// Enum available loco mode
var LOCO_MODE = {
    ANALOG: 0,  // Analog mode is for old DC locomotives that use a variable voltage on the track to control speed.
    MARKLIN: 1, // Märklin mode is for old marklin analog AC (with relay dir) Märklin locomotives.
    DCC: 2      // DCC mode is for Digital Command Control, a standard for digital model railway control.
};

var LOCO_DIR = {
    FORWARD: 0, // Forward direction
    BACKWARD: 1 // Backward direction
};

var Loco = {
    Mode: LOCO_MODE.DCC,
    ID: 0,
    Speed: 0,
    Dir: LOCO_DIR.FORWARD,
    Scale: 1,    // Example real loco speed is 45Kmh/max, so what are step (128 for digital to represent 0-200Kmh) per Kmh
    MaxSpeed: 100, // Max speed in DCC step (<129) to reach scale speed (e.g. 45Kmh)
    setMode: function(mode) {
        this.Mode = mode;
    },
    setID: function(id) {
        this.ID = id;
    },
    setSpeed: function(speed) {
        this.Speed = speed;
        setSpeed(speed); // Update the speedometer needle
    },
    setDir: function(dir) {
        this.Dir = dir;
    }
};

/**
 * Update the speedometer based on the slider value. The slider value is expected to be in the range 0-128, 
 * when a value is received, it is converted to a speed in Kmh based on the loco's scale and max speed, 
 * then the speedometer needle is updated accordingly.
 * 
 * @param {int} value 
 */
function updateSpeedometer(value) {
    Loco.setSpeed(parseInt(value));
}

/**
 * Speed is expected to be in the range 0-200. This function maps it to an angle for the needle.
 * at 100Kmh, needle is vertical, it's length is 50px, and it rotates from -120deg (0 speed) to +120deg (max speed).
 * At speed=100, x2=150, y2=70
 */
function setSpeed(speed) 
{
    // Clamp speed
    speed = Math.max(0, Math.min(200, speed));
    // Map speed to angle: 0 = -120deg, 100 = 0deg, 200 = +120deg
    var angle = -120 + (speed / 200) * 240;
    var rad = angle * Math.PI / 180;
    var r = 50; // needle length
    var cx = 150, cy = 120;
    var x2 = cx + r * Math.sin(rad); // Use sin for x, cos for y to match SVG coordinate system
    var y2 = cy - r * Math.cos(rad);
    document.getElementById('needle').setAttribute('x2', x2);
    document.getElementById('needle').setAttribute('y2', y2);
}

// Example: set speed to 0 initially
setSpeed(0);