com.github.dakusui.crest.core.ChainedFunction Maven / Gradle / Ivy

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package com.github.dakusui.crest.core;

import java.util.function.Function;

import static java.util.Objects.requireNonNull;

public interface ChainedFunction extends Function {
  @Override
   ChainedFunction andThen(Function after);

  ChainedFunction previous();

  Function chained();

  static  ChainedFunction chain(ChainedFunction function, Function next) {
    return new Impl(function, next);
  }

  /**
   * Creates a {@code ChainedFunction} from a given function {@code func}.
   * Returned function does not have one previous to it. In other words, it will
   * be a 'head' of a chain.
   *
   * @param func A function from which a returned function is created.
   * @param  Input
   * @param  Output
   *
   * @return created {@code ChainedFunction}
   */
  static  ChainedFunction create(Function func) {
    return new ChainedFunction() {
      @Override
      public  ChainedFunction andThen(Function after) {
        return chain(this, after);
      }

      @Override
      public ChainedFunction previous() {
        return null;
      }

      @SuppressWarnings("unchecked")
      @Override
      public Function chained() {
        return (Function) func;
      }

      @Override
      public R apply(T t) {
        return chained().apply(t);
      }

      @Override
      public String toString() {
        return chained().toString();
      }
    };
  }

  class Impl implements ChainedFunction {

    private final Function        func;
    private final ChainedFunction previous;

    Impl(ChainedFunction previous, Function func) {
      this.previous = previous;
      this.func = requireNonNull(func);
    }

    @SuppressWarnings("unchecked")
    @Override
    public R apply(T t) {
      return this.chained().apply(this.previous().apply(t));
    }

    @Override
    public  ChainedFunction andThen(Function after) {
      return ChainedFunction.chain(this, after);
    }

    @SuppressWarnings("unchecked")
    @Override
    public ChainedFunction previous() {
      return (ChainedFunction) previous;
    }

    @SuppressWarnings("unchecked")
    @Override
    public Function chained() {
      return (Function) func;
    }

    @Override
    public String toString() {
      return previous().toString() + chained().toString();
    }
  }
}