Introduce movement Rays

These reflect the fact that a piece can't jump over another piece
(unless it's a knight).

Issue #5

rs/src/board.rs

@@ -47,12 +47,6 @@ impl Position {
             self.file.delta(delta_file)?,
         ))
     }
-    fn deltas_to_valid_positions(&self, deltas: &[(i8, i8)]) -> Vec<Position> {
-        deltas
-            .iter()
-            .filter_map(|&delta_rank_file| self.delta(delta_rank_file).ok())
-            .collect()
-    }
 }
 
 #[derive(PartialEq, Eq, Hash, Clone, Copy)]
@@ -173,30 +167,73 @@ pub struct Piece {
     pub piece_type: PieceType,
 }
 
+struct Ray {
+    unit: (i8, i8),
+    coefs: Option<Vec<u8>>,
+    source: Position,
+    current: u8,
+}
+
+impl Ray {
+    fn new(unit: (i8, i8), coefs: Option<Vec<u8>>, source: Position) -> Self {
+        Ray {
+            unit,
+            coefs,
+            source,
+            current: 0,
+        }
+    }
+}
+
+impl Iterator for Ray {
+    type Item = Position;
+    fn next(&mut self) -> Option<Position> {
+        let (delta_unit_rank, delta_unit_file) = self.unit;
+        let coef = i8::try_from(match &self.coefs {
+            None => self.current + 1,
+            Some(coefs) => {
+                let crt_usize = self.current as usize;
+                if crt_usize >= coefs.len() {
+                    return None;
+                }
+                coefs[crt_usize]
+            }
+        })
+        .unwrap();
+        let delta = (
+            delta_unit_rank.checked_mul(coef).unwrap(),
+            delta_unit_file.checked_mul(coef).unwrap(),
+        );
+        let rval = self.source.delta(delta).ok();
+        self.current = self.current.wrapping_add(1);
+        rval
+    }
+}
+
 impl Piece {
-    fn get_moves(&self, position: &Position) -> Vec<Position> {
-        let deltas = match self.piece_type {
-            PieceType::Pawn => self._pawn_get_move_deltas(position),
-        };
-        position.deltas_to_valid_positions(&deltas)
-    }
-    fn get_captures(&self, position: &Position) -> Vec<Position> {
-        let deltas = match self.piece_type {
-            PieceType::Pawn => self._pawn_get_capture_deltas(),
-        };
-        position.deltas_to_valid_positions(&deltas)
-    }
-    fn _pawn_get_move_deltas(&self, position: &Position) -> Vec<(i8, i8)> {
+    fn get_move_rays(&self, position: &Position) -> Vec<Ray> {
+        match self.piece_type {
+            PieceType::Pawn => {
                 let direction = self.color.get_direction();
-        if position.rank == self.color.get_pawn_rank() {
-            vec![(direction, 0), (2 * direction, 0)]
+                let coefs = if position.rank == self.color.get_pawn_rank() {
+                    vec![1, 2]
                 } else {
-            vec![(direction, 0)]
+                    vec![1]
+                };
+                vec![Ray::new((direction, 0), Some(coefs), position.clone())]
             }
         }
-    fn _pawn_get_capture_deltas(&self) -> Vec<(i8, i8)> {
+    }
+    fn get_capture_rays(&self, position: &Position) -> Vec<Ray> {
+        match self.piece_type {
+            PieceType::Pawn => {
                 let direction = self.color.get_direction();
-        vec![(direction, 1), (direction, -1)]
+                vec![
+                    Ray::new((direction, 1), Some(vec![1]), position.clone()),
+                    Ray::new((direction, -1), Some(vec![1]), position.clone()),
+                ]
+            }
+        }
     }
 }
 
@@ -214,7 +251,7 @@ impl Board {
             None => self.state.remove(&position),
         };
     }
-    fn move_from_to(
+    fn relocate(
         &mut self,
         source: &Position,
         target: Position,
@@ -240,6 +277,17 @@ impl Board {
     pub fn iter(&self) -> impl Iterator<Item = (&Position, &Piece)> {
         self.state.iter()
     }
+    fn cut_move_ray(&self, ray: Ray) -> impl Iterator<Item = Position> + '_ {
+        ray.into_iter().take_while(|position| self.get_at(position).is_none())
+    }
+    fn find_capture(&self, ray: Ray) -> Option<Position> {
+        // I'm not expecting to call this if there's no piece in the position
+        let crt_piece = self.get_at(&ray.source).unwrap();
+        ray.into_iter().find(|p| match self.get_at(p) {
+            None => false,
+            Some(piece) => piece.color != crt_piece.color,
+        })
+    }
     pub fn get_legal_moves(
         &self,
         position: &Position,
@@ -249,16 +297,13 @@ impl Board {
             Some(piece) => piece,
         };
         let valid_moves = piece
-            .get_moves(position)
+            .get_move_rays(position)
             .into_iter()
-            .filter(|pos| self.get_at(pos).is_none());
-        let valid_captures =
-            piece.get_captures(position).into_iter().filter(|pos| match self
-                .get_at(pos)
-            {
-                None => false,
-                Some(other_piece) => (other_piece.color != piece.color),
-            });
+            .flat_map(|ray| self.cut_move_ray(ray));
+        let valid_captures = piece
+            .get_capture_rays(position)
+            .into_iter()
+            .filter_map(|ray| self.find_capture(ray));
         Some(valid_moves.chain(valid_captures).collect())
     }
     pub fn make_move(
@@ -270,7 +315,7 @@ impl Board {
             Err(())
         } else {
             // We checked that there is a piece at source in get_legal_moves
-            self.move_from_to(source, target)
+            self.relocate(source, target)
         }
     }
 }