/*
 * Copyright 2013 Square Inc.
 *
 * 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.squareup.wire;

import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Converts values of an enum to and from integers.
 */
final class EnumAdapter<E extends ProtoEnum> {
  private final Map<Integer, E> fromInt = new LinkedHashMap<Integer, E>();

  EnumAdapter(Class<E> type) {
    for (E value : type.getEnumConstants()) {
      fromInt.put(value.getValue(), value);
    }
  }

  public int toInt(E e) {
    return e.getValue();
  }

  public E fromInt(int value) {
    return fromInt.get(value);
  }
}

/*
 * Copyright 2013 Square Inc.
 *
 * 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.squareup.wire;

import java.util.Arrays;
import java.util.Comparator;

/**
 * Converts values of an enum to and from integers.
 */
final class EnumAdapter<E extends ProtoEnum> {
  private static final Comparator<ProtoEnum> COMPARATOR = new Comparator<ProtoEnum>() {
    @Override public int compare(ProtoEnum o1, ProtoEnum o2) {
      return o1.getValue() - o2.getValue();
    }
  };

  private final Class<E> type;

  private final int[] values;
  private final E[] constants;

  EnumAdapter(Class<E> type) {
    this.type = type;

    constants = type.getEnumConstants();
    Arrays.sort(constants, COMPARATOR);

    values = new int[constants.length];
    for (int i = 0; i < constants.length; i++) {
      values[i] = constants[i].getValue();
    }
  }

  public int toInt(E e) {
    return e.getValue();
  }

  public E fromInt(int value) {
    int index = Arrays.binarySearch(values, value);
    if (index < 0) {
      throw new IllegalArgumentException(
          "Unknown enum tag " + value + " for " + type.getCanonicalName());
    }
    return constants[index];
  }
}

Replace the enum adapter tag map with an integer BST.
Replace the enum adapter tag map with an integer BST.

By not using a the map we avoid boxing the integer in both directions and the overhead of the underlying wrapper objects. The sorted array of enum values and the mirrored key array allows us to use a binary-search for reverse lookups. This operation is O(log n) which, while slower than the map's O(1), has no significant performance impact for enums with less then hundreds of values.
