/*
 * Copyright (C) 2016 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.graph;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.Beta;
import com.google.common.base.MoreObjects;
import com.google.common.base.MoreObjects.ToStringHelper;
import com.google.common.base.Objects;
import com.google.common.collect.Maps;
import com.google.common.collect.Ordering;
import com.google.errorprone.annotations.Immutable;
import java.util.Comparator;
import java.util.Map;
import org.checkerframework.checker.nullness.qual.Nullable;

Used to represent the order of elements in a data structure that supports different options for
iteration order guarantees.
Example usage:

MutableGraph<Integer> graph =
    GraphBuilder.directed().nodeOrder(ElementOrder.<Integer>natural()).build();

Author:
Joshua O'Madadhain
Since:
20.0/**
 * Used to represent the order of elements in a data structure that supports different options for
 * iteration order guarantees.
 *
 * <p>Example usage:
 *
 * <pre>{@code
 * MutableGraph<Integer> graph =
 *     GraphBuilder.directed().nodeOrder(ElementOrder.<Integer>natural()).build();
 * }</pre>
 *
 * @author Joshua O'Madadhain
 * @since 20.0
 */
@Beta
@Immutable
public final class ElementOrder<T> {
  private final Type type;

  @SuppressWarnings("Immutable") // Hopefully the comparator provided is immutable!
  private final @Nullable Comparator<T> comparator;

  
The type of ordering that this object specifies.

  
UNORDERED: no order is guaranteed.
  
STABLE: ordering is guaranteed to follow a pattern that won't change between releases.
      Some methods may have stronger guarantees.
  
INSERTION: insertion ordering is guaranteed.
  
SORTED: ordering according to a supplied comparator is guaranteed.

/**
   * The type of ordering that this object specifies.
   *
   * <ul>
   *   <li>UNORDERED: no order is guaranteed.
   *   <li>STABLE: ordering is guaranteed to follow a pattern that won't change between releases.
   *       Some methods may have stronger guarantees.
   *   <li>INSERTION: insertion ordering is guaranteed.
   *   <li>SORTED: ordering according to a supplied comparator is guaranteed.
   * </ul>
   */
  public enum Type {
    UNORDERED,
    STABLE,
    INSERTION,
    SORTED
  }

  private ElementOrder(Type type, @Nullable Comparator<T> comparator) {
    this.type = checkNotNull(type);
    this.comparator = comparator;
    checkState((type == Type.SORTED) == (comparator != null));
  }

  
Returns an instance which specifies that no ordering is guaranteed. /** Returns an instance which specifies that no ordering is guaranteed. */
  public static <S> ElementOrder<S> unordered() {
    return new ElementOrder<S>(Type.UNORDERED, null);
  }

  
Returns an instance which specifies that ordering is guaranteed to be always be the same across
iterations, and across releases. Some methods may have stronger guarantees.
This instance is only useful in combination with incidentEdgeOrder, e.g. 
graphBuilder.incidentEdgeOrder(ElementOrder.stable()). 
In combination with incidentEdgeOrder
incidentEdgeOrder(ElementOrder.stable()) guarantees the ordering of the returned collections of the following methods: 

  
For Graph and ValueGraph: 

        
edges(): Stable order 
adjacentNodes(node): Connecting edge insertion order 
predecessors(node): Connecting edge insertion order 
successors(node): Connecting edge insertion order 
incidentEdges(node): Edge insertion order 
  
For Network: 

        
adjacentNodes(node): Stable order 
predecessors(node): Connecting edge insertion order 
successors(node): Connecting edge insertion order 
incidentEdges(node): Stable order 
inEdges(node): Edge insertion order 
outEdges(node): Edge insertion order 
adjacentEdges(edge): Stable order 
edgesConnecting(nodeU, nodeV): Edge insertion order 

Since:
29.0/**
   * Returns an instance which specifies that ordering is guaranteed to be always be the same across
   * iterations, and across releases. Some methods may have stronger guarantees.
   *
   * <p>This instance is only useful in combination with {@code incidentEdgeOrder}, e.g. {@code
   * graphBuilder.incidentEdgeOrder(ElementOrder.stable())}.
   *
   * <h3>In combination with {@code incidentEdgeOrder}</h3>
   *
   * <p>{@code incidentEdgeOrder(ElementOrder.stable())} guarantees the ordering of the returned
   * collections of the following methods:
   *
   * <ul>
   *   <li>For {@link Graph} and {@link ValueGraph}:
   *       <ul>
   *         <li>{@code edges()}: Stable order
   *         <li>{@code adjacentNodes(node)}: Connecting edge insertion order
   *         <li>{@code predecessors(node)}: Connecting edge insertion order
   *         <li>{@code successors(node)}: Connecting edge insertion order
   *         <li>{@code incidentEdges(node)}: Edge insertion order
   *       </ul>
   *   <li>For {@link Network}:
   *       <ul>
   *         <li>{@code adjacentNodes(node)}: Stable order
   *         <li>{@code predecessors(node)}: Connecting edge insertion order
   *         <li>{@code successors(node)}: Connecting edge insertion order
   *         <li>{@code incidentEdges(node)}: Stable order
   *         <li>{@code inEdges(node)}: Edge insertion order
   *         <li>{@code outEdges(node)}: Edge insertion order
   *         <li>{@code adjacentEdges(edge)}: Stable order
   *         <li>{@code edgesConnecting(nodeU, nodeV)}: Edge insertion order
   *       </ul>
   * </ul>
   *
   * @since 29.0
   */
  public static <S> ElementOrder<S> stable() {
    return new ElementOrder<S>(Type.STABLE, null);
  }

  
Returns an instance which specifies that insertion ordering is guaranteed. /** Returns an instance which specifies that insertion ordering is guaranteed. */
  public static <S> ElementOrder<S> insertion() {
    return new ElementOrder<S>(Type.INSERTION, null);
  }

  
Returns an instance which specifies that the natural ordering of the elements is guaranteed.
/**
   * Returns an instance which specifies that the natural ordering of the elements is guaranteed.
   */
  public static <S extends Comparable<? super S>> ElementOrder<S> natural() {
    return new ElementOrder<S>(Type.SORTED, Ordering.<S>natural());
  }

  
Returns an instance which specifies that the ordering of the elements is guaranteed to be determined by comparator. /**
   * Returns an instance which specifies that the ordering of the elements is guaranteed to be
   * determined by {@code comparator}.
   */
  public static <S> ElementOrder<S> sorted(Comparator<S> comparator) {
    return new ElementOrder<S>(Type.SORTED, checkNotNull(comparator));
  }

  
Returns the type of ordering used. /** Returns the type of ordering used. */
  public Type type() {
    return type;
  }

  
Returns the Comparator used. 
Throws:
UnsupportedOperationException – if comparator is not defined/**
   * Returns the {@link Comparator} used.
   *
   * @throws UnsupportedOperationException if comparator is not defined
   */
  public Comparator<T> comparator() {
    if (comparator != null) {
      return comparator;
    }
    throw new UnsupportedOperationException("This ordering does not define a comparator.");
  }

  @Override
  public boolean equals(@Nullable Object obj) {
    if (obj == this) {
      return true;
    }
    if (!(obj instanceof ElementOrder)) {
      return false;
    }

    ElementOrder<?> other = (ElementOrder<?>) obj;
    return (type == other.type) && Objects.equal(comparator, other.comparator);
  }

  @Override
  public int hashCode() {
    return Objects.hashCode(type, comparator);
  }

  @Override
  public String toString() {
    ToStringHelper helper = MoreObjects.toStringHelper(this).add("type", type);
    if (comparator != null) {
      helper.add("comparator", comparator);
    }
    return helper.toString();
  }

  
Returns an empty mutable map whose keys will respect this ElementOrder. /** Returns an empty mutable map whose keys will respect this {@link ElementOrder}. */
  <K extends T, V> Map<K, V> createMap(int expectedSize) {
    switch (type) {
      case UNORDERED:
        return Maps.newHashMapWithExpectedSize(expectedSize);
      case INSERTION:
      case STABLE:
        return Maps.newLinkedHashMapWithExpectedSize(expectedSize);
      case SORTED:
        return Maps.newTreeMap(comparator());
      default:
        throw new AssertionError();
    }
  }

  @SuppressWarnings("unchecked")
  <T1 extends T> ElementOrder<T1> cast() {
    return (ElementOrder<T1>) this;
  }
}