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#import "board.typ": at, is-black, is-white, on-board, piece-type |
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#let enemy(turn, target) = if turn == "white" { is-black(target) } else { is-white(target) } |
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#let pawn-dir(turn) = if turn == "white" { -1 } else { 1 } |
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#let pawn-moves(grid, col, row, turn, ep: none) = { // returns list of (dest-col, dest-row, prom?), ep == en passant |
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let moves = () |
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let start-row = if turn == "white" { 7 } else { 2 } |
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let dir = pawn-dir(turn) |
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// forward one |
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let nr = row + dir |
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if on-board(col, nr) and at(grid, col, nr) == "." { |
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if nr == 1 or nr == 8 { |
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for prom in ("Q", "R", "B", "N") { moves.push((col, nr, prom)) } |
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} else { moves.push((col, nr)) } |
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// forward two from start |
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let nr2 = row + 2 * dir |
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if row == start-row and at(grid, col, nr2) == "." { moves.push((col, nr2)) } |
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} |
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// captures |
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for dc in (-1, 1) { |
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let nc = col + dc |
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let nr = row + dir |
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if on-board(nc, nr) { |
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if enemy(turn, at(grid, nc, nr)) { |
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if nr == 1 or nr == 8 { |
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for prom in ("Q", "R", "B", "N") { moves.push((nc, nr, prom)) } |
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} else { |
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moves.push((nc, nr)) |
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} |
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} |
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// en passant capture: pawn ends on ep square, captured pawn is one rank behind |
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if ep != none and nc == ep.at(0) { |
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let captured-row = ep.at(1) - dir |
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if enemy(turn, at(grid, nc, captured-row)) { moves.push((ep.at(0), ep.at(1))) } |
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} |
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} |
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} |
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moves |
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} |
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#let knight-offsets = ((-2, -1), (-2, 1), (-1, -2), (-1, 2), (1, -2), (1, 2), (2, -1), (2, 1)) |
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#let knight-moves(grid, col, row, turn) = { |
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let moves = () |
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for (dc, dr) in knight-offsets { |
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let nc = col + dc |
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let nr = row + dr |
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if on-board(nc, nr) { |
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let target = at(grid, nc, nr) |
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if target == "." or enemy(turn, target) { |
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moves.push((nc, nr)) |
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} |
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} |
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} |
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moves |
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} |
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#let sliding-moves(grid, col, row, turn, dirs) = { |
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let moves = () |
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for (dc, dr) in dirs { |
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let nc = col + dc |
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let nr = row + dr |
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while on-board(nc, nr) { |
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let target = at(grid, nc, nr) |
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if target == "." { |
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moves.push((nc, nr)) |
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} else if enemy(turn, target) { |
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moves.push((nc, nr)) |
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break |
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} else { break } |
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nc = nc + dc |
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nr = nr + dr |
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} |
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} |
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moves |
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} |
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#let bishop-dirs = ((-1, -1), (-1, 1), (1, -1), (1, 1)) |
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#let bishop-moves(grid, col, row, turn) = sliding-moves(grid, col, row, turn, bishop-dirs) |
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#let rook-dirs = ((-1, 0), (1, 0), (0, -1), (0, 1)) |
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#let rook-moves(grid, col, row, turn) = sliding-moves(grid, col, row, turn, rook-dirs) |
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#let queen-moves(grid, col, row, turn) = { |
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let moves = () |
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for m in bishop-moves(grid, col, row, turn) { moves.push(m) } |
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for m in rook-moves(grid, col, row, turn) { moves.push(m) } |
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moves |
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} |
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#let king-dirs = ((-1, -1), (-1, 0), (-1, 1), (0, -1), (0, 1), (1, -1), (1, 0), (1, 1)) |
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#let king-moves(grid, col, row, turn) = { |
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let moves = () |
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for (dc, dr) in king-dirs { |
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let nc = col + dc |
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let nr = row + dr |
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if on-board(nc, nr) { |
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if at(grid, nc, nr) == "." or enemy(turn, at(grid, nc, nr)) { |
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moves.push((nc, nr)) |
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} |
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} |
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} |
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moves |
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} |
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#let generate-moves-for(grid, col, row, turn, ep: none) = { |
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let p = at(grid, col, row) |
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if p == "." { return () } |
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if turn == "white" and not is-white(p) { return () } |
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if turn == "black" and not is-black(p) { return () } |
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let type = piece-type(p) |
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if type == "P" { return pawn-moves(grid, col, row, turn, ep: ep) } |
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if type == "N" { return knight-moves(grid, col, row, turn) } |
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if type == "B" { return bishop-moves(grid, col, row, turn) } |
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if type == "R" { return rook-moves(grid, col, row, turn) } |
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if type == "Q" { return queen-moves(grid, col, row, turn) } |
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if type == "K" { return king-moves(grid, col, row, turn) } |
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() |
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} |