From 8170df95ade2fe233b86c4405bd92e28fc95c7ff Mon Sep 17 00:00:00 2001
From: Eugene Blikh <bigbes@gmail.com>
Date: Tue, 28 Apr 2026 03:05:31 +0300
Subject: [PATCH] crew-movement: walkability + BFS pathfinding with tests

---
 tiles.go      |  59 +++++++++++++++++++++++++++++
 tiles_test.go | 103 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 162 insertions(+)
 create mode 100644 tiles.go
 create mode 100644 tiles_test.go

diff --git a/tiles.go b/tiles.go
new file mode 100644
index 0000000000000000000000000000000000000000..d0a346836acca1dc5a58aa14ba576d8dcb7746b4
--- /dev/null
+++ b/tiles.go
@@ -0,0 +1,59 @@
+package main
+
+func walkableTiles(s Ship) map[[2]int]bool {
+	walk := make(map[[2]int]bool)
+	for _, r := range s.Rooms {
+		for y := r.GridY; y < r.GridY+r.GridH; y++ {
+			for x := r.GridX; x < r.GridX+r.GridW; x++ {
+				walk[[2]int{x, y}] = true
+			}
+		}
+	}
+	return walk
+}
+
+func bfsPath(walk map[[2]int]bool, from, to [2]int) [][2]int {
+	if from == to {
+		return nil
+	}
+	if !walk[to] {
+		return nil
+	}
+
+	neighbours := [4][2]int{{1, 0}, {-1, 0}, {0, 1}, {0, -1}}
+	visited := map[[2]int]bool{from: true}
+	parent := map[[2]int][2]int{}
+	queue := [][2]int{from}
+
+	for len(queue) > 0 {
+		cur := queue[0]
+		queue = queue[1:]
+		for _, d := range neighbours {
+			next := [2]int{cur[0] + d[0], cur[1] + d[1]}
+			if !walk[next] || visited[next] {
+				continue
+			}
+			visited[next] = true
+			parent[next] = cur
+			if next == to {
+				return reconstructPath(parent, from, to)
+			}
+			queue = append(queue, next)
+		}
+	}
+	return nil
+}
+
+func reconstructPath(parent map[[2]int][2]int, from, to [2]int) [][2]int {
+	var path [][2]int
+	cur := to
+	for cur != from {
+		path = append(path, cur)
+		cur = parent[cur]
+	}
+	// reverse
+	for i, j := 0, len(path)-1; i < j; i, j = i+1, j-1 {
+		path[i], path[j] = path[j], path[i]
+	}
+	return path
+}
diff --git a/tiles_test.go b/tiles_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..52848fe7c0a9a275c9fcf895601d6401639af549
--- /dev/null
+++ b/tiles_test.go
@@ -0,0 +1,103 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestWalkableTiles_coversAllRooms(t *testing.T) {
+	s := NewPlayerShip()
+	walk := walkableTiles(s)
+	if len(walk) != 54 {
+		t.Fatalf("expected 54 walkable tiles, got %d", len(walk))
+	}
+	// Spot-check one tile from each room
+	checks := [][2]int{
+		{4, 10}, // Pilot center
+		{7, 7},  // Weapons
+		{7, 10}, // Shields
+		{7, 13}, // MedBay
+		{11, 10}, // Engines center
+	}
+	for _, tc := range checks {
+		if !walk[tc] {
+			t.Errorf("expected tile %v to be walkable", tc)
+		}
+	}
+	// Off-ship tile must be absent
+	if walk[[2]int{0, 0}] {
+		t.Error("tile (0,0) must not be walkable")
+	}
+}
+
+func TestWalkableTiles_ignoresOutside(t *testing.T) {
+	s := NewPlayerShip()
+	walk := walkableTiles(s)
+	if walk[[2]int{0, 0}] {
+		t.Error("tile (0,0) must not be walkable")
+	}
+	if walk[[2]int{20, 20}] {
+		t.Error("tile (20,20) must not be walkable")
+	}
+}
+
+func TestBFSPath_sameTile(t *testing.T) {
+	s := NewPlayerShip()
+	walk := walkableTiles(s)
+	path := bfsPath(walk, [2]int{4, 10}, [2]int{4, 10})
+	if len(path) != 0 {
+		t.Errorf("expected empty path for same-tile, got %v", path)
+	}
+}
+
+func TestBFSPath_adjacentTile(t *testing.T) {
+	s := NewPlayerShip()
+	walk := walkableTiles(s)
+	path := bfsPath(walk, [2]int{4, 10}, [2]int{5, 10})
+	if len(path) != 1 {
+		t.Fatalf("expected path of length 1, got %d: %v", len(path), path)
+	}
+	if path[0] != ([2]int{5, 10}) {
+		t.Errorf("expected path[0] == {5,10}, got %v", path[0])
+	}
+}
+
+func TestBFSPath_unreachable(t *testing.T) {
+	s := NewPlayerShip()
+	walk := walkableTiles(s)
+	path := bfsPath(walk, [2]int{4, 10}, [2]int{0, 0})
+	if len(path) != 0 {
+		t.Errorf("expected empty path for unreachable target, got %v", path)
+	}
+}
+
+func TestBFSPath_throughShields(t *testing.T) {
+	s := NewPlayerShip()
+	walk := walkableTiles(s)
+	from := [2]int{4, 10}
+	to := [2]int{11, 10}
+	path := bfsPath(walk, from, to)
+	if len(path) != 7 {
+		t.Fatalf("expected path length 7, got %d: %v", len(path), path)
+	}
+	if path[len(path)-1] != to {
+		t.Errorf("expected last tile %v, got %v", to, path[len(path)-1])
+	}
+	for _, tile := range path {
+		if !walk[tile] {
+			t.Errorf("path contains non-walkable tile %v", tile)
+		}
+	}
+}
+
+func TestBFSPath_deterministic(t *testing.T) {
+	s := NewPlayerShip()
+	walk := walkableTiles(s)
+	from := [2]int{4, 10}
+	to := [2]int{11, 10}
+	p1 := bfsPath(walk, from, to)
+	p2 := bfsPath(walk, from, to)
+	if !reflect.DeepEqual(p1, p2) {
+		t.Errorf("non-deterministic: first=%v second=%v", p1, p2)
+	}
+}