ecsjs/src/types.ts

An entity component system library for JavaScript

export const ComponentMapKey = "ComponentMap"
export const ComponentClassesMapKey = "ComponentClassesMap"

export type KeyCollection<T> = { [key: string]: T }

export interface Component { }

/**
 * @category Types
 * @example
 * 
 * class PositionComponent {
 *  constructor(x, y) {
 *    this.x = x;
 *    this.y = y;
 *  }
 * }
 */
export type ComponentClass<ComponentInstance> = new (...args: any[]) => ComponentInstance

/**
* Used for infering generic type spread for classes
*/
export type ComponentClasses<TClasses extends Component[]> =
  { [Index in keyof TClasses]: TClasses[Index] }

/**
 * Used for infering generic type spread for class instances
 */
export type ComponentInstances<TClasses extends ComponentClass<any>[]> =
  // return a single variadic item when only 1 item is specified
  TClasses['length'] extends 1 ? TClasses[0] extends ComponentClass<infer R> ? R : never
  // otherwise return an array of variadic types
  : {
    [Index in keyof TClasses]: TClasses[Index] extends ComponentClass<infer R> ? R : never
  }

export type IteratorResult<T> = {
  done: boolean,
  value: T
}

export type Iterator<T> = {
  next: () => IteratorResult<T>
  reset: () => void
  [Symbol.iterator]: () => Iterator<T>
}

/**
 * allow late bound assignment type for intellisense
 * @category Types
 * @example
 * 
 * let someIterator: IComponentIterator<[Player, Position]>
 * 
 * // assignment made somewhere else in the code
 * const [player, position] = someIterator(Player, Position) ?? []
 * position?.x = 123 // position will have intellisense
 */
export type IComponentIterator<T extends Component[]>
  = Iterator<ComponentClasses<[number, ...T]>>