/*************************************************************************************************************************
File:       alternateConnections.js
Purpose:    This file provides interface and utiltiy methods for communicating with the server as a sketch for what a 
            mobile cab could look like.  It serves to illustrate that the simulation can be controlled from a separate
            place than the main view webpage.  This script also populates the controls on alternatePage.html.

Written by John McGorey - Spring 2019 - Using Microsoft Visual Studio Code 2019
For use in the St. Norbert College CSCI460 Senior Capstone Experience
**************************************************************************************************************************/
const url = "http://localhost:3000/"; // Change this to reflect where the server is being hosted

// URL Parameter Constants
// These are used to send information to the server via the querystring
const TRAIN_SPEED = "speed";
const TRAIN_ID = "train_id";
const TURNOUT_ID = "turnout_id";

// Response Status Constants
const ERROR_STATUS = "ERROR";       // The requested operation was a failure
const SUCCESS_STATUS = "SUCCESS";   // The requested operation was a success

//----------------------------------------------------------------------------------------------------
// Script execution starts here
//----------------------------------------------------------------------------------------------------
getTurnouts(function(turnouts) {
   let element = document.getElementById('turnoutId');
   if (element) {
       for (let i = 0; i < turnouts.length; i++) {
           element.options[i] = new Option("Turnout " + i, i);
       }
   } 
});

getTrains(function(trains) {
    let element = document.getElementById('trainId');
    if (element) {
        for (let i = 0; i < trains.length; i++) {
            element.options[i] = new Option("Train " + i, i);
        }
    }
});

//----------------------------------------------------------------------------------------------------
// Function Definitions
//----------------------------------------------------------------------------------------------------
function sendRequest(requestUrl, callback) {
    /***************************************************************************************
        Function:   sendRequest
        Purpose:    Sends an HTTP request to the URL specified by requestUrl.  When the
                    request returns with a response, execute the specified callback with
                    status of the response and the response body.

        Input:      requestUrl - The URL to send the http request to.  If the request operation
                                 requires parameters, those should be added to the URL as a
                                 queryString before the URL is passed to this function.
                    
                    callback   - The function to call when the request returns a response

        Output:  (Via callback)
                    status - Either ERROR_STATUS or SUCCESS_STATUS, depending if the response
                             body contained the word 'Error'.
                    
                    request.response - The body of the response, containing the info the
                                       server sends back
    ****************************************************************************************/
    let request = new XMLHttpRequest();
    request.timeout = 10000; // Timeout of 10 seconds

    request.open('GET', requestUrl);

    request.responseType = 'text';

    request.onload = function() {
        // Determine if the request was successful
        let status;
        if (request.response.includes('Error'))
            status = ERROR_STATUS;
        else
            status = SUCCESS_STATUS;
        callback(status , request.response);

    }; // This function will be called when the HTTP request gets a response

    request.send(); // Send out the request and wait for a response
}

function setTrainSpeed(train_id, speed) {
    /***************************************************************************************
        Function:   setTrainSpeed
        Purpose:    This function takes in a train id number and a speed value and sets the
                    speed of the specified train to that value via an HTTP request to the
                    server.

        Input:      train_id - The id of the train whose speed to modify
                    speed    - The speed value to set the train to

        Note:  There is nothing of import in the response to this request, so this function
               only logs if something went wrong.
    ****************************************************************************************/
    let request_url = url + "setTrainSpeed/?";
    request_url += TRAIN_ID + "=" + train_id;
    request_url += "&" + TRAIN_SPEED + "=" + speed;

    sendRequest(request_url, function(status, response) {
        if (status == "SUCCESS")
        {
            //  Train speed updated successfully
        }
        else 
        {
            console.log(response); // If something goes wrong, log it
        }
    });
}

function getTrains(callback) {
    /***************************************************************************************
        Function:   getTrains
        Purpose:    This function sends a request to the server to get a list of the trains
                    in the simiulation & their statuses.  The response from the server
                    contains a JSON string containing the train information, which is 
                    parsed into an array of objects and passed on to the callback.

        Input:      callback - The function to call when the server returns the list of trains
    ****************************************************************************************/
    let request_url = url + "getTrains/";
    sendRequest(request_url, function(status, response) {
        if (status == SUCCESS_STATUS) {
            // In this case, the response is a JSON string containing the trains in the simulation
            let train_objs = JSON.parse(response);
            if (callback) // Send the resultant object to the callback for processing
                callback(train_objs);
        }
    });
}

function getTurnouts(callback)
{
    /***************************************************************************************
        Function:   getTurnouts
        Purpose:    This function sends a request to the server to get a list of the turnouts
                    in the simulation & their statuses.  The response from the server contains
                    a JSON string describing the turnouts' information.  This info is then
                    parsed into an array of objects and passed on to the callback for processing

        Input:      callback - The function to call when the server returns the list of turnouts
    ****************************************************************************************/
    let request_url = url + "getTurnouts/";
    sendRequest(request_url, function(status, response) {
        if (status == SUCCESS_STATUS) {
            // In this case, the response is a JSON string contaning all of the turnouts in the simulation
            let turnout_objs = JSON.parse(response);
            if (callback)
                callback(turnout_objs);
        }
    });
}

function switchTurnout(turnout_id) {
    /***************************************************************************************
        Function:   switchTurnout
        Purpose:    This function takes in a turnout ID number and sends a request to the
                    server to switch that particular turnout.

        Input:      turnout_id - The id number of the turnout to switch
    ****************************************************************************************/
    let request_url = url + "switchTurnout/?" + TURNOUT_ID + "=" + turnout_id;
    sendRequest(request_url, function(status, response) {
        console.log("Switching Turnout " + turnout_id + ": ", response);
    });
}