Draughts Move Judge

List every legal move for one side in a position of English draughts (checkers).

Board. board is 8 strings of 8 characters, row 0 being rank 8 (the top) and column 0 being file a. w and b are white and black men, W and B are kings, . is an empty square. A square is named by its file and rank, so board[7][0] is a1. White moves toward rank 8, black toward rank 1.

Moves. All movement is diagonal.

• A man moves one square forward diagonally (two choices) onto an empty square. A king moves one square in any of the four diagonal directions.
• A jump passes over an adjacent enemy piece (man or king) and lands on the empty square directly behind it; the jumped piece is captured. Men jump only forward, kings in all four directions. A piece cannot be jumped twice in one move, and a jump cannot land on an occupied square.
• Capturing is mandatory: if the player has any jump available, every legal move is a capture and plain moves are not legal.
• A capturing move must keep jumping: after each jump, if the same piece can jump again it must, and the move ends only when no further jump is possible. When there is a choice, either jump may be taken (the longest sequence is not required). The square the piece started on counts as empty during the move.
• If a man lands on the far rank (rank 8 for white, rank 1 for black) during a capture, it becomes a king and the move ends there.

Input: board and player ("w" or "b"), the side to move.

Output: all legal moves as strings, sorted in ascending order. A plain move is "c3-d4", a capture lists the start square followed by each landing square: "c3xe5xg7". If the player has no legal move, return an empty list.