From d191686168e6b8012369a31abb686d680fecf8e6 Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Tue, 22 Oct 2024 16:25:49 -0400
Subject: [PATCH] Rudimentary matching works

---
 main.go     | 16 +++++++++++-----
 matching.go | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+), 5 deletions(-)
 create mode 100644 matching.go

diff --git a/main.go b/main.go
index cc62206..e885475 100644
--- a/main.go
+++ b/main.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"os"
 	"slices"
 )
 
@@ -157,13 +158,18 @@ func thompson(re string) State {
 }
 
 func main() {
+	if len(os.Args) < 3 {
+		fmt.Println("ERROR: Missing cmdline args")
+	}
 	var re string
-	//	fmt.Scanln(&re)
-	re = "abab|abbb"
+	re = os.Args[1]
 	re_postfix := shuntingYard(re)
 	fmt.Println(re_postfix)
 	start := thompson(re_postfix)
-	UNUSED(start)
+	s, e, matched := match(&start, os.Args[2])
+	if matched {
+		fmt.Printf("Matched from %d to %d\n", s, e)
+	} else {
+		fmt.Printf("No match found.\n")
+	}
 }
-
-func UNUSED[T any](val T) {}
diff --git a/matching.go b/matching.go
new file mode 100644
index 0000000..4678cdf
--- /dev/null
+++ b/matching.go
@@ -0,0 +1,52 @@
+package main
+
+// match tries to match the regex represented by given start-state, with
+// the given string
+func match(start *State, str string) (startIdx int, endIdx int, matched bool) {
+	currentStates := make([]*State, 0)
+	tempStates := make([]*State, 0) // Used to store states that should be used in next loop iteration
+	i := 0                          // Index in string
+	// Increment until we hit a character matching the start state
+	if start.isEmpty == false {
+		for int(str[i]) != start.content {
+			i++
+		}
+	}
+	currentStates = append(currentStates, start)
+	startIdx = i
+	i++ // Advance to next character so that we can check for transitions
+	// Main loop
+	for i < len(str) {
+		// If there are any 0-transitions, take those
+		// TODO: Maybe I need to keep taking 0-transitions until I don't have anymore. Needs to be tested
+		for _, state := range currentStates {
+			if len(state.transitions[EPSILON]) > 0 {
+				tempStates = append(tempStates, state.transitions[EPSILON]...)
+			}
+		}
+		copy(currentStates, tempStates)
+		tempStates = nil
+
+		// Take any transitions corresponding to current character
+		for _, state := range currentStates {
+			if len(state.transitions[int(str[i])]) > 0 {
+				tempStates = append(tempStates, state.transitions[int(str[i])]...)
+			}
+		}
+		copy(currentStates, tempStates)
+		tempStates = nil
+
+		// If any of the current-states is a last state, return true.
+		for _, state := range currentStates {
+			if state.isLast {
+				endIdx = i
+				return startIdx, endIdx, true
+			}
+		}
+		i++
+	}
+
+	// We don't seem to have reached a last-state. Return fals
+	return -1, -1, false
+
+}