From f4ac92ff894982d85dddee439f93ce6bd05cb578 Mon Sep 17 00:00:00 2001
From: Pavel Lutskov <pavel.lutskov@gmail.com>
Date: Wed, 5 Mar 2025 21:40:20 +0100
Subject: [PATCH] Implement basic move evaluation

It ain't much but it's honest work
---
 rs/src/board.rs  |  2 ++
 rs/src/engine.rs | 64 ++++++++++++++++++++++++++++++++++++++++++------
 rs/src/ui.rs     |  4 +--
 3 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/rs/src/board.rs b/rs/src/board.rs
index 8cf5b8b..3099cdb 100644
--- a/rs/src/board.rs
+++ b/rs/src/board.rs
@@ -264,6 +264,7 @@ impl PieceType {
     }
 }
 
+#[derive(Clone)]
 pub struct Piece {
     pub color: Color,
     pub piece_type: PieceType,
@@ -292,6 +293,7 @@ impl Piece {
     }
 }
 
+#[derive(Clone)]
 pub struct Board {
     state: HashMap<Position, Piece>,
 }
diff --git a/rs/src/engine.rs b/rs/src/engine.rs
index 42e3482..6203a1b 100644
--- a/rs/src/engine.rs
+++ b/rs/src/engine.rs
@@ -1,5 +1,19 @@
 use crate::board;
-use rand::seq::IteratorRandom;
+use crate::rand::Rng;
+
+impl board::PieceType {
+    fn value(&self) -> f32 {
+        match self {
+            board::PieceType::Pawn => 1.0,
+            board::PieceType::Knight => 3.0,
+        }
+    }
+}
+
+pub struct Move_ {
+    pub source: board::Position,
+    pub target: board::Position,
+}
 
 pub struct Engine {
     board: board::Board,
@@ -43,16 +57,38 @@ impl Engine {
             self.board.relocate(source, target)
         }
     }
-    pub fn choose_move(
+    pub fn evaluate_position(&self, 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())
+            .sum()
+    }
+    pub fn evaluate_move(
         &self,
         color: &board::Color,
-    ) -> Option<(board::Position, board::Position)> {
-        self.board
+        move_: &Move_,
+    ) -> Result<f32, ()> {
+        let mut board = self.board.clone();
+        board.relocate(&move_.source, move_.target.clone())?;
+        Ok(match color {
+            board::Color::White => 1.0,
+            board::Color::Black => -1.0,
+        } * self.evaluate_position(&board))
+    }
+    pub fn choose_move(&self, color: &board::Color) -> Option<Move_> {
+        let all_moves = self
+            .board
             .iter()
             .filter_map(|(source, piece)| {
                 if &piece.color == color {
                     if let Ok(targets) = self.get_legal_moves(source) {
-                        Some(targets.map(|target| (source.clone(), target)))
+                        Some(targets.map(|target| Move_ {
+                            source: source.clone(),
+                            target,
+                        }))
                     } else {
                         None
                     }
@@ -60,7 +96,21 @@ impl Engine {
                     None
                 }
             })
-            .flatten()
-            .choose(&mut rand::thread_rng())
+            .flatten();
+        let mut rng = rand::thread_rng();
+        Some(
+            all_moves
+                .map(|move_| {
+                    (
+                        self.evaluate_move(color, &move_).unwrap()
+                            + rng.gen::<f32>() * 0.1,
+                        move_,
+                    )
+                })
+                .max_by(|(score1, _), (score2, _)| {
+                    score1.partial_cmp(score2).unwrap()
+                })?
+                .1,
+        )
     }
 }
diff --git a/rs/src/ui.rs b/rs/src/ui.rs
index b05867e..d54d257 100644
--- a/rs/src/ui.rs
+++ b/rs/src/ui.rs
@@ -258,8 +258,8 @@ impl Ui {
                         format!("Couldn't parse color code {}", color_char)
                     })?,
                 ) {
-                    Some((source, target)) => {
-                        Ok(format!("{},{}", source, target))
+                    Some(move_) => {
+                        Ok(format!("{},{}", move_.source, move_.target))
                     }
                     None => {
                         Err(format!("No move possible for {}", color_char))