/**
 * REFERENCE TOOL: Svelte + SvelteKit Best Practices & Patterns
 * 
 * Every Svelte file follows these patterns. No exceptions.
 */

// ============================================================================
// PATTERN 1: Svelte Store Pattern
// ============================================================================

/**
 * STORE: authStore
 * PURPOSE: Centralized auth state (user, tokens, login status)
 * UPDATES: Called only through explicit update functions
 * SUBSCRIBERS: Any component needing auth state
 * 
 * Files reference this store: components that check auth, routes that require auth
 */

// File: src/stores/auth.ts
import { writable, derived } from 'svelte/store';

/**
 * USER STORE
 * Holds current user info from Microsoft
 */
export const user = writable<User | null>(null);

/**
 * ACCESS TOKEN STORE
 * Holds current access token (short-lived, 1 hour)
 * RULE: Cleared when token expires
 * RULE: Never persisted to localStorage
 */
export const accessToken = writable<string | null>(null);

/**
 * TOKEN EXPIRY STORE
 * When does current token expire (timestamp in ms)
 */
export const tokenExpiry = writable<number | null>(null);

/**
 * DERIVED: Is authenticated?
 * Returns true if user exists and token is not expired
 */
export const isAuthenticated = derived(
  [user, tokenExpiry],
  ([$user, $expiry]) => {
    return !!$user && $expiry && Date.now() < $expiry;
  }
);

/**
 * UPDATE FUNCTION: Set user after login
 * 
 * CALLED BY: OAuth callback handler
 * UPDATES: user, accessToken, tokenExpiry
 * SIDE EFFECTS: Stores token in sessionStorage, sets up refresh timer
 */
export async function setAuthUser(
  userInfo: User,
  token: string,
  expiresIn: number
): Promise<void> {
  // Update stores
  user.set(userInfo);
  accessToken.set(token);
  tokenExpiry.set(Date.now() + expiresIn * 1000);
  
  // Store in sessionStorage (safe, lost on browser close)
  sessionStorage.setItem('ms_access_token', token);
  sessionStorage.setItem('ms_token_expiry', (Date.now() + expiresIn * 1000).toString());
  
  // Set up automatic refresh timer (5 minutes before expiry)
  const refreshIn = (expiresIn * 1000) - (5 * 60 * 1000);
  setTimeout(() => {
    refreshAccessToken();
  }, refreshIn);
  
  console.log('Auth user set:', userInfo.displayName);
}

/**
 * UPDATE FUNCTION: Refresh token via backend
 * 
 * CALLED BY: Automatic timer (5 min before expiry), before API calls
 * SIDE EFFECTS: Updates accessToken, tokenExpiry, sessionStorage
 */
export async function refreshAccessToken(): Promise<void> {
  try {
    const response = await fetch('/api/auth/refresh', {
      method: 'POST',
      headers: { 'Authorization': `Bearer ${get(user)?.id}` },
    });
    
    if (!response.ok) {
      // Token refresh failed
      clearAuth();  // Force re-login
      throw new Error('Token refresh failed');
    }
    
    const { accessToken: newToken, expiresIn } = await response.json();
    
    // Update stores
    accessToken.set(newToken);
    tokenExpiry.set(Date.now() + expiresIn * 1000);
    sessionStorage.setItem('ms_access_token', newToken);
    sessionStorage.setItem('ms_token_expiry', (Date.now() + expiresIn * 1000).toString());
    
    // Reset refresh timer
    setTimeout(() => {
      refreshAccessToken();
    }, (expiresIn * 1000) - (5 * 60 * 1000));
    
    console.log('Access token refreshed');
  } catch (error) {
    console.error('Token refresh error:', error);
    clearAuth();
  }
}

/**
 * UPDATE FUNCTION: Logout
 * 
 * CALLED BY: Logout button, auth failures
 * SIDE EFFECTS: Clears all auth stores, sessionStorage, redirects
 */
export async function clearAuth(): Promise<void> {
  user.set(null);
  accessToken.set(null);
  tokenExpiry.set(null);
  sessionStorage.removeItem('ms_access_token');
  sessionStorage.removeItem('ms_token_expiry');
  
  // Call backend logout (optional, clears refresh token from PocketBase)
  try {
    await fetch('/api/auth/logout', { method: 'POST' });
  } catch (e) {
    console.error('Logout API error:', e);
  }
  
  console.log('Auth cleared');
}

// ============================================================================
// PATTERN 2: Svelte Component with Auth Requirement
// ============================================================================

/**
 * COMPONENT: JobList.svelte
 * PURPOSE: Display list of jobs from Microsoft Graph
 * REQUIRES: User to be authenticated
 * 
 * Reactive: $isAuthenticated, $jobs, searchQuery
 * Events: None (pure presentation)
 * API calls: Loads jobs via GraphService
 */

// File: src/components/JobList.svelte
<script lang="ts">
  // Imports - organize by type
  import { onMount } from 'svelte';
  import { isAuthenticated, accessToken } from '../stores/auth';
  import { jobs, jobsLoading, searchJobs } from '../stores/jobs';
  import JobCard from './JobCard.svelte';
  import SearchBar from './SearchBar.svelte';
  
  // Props (none in this case)
  export let jobCategory: string = 'all';
  
  // Reactive state
  let searchQuery = '';
  let filteredJobs: Job[] = [];
  
  // Lifecycle: Load jobs on component mount
  onMount(async () => {
    if (!$isAuthenticated) {
      return;  // Don't load if not authenticated
    }
    
    jobsLoading.set(true);
    try {
      await searchJobs(jobCategory);
    } catch (error) {
      console.error('Failed to load jobs:', error);
    } finally {
      jobsLoading.set(false);
    }
  });
  
  // Reactive: Filter jobs based on search query
  $: filteredJobs = $jobs.filter(job => 
    job.title.toLowerCase().includes(searchQuery.toLowerCase()) ||
    job.company.toLowerCase().includes(searchQuery.toLowerCase())
  );
  
  // Event handler: Search input
  function handleSearch(e: CustomEvent<string>) {
    searchQuery = e.detail;
  }
</script>

{#if !$isAuthenticated}
  <div class="p-4 bg-yellow-50 text-yellow-800 rounded">
    Please sign in to view jobs
  </div>
{:else if $jobsLoading}
  <div class="p-4">Loading jobs...</div>
{:else if filteredJobs.length === 0}
  <div class="p-4">No jobs found matching your search</div>
{:else}
  <div class="space-y-4">
    <SearchBar on:search={handleSearch} />
    <div class="grid grid-cols-1 gap-4">
      {#each filteredJobs as job (job.id)}
        <JobCard {job} />
      {/each}
    </div>
  </div>
{/if}

<style>
  /* Use TailwindCSS classes only, no custom CSS needed here */
</style>

// ============================================================================
// PATTERN 3: API Service Layer
// ============================================================================

/**
 * SERVICE: graphService
 * PURPOSE: Handle all Microsoft Graph API calls with proper headers
 * DEPENDENCIES: accessToken store, error handling
 * 
 * Exports: Functions for each Graph API operation
 * Error handling: Throws errors that UI catches
 */

// File: src/services/graphService.ts
import { get } from 'svelte/store';
import { accessToken, refreshAccessToken, clearAuth } from '../stores/auth';

/**
 * Helper: Ensure token is valid before API call
 * 
 * Checks if token expired, refreshes if needed
 * Throws if no token available
 */
async function ensureValidToken(): Promise<string> {
  const token = get(accessToken);
  if (!token) {
    throw new Error('No access token available - not authenticated');
  }
  
  // Check if token might be expired, refresh proactively
  const expiry = Number(sessionStorage.getItem('ms_token_expiry') || 0);
  if (expiry - Date.now() < 5 * 60 * 1000) {
    // Token expires in less than 5 minutes, refresh now
    await refreshAccessToken();
  }
  
  return get(accessToken) || token;
}

/**
 * API CALL: Get list of files in OneDrive
 * 
 * Endpoint: GET https://graph.microsoft.com/v1.0/me/drive/root/children
 * Scopes required: Files.Read.All
 * Caching: Results cached in IndexedDB via jobsStore
 * 
 * Errors:
 *   - 401: Token invalid, user redirected to login
 *   - 403: Insufficient permissions
 *   - 404: Folder not found
 *   - 429: Rate limited, should retry with backoff
 */
export async function listFiles(folderId: string = 'root'): Promise<File[]> {
  const token = await ensureValidToken();
  
  const endpoint = folderId === 'root'
    ? 'https://graph.microsoft.com/v1.0/me/drive/root/children'
    : `https://graph.microsoft.com/v1.0/me/drive/items/${folderId}/children`;
  
  try {
    const response = await fetch(endpoint, {
      headers: {
        Authorization: `Bearer ${token}`,
        'Content-Type': 'application/json',
      },
    });
    
    if (response.status === 401) {
      // Token invalid, clear auth and redirect
      clearAuth();
      throw new Error('Session expired - please log in again');
    }
    
    if (!response.ok) {
      const error = await response.json().catch(() => ({ message: response.statusText }));
      throw new Error(`Graph API error ${response.status}: ${error.message}`);
    }
    
    const data = await response.json();
    return data.value || [];
  } catch (error) {
    console.error('Graph API error:', error);
    throw error;
  }
}

// ============================================================================
// PATTERN 4: Data Store (Derived from API)
// ============================================================================

/**
 * STORE: jobs
 * PURPOSE: Cached list of jobs loaded from device storage (IndexedDB)
 * UPDATES: Called by services after fetching from Graph API
 * PERSISTENCE: IndexedDB database
 * 
 * STRUCTURE:
 * - jobs: Job[] - Current list of jobs
 * - jobsLoading: boolean - Loading state
 * - jobsError: string | null - Last error if any
 */

// File: src/stores/jobs.ts
import { writable } from 'svelte/store';
import { loadJobsFromDB, saveJobsToDBt } from '../services/storageService';

export const jobs = writable<Job[]>([]);
export const jobsLoading = writable(false);
export const jobsError = writable<string | null>(null);

/**
 * Load jobs from device storage
 * 
 * Called on app init
 * Populates jobs store from IndexedDB
 */
export async function loadJobs(): Promise<void> {
  jobsLoading.set(true);
  try {
    const cachedJobs = await loadJobsFromDB();
    jobs.set(cachedJobs);
    jobsError.set(null);
  } catch (error) {
    console.error('Failed to load jobs:', error);
    jobsError.set((error as Error).message);
  } finally {
    jobsLoading.set(false);
  }
}

/**
 * Search jobs locally (no API call needed)
 * 
 * All job data is already in device storage
 * This filters locally for instant results
 */
export async function searchJobs(query: string): Promise<Job[]> {
  // Get current jobs
  const allJobs = get(jobs);
  
  // Filter based on query
  const results = allJobs.filter(job =>
    job.title.toLowerCase().includes(query.toLowerCase()) ||
    job.company.toLowerCase().includes(query.toLowerCase()) ||
    job.description.toLowerCase().includes(query.toLowerCase())
  );
  
  return results;
}

// ============================================================================
// PATTERN 5: Layout Component (Root)
// ============================================================================

/**
 * COMPONENT: +layout.svelte
 * PURPOSE: Root layout for all pages
 * FEATURES: Navigation, auth check, error handling
 * 
 * Lifecycle: Checks auth on mount, refreshes token
 */

// File: src/routes/+layout.svelte
<script lang="ts">
  import { onMount } from 'svelte';
  import { isAuthenticated, user, clearAuth } from '../stores/auth';
  import { loadJobs } from '../stores/jobs';
  import Navigation from '../components/Navigation.svelte';
  import ErrorBoundary from '../components/ErrorBoundary.svelte';
  
  let error: Error | null = null;
  
  onMount(async () => {
    // Load cached jobs on app startup
    try {
      await loadJobs();
    } catch (e) {
      console.error('Failed to load initial jobs:', e);
      error = e as Error;
    }
  });
</script>

<div class="min-h-screen bg-gray-50">
  <Navigation />
  
  {#if error}
    <ErrorBoundary {error} />
  {/if}
  
  <main class="container mx-auto p-4">
    <slot />
  </main>
</div>

<style>
  /* Global styles as needed */
</style>

// ============================================================================
// PATTERN 6: Route Page with Auth Guard
// ============================================================================

/**
 * PAGE: +page.svelte (Home)
 * PURPOSE: Job listing homepage
 * AUTH: Redirects to login if not authenticated
 */

// File: src/routes/+page.svelte
<script lang="ts">
  import { goto } from '$app/navigation';
  import { onMount } from 'svelte';
  import { isAuthenticated } from '../stores/auth';
  import JobList from '../components/JobList.svelte';
  
  onMount(() => {
    if (!$isAuthenticated) {
      goto('/signin');
    }
  });
</script>

{#if $isAuthenticated}
  <h1 class="text-3xl font-bold mb-6">Job Listings</h1>
  <JobList />
{/if}

// File: src/routes/signin/+page.svelte (OAuth login page)
<script lang="ts">
  import { goto } from '$app/navigation';
  import { isAuthenticated } from '../../stores/auth';
  
  onMount(() => {
    if ($isAuthenticated) {
      goto('/');  // Already logged in
    }
  });
  
  function handleLogin() {
    // Initiate OAuth flow
    initiateOAuthFlow();
  }
</script>

<div class="flex items-center justify-center min-h-screen">
  <button
    on:click={handleLogin}
    class="px-8 py-4 bg-blue-600 text-white rounded-lg hover:bg-blue-700"
  >
    Sign in with Microsoft
  </button>
</div>

// ============================================================================
// SUMMARY
// ============================================================================

/**
 * SVELTE PATTERNS - GOLDEN RULES:
 * 
 * 1. STORES: Centralize state, update via explicit functions
 * 2. COMPONENTS: Keep reactive, let stores handle state
 * 3. SERVICES: Handle API calls with error handling, never expose tokens
 * 4. LIFECYCLE: Use onMount for async operations
 * 5. DERIVED: Use derived stores for computed state (isAuthenticated)
 * 6. REACTIVITY: Use $store syntax to subscribe in templates
 * 7. PROPS: Always document and type check
 * 8. ERROR HANDLING: Catch all async operations, display to user
 * 9. PERSISTENCE: Use IndexedDB for device storage, sessionStorage for tokens
 * 10. TESTING: Every component independently testable
 */