/**
 * Thin wrappers over the server's REST API.
 *
 * Pattern: one async function per endpoint. Each one builds the request,
 * awaits the response, throws on non-2xx, and parses the JSON body. The UI
 * imports these by name, so changing a URL or shape only ever touches one
 * file.
 *
 * The `request` helper centralises the fetch + JSON + error-handling
 * boilerplate so the individual functions stay one-liners. Add a header
 * (auth tokens, etc.) here and every endpoint picks it up.
 *
 * Errors are surfaced as `Error` instances with the status code and body in
 * the message — the App component catches them and shows the message in the
 * UI. If you need structured error objects (with codes the UI can branch
 * on), augment `request` to JSON-parse non-2xx bodies and throw a typed
 * subclass.
 */

import type { Category, Todo } from './types';

async function request<T>(path: string, init?: RequestInit): Promise<T> {
  const res = await fetch(path, {
    ...init,
    headers: {
      'Content-Type': 'application/json',
      ...init?.headers,
    },
  });
  if (!res.ok) {
    throw new Error(`Request failed: ${res.status} ${await res.text()}`);
  }
  return res.json() as Promise<T>;
}

export function getCategories(): Promise<Category[]> {
  return request<Category[]>('/categories');
}

export function createCategory(name: string, color: string): Promise<Category> {
  return request<Category>('/categories', {
    method: 'POST',
    body: JSON.stringify({ name, color }),
  });
}

export function updateCategory(id: number, data: Partial<Pick<Category, 'name' | 'color'>>): Promise<Category> {
  return request<Category>(`/categories/${id}`, {
    method: 'PATCH',
    body: JSON.stringify(data),
  });
}

export function deleteCategory(id: number): Promise<{ ok: true }> {
  return request<{ ok: true }>(`/categories/${id}`, { method: 'DELETE' });
}

export function getTodos(categoryId: number | null): Promise<Todo[]> {
  const query = categoryId ? `?category_id=${categoryId}` : '';
  return request<Todo[]>(`/todos${query}`);
}

export function createTodo(title: string, categoryId: number | null): Promise<Todo> {
  return request<Todo>('/todos', {
    method: 'POST',
    body: JSON.stringify({ title, category_id: categoryId }),
  });
}

export function updateTodo(id: number, data: Partial<Pick<Todo, 'title' | 'completed' | 'category_id'>>): Promise<Todo> {
  return request<Todo>(`/todos/${id}`, {
    method: 'PATCH',
    body: JSON.stringify(data),
  });
}

export function deleteTodo(id: number): Promise<{ ok: true }> {
  return request<{ ok: true }>(`/todos/${id}`, { method: 'DELETE' });
}