Support for sticky date headers

Closes #4696
// FREEBIE

src/org/thoughtcrime/securesms/util/DateUtils.java

@@ -18,6 +18,7 @@ package org.thoughtcrime.securesms.util;
 
 import android.content.Context;
 import android.os.Build;
+import android.support.annotation.NonNull;
 import android.text.format.DateFormat;
 
 import java.text.SimpleDateFormat;
@@ -37,6 +38,10 @@ public class DateUtils extends android.text.format.DateUtils {
     return System.currentTimeMillis() - millis <= unit.toMillis(span);
   }
 
+  private static boolean isYesterday(final long when) {
+    return DateUtils.isToday(when + TimeUnit.DAYS.toMillis(1));
+  }
+
   private static int convertDelta(final long millis, TimeUnit to) {
     return (int) to.convert(System.currentTimeMillis() - millis, TimeUnit.MILLISECONDS);
   }
@@ -111,6 +116,19 @@ public class DateUtils extends android.text.format.DateUtils {
     return new SimpleDateFormat(dateFormatPattern, locale);
   }
 
+  public static String getRelativeDate(@NonNull Context context,
+                                       @NonNull Locale locale,
+                                       long timestamp)
+  {
+    if (isToday(timestamp)) {
+      return context.getString(R.string.DateUtils_today);
+    } else if (isYesterday(timestamp)) {
+      return context.getString(R.string.DateUtils_yesterday);
+    } else {
+      return getFormattedDateTime(timestamp, "EEE, MMM d, yyyy", locale);
+    }
+  }
+
   private static String getLocalizedPattern(String template, Locale locale) {
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2) {
       return DateFormat.getBestDateTimePattern(locale, template);

src/org/thoughtcrime/securesms/util/StickyHeaderDecoration.java

@@ -0,0 +1,201 @@
+package org.thoughtcrime.securesms.util;
+
+import android.graphics.Canvas;
+import android.graphics.Rect;
+import android.os.Build.VERSION;
+import android.support.v4.view.ViewCompat;
+import android.support.v7.widget.LinearLayoutManager;
+import android.support.v7.widget.RecyclerView;
+import android.support.v7.widget.RecyclerView.ViewHolder;
+import android.view.View;
+import android.view.ViewGroup;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A sticky header decoration for android's RecyclerView.
+ * Currently only supports LinearLayoutManager in VERTICAL orientation.
+ */
+public class StickyHeaderDecoration extends RecyclerView.ItemDecoration {
+
+  private final Map<Long, ViewHolder> headerCache;
+  private final StickyHeaderAdapter   adapter;
+  private final boolean               renderInline;
+
+  /**
+   * @param adapter the sticky header adapter to use
+   */
+  public StickyHeaderDecoration(StickyHeaderAdapter adapter, boolean renderInline) {
+    this.adapter      = adapter;
+    this.headerCache  = new HashMap<>();
+    this.renderInline = renderInline;
+  }
+
+  /**
+   * {@inheritDoc}
+   */
+  @Override
+  public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
+                             RecyclerView.State state)
+  {
+    int position = parent.getChildAdapterPosition(view);
+
+    int headerHeight = 0;
+    if (position != RecyclerView.NO_POSITION && hasHeader(parent, position)) {
+      View header = getHeader(parent, position).itemView;
+      headerHeight = getHeaderHeightForLayout(header);
+    }
+
+    outRect.set(0, headerHeight, 0, 0);
+  }
+
+  private boolean hasHeader(RecyclerView parent, int adapterPos) {
+    boolean isReverse = isReverseLayout(parent);
+    if (isReverse && adapterPos == parent.getAdapter().getItemCount() - 1 ||
+        !isReverse && adapterPos == 0) {
+      return true;
+    }
+
+    int previous = adapterPos + (isReverse ? 1 : -1);
+    return adapter.getHeaderId(adapterPos) != adapter.getHeaderId(previous);
+  }
+
+  private ViewHolder getHeader(RecyclerView parent, int position) {
+    final long key = adapter.getHeaderId(position);
+
+    if (headerCache.containsKey(key)) {
+      return headerCache.get(key);
+    } else {
+      final ViewHolder holder = adapter.onCreateHeaderViewHolder(parent);
+      final View header = holder.itemView;
+
+      //noinspection unchecked
+      adapter.onBindHeaderViewHolder(holder, position);
+
+      int widthSpec = View.MeasureSpec.makeMeasureSpec(parent.getWidth(), View.MeasureSpec.EXACTLY);
+      int heightSpec = View.MeasureSpec.makeMeasureSpec(parent.getHeight(), View.MeasureSpec.UNSPECIFIED);
+
+      int childWidth = ViewGroup.getChildMeasureSpec(widthSpec,
+                                                     parent.getPaddingLeft() + parent.getPaddingRight(), header.getLayoutParams().width);
+      int childHeight = ViewGroup.getChildMeasureSpec(heightSpec,
+                                                      parent.getPaddingTop() + parent.getPaddingBottom(), header.getLayoutParams().height);
+
+      header.measure(childWidth, childHeight);
+      header.layout(0, 0, header.getMeasuredWidth(), header.getMeasuredHeight());
+
+      headerCache.put(key, holder);
+
+      return holder;
+    }
+  }
+
+  /**
+   * {@inheritDoc}
+   */
+  @Override
+  public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
+    final int count = parent.getChildCount();
+
+    for (int layoutPos = 0; layoutPos < count; layoutPos++) {
+      final View child = parent.getChildAt(translatedChildPosition(parent, layoutPos));
+
+      final int adapterPos = parent.getChildAdapterPosition(child);
+
+      if (adapterPos != RecyclerView.NO_POSITION && (layoutPos == 0 || hasHeader(parent, adapterPos))) {
+        View header = getHeader(parent, adapterPos).itemView;
+        c.save();
+        final int left = child.getLeft();
+        final int top = getHeaderTop(parent, child, header, adapterPos, layoutPos);
+        c.translate(left, top);
+        header.draw(c);
+        c.restore();
+      }
+    }
+  }
+
+  private int getHeaderTop(RecyclerView parent, View child, View header, int adapterPos,
+                           int layoutPos)
+  {
+    int headerHeight = getHeaderHeightForLayout(header);
+    int top = getChildY(parent, child) - headerHeight;
+    if (layoutPos == 0) {
+      final int count = parent.getChildCount();
+      final long currentId = adapter.getHeaderId(adapterPos);
+      // find next view with header and compute the offscreen push if needed
+      for (int i = 1; i < count; i++) {
+        int adapterPosHere = parent.getChildAdapterPosition(parent.getChildAt(translatedChildPosition(parent, i)));
+        if (adapterPosHere != RecyclerView.NO_POSITION) {
+          long nextId = adapter.getHeaderId(adapterPosHere);
+          if (nextId != currentId) {
+            final View next = parent.getChildAt(translatedChildPosition(parent, i));
+            final int offset = getChildY(parent, next) - (headerHeight + getHeader(parent, adapterPosHere).itemView.getHeight());
+            if (offset < 0) {
+              return offset;
+            } else {
+              break;
+            }
+          }
+        }
+      }
+
+      top = Math.max(0, top);
+    }
+
+    return top;
+  }
+
+  private int translatedChildPosition(RecyclerView parent, int position) {
+    return isReverseLayout(parent) ? parent.getChildCount() - 1 - position : position;
+  }
+
+  private int getChildY(RecyclerView parent, View child) {
+    if (VERSION.SDK_INT < 11) {
+      Rect rect = new Rect();
+      parent.getChildVisibleRect(child, rect, null);
+      return rect.top;
+    } else {
+      return (int)ViewCompat.getY(child);
+    }
+  }
+
+  private int getHeaderHeightForLayout(View header) {
+    return renderInline ? 0 : header.getHeight();
+  }
+
+  private boolean isReverseLayout(final RecyclerView parent) {
+    return (parent.getLayoutManager() instanceof LinearLayoutManager) &&
+        ((LinearLayoutManager)parent.getLayoutManager()).getReverseLayout();
+  }
+
+  /**
+   * The adapter to assist the {@link StickyHeaderDecoration} in creating and binding the header views.
+   *
+   * @param <T> the header view holder
+   */
+  public interface StickyHeaderAdapter<T extends ViewHolder> {
+
+    /**
+     * Returns the header id for the item at the given position.
+     *
+     * @param position the item position
+     * @return the header id
+     */
+    long getHeaderId(int position);
+
+    /**
+     * Creates a new header ViewHolder.
+     *
+     * @param parent the header's view parent
+     * @return a view holder for the created view
+     */
+    T onCreateHeaderViewHolder(ViewGroup parent);
+
+    /**
+     * Updates the header view to reflect the header data for the given position
+     * @param viewHolder the header view holder
+     * @param position the header's item position
+     */
+    void onBindHeaderViewHolder(T viewHolder, int position);
+  }
+}