const config = {
    "add": [
        { "name": "X-Content-Type-Options", "value": "nosniff" },
        { "name": "X-XSS-Protection", "value": "10;mode=block" },
        { "name": "X-Frame-Options", "value": "deny" },
        { "name": "Strict-Transport-Security", "value": "max-age=31536000;includeSubDomains" }
    ],
    "replace": [],
    "remove": [],
    "append": [],
};


exports.handler = async (event, context, callback) => {

    const response = event.Records[0].cf.response;
    const respHeaders = response.headers;

    let addHeaders = config['add'];
    let replaceHeaders = config['replace'];
    let removeHeaders = config['remove'];
    let appendHeaders = config['append'];

    // If and only if the header is already set, replace its old value with the new one. Ignored if the header is not already set.
    if (replaceHeaders) {
        for (let i = 0; i < replaceHeaders.length; i++) {
            let h = replaceHeaders[i];
            if (respHeaders[h['name'].toLowerCase()]) {
                respHeaders[h['name'].toLowerCase()] = h['value'].split(',').map((v) => { return { 'key': h['name'], 'value': v.trim() } });
                console.log(`Replaced Header(${h['name']}).`);
            }
            else {
                console.log(`Header(${h['name']}) does not exists, ignore replacing.`);
            }
        }
    }

    // Unset the header(s) with the given name.
    if (removeHeaders) {
        for (let i = 0; i < removeHeaders.length; i++) {
            let h = removeHeaders[i];
            if (respHeaders[h['name'].toLowerCase()]) {
                delete respHeaders[h['name'].toLowerCase()];
                console.log(`Removed Header(${h['name']}).`);
            }
            else {
                console.log(`Header(${h['name']}) does not exists, ignore removing.`);
            }
        }
    }

    // If the header is not set, set it with the given value. If it is already set, a new header with the same name and the new value will be set.
    if (appendHeaders) {
        for (let i = 0; i < appendHeaders.length; i++) {
            let h = appendHeaders[i];
            if (respHeaders[h['name'].toLowerCase()]) {
                respHeaders[h['name'].toLowerCase()] = respHeaders[h['name'].toLowerCase()].concat(h['value'].split(',').map((v) => { return { 'key': h['name'], 'value': v.trim() } }));
                console.log(`Appended Header(${h['name']}).`);
            }
            else {
                respHeaders[h['name'].toLowerCase()] = h['value'].split(',').map((v) => { return { 'key': h['name'], 'value': v.trim() } });
                console.log(`Added(by append) Header(${h['name']}).`);
            }
        }
    }

    // Add function must be after Replace/Remove/Append. Otherwise added headers may be overwritten.
    // If and only if the header is not already set, set a new header with the given value. Ignored if the header is already set.
    if (addHeaders) {
        for (let i = 0; i < addHeaders.length; i++) {
            let h = addHeaders[i];
            if (respHeaders[h['name'].toLowerCase()]) {
                console.log(`Header(${h['name']}) already exists, ignore adding.`);
            }
            else {
                respHeaders[h['name'].toLowerCase()] = h['value'].split(',').map((v) => { return { 'key': h['name'], 'value': v.trim() } });
                console.log(`Added Header(${h['name']}).`);
            }
        }
    }


    callback(null, response);
};