From 78027aaaa063038413daf6a1555f30a29f67a74f Mon Sep 17 00:00:00 2001
From: CrispyPin <crispin@tasa.se>
Date: Sat, 7 Dec 2024 23:19:32 +0100
Subject: [PATCH] fix update order dependent behavior of wires when flipped

---
 src/marble_engine.rs | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/src/marble_engine.rs b/src/marble_engine.rs
index e4c997c..bb897fe 100644
--- a/src/marble_engine.rs
+++ b/src/marble_engine.rs
@@ -17,6 +17,7 @@ pub struct Machine {
 	marbles: Vec<Pos>,
 	powered: Vec<Pos>,
 	events: Vec<Event>,
+	flipper_events: Vec<Pos>,
 
 	input: Vec<u8>,
 	input_index: usize,
@@ -45,6 +46,7 @@ impl Machine {
 			marbles: Vec::new(),
 			powered: Vec::new(),
 			events: Vec::new(),
+			flipper_events: Vec::new(),
 			input,
 			input_index: 0,
 			output: Vec::new(),
@@ -290,11 +292,31 @@ impl Machine {
 		}
 
 		// process triggers
+		self.flipper_events.clear();
 		for pos in triggers_activated {
 			for dir in Direction::ALL {
 				self.propagate_power(dir, dir.step(pos));
 			}
 		}
+
+		// process flipped tiles
+		for &p in &self.flipper_events {
+			let Some(target) = self.board.get_mut(p) else {
+				continue;
+			};
+			match target {
+				Tile::Powerable(PTile::Wire(wire_type), _) => {
+					*wire_type = match *wire_type {
+						WireType::Vertical => WireType::Horizontal,
+						WireType::Horizontal => WireType::Vertical,
+						WireType::Cross => WireType::Cross,
+					}
+				}
+				Tile::Mirror(mirror) => mirror.flip(),
+				Tile::Arrow(dir) => *dir = dir.opposite(),
+				_ => (),
+			};
+		}
 	}
 
 	fn propagate_power(&mut self, dir: Direction, pos: Pos) {
@@ -359,21 +381,7 @@ impl Machine {
 					}
 				}
 				PTile::Flipper => {
-					let Some(target) = self.board.get_mut(front_pos) else {
-						return;
-					};
-					match target {
-						Tile::Powerable(PTile::Wire(wire_type), _) => {
-							*wire_type = match *wire_type {
-								WireType::Vertical => WireType::Horizontal,
-								WireType::Horizontal => WireType::Vertical,
-								WireType::Cross => WireType::Cross,
-							}
-						}
-						Tile::Mirror(mirror) => mirror.flip(),
-						Tile::Arrow(dir) => *dir = dir.opposite(),
-						_ => (),
-					};
+					self.flipper_events.push(front_pos);
 				}
 				PTile::Gate(gate) => {
 					let gate = *gate;