From 8e8e9e133ff1c55c638a6b581e1efb1c2112ddc6 Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Tue, 29 Oct 2024 20:07:30 -0400
Subject: [PATCH] Fixed matching greediness eg. a(a|b)*a would not match 'aaa'
 in 'aaab'

---
 matching.go | 49 +++++++++++++++++++++++++++++++++++++------------
 1 file changed, 37 insertions(+), 12 deletions(-)

diff --git a/matching.go b/matching.go
index 0fc0cbe..fcc972f 100644
--- a/matching.go
+++ b/matching.go
@@ -56,6 +56,11 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
 	}
 	currentStates = append(currentStates, start)
 
+	// Hold a list of match indices for the current run. When we
+	// can no longer find a match, the match with the largest range is
+	// chosen as the match for the entire string.
+	// This allows us to pick the longest possible match (which is how greedy matching works).
+	tempIndices := make([]matchIndex, 0)
 	// Main loop
 	for i < len(str) {
 		foundPath = false
@@ -74,7 +79,7 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
 			}
 		}
 
-		currentStates = append(currentStates, tempStates...)
+		currentStates, _ = unique_append(currentStates, tempStates...)
 		tempStates = nil
 
 		// Take any transitions corresponding to current character
@@ -83,20 +88,28 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
 				tempStates = append(tempStates, state.transitions[int(str[i])]...)
 				foundPath = true
 			}
+			if state.isLast {
+				endIdx = i
+				tempIndices, _ = unique_append(tempIndices, matchIndex{startIdx + offset, endIdx + offset})
+			}
 		}
-
+		// Recursion - match with rest of string if we have nowhere to go. If we haven't moved in the string, increment the counter by 1 to ensure we don't keep trying the same string over and over
 		if foundPath == false {
-			// This enables the 'greedy' behavior - last-state status is only checked if we didn't find a path forward
-			for _, state := range currentStates {
-				if state.isLast {
-					endIdx = i
-					indices, _ = unique_append(indices, matchIndex{startIdx + offset, endIdx + offset})
-				}
-			}
-			// Recursion - match with rest of string if we have nowhere to go. If we haven't moved in the string, increment the counter by 1 to ensure we don't keep trying the same string over and over
 			if i == startingFrom {
 				i++
 			}
+			// Get the maximum index-range from the list
+			if len(tempIndices) > 0 {
+				indexToAdd := Reduce(tempIndices, func(i1 matchIndex, i2 matchIndex) matchIndex {
+					r1 := i1.endIdx - i1.startIdx
+					r2 := i2.endIdx - i2.startIdx
+					if r1 >= r2 {
+						return i1
+					}
+					return i2
+				})
+				indices, _ = unique_append(indices, indexToAdd)
+			}
 			return findAllMatchesHelper(start, str[i:], indices, offset+i)
 		}
 		currentStates = make([]*State, len(tempStates))
@@ -123,12 +136,24 @@ func findAllMatchesHelper(start *State, str string, indices []matchIndex, offset
 	tempStates = nil
 
 	for _, state := range currentStates {
-		// Only add the match if we the start index is in bounds
+		// Only add the match if the start index is in bounds
 		if state.isLast && startIdx+offset < len(str)+offset {
 			endIdx = i
-			indices, _ = unique_append(indices, matchIndex{startIdx + offset, endIdx + offset})
+			tempIndices, _ = unique_append(tempIndices, matchIndex{startIdx + offset, endIdx + offset})
 		}
 	}
+	// Get the maximum index-range from the list
+	if len(tempIndices) > 0 {
+		indexToAdd := Reduce(tempIndices, func(i1 matchIndex, i2 matchIndex) matchIndex {
+			r1 := i1.endIdx - i1.startIdx
+			r2 := i2.endIdx - i2.startIdx
+			if r1 >= r2 {
+				return i1
+			}
+			return i2
+		})
+		indices, _ = unique_append(indices, indexToAdd)
+	}
 
 	// Default
 	return indices