src/com/android/tradefed/util/RegexTrie.java

/*
 * Copyright (C) 2010 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.android.tradefed.util;

import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.regex.Pattern;
import java.util.regex.Matcher;

/**
 * The RegexTrie is a trie where each _stored_ segment of the key is a regex {@link Pattern}.  Thus,
 * the full _stored_ key is a List<Pattern> rather than a String as in a standard trie.  Note that
 * the {@link get(Object key)} requires a List<String>, which will be matched against the
 * {@link Pattern}s, rather than checked for equality as in a standard trie.  It will likely perform
 * poorly for large datasets.
 */
public class RegexTrie<V> {
    private V mValue = null;
    private Map<Pattern, RegexTrie<V>> mChildren = new LinkedHashMap<Pattern, RegexTrie<V>>();

    public void clear() {
        mValue = null;
        for (RegexTrie child : mChildren.values()) {
            child.clear();
        }
        mChildren.clear();
    }

    boolean containsKey(String... strings) {
        return retrieve(strings) != null;
    }

    V recursivePut(V value, List<Pattern> patterns) {
        // Cases:
        // 1) patterns is empty -- set our value
        // 2) patterns is non-empty -- recurse downward, creating a child if necessary
        if (patterns.isEmpty()) {
            V oldValue = mValue;
            mValue = value;
            return oldValue;
        } else {
            Pattern curKey = patterns.get(0);
            List<Pattern> nextKeys = patterns.subList(1, patterns.size());

            // Create a new child to handle
            RegexTrie<V> nextChild = mChildren.get(curKey);
            if (nextChild == null) {
                nextChild = new RegexTrie<V>();
                mChildren.put(curKey, nextChild);
            }
            return nextChild.recursivePut(value, nextKeys);
        }
    }

    public V put(V value, Pattern... patterns) {
        if (patterns.length == 0) {
            throw new IllegalArgumentException("pattern list must be non-empty");
        }
        List<Pattern> pList = Arrays.asList(patterns);
        return recursivePut(value, pList);
    }

    /**
     * This helper method takes a list of regular expressions as Strings and compiles them
     * on-the-fly before recursing
     */
    public V put(V value, String... regexen) {
        Pattern[] patterns = new Pattern[regexen.length];
        for (int i = 0; i < regexen.length; ++i) {
            patterns[i] = Pattern.compile(regexen[i]);
        }
        return put(value, patterns);
    }

    V recursiveRetrieve(List<String> strings) {
        // Cases:
        // 1) strings is empty -- return our value
        // 2) strings is non-empty -- find the first child that matches, recurse downward
        if (strings.isEmpty()) {
            return mValue;
        } else {
            String curKey = strings.get(0);
            List<String> nextKeys = strings.subList(1, strings.size());

            for (Map.Entry<Pattern, RegexTrie<V>> child : mChildren.entrySet()) {
                Matcher matcher = child.getKey().matcher(curKey);
                if (matcher.matches()) {
                    return child.getValue().recursiveRetrieve(nextKeys);
                }
            }

            // no match
            return null;
        }
    }

    public V retrieve(String... strings) {
        if (strings.length == 0) {
            throw new IllegalArgumentException("string list must be non-empty");
        }
        List<String> sList = Arrays.asList(strings);
        return recursiveRetrieve(sList);
    }

    @Override
    public String toString() {
        return String.format("{V: %s, C: %s}", mValue, mChildren);
    }
}