function compute()
{
    /*
     * Get framerate, start frame, and end frame from corresponding elements
     * Double check they all have a value
     */
    const fps = parseInt(document.getElementById("framerate").value);
    const sframe = document.getElementById("startobj").value;
    const eframe = document.getElementById("endobj").value;

    if (typeof (sframe) === "undefined" || typeof (eframe) === "undefined"
        || typeof (fps) === "undefined")
        return;

    const frames = (eframe - sframe) * fps;
    const s = Math.floor(frames / fps);

    /* Show the time and mod message in the DOM */
    const ftime = time_format(s);
    const mod_message = `Mod Note: Retimed (Start: Frame ${sframe * fps}, End: ${
        eframe * fps}, FPS: ${fps}, Total Time: ${ftime})`;

    document.getElementById("time").value = ftime;
    document.getElementById("mod_message").disabled = false;
    document.getElementById("mod_message").innerText = mod_message;
    document.getElementById("mod_message_button").disabled = false;
}

/* Convert seconds to human readable time */
function time_format(t)
{
    const h = ~~(t / 3600);
    const m = ~~((t % 3600) / 60);
    const s = ~~t % 60;
    let ret = "";

    if (h > 0)
        ret += h + ":" + (m < 10 ? "0" : "");

    ret += m + ":" + (s < 10 ? "0" : "");
    ret += s;

    /* Milliseconds */
    const st = t.toString();
    if (!isNaN(t) && st.indexOf(".") != -1)
        ret += "." + st.split(".")[1];

    return ret;
}

/* Allow user to copy mod message to clipboard */
function copy_mod_message()
{
    const text_area = document.getElementById("mod_message");
    text_area.focus();
    text_area.select();
    document.execCommand("copy");
    // document.getElementById("mod_message").innerText = text_area.value + "\n\nCopied to clipboard
    // successfully!"
}

/* If framerate is invalid, show an error message and disable start and end frame fields */
const check_fps =
    (event) => {
        if (event.target.value === "" || parseInt(event.target.value) <= 0
            || isNaN(parseInt(event.target.value))) {
            document.getElementById("framerate")
                .setCustomValidity("Please enter a valid framerate.");
            document.getElementById("framerate").reportValidity();
            document.getElementById("startobj").disabled = true;
            document.getElementById("endobj").disabled = true;
            document.getElementById("compute_button").disabled = true;
        } else {
            document.getElementById("startobj").disabled = false;
            document.getElementById("endobj").disabled = false;
            document.getElementById("compute_button").disabled = false;
        }
    }

/* Get current frame from input field (either start time or end time) */
const parse_time = (event) => {
    let inptext_frame = (JSON.parse(event.target.value)).lct;
    if (typeof inptext_frame !== "undefined") {
        const fps = parseInt(document.getElementById("framerate").value);
        const frame_from_obj = (t, fps) => Math.floor(t * fps) / fps;
        const fframe = frame_from_obj(inptext_frame, fps);
        document.getElementById(event.target.id).value = `${fframe}`;
    }
}