function Datasource(element) {
    this.url = element.dataset.url;
    this.slots = JSON.parse(element.dataset.slots) || {};

    function buildUrl(url, slots) {
        var parsedUrl = url;
        Object.keys(slots).forEach(function(slot) {
            var reg = new RegExp(`\\{\\{${slot}\\}\\}`, "gi");
            parsedUrl = parsedUrl.replace(reg, slots[slot]);
        });
        return parsedUrl;
    }

    function dataSourceFetch(url) {
        return fetch(url).then(function(data) {
                return data.json();
            })
            .catch(error => console.log(error))
    }

    function run() {
        var url = buildUrl(this.url, this.slots);
        dataSourceFetch(url).then(function(data) {
            emitEvent(element, 'data', [data]);
        })
    }

    function set(name, value) {
        this.slots[name] = value;
        element.dataset.slots = JSON.stringify(this.slots);
    }
    this.run = run.bind(this);
    this.set = set.bind(this);
}

function parseJSON_SQL(data) {
    var headers = data.meta.map(function(head) { return head.column; });
    var newData = data.data.slice(0);
    newData.unshift(headers);
    return newData;
}

function pivotTable(data) {
    data.shift();
    var header = ['year'];
    var dataIterator = data.entries();
    var prevYear;
    var result = [];
    var res;
    while (!(iteratee = dataIterator.next()).done) {
        var item = iteratee.value[1];
        var year = item[0];
        var desc = item[1];
        var value = item[2];
        var index = header.indexOf(desc);
        index = index < 0 ? header.push(desc) - 1 : index;
        if (year != prevYear) {
            res = [year];
            result.push(res);
            prevYear = year;
        }
        res[index] = value;
    }
    result.unshift(header);
    return result;
}