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function preload() {
  // Load Earth texture from a reliable CDN
  // Using the specific r147 tag for reliable access on raw.githubusercontent.com
  earthTexture = loadImage('https://raw.githubusercontent.com/mrdoob/three.js/r147/examples/textures/planets/earth_atmos_2048.jpg');

  // Load a font for WEBGL text from fontsource CDN (unpkg.com is reliable)
  webglFont = loadFont('https://unpkg.com/@fontsource/roboto@latest/files/roboto-latin-400-normal.woff');
}

function setup() {
  // Create a WEBGL canvas for 3D rendering
  createCanvas(windowWidth, windowHeight, WEBGL);

  // Set up camera controls (mouse interaction to rotate/zoom the scene)
  orbitControl();

  // No outlines for the spheres
  noStroke();

  // Set a frame rate for more consistent simulation steps
  frameRate(60);

  // Set the font for WEBGL text
  textFont(webglFont);
  textSize(16);

  // Generate star positions
  for (let i = 0; i < NUM_STARS; i++) {
    stars.push(createVector(
      random(-width * 2, width * 2), // Larger range for stars
      random(-height * 2, height * 2),
      random(-width * 2, width * 2)
    ));
  }

  // --- Initialize GUI ---
  const gui = new dat.GUI();
  gui.add(params, 'gConstant', 0.0001, 0.01).step(0.0001).name('G Constant').onChange(resetSimulation);
  gui.add(params, 'earthMass', 100, 5000).step(10).name('Earth Mass').onChange(resetSimulation);
  gui.add(params, 'satelliteMass', 0.1, 5).step(0.1).name('Satellite Mass').onChange(resetSimulation);

  const satelliteFolder = gui.addFolder('Satellite Initial State');
  satelliteFolder.add(params, 'satelliteInitialX', -width, width).step(1).name('Position X').onChange(resetSimulation);
  satelliteFolder.add(params, 'satelliteInitialY', -height, height).step(1).name('Position Y').onChange(resetSimulation);
  satelliteFolder.add(params, 'satelliteInitialZ', -width, width).step(1).name('Position Z').onChange(resetSimulation);
  satelliteFolder.add(params, 'satelliteInitialVelX', -10, 10).step(0.1).name('Velocity X').onChange(resetSimulation);
  satelliteFolder.add(params, 'satelliteInitialVelY', -10, 10).step(0.1).name('Velocity Y').onChange(resetSimulation);
  satelliteFolder.add(params, 'satelliteInitialVelZ', -10, 10).step(0.1).name('Velocity Z').onChange(resetSimulation);
  satelliteFolder.add(params, 'resetSimulation').name('Reset Simulation');

  // Initial simulation setup
  resetSimulation();
}

function resetSimulation() {
  // Initialize satellite position and velocity for an initial orbit
  // For a stable circular orbit, v = sqrt(G*M/r)
  const initialDistance = EARTH_RADIUS * 3; // Start satellite 3 times Earth's radius away
  satellitePos = createVector(
    params.satelliteInitialX,
    params.satelliteInitialY,
    params.satelliteInitialZ
  );

  // Calculate initial velocity for a roughly circular orbit at this distance
  // If satellite is at origin, use default initialDistance to avoid division by zero
  const currentDistance = satellitePos.mag();
  const effectiveDistance = currentDistance === 0 ? initialDistance : currentDistance;
  const circularSpeed = sqrt(params.gConstant * params.earthMass / effectiveDistance);

  // Default velocity for circular orbit, then apply GUI overrides
  satelliteVel = createVector(0, circularSpeed, 0);

  // Apply GUI velocity overrides
  satelliteVel.x = params.satelliteInitialVelX;
  satelliteVel.y = params.satelliteInitialVelY;
  satelliteVel.z = params.satelliteInitialVelZ;

  // Clear the orbit path
  orbitPath = [];
}

function draw() {
  // --- Rendering ---
  background(0); // Black background (space)
  ambientLight(50); // General ambient light
  directionalLight(255, 255, 255, -1, 0, 0); // White light from the right side

  // --- Draw Stars ---
  push();
  fill(255);
  for (let i = 0; i < NUM_STARS; i++) {
    push();
    translate(stars[i].x, stars[i].y, stars[i].z);
    sphere(0.5); // Small sphere for each star
    pop();
  }
  pop();

  // --- Draw Earth (Central Body) ---
  push();
  texture(earthTexture); // Apply Earth texture
  sphere(EARTH_RADIUS);
  pop();

  // --- Physics Calculation ---
  // Calculate the gravitational force on the satellite
  const force = calculateGravitationalForce(satellitePos, params.satelliteMass, createVector(0, 0, 0), params.earthMass);

  // Apply the force to get acceleration (F = ma => a = F/m)
  const acceleration = p5.Vector.div(force, params.satelliteMass);

  // Update satellite's velocity
  satelliteVel.add(acceleration);

  // Update satellite's position
  satellitePos.add(satelliteVel);

  // --- Draw Detailed Satellite ---
  drawDetailedSatellite();

  // --- Draw Orbit Trail ---
  orbitPath.push(satellitePos.copy()); // Store current position
  if (orbitPath.length > ORBIT_TRAIL_LENGTH) {
    orbitPath.shift(); // Remove oldest position if path is too long
  }

  // Draw the path as a line
  push();
  stroke(255, 150, 0, 200); // Orange for orbit path, slightly transparent
  noFill();
  beginShape();
  for (let i = 0; i < orbitPath.length; i++) {
    vertex(orbitPath[i].x, orbitPath[i].y, orbitPath[i].z);
  }
  endShape();
  pop();
  noStroke(); // Turn stroke off for next frame

  // --- Display Information ---
  push();
  // Move text to a fixed position on the screen
  camera(); // Reset camera transformations for text
  translate(-width / 2 + 20, -height / 2 + 20, 0); // Top-left corner

  fill(255); // White text
  textAlign(LEFT, TOP);
  let distanceToEarth = satellitePos.mag();
  let altitude = distanceToEarth - EARTH_RADIUS; // Altitude relative to Earth's surface
  let satelliteSpeed = satelliteVel.mag();

  // Estimate orbital period (very rough for non-circular orbits)
  let orbitalPeriodEstimate = (TWO_PI * distanceToEarth) / satelliteSpeed;

  text(`Simulation Details:`, 0, 0);
  text(`G Constant: ${params.gConstant}`, 0, 20);
  text(`Earth Mass: ${params.earthMass}`, 0, 40);
  text(`Satellite Mass: ${params.satelliteMass}`, 0, 60);

  text(`\nSatellite Orbit Details:`, 0, 80);
  text(`Distance to Earth: ${distanceToEarth.toFixed(2)} units`, 0, 100);
  text(`Altitude: ${altitude.toFixed(2)} units`, 0, 120);
  text(`Satellite Speed: ${satelliteSpeed.toFixed(2)} units/frame`, 0, 140);
  if (satelliteSpeed > 0) {
    text(`Estimated Orbital Period: ${orbitalPeriodEstimate.toFixed(2)} frames`, 0, 160);
  } else {
    text(`Estimated Orbital Period: N/A`, 0, 160);
  }
  pop();
}

function calculateGravitationalForce(pos1, mass1, pos2, mass2) {
  // Vector from pos1 to pos2
  const direction = p5.Vector.sub(pos2, pos1);
  const distance = direction.mag();

  // Ensure distance is not zero to prevent division by zero
  if (distance === 0) {
    return createVector(0, 0, 0);
  }

  // Calculate magnitude of gravitational force
  const forceMagnitude = (params.gConstant * mass1 * mass2) / (distance * distance);

  // Normalize direction vector and scale by force magnitude
  direction.normalize();
  direction.mult(forceMagnitude);

  return direction;
}

function drawDetailedSatellite() {
  push();
  translate(satellitePos.x, satellitePos.y, satellitePos.z);
  specularMaterial(150, 150, 150); // Gray metallic for satellite body

  // Main body (a small box)
  box(SATELLITE_RADIUS * 0.8, SATELLITE_RADIUS * 1.5, SATELLITE_RADIUS * 0.8);

  // Solar panels
  push();
  fill(50, 50, 100); // Dark blue for solar panels
  translate(SATELLITE_RADIUS * 0.8, 0, 0);
  box(SATELLITE_RADIUS * 0.1, SATELLITE_RADIUS * 2, SATELLITE_RADIUS * 1.5);
  pop();

  push();
  fill(50, 50, 100); // Dark blue for solar panels
  translate(-SATELLITE_RADIUS * 0.8, 0, 0);
  box(SATELLITE_RADIUS * 0.1, SATELLITE_RADIUS * 2, SATELLITE_RADIUS * 1.5);
  pop();

  // Antenna
  push();
  fill(200, 150, 0); // Gold/brass color for antenna
  translate(0, SATELLITE_RADIUS * 0.75, 0);
  cylinder(SATELLITE_RADIUS * 0.1, SATELLITE_RADIUS * 0.5);
  pop();

  pop();
}

function windowResized() {
  resizeCanvas(windowWidth, windowHeight);
}