import { IterableX } from './iterablex.js';

class GenerateIterable<TState, TResult> extends IterableX<TResult> {
  private _initialState: TState;
  private _condition: (value: TState) => boolean;
  private _iterate: (value: TState) => TState;
  private _resultSelector: (value: TState) => TResult;

  constructor(
    initialState: TState,
    condition: (value: TState) => boolean,
    iterate: (value: TState) => TState,
    resultSelector: (value: TState) => TResult
  ) {
    super();
    this._initialState = initialState;
    this._condition = condition;
    this._iterate = iterate;
    this._resultSelector = resultSelector;
  }

  *[Symbol.iterator]() {
    for (let i = this._initialState; this._condition(i); i = this._iterate(i)) {
      yield this._resultSelector(i);
    }
  }
}

/**
 * Generates an iterable sequence by running a state-driven loop producing the sequence's elements.
 *
 * @template TState The type of the state used in the generator loop.
 * @template TResult The type of the elements in the produced sequence.
 * @param {TState} initialState The initial state.
 * @param {((value: TState) => boolean)} condition Condition to terminate generation (upon returning false).
 * @param {((value: TState) => TState)} iterate Iteration step function.
 * @param {((value: TState) => TResult)} resultSelector Selector function for results produced in
 * the sequence.
 * @returns {IterableX<TResult>} The generated iterable sequence.
 */
export function generate<TState, TResult>(
  initialState: TState,
  condition: (value: TState) => boolean,
  iterate: (value: TState) => TState,
  resultSelector: (value: TState) => TResult
): IterableX<TResult> {
  return new GenerateIterable<TState, TResult>(initialState, condition, iterate, resultSelector);
}