rheinsw-mono-repo/internal_frontend/lib/api/auth/tokenUtils.ts

interface JwtPayload {
    exp: number;
    iat?: number;
    sub?: string;

    [key: string]: unknown; // for any extra claims
}

interface TokenRefreshResult {
    access_token: string;
    refresh_token?: string;
    expires_in?: number;
}

// Function to decode JWT payload without verification (for local expiration check)
export function decodeJwtPayload(token: string): JwtPayload | null {
    try {
        const base64Url = token.split('.')[1];
        const base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
        const jsonPayload = decodeURIComponent(
            atob(base64)
                .split('')
                .map(c => '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2))
                .join('')
        );
        return JSON.parse(jsonPayload);
    } catch (error) {
        console.error("[auth] Failed to decode JWT payload:", error);
        return null;
    }
}

// Function to check if token is expired or about to expire (within 5 minutes)
export function isTokenExpiring(token: string, bufferTimeMinutes: number = 5): boolean {
    const payload = decodeJwtPayload(token);
    if (!payload || !payload.exp) {
        return true; // Consider invalid tokens as expired
    }
    const currentTime = Math.floor(Date.now() / 1000);
    const expirationTime = payload.exp;
    const bufferTime = bufferTimeMinutes * 60; // Convert minutes to seconds
    const timeUntilExpiration = expirationTime - currentTime;

    // Log token expiration warning message
    if (timeUntilExpiration <= bufferTime) {
        const expirationDate = new Date(expirationTime * 1000);
        if (timeUntilExpiration <= 0) {
            console.warn(`[auth] Token has already expired at ${expirationDate.toISOString()}`);
        } else {
            const minutesUntilExpiration = Math.floor(timeUntilExpiration / 60);
            const secondsUntilExpiration = timeUntilExpiration % 60;
            console.warn(`[auth] Token will expire in ${minutesUntilExpiration}m ${secondsUntilExpiration}s at ${expirationDate.toISOString()}`);
        }
    }

    return timeUntilExpiration <= bufferTime;
}

// Function to refresh token using refresh token
export async function refreshAccessToken(refreshToken: string): Promise<TokenRefreshResult | null> {
    try {
        const {
            KEYCLOAK_CLIENT_ID,
            KEYCLOAK_CLIENT_SECRET,
            KEYCLOAK_ISSUER,
        } = process.env;

        if (!KEYCLOAK_CLIENT_ID || !KEYCLOAK_CLIENT_SECRET || !KEYCLOAK_ISSUER) {
            console.error("[auth] Missing Keycloak configuration for token refresh");
            return null;
        }

        const tokenEndpoint = `${KEYCLOAK_ISSUER}/protocol/openid-connect/token`;

        const response = await fetch(tokenEndpoint, {
            method: 'POST',
            headers: {
                'Content-Type': 'application/x-www-form-urlencoded',
            },
            body: new URLSearchParams({
                grant_type: 'refresh_token',
                client_id: KEYCLOAK_CLIENT_ID,
                client_secret: KEYCLOAK_CLIENT_SECRET,
                refresh_token: refreshToken,
            }),
        });

        if (!response.ok) {
            console.error("[auth] Failed to refresh token:", response.status, response.statusText);
            return null;
        }

        const data = await response.json();
        return data as TokenRefreshResult;
    } catch (error) {
        console.error("[auth] Error refreshing token:", error);
        return null;
    }
}

// Helper function to get just the access token (for backward compatibility)
export async function getRefreshedAccessToken(refreshToken: string): Promise<string | null> {
    const result = await refreshAccessToken(refreshToken);
    return result?.access_token || null;
}

// Centralized function to get a valid access token (refreshing if needed)
export async function getAccessToken(accessToken?: string, refreshToken?: string): Promise<{
    accessToken: string | null;
    refreshToken?: string | null;
    refreshed: boolean;
}> {
    // If no access token provided, return null
    if (!accessToken) {
        return {accessToken: null, refreshed: false};
    }

    // Check if token is expiring within 1 minute (as requested in issue)
    if (!isTokenExpiring(accessToken, 1)) {
        return {accessToken, refreshed: false};
    }

    console.log("[auth] Access token is expiring within 1 minute, attempting refresh");

    // If no refresh token, return the current token (might be expired)
    if (!refreshToken) {
        console.warn("[auth] No refresh token available for refresh");
        return {accessToken, refreshed: false};
    }

    try {
        const refreshResult = await refreshAccessToken(refreshToken);
        if (refreshResult) {
            return {
                accessToken: refreshResult.access_token,
                refreshToken: refreshResult.refresh_token || refreshToken,
                refreshed: true
            };
        } else {
            console.warn("[auth] Failed to refresh token, returning current token");
            return {accessToken, refreshed: false};
        }
    } catch (error) {
        console.error("[auth] Error refreshing token:", error);
        return {accessToken, refreshed: false};
    }
}