export default class Base {

  map = [];

  pool = [];

  static schema;

  allocateMany(count) {
    const results = [];
    while (count-- > 0 && this.pool.length > 0) {
      results.push(this.pool.pop());
    }
    return results;
  }

  create(entity, values) {
    this.createMany([[entity, values]]);
  }

  destroy(entity) {
    this.destroyMany([entity]);
  }

  destroyMany(entities) {
    this.freeMany(
      entities
        .map((entity) => {
          if ('undefined' !== typeof this.map[entity]) {
            return this.map[entity];
          }
          throw new Error(`can't free for non-existent entity ${entity}`);
        }),
    );
    for (let i = 0; i < entities.length; i++) {
      this.map[entities[i]] = undefined;
    }
  }

  static filterDefaults(instance) {
    const json = {};
    for (const [i, {defaultValue}] of this.schema) {
      if (i in instance && instance[i] !== defaultValue) {
        json[i] = instance[i];
      }
    }
    return json;
  }

  freeMany(indices) {
    for (let i = 0; i < indices.length; ++i) {
      this.pool.push(indices[i]);
    }
  }

  insertMany(entities) {
    const creating = [];
    for (let i = 0; i < entities.length; i++) {
      const [entity, values] = entities[i];
      if (!this.get(entity)) {
        creating.push([entity, values]);
      }
      else {
        const instance = this.get(entity);
        for (const i in values) {
          instance[i] = values[i];
        }
      }
    }
    this.createMany(creating);
  }

  // eslint-disable-next-line no-unused-vars
  markChange(entity, components) {}

  mergeDiff(original, update) {
    return {...original, ...update};
  }

  sizeOf(entity) {
    return this.constructor.schema.sizeOf(this.get(entity));
  }

  static wrap(name, ecs) {
    class WrappedComponent extends this {
      markChange(entity, key, value) {
        ecs.markChange(entity, {[name]: {[key]: value}})
      }
    }
    return new WrappedComponent();
  }

}