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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();
if (weights.length == 0) {
builder.append("default priority");
} else {
builder.append("priority [");
for (int i = 0; i < weights.length; ++i) {
if (i != 0) {
builder.append(", ");
}
builder.append(weights[i]);
}
builder.append("]");
}
if (seq != 0) {
builder.append(" + ")
.append(seq);
}
return builder.toString();
}
}
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