// Auto-pilot for docking with the International Space Station
//
// The program uses Artificial Intelligence and Decision Trees (i.e. basic kinematics and a bunch of if statements)
// to perform docking with the ISS from any starting position.
//
// To use it:
// - open the SpaceX simulation website: https://iss-sim.spacex.com/
// - open the Developer's console and paste the contents of this file
//
// Demo: https://youtu.be/jWQQH2_UGLw
//

function el(v)      { return document.getElementById(v); }
function blink(e)   { e.style.backgroundColor='red'; setTimeout(()=>{ e.style.backgroundColor=''; }, 100); }

// Sensor data

function getPitch(i)    { return parseFloat(el('pitch').children[i].innerText); }
function getYaw(i)      { return parseFloat(el('yaw').children[i].innerText); }
function getRoll(i)     { return parseFloat(el('roll').children[i].innerText); }
function getRange()     { return parseFloat(el('range').children[1].innerText); }
function getRangeX()    { return parseFloat(el('x-range').children[0].innerText); }
function getRangeY()    { return parseFloat(el('y-range').children[0].innerText); }
function getRangeZ()    { return parseFloat(el('z-range').children[0].innerText); }
function getRate()      { return parseFloat(el('rate').children[1].innerText); }

// Controls

function moveForward()  { e = el('translate-forward-button');   blink(e); e.click(); }
function moveBackward() { e = el('translate-backward-button');  blink(e); e.click(); }
function moveUp()       { e = el('translate-up-button');        blink(e); e.click(); }
function moveDown()     { e = el('translate-down-button');      blink(e); e.click(); }
function moveLeft()     { e = el('translate-left-button');      blink(e); e.click(); }
function moveRight()    { e = el('translate-right-button');     blink(e); e.click(); }

function yawLeft()      { e = el('yaw-left-button');    blink(e); e.click(); }
function yawRight()     { e = el('yaw-right-button');   blink(e); e.click(); }
function pitchUp()      { e = el('pitch-up-button');    blink(e); e.click(); }
function pitchDown()    { e = el('pitch-down-button');  blink(e); e.click(); }
function rollLeft()     { e = el('roll-left-button');   blink(e); e.click(); }
function rollRight()    { e = el('roll-right-button');  blink(e); e.click(); }

// Artificial Intelligence

var a = 0.1;
var dt = 0.100;

var cnt = 0;
var hist = {
    yaw:    [0, 0, 0],
    roll:   [0, 0, 0],
    pitch:  [0, 0, 0],
    y:      [0, 0, 0],
    z:      [0, 0, 0],
    r:      [0, 0, 0]
};

function AI(dt, x, v, a, finc, fdec) {
    T = dt*Math.abs(v/a);
    var target = x + v*T - 0.5*Math.sign(v)*a*T*T;
    setTimeout(target < 0.0 ? finc : target > 0.0 ? fdec : ()=>{}, 0.8*Math.random()*dt*1000);
}

function v(x) {
    var i = cnt - 3; if (i < 0) i += 3; var p0 = hist[x][i];
    var i = cnt - 1; if (i < 0) i += 3; var p2 = hist[x][i];

    return (p2 - p0)/(2*dt);
}

// Decision tree

function update() {
    okYaw   = Math.abs(getYaw(0)) < 2.0;
    okRoll  = Math.abs(getRoll(0)) < 2.0;
    okPitch = Math.abs(getPitch(0)) < 2.0;

    hist['yaw'][cnt]    = getYaw(0);
    hist['roll'][cnt]   = getRoll(0);
    hist['pitch'][cnt]  = getPitch(0);
    hist['y'][cnt]      = getRangeY(0);
    hist['z'][cnt]      = getRangeZ(0);
    hist['r'][cnt]      = getRange() - 2.0;

    if (++cnt > 2) cnt = 0;

    if (okYaw && okRoll && okPitch) {
        AI(dt, getRangeY(), v('y'), a, moveRight,   moveLeft);
        AI(dt, getRangeZ(), v('z'), a, moveUp,      moveDown);

        if (Math.abs(getRangeY() < 10.0) && Math.abs(getRangeZ() < 10.0)) {
            if (getRange() > 2.0) {
                AI(dt, getRange() - 2.0, v('r'), 0.5*a, moveBackward, moveForward);
            } else {
                if (getRate() < -0.15) {
                    moveBackward();
                } else if (getRate() > -0.05) {
                    moveForward();
                }
            }
        }
    }

    if (okYaw && okRoll && okPitch) {
        AI(dt, getYaw(0),   -getYaw(1),   0.2*a, yawLeft,  yawRight);
        AI(dt, getRoll(0),  -getRoll(1),  0.2*a, rollLeft, rollRight);
        AI(dt, getPitch(0), -getPitch(1), 0.2*a, pitchUp,  pitchDown);
    } else {
        AI(dt, getYaw(0),   v('yaw'),   a, yawLeft,  yawRight);
        AI(dt, getRoll(0),  v('roll'),  a, rollLeft, rollRight);
        AI(dt, getPitch(0), v('pitch'), a, pitchUp,  pitchDown);
    }

    setTimeout(update, dt*1000);
}

update();