Shared/Localizations: Add translatable Units formatting (#5063)

Content.Shared/Localizations/Localization.cs

@@ -33,6 +33,7 @@ namespace Content.Shared.Localizations
             loc.AddFunction(culture, "PRESSURE", FormatPressure);
             loc.AddFunction(culture, "POWERWATTS", FormatPowerWatts);
             loc.AddFunction(culture, "POWERJOULES", FormatPowerJoules);
+            loc.AddFunction(culture, "UNITS", FormatUnits);
             loc.AddFunction(culture, "TOSTRING", args => FormatToString(culture, args));
             loc.AddFunction(culture, "LOC", FormatLoc);
         }
@@ -85,5 +86,45 @@ namespace Content.Shared.Localizations
         {
             return FormatUnitsGeneric(args, "zzzz-fmt-power-joules");
         }
+
+        private static ILocValue FormatUnits(LocArgs args)
+        {
+            if (!Units.Types.TryGetValue(((LocValueString) args.Args[0]).Value, out var ut))
+                throw new ArgumentException($"Unknown unit type {((LocValueString) args.Args[0]).Value}");
+
+            var fmtstr = ((LocValueString) args.Args[1]).Value;
+
+            double max = Double.NegativeInfinity;
+            var iargs = new double[args.Args.Count - 1];
+            for (var i = 2; i < args.Args.Count; i++)
+            {
+                var n = ((LocValueNumber) args.Args[i]).Value;
+                if (n > max)
+                    max = n;
+
+                iargs[i - 2] = n;
+            }
+
+            if (!ut!.TryGetUnit(max, out var mu))
+                throw new ArgumentException("Unit out of range for type");
+
+            var fargs = new object[iargs.Length];
+
+            for (var i = 0; i < iargs.Length; i++)
+                fargs[i] = iargs[i] * mu.Factor;
+
+            fargs[^1] = Loc.GetString($"units-{mu.Unit.ToLower()}");
+
+            // Before anyone complains about "{"+"${...}", at least it's better than MS's approach...
+            // https://docs.microsoft.com/en-us/dotnet/standard/base-types/composite-formatting#escaping-braces
+            // 
+            // Note that the closing brace isn't replaced so that format specifiers can be applied.
+            var res = String.Format(
+                    fmtstr.Replace("{UNIT", "{" + $"{fargs.Length - 1}"),
+                    fargs
+            );
+
+            return new LocValueString(res);
+        }
     }
 }