Build format presets from the regional format

DesktopClock.Tests/FormatPresetsTests.cs

@@ -0,0 +1,67 @@
+using System;
+using System.Globalization;
+using System.Linq;
+
+namespace DesktopClock.Tests;
+
+[UseUICulture("en-US")]
+public class FormatPresetsTests
+{
+    private static DateTimeFormatInfo Region(string culture) => CultureInfo.GetCultureInfo(culture).DateTimeFormat;
+
+    [Fact]
+    public void ForClock_KeepsTheUsFormats()
+    {
+        var presets = FormatPresets.ForClock(Region("en-US")).ToDictionary(p => p.Name, p => p.Format);
+
+        Assert.Equal("{h:mm tt}", presets["Time"]);
+        Assert.Equal("{HH:mm}", presets["Time, 24-hour"]);
+        Assert.Equal("{h:mm:ss tt}", presets["Time with seconds"]);
+        Assert.Equal("{ddd}, {MMM d}, {h:mm tt}", presets["Date and time"]);
+        Assert.Equal("{dddd}, {MMMM d}", presets["Date only"]);
+    }
+
+    [Fact]
+    public void ForClock_FollowsRegionalTimeAndDateOrder()
+    {
+        var german = FormatPresets.ForClock(Region("de-DE")).ToDictionary(p => p.Name, p => p.Format);
+        Assert.Equal("{HH:mm}", german["Time"]);
+        Assert.Equal("{dddd}, {d. MMMM}", german["Date only"]);
+
+        var chinese = FormatPresets.ForClock(Region("zh-CN")).ToDictionary(p => p.Name, p => p.Format);
+        Assert.Equal("{dddd}, {M月d日}", chinese["Date only"]);
+    }
+
+    [Theory]
+    [InlineData("en-US", true)]
+    [InlineData("ko-KR", true)]
+    [InlineData("de-DE", false)]
+    [InlineData("ja-JP", false)]
+    [InlineData("fr-CA", false)]
+    public void ForClock_OnlyOffersA24HourPresetWhereTheRegionUses12Hours(string culture, bool expected)
+    {
+        Assert.Equal(expected, FormatPresets.Uses12HourClock(Region(culture)));
+        Assert.Equal(expected, FormatPresets.ForClock(Region(culture)).Any(p => p.Name == "Time, 24-hour"));
+    }
+
+    [Fact]
+    public void DefaultClockFormat_FollowsTheRegion()
+    {
+        Assert.Equal("{ddd}, {MMM d}, {h:mm:ss tt}", FormatPresets.DefaultClockFormat(Region("en-US")));
+        Assert.Equal("{ddd}, {d. MMM}, {HH:mm:ss}", FormatPresets.DefaultClockFormat(Region("de-DE")));
+    }
+
+    [Fact]
+    public void AllPresets_RenderInEveryRegion()
+    {
+        var now = new DateTimeOffset(2026, 9, 22, 13, 1, 22, TimeSpan.Zero);
+
+        foreach (var culture in CultureInfo.GetCultures(CultureTypes.SpecificCultures))
+        {
+            var formats = FormatPresets.ForClock(culture.DateTimeFormat).Select(p => p.Format).Append(FormatPresets.DefaultClockFormat(culture.DateTimeFormat));
+
+            foreach (var format in formats)
+                Assert.True(Tokenizer.FormatWithTokenizerOrFallBack(now, format, culture) != Tokenizer.FormatErrorMessage, $"{culture.Name}: {format}");
+        }
+    }
+}

DesktopClock/CountdownTargetEditor.xaml.cs

@@ -68,7 +68,7 @@ private void BuildPresetButtons()
 
             var example = new TextBlock
             {
-                Text = $"{getTarget():ddd, MMM d} {getTarget():t}",
+                Text = getTarget().ToString($"ddd, {FormatPresets.ShortMonthDayPattern(CultureInfo.CurrentCulture.DateTimeFormat)} {CultureInfo.CurrentCulture.DateTimeFormat.ShortTimePattern}"),
                 FontSize = 12,
                 TextTrimming = TextTrimming.CharacterEllipsis,
             };

DesktopClock/FormatEditor.xaml.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Globalization;
 using System.Windows;
 using System.Windows.Controls;
@@ -23,18 +24,7 @@ public enum FormatEditorMode
 public partial class FormatEditor : UserControl
 {
     // Presets cover the scenarios users most commonly ask for; the raw box stays the escape hatch.
-    private static readonly (string Name, string Format)[] ClockPresets =
-    {
-        (Loc.Get("ClockPresetTime"), "{h:mm tt}"),
-        (Loc.Get("ClockPresetTime24"), "{HH:mm}"),
-        (Loc.Get("ClockPresetTimeSeconds"), "{h:mm:ss tt}"),
-        (Loc.Get("ClockPresetDayTime"), "{ddd}, {h:mm tt}"),
-        (Loc.Get("ClockPresetDateTime"), "{ddd}, {MMM dd}, {h:mm tt}"),
-        (Loc.Get("ClockPresetFullDateTime"), "{dddd}, {MMMM dd}, {h:mm tt}"),
-        (Loc.Get("ClockPresetDateOnly"), "{dddd}, {MMMM dd}"),
-        (Loc.Get("ClockPresetSortable"), "{yyyy-MM-dd} {HH:mm}"),
-        (Loc.Get("ClockPresetIsoWeek"), "{weekYear}-W{week}"),
-    };
+    private static readonly IReadOnlyList<(string Name, string Format)> ClockPresets = FormatPresets.ForClock(CultureInfo.CurrentCulture.DateTimeFormat);
 
     private static readonly (string Name, string Format)[] CountdownPresets =
     {
@@ -55,7 +45,7 @@ private static readonly (string Name, string Token)[] ClockTokens =
         (Loc.Get("TokenMonth"), "{MMM}"),
         (Loc.Get("TokenMonthFull"), "{MMMM}"),
         (Loc.Get("TokenYear"), "{yyyy}"),
-        (Loc.Get("TokenTime"), "{h:mm tt}"),
+        (Loc.Get("TokenTime"), "{" + CultureInfo.CurrentCulture.DateTimeFormat.ShortTimePattern + "}"),
         (Loc.Get("TokenTime24"), "{HH:mm}"),
         (Loc.Get("TokenSeconds"), "{ss}"),
         (Loc.Get("TokenWeekNumber"), "{week}"),

DesktopClock/Properties/Settings.cs

@@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using System.Globalization;
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Windows.Media;
@@ -117,7 +118,7 @@ public static void TrySaveIfLoaded()
     /// Change it when you want a different arrangement, such as adding the weekday, seconds, or a shorter date.
     /// See: <see href="https://learn.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings">Custom date and time format strings</see>.
     /// </remarks>
-    public string Format { get; set; } = "{ddd}, {MMM dd}, {h:mm:ss tt}";
+    public string Format { get; set; } = FormatPresets.DefaultClockFormat(CultureInfo.CurrentCulture.DateTimeFormat);
 
     /// <summary>
     /// Format string used while <see cref="CountdownTo"/> is enabled.

DesktopClock/Utilities/FormatPresets.cs

@@ -0,0 +1,52 @@
+using System.Collections.Generic;
+using System.Globalization;
+using System.Text.RegularExpressions;
+
+namespace DesktopClock;
+
+/// <summary>
+/// Clock formats built from the Windows regional format, so times are 24-hour where people expect it and dates follow the local day and month order.
+/// </summary>
+public static class FormatPresets
+{
+    /// <summary>
+    /// The clock's default format: short weekday, short date, and time with seconds, such as "Tue, Sep 22, 1:01:22 PM" in the US or "Di., 22. Sep., 13:01:22" in Germany.
+    /// </summary>
+    public static string DefaultClockFormat(DateTimeFormatInfo format) =>
+        $"{{ddd}}, {Token(ShortMonthDayPattern(format))}, {Token(format.LongTimePattern)}";
+
+    /// <summary>
+    /// One-click clock formats for common scenarios.
+    /// </summary>
+    public static IReadOnlyList<(string Name, string Format)> ForClock(DateTimeFormatInfo format)
+    {
+        var time = Token(format.ShortTimePattern);
+        var monthDay = Token(format.MonthDayPattern);
+        var presets = new List<(string Name, string Format)> { (Loc.Get("ClockPresetTime"), time) };
+
+        // A 24-hour preset only adds something where the regional time is 12-hour.
+        if (Uses12HourClock(format))
+            presets.Add((Loc.Get("ClockPresetTime24"), "{HH:mm}"));
+
+        presets.Add((Loc.Get("ClockPresetTimeSeconds"), Token(format.LongTimePattern)));
+        presets.Add((Loc.Get("ClockPresetDayTime"), $"{{ddd}}, {time}"));
+        presets.Add((Loc.Get("ClockPresetDateTime"), $"{{ddd}}, {Token(ShortMonthDayPattern(format))}, {time}"));
+        presets.Add((Loc.Get("ClockPresetFullDateTime"), $"{{dddd}}, {monthDay}, {time}"));
+        presets.Add((Loc.Get("ClockPresetDateOnly"), $"{{dddd}}, {monthDay}"));
+        presets.Add((Loc.Get("ClockPresetSortable"), "{yyyy-MM-dd} {HH:mm}"));
+        presets.Add((Loc.Get("ClockPresetIsoWeek"), "{weekYear}-W{week}"));
+        return presets;
+    }
+
+    /// <summary>
+    /// The regional month and day with an abbreviated month, such as "MMM d" in the US or "d. MMM" in Germany.
+    /// </summary>
+    public static string ShortMonthDayPattern(DateTimeFormatInfo format) => format.MonthDayPattern.Replace("MMMM", "MMM");
+
+    /// <summary>
+    /// Whether the regional time format uses a 12-hour clock. Quoted text is skipped so a literal like the "h" in Canadian French "HH 'h' mm" doesn't count.
+    /// </summary>
+    public static bool Uses12HourClock(DateTimeFormatInfo format) => Regex.Replace(format.ShortTimePattern, "'[^']*'", "").Contains("h");
+
+    private static string Token(string pattern) => "{" + pattern + "}";
+}