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.server.display;
  
  import android.util.Slog;
  
  import com.android.internal.annotations.VisibleForTesting;
  
  import java.io.PrintWriter;
  import java.util.Arrays;
  
  /**
   * A helper class for handling access to illuminance hysteresis level values.
   */
  @VisibleForTesting
  public class HysteresisLevels {
      private static final String TAG = "HysteresisLevels";
  
      // Default hysteresis constraints for brightening or darkening.
      // The recent value must have changed by at least this fraction relative to the
      // current value before a change will be considered.
      private static final float DEFAULT_BRIGHTENING_HYSTERESIS = 0.10f;
      private static final float DEFAULT_DARKENING_HYSTERESIS = 0.20f;
  
      private static final boolean DEBUG = false;
  
      private final float[] mBrighteningThresholds;
      private final float[] mDarkeningThresholds;
      private final float[] mThresholdLevels;
  
      /**
       * Creates a {@code HysteresisLevels} object with the given equal-length
       * integer arrays.
       * @param brighteningThresholds an array of brightening hysteresis constraint constants.
       * @param darkeningThresholds an array of darkening hysteresis constraint constants.
       * @param thresholdLevels a monotonically increasing array of threshold levels.
      */
      HysteresisLevels(int[] brighteningThresholds, int[] darkeningThresholds,
              int[] thresholdLevels) {
          if (brighteningThresholds.length != darkeningThresholds.length
                  || darkeningThresholds.length != thresholdLevels.length + 1) {
              throw new IllegalArgumentException("Mismatch between hysteresis array lengths.");
          }
          mBrighteningThresholds = setArrayFormat(brighteningThresholds, 1000.0f);
          mDarkeningThresholds = setArrayFormat(darkeningThresholds, 1000.0f);
          mThresholdLevels = setArrayFormat(thresholdLevels, 1.0f);
      }
  
      /**
       * Return the brightening hysteresis threshold for the given value level.
       */
      public float getBrighteningThreshold(float value) {
          float brightConstant = getReferenceLevel(value, mBrighteningThresholds);
          float brightThreshold = value * (1.0f + brightConstant);
          if (DEBUG) {
              Slog.d(TAG, "bright hysteresis constant=" + brightConstant + ", threshold="
                      + brightThreshold + ", value=" + value);
          }
          return brightThreshold;
      }
  
      /**
       * Return the darkening hysteresis threshold for the given value level.
       */
      public float getDarkeningThreshold(float value) {
          float darkConstant = getReferenceLevel(value, mDarkeningThresholds);
          float darkThreshold = value * (1.0f - darkConstant);
          if (DEBUG) {
              Slog.d(TAG, "dark hysteresis constant=: " + darkConstant + ", threshold="
                      + darkThreshold + ", value=" + value);
          }
          return darkThreshold;
      }
  
      /**
       * Return the hysteresis constant for the closest threshold value from the given array.
       */
      private float getReferenceLevel(float value, float[] referenceLevels) {
          int index = 0;
          while (mThresholdLevels.length > index && value >= mThresholdLevels[index]) {
              ++index;
          }
          return referenceLevels[index];
      }
  
      /**
       * Return a float array where each i-th element equals {@code configArray[i]/divideFactor}.
       */
      private float[] setArrayFormat(int[] configArray, float divideFactor) {
          float[] levelArray = new float[configArray.length];
          for (int index = 0; levelArray.length > index; ++index) {
              levelArray[index] = (float)configArray[index] / divideFactor;
          }
          return levelArray;
      }
  
      void dump(PrintWriter pw) {
          pw.println("HysteresisLevels");
          pw.println("  mBrighteningThresholds=" + Arrays.toString(mBrighteningThresholds));
          pw.println("  mDarkeningThresholds=" + Arrays.toString(mDarkeningThresholds));
          pw.println("  mThresholdLevels=" + Arrays.toString(mThresholdLevels));
      }
  }
  