function integerToBytes(integer, numBytes) {
    const bytesArray = new Array(numBytes).fill(0);
    for (let i = 0; i < numBytes; i++) {
        bytesArray[numBytes - i - 1] = integer & 0xff;
        integer >>= 8;
    }
    return Uint8Array.from(bytesArray);
}

function concatenateUInt8Arrays(array1, array2) {
    const newArray = new Uint8Array(array1.length + array2.length);
    newArray.set(array1);
    newArray.set(array2, array1.length);
    return newArray;
}

/*
Convert an ArrayBuffer into a string
from https://developer.chrome.com/blog/how-to-convert-arraybuffer-to-and-from-string/
*/
function ab2str(buf) {
  return String.fromCharCode.apply(null, new Uint8Array(buf));
}

/*
Export the given key and write it into the "exported-key" space.
*/
async function exportCryptoKeyPem(key) {
  const exported = await window.crypto.subtle.exportKey("spki", key);
  const exportedAsString = ab2str(exported);
  const exportedAsBase64 = btoa(exportedAsString);
  return exportedAsBase64;
}

async function exportCryptoKey(key) {
  const exported = await window.crypto.subtle.exportKey("jwk", key);
  return JSON.stringify(exported, null, " ");
}

async function createKeyPair() {
    const crypto = window.crypto.subtle
    const keyPair = await window.crypto.subtle.generateKey(
        {
            name: "RSA-OAEP",
            modulusLength: 2048,
            publicExponent: new Uint8Array([4, 0, 1]),
            hash: "SHA-256",
        },
        true,
        ["encrypt", "decrypt"]
    );
    return keyPair;
}

let keyPair = createKeyPair();
let loginForm = document.getElementById('login-form');
let loginButton = document.getElementById('login-button');
let nonce = null
loginButton.addEventListener('click', async evt => {
    const publicKey = (await keyPair).publicKey;
    const publicKeyPem = await exportCryptoKeyPem(publicKey);
    fetch('api/login', {
        method: 'POST',
        headers: {
            'public-key' : publicKeyPem,
            'Content-Type': 'application/json'
        },
        body: JSON.stringify({ username: loginForm.username.value, password: loginForm.password.value})
    }).then(async response => {
        const nonceHeader = response.headers.get('nonce');
        const encryptedNonce = atob(nonceHeader);
        const privateKey = (await keyPair).privateKey;
        const crypto = window.crypto.subtle;
        const encryptedBuffer = Uint8Array.from(atob(nonceHeader), c => c.charCodeAt(0));
        nonce = await crypto.decrypt({ name: "RSA-OAEP" }, privateKey, encryptedBuffer)
            .then(it => new Uint8Array(it));
        return response.text();
    }).then(text => {
        let paragraph = document.createElement('p');
        paragraph.textContent = text;
        document.body.appendChild(paragraph);
    });
});

let button = document.createElement('button');
button.textContent = 'Press me'
document.body.appendChild(button);

button.addEventListener('click', async evt => {
    let header = {};
    if(nonce != null) {
        const crypto = window.crypto.subtle;
        const epochTick = Math.floor(new Date().getTime() / 10000)
        const data = concatenateUInt8Arrays(nonce, integerToBytes(epochTick, 8))
        const hash = new Uint8Array(await crypto.digest("SHA-256", data));
        const token = btoa(Array.from(hash, byte => String.fromCharCode(byte)).join(''));
        headers = {
            'x-token': token
        };
    }
    fetch('api/hello', {
        method: 'GET',
        headers
    }).then(response => response.text()).then(text => {
        let paragraph = document.createElement('p');
        paragraph.textContent = text;
        document.body.appendChild(paragraph);
    });
});