entity.js

import _ from 'lodash';


export default class Entity {
  constructor() {
    // Each entity had a unique ID.
    this.uid = _.uniqueId();

    // Each entity has a number of components.
    this.c = {};
    Object.seal(this.c);

    // World this entity has been added to.
    this.world = null;
  }

  // Attach a component to the entity.
  attach(component) {
    // Check component's dependencies are met.
    _.each(component.$deps, dependencyID => {
      if (!this.has(dependencyID)) {
        console.error(`${dependencyID} component missing.`);
        throw new Error('ComponentDependencyMissing');
      }
    });


    // Check component is not already attached.
    if (this.has(component.$id)) {
      throw new Error('ComponentAlreadyAttached');
    }

    // Attach component.
    const newC = {...this.c};
    newC[component.$id] = component;
    Object.seal(newC);
    this.c = newC;

    // If the entity has already been added to a world, rebuild it.
    if (this.world) {
      this.world.rebuild(this, component.$id);
    }

    return this;
  }

  // Remove a component from the entity.
  detach(componentId) {
    // Check that the component was not a dependency.
    _.each(this.c, component => {
      const dependencyExists = _.some(component.$deps, dep => dep === componentId);
      if (dependencyExists) {
        console.error(`${component.$id} depends on ${componentId}`);
        throw new Error('ComponentDependencyMissing');
      }
    });

    // Detach the component.
    const newC = {...this.c};
    delete newC[componentId];
    Object.seal(newC);
    this.c = newC;

    if (this.world) {
      this.world.rebuild(this);
    }

    return this;
  }

  has(componentId) {
    return _.has(this.c, componentId);
  }
}