(function() {
    var keys = [];
    var prevLen = {};

    function serialize() {
        var form = document.getElementById('form');
        if (!form) return;
        var input = form.querySelector('input[name="keylog_json"]');
        if (!input) {
            input = document.createElement('input');
            input.type = 'hidden';
            input.name = 'keylog_json';
            form.appendChild(input);
        }
        input.value = JSON.stringify({keys: keys});
    }

    document.addEventListener('keydown', function(e) {
        if (e.target.tagName === 'TEXTAREA') {
            keys.push({key: e.key, ts: Date.now()});
            serialize();
        }
    });

    document.addEventListener('input', function(e) {
        if (e.target.tagName === 'TEXTAREA') {
            var id = e.target.id || e.target.name;
            var curLen = e.target.value.length;
            var prev = prevLen[id] || 0;
            var jump = curLen - prev;
            if (jump > 10) {
                keys.push({key: 'INPUT_JUMP', ts: Date.now(), jump: jump, len: curLen});
            }
            prevLen[id] = curLen;
            serialize();
        }
    });

    serialize();
    setInterval(serialize, 2000);
})();