content: /*
   *  Licensed to the Apache Software Foundation (ASF) under one
   *  or more contributor license agreements.  See the NOTICE file
   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you 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 org.apache.causeway.applib.util;
  
  import java.util.BitSet;
  import java.util.List;
  import java.util.Objects;
  import java.util.function.Function;
  import java.util.stream.Collectors;
  
  import org.apache.causeway.commons.internal.collections._Lists;
  
  /**
   * Fluent Object to String Composition.
   *
   * @param <T>
   * @since 2.0 {@index}
   *
   */
  public class ToString<T> {
  
      public static <T> ToString<T> toString(String name, Function<? super T, ?> getter) {
          Objects.requireNonNull(name);
          Objects.requireNonNull(getter);
          return new ToString<>(name, getter, false);
      }
  
      public static <T> ToString<T> toStringOmitIfAbsent(String name, Function<? super T, ?> getter) {
          Objects.requireNonNull(name);
          Objects.requireNonNull(getter);
          return new ToString<>(name, getter, true);
      }
  
      private final List<String> names = _Lists.newArrayList();
      private final List<Function<? super T, ?>> getters = _Lists.newArrayList();
      private final BitSet omitIfAbsent = new BitSet();
  
      private ToString(String name, Function<? super T, ?> getter, boolean omitIfAbsent) {
          addBit(omitIfAbsent);
          names.add(name);
          getters.add(getter);
      }
  
      public ToString<T> thenToString(String name, Function<? super T, ?> getter){
          Objects.requireNonNull(name);
          Objects.requireNonNull(getter);
          addBit(false);
          names.add(name);
          getters.add(getter);
          return this;
      }
  
      public ToString<T> thenToStringOmitIfAbsent(String name, Function<? super T, ?> getter){
          Objects.requireNonNull(name);
          Objects.requireNonNull(getter);
          addBit(true);
          names.add(name);
          getters.add(getter);
          return this;
      }
  
      public String toString(T target){
          return toString(target, value->""+value);
      }
  
      public String toString(T target, Function<Object, String> valueToStringFunction){
  
          if(valueToStringFunction==null) {
              return toString(target);
          }
  
          if(target==null) {
              return "null";
          }
  
          Objects.requireNonNull(valueToStringFunction);
  
          final int[] index = {-1}; // value reference
  
          return String.format("%s{%s}",
  
                  target.getClass().getSimpleName(),
  
                  getters.stream()
                  .peek(__->index[0]++)
                  .map(getter->getter.apply(target))
                  .filter(value->value!=null || !omitIfAbsent.get(index[0]))
                  .map(valueToStringFunction)
                  .map(valueLiteral->names.get(index[0])+"="+valueLiteral)
                  .collect(Collectors.joining(", "))
  
                  );
      }
  
      // -- HELPER
  
      private void addBit(boolean bit) {
          final int index = names.size();
          if(bit) {
              omitIfAbsent.set(index);
          } else {
              omitIfAbsent.clear(index);
          }
      }
  
  }
  