Display day change messages

Similar to weechat.look.day_change.

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

@@ -8,6 +8,11 @@ import com.ubergeek42.WeechatAndroid.utils.Linkify
 import com.ubergeek42.WeechatAndroid.utils.Utils
 import com.ubergeek42.WeechatAndroid.utils.invalidatableLazy
 import com.ubergeek42.weechat.Color
+import java.time.Instant
+import java.time.LocalDate
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+import java.time.format.FormatStyle
 import java.util.*
 import kotlin.properties.Delegates.observable
 
@@ -46,6 +51,13 @@ class Lines {
     var maxUnfilteredSize = P.lineIncrement
         private set
 
+    private var unfilteredDate = LocalDate.MIN
+    private var filteredDate = LocalDate.MIN
+
+    private var lastOldDate = LocalDate.MIN
+    private var lastNewDate = LocalDate.MIN
+    private lateinit var lastDateLine: Line
+
     // after reconnecting, in *full sync mode*, we are receiving and adding new lines to buffers.
     // there can be inconsistencies; if some lines were added while we were offline,
     // we can't display them, but can display what's on top and what's on bottom.
@@ -91,17 +103,53 @@ class Lines {
         if (status != Status.Fetching) return
         unfiltered.clear()
         filtered.clear()
+        unfilteredDate = LocalDate.MIN
+        filteredDate = LocalDate.MIN
+
         for (line in lines) {
             addLast(line)
         }
     }
 
+    private fun getDateChangeLine(oldDate: LocalDate, newDate: LocalDate) : Line {
+        if (lastOldDate != oldDate || lastNewDate != newDate) {
+            val tstamp = newDate.atStartOfDay(ZoneId.systemDefault()).toEpochSecond() * 1000
+            var msg = newDate.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM))
+            if (oldDate.plusDays(1) != newDate) {
+                msg += " (" +
+                       oldDate.format(DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM)) +
+                       ")"
+            }
+            msg += " --"
+            lastDateLine = Line(++fakePointerCounter, LineSpec.Type.Other, tstamp, "--", msg,
+                                nick = null, isVisible = true, isHighlighted = false,
+                                LineSpec.DisplayAs.Unspecified, LineSpec.NotifyLevel.Low)
+            lastOldDate = oldDate
+            lastNewDate = newDate
+        }
+        return lastDateLine
+    }
+
     fun addLast(line: Line) {
         if (shouldAddSquiggleOnNewLine) {
             shouldAddSquiggleOnNewLine = false
             if (status == Status.Init && unfiltered.size > 0) addLast(SquiggleLine())   // invisible
         }
 
+        val newDate = Instant.ofEpochSecond(line.timestamp / 1000)
+                      .atZone(ZoneId.systemDefault())
+                      .toLocalDate()
+
+        if (unfilteredDate != newDate) {
+            unfiltered.addLast(getDateChangeLine(unfilteredDate, newDate))
+            unfilteredDate = newDate
+        }
+
+        if (line.isVisible && filteredDate != newDate) {
+            filtered.addLast(getDateChangeLine(filteredDate, newDate))
+            filteredDate = newDate
+        }
+
         if (shouldAddSquiggleOnNewVisibleLine && line.isVisible) {
             shouldAddSquiggleOnNewVisibleLine = false
             if (status == Status.Init && filtered.size > 0) {