[board] Move position flags to a Flags struct in its own module

board/src/position/flags.rs

@@ -0,0 +1,73 @@
+// Eryn Wells <eryn@erynwells.me>
+
+use super::position::BoardSide;
+use crate::piece::Color;
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub(super) struct Flags(u8);
+
+impl Flags {
+    #[inline]
+    pub(super) fn player_has_right_to_castle_flag_offset(color: Color, side: BoardSide) -> u8 {
+        ((color as u8) << 1) + side as u8
+    }
+
+    pub(super) fn player_has_right_to_castle(&self, color: Color, side: BoardSide) -> bool {
+        (self.0 & (1 << Self::player_has_right_to_castle_flag_offset(color, side))) != 0
+    }
+
+    pub(super) fn set_player_has_right_to_castle_flag(&mut self, color: Color, side: BoardSide) {
+        self.0 |= 1 << Self::player_has_right_to_castle_flag_offset(color, side);
+    }
+
+    pub(super) fn clear_player_has_right_to_castle_flag(&mut self, color: Color, side: BoardSide) {
+        self.0 &= !(1 << Self::player_has_right_to_castle_flag_offset(color, side));
+    }
+}
+
+impl Default for Flags {
+    fn default() -> Self {
+        Flags(0b00001111)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::Color;
+
+    #[test]
+    fn castle_flags() {
+        assert_eq!(
+            Flags::player_has_right_to_castle_flag_offset(Color::White, BoardSide::King),
+            0
+        );
+        assert_eq!(
+            Flags::player_has_right_to_castle_flag_offset(Color::White, BoardSide::Queen),
+            1
+        );
+        assert_eq!(
+            Flags::player_has_right_to_castle_flag_offset(Color::Black, BoardSide::King),
+            2
+        );
+        assert_eq!(
+            Flags::player_has_right_to_castle_flag_offset(Color::Black, BoardSide::Queen),
+            3
+        );
+    }
+
+    #[test]
+    fn defaults() {
+        let mut flags: Flags = Default::default();
+        assert!(flags.player_has_right_to_castle(Color::White, BoardSide::King));
+        assert!(flags.player_has_right_to_castle(Color::White, BoardSide::Queen));
+        assert!(flags.player_has_right_to_castle(Color::Black, BoardSide::King));
+        assert!(flags.player_has_right_to_castle(Color::Black, BoardSide::Queen));
+
+        flags.clear_player_has_right_to_castle_flag(Color::White, BoardSide::Queen);
+        assert!(flags.player_has_right_to_castle(Color::White, BoardSide::King));
+        assert!(!flags.player_has_right_to_castle(Color::White, BoardSide::Queen));
+        assert!(flags.player_has_right_to_castle(Color::Black, BoardSide::King));
+        assert!(flags.player_has_right_to_castle(Color::Black, BoardSide::Queen));
+    }
+}