boardgame-core/src/utils/entity.ts

import {Signal, signal} from "@preact/signals-core";

export type Entity = {
  id: string;
};

export type EntityAccessor<T extends Entity> = {
  id: string;
  value: T;
}

function createReactiveProxy<T extends Entity>(entitySignal: Signal<T>): T {
  return new Proxy({} as T, {
    get(_target, prop) {
      const current = entitySignal.value;
      const value = current[prop as keyof T];
      if (typeof value === 'function') {
        return value.bind(current);
      }
      return value;
    },
    set(_target, prop, value) {
      const current = entitySignal.value;
      entitySignal.value = { ...current, [prop]: value };
      return true;
    },
    ownKeys(_target) {
      return Reflect.ownKeys(entitySignal.value);
    },
    getOwnPropertyDescriptor(_target, prop) {
      return Reflect.getOwnPropertyDescriptor(entitySignal.value, prop);
    },
  });
}

function createReactiveAccessor<T extends Entity>(id: string, entitySignal: Signal<T>): EntityAccessor<T> {
  const proxy = createReactiveProxy(entitySignal);
  return {
    id,
    get value() {
      return proxy;
    },
    set value(value: T) {
      entitySignal.value = value;
    }
  } as EntityAccessor<T>;
}

export function createEntityCollection<T extends Entity>() {
  const collection = signal({} as Record<string, Signal<T>>);
  const remove = (...ids: string[]) => {
    collection.value = Object.fromEntries(
      Object.entries(collection.value).filter(([id]) => !ids.includes(id)),
    );
  };
  
  const add = (...entities: T[]) => {
    collection.value = {
      ...collection.value,
      ...Object.fromEntries(entities.map((entity) => [entity.id, signal(entity)])),
    };
  };
  
  const get = (id: string): EntityAccessor<T> => {
    const entitySignal = collection.value[id];
    if (!entitySignal) {
      return {
        id,
        get value() {
          return undefined as unknown as T;
        },
        set value(_value: T) {}
      } as EntityAccessor<T>;
    }
    return createReactiveAccessor(id, entitySignal);
  }
  
  return {
    collection,
    remove,
    add,
    get
  }
}