On lines listed, also diff line contents

When buffer is cleared using `/buffer clear` and more lines are added,
line pointers may be reused. Before, if the app was disconnected during
these events, after reconnection it was possible for the lines to appear out
of order. This happened because normally we calculate diff using pointers
only, and if we had an older line with the same pointer as the newer one,
the adapter would reuse the old view holder, which might've been displaying
the wrong line.

This fixes the issue by also looking at line contents while diffing.

This solution is not ideal:

* While we can reliably tell whether the contents of two lines are the same,
  during the diffing we also want to know whether two lines represent the
  same thing, even if the contents have changed. As the pointer can be
  reused, sometimes `areItemsTheSame` will return a false positive. However,
  with this change the negative effect of this shouldn't go beyond wrong
  animation being applied.

* Read marker may appear in a wrong place. We save the pointer to the last
  read line locally, and if the pointer is reused, there's no way for us to
  tell that the line is wrong.

Fixes #577

app/src/main/java/com/ubergeek42/WeechatAndroid/adapters/ChatLinesAdapter.kt

@@ -31,29 +31,28 @@ import com.ubergeek42.WeechatAndroid.Weechat
 import com.ubergeek42.WeechatAndroid.copypaste.showCopyDialog
 import com.ubergeek42.WeechatAndroid.relay.Buffer
 import com.ubergeek42.WeechatAndroid.relay.BufferEye
+import com.ubergeek42.WeechatAndroid.relay.HeaderLine
 import com.ubergeek42.WeechatAndroid.relay.Line
 import com.ubergeek42.WeechatAndroid.relay.LineSpec
 import com.ubergeek42.WeechatAndroid.relay.Lines
 import com.ubergeek42.WeechatAndroid.relay.MarkerLine
 import com.ubergeek42.WeechatAndroid.relay.SquiggleLine
-import com.ubergeek42.WeechatAndroid.relay.HeaderLine
 import com.ubergeek42.WeechatAndroid.search.Search
 import com.ubergeek42.WeechatAndroid.service.P
 import com.ubergeek42.WeechatAndroid.upload.i
 import com.ubergeek42.WeechatAndroid.upload.main
-import com.ubergeek42.WeechatAndroid.views.AnimatedRecyclerView
-import com.ubergeek42.WeechatAndroid.views.Animation
 import com.ubergeek42.WeechatAndroid.utils.Toaster
 import com.ubergeek42.WeechatAndroid.utils.forEachReversedIndexed
 import com.ubergeek42.WeechatAndroid.utils.isAnyOf
 import com.ubergeek42.WeechatAndroid.utils.ulet
+import com.ubergeek42.WeechatAndroid.views.AnimatedRecyclerView
+import com.ubergeek42.WeechatAndroid.views.Animation
 import com.ubergeek42.WeechatAndroid.views.LineView
 import com.ubergeek42.WeechatAndroid.views.solidColor
 import com.ubergeek42.WeechatAndroid.views.updateMargins
 import com.ubergeek42.cats.Kitty
 import com.ubergeek42.cats.Root
 import com.ubergeek42.weechat.ColorScheme
-import java.util.*
 
 
 class ChatLinesAdapter @MainThread constructor(
@@ -218,13 +217,17 @@ class ChatLinesAdapter @MainThread constructor(
     private var updateStep = 0
     private var style = 0
 
-    @AnyThread @Synchronized private fun onLinesChanged(animation: Animation) = ulet(buffer) { buffer ->
+    @AnyThread @Synchronized private fun onLinesChanged(
+        animation: Animation = Animation.Default,
+        diffLineContents: Boolean = false
+    ) = ulet(buffer) { buffer ->
         val thisUpdateStep = synchronized (updateLock) { ++updateStep }
 
         val newLines = buffer.getLinesCopy()
         val newStyle = buffer.style     // todo synchronization?
 
-        val diffResult = DiffUtil.calculateDiff(DiffCallback(lines, newLines, style == newStyle), false)
+        val diffCallback = DiffCallback(lines, newLines, style == newStyle, diffLineContents)
+        val diffResult = DiffUtil.calculateDiff(diffCallback, false)
 
         Weechat.runOnMainThreadASAP {
             synchronized (updateLock) {
@@ -253,27 +256,27 @@ class ChatLinesAdapter @MainThread constructor(
     ////////////////////////////////////////////////////////////////////////////////////////////////
 
     @MainThread @Synchronized override fun onGlobalPreferencesChanged(numberChanged: Boolean) {
-        onLinesChanged(Animation.Default)
+        onLinesChanged()
     }
 
     @WorkerThread override fun onLinesListed() {
-        onLinesChanged(Animation.NewLinesFetched)
+        onLinesChanged(Animation.NewLinesFetched, diffLineContents = true)
     }
 
     @AnyThread override fun onLineAdded() {
         onLinesChanged(Animation.LastLineAdded)
     }
 
     @WorkerThread override fun onTitleChanged() {
-        onLinesChanged(Animation.Default)
+        onLinesChanged()
     }
 
     @WorkerThread override fun onBufferClosed() {}
 
     ////////////////////////////////////////////////////////////////////////////////////////////////
 
     @MainThread fun loadLinesWithoutAnimation() {
-        onLinesChanged(Animation.None)
+        onLinesChanged(Animation.None, diffLineContents = true)
     }
 
     @MainThread @Synchronized fun loadLinesSilently() = ulet(buffer) { buffer ->
@@ -323,6 +326,7 @@ class ChatLinesAdapter @MainThread constructor(
         private val oldLines: List<Line>,
         private val newLines: List<Line>,
         private val sameStyle: Boolean,
+        private val diffLineContents: Boolean,
     ) : DiffUtil.Callback() {
         override fun getOldListSize() = oldLines.size
         override fun getNewListSize() = newLines.size
@@ -332,10 +336,16 @@ class ChatLinesAdapter @MainThread constructor(
         }
 
         override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
-            if (newItemPosition == 0) {
-                return oldLines[oldItemPosition] === newLines[newItemPosition]
+            return if (newItemPosition == 0) {
+                // Header line, always present
+                oldLines[oldItemPosition] === newLines[newItemPosition]
+            } else if (!sameStyle) {
+                false
+            } else if (diffLineContents) {
+                oldLines[oldItemPosition].visuallyEqualsTo(newLines[newItemPosition])
+            } else {
+                true
             }
-            return sameStyle
         }
     }
 }

app/src/main/java/com/ubergeek42/WeechatAndroid/relay/Line.kt

@@ -21,7 +21,7 @@ import com.ubergeek42.weechat.Color
 import com.ubergeek42.weechat.ColorScheme
 
 
-open class Line constructor(
+open class Line(
     @JvmField val pointer: Long,
     @JvmField val type: LineSpec.Type,
     @JvmField val timestamp: Long,
@@ -103,5 +103,13 @@ open class Line constructor(
     val timestampedIrcLikeString: String get() =
             timestampString?.let { timestamp -> "$timestamp $ircLikeString" } ?: ircLikeString
 
+    fun visuallyEqualsTo(other: Line) =
+        type == other.type &&
+        timestamp == other.timestamp &&
+        rawPrefix == other.rawPrefix &&
+        rawMessage == other.rawMessage &&
+        isHighlighted == other.isHighlighted &&
+        displayAs == other.displayAs
+
     override fun toString() = "Line(${pointer.as0x}): $ircLikeString)"
 }