internal final class Pawn: Piece {
	internal var kind: Kind = .Pawn
	internal weak var board: Board?
	internal var color: Color
	internal var position: Square.Position
	internal var pseudoLegalPositions: [Square.Position] {
		let sign: Int8 = color == .Black ? -1 : 1
		let rank = Int8(position.rank)
		let directions: [Square.Position] = [
			.init(file: position.file, rank: rank + 1 * sign),
			.init(file: position.file, rank: rank + 2 * sign),
			.init(file: position.file + 1, rank: rank + 1 * sign),
			.init(file: position.file - 1, rank: rank + 1 * sign)
		]
		// TODO: Handle en passant
		return directions.filter { 
			let index = $0.index
			return index < 1 || index > 63
		}
	}
	internal var legalPositions: [Square.Position] {
		pseudoLegalPositions.filter { isLegal(on: $0) }
	}

	internal var unicodeRepresentation: String {
		color == .Black ? "♟" : "♙"
	}

	internal func move(to dst: Square.Position) -> Bool {
		guard board != nil else {
			return false
		}

		if !(legalPositions.contains { $0 == dst }) {
			return false
		}

		if let board = board, var s = board[position], var d = board[dst] {
			s.piece = self
			d.piece = nil
		}

		position = dst

		return true
	}

	internal func isLegal(on pos: Square.Position) -> Bool {
		// TODO: Handle "En-Passant"
		if let board = board, let s = board[pos] {
			if let p = s.piece {
				if p.color == color { return false }
				if p.kind == .King {
					// TODO: Notify board of check
					return false
				}
			}

		}
		return true
	}

	internal init(
		color: Color, on position: Square.Position
	) {
		self.color = color
		self.position = position
	}
}