import { take as takeToolkit } from '../../array/take.ts';
import { combineEagerAndLazyFunctions, createLazyFunction } from '../_internal/lazy.ts';

/**
 * Creates a function that returns the first `count` elements of an array. If
 * `count` is greater than the array length, the whole array is returned. Use it
 * with {@link pipe}.
 *
 * The returned function is **lazy-capable** for a non-negative integer `count`:
 * inside a {@link pipe} it stops the walk as soon as `count` elements have been
 * collected, so preceding lazy functions never process the rest of the input.
 *
 * @template T - The type of elements in the array.
 * @param count - The number of elements to take from the front of the array.
 * @returns A function that maps a `readonly T[]` to a new `T[]`.
 *
 * @example
 * import { pipe, take } from 'es-toolkit/fp';
 *
 * pipe([1, 2, 3, 4, 5], take(3)); // => [1, 2, 3]
 *
 * @example
 * // Early termination: `map` only runs three times.
 * pipe([1, 2, 3, 4, 5], map(expensive), take(3));
 */
export function take<T>(count: number): (array: readonly T[]) => T[] {
  function takeEager(array: readonly T[]): T[] {
    return takeToolkit(array, count);
  }

  // The lazy fast-path can only represent "the first `count` elements" for a
  // non-negative integer. For other values es-toolkit's `take` defers to
  // `Array.prototype.slice(0, count)` (which, for negatives, drops from the
  // end) — that cannot be streamed forward, so we keep the eager path.
  if (!Number.isInteger(count) || count < 0) {
    return takeEager;
  }

  const takeLazy = createLazyFunction<T, T>((value, index, emit) => {
    if (index >= count) {
      return false;
    }
    emit(value);
    return index < count - 1;
  });

  return combineEagerAndLazyFunctions(takeEager, takeLazy, { shortCircuit: true });
}
