Make minmax slighly less ugly

Can't vouch for correctness yet tho

rs/src/board.rs

@@ -27,6 +27,12 @@ impl Color {
     }
 }
 
+#[derive(Debug)]
+pub struct Move_ {
+    pub source: Position,
+    pub target: Position,
+}
+
 #[derive(PartialEq, Eq, Hash, Clone, Debug)]
 pub struct Position {
     pub file: File,
@@ -381,4 +387,31 @@ impl Board {
             Err(())
         }
     }
+    pub fn get_legal_moves(
+        &self,
+        position: &Position,
+    ) -> Result<impl Iterator<Item = Position> + '_, ()> {
+        Ok(self.find_moves(position)?.chain(self.find_captures(position)?))
+    }
+    pub fn all_moves_for_color(
+        &self,
+        color: Color,
+    ) -> impl Iterator<Item = Move_> + '_ {
+        self.iter()
+            .filter_map(move |(source, piece)| {
+                if piece.color == color {
+                    if let Ok(targets) = self.get_legal_moves(source) {
+                        Some(targets.map(|target| Move_ {
+                            source: source.clone(),
+                            target,
+                        }))
+                    } else {
+                        None
+                    }
+                } else {
+                    None
+                }
+            })
+            .flatten()
+    }
 }

rs/src/engine.rs

@@ -1,5 +1,5 @@
 use crate::board;
-use crate::rand::Rng;
+use crate::board::Move_;
 
 impl board::PieceType {
     fn value(&self) -> f32 {
@@ -10,10 +10,13 @@ impl board::PieceType {
     }
 }
 
-#[derive(Debug)]
-pub struct Move_ {
-    pub source: board::Position,
-    pub target: board::Position,
+impl board::Color {
+    fn sign(&self) -> f32 {
+        match self {
+            board::Color::Black => -1.0,
+            board::Color::White => 1.0,
+        }
+    }
 }
 
 pub struct Engine {
@@ -37,121 +40,56 @@ impl Engine {
     pub fn set_state(&mut self, board: board::Board) {
         self.board = board;
     }
-    pub fn get_legal_moves<'a>(
-        board: &'a board::Board,
-        position: &board::Position,
-    ) -> Result<impl Iterator<Item = board::Position> + 'a, ()> {
-        Ok(board.find_moves(position)?.chain(board.find_captures(position)?))
-    }
     pub fn make_move(
         &mut self,
         source: &board::Position,
         target: board::Position,
     ) -> Result<(), ()> {
-        if !Engine::get_legal_moves(&self.board, source)?
-            .any(|pos| pos == target)
-        {
+        if !self.board.get_legal_moves(source)?.any(|pos| pos == target) {
             Err(())
         } else {
             // We checked that there is a piece at source in get_legal_moves
             self.board.relocate(source, target)
         }
     }
+    pub fn choose_move(&self, color: &board::Color) -> Option<Move_> {
+        Some(
+            self.board
+                .all_moves_for_color(color.clone())
+                .map(|m| {
+                    let mut board = self.board.clone();
+                    board.relocate(&m.source, m.target.clone()).unwrap();
+                    (minmax(1, &board, color), m)
+                })
+                .max_by(|(s1, _), (s2, _)| s1.partial_cmp(s2).unwrap())?
+                .1,
+        )
+    }
+}
+
 pub fn evaluate_position(board: &board::Board) -> f32 {
     board
         .iter()
-            .map(|(_, piece)| match piece.color {
-                board::Color::White => 1.0,
-                board::Color::Black => -1.0,
-            } * piece.piece_type.value())
+        .map(|(_, piece)| piece.color.sign() * piece.piece_type.value())
         .sum()
 }
-    pub fn evaluate_move(
-        move_: &Move_,
-        board: &board::Board,
-        color: &board::Color,
-    ) -> Result<f32, ()> {
-        let mut board = board.clone();
-        board.relocate(&move_.source, move_.target.clone())?;
-        Ok(match color {
-            board::Color::White => 1.0,
-            board::Color::Black => -1.0,
-        } * Engine::evaluate_position(&board))
-    }
-    fn minmax(
-        depth: i8,
-        board: &board::Board,
-        color: &board::Color,
-    ) -> Option<(f32, Move_)> {
-        eprintln!("Entering minmax for {} at depth {}", color, depth);
-        let all_moves = board
-            .iter()
-            .filter_map(|(source, piece)| {
-                if &piece.color == color {
-                    if let Ok(targets) = Engine::get_legal_moves(board, source)
-                    {
-                        Some(targets.map(|target| Move_ {
-                            source: source.clone(),
-                            target,
-                        }))
-                    } else {
-                        None
-                    }
-                } else {
-                    None
-                }
-            })
-            .flatten();
+
+fn minmax(depth: i8, board: &board::Board, color: &board::Color) -> f32 {
     if depth == 0 {
-            Engine::best_immediate_move(board, color, all_moves)
-        } else if depth > 0 {
-            let best_given_opponent = all_moves.map(|move_| {
-                eprintln!("Finding opponent moves for {:?}", move_);
+        evaluate_position(board) * color.sign()
+    } else {
+        let best_opponent_move_score = board
+            .all_moves_for_color(color.other())
+            .map(|m| {
                 let mut board = board.clone();
-                board.relocate(&move_.source, move_.target.clone()).unwrap();
-                let result = if let Some((opponent_score, _)) =
-                    Engine::minmax(depth - 1, &board, &color.other())
-                {
-                    (-opponent_score, move_)
-                } else {
-                    (0.0, move_)
-                };
-                eprintln!(
-                    "Move {:?} got opponent minmax score {} for {:?}",
-                    result.1, result.0, color
-                );
-                result
-            });
-            best_given_opponent
-                .max_by(|(s1, _), (s2, _)| s1.partial_cmp(s2).unwrap())
-        } else {
-            panic!();
-        }
-    }
-    fn best_immediate_move(
-        board: &board::Board,
-        color: &board::Color,
-        moves: impl Iterator<Item = Move_>,
-    ) -> Option<(f32, Move_)> {
-        let mut rng = rand::thread_rng();
-        Some(
-            moves
-                .map(|move_| {
-                    let score = Engine::evaluate_move(&move_, board, color)
-                        .unwrap()
-                        + rng.gen::<f32>() * 0.05;
-                    eprintln!(
-                        "Move {:?} got immediate score {} for {:?}",
-                        move_, score, color
-                    );
-                    (score, move_)
+                board.relocate(&m.source, m.target).unwrap();
+                minmax(depth - 1, &board, &color.other())
             })
-                .max_by(|(score1, _), (score2, _)| {
-                    score1.partial_cmp(score2).unwrap()
-                })?,
-        )
-    }
-    pub fn choose_move(&self, color: &board::Color) -> Option<Move_> {
-        Some(Engine::minmax(1, &self.board, color)?.1)
+            .max_by(|s1, s2| s1.partial_cmp(s2).unwrap());
+        if let Some(s) = best_opponent_move_score {
+            -s
+        } else {
+            minmax(0, board, color)
+        }
     }
 }

rs/src/ui.rs

@@ -219,10 +219,7 @@ impl Ui {
                 board::Position::parse(position_str).map_err(|_| {
                     format!("Error parsing position {}", position_str)
                 })?;
-            match engine::Engine::get_legal_moves(
-                &self.engine.board,
-                &position,
-            ) {
+            match self.engine.board.get_legal_moves(&position) {
                 Err(_) => {
                     let error = format!("No moves possible from {}", position);
                     Err(error)