/* Copyright rememberjava.com. Licensed under GPL 3. See http://rememberjava.com/license */
package com.rememberjava.lambda;

import static org.junit.Assert.assertEquals;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collector;
import java.util.stream.Collectors;

import org.junit.Test;

public class IdentityCollectorsTest {

  /**
   * Returns a specialised {@link Collector} which results in a {@link Map}
   * where the keys are the elements of the stream, and the values is provided
   * by the given mapping function.
   * 
   * @param <T> the type of the input elements, and keys of the Map
   * @param <U> the output type of the value mapping function
   * 
   * @param valueMapper a mapping function to produce values
   * @return a {@code Collector} which collects elements into a {@code Map}
   *         whose keys are as given by the stream, and values are the result of
   *         applying the given mapping function to the input elements.
   */
  public static <T, U> Collector<T, ?, Map<T, U>> identityToValue(
      Function<? super T, ? extends U> valueMapper) {
    return Collectors.toMap(Function.identity(), valueMapper);
  }
  
  /**
   * Returns a {@link Map} based on the given {@link Collection}. The keys are
   * the elements of the Collection, and the values is provided by the given
   * mapping function.
   * 
   * @param <T> the type of the input elements, and keys of the Map
   * @param <U> the output type of the value mapping function
   * 
   * @param c Collection of elements to map
   * @param valueMapper a mapping function to produce values
   * @return a {@code Map} whose keys are as given by the Collection, and values
   *         are the result of applying the given mapping function to the input
   *         elements.
   */
  public static <T, U> Map<T, U> identityToValue(
      Collection<T> c, Function<? super T, ? extends U> valueMapper) {
      return c.stream().collect(identityToValue(valueMapper));
  }

  /**
   * Returns a specialised {@link Collector} which results in a {@link Map}
   * where the keys are provided by the given mapping function, and the values
   * are the elements of the stream. 
   * 
   * @param <T> the type of the input elements, and values of the Map
   * @param <K> the output type of the key mapping function
   * 
   * @param keyMapper a mapping function to produce keys
   * @return a {@code Collector} which collects elements into a {@code Map}
   *         whose keys are the result of applying the given mapping function
   *         to the input elements, and values are as given by the stream.
   */
  public static <T, K> Collector<T, ?, Map<K, T>> keytoIdentity(
      Function<? super T, ? extends K> keyMapper) {
    return Collectors.toMap(keyMapper, Function.identity());
  }

  /**
   * Returns a {@link Map} based on the given {@link Collection}. The keys are
   * provided by the given mapping function, and the values are the elements of
   * the Collection. 
   * 
   * @param <T> the type of the input elements, and values of the Map
   * @param <K> the output type of the key mapping function
   * 
   * @param c Collection of elements to map
   * @param valueMapper a mapping function to produce values
   * @return a {@code Map} whose keys are the result of applying the given
   *         mapping function to the input elements, and values are as given
   *         by the stream.
   */
  public static <T, K> Map<K, T> keytoIdentity(
      Collection<T> c, Function<? super T, ? extends K> keyMapper) {
    return c.stream().collect(keytoIdentity(keyMapper));
  }

  @Test
  public void keytoIdentityTest() {
    List<Class<?>> classes = Arrays.asList(String.class, ArrayList.class);
    
    Map<String, Class<?>> nameMap = classes.stream()
        .filter(c -> c.getName().contains("java.lang"))
        .collect(keytoIdentity(c -> c.getSimpleName()));
    assertEquals(String.class, nameMap.get("String"));

    Map<String, Class<?>> nameMap2 = keytoIdentity(classes, c -> c.getSimpleName());
    assertEquals(ArrayList.class, nameMap2.get("ArrayList"));
  }

  @Test
  public void identityToValueTest() {
    List<String> files = Arrays.asList("index.html", "about.html");

    Map<String, byte[]> fileCache = files.stream()
        .filter(f -> f.contains("index"))
        .collect(identityToValue(f -> loadFile(f)));
    assertEquals("index.html", new String(fileCache.get("index.html")));

    Map<String, byte[]> fileCache2 = identityToValue(files, this::loadFile);
    assertEquals("about.html", new String(fileCache2.get("about.html")));
  }

  public byte[] loadFile(String name) {
    // Returns a dummy value for the sake of the test. 
    return name.getBytes();
  }
}