/*
 * Copyright (C) 2009 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.escape;

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

import java.util.Collections;
import java.util.Map;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;

/**
 * An implementation-specific parameter class suitable for initializing
 * {@link ArrayBasedCharEscaper} or {@link ArrayBasedUnicodeEscaper} instances.
 * This class should be used when more than one escaper is created using the
 * same character replacement mapping to allow the underlying (implementation
 * specific) data structures to be shared.
 *
 * <p>
 * The size of the data structure used by ArrayBasedCharEscaper and
 * ArrayBasedUnicodeEscaper is proportional to the highest valued character that
 * has a replacement. For example a replacement map containing the single
 * character '{@literal \}u1000' will require approximately 16K of memory. As
 * such sharing this data structure between escaper instances is the primary
 * goal of this class.
 *
 * @author David Beaumont
 * @since 15.0
 */
@Beta
@GwtCompatible
public final class ArrayBasedEscaperMap {
	/**
	 * Returns a new ArrayBasedEscaperMap for creating ArrayBasedCharEscaper or
	 * ArrayBasedUnicodeEscaper instances.
	 *
	 * @param replacements a map of characters to their escaped representations
	 */
	public static ArrayBasedEscaperMap create(Map<Character, String> replacements) {
		return new ArrayBasedEscaperMap(createReplacementArray(replacements));
	}

	// The underlying replacement array we can share between multiple escaper
	// instances.
	private final char[][] replacementArray;

	private ArrayBasedEscaperMap(char[][] replacementArray) {
		this.replacementArray = replacementArray;
	}

	// Returns the non-null array of replacements for fast lookup.
	char[][] getReplacementArray() {
		return replacementArray;
	}

	// Creates a replacement array from the given map. The returned array is a
	// linear lookup table of replacement character sequences indexed by the
	// original character value.
	@VisibleForTesting
	static char[][] createReplacementArray(Map<Character, String> map) {
		checkNotNull(map); // GWT specific check (do not optimize)
		if (map.isEmpty()) {
			return EMPTY_REPLACEMENT_ARRAY;
		}
		char max = Collections.max(map.keySet());
		char[][] replacements = new char[max + 1][];
		for (char c : map.keySet()) {
			replacements[c] = map.get(c).toCharArray();
		}
		return replacements;
	}

	// Immutable empty array for when there are no replacements.
	private static final char[][] EMPTY_REPLACEMENT_ARRAY = new char[0][0];
}