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package fj.parser;

import fj.F;
import fj.F2;
import static fj.Function.curry;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * A parse result made up of a value (A) and the remainder of the parse input (I).
 *
 * @version %build.number%
 */
public final class Result implements Iterable {
  private final I i;
  private final A a;

  private Result(final I i, final A a) {
    this.i = i;
    this.a = a;
  }

  /**
   * The remainder of the parse input.
   *
   * @return The remainder of the parse input.
   */
  public I rest() {
    return i;
  }

  /**
   * The parsed value.
   *
   * @return The parsed value.
   */
  public A value() {
    return a;
  }

  /**
   * Maps the given function across the remainder of the parse input.
   *
   * @param f The function to map with.
   * @return A result with a different parse input.
   */
  public  Result mapRest(final F f) {
    return result(f.f(i), a);
  }

  /**
   * First-class function mapping across the remainder of the parse input.
   *
   * @return A first-class function mapping across the remainder of the parse input.
   */
  public  F, Result> mapRest() {
    return f -> mapRest(f);
  }

  /**
   * Maps the given function across the parse value.
   *
   * @param f The function to map with.
   * @return A result with a different parse value.
   */
  public  Result mapValue(final F f) {
    return result(i, f.f(a));
  }

  /**
   * First-class function mapping across the parse value.
   *
   * @return A first-class function mapping across the parse value.
   */
  public  F, Result> mapValue() {
    return f -> mapValue(f);
  }

  /**
   * A bifunctor map across both the remainder of the parse input and the parse value.
   *
   * @param f The function to map the remainder of the parse input with.
   * @param g The function to map the parse value with.
   * @return A result with a different parse input and parse value.
   */
  public  Result bimap(final F f, final F g) {
    return mapRest(f).mapValue(g);
  }

  /**
   * First-class bifunctor map.
   *
   * @return A first-class bifunctor map.
   */
  public  F, F, Result>> bimap() {
    return curry((f, g) -> bimap(f, g));
  }

  /**
   * Returns an iterator over the parse value. This method exists to permit the use in a for-each loop.
   *
   * @return An iterator over the parse value.
   */
  public Iterator iterator() {
    return new Iterator() {
      private boolean r;

      public boolean hasNext() {
        return !r;
      }

      public A next() {
        if (r)
          throw new NoSuchElementException();
        else {
          r = true;
          return a;
        }
      }

      public void remove() {
        throw new UnsupportedOperationException();
      }
    };
  }

  /**
   * Construct a result with the given remainder of the parse input and parse value.
   *
   * @param i The remainder of the parse input.
   * @param a The parse value.
   * @return A result with the given remainder of the parse input and parse value.
   */
  public static  Result result(final I i, final A a) {
    return new Result(i, a);
  }

  /**
   * First-class construction of a result.
   *
   * @return A first-class function for construction of a result.
   */
  public static  F>> result() {
    return curry((i, a) -> result(i, a));
  }

}