package it.cavallium.strangedb.functionalinterfaces;

import java.io.IOException;
import java.util.Objects;

/**
 * Represents a function that accepts one argument and produces a result.
 *
 * <p>This is a <a href="package-summary.html">functional interface</a>
 * whose functional method is {@link #apply(Object)}.
 *
 * @param <T> the type of the input to the function
 * @param <R> the type of the result of the function
 *
 * @since 1.8
 */
@FunctionalInterface
public interface FunctionWithIO<T, R> {

	/**
	 * Applies this function to the given argument.
	 *
	 * @param t the function argument
	 * @return the function result
	 */
	R apply(T t) throws IOException;

	/**
	 * Returns a composed function that first applies the {@code before}
	 * function to its input, and then applies this function to the result.
	 * If evaluation of either function throws an exception, it is relayed to
	 * the caller of the composed function.
	 *
	 * @param <V> the type of input to the {@code before} function, and to the
	 *           composed function
	 * @param before the function to apply before this function is applied
	 * @return a composed function that first applies the {@code before}
	 * function and then applies this function
	 * @throws NullPointerException if before is null
	 *
	 * @see #andThen(FunctionWithIO)
	 */
	default <V> FunctionWithIO<V, R> compose(FunctionWithIO<? super V, ? extends T> before) {
		Objects.requireNonNull(before);
		return (V v) -> apply(before.apply(v));
	}

	/**
	 * Returns a composed function that first applies this function to
	 * its input, and then applies the {@code after} function to the result.
	 * If evaluation of either function throws an exception, it is relayed to
	 * the caller of the composed function.
	 *
	 * @param <V> the type of output of the {@code after} function, and of the
	 *           composed function
	 * @param after the function to apply after this function is applied
	 * @return a composed function that first applies this function and then
	 * applies the {@code after} function
	 * @throws NullPointerException if after is null
	 *
	 * @see #compose(FunctionWithIO)
	 */
	default <V> FunctionWithIO<T, V> andThen(FunctionWithIO<? super R, ? extends V> after) {
		Objects.requireNonNull(after);
		return (T t) -> after.apply(apply(t));
	}

	/**
	 * Returns a function that always returns its input argument.
	 *
	 * @param <T> the type of the input and output objects to the function
	 * @return a function that always returns its input argument
	 */
	static <T> FunctionWithIO<T, T> identity() {
		return t -> t;
	}
}