feat: Add setting to display ISO date and time in message list.

Author: alpharesearch

core/preference/api/src/commonMain/kotlin/net/thunderbird/core/preference/display/visualSettings/message/list/MessageListDateTimeFormat.kt

@@ -21,4 +21,11 @@ enum class MessageListDateTimeFormat {
      *      - Examples: "1/23/2026 1:23PM" "23/1/2026 13:23"
      */
     Full,
+
+    /**
+     * ISO 8601 option, which is often requested by power users who prefer a
+     * deterministic, unambiguous format over the system locale defaults.
+     *      - Examples: "2026-01-23 13:23"
+     */
+    ISO,
 }

legacy/ui/legacy/src/main/java/com/fsck/k9/ui/helper/RelativeDateTimeFormatter.kt

@@ -31,17 +31,25 @@ constructor(
         @OptIn(ExperimentalTime::class)
         val now = clock.now().toCalendar()
         val date = timestamp.toCalendar()
-        val format = if (dateTimeFormat == MessageListDateTimeFormat.Full) {
-            FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR or FORMAT_NUMERIC_DATE or FORMAT_SHOW_TIME
-        } else {
-            when {
-                date.isToday() -> FORMAT_SHOW_TIME
-                date.isWithinPastSevenDaysOf(now) -> FORMAT_SHOW_WEEKDAY or FORMAT_ABBREV_WEEKDAY
-                date.isSameYearAs(now) -> FORMAT_SHOW_DATE or FORMAT_ABBREV_MONTH
-                else -> FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR or FORMAT_NUMERIC_DATE
+        return when (dateTimeFormat) {
+            MessageListDateTimeFormat.Contextual -> {
+                val flags = when {
+                    date.isToday() -> FORMAT_SHOW_TIME
+                    date.isWithinPastSevenDaysOf(now) -> FORMAT_SHOW_WEEKDAY or FORMAT_ABBREV_WEEKDAY
+                    date.isSameYearAs(now) -> FORMAT_SHOW_DATE or FORMAT_ABBREV_MONTH
+                    else -> FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR or FORMAT_NUMERIC_DATE
+                }
+                DateUtils.formatDateRange(context, timestamp, timestamp, flags)
+            }
+            MessageListDateTimeFormat.Full -> {
+                val flags = FORMAT_SHOW_TIME or FORMAT_SHOW_DATE or FORMAT_SHOW_YEAR or FORMAT_NUMERIC_DATE
+                DateUtils.formatDateRange(context, timestamp, timestamp, flags)
+            }
+            MessageListDateTimeFormat.ISO -> {
+                val sdf = java.text.SimpleDateFormat("yyyy-MM-dd HH:mm", java.util.Locale.US)
+                sdf.format(java.util.Date(timestamp))
             }
         }
-        return DateUtils.formatDateRange(context, timestamp, timestamp, format)
     }
 }
 

legacy/ui/legacy/src/main/res/values/arrays.xml

@@ -47,5 +47,6 @@
     <string-array name="message_list_date_time_format_values">
         <item>Contextual</item>
         <item>Full</item>
+        <item>ISO</item>
     </string-array>
 </resources>

legacy/ui/legacy/src/main/res/values/arrays_general_settings_strings.xml

@@ -175,6 +175,7 @@
     <string-array name="message_list_date_time_format_entries">
         <item>@string/general_settings_message_list_date_time_format_contextual</item>
         <item>@string/general_settings_message_list_date_time_format_full</item>
+        <item>@string/general_settings_message_list_date_time_format_iso</item>
     </string-array>
 
     <string-array name="post_remove_navigation_entries">

legacy/ui/legacy/src/main/res/values/strings.xml

@@ -320,6 +320,8 @@
     <string name="general_settings_message_list_date_time_format_contextual">Contextual</string>
     <!-- Message List Date/Time format setting option: full -->
     <string name="general_settings_message_list_date_time_format_full">Full</string>
+    <!-- Message List Date/Time format setting option: ISO -->
+    <string name="general_settings_message_list_date_time_format_iso">ISO</string>
 
     <string name="global_settings_privacy_hide_useragent">Hide mail client</string>
     <string name="global_settings_privacy_hide_useragent_detail">Remove User-Agent from mail headers</string>

legacy/ui/legacy/src/test/java/com/fsck/k9/ui/helper/RelativeDateTimeFormatterTest.kt

@@ -159,6 +159,25 @@ class RelativeDateTimeFormatterTest : RobolectricTest() {
         assertThat(displayDate).isEqualTo("12/31/2019, 11:59 PM")
     }
 
+    @Test
+    fun oneMinuteAgo_shouldReturnISODate() {
+        setClockTo("2020-05-17T15:42")
+        val date = "2020-05-17T15:41".toEpochMillis()
+
+        val displayDate = dateTimeFormatter.formatDate(date, MessageListDateTimeFormat.ISO)
+
+        assertThat(displayDate).isEqualTo("2020-05-17 15:41")
+    }
+
+    @Test
+    fun endOfLastYear_shouldReturnISODate() {
+        setClockTo("2020-05-17T15:42")
+        val date = LocalDateTime.parse("2019-12-31T23:59").toEpochMillis()
+
+        val displayDate = dateTimeFormatter.formatDate(date, MessageListDateTimeFormat.ISO)
+
+        assertThat(displayDate).isEqualTo("2019-12-31 23:59")
+    }
     private fun setClockTo(time: String) {
         val dateTime = LocalDateTime.parse(time)
         val timeInMillis = dateTime.toEpochMillis()