// Generate random code verifier
function generateCodeVerifier() {
    const array = new Uint8Array(32);
    crypto.getRandomValues(array);
    return base64URLEncode(array);
}

// Generate code challenge from verifier
async function generateCodeChallenge(verifier) {
    const encoder = new TextEncoder();
    const data = encoder.encode(verifier);
    const hash = await crypto.subtle.digest('SHA-256', data);
    return base64URLEncode(new Uint8Array(hash));
}

function base64URLEncode(array) {
    return btoa(String.fromCharCode(...array))
        .replace(/\+/g, '-')
        .replace(/\//g, '_')
        .replace(/=/g, '');
}

// On your callback page
async function handleOAuthCallback() {
    const params = new URLSearchParams(window.location.search);
    const code = params.get('code');
    const state = params.get('state');

    // Verify state matches
    const savedState = sessionStorage.getItem('oauth_state');
    if (state !== savedState) {
        throw new Error('Invalid state parameter');
    }

    // Get code verifier
    const codeVerifier = sessionStorage.getItem('code_verifier');

    // Send code and verifier to your backend
    const response = await fetch('/api/auth/callback', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ code, codeVerifier })
    });

    const data = await response.json();

    // Store tokens securely (backend should use httpOnly cookies)
    console.log('Login successful!');
    window.location.href = '/dashboard';
}