Finished support for -m flag; refactoring pending

main.go

@@ -698,6 +698,12 @@ func main() {
 		}
 		test_runes = []rune(test_str)
 		matchIndices := findAllMatches(startState, test_runes, numGroups)
+
+		// If we are trying to print an invalid index, we just assume no specific matches will be printed.
+		if matchNumFlagEnabled && *matchNum > len(matchIndices) {
+			matchNumFlagEnabled = false
+		}
+
 		if *printMatchesFlag {
 			// if we are in single line mode, print the line on which
 			// the matches occur
@@ -759,21 +765,29 @@ func main() {
 		if substituteFlagEnabled {
 			for i := range test_runes {
 				inMatchIndex := false
-				for _, idx := range matchIndices {
-					if i == idx[0].startIdx {
+				for idx, m := range matchIndices {
+					if !matchNumFlagEnabled || (idx+1) == *matchNum {
+						if i == m[0].startIdx {
 							fmt.Fprintf(out, "%s", *substituteText)
-						i = idx[0].endIdx
+							i = m[0].endIdx
 							inMatchIndex = true
 							break
 						}
 					}
+				}
 				if !inMatchIndex {
 					fmt.Fprintf(out, "%c", test_runes[i])
 				}
 			}
 		} else {
 			for i, c := range test_runes {
-				if indicesToPrint.contains(i) {
+				// Explanation:
+				// 	We print a letter in red if:
+				// 		1. It is in the 'indicesToPrint'
+				// 		2. One of the following:
+				// 			a. The '-m' flag is disabled
+				// 			b. The '-m' flag is enabled, and our current index is in the bounds of the specific match
+				if indicesToPrint.contains(i) && (!matchNumFlagEnabled || (i >= matchIndices[*matchNum-1][0].startIdx && i < matchIndices[*matchNum-1][0].endIdx)) {
 					color.New(color.FgRed).Fprintf(out, "%c", c)
 					// Newline after every match - only if -o is enabled and -v is disabled.
 					if *onlyFlag && !(*invertFlag) {