/*
 * Copyright (C) 2015 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.setupwizardlib.items;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.util.SparseIntArray;
import java.util.ArrayList;
import java.util.List;

public class ItemGroup extends AbstractItemHierarchy
    implements ItemInflater.ItemParent, ItemHierarchy.Observer {

  /* static section */

  private static final String TAG = "ItemGroup";

  /**
   * Binary search for the closest value that's smaller than or equal to {@code value}, and return
   * the corresponding key.
   */
  private static int binarySearch(SparseIntArray array, int value) {
    final int size = array.size();
    int lo = 0;
    int hi = size - 1;

    while (lo <= hi) {
      final int mid = (lo + hi) >>> 1;
      final int midVal = array.valueAt(mid);

      if (midVal < value) {
        lo = mid + 1;
      } else if (midVal > value) {
        hi = mid - 1;
      } else {
        return array.keyAt(mid); // value found
      }
    }
    // Value not found. Return the last item before our search range, which is the closest
    // value smaller than the value we are looking for.
    return array.keyAt(lo - 1);
  }

  /**
   * Same as {@link List#indexOf(Object)}, but using identity comparison rather than {@link
   * Object#equals(Object)}.
   */
  private static <T> int identityIndexOf(List<T> list, T object) {
    final int count = list.size();
    for (int i = 0; i < count; i++) {
      if (list.get(i) == object) {
        return i;
      }
    }
    return -1;
  }

  /* non-static section */

  private final List<ItemHierarchy> children = new ArrayList<>();

  /**
   * A mapping from the index of an item hierarchy in children, to the first position in which the
   * corresponding child hierarchy represents. For example:
   *
   * <p>ItemHierarchy Item Item Position Index
   *
   * <p>0 [ Wi-Fi AP 1 ] 0 | Wi-Fi AP 2 | 1 | Wi-Fi AP 3 | 2 | Wi-Fi AP 4 | 3 [ Wi-Fi AP 5 ] 4
   *
   * <p>1 [ <Empty Item Hierarchy> ]
   *
   * <p>2 [ Use cellular data ] 5
   *
   * <p>3 [ Don't connect ] 6
   *
   * <p>For this example of Wi-Fi screen, the following mapping will be produced: [ 0 -> 0 | 2 -> 5
   * | 3 -> 6 ]
   *
   * <p>Also note how ItemHierarchy index 1 is not present in the map, because it is empty.
   *
   * <p>ItemGroup uses this map to look for which ItemHierarchy an item at a given position belongs
   * to.
   */
  private final SparseIntArray hierarchyStart = new SparseIntArray();

  private int count = 0;
  private boolean dirty = false;

  public ItemGroup() {
    super();
  }

  public ItemGroup(Context context, AttributeSet attrs) {
    // Constructor for XML inflation
    super(context, attrs);
  }

  /** Add a child hierarchy to this item group. */
  @Override
  public void addChild(ItemHierarchy child) {
    dirty = true;
    children.add(child);
    child.registerObserver(this);

    final int count = child.getCount();
    if (count > 0) {
      notifyItemRangeInserted(getChildPosition(child), count);
    }
  }

  /**
   * Remove a previously added child from this item group.
   *
   * @return True if there is a match for the child and it is removed. False if the child could not
   *     be found in our list of child hierarchies.
   */
  public boolean removeChild(ItemHierarchy child) {
    final int childIndex = identityIndexOf(children, child);
    final int childPosition = getChildPosition(childIndex);
    dirty = true;
    if (childIndex != -1) {
      final int childCount = child.getCount();
      children.remove(childIndex);
      child.unregisterObserver(this);
      if (childCount > 0) {
        notifyItemRangeRemoved(childPosition, childCount);
      }
      return true;
    }
    return false;
  }

  /** Remove all children from this hierarchy. */
  public void clear() {
    if (children.isEmpty()) {
      return;
    }

    final int numRemoved = getCount();

    for (ItemHierarchy item : children) {
      item.unregisterObserver(this);
    }
    dirty = true;
    children.clear();
    notifyItemRangeRemoved(0, numRemoved);
  }

  @Override
  public int getCount() {
    updateDataIfNeeded();
    return count;
  }

  @Override
  public IItem getItemAt(int position) {
    int itemIndex = getItemIndex(position);
    ItemHierarchy item = children.get(itemIndex);
    int subpos = position - hierarchyStart.get(itemIndex);
    return item.getItemAt(subpos);
  }

  @Override
  public void onChanged(ItemHierarchy hierarchy) {
    // Need to set dirty, because our children may have gotten more items.
    dirty = true;
    notifyChanged();
  }

  /**
   * @return The "Item Position" of the given child, or -1 if the child is not found. If the given
   *     child is empty, position of the next visible item is returned.
   */
  private int getChildPosition(ItemHierarchy child) {
    // Check the identity of the child rather than using .equals(), because here we want
    // to find the index of the instance itself rather than something that equals to it.
    return getChildPosition(identityIndexOf(children, child));
  }

  private int getChildPosition(int childIndex) {
    updateDataIfNeeded();
    if (childIndex != -1) {
      int childPos = -1;
      int childCount = children.size();
      for (int i = childIndex; childPos < 0 && i < childCount; i++) {
        // Find the position of the first visible child after childIndex. This is required
        // when removing the last item from a nested ItemGroup.
        childPos = hierarchyStart.get(i, -1);
      }
      if (childPos < 0) {
        // If the last item in a group is being removed, there will be no visible item.
        // In that case return the count instead, since that is where the item would have
        // been if the child is not empty.
        childPos = getCount();
      }
      return childPos;
    }
    return -1;
  }

  @Override
  public void onItemRangeChanged(ItemHierarchy itemHierarchy, int positionStart, int itemCount) {
    // No need to set dirty because onItemRangeChanged does not include any structural changes.
    final int childPosition = getChildPosition(itemHierarchy);
    if (childPosition >= 0) {
      notifyItemRangeChanged(childPosition + positionStart, itemCount);
    } else {
      Log.e(TAG, "Unexpected child change " + itemHierarchy);
    }
  }

  @Override
  public void onItemRangeInserted(ItemHierarchy itemHierarchy, int positionStart, int itemCount) {
    dirty = true;
    final int childPosition = getChildPosition(itemHierarchy);
    if (childPosition >= 0) {
      notifyItemRangeInserted(childPosition + positionStart, itemCount);
    } else {
      Log.e(TAG, "Unexpected child insert " + itemHierarchy);
    }
  }

  @Override
  public void onItemRangeMoved(
      ItemHierarchy itemHierarchy, int fromPosition, int toPosition, int itemCount) {
    dirty = true;
    final int childPosition = getChildPosition(itemHierarchy);
    if (childPosition >= 0) {
      notifyItemRangeMoved(childPosition + fromPosition, childPosition + toPosition, itemCount);
    } else {
      Log.e(TAG, "Unexpected child move " + itemHierarchy);
    }
  }

  @Override
  public void onItemRangeRemoved(ItemHierarchy itemHierarchy, int positionStart, int itemCount) {
    dirty = true;
    final int childPosition = getChildPosition(itemHierarchy);
    if (childPosition >= 0) {
      notifyItemRangeRemoved(childPosition + positionStart, itemCount);
    } else {
      Log.e(TAG, "Unexpected child remove " + itemHierarchy);
    }
  }

  @Override
  public ItemHierarchy findItemById(int id) {
    if (id == getId()) {
      return this;
    }
    for (ItemHierarchy child : children) {
      ItemHierarchy childFindItem = child.findItemById(id);
      if (childFindItem != null) {
        return childFindItem;
      }
    }
    return null;
  }

  /** If dirty, this method will recalculate the number of items and hierarchyStart. */
  private void updateDataIfNeeded() {
    if (dirty) {
      count = 0;
      hierarchyStart.clear();
      for (int itemIndex = 0; itemIndex < children.size(); itemIndex++) {
        ItemHierarchy item = children.get(itemIndex);
        if (item.getCount() > 0) {
          hierarchyStart.put(itemIndex, count);
        }
        count += item.getCount();
      }
      dirty = false;
    }
  }

  /**
   * Use binary search to locate the item hierarchy a position is contained in.
   *
   * @return Index of the item hierarchy which is responsible for the item at {@code position}.
   */
  private int getItemIndex(int position) {
    updateDataIfNeeded();
    if (position < 0 || position >= count) {
      throw new IndexOutOfBoundsException("size=" + count + "; index=" + position);
    }
    int result = binarySearch(hierarchyStart, position);
    if (result < 0) {
      throw new IllegalStateException("Cannot have item start index < 0");
    }
    return result;
  }
}