with this name already exists');
    }

    return this.categoryRepository.create({
      name: data.name,
      description: data.description,
      color: data.color,
      user: {
        connect: {id: userId}
      }
    });
  }

  /**
   * Get all categories for a user
   */
  async getAllByUser(userId: string): Promise<DebtCategory[]> {
    return this.categoryRepository.findAllByUser(userId);
  }

  /**
   * Get categories with statistics
   */
  async getWithStats(userId: string): Promise<DebtCategoryWithStats[]> {
    return this.categoryRepository.getWithStats(userId);
  }

  /**
   * Get a single category by ID
   */
  async getById(id: string, userId: string): Promise<DebtCategory> {
    const category = await this.categoryRepository.findById(id);

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

    if (category.userId !== userId) {
      throw new ForbiddenError('Access denied');
    }

    return category;
  }

  /**
   * Update a category
   */
  async update(id: string, userId: string, data: UpdateDebtCategoryDTO): Promise<DebtCategory> {
    await this.getById(id, userId);

    if (data.name) {
      this.validateCategoryData(data as CreateDebtCategoryDTO);

      // Check for duplicate name (excluding current category)
      const existing = await this.categoryRepository.findByName(userId, data.name);
      if (existing && existing.id !== id) {
        throw new ConflictError('A category with this name already exists');
      }
    }

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

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

    // Check if category has accounts
    // Note: Cascade delete will remove all accounts and payments
    // You might want to prevent deletion if there are accounts
    // Uncomment below to prevent deletion:
    // if (category.accounts && category.accounts.length > 0) {
    //   throw new ValidationError('Cannot delete category with existing accounts');
    // }

    await this.categoryRepository.delete(id);
  }

  /**
   * Validate category data
   */
  private validateCategoryData(data: CreateDebtCategoryDTO | UpdateDebtCategoryDTO): void {
    if (data.color) {
      // Validate hex color format
      const hexColorRegex = /^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/;
      if (!hexColorRegex.test(data.color)) {
        throw new ValidationError('Color must be a valid hex color (e.g., #FF5733)');
      }
    }
  }
}