/**
    * Copyright 2014 Netflix, Inc.
    * 
    * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
    * compliance with the License. You may obtain a copy of the License at
    * 
    * http://www.apache.org/licenses/LICENSE-2.0
    * 
    * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  package rx.internal.util;
  
  import rx.functions.Func0;
  import rx.functions.Func1;
  import rx.functions.Func2;
  import rx.functions.Func3;
  import rx.functions.Func4;
  import rx.functions.Func5;
  import rx.functions.Func6;
  import rx.functions.Func7;
  import rx.functions.Func8;
  import rx.functions.Func9;
  import rx.functions.FuncN;
  
  /**
   * Utility functions for internal use that we don't want part of the public API. 
   */
  public final class UtilityFunctions {
  
      /**
       * Returns a function that always returns {@code true}.
       *
       * @return a {@link Func1} that accepts an Object and returns the Boolean {@code true}
       */
      public static <T> Func1<? super T, Boolean> alwaysTrue() {
          return AlwaysTrue.INSTANCE;
      }
  
      /**
       * Returns a function that always returns {@code false}.
       *
       * @return a {@link Func1} that accepts an Object and returns the Boolean {@code false}
       */
      public static <T> Func1<? super T, Boolean> alwaysFalse() {
          return AlwaysFalse.INSTANCE;
      }
  
      /**
       * Returns a function that always returns the Object it is passed.
       *
       * @return a {@link Func1} that accepts an Object and returns the same Object
       */
      public static <T> Func1<T, T> identity() {
          return new Func1<T, T>() {
              @Override
              public T call(T o) {
                  return o;
              }
          };
      }
  
      private enum AlwaysTrue implements Func1<Object, Boolean> {
          INSTANCE;
  
          @Override
          public Boolean call(Object o) {
              return true;
          }
      }
  
      private enum AlwaysFalse implements Func1<Object, Boolean> {
          INSTANCE;
  
          @Override
          public Boolean call(Object o) {
              return false;
          }
      }
  
      /**
       * Returns a function that merely returns {@code null}, without side effects.
       *
       * @return a function that returns {@code null}
       */
      @SuppressWarnings("unchecked")
      public static <T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, R> NullFunction<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, R> returnNull() {
          return NULL_FUNCTION;
      }
  
      @SuppressWarnings("rawtypes")
      private static final NullFunction NULL_FUNCTION = new NullFunction();
  
      private static final class NullFunction<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, R> implements
              Func0<R>,
              Func1<T0, R>,
              Func2<T0, T1, R>,
              Func3<T0, T1, T2, R>,
             Func4<T0, T1, T2, T3, R>,
             Func5<T0, T1, T2, T3, T4, R>,
             Func6<T0, T1, T2, T3, T4, T5, R>,
             Func7<T0, T1, T2, T3, T4, T5, T6, R>,
             Func8<T0, T1, T2, T3, T4, T5, T6, T7, R>,
             Func9<T0, T1, T2, T3, T4, T5, T6, T7, T8, R>,
             FuncN<R> {
         @Override
         public R call() {
             return null;
         }
 
         @Override
         public R call(T0 t1) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2, T2 t3) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2, T2 t3, T3 t4) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2, T2 t3, T3 t4, T4 t5) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2, T2 t3, T3 t4, T4 t5, T5 t6) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2, T2 t3, T3 t4, T4 t5, T5 t6, T6 t7) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2, T2 t3, T3 t4, T4 t5, T5 t6, T6 t7, T7 t8) {
             return null;
         }
 
         @Override
         public R call(T0 t1, T1 t2, T2 t3, T3 t4, T4 t5, T5 t6, T6 t7, T7 t8, T8 t9) {
             return null;
         }
 
         @Override
         public R call(Object... args) {
             return null;
         }
     }
     
 }