// Run input as command if possible
function runCommand(input) {
    // Return on no input
    if (input === "")
        return "";

    // Exit current level
    const modeSplit = chatMode.split(' ');
    if (modeSplit[0] !== "default") {
        const lowerIn = input.toLowerCase();
        if (lowerIn.startsWith("exit")) {
            cmd_exit();
            return "";
        } else if (lowerIn.startsWith("clear")) {
            cmd_clear();
            return "";
        }
    }

    // Handle different chat modes
    switch (modeSplit[0]) {
        case "msg":
            directMessage(modeSplit[1].split(','), input);
            renameToSelf();
            return "";
        // case "chat":
        //     renameToSelf();
        //     return "";
    }

    // Default chat mode:
    let output = "";
    const lowerIn = input.toLowerCase();

    // Go through properties of window
    for (const func in window) {
        const splits = func.split("cmd_");
        // If property is prefixed with 'cmd_' (a 'command', so an executable function)
        if (splits.length === 2) {
            const name = splits[1];
            const lowerNm = name.toLowerCase();
            // If command is called without parameters
            if (lowerIn === lowerNm) {
                output = window[func]();
                break;
                // If command is called with parameters
            } else if (lowerIn.startsWith(lowerNm + " ")) {
                // Parameters always follow the command name after first space
                const params = input.split(" ").filter((e,i)=>i!==0);
                output = window[func](params);
                break;
            }
        }
    }

    // Standard output:
    if (output === "")
        output = `${input.split(" ")[0]}: command not found`;
    if (output === undefined)
        output = "";

    // Return command output
    return output;
}

// Display 'help' message
function cmd_help() {
    return "Commands list:<br>" +
        "   -about    Information about this website<br>"+
        "   -reload   Reload the page (deletes all session data)<br>" +
        "   -clear    Clear terminal screen (keeps all session data)<br>" +
        "   -history  Displays the command history of this session<br>" +
        "   -exec     Execute arbitrary math and logic equations<br>" +
        "   -nick     Choose your username. Do not use spaces in it<br>" +
        "   -msg      Open a direct chat to the provided user by name<br>" +
        "   -ls       List all connected users by name and id<br>" +
        "   -ping     Ping the host to request two-way-delay";
}

// Display 'about' message
function cmd_about() {
    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.";
}

// Reload page
function cmd_reload() {
    window.location.reload();
}

// Clear terminal window
function cmd_clear() {
    setTimeout(() => {
        const tbc = tbDiv.children;
        for (let i = tbc.length-3; i > 1; i--)
            tbDiv.removeChild(tbc[i]);

        const prelink = document.createElement("a");
        prelink.innerHTML = pretext.current;
        tbDiv.replaceChild(prelink, tbc[1]);

        cursorPosition = 0;
        cursorYOffset = 7;

        updateCursor();
    }, 50);
    return null;
}

// Display the command history line by line
function cmd_history() {
    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;
}

// Execute arbitrary math and logic equations
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 eval(str).toString();
}

// Echo out any given text
function cmd_echo(input) {
    if (input === undefined)
        return " ";
    return input.join(' ');
}

// Set users' name
function cmd_nick(input) {
    if (input === undefined)
        return "No nickname was given!";
    if (!!window.localStorage.getItem("connected"))
        sendNickname(input[0]);
    else
        connect(input[0]);
    return null;
}

// Initialize direct chat
function cmd_msg(input) {
    if (input === undefined)
        return "No recipient was given!";
    if (!window.localStorage.getItem("connected"))
        return "You are not connected! Use the 'nick' command to connect using your username.";
    if (window.localStorage.getItem("name") === "")
        return "You do not have a name!";
    // Get recipient username without spaces and pretext
    const username = input[0];
    pretext.current = `Chat (${username})> `;
    // Set chat mode to direct messages and start pulling
    chatMode = `msg ${username}`;
    userData.chatPull = setInterval(getChatMessages, 500);
}

// Exit current level (example: chat -> main)
function cmd_exit(error) {
    const level = chatMode.split(' ')[0];
    if (level === "default")
        return "Already at top-level!";

    // Set mode to default and reset pretext
    chatMode = "default";
    pretext.current = pretext.original;
    // Do individual resets
    switch (level) {
        // case "chat":
        case "msg":
            // Stop chat pulling
            clearInterval(userData.chatPull);
            break;
    }

    // Exit was called automatically. Print error.
    if (error)
        outputText({output: error});
}

// List all users to be able to chat with
function cmd_ls() {
    if (!window.localStorage.getItem("connected"))
        return "You are not connected! Use the 'nick' command to connect using your username.";
    requestUsernames();
    return null;
}

// Ping host for two-way-delay
function cmd_ping() {
    if (!window.localStorage.getItem("connected"))
        return "You are not connected! Use the 'nick' command to connect using your username.";
    requestPing();
    return null;
}

// User wants to log out
function cmd_logout() {
    if (!window.localStorage.getItem("connected"))
        return "You are not even connected yet!";
    disconnect();
}