From bf2bccbc7d0fe3dee3c16753fa5373670b65285f Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Mon, 22 Jan 2024 08:12:55 -0800
Subject: [PATCH] [board] Implement PositionBuilder::from_position

Create a PositionBuilder from a Position.
---
 .../src/position/builders/position_builder.rs | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/board/src/position/builders/position_builder.rs b/board/src/position/builders/position_builder.rs
index 1d8c3fb..7c68413 100644
--- a/board/src/position/builders/position_builder.rs
+++ b/board/src/position/builders/position_builder.rs
@@ -25,6 +25,27 @@ impl Builder {
         Self::default()
     }
 
+    pub fn from_position(position: &Position) -> Self {
+        let pieces = BTreeMap::from_iter(
+            position
+                .pieces(Color::White)
+                .chain(position.pieces(Color::Black))
+                .map(|placed_piece| (placed_piece.square(), *placed_piece.piece())),
+        );
+
+        let white_king = position.king_square(Color::White);
+        let black_king = position.king_square(Color::Black);
+
+        Self {
+            player_to_move: position.player_to_move(),
+            flags: position.flags(),
+            pieces,
+            kings: [white_king, black_king],
+            ply_counter: position.ply_counter(),
+            move_number: position.move_number(),
+        }
+    }
+
     pub fn to_move(&mut self, player: Color) -> &mut Self {
         self.player_to_move = player;
         self