silphius/app/ecs/entity-factory.js

class Node {
  children = {};
  class;
}

export default class EntityFactory {

  $$tries = new Node();

  makeClass(componentNames, Components) {
    const sorted = componentNames.toSorted();
    let walk = this.$$tries;
    let i = 0;
    while (i < sorted.length) {
      if (!walk.children[sorted[i]]) {
        walk.children[sorted[i]] = new Node();
      }
      walk = walk.children[sorted[i]];
      i += 1;
    }
    if (!walk.class) {
      class Entity {
        static componentNames = sorted;
        constructor(id) {
          this.id = id;
        }
        size() {
          let size = 0;
          for (const componentName of this.constructor.componentNames) {
            const instance = Components[componentName];
            size += 2 + 4 + instance.constructor.schema.sizeOf(instance.get(this.id));
          }
          // ID + # of components.
          return size + 4 + 2;
        }
      }
      const properties = {};
      for (const type of sorted) {
        properties[type] = {};
        const get = Components[type].get.bind(Components[type]);
        properties[type].get = function() {
          return get(this.id);
        };
      }
      Object.defineProperties(Entity.prototype, properties);
      Entity.prototype.toJSON = new Function('', `
        return {
          ${sorted.map((type) => `${type}: this.${type}.toJSON()`).join(', ')}
        };
      `);
      Entity.prototype.toNet = new Function('', `
        return {
          ${sorted.map((type) => `${type}: this.${type}.toNet()`).join(', ')}
        };
      `);
      walk.class = Entity;
    }
    return walk.class;
  }
}