let AUTHORIZATION_URL = 'http://localhost:8010/Sitefinity/Authenticate/OpenID/connect/authorize';
let PRESS_RELEASES_URL = 'http://localhost:8010/api/default/pressreleases';
let ACCESS_TOKEN_KEY = 'access_token';
let ACCESS_TOKEN_EXP_KEY = 'access_token_exp';

window.onload = () => {
    // STS redirect URI. Access token is being received here
    if (window.location.hash) {
        let tokenResponse = getTokenResponse();
        saveToLocalStorage(tokenResponse.access_token);
    }
    // Token has expired or is not present. Requests new access token
    else if (hasExpired()) {
        let authFrame = appendAuthFrame();
        getToken(authFrame, () => {
            let token = localStorage[ACCESS_TOKEN_KEY];
            logPressReleases(token);
            authFrame.remove();
        });
    }
    // Token is available for use
    else {
        let token = localStorage[ACCESS_TOKEN_KEY];
        logPressReleases(token);
    }
}

function getToken(authFrame, callback) {
    // Prevents CSRF (Cross-Site Request Forgery) attacks
    let state = rand();
    let nonce = rand();
    localStorage['state'] = state;
    localStorage['nonce'] = nonce;

    let authorizationUrl = AUTHORIZATION_URL;
    let clientId = 'sitefinity';
    let redirectUri = getCurrentUri();
    let responseType = 'id_token token';
    let scope = 'openid email profile';
    let url = authorizationUrl + '?' +
        'client_id=' + encodeURI(clientId) + '&' +
        'redirect_uri=' + encodeURI(redirectUri) + '&' +
        'response_type=' + encodeURI(responseType) + '&' +
        'scope=' + encodeURI(scope) + '&' +
        'state=' + encodeURI(state) + '&' +
        'nonce=' + encodeURI(nonce);
    authFrame.src = url;
    authFrame.addEventListener('load', () => {
        callback();
    });
}

function getTokenResponse() {
    let hash = window.location.hash.substr(1);
    let result = hash.split('&').reduce((result, item) => {
        let parts = item.split('=');
        result[parts[0]] = parts[1];
        return result;
    }, {});

    return result;
}

function appendAuthFrame() {
    let authFrame = document.createElement('iframe');
    authFrame.style.display = 'none';
    document.body.appendChild(authFrame);
    return authFrame;
}

function hasExpired() {
    if (!localStorage[ACCESS_TOKEN_KEY] || !localStorage[ACCESS_TOKEN_EXP_KEY]) {
        return true;
    }

    let currentDate = new Date();
    let expirationDate = new Date(localStorage[ACCESS_TOKEN_EXP_KEY]);
    return currentDate > expirationDate;
}

function decodeJwt(token) {
    let base64Url = token.split('.')[1];
    let base64 = base64Url.replace('-', '+').replace('_', '/');
    return JSON.parse(window.atob(base64));
}

function getExpirationDate(token) {
    let tokenInfo = decodeJwt(token);
    let expirationDate = new Date(tokenInfo.exp * 1000);
    return expirationDate;
}

function saveToLocalStorage(token) {
    localStorage[ACCESS_TOKEN_KEY] = token;
    localStorage[ACCESS_TOKEN_EXP_KEY] = getExpirationDate(token);
}

function logPressReleases(token) {
    getJSON(PRESS_RELEASES_URL, token)
        .then(console.log)
        .catch(console.log);
}

function getJSON(url, token) {
    return new Promise((resolve, reject) => {
        let xhr = new XMLHttpRequest();
        xhr.responseType = 'json';

        xhr.onload = () => {
            try {
                if (xhr.status === 200) {
                    let response = xhr.response;
                    if (typeof response === 'string') {
                        response = JSON.parse(response);
                    }
                    resolve(response);
                }
                else {
                    reject(Error(`${xhr.statusText} (${xhr.status})`));
                }
            }
            catch (err) {
                reject(err);
            }
        }

        xhr.onerror = () => {
            reject(Error('Network error'));
        }

        xhr.open('GET', url);
        xhr.setRequestHeader('Authorization', `Bearer ${token}`);
        xhr.send();
    });
}

function getCurrentUri() {
    return window.location.href.split('?')[0];
}

function rand() {
    return (Date.now() + '' + Math.random()).replace('.', '');
}