content: /*
   * Copyright (C) 2016 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.internal.util;
  
  import android.os.Message;
  import android.util.Log;
  import android.util.SparseArray;
  
  import java.lang.reflect.Field;
  import java.lang.reflect.Modifier;
  
  /**
   * Static utility class for dealing with {@link Message} objects.
   */
  public class MessageUtils {
  
      private static final String TAG = MessageUtils.class.getSimpleName();
      private static final boolean DBG = false;
  
      /** Thrown when two different constants have the same value. */
      public static class DuplicateConstantError extends Error {
          private DuplicateConstantError() {}
          public DuplicateConstantError(String name1, String name2, int value) {
              super(String.format("Duplicate constant value: both %s and %s = %d",
                  name1, name2, value));
          }
      }
  
      /**
       * Finds the names of integer constants. Searches the specified {@code classes}, looking for
       * accessible static integer fields whose names begin with one of the specified
       * {@code prefixes}.
       *
       * @param classes the classes to examine.
       * @param prefixes only consider fields names starting with one of these prefixes.
       * @return a {@link SparseArray} mapping integer constants to their names.
       */
      public static SparseArray<String> findMessageNames(Class[] classes, String[] prefixes) {
          SparseArray<String> messageNames = new SparseArray<>();
          for (Class c : classes) {
              String className = c.getName();
              if (DBG) Log.d(TAG, "Examining class " + className);
  
              Field[] fields;
              try {
                  fields = c.getDeclaredFields();
              } catch (SecurityException e) {
                  Log.e(TAG, "Can't list fields of class " + className);
                  continue;
              }
  
              for (Field field : fields) {
                  int modifiers = field.getModifiers();
                  if (!Modifier.isStatic(modifiers) | !Modifier.isFinal(modifiers)) {
                      continue;
                  }
  
                  String name = field.getName();
                  for (String prefix : prefixes) {
                      // Does this look like a constant?
                      if (!name.startsWith(prefix)) {
                          continue;
                      }
  
                      try {
                          // TODO: can we have the caller try to access the field instead, so we don't
                          // expose constants it does not have access to?
                          field.setAccessible(true);
  
                          // Fetch the constant's value.
                          int value;
                          try {
                              value = field.getInt(null);
                          } catch (IllegalArgumentException | ExceptionInInitializerError e) {
                              // The field is not an integer (or short or byte), or c's static
                              // initializer failed and we have no idea what its value is.
                              // Either way, give up on this field.
                              break;
                          }
  
                          // Check for duplicate values.
                          String previousName = messageNames.get(value);
                          if (previousName != null && !previousName.equals(name)) {
                              throw new DuplicateConstantError(name, previousName, value);
                          }
  
                          messageNames.put(value, name);
                          if (DBG) {
                              Log.d(TAG, String.format("Found constant: %s.%s = %d",
                                      className, name, value));
                          }
                      } catch (SecurityException | IllegalAccessException e) {
                          // Not allowed to make the field accessible, or no access. Ignore.
                          continue;
                      }
                  }
              }
          }
          return messageNames;
      }
  
      /**
       * Default prefixes for constants.
       */
      public static final String[] DEFAULT_PREFIXES = {"CMD_", "EVENT_"};
  
      /**
       * Finds the names of integer constants. Searches the specified {@code classes}, looking for
       * accessible static integer values whose names begin with {@link #DEFAULT_PREFIXES}.
       *
       * @param classNames the classes to examine.
       * @return a {@link SparseArray} mapping integer constants to their names.
       */
      public static SparseArray<String> findMessageNames(Class[] classNames) {
          return findMessageNames(classNames, DEFAULT_PREFIXES);
      }
  }
  
  