Move a whole bunch of stuff to the new chessfriend_board package

board/src/en_passant.rs

@@ -0,0 +1,48 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use chessfriend_core::{Rank, Square};
+
+/// En passant information.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct EnPassant {
+    target: Square,
+    capture: Square,
+}
+
+impl EnPassant {
+    fn _capture_square(target: Square) -> Option<Square> {
+        let (file, rank) = target.file_rank();
+        match rank {
+            Rank::THREE => Some(Square::from_file_rank(file, Rank::FOUR)),
+            Rank::SIX => Some(Square::from_file_rank(file, Rank::FIVE)),
+            _ => None,
+        }
+    }
+
+    /// Return en passant information for a particular target square. The target
+    /// square is the square a pawn capturing en passant will move to.
+    ///
+    /// Return `None` if the square is not eligible for en passant.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// use chessfriend_board::en_passant::EnPassant;
+    /// use chessfriend_core::Square;
+    /// assert!(EnPassant::from_target_square(Square::E3).is_some());
+    /// assert!(EnPassant::from_target_square(Square::B4).is_none());
+    /// ```
+    pub fn from_target_square(target: Square) -> Option<Self> {
+        Self::_capture_square(target).map(|capture| Self { target, capture })
+    }
+
+    /// The square the capturing piece will move to.
+    pub fn target_square(self) -> Square {
+        self.target
+    }
+
+    /// The square on which the captured pawn sits.
+    pub fn capture_square(self) -> Square {
+        self.capture
+    }
+}