From d6119de05ad6894466ebbc4ed9ae083e76055626 Mon Sep 17 00:00:00 2001
From: cool-mist <n.suryap@gmail.com>
Date: Sat, 4 Jan 2025 19:29:22 +0530
Subject: [PATCH] Add solver

---
 src/engine/board.rs  |  11 +++--
 src/main.rs          |   3 ++
 src/solver/mod.rs    |   1 +
 src/solver/solver.rs | 110 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 120 insertions(+), 5 deletions(-)
 create mode 100644 src/solver/mod.rs
 create mode 100644 src/solver/solver.rs

diff --git a/src/engine/board.rs b/src/engine/board.rs
index c378d4a..235b064 100644
--- a/src/engine/board.rs
+++ b/src/engine/board.rs
@@ -7,14 +7,15 @@ use super::{
     square::{sq, Square},
 };
 
+#[derive(Clone)]
 pub(crate) struct Board {
     pub(crate) cells: [[Square; 4]; 4],
-    legal_moves: HashSet<Move>,
-    pieces_remaining: i8,
-    game_state: GameState,
+    pub(crate) legal_moves: HashSet<Move>,
+    pub(crate) game_state: GameState,
+    pieces_remaining: u8,
 }
 
-#[derive(PartialEq, Eq, Debug)]
+#[derive(PartialEq, Eq, Debug, Clone)]
 pub enum GameState {
     NotStarted,
     InProgress,
@@ -256,7 +257,7 @@ impl Board {
         if (start.rank < 3 && start.file > 0) {
             let mut south = start.rank;
             let mut west = start.file;
-            while south < 4 && west != 0 {
+            while south < 3 && west != 0 {
                 south += 1;
                 west -= 1;
                 if let Some(piece) = self.cells[west][south].occupied() {
diff --git a/src/main.rs b/src/main.rs
index 1aab287..cc451e9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,7 @@
 #[allow(unused)]
 mod engine;
 
+#[allow(unused)]
+mod solver;
+
 fn main() {}
diff --git a/src/solver/mod.rs b/src/solver/mod.rs
new file mode 100644
index 0000000..7f10d6f
--- /dev/null
+++ b/src/solver/mod.rs
@@ -0,0 +1 @@
+pub(crate) mod solver;
diff --git a/src/solver/solver.rs b/src/solver/solver.rs
new file mode 100644
index 0000000..362bff6
--- /dev/null
+++ b/src/solver/solver.rs
@@ -0,0 +1,110 @@
+use crate::engine::{
+    board::{Board, GameState},
+    r#move::Move,
+};
+
+pub(crate) struct Solver {
+    pub(crate) board: Board,
+    moves: Vec<Move>,
+}
+
+impl Solver {
+    pub(crate) fn new(board: Board) -> Solver {
+        Solver {
+            board,
+            moves: vec![],
+        }
+    }
+
+    fn clone(&self, m: Move) -> Self {
+        let mut moves = self.moves.clone();
+        let mut board = self.board.clone();
+        moves.push(m.clone());
+        board.make_move(m);
+        Solver { board, moves }
+    }
+
+    pub(crate) fn solve(&self) -> Vec<Vec<Move>> {
+        let mut solutions = Vec::new();
+        if let GameState::Won = self.board.game_state {
+            solutions.push(self.moves.clone());
+            return solutions;
+        }
+
+        let GameState::InProgress = self.board.game_state else {
+            return solutions;
+        };
+
+        self.board.legal_moves.iter().for_each(|m| {
+            let mut solver = self.clone(m.clone());
+            let more_solutions = solver.solve();
+            solutions.extend(more_solutions);
+        });
+
+        solutions
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::engine::{
+        coord::{at, Coord},
+        piece::{p, Piece},
+        square::{sq, Square},
+    };
+
+    use super::*;
+
+    #[test]
+    fn solver_smoke() {
+        let mut board = Board::new();
+        // . R . .
+        // R . . P
+        // B . B N
+        // P . N .
+
+        board.set(sq!("P", "a1"));
+        board.set(sq!("B", "a2"));
+        board.set(sq!("R", "a3"));
+        board.set(sq!("R", "b4"));
+        board.set(sq!("N", "c1"));
+        board.set(sq!("B", "c2"));
+        board.set(sq!("N", "d2"));
+        board.set(sq!("P", "d3"));
+
+        let solver = Solver::new(board.clone());
+        let solutions = solver.solve();
+
+        assert_eq!(10, solutions.len());
+
+        for solution in solutions {
+            let mut board = board.clone();
+            solution.iter().for_each(|m| {
+                board.make_move(m.clone());
+            });
+            assert_eq!(GameState::Won, board.game_state);
+        }
+    }
+
+    #[test]
+    fn solver_smoke_no_solution() {
+        // . R . .
+        // R . . .
+        // B . B N
+        // P . N .
+
+        let mut board = Board::new();
+        board.set(sq!("P", "a1"));
+        board.set(sq!("B", "a2"));
+        board.set(sq!("R", "a3"));
+        board.set(sq!("R", "b4"));
+        board.set(sq!("N", "c1"));
+        board.set(sq!("B", "c2"));
+        board.set(sq!("N", "d2"));
+
+        let solver = Solver::new(board.clone());
+        let solutions = solver.solve();
+
+        assert_eq!(0, solutions.len());
+    }
+}