content: /*
   * Copyright (C) 2017 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.widget;
  
  import android.view.View;
  
  /**
   * A helper class to do scroll offset calculations.
   */
  class ScrollbarHelper {
  
      /**
       * @param startChild View closest to start of the list. (top or left)
       * @param endChild   View closest to end of the list (bottom or right)
       */
      static int computeScrollOffset(RecyclerView.State state, OrientationHelper orientation,
              View startChild, View endChild, RecyclerView.LayoutManager lm,
              boolean smoothScrollbarEnabled, boolean reverseLayout) {
          if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null
                  || endChild == null) {
              return 0;
          }
          final int minPosition = Math.min(lm.getPosition(startChild),
                  lm.getPosition(endChild));
          final int maxPosition = Math.max(lm.getPosition(startChild),
                  lm.getPosition(endChild));
          final int itemsBefore = reverseLayout
                  ? Math.max(0, state.getItemCount() - maxPosition - 1)
                  : Math.max(0, minPosition);
          if (!smoothScrollbarEnabled) {
              return itemsBefore;
          }
          final int laidOutArea = Math.abs(orientation.getDecoratedEnd(endChild)
                  - orientation.getDecoratedStart(startChild));
          final int itemRange = Math.abs(lm.getPosition(startChild)
                  - lm.getPosition(endChild)) + 1;
          final float avgSizePerRow = (float) laidOutArea / itemRange;
  
          return Math.round(itemsBefore * avgSizePerRow + (orientation.getStartAfterPadding()
                  - orientation.getDecoratedStart(startChild)));
      }
  
      /**
       * @param startChild View closest to start of the list. (top or left)
       * @param endChild   View closest to end of the list (bottom or right)
       */
      static int computeScrollExtent(RecyclerView.State state, OrientationHelper orientation,
              View startChild, View endChild, RecyclerView.LayoutManager lm,
              boolean smoothScrollbarEnabled) {
          if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null
                  || endChild == null) {
              return 0;
          }
          if (!smoothScrollbarEnabled) {
              return Math.abs(lm.getPosition(startChild) - lm.getPosition(endChild)) + 1;
          }
          final int extend = orientation.getDecoratedEnd(endChild)
                  - orientation.getDecoratedStart(startChild);
          return Math.min(orientation.getTotalSpace(), extend);
      }
  
      /**
       * @param startChild View closest to start of the list. (top or left)
       * @param endChild   View closest to end of the list (bottom or right)
       */
      static int computeScrollRange(RecyclerView.State state, OrientationHelper orientation,
              View startChild, View endChild, RecyclerView.LayoutManager lm,
              boolean smoothScrollbarEnabled) {
          if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null
                  || endChild == null) {
              return 0;
          }
          if (!smoothScrollbarEnabled) {
              return state.getItemCount();
          }
          // smooth scrollbar enabled. try to estimate better.
          final int laidOutArea = orientation.getDecoratedEnd(endChild)
                  - orientation.getDecoratedStart(startChild);
          final int laidOutRange = Math.abs(lm.getPosition(startChild)
                  - lm.getPosition(endChild))
                  + 1;
          // estimate a size for full list.
          return (int) ((float) laidOutArea / laidOutRange * state.getItemCount());
      }
  }
  