feat(markdown): support timestamps

Signed-off-by: Infi <wingit@geist.ga>

app/src/main/java/chat/revolt/components/generic/Markdown.kt

@@ -29,6 +29,7 @@ import chat.revolt.internals.markdown.CustomEmoteRule
 import chat.revolt.internals.markdown.MarkdownContext
 import chat.revolt.internals.markdown.MarkdownParser
 import chat.revolt.internals.markdown.MarkdownState
+import chat.revolt.internals.markdown.TimestampRule
 import chat.revolt.internals.markdown.UserMentionRule
 import chat.revolt.internals.markdown.createCodeRule
 import chat.revolt.internals.markdown.createInlineCodeRule
@@ -61,6 +62,7 @@ fun UIMarkdown(
                 UserMentionRule(),
                 ChannelMentionRule(),
                 CustomEmoteRule(),
+                TimestampRule(),
             )
             .addRules(
                 createCodeRule(context, codeBlockColor.toArgb()),

app/src/main/java/chat/revolt/internals/markdown/MarkdownNodes.kt

@@ -1,7 +1,15 @@
 package chat.revolt.internals.markdown
 
 import android.text.SpannableStringBuilder
+import android.text.format.DateUtils
+import android.util.Log
 import com.discord.simpleast.core.node.Node
+import kotlinx.datetime.Clock
+import kotlinx.datetime.Instant
+import kotlinx.datetime.toJavaInstant
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+import java.util.Locale
 
 class UserMentionNode(private val userId: String) : Node<MarkdownContext>() {
     override fun render(builder: SpannableStringBuilder, renderContext: MarkdownContext) {
@@ -30,3 +38,67 @@ class CustomEmoteNode(private val emoteId: String) : Node<MarkdownContext>() {
         )
     }
 }
+
+class TimestampNode(private val timestamp: Long, private val modifier: String? = null) :
+    Node<MarkdownContext>() {
+    override fun render(builder: SpannableStringBuilder, renderContext: MarkdownContext) {
+        val normalisedModifier = modifier.orEmpty().removePrefix(":")
+
+        val instant = Instant.fromEpochSeconds(timestamp)
+        val javaInstant = instant.toJavaInstant()
+
+        try {
+            if (timestamp < 0) {
+                builder.append("<invalid timestamp>")
+                return
+            }
+
+            val outString = when (normalisedModifier) {
+                // 22:22
+                "t" -> DateTimeFormatter.ofPattern("HH:mm")
+                    .withLocale(Locale.getDefault())
+                    .withZone(ZoneId.systemDefault())
+                    .format(javaInstant)
+
+                // 22:22:22
+                "T" -> DateTimeFormatter.ofPattern("HH:mm:ss")
+                    .withLocale(Locale.getDefault())
+                    .withZone(ZoneId.systemDefault())
+                    .format(javaInstant)
+
+                // 22 September 2022
+                "D" -> DateTimeFormatter.ofPattern("dd MMMM yyyy")
+                    .withLocale(Locale.getDefault())
+                    .withZone(ZoneId.systemDefault())
+                    .format(javaInstant)
+
+                // 22 September 2022 22:22
+                "f" -> DateTimeFormatter.ofPattern("dd MMMM yyyy HH:mm")
+                    .withLocale(Locale.getDefault())
+                    .withZone(ZoneId.systemDefault())
+                    .format(javaInstant)
+
+                // Thursday, 22 September 2022 22:22
+                "F" -> DateTimeFormatter.ofPattern("EEEE, dd MMMM yyyy HH:mm")
+                    .withLocale(Locale.getDefault())
+                    .withZone(ZoneId.systemDefault())
+                    .format(javaInstant)
+
+                // 9 months ago
+                "R" -> DateUtils.getRelativeTimeSpanString(
+                    timestamp * 1000,
+                    Clock.System.now().toEpochMilliseconds(),
+                    DateUtils.MINUTE_IN_MILLIS
+                )
+
+                // Fallback. Shouldn't happen
+                else -> timestamp.toString()
+            }
+
+            builder.append(outString)
+        } catch (e: Exception) {
+            Log.e("TimestampNode", "Failed to parse timestamp", e)
+            builder.append("<invalid timestamp>")
+        }
+    }
+}

app/src/main/java/chat/revolt/internals/markdown/MarkdownRules.kt

@@ -47,6 +47,26 @@ class CustomEmoteRule<S> :
     }
 }
 
+class TimestampRule<S> :
+    Rule<MarkdownContext, TimestampNode, S>(Pattern.compile("^<t:([0-9]+?)(:[tTDfFR])?>")) {
+    override fun parse(
+        matcher: Matcher,
+        parser: Parser<MarkdownContext, in TimestampNode, S>,
+        state: S
+    ): ParseSpec<MarkdownContext, S> {
+        return ParseSpec.createTerminal(
+            TimestampNode(
+                try {
+                    matcher.group(1)!!.toLong()
+                } catch (e: NumberFormatException) {
+                    -1
+                },
+                matcher.group(2)
+            ), state
+        )
+    }
+}
+
 fun <RC, S> createInlineCodeRule(context: Context, backgroundColor: Int): Rule<RC, Node<RC>, S> {
     return CodeRules.createInlineCodeRule(
         { listOf(TextAppearanceSpan(context, R.style.Code_TextAppearance)) },

app/src/main/java/chat/revolt/screens/chat/views/channel/ChannelScreen.kt

@@ -70,6 +70,7 @@ import chat.revolt.internals.markdown.CustomEmoteRule
 import chat.revolt.internals.markdown.MarkdownContext
 import chat.revolt.internals.markdown.MarkdownParser
 import chat.revolt.internals.markdown.MarkdownState
+import chat.revolt.internals.markdown.TimestampRule
 import chat.revolt.internals.markdown.UserMentionRule
 import chat.revolt.internals.markdown.createCodeRule
 import chat.revolt.internals.markdown.createInlineCodeRule
@@ -256,6 +257,7 @@ fun ChannelScreen(
                                         UserMentionRule(),
                                         ChannelMentionRule(),
                                         CustomEmoteRule(),
+                                        TimestampRule(),
                                     )
                                     .addRules(
                                         createCodeRule(context, codeBlockColor.toArgb()),