From 13aa9ffffe827b97fbb760210b889909ff09c572 Mon Sep 17 00:00:00 2001
From: Mitchell M <mitchoah@gmail.com>
Date: Sun, 21 Dec 2025 20:15:59 -0600
Subject: [PATCH] engine WIP

---
 tak_lib/src/engine.rs | 73 ++++++++++++++++++++++++++++++++++++++++++
 tak_lib/src/lib.rs    | 74 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 146 insertions(+), 1 deletion(-)
 create mode 100644 tak_lib/src/engine.rs

diff --git a/tak_lib/src/engine.rs b/tak_lib/src/engine.rs
new file mode 100644
index 0000000..afb0f7a
--- /dev/null
+++ b/tak_lib/src/engine.rs
@@ -0,0 +1,73 @@
+use crate::{
+    Board, Direction, Move,
+    piece::{ColoredPiece, Piece},
+};
+
+impl<const N: usize> Board<N> {
+    pub fn moves(&self) -> impl Iterator<Item = Move<N>> {
+        let to_move = self.to_move;
+        let tiles = &self.tiles;
+        let can_place_caps = if Self::N_CAPS == 0 {
+            false
+        } else {
+            let caps_on_board = self
+                .tiles
+                .iter()
+                .flat_map(|col| col.iter())
+                .filter(|t| {
+                    let piece = t.top_piece();
+                    piece.color_opt() == Some(to_move) && piece.piece() == Piece::Caps
+                })
+                .count() as u8;
+            caps_on_board < Self::N_CAPS
+        };
+
+        let chords = (0..(N as u8)).flat_map(|x| (0..(N as u8)).map(move |y| (x, y)));
+
+        chords.flat_map(move |(x, y)| {
+            let top_piece = tiles[x as usize][y as usize].top_piece();
+            if top_piece == ColoredPiece::None {
+                // possible moves are place moves
+                get_placement_moves(x, y, can_place_caps)
+            } else if top_piece.color() == to_move {
+                get_movement_moves(x, y, tiles[x as usize][y as usize].stack_len())
+            } else {
+                Vec::with_capacity(0)
+            }
+        })
+    }
+}
+
+fn get_placement_moves<const N: usize>(x: u8, y: u8, can_place_caps: bool) -> Vec<Move<N>> {
+    let mut moves = Vec::with_capacity(2 + can_place_caps as usize);
+    moves.push(Move::Place {
+        piece: Piece::Flat,
+        at: (x, y),
+    });
+    moves.push(Move::Place {
+        piece: Piece::Wall,
+        at: (x, y),
+    });
+    if can_place_caps {
+        moves.push(Move::Place {
+            piece: Piece::Caps,
+            at: (x, y),
+        });
+    }
+    moves
+}
+
+fn get_movement_moves<const N: usize>(x: u8, y: u8, stack_len: u8) -> Vec<Move<N>> {
+    let max_grab = u8::min(N as u8, stack_len + 1);
+
+    // East
+    let max_dist_east = max_grab.min(N as u8 - x - 1);
+    // North
+    let max_dist_north = max_grab.min(N as u8 - y - 1);
+    // West
+    let max_dist_west = max_grab.min(x);
+    // South
+    let max_dist_south = max_grab.min(y);
+}
+
+fn get_drop_amounts<const N: usize>(max_grab: u8, max_dist: u8) -> impl Iterator<Item = [u8; N]> {}
diff --git a/tak_lib/src/lib.rs b/tak_lib/src/lib.rs
index 17d9ebd..25fe370 100644
--- a/tak_lib/src/lib.rs
+++ b/tak_lib/src/lib.rs
@@ -1,10 +1,82 @@
+pub mod engine;
 pub mod piece;
 pub mod tile;
 
-use crate::{piece::Color, tile::Tile};
+use crate::{
+    piece::{Color, Piece},
+    tile::Tile,
+};
+use std::fmt::Display;
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum Direction {
+    East,
+    North,
+    West,
+    South,
+}
+impl Display for Direction {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Direction::East => write!(f, "e"),
+            Direction::North => write!(f, "n"),
+            Direction::West => write!(f, "w"),
+            Direction::South => write!(f, "s"),
+        }
+    }
+}
+impl Direction {
+    const ALL: [Direction; 4] = [
+        Direction::East,
+        Direction::North,
+        Direction::West,
+        Direction::South,
+    ];
+}
 
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
 pub struct Board<const N: usize> {
     to_move: Color,
     tiles: [[Tile; N]; N],
 }
+
+impl<const N: usize> Board<N> {
+    /// The number of capstones in each players' pouches.
+    pub const N_STONES: u8 = match N {
+        3 => 10,
+        4 => 15,
+        5 => 21,
+        6 => 30,
+        8 => 50,
+        _ => panic!("N must be 3, 4, 5, 6, or 8"),
+    };
+    /// The number of capstones in the players' pouches.
+    pub const N_CAPS: u8 = match N {
+        3 => 0,
+        4 => 0,
+        5 => 1,
+        6 => 1,
+        8 => 2,
+        _ => panic!("N must be 3, 4, 5, 6, or 8"),
+    };
+
+    pub fn new() -> Self {
+        Board {
+            to_move: Color::White,
+            tiles: [[Tile::EMPTY; N]; N],
+        }
+    }
+}
+
+pub enum Move<const N: usize> {
+    Place {
+        piece: Piece,
+        at: (u8, u8),
+    },
+    Move {
+        from: (u8, u8),
+        count: u8,
+        dir: Direction,
+        drop: [u8; N],
+    },
+}