From 1bafdcdb7e14e531aefc65a58c9cdb43df4230f5 Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Wed, 30 Oct 2024 09:33:25 -0400
Subject: [PATCH] Added support for inverted matches; moved escape character
 detection to its own function

---
 main.go | 51 +++++++++++++++++++++++----------------------------
 1 file changed, 23 insertions(+), 28 deletions(-)

diff --git a/main.go b/main.go
index bc96293..1c05625 100644
--- a/main.go
+++ b/main.go
@@ -44,6 +44,16 @@ func shuntingYard(re string) []postfixNode {
 	for i < len(re_runes) {
 		re_postfix = append(re_postfix, re_runes[i])
 		if re_runes[i] == '[' && (i == 0 || re_runes[i-1] != '\\') { // We do not touch things inside brackets, unless they are escaped
+			re_postfix[len(re_postfix)-1] = LBRACKET // Replace the '[' character with LBRACKET. This allows for easier parsing og all characters (including opening and closing brackets) within the character class
+			invertMatch := false
+			toAppend := make([]rune, 0)                      // Holds all the runes in the current character class
+			if i < len(re_runes)-1 && re_runes[i+1] == '^' { // Inverting class - match everything NOT in brackets
+				invertMatch = true
+				i++
+			}
+			if i < len(re_runes)-1 && re_runes[i+1] == ']' { // Nothing inside brackets - panic.
+				panic("Empty character class.")
+			}
 			for re_runes[i] != ']' {
 				i++ // Skip all characters inside brackets
 				// TODO: Check for escaped characters
@@ -57,15 +67,21 @@ func shuntingYard(re string) []postfixNode {
 					}
 
 					for i := rangeStart; i <= rangeEnd; i++ {
-						re_postfix = append(re_postfix, i)
+						toAppend = append(toAppend, i)
 					}
 
 					i += 2 // Skip start and hyphen (end will automatically be skipped on next iteration of loop)
 					continue
 				}
-				re_postfix = append(re_postfix, re_runes[i])
+				toAppend = append(toAppend, re_runes[i])
 			}
-			continue
+			// Replace the last character (which should have been ']', with RBRACKET
+			toAppend[len(toAppend)-1] = RBRACKET
+			if invertMatch {
+				toAppend = setDifference(dotChars(), toAppend) // Take the inverse of the set by getting the difference between it and all dot characters
+				toAppend = append(toAppend, RBRACKET)          // Since RBRACKET doesn't exist in dotChars, it wouldn't have been return in setDifference. We manually append it here.
+			}
+			re_postfix = append(re_postfix, toAppend...)
 		}
 		if (re_runes[i] != '(' && re_runes[i] != '|' && re_runes[i] != '\\') || (i > 0 && re_runes[i-1] == '\\') { // Every character should be concatenated if it is escaped
 			if i < len(re_runes)-1 {
@@ -104,28 +120,7 @@ func shuntingYard(re string) []postfixNode {
 				panic("ERROR: Backslash with no escape character.")
 			}
 			i++
-			switch re_postfix[i] {
-			case 's': // Whitespace
-				outQueue = append(outQueue, newPostfixNode(whitespaceChars...))
-			case 'S': // Non-whitespace - I am doing this in a fancy way, generating all dot characters, then removing whitespace characters from it
-				outQueue = append(outQueue, newPostfixNode(slices.DeleteFunc(dotChars(), func(r rune) bool {
-					return slices.Contains(whitespaceChars, r)
-				})...))
-			case 'd': // Digits
-				outQueue = append(outQueue, newPostfixNode(digitChars...))
-			case 'D': // Non-digits - same fancy way as 'S'
-				outQueue = append(outQueue, newPostfixNode(slices.DeleteFunc(dotChars(), func(r rune) bool {
-					return slices.Contains(digitChars, r)
-				})...))
-			case 'w': // word character
-				outQueue = append(outQueue, newPostfixNode(wordChars...))
-			case 'W': // Non-word character - same fancy way as 'S' and 'D'
-				outQueue = append(outQueue, newPostfixNode(slices.DeleteFunc(dotChars(), func(r rune) bool {
-					return slices.Contains(wordChars, r)
-				})...))
-			default: // None of the above - append it as a regular character
-				outQueue = append(outQueue, newPostfixCharNode(re_postfix[i]))
-			}
+			outQueue = append(outQueue, newEscapedNode(re_postfix[i]))
 			continue // Escaped character will automatically be skipped when loop variable increments
 		}
 
@@ -153,11 +148,11 @@ func shuntingYard(re string) []postfixNode {
 				}
 			}
 		}
-		if c == '[' { // Used for character classes
+		if c == LBRACKET { // Used for character classes
 			i++                      // Step forward so we can look at the character class
 			chars := make([]rune, 0) // List of characters -  used only for character classes
 			for i < len(re_postfix) {
-				if re_postfix[i] == ']' {
+				if re_postfix[i] == RBRACKET {
 					break
 				}
 				chars = append(chars, re_postfix[i])
@@ -167,7 +162,7 @@ func shuntingYard(re string) []postfixNode {
 				panic("ERROR: Opening bracket without closing bracket.")
 			}
 			outQueue = append(outQueue, newPostfixNode(chars...))
-			i++ // Step forward to skip closing bracket
+			//	i++ // Step forward to skip closing bracket
 			continue
 		}
 		if c == '(' {