import { MassObject } from './object.js';
import { 
  MASS_CREATION_RATE, 
  DISPLAY_OBJECTS_INFO,
  MOTION_TIME_SCALE,
} from './config.js';

export class Objects {
  objects = [];
  creatingObject = undefined;
  selectedObject = undefined;

  constructor(sim) {
    this.sim = sim;
  }

  // Create an object with mass that grows as pointer is held down
  createObject(x, y) {
    const idx = this.objects.length;
    const obj = new MassObject(x, y, idx);
    this.creatingObject = idx;
    this.objects.push(obj);
  }

  doneCreatingObject() {
    this.creatingObject = undefined;
  }

  object(i) {
    return this.objects[i];
  }

  selectObject(i) {
    this.selectedObject = i;
  }

  deselect() {
    this.selectedObject = undefined;
  }

  getSelectedOrCreating() {
    let i = this.creatingObject ?? this.selectedObject;
    if (i !== undefined) {
      return this.objects[i];
    }
  }

  get length() {
    return this.objects.length;
  }

  objectAtLocation(x, y) {
    for (let i = 0; i < this.objects.length; i++) {
      const obj = this.objects[i];
      // If distance to object is less than object's radius, we are touching the object
      const dist = Math.pow((obj.position.x - x)**2 + (obj.position.y - y)**2, 1/2);
      if (dist <= obj.radius) {
        return i;
      }
    }
  }


  handlePointerDown({x, y}) {
    // If pointer is touching an object, select the object
    const touchingObject = this.objectAtLocation(x, y);
   
    if (touchingObject !== undefined) {
      this.selectObject(touchingObject);
    } else {
      // Otherwise, create a new object
      this.createObject(x, y);
    }
  }

  handlePointerUp({x, y}) {
    this.doneCreatingObject();
    this.deselect();
  }

  computeFrame(elapsedTime) {
    // If we're creating an object, increment its mass
    // with the mass creation rate accelerating over time
    if (this.creatingObject !== undefined) {
      const obj = this.objects[this.creatingObject];
      const rate = MASS_CREATION_RATE * obj.age;
      obj.mass += rate * elapsedTime;
    }

    if (this.sim.playing) {
      // Update positions. Simple Euler method for now.
      for (let i = 0; i < this.objects.length; i++) {
        const obj = this.objects[i];
        obj.position.x += obj.velocity.x * MOTION_TIME_SCALE;
        obj.position.y += obj.velocity.y * MOTION_TIME_SCALE;
      }
    }

    // Display objects info
    if (DISPLAY_OBJECTS_INFO) {
      for (let i = 0; i < this.objects.length; i++) {
        const obj = this.objects[i];
        const speed = Math.pow(obj.velocity.x ** 2 + obj.velocity.y ** 2, 1/2);
        // Invert y so that the angle is counterclockwise from x-axis
        const direction = Math.atan2(-obj.velocity.y, obj.velocity.x) * 180 / Math.PI;
        this.sim.info[`Object ${i}`] = [
          `${obj.position.x}, `, 
          `${obj.position.y}, `, 
          `${obj.mass.toPrecision(6)} kg, `,
          `${speed.toPrecision(2)} m/s, ${direction.toPrecision(2)}°`, 
        ];
      }
    }
  }
}