Refactor system/member privacy commands

PluralKit.Core/Models/Privacy/PrivacyExt.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace PluralKit.Core
+{
+    public static class PrivacyExt
+    {
+        public static bool CanAccess(this PrivacyLevel level, LookupContext ctx) =>
+            level == PrivacyLevel.Public || ctx == LookupContext.ByOwner;
+
+        public static string LevelName(this PrivacyLevel level) => 
+            level == PrivacyLevel.Public ? "public" : "private";
+
+        public static T Get<T>(this PrivacyLevel level, LookupContext ctx, T input, T fallback = default) =>
+            level.CanAccess(ctx) ? input : fallback;
+        
+        public static string Explanation(this PrivacyLevel level) =>
+            level switch
+            {
+                PrivacyLevel.Private => "**Private** (visible only when queried by you)",
+                PrivacyLevel.Public => "**Public** (visible to everyone)",
+                _ => throw new ArgumentOutOfRangeException(nameof(level), level, null)
+            };
+
+        public static bool TryGet<T>(this PrivacyLevel level, LookupContext ctx, T input, out T output, T absentValue = default)
+        {
+            output = default;
+            if (!level.CanAccess(ctx))
+                return false;
+            if (Equals(input, absentValue))
+                return false;
+
+            output = input;
+            return true;
+        }
+    }
+}