From 75d2df1aa5a7ec0518ea6cfe51d6ca8f44226649 Mon Sep 17 00:00:00 2001
From: Ian Gulliver <flamingcow@gmail.com>
Date: Sat, 24 Sep 2022 17:24:37 -0700
Subject: [PATCH] Document state transitions

---
 ultrasonic2relay/main.go | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/ultrasonic2relay/main.go b/ultrasonic2relay/main.go
index f84da04..d03f369 100644
--- a/ultrasonic2relay/main.go
+++ b/ultrasonic2relay/main.go
@@ -84,6 +84,13 @@ func main() {
 			}
 		}
 
+		// States:
+		// on 0, off *,   r Off, onUntil zero   -> stable
+		// on 1, off *,   r Off, onUntil zero   -> turn on
+		// on *, off *,   r On,  onUntil future -> stay on
+		// on *, off *,   r On,  onUntil past   -> turn off
+		// on *, off all, r Off, onUntil past   -> reset state
+
 		if on > 0 {
 			// At least one on, turn on
 			if onUntil.IsZero() {
@@ -97,6 +104,7 @@ func main() {
 			}
 		}
 
+		// Time target expired
 		if !onUntil.IsZero() && onUntil.Before(time.Now()) {
 			r.Off()
 		}