feat(commands): add DecayLine formatter (6b)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: HandyS11

src/RustPlusBot.Features.Commands/Formatting/DecayLine.cs

@@ -0,0 +1,42 @@
+using System.Globalization;
+using RustPlusBot.Features.ItemData.Data;
+
+namespace RustPlusBot.Features.Commands.Formatting;
+
+/// <summary>Formats the one-line decay reply.</summary>
+internal static class DecayLine
+{
+    /// <summary>Formats base decay, any present environment variant, and HP for an item.</summary>
+    /// <param name="item">The item (must have non-null <see cref="ItemRecord.Decay"/>).</param>
+    public static string Format(ItemRecord item)
+    {
+        ArgumentNullException.ThrowIfNull(item);
+        ArgumentNullException.ThrowIfNull(item.Decay);
+        var decay = item.Decay;
+
+        var parts = new List<string>();
+        Add(parts, null, decay.Seconds);
+        Add(parts, "outside", decay.OutsideSeconds);
+        Add(parts, "inside", decay.InsideSeconds);
+        Add(parts, "underwater", decay.UnderwaterSeconds);
+
+        var decayPart = parts.Count > 0 ? string.Join(", ", parts) : "—";
+        var hp = decay.Hp is { } h
+            ? string.Create(CultureInfo.InvariantCulture, $" · {h} HP")
+            : string.Empty;
+        return string.Create(CultureInfo.InvariantCulture, $"{item.Name} decays in {decayPart}{hp}");
+
+        static void Add(List<string> into, string? label, int? seconds)
+        {
+            if (seconds is not { } s)
+            {
+                return;
+            }
+
+            var compact = DurationFormat.Compact(TimeSpan.FromSeconds(s));
+            into.Add(label is null
+                ? compact
+                : string.Create(CultureInfo.InvariantCulture, $"{label} {compact}"));
+        }
+    }
+}

tests/RustPlusBot.Features.Commands.Tests/Formatting/DecayFormatterTests.cs

@@ -0,0 +1,28 @@
+using RustPlusBot.Features.Commands.Formatting;
+using RustPlusBot.Features.ItemData.Data;
+
+namespace RustPlusBot.Features.Commands.Tests.Formatting;
+
+public sealed class DecayFormatterTests
+{
+    [Fact]
+    public void DecayLine_ShowsBaseDecayAndHp()
+    {
+        var item = new ItemRecord(1, "Stone Barricade", 1, null, null, null, null,
+            new DecayInfo(900, null, null, null, 100), null);
+        var line = DecayLine.Format(item);
+        Assert.Contains("Stone Barricade", line, StringComparison.Ordinal);
+        Assert.Contains("15m", line, StringComparison.Ordinal);
+        Assert.Contains("100", line, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void DecayLine_ShowsVariantsWhenPresent()
+    {
+        var item = new ItemRecord(1, "Wall", 1, null, null, null, null,
+            new DecayInfo(null, 3600, 7200, null, 250), null);
+        var line = DecayLine.Format(item);
+        Assert.Contains("outside", line, StringComparison.Ordinal);
+        Assert.Contains("inside", line, StringComparison.Ordinal);
+    }
+}