/*
    * Copyright (C) 2008 The Guava Authors
    *
    * 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 com.google.common.base;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.Beta;
  import com.google.common.annotations.GwtCompatible;
  
  import java.io.IOException;
  import java.util.AbstractList;
  import java.util.Arrays;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Map.Entry;
  
  import javax.annotation.CheckReturnValue;
  import javax.annotation.Nullable;
  
  /**
   * An object which joins pieces of text (specified as an array, {@link Iterable}, varargs or even a
   * {@link Map}) with a separator. It either appends the results to an {@link Appendable} or returns
   * them as a {@link String}. Example: <pre>   {@code
   *
   *   Joiner joiner = Joiner.on("; ").skipNulls();
   *    . . .
   *   return joiner.join("Harry", null, "Ron", "Hermione");}</pre>
   *
   * <p>This returns the string {@code "Harry; Ron; Hermione"}. Note that all input elements are
   * converted to strings using {@link Object#toString()} before being appended.
   *
   * <p>If neither {@link #skipNulls()} nor {@link #useForNull(String)} is specified, the joining
   * methods will throw {@link NullPointerException} if any given element is null.
   *
   * <p><b>Warning: joiner instances are always immutable</b>; a configuration method such as {@code
   * useForNull} has no effect on the instance it is invoked on! You must store and use the new joiner
   * instance returned by the method. This makes joiners thread-safe, and safe to store as {@code
   * static final} constants. <pre>   {@code
   *
   *   // Bad! Do not do this!
   *   Joiner joiner = Joiner.on(',');
   *   joiner.skipNulls(); // does nothing!
   *   return joiner.join("wrong", null, "wrong");}</pre>
   *   
   * <p>See the Guava User Guide article on <a href=
   * "http://code.google.com/p/guava-libraries/wiki/StringsExplained#Joiner">{@code Joiner}</a>. 
   *
   * @author Kevin Bourrillion
   * @since 2.0 (imported from Google Collections Library)
   */
  @GwtCompatible
  public class Joiner {
    /**
     * Returns a joiner which automatically places {@code separator} between consecutive elements.
     */
    public static Joiner on(String separator) {
      return new Joiner(separator);
    }
  
    /**
     * Returns a joiner which automatically places {@code separator} between consecutive elements.
     */
    public static Joiner on(char separator) {
      return new Joiner(String.valueOf(separator));
    }
  
    private final String separator;
  
    private Joiner(String separator) {
      this.separator = checkNotNull(separator);
    }
  
    private Joiner(Joiner prototype) {
      this.separator = prototype.separator;
    }
  
    /**
     * Appends the string representation of each of {@code parts}, using the previously configured
     * separator between each, to {@code appendable}.
     */
    public <A extends Appendable> A appendTo(A appendable, Iterable<?> parts) throws IOException {
      return appendTo(appendable, parts.iterator());
    }
  
    /**
    * Appends the string representation of each of {@code parts}, using the previously configured
    * separator between each, to {@code appendable}.
    *
    * @since 11.0
    */
   public <A extends Appendable> A appendTo(A appendable, Iterator<?> parts) throws IOException {
     checkNotNull(appendable);
     if (parts.hasNext()) {
       appendable.append(toString(parts.next()));
       while (parts.hasNext()) {
         appendable.append(separator);
         appendable.append(toString(parts.next()));
       }
     }
     return appendable;
   }
 
   /**
    * Appends the string representation of each of {@code parts}, using the previously configured
    * separator between each, to {@code appendable}.
    */
   public final <A extends Appendable> A appendTo(A appendable, Object[] parts) throws IOException {
     return appendTo(appendable, Arrays.asList(parts));
   }
 
   /**
    * Appends to {@code appendable} the string representation of each of the remaining arguments.
    */
   public final <A extends Appendable> A appendTo(
       A appendable, @Nullable Object first, @Nullable Object second, Object... rest)
           throws IOException {
     return appendTo(appendable, iterable(first, second, rest));
   }
 
   /**
    * Appends the string representation of each of {@code parts}, using the previously configured
    * separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
    * Iterable)}, except that it does not throw {@link IOException}.
    */
   public final StringBuilder appendTo(StringBuilder builder, Iterable<?> parts) {
     return appendTo(builder, parts.iterator());
   }
 
   /**
    * Appends the string representation of each of {@code parts}, using the previously configured
    * separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
    * Iterable)}, except that it does not throw {@link IOException}.
    *
    * @since 11.0
    */
   public final StringBuilder appendTo(StringBuilder builder, Iterator<?> parts) {
     try {
       appendTo((Appendable) builder, parts);
     } catch (IOException impossible) {
       throw new AssertionError(impossible);
     }
     return builder;
   }
 
   /**
    * Appends the string representation of each of {@code parts}, using the previously configured
    * separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
    * Iterable)}, except that it does not throw {@link IOException}.
    */
   public final StringBuilder appendTo(StringBuilder builder, Object[] parts) {
     return appendTo(builder, Arrays.asList(parts));
   }
 
   /**
    * Appends to {@code builder} the string representation of each of the remaining arguments.
    * Identical to {@link #appendTo(Appendable, Object, Object, Object...)}, except that it does not
    * throw {@link IOException}.
    */
   public final StringBuilder appendTo(
       StringBuilder builder, @Nullable Object first, @Nullable Object second, Object... rest) {
     return appendTo(builder, iterable(first, second, rest));
   }
 
   /**
    * Returns a string containing the string representation of each of {@code parts}, using the
    * previously configured separator between each.
    */
   public final String join(Iterable<?> parts) {
     return join(parts.iterator());
   }
 
   /**
    * Returns a string containing the string representation of each of {@code parts}, using the
    * previously configured separator between each.
    *
    * @since 11.0
    */
   public final String join(Iterator<?> parts) {
     return appendTo(new StringBuilder(), parts).toString();
   }
 
   /**
    * Returns a string containing the string representation of each of {@code parts}, using the
    * previously configured separator between each.
    */
   public final String join(Object[] parts) {
     return join(Arrays.asList(parts));
   }
 
   /**
    * Returns a string containing the string representation of each argument, using the previously
    * configured separator between each.
    */
   public final String join(@Nullable Object first, @Nullable Object second, Object... rest) {
     return join(iterable(first, second, rest));
   }
 
   /**
    * Returns a joiner with the same behavior as this one, except automatically substituting {@code
    * nullText} for any provided null elements.
    */
   @CheckReturnValue
   public Joiner useForNull(final String nullText) {
     checkNotNull(nullText);
     return new Joiner(this) {
       @Override CharSequence toString(@Nullable Object part) {
         return (part == null) ? nullText : Joiner.this.toString(part);
       }
 
       @Override public Joiner useForNull(String nullText) {
         throw new UnsupportedOperationException("already specified useForNull");
       }
 
       @Override public Joiner skipNulls() {
         throw new UnsupportedOperationException("already specified useForNull");
       }
     };
   }
 
   /**
    * Returns a joiner with the same behavior as this joiner, except automatically skipping over any
    * provided null elements.
    */
   @CheckReturnValue
   public Joiner skipNulls() {
     return new Joiner(this) {
       @Override public <A extends Appendable> A appendTo(A appendable, Iterator<?> parts)
           throws IOException {
         checkNotNull(appendable, "appendable");
         checkNotNull(parts, "parts");
         while (parts.hasNext()) {
           Object part = parts.next();
           if (part != null) {
             appendable.append(Joiner.this.toString(part));
             break;
           }
         }
         while (parts.hasNext()) {
           Object part = parts.next();
           if (part != null) {
             appendable.append(separator);
             appendable.append(Joiner.this.toString(part));
           }
         }
         return appendable;
       }
 
       @Override public Joiner useForNull(String nullText) {
         throw new UnsupportedOperationException("already specified skipNulls");
       }
 
       @Override public MapJoiner withKeyValueSeparator(String kvs) {
         throw new UnsupportedOperationException("can't use .skipNulls() with maps");
       }
     };
   }
 
   /**
    * Returns a {@code MapJoiner} using the given key-value separator, and the same configuration as
    * this {@code Joiner} otherwise.
    */
   @CheckReturnValue
   public MapJoiner withKeyValueSeparator(String keyValueSeparator) {
     return new MapJoiner(this, keyValueSeparator);
   }
 
   /**
    * An object that joins map entries in the same manner as {@code Joiner} joins iterables and
    * arrays. Like {@code Joiner}, it is thread-safe and immutable.
    *
    * <p>In addition to operating on {@code Map} instances, {@code MapJoiner} can operate on {@code
    * Multimap} entries in two distinct modes:
    *
    * <ul>
    * <li>To output a separate entry for each key-value pair, pass {@code multimap.entries()} to a
    *     {@code MapJoiner} method that accepts entries as input, and receive output of the form
    *     {@code key1=A&key1=B&key2=C}.
    * <li>To output a single entry for each key, pass {@code multimap.asMap()} to a {@code MapJoiner}
    *     method that accepts a map as input, and receive output of the form {@code
    *     key1=[A, B]&key2=C}.
    * </ul>
    *
    * @since 2.0 (imported from Google Collections Library)
    */
   public static final class MapJoiner {
     private final Joiner joiner;
     private final String keyValueSeparator;
 
     private MapJoiner(Joiner joiner, String keyValueSeparator) {
       this.joiner = joiner; // only "this" is ever passed, so don't checkNotNull
       this.keyValueSeparator = checkNotNull(keyValueSeparator);
     }
 
     /**
      * Appends the string representation of each entry of {@code map}, using the previously
      * configured separator and key-value separator, to {@code appendable}.
      */
     public <A extends Appendable> A appendTo(A appendable, Map<?, ?> map) throws IOException {
       return appendTo(appendable, map.entrySet());
     }
 
     /**
      * Appends the string representation of each entry of {@code map}, using the previously
      * configured separator and key-value separator, to {@code builder}. Identical to {@link
      * #appendTo(Appendable, Map)}, except that it does not throw {@link IOException}.
      */
     public StringBuilder appendTo(StringBuilder builder, Map<?, ?> map) {
       return appendTo(builder, map.entrySet());
     }
 
     /**
      * Returns a string containing the string representation of each entry of {@code map}, using the
      * previously configured separator and key-value separator.
      */
     public String join(Map<?, ?> map) {
       return join(map.entrySet());
     }
 
     /**
      * Appends the string representation of each entry in {@code entries}, using the previously
      * configured separator and key-value separator, to {@code appendable}.
      *
      * @since 10.0
      */
     @Beta
     public <A extends Appendable> A appendTo(A appendable, Iterable<? extends Entry<?, ?>> entries)
         throws IOException {
       return appendTo(appendable, entries.iterator());
     }
 
     /**
      * Appends the string representation of each entry in {@code entries}, using the previously
      * configured separator and key-value separator, to {@code appendable}.
      *
      * @since 11.0
      */
     @Beta
     public <A extends Appendable> A appendTo(A appendable, Iterator<? extends Entry<?, ?>> parts)
         throws IOException {
       checkNotNull(appendable);
       if (parts.hasNext()) {
         Entry<?, ?> entry = parts.next();
         appendable.append(joiner.toString(entry.getKey()));
         appendable.append(keyValueSeparator);
         appendable.append(joiner.toString(entry.getValue()));
         while (parts.hasNext()) {
           appendable.append(joiner.separator);
           Entry<?, ?> e = parts.next();
           appendable.append(joiner.toString(e.getKey()));
           appendable.append(keyValueSeparator);
           appendable.append(joiner.toString(e.getValue()));
         }
       }
       return appendable;
     }
 
     /**
      * Appends the string representation of each entry in {@code entries}, using the previously
      * configured separator and key-value separator, to {@code builder}. Identical to {@link
      * #appendTo(Appendable, Iterable)}, except that it does not throw {@link IOException}.
      *
      * @since 10.0
      */
     @Beta
     public StringBuilder appendTo(StringBuilder builder, Iterable<? extends Entry<?, ?>> entries) {
       return appendTo(builder, entries.iterator());
     }
 
     /**
      * Appends the string representation of each entry in {@code entries}, using the previously
      * configured separator and key-value separator, to {@code builder}. Identical to {@link
      * #appendTo(Appendable, Iterable)}, except that it does not throw {@link IOException}.
      *
      * @since 11.0
      */
     @Beta
     public StringBuilder appendTo(StringBuilder builder, Iterator<? extends Entry<?, ?>> entries) {
       try {
         appendTo((Appendable) builder, entries);
       } catch (IOException impossible) {
         throw new AssertionError(impossible);
       }
       return builder;
     }
 
     /**
      * Returns a string containing the string representation of each entry in {@code entries}, using
      * the previously configured separator and key-value separator.
      *
      * @since 10.0
      */
     @Beta
     public String join(Iterable<? extends Entry<?, ?>> entries) {
       return join(entries.iterator());
     }
 
     /**
      * Returns a string containing the string representation of each entry in {@code entries}, using
      * the previously configured separator and key-value separator.
      *
      * @since 11.0
      */
     @Beta
     public String join(Iterator<? extends Entry<?, ?>> entries) {
       return appendTo(new StringBuilder(), entries).toString();
     }
 
     /**
      * Returns a map joiner with the same behavior as this one, except automatically substituting
      * {@code nullText} for any provided null keys or values.
      */
     @CheckReturnValue
     public MapJoiner useForNull(String nullText) {
       return new MapJoiner(joiner.useForNull(nullText), keyValueSeparator);
     }
   }
 
   CharSequence toString(Object part) {
     checkNotNull(part);  // checkNotNull for GWT (do not optimize).
     return (part instanceof CharSequence) ? (CharSequence) part : part.toString();
   }
 
   private static Iterable<Object> iterable(
       final Object first, final Object second, final Object[] rest) {
     checkNotNull(rest);
     return new AbstractList<Object>() {
       @Override public int size() {
         return rest.length + 2;
       }
 
       @Override public Object get(int index) {
         switch (index) {
           case 0:
             return first;
           case 1:
             return second;
           default:
             return rest[index - 2];
         }
       }
     };
   }
 }