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-rw-r--r--sangria-core/src/main/java/com/tavianator/sangria/core/Priority.java149
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+/****************************************************************************
+ * Sangria *
+ * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com> *
+ * *
+ * 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.tavianator.sangria.core;
+
+import java.util.*;
+
+import com.google.common.collect.ComparisonChain;
+import com.google.common.primitives.Ints;
+
+/**
+ * A loosely-coupled, infinitely divisible priority/weight system.
+ *
+ * <p>
+ * This class implements an extensible priority system based on lexicographical ordering. In its simplest use, {@code
+ * Priority.create(0)} is ordered before {@code Priority.create(1)}, then {@code Priority.create(2)}, etc.
+ * </p>
+ *
+ * <p>
+ * To create a priority that is ordered between two existing ones, simply add another parameter: {@code
+ * Priority.create(1, 1)} comes after {@code Priority.create(1)}, but before {@code Priority.create(2)}. In this way,
+ * priorities can always be inserted anywhere in a sequence.
+ * </p>
+ *
+ * <p>
+ * The {@link #next()} method creates a priority that is ordered immediately following the current one, and is distinct
+ * from all priorities obtained by any other means. This provides a convenient way to order entire segments of lists.
+ * </p>
+ *
+ * <p>
+ * A special priority, obtained by {@code Priority.getDefault()}, sorts before all other priorities.
+ * </p>
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.1
+ * @since 1.1
+ */
+public class Priority implements Comparable<Priority> {
+ private static final Priority DEFAULT = new Priority(new int[0], 0);
+ private static final Comparator<int[]> COMPARATOR = Ints.lexicographicalComparator();
+
+ private final int[] weights;
+ private final int seq;
+
+ /**
+ * @return The default priority, which comes before all other priorities.
+ */
+ public static Priority getDefault() {
+ return DEFAULT;
+ }
+
+ /**
+ * Create a {@link Priority} with the given sequence.
+ *
+ * @param weight The first value of the weight sequence.
+ * @param weights An integer sequence. These sequences are sorted lexicographically, so {@code Priority.create(1)}
+ * sorts before {@code Priority.create(1, 1)}, which sorts before {@code Priority.create(2)}.
+ * @return A new {@link Priority}.
+ */
+ public static Priority create(int weight, int... weights) {
+ int[] newWeights = new int[weights.length + 1];
+ newWeights[0] = weight;
+ System.arraycopy(weights, 0, newWeights, 1, weights.length);
+ return new Priority(newWeights, 0);
+ }
+
+ private Priority(int[] weights, int seq) {
+ this.weights = weights;
+ this.seq = seq;
+ }
+
+ /**
+ * @return Whether this priority originated in a call to {@link #getDefault()}.
+ */
+ public boolean isDefault() {
+ return weights.length == 0;
+ }
+
+ /**
+ * @return A new {@link Priority} which immediately follows this one, and which is distinct from all other
+ * priorities obtained by {@link #create(int, int...)}.
+ */
+ public Priority next() {
+ return new Priority(weights, seq + 1);
+ }
+
+ @Override
+ public boolean equals(Object obj) {
+ if (obj == this) {
+ return true;
+ } else if (!(obj instanceof Priority)) {
+ return false;
+ }
+
+ Priority other = (Priority)obj;
+ return Arrays.equals(weights, other.weights)
+ && seq == other.seq;
+ }
+
+ @Override
+ public int hashCode() {
+ return Arrays.hashCode(weights) + seq;
+ }
+
+ @Override
+ public int compareTo(Priority o) {
+ return ComparisonChain.start()
+ .compare(weights, o.weights, COMPARATOR)
+ .compare(seq, o.seq)
+ .result();
+ }
+
+ @Override
+ public String toString() {
+ StringBuilder builder = new StringBuilder("Priority.");
+ if (weights.length == 0) {
+ builder.append("getDefault()");
+ } else {
+ builder.append("create(");
+ for (int i = 0; i < weights.length; ++i) {
+ if (i != 0) {
+ builder.append(", ");
+ }
+ builder.append(weights[i]);
+ }
+ builder.append(")");
+ }
+ if (seq != 0) {
+ builder.append(".next(")
+ .append(seq)
+ .append(")");
+ }
+ return builder.toString();
+ }
+}