redoing bump

kiln-core/src/board.rs

@@ -252,6 +252,41 @@ impl Board {
             .is_some_and(|s| s.pushable().allows(dir))
     }
 
+    /// The object that a move **into** `(x, y)` heading `dir` bumps, if any.
+    ///
+    /// Walks the chain of pushable crates from the target cell in `dir` until it
+    /// reaches something that stops it, and reports the object it presses against:
+    /// - a solid object in the target cell (or at the end of a crate chain) is the
+    ///   bumped object,
+    /// - open space or the player means nothing is bumped,
+    /// - a non-pushable terrain cell (a wall) blocks the chain with no object to bump.
+    ///
+    /// This is what lets *any* solid — the player, another object, or a pushed
+    /// crate — trigger a `bump`: the bumper need not be an object, since we only
+    /// return the *bumped* object's id (the direction it came from is supplied by
+    /// the caller from its move direction).
+    pub fn bump_target(&self, x: usize, y: usize, dir: Direction) -> Option<ObjectId> {
+        let (dx, dy): (i64, i64) = dir.into();
+        let (mut cx, mut cy) = (x, y);
+        loop {
+            match self.solid_at(cx, cy) {
+                None => return None,                       // open space: nothing bumped
+                Some(s) if s.object_id().is_some() => return s.object_id(), // hit an object
+                Some(s) if s.player() => return None,      // the player is never "bumped"
+                // A terrain cell: a pushable crate is walked through; a wall stops us.
+                Some(_) if self.is_pushable(cx, cy, dir) => {
+                    let next = (cx as i64 + dx, cy as i64 + dy);
+                    if !self.in_bounds(next) {
+                        return None; // crate chain runs off the board
+                    }
+                    cx = next.0 as usize;
+                    cy = next.1 as usize;
+                }
+                Some(_) => return None, // non-pushable terrain (wall): no object behind it here
+            }
+        }
+    }
+
     /// Whether the chain of pushable solids starting at `(x, y)` can be shoved one
     /// step in `dir` — i.e. the chain ends at a passable cell rather than the board
     /// edge or a non-pushable solid.