From ce8910eee718fbba261ba142e45b325db3411283 Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor@ccxvii.net>
Date: Tue, 27 Sep 2022 01:24:32 +0200
Subject: Allow disrupted units to co-exist without creating a battle hex.

Don't create an engagement when retreating.
Fix supply lines in co-exist hexes.
Fix supply lines in former co-exist hexes when one side recovers.
---
 rules.js | 38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/rules.js b/rules.js
index 8e67ee2..6d53263 100644
--- a/rules.js
+++ b/rules.js
@@ -661,9 +661,13 @@ function is_allied_hex(x) {
 }
 
 function is_battle_hex(x) {
+	// battle hex if both sides present and at least one is undisrupted
+	// disrupted units from both sides can peacefully co-exist
 	if (presence_invalid)
 		update_presence()
-	return (presence_axis[x] !== 0) && (presence_allied[x] !== 0)
+	let a = presence_axis[x]
+	let b = presence_allied[x]
+	return (a > 1 && b > 0) || (b > 1 && a > 0)
 }
 
 function is_enemy_hex(x) {
@@ -1146,9 +1150,11 @@ function is_supply_line_blocked(here, next, side) {
 
 	// out of battle hex
 	// can only cannot trace out through friendly sides
-	if (supply_friendly[here] && supply_enemy[here])
-		if (!set_has(supply_defender_sides, side))
-			return true
+	if (supply_friendly[here] > 0 && supply_enemy[here] > 0) {
+		if (set_has(game.axis_hexes, here) || set_has(game.allied_hexes, here))
+			if (!set_has(supply_defender_sides, side))
+				return true
+	}
 
 	return false
 }
@@ -1609,16 +1615,16 @@ function search_redeploy(start) {
 
 // Breadth First Search
 function search_path_bfs(from, cost, start, road, max_cost, retreat, sline, sdist) {
-	let path_enemy, friendly_sides
+	let path_enemy, enemy_sides
 
 	if (presence_invalid)
 		update_presence()
 	if (is_axis_player()) {
 		path_enemy = presence_allied
-		friendly_sides = game.axis_sides
+		enemy_sides = game.allied_sides
 	} else {
 		path_enemy = presence_axis
-		friendly_sides = game.allied_sides
+		enemy_sides = game.axis_sides
 	}
 
 	from.fill(0)
@@ -1671,7 +1677,7 @@ function search_path_bfs(from, cost, start, road, max_cost, retreat, sline, sdis
 			let next_enemy = path_enemy[next]
 			if (retreat) {
 				// must cross friendly hex-side to disengage
-				if (here === start && !set_has(friendly_sides, side))
+				if (here === start && set_has(enemy_sides, side))
 					continue
 				// may only ignore unshielded disrupted units
 				if (next_enemy & 2) // has undisrupted enemy
@@ -1880,7 +1886,7 @@ function can_unit_disengage_and_withdraw(who) {
 		let from = unit_hex(who)
 		for_each_adjacent_hex(from, to => {
 			let side = to_side_id(from, to)
-			if (is_friendly_hexside(side) && !has_enemy_unit(to))
+			if (!is_enemy_hexside(side) && !has_undisrupted_enemy_unit(to))
 				if (sline[side] && sdist[to] <= sdist[from])
 					result = true
 		})
@@ -1893,7 +1899,7 @@ function can_unit_disengage_and_move(who) {
 	let result = false
 	for_each_adjacent_hex(from, to => {
 		let side = to_side_id(from, to)
-		if (is_friendly_hexside(side) && !has_enemy_unit(to))
+		if (!is_enemy_hexside(side) && !has_undisrupted_enemy_unit(to))
 			result = true
 	})
 	return result
@@ -2731,7 +2737,7 @@ function goto_initial_supply_check_recover() {
 function goto_initial_supply_check_rout() {
 	let rout = false
 	for (let x of all_hexes)
-		if (is_friendly_rout_hex(x))
+		if (is_enemy_rout_hex(x))
 			rout = true
 	if (rout)
 		game.state = 'initial_supply_check_rout'
@@ -3670,12 +3676,20 @@ function move_via(who, to, speed, move) {
 	return game.hexside.via.length === 1
 }
 
+function is_engagement_move(to) {
+	if (game.retreat > 0) {
+		// retreating units may co-exist with disrupted enemy units
+		return has_undisrupted_enemy_unit(to)
+	}
+	return has_enemy_unit(to)
+}
+
 function move_unit(who, to, speed, move) {
 	let from = unit_hex(who)
 
 	game.used |= move
 
-	if (is_forced_march_move(from, to, speed) || has_enemy_unit(to)) {
+	if (is_forced_march_move(from, to, speed) || is_engagement_move(to)) {
 		if (move_via(who, to, speed, move)) {
 			if (game.hexside.forced[0])
 				forced_march_via(who, game.hexside.via[0], to, move)
-- 
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