function cmd_help() {
    // Display 'help' message
    return "Commands list:<br>" +
        "   -about    Information about this website<br>"+
        "   -clear    Clear terminal screen<br>" +
        "   -history  Displays the command history of this session<br>" +
        "   -exec     Execute arbitrary math and logic equations";
}

function cmd_about() {
    // Display 'about' message
    return "This website is based on the general idea and design of a terminal.<br>" +
        "It serves the purpose of a homepage. It exists just for the fun of creating it.";
}

function cmd_clear() {
    // Clear terminal by reloading page
    window.location.reload();
}

function cmd_history() {
    // Display the command history line by line
    let output = "";

    const hl = history.list;
    for (let i = 0; i < hl.length; i++) {
        const lineBreak = (i !== hl.length - 1) ? "<br>" : "";
        output += `${i+1} ${hl[i]}${lineBreak}`;
    }

    return output;
}

function cmd_exec(input) {
    // No input was given
    if (input === undefined)
        return "You must enter parameters!";
    // Input contains letters or invalid characters
    const str = input.join(' ');
    if (/[',:;a-zA-Z]/.test(str) || str === "")
        return "Invalid input!";
    // Input is inside of character range with exceptions
    const chars = str.split('').filter(e => {
        const code = e.charCodeAt(0);
        const s = code ===  32;
        const a = code >    36;
        const b = code <    63;
        const c = code ===  94;
        const d = code === 124;
        return !(s || a && b || c || d);
    });
    // If exceptions remain, invalid input was given
    if (chars.length > 0)
        return "Invalid input!";
    // Execute input and return output
    return (new Function(`return ${str}`))().toString();
}

function cmd_echo(input) {
    if (input === undefined)
        return " ";
    return input.join(' ');
}

function cmd_nick(input) {
    if (input === undefined)
        return "No nickname was given!";
    user.name = input[0];
    fetch('/nickname', {
        method: 'POST',
        headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/json'
        },
        body: JSON.stringify({
            name: user.name,
            id: user.id
        })
    }).then(res => {
        if (res.status === 200) {
            user.connected = true;
            return res.json();
        }
    }).then(res => {
        if (res === undefined)
            return;
        if (res)
            outputText({output: `Applied name '${user.name}'.`});
        else {
            outputText({output: `Name '${user.name}' is already taken!.`});
            user.name = "";
        }
    });
    return null;
}

function cmd_msg(input) {
    if (input === undefined)
        return "No username given!";
    if (!user.connected)
        return "You are not connected!";
    const username = input[0];
    pretext = `Chat (${username})> `;
    chatMode = `msg ${username}`;
    fetch('/chatInit', {
        method: 'POST',
        headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/json'
        },
        body: JSON.stringify({
            name: username,
            id: user.id
        })
    }).then(res => {});
}

function cmd_exit() {
    if (chatMode.split(' ')[0] !== "default")
        chatMode = "default";
}