Oleksandr Smirnov
Oleksandr Smirnov
olexsmir@gmail.com only export chess as part of public api; merge moves.typ and rules.typ, 27 days ago
olexsmir@gmail.com only export chess as part of public api; merge moves.typ and rules.typ, 27 days ago
| 1 | #import "board.typ": at, copy-grid, find-pieces, is-black, is-white, on-board, piece-type |
| 2 | |
| 3 | // move generation |
| 4 | |
| 5 | #let enemy(turn, target) = if turn == "white" { is-black(target) } else { is-white(target) } |
| 6 | |
| 7 | #let pawn-dir(turn) = if turn == "white" { -1 } else { 1 } |
| 8 | #let pawn-moves(grid, col, row, turn, ep: none) = { |
| 9 | let moves = () |
| 10 | let start-row = if turn == "white" { 7 } else { 2 } |
| 11 | let dir = pawn-dir(turn) |
| 12 | |
| 13 | // forward one |
| 14 | let nr = row + dir |
| 15 | if on-board(col, nr) and at(grid, col, nr) == "." { |
| 16 | if nr == 1 or nr == 8 { |
| 17 | for prom in ("Q", "R", "B", "N") { moves.push((col, nr, prom)) } |
| 18 | } else { moves.push((col, nr)) } |
| 19 | |
| 20 | // forward two from start |
| 21 | let nr2 = row + 2 * dir |
| 22 | if row == start-row and at(grid, col, nr2) == "." { moves.push((col, nr2)) } |
| 23 | } |
| 24 | |
| 25 | // captures |
| 26 | for dc in (-1, 1) { |
| 27 | let nc = col + dc |
| 28 | let nr = row + dir |
| 29 | if on-board(nc, nr) { |
| 30 | if enemy(turn, at(grid, nc, nr)) { |
| 31 | if nr == 1 or nr == 8 { |
| 32 | for prom in ("Q", "R", "B", "N") { moves.push((nc, nr, prom)) } |
| 33 | } else { |
| 34 | moves.push((nc, nr)) |
| 35 | } |
| 36 | } |
| 37 | |
| 38 | // en passant capture: pawn ends on ep square, captured pawn is one rank behind |
| 39 | if ep != none and nc == ep.at(0) { |
| 40 | let captured-row = ep.at(1) - dir |
| 41 | if enemy(turn, at(grid, nc, captured-row)) { moves.push((ep.at(0), ep.at(1))) } |
| 42 | } |
| 43 | } |
| 44 | } |
| 45 | |
| 46 | moves |
| 47 | } |
| 48 | |
| 49 | #let knight-offsets = ((-2, -1), (-2, 1), (-1, -2), (-1, 2), (1, -2), (1, 2), (2, -1), (2, 1)) |
| 50 | #let knight-moves(grid, col, row, turn) = { |
| 51 | let moves = () |
| 52 | for (dc, dr) in knight-offsets { |
| 53 | let nc = col + dc |
| 54 | let nr = row + dr |
| 55 | if on-board(nc, nr) { |
| 56 | let target = at(grid, nc, nr) |
| 57 | if target == "." or enemy(turn, target) { |
| 58 | moves.push((nc, nr)) |
| 59 | } |
| 60 | } |
| 61 | } |
| 62 | moves |
| 63 | } |
| 64 | |
| 65 | #let sliding-moves(grid, col, row, turn, dirs) = { |
| 66 | let moves = () |
| 67 | for (dc, dr) in dirs { |
| 68 | let nc = col + dc |
| 69 | let nr = row + dr |
| 70 | while on-board(nc, nr) { |
| 71 | let target = at(grid, nc, nr) |
| 72 | if target == "." { |
| 73 | moves.push((nc, nr)) |
| 74 | } else if enemy(turn, target) { |
| 75 | moves.push((nc, nr)) |
| 76 | break |
| 77 | } else { break } |
| 78 | nc = nc + dc |
| 79 | nr = nr + dr |
| 80 | } |
| 81 | } |
| 82 | moves |
| 83 | } |
| 84 | |
| 85 | #let bishop-dirs = ((-1, -1), (-1, 1), (1, -1), (1, 1)) |
| 86 | #let bishop-moves(grid, col, row, turn) = sliding-moves(grid, col, row, turn, bishop-dirs) |
| 87 | |
| 88 | #let rook-dirs = ((-1, 0), (1, 0), (0, -1), (0, 1)) |
| 89 | #let rook-moves(grid, col, row, turn) = sliding-moves(grid, col, row, turn, rook-dirs) |
| 90 | |
| 91 | #let queen-moves(grid, col, row, turn) = { |
| 92 | let moves = () |
| 93 | for m in bishop-moves(grid, col, row, turn) { moves.push(m) } |
| 94 | for m in rook-moves(grid, col, row, turn) { moves.push(m) } |
| 95 | moves |
| 96 | } |
| 97 | |
| 98 | #let king-dirs = ((-1, -1), (-1, 0), (-1, 1), (0, -1), (0, 1), (1, -1), (1, 0), (1, 1)) |
| 99 | #let king-moves(grid, col, row, turn) = { |
| 100 | let moves = () |
| 101 | for (dc, dr) in king-dirs { |
| 102 | let nc = col + dc |
| 103 | let nr = row + dr |
| 104 | if on-board(nc, nr) { |
| 105 | if at(grid, nc, nr) == "." or enemy(turn, at(grid, nc, nr)) { |
| 106 | moves.push((nc, nr)) |
| 107 | } |
| 108 | } |
| 109 | } |
| 110 | moves |
| 111 | } |
| 112 | |
| 113 | #let generate-moves-for(grid, col, row, turn, ep: none) = { |
| 114 | let p = at(grid, col, row) |
| 115 | if p == "." { return () } |
| 116 | if turn == "white" and not is-white(p) { return () } |
| 117 | if turn == "black" and not is-black(p) { return () } |
| 118 | |
| 119 | let type = piece-type(p) |
| 120 | if type == "P" { return pawn-moves(grid, col, row, turn, ep: ep) } |
| 121 | if type == "N" { return knight-moves(grid, col, row, turn) } |
| 122 | if type == "B" { return bishop-moves(grid, col, row, turn) } |
| 123 | if type == "R" { return rook-moves(grid, col, row, turn) } |
| 124 | if type == "Q" { return queen-moves(grid, col, row, turn) } |
| 125 | if type == "K" { return king-moves(grid, col, row, turn) } |
| 126 | () |
| 127 | } |
| 128 | |
| 129 | // chess rules |
| 130 | |
| 131 | #let is-attacked(grid, col, row, by-color) = { |
| 132 | let enemy(piece) = if by-color == "white" { is-white(piece) } else { is-black(piece) } |
| 133 | |
| 134 | // knight attacks |
| 135 | for (dc, dr) in knight-offsets { |
| 136 | let p = at(grid, col + dc, row + dr) |
| 137 | if p != "." and piece-type(p) == "N" and enemy(p) { return true } |
| 138 | } |
| 139 | |
| 140 | // king attacks |
| 141 | for (dc, dr) in king-dirs { |
| 142 | let p = at(grid, col + dc, row + dr) |
| 143 | if p != "." and piece-type(p) == "K" and enemy(p) { return true } |
| 144 | } |
| 145 | |
| 146 | // pawn attacks |
| 147 | let pawn-checks = if by-color == "white" { ((-1, 1), (1, 1)) } else { ((-1, -1), (1, -1)) } |
| 148 | for (dc, dr) in pawn-checks { |
| 149 | let p = at(grid, col + dc, row + dr) |
| 150 | if p != "." and piece-type(p) == "P" and enemy(p) { return true } |
| 151 | } |
| 152 | |
| 153 | // sliding pieces |
| 154 | for (dirs, types) in ((bishop-dirs, ("B", "Q")), (rook-dirs, ("R", "Q"))) { |
| 155 | for (dc, dr) in dirs { |
| 156 | let nc = col + dc |
| 157 | let nr = row + dr |
| 158 | while on-board(nc, nr) { |
| 159 | let p = at(grid, nc, nr) |
| 160 | if p != "." { |
| 161 | if enemy(p) and types.contains(piece-type(p)) { return true } |
| 162 | break // blocked by any piece |
| 163 | } |
| 164 | nc += dc |
| 165 | nr += dr |
| 166 | } |
| 167 | } |
| 168 | } |
| 169 | |
| 170 | false |
| 171 | } |
| 172 | |
| 173 | #let is-in-check(grid, turn) = { |
| 174 | let king-char = if turn == "white" { "K" } else { "k" } |
| 175 | let enemy = if turn == "white" { "black" } else { "white" } |
| 176 | for r in range(8) { |
| 177 | for c in range(8) { |
| 178 | if grid.at(r).at(c) == king-char { |
| 179 | return is-attacked(grid, c + 1, r + 1, enemy) |
| 180 | } |
| 181 | } |
| 182 | } |
| 183 | false |
| 184 | } |
| 185 | |
| 186 | #let can-castle(grid, row, empty-cols, check-cols, enemy) = { |
| 187 | if is-attacked(grid, 5, row, enemy) { return false } |
| 188 | for c in empty-cols { if at(grid, c, row) != "." { return false } } |
| 189 | for c in check-cols { if is-attacked(grid, c, row, enemy) { return false } } |
| 190 | true |
| 191 | } |
| 192 | |
| 193 | #let has-legal-move(grid, turn, ep: none, castles: "") = { |
| 194 | for r in range(8) { |
| 195 | for c in range(8) { |
| 196 | let p = grid.at(r).at(c) |
| 197 | if p == "." { continue } |
| 198 | if turn == "white" and not is-white(p) { continue } |
| 199 | if turn == "black" and not is-black(p) { continue } |
| 200 | |
| 201 | let type = piece-type(p) |
| 202 | |
| 203 | let col = c + 1 |
| 204 | let row = r + 1 |
| 205 | let raw-moves = if type == "P" { pawn-moves(grid, col, row, turn, ep: ep) } else { |
| 206 | generate-moves-for(grid, col, row, turn, ep: ep) |
| 207 | } |
| 208 | |
| 209 | for m in raw-moves { |
| 210 | let (dc, dr) = (m.at(0), m.at(1)) |
| 211 | let new-grid = copy-grid(grid) |
| 212 | new-grid.at(r).at(c) = "." |
| 213 | let mover = p |
| 214 | let is-pawn = type == "P" |
| 215 | if is-pawn and (dr == 1 or dr == 8) { |
| 216 | mover = if turn == "white" { "Q" } else { "q" } |
| 217 | } |
| 218 | new-grid.at(dr - 1).at(dc - 1) = mover |
| 219 | if is-pawn and ep != none and dc == ep.at(0) and dr == ep.at(1) { |
| 220 | let captured-row = if turn == "white" { dr + 1 } else { dr - 1 } |
| 221 | new-grid.at(captured-row - 1).at(dc - 1) = "." |
| 222 | } |
| 223 | if not is-in-check(new-grid, turn) { return true } |
| 224 | } |
| 225 | } |
| 226 | } |
| 227 | |
| 228 | let enemy = if turn == "white" { "black" } else { "white" } |
| 229 | let options = if turn == "white" { |
| 230 | (("K", 8, (6, 7), (6, 7)), ("Q", 8, (2, 3, 4), (3, 4))) |
| 231 | } else { |
| 232 | (("k", 1, (6, 7), (6, 7)), ("q", 1, (2, 3, 4), (3, 4))) |
| 233 | } |
| 234 | |
| 235 | for (flag, row, empty, check) in options { |
| 236 | if castles.contains(flag) and can-castle(grid, row, empty, check, enemy) { return true } |
| 237 | } |
| 238 | |
| 239 | false |
| 240 | } |