Refactor message filter grammar and add `~` as an alias for `-` in negated filters for better UX when using CLI

DiscordChatExporter.Core/Exporting/Filtering/Parsing/FilterGrammar.cs

@@ -15,16 +15,17 @@ internal static class FilterGrammar
         from close in Character.EqualTo(open)
         select value;
 
-    private static readonly TextParser<char> FreeCharacter =
-        Character.Matching(c =>
+    private static readonly TextParser<string> UnquotedString =
+        Parse.OneOf(
+            EscapedCharacter,
+            Character.Matching(
+                c =>
                     !char.IsWhiteSpace(c) &&
                     // Avoid all special tokens used by the grammar
-                c is not ('(' or ')' or '"' or '\'' or '-' or '|' or '&'),
+                    c is not ('(' or ')' or '"' or '\'' or '-' or '~' or '|' or '&'),
                 "any character except whitespace or `(`, `)`, `\"`, `'`, `-`, `|`, `&`"
-        );
-
-    private static readonly TextParser<string> UnquotedString =
-        Parse.OneOf(EscapedCharacter, FreeCharacter).AtLeastOnce().Text();
+            )
+        ).AtLeastOnce().Text();
 
     private static readonly TextParser<string> String =
         Parse.OneOf(QuotedString, UnquotedString).Named("text string");
@@ -64,19 +65,7 @@ internal static class FilterGrammar
         .Select(k => (MessageFilter) new HasMessageFilter(k))
         .Named("has:<value>");
 
-    private static readonly TextParser<MessageFilter> NegatedFilter = Character
-        .EqualTo('-')
-        .IgnoreThen(Parse.Ref(() => StandaloneFilter!))
-        .Select(f => (MessageFilter) new NegatedMessageFilter(f));
-
-    private static readonly TextParser<MessageFilter> GroupedFilter =
-        from open in Character.EqualTo('(')
-        from content in Parse.Ref(() => BinaryExpressionFilter!).Token()
-        from close in Character.EqualTo(')')
-        select content;
-
-    private static readonly TextParser<MessageFilter> StandaloneFilter = Parse.OneOf(
-        GroupedFilter,
+    private static readonly TextParser<MessageFilter> PrimitiveFilter = Parse.OneOf(
         FromFilter,
         MentionsFilter,
         ReactionFilter,
@@ -84,19 +73,33 @@ internal static class FilterGrammar
         ContainsFilter
     );
 
-    private static readonly TextParser<MessageFilter> UnaryExpressionFilter = Parse.OneOf(
-        NegatedFilter,
-        StandaloneFilter
-    );
+    private static readonly TextParser<MessageFilter> GroupedFilter =
+        from open in Character.EqualTo('(')
+        from content in Parse.Ref(() => ChainedFilter!).Token()
+        from close in Character.EqualTo(')')
+        select content;
 
-    private static readonly TextParser<MessageFilter> BinaryExpressionFilter = Parse.Chain(
+    private static readonly TextParser<MessageFilter> NegatedFilter = Character
+        // Dash is annoying to use from CLI due to conflicts with options, so we provide tilde as an alias
+        .In('-', '~')
+        .IgnoreThen(Parse.OneOf(GroupedFilter, PrimitiveFilter))
+        .Select(f => (MessageFilter) new NegatedMessageFilter(f));
+
+    private static readonly TextParser<MessageFilter> ChainedFilter = Parse.Chain(
+        // Operator
         Parse.OneOf(
             // Explicit operator
             Character.In('|', '&').Token().Try(),
             // Implicit operator (resolves to 'and')
             Character.WhiteSpace.AtLeastOnce().IgnoreThen(Parse.Return(' '))
         ),
-        UnaryExpressionFilter,
+        // Operand
+        Parse.OneOf(
+            NegatedFilter,
+            GroupedFilter,
+            PrimitiveFilter
+        ),
+        // Reducer
         (op, left, right) => op switch
         {
             '|' => new BinaryExpressionMessageFilter(left, right, BinaryExpressionKind.Or),
@@ -105,5 +108,5 @@ internal static class FilterGrammar
     );
 
     public static readonly TextParser<MessageFilter> Filter =
-        BinaryExpressionFilter.Token().AtEnd();
+        ChainedFilter.Token().AtEnd();
 }