Refactor command system

PluralKit.Bot/CommandSystem/Parameters.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+
+namespace PluralKit.Bot.CommandSystem
+{
+    public class Parameters
+    {
+        private static readonly Dictionary<char, char> _quotePairs = new Dictionary<char, char>()
+        {
+            {'\'', '\''}, {'"', '"'}
+        };
+
+        private readonly string _cmd;
+        private int _ptr;
+
+        public Parameters(string cmd)
+        {
+            _cmd = cmd;
+            _ptr = 0;
+        }
+
+        public string Pop()
+        {
+            var positions = NextWordPosition();
+            if (positions == null) return "";
+
+            var (start, end, advance) = positions.Value;
+            _ptr = end + advance;
+            return _cmd.Substring(start, end - start).Trim();
+        }
+
+        public string Peek()
+        {
+            var positions = NextWordPosition();
+            if (positions == null) return "";
+
+            var (start, end, _) = positions.Value;
+            return _cmd.Substring(start, end - start).Trim();
+        }
+
+        public string Remainder() => _cmd.Substring(_ptr).Trim();
+        public string FullCommand => _cmd;
+
+        // Returns tuple of (startpos, endpos, advanceafter)
+        private ValueTuple<int, int, int>? NextWordPosition()
+        {
+            // Is this the end of the string?
+            if (_cmd.Length <= _ptr) return null;
+
+            // Is this a quoted word?
+            if (_quotePairs.ContainsKey(_cmd[_ptr]))
+            {
+                // This is a quoted word, find corresponding end quote and return span
+                var endQuote = _quotePairs[_cmd[_ptr]];
+                var endQuotePosition = _cmd.IndexOf(endQuote, _ptr + 1);
+                
+                // Position after the end quote should be a space (or EOL)
+                // Otherwise treat it as a standard word that's not quoted
+                if (_cmd.Length == endQuotePosition + 1 || _cmd[endQuotePosition + 1] == ' ')
+                {
+                    if (endQuotePosition == -1)
+                    {
+                        // This is an unterminated quoted word, just return the entire word including the start quote
+                        // TODO: should we do something else here?
+                        return (_ptr, _cmd.Length, 0);
+                    }
+
+                    return (_ptr + 1, endQuotePosition, 1);
+                }
+            }
+
+            // Not a quoted word, just find the next space and return as appropriate
+            var wordEnd = _cmd.IndexOf(' ', _ptr + 1);
+            return wordEnd != -1 ? (_ptr, wordEnd, 1) : (_ptr, _cmd.Length, 0);
+        }
+    }
+}