From 09fded7925fe932927c8308de446e29d03d8eccd Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor@ccxvii.net>
Date: Thu, 9 Mar 2023 12:00:38 +0100
Subject: Allow backtracking from supply chains!

A supply chain can backtrack over another supply chain.

Example:
Axis Unit A is in supply in Skeleidima.
It can trace supply via Ghemines.
It can also trace supply via Msus/Antelat/Agedabia.

Axis Unit B in Mechili SW can trace a line to A in Skeleidima.
This line overlaps with the Skeleidima/Msus/Antelat line, and our
"don't backtrack" code would either prevent one of these lines from
forming.

Track the "visit depth" instead of a boolean, and increase the
depth every time we start a new supply line. Allow re-visits of a hex
unless it's been visited before during this depth, or unless it is the
head of a supply line.
---
 rules.js | 36 ++++++++++++++++++++----------------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/rules.js b/rules.js
index dfacafe..3408f96 100644
--- a/rules.js
+++ b/rules.js
@@ -1165,13 +1165,14 @@ function is_supply_line_blocked(here, next, side) {
 	return false
 }
 
-function trace_supply_highway(here) {
+function trace_supply_highway(here, v) {
 	if (supply_src[here])
 		return true
 
 	let has_supply = false
 
-	supply_visited[here] = 1
+	let save_v = supply_visited[here]
+	supply_visited[here] = v
 
 	for (let s = 0; s < 6; ++s) {
 		let next = here + hexnext[s]
@@ -1179,7 +1180,8 @@ function trace_supply_highway(here) {
 		if (next < first_hex || next > last_hex || !hex_exists[next])
 			continue
 
-		if (supply_visited[next])
+		let next_v = supply_visited[next]
+		if (next_v === v || (next_v > 0 && supply_friendly[next] > 1))
 			continue
 
 		let side = to_side(here, next, s)
@@ -1189,12 +1191,12 @@ function trace_supply_highway(here) {
 		let road = side_road[side]
 		if (road === HIGHWAY) {
 			if (supply_friendly[next] > 1) {
-				if (supply_net[next] || trace_supply_chain(next, 0, 3)) {
+				if (supply_net[next] || trace_supply_chain(next, 0, 3, v+1)) {
 					supply_line[side] = 1
 					has_supply = true
 				}
 			} else {
-				if (trace_supply_highway(next)) {
+				if (trace_supply_highway(next, v)) {
 					supply_line[side] = 1
 					has_supply = true
 				}
@@ -1202,7 +1204,7 @@ function trace_supply_highway(here) {
 		}
 	}
 
-	supply_visited[here] = 0
+	supply_visited[here] = save_v
 
 	if (has_supply)
 		supply_net[here] = 1
@@ -1210,13 +1212,14 @@ function trace_supply_highway(here) {
 	return has_supply
 }
 
-function trace_supply_chain(here, n, range) {
+function trace_supply_chain(here, n, range, v) {
 	if (supply_src[here])
 		return true
 
 	let has_supply = false
 
-	supply_visited[here] = 1
+	let save_v = supply_visited[here]
+	supply_visited[here] = v
 
 	for (let s = 0; s < 6; ++s) {
 		let next = here + hexnext[s]
@@ -1224,7 +1227,8 @@ function trace_supply_chain(here, n, range) {
 		if (next < first_hex || next > last_hex || !hex_exists[next])
 			continue
 
-		if (supply_visited[next])
+		let next_v = supply_visited[next]
+		if (next_v === v || (next_v > 0 && supply_friendly[next] > 1))
 			continue
 
 		let side = to_side(here, next, s)
@@ -1233,7 +1237,7 @@ function trace_supply_chain(here, n, range) {
 
 		let road = side_road[side]
 		if (road === HIGHWAY) {
-			if (trace_supply_highway(next)) {
+			if (trace_supply_highway(next, v)) {
 				supply_line[side] = 1
 				has_supply = true
 			}
@@ -1242,12 +1246,12 @@ function trace_supply_chain(here, n, range) {
 		let next_range = min(range, SUPPLY_RANGE[road])
 		if (n + 1 <= next_range) {
 			if (supply_friendly[next] > 1) {
-				if (supply_net[next] || trace_supply_chain(next, 0, 3)) {
+				if (supply_net[next] || trace_supply_chain(next, 0, 3, v+1)) {
 					supply_line[side] = 1
 					has_supply = true
 				}
 			} else {
-				if (trace_supply_chain(next, n + 1, next_range)) {
+				if (trace_supply_chain(next, n + 1, next_range, v)) {
 					supply_line[side] = 1
 					has_supply = true
 				}
@@ -1255,7 +1259,7 @@ function trace_supply_chain(here, n, range) {
 		}
 	}
 
-	supply_visited[here] = 0
+	supply_visited[here] = save_v
 
 	if (has_supply)
 		supply_net[here] = 1
@@ -1289,7 +1293,7 @@ function trace_supply_network(start) {
 		if (supply_friendly[x] > 0 && x !== start) {
 			if (supply_friendly[x] > 1 && supply_net[x])
 				continue
-			trace_supply_chain(x, 0, 3)
+			trace_supply_chain(x, 0, 3, 1)
 		}
 	}
 }
@@ -1312,7 +1316,7 @@ function trace_fortress_network(fortress, ss) {
 			if (is_map_hex(x) && x !== fortress) {
 				if (supply_friendly[x] > 1 && supply_net[x])
 					continue
-				trace_supply_chain(x, 0, 3)
+				trace_supply_chain(x, 0, 3, 1)
 			}
 		}
 	}
@@ -1348,7 +1352,7 @@ function can_trace_supply_to_base_or_fortress(base, from) {
 	supply_visited.fill(0)
 	supply_src.fill(0)
 	supply_src[base] = 1
-	return trace_supply_chain(from, 0, 3)
+	return trace_supply_chain(from, 0, 3, 1, 1)
 }
 
 function update_axis_supply() {
-- 
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