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/*
* Copyright (C) 2022 The Android Open Source Project
*
* 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.tonicsystems.jarjar;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.TreeMap;
/**
* A prefix trie of {@link Wildcard}, where the prefix is obtained from {@link
* Wildcard#getPlainTextPrefix()}.
*
* <p>This allows quick lookup of applicable wildcards in the common case where wildcards have a
* non-empty plain-text prefix.
*/
public class WildcardTrie {
private final TreeMap<String, WildcardTrie> subTries = new TreeMap<>();
private final List<Wildcard> wildcards = new ArrayList<>();
private final String prefix;
public WildcardTrie(List<Wildcard> wildcards) {
this("");
final ArrayList<Wildcard> lst = new ArrayList<>(wildcards);
// Sort values to ensure that wildcards that prefix others are added first
lst.sort(Comparator.comparing(Wildcard::getPlainTextPrefix));
for (Wildcard w : lst) {
final String prefix = w.getPlainTextPrefix();
final WildcardTrie prefixTrie = findSubTrieWhichPrefixes(prefix, this);
if (prefixTrie.prefix.equals(prefix)) {
prefixTrie.wildcards.add(w);
} else {
final WildcardTrie newTrie = new WildcardTrie(prefix);
newTrie.wildcards.add(w);
prefixTrie.subTries.put(prefix, newTrie);
}
}
}
private WildcardTrie(String prefix) {
this.prefix = prefix;
}
private static WildcardTrie findSubTrieWhichPrefixes(String value, WildcardTrie baseTrie) {
final String possiblePrefix = baseTrie.subTries.floorKey(value);
// Because each level of the trie does not contain keys that are prefixes of each other,
// there can be at most one prefix of the value at that level, and that prefix will be the
// highest key ordered before the value (any non-prefix key would have a character
// difference with the prefix and so be ordered before the prefix or after the value).
if (possiblePrefix != null && value.startsWith(possiblePrefix)) {
return findSubTrieWhichPrefixes(value, baseTrie.subTries.get(possiblePrefix));
}
return baseTrie;
}
public List<Wildcard> getPossibleMatches(String value) {
WildcardTrie baseTrie = this;
List<Wildcard> prefixMatches =
wildcards.isEmpty()
// If there's no match, don't even allocate a list and use the singleton emptyList
? Collections.emptyList()
: new ArrayList<>(wildcards);
while (true) {
final String possiblePrefix = baseTrie.subTries.floorKey(value);
if (possiblePrefix != null && value.startsWith(possiblePrefix)) {
baseTrie = baseTrie.subTries.get(possiblePrefix);
if (prefixMatches.isEmpty()) {
prefixMatches = new ArrayList<>(baseTrie.wildcards);
} else {
prefixMatches.addAll(baseTrie.wildcards);
}
} else {
prefixMatches.sort(Comparator.comparing(Wildcard::getRuleIndex));
return prefixMatches;
}
}
}
}
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