import { Injectable, inject } from '@angular/core';
import { HttpClient, HttpParams } from '@angular/common/http';
import { Observable, Subject, timer } from 'rxjs';
import { debounce, retry, catchError, tap, map } from 'rxjs/operators';
import { Project, Category, Subcategory, Item, ItemsListResponse } from '../models';
import { MockDataService } from './mock-data.service';
import { environment } from '../../environments/environment';

@Injectable({
  providedIn: 'root'
})
export class ApiService {
  private http = inject(HttpClient);
  private mockService = inject(MockDataService);
  private readonly API_BASE = environment.apiUrl;
  
  // Debounced save queue
  private saveQueue$ = new Subject<SaveOperation>();
  
  constructor() {
    // Set up auto-save with 500ms debounce
    this.saveQueue$
      .pipe(debounce(() => timer(500)))
      .subscribe(operation => {
        this.executeSave(operation);
      });
  }

  // Projects
  getProjects(): Observable<Project[]> {
    if (environment.useMockData) return this.mockService.getProjects();
    return this.http.get<Project[]>(`${this.API_BASE}/projects`).pipe(
      retry(2),
      catchError(this.handleError)
    );
  }

  // Categories
  getCategories(projectId: string): Observable<Category[]> {
    if (environment.useMockData) return this.mockService.getCategories(projectId);
    return this.http.get<Category[]>(`${this.API_BASE}/projects/${projectId}/categories`).pipe(
      retry(2),
      catchError(this.handleError)
    );
  }

  getCategory(categoryId: string): Observable<Category> {
    if (environment.useMockData) return this.mockService.getCategory(categoryId);
    return this.http.get<Category>(`${this.API_BASE}/categories/${categoryId}`).pipe(
      retry(2),
      catchError(this.handleError)
    );
  }

  updateCategory(categoryId: string, data: Partial<Category>): Observable<Category> {
    if (environment.useMockData) return this.mockService.updateCategory(categoryId, data);
    return this.http.patch<Category>(`${this.API_BASE}/categories/${categoryId}`, data).pipe(
      retry(1),
      catchError(this.handleError)
    );
  }

  createCategory(projectId: string, data: Partial<Category>): Observable<Category> {
    if (environment.useMockData) return this.mockService.createCategory(projectId, data);
    return this.http.post<Category>(`${this.API_BASE}/projects/${projectId}/categories`, data).pipe(
      catchError(this.handleError)
    );
  }

  deleteCategory(categoryId: string): Observable<void> {
    if (environment.useMockData) return this.mockService.deleteCategory(categoryId);
    return this.http.delete<void>(`${this.API_BASE}/categories/${categoryId}`).pipe(
      catchError(this.handleError)
    );
  }

  // Subcategories
  getSubcategories(categoryId: string): Observable<Subcategory[]> {
    if (environment.useMockData) {
      return this.mockService.getCategory(categoryId).pipe(
        map(cat => cat.subcategories || [])
      );
    }
    return this.http.get<Subcategory[]>(`${this.API_BASE}/categories/${categoryId}/subcategories`).pipe(
      retry(2),
      catchError(this.handleError)
    );
  }

  getSubcategory(subcategoryId: string): Observable<Subcategory> {
    if (environment.useMockData) return this.mockService.getSubcategory(subcategoryId);
    return this.http.get<Subcategory>(`${this.API_BASE}/subcategories/${subcategoryId}`).pipe(
      retry(2),
      catchError(this.handleError)
    );
  }

  updateSubcategory(subcategoryId: string, data: Partial<Subcategory>): Observable<Subcategory> {
    if (environment.useMockData) return this.mockService.updateSubcategory(subcategoryId, data);
    return this.http.patch<Subcategory>(`${this.API_BASE}/subcategories/${subcategoryId}`, data).pipe(
      retry(1),
      catchError(this.handleError)
    );
  }

  createSubcategory(parentId: string, parentType: 'category' | 'subcategory', data: Partial<Subcategory>): Observable<Subcategory> {
    if (environment.useMockData) return this.mockService.createSubcategory(parentId, data);
    const endpoint = parentType === 'category'
      ? `${this.API_BASE}/categories/${parentId}/subcategories`
      : `${this.API_BASE}/subcategories/${parentId}/subcategories`;
    return this.http.post<Subcategory>(endpoint, data).pipe(
      catchError(this.handleError)
    );
  }

  deleteSubcategory(subcategoryId: string): Observable<void> {
    if (environment.useMockData) return this.mockService.deleteSubcategory(subcategoryId);
    return this.http.delete<void>(`${this.API_BASE}/subcategories/${subcategoryId}`).pipe(
      catchError(this.handleError)
    );
  }

  // Items
  getItems(subcategoryId: string, page = 1, limit = 20, search?: string, filters?: ItemFilters): Observable<ItemsListResponse> {
    if (environment.useMockData) return this.mockService.getItems(subcategoryId, page, limit, search, filters);
    
    let params = new HttpParams()
      .set('page', page.toString())
      .set('limit', limit.toString());
    
    if (search) {
      params = params.set('search', search);
    }
    
    if (filters?.visible !== undefined) {
      params = params.set('visible', filters.visible.toString());
    }
    
    if (filters?.tags?.length) {
      params = params.set('tags', filters.tags.join(','));
    }

    return this.http.get<ItemsListResponse>(`${this.API_BASE}/subcategories/${subcategoryId}/items`, { params }).pipe(
      retry(2),
      catchError(this.handleError)
    );
  }

  getItem(itemId: string): Observable<Item> {
    if (environment.useMockData) return this.mockService.getItem(itemId);
    return this.http.get<Item>(`${this.API_BASE}/items/${itemId}`).pipe(
      retry(2),
      catchError(this.handleError)
    );
  }

  updateItem(itemId: string, data: Partial<Item>): Observable<Item> {
    if (environment.useMockData) return this.mockService.updateItem(itemId, data);
    return this.http.patch<Item>(`${this.API_BASE}/items/${itemId}`, data).pipe(
      retry(1),
      catchError(this.handleError)
    );
  }

  createItem(subcategoryId: string, data: Partial<Item>): Observable<Item> {
    if (environment.useMockData) return this.mockService.createItem(subcategoryId, data);
    return this.http.post<Item>(`${this.API_BASE}/subcategories/${subcategoryId}/items`, data).pipe(
      catchError(this.handleError)
    );
  }

  deleteItem(itemId: string): Observable<void> {
    if (environment.useMockData) return this.mockService.deleteItem(itemId);
    return this.http.delete<void>(`${this.API_BASE}/items/${itemId}`).pipe(
      catchError(this.handleError)
    );
  }

  bulkUpdateItems(itemIds: string[], data: Partial<Item>): Observable<void> {
    if (environment.useMockData) return this.mockService.bulkUpdateItems(itemIds, data);
    return this.http.patch<void>(`${this.API_BASE}/items/bulk`, { itemIds, data }).pipe(
      retry(1),
      catchError(this.handleError)
    );
  }

  // Image upload
  uploadImage(file: File): Observable<{ url: string }> {
    if (environment.useMockData) return this.mockService.uploadImage(file);
    
    const formData = new FormData();
    formData.append('image', file);
    
    return this.http.post<{ url: string }>(`${this.API_BASE}/upload`, formData).pipe(
      retry(1),
      catchError(this.handleError)
    );
  }

  // Debounced auto-save
  queueSave(type: 'category' | 'subcategory' | 'item', id: string, field: string, value: any) {
    this.saveQueue$.next({ type, id, field, value });
  }

  private executeSave(operation: SaveOperation) {
    const data = { [operation.field]: operation.value };
    
    let request: Observable<any>;
    switch (operation.type) {
      case 'category':
        request = this.updateCategory(operation.id, data);
        break;
      case 'subcategory':
        request = this.updateSubcategory(operation.id, data);
        break;
      case 'item':
        request = this.updateItem(operation.id, data);
        break;
    }

    request.subscribe({
      next: () => console.log(`Saved ${operation.type} ${operation.id} - ${operation.field}`),
      error: (err) => console.error(`Failed to save ${operation.type}`, err)
    });
  }

  private handleError(error: any): Observable<never> {
    let errorMessage = 'An unexpected error occurred';
    
    if (error.error instanceof ErrorEvent) {
      // Client-side or network error
      errorMessage = `Network error: ${error.error.message}`;
    } else if (error.status) {
      // Backend returned an unsuccessful response code
      switch (error.status) {
        case 400:
          errorMessage = error.error?.message || 'Invalid request';
          break;
        case 401:
          errorMessage = 'Unauthorized. Please log in again.';
          break;
        case 403:
          errorMessage = 'You do not have permission to perform this action';
          break;
        case 404:
          errorMessage = 'Resource not found';
          break;
        case 409:
          errorMessage = error.error?.message || 'Conflict: Resource already exists or has conflicts';
          break;
        case 422:
          errorMessage = error.error?.message || 'Validation failed';
          break;
        case 500:
          errorMessage = 'Server error. Please try again later.';
          break;
        case 503:
          errorMessage = 'Service unavailable. Please try again later.';
          break;
        default:
          errorMessage = error.error?.message || `Error: ${error.status} - ${error.statusText}`;
      }
    }
    
    console.error('API Error:', {
      message: errorMessage,
      status: error.status,
      error: error.error,
      url: error.url
    });
    
    throw { message: errorMessage, status: error.status, originalError: error };
  }
}

interface SaveOperation {
  type: 'category' | 'subcategory' | 'item';
  id: string;
  field: string;
  value: any;
}

interface ItemFilters {
  visible?: boolean;
  tags?: string[];
}