diff --git a/petri/src/lib.rs b/petri/src/lib.rs
index fe9ede4..2afa764 100644
--- a/petri/src/lib.rs
+++ b/petri/src/lib.rs
@@ -13,6 +13,17 @@ pub struct Dish {
 	pub rules: Vec<Rule>,
 	pub types: Vec<CellData>,
 	pub groups: Vec<CellGroup>,
+	#[serde(skip)]
+	cache: Vec<RuleCache>,
+	#[serde(skip)]
+	match_cache: Vec<usize>,
+}
+
+#[derive(Debug)]
+struct RuleCache {
+	rule: usize,
+	variant: usize,
+	matches: Vec<(isize, isize)>,
 }
 
 #[derive(Debug, Default, Serialize, Deserialize)]
@@ -359,6 +370,8 @@ impl Dish {
 				void: true,
 				cells: vec![Cell(0)],
 			}],
+			cache: Vec::new(),
+			match_cache: Vec::new(),
 		}
 	}
 
@@ -366,6 +379,76 @@ impl Dish {
 		for rule in &mut self.rules {
 			rule.generate_variants();
 		}
+		self.rebuild_cache();
+	}
+
+	pub fn rebuild_cache(&mut self) {
+		self.cache.clear();
+		self.match_cache.clear();
+	}
+
+	pub fn update_cache(&mut self, x: isize, y: isize, width: usize, height: usize) {
+		fn overlap(
+			(x1, y1, w1, h1): (isize, isize, usize, usize),
+			(x2, y2, w2, h2): (isize, isize, usize, usize),
+		) -> bool {
+			let horizontal = x1..(x1.wrapping_add_unsigned(w1));
+			let vertical = y1..(y1.wrapping_add_unsigned(h1));
+			horizontal.contains(&x2)
+				|| horizontal.contains(&x2.wrapping_add_unsigned(w2))
+				|| vertical.contains(&y2)
+				|| vertical.contains(&y2.wrapping_add_unsigned(h2))
+		}
+		let edited_rect = (x, y, width, height);
+
+		for cache in &mut self.cache {
+			let rule = &self.rules[cache.rule].variants[cache.variant];
+			let rule_width = rule.width;
+			let rule_height = rule.height;
+
+			// discard all overlapping matches
+			let mut i = 0;
+			while i < cache.matches.len() {
+				let matc = cache.matches[i];
+				let match_rect = (matc.0, matc.1, rule_width, rule_height);
+				if overlap(edited_rect, match_rect) {
+					cache.matches.swap_remove(i);
+				} else {
+					i += 1;
+				}
+			}
+			// check entire changed area and add matches
+			let border_x = rule_width - 1;
+			let border_y = rule_height - 1;
+
+			for px in (x.wrapping_sub_unsigned(border_x))..(x.wrapping_add_unsigned(width)) {
+				for py in (y.wrapping_sub_unsigned(border_y))..(y.wrapping_add_unsigned(height)) {
+					// borrow checker bad >:(
+					// if self.subrule_matches(px, py, &rule) {
+
+					// }
+				}
+			}
+			// TODO
+		}
+	}
+
+	pub fn fire_once(&mut self) {
+		if self.match_cache.is_empty() {
+			return;
+		}
+		let i = random::<usize>() % self.match_cache.len();
+		let i = self.match_cache[i];
+		let rule_cache = &self.cache[i];
+		let match_pos_index = random::<usize>() % rule_cache.matches.len();
+		let (x, y) = rule_cache.matches[match_pos_index];
+
+		let rule = &self.rules[rule_cache.rule].variants[rule_cache.variant];
+		let width = rule.width;
+		let height = rule.height;
+
+		self.apply_rule(x, y, rule_cache.rule, rule_cache.variant);
+		self.update_cache(x, y, width, height);
 	}
 
 	pub fn fire_blindly(&mut self) {
@@ -381,12 +464,8 @@ impl Dish {
 		if enabled_rules.is_empty() {
 			return;
 		}
-		let rule = random::<usize>() % enabled_rules.len();
-		let rule = enabled_rules[rule];
-		self.fire_rule(rule);
-	}
-
-	fn fire_rule(&mut self, rule_index: usize) {
+		let enabled_rule_index = random::<usize>() % enabled_rules.len();
+		let rule_index = enabled_rules[enabled_rule_index];
 		let rule = &self.rules[rule_index];
 		let variant_index = random::<usize>() % rule.variants.len();
 		let variant = &rule.variants[variant_index].clone();
@@ -397,17 +476,22 @@ impl Dish {
 		let y = ((random::<usize>() % (CHUNK_SIZE + border_y)) as isize)
 			.wrapping_sub_unsigned(border_y);
 
-		if !self.subrule_matches(x, y, variant) {
-			return;
+		if self.subrule_matches(x, y, variant) {
+			self.apply_rule(x, y, rule_index, variant_index);
 		}
+	}
 
-		let fail: u8 = random();
-		if rule.failrate > fail {
+	fn apply_rule(&mut self, x: isize, y: isize, rule_index: usize, variant_index: usize) {
+		let rule = &self.rules[rule_index];
+		let variant = &rule.variants[variant_index].clone();
+
+		if rule.failrate > random() {
 			return;
 		}
 
 		let width = variant.width;
 		let height = variant.height;
+
 		let mut old_state = Vec::new();
 		for dy in 0..height {
 			for dx in 0..width {
@@ -436,6 +520,7 @@ impl Dish {
 					RuleCellTo::Copy(x, y) => {
 						let index = x + y * variant.width;
 						if index >= old_state.len() {
+							// TODO sanitize the rules somewhere else and remove this bounds check
 							// the copy source is outside the rule bounds
 							continue;
 						}
@@ -494,6 +579,7 @@ impl Dish {
 		if x >= CHUNK_SIZE || y >= CHUNK_SIZE {
 			return;
 		}
+		self.update_cache(x as isize, y as isize, 1, 1);
 		self.chunk.set_cell(x, y, cell)
 	}
 }