King's Escape

Create a function that takes a chess position (black pieces to move next) and returns the status of the black king.

• The black king is safe if no white pieces threaten it.
• The black king is checked if one white piece threatens it and the king can escape to an unthreatened square.
• The black king is double-checked if two white pieces threaten it and the king can escape to an unthreatened square.
• The black king is checkmated if it is attacked and cannot escape.
• White pieces are represented with uppercase letters: Pawn P, Knight N, Bishop B, Rook R, Queen Q, King K. Black pieces are represented with lowercase letters.
• The program must return the possible escape positions (if they exist) as an array of tuples (x, y) being x, the horizontal position of the escape square, and y the vertical position of the escape square. The escape positions must be sorted by x and then y, always from the lowest value to the highest value.
• The chessboard will always have 8 rows and 8 columns. 0 <= x < 8 and 0 <= y < 8. The white queen starts at (7, 3).
• A stalemate occurs when a player, on their turn, has no legal moves, and the player's king is not in check. Stalemate is not a possibility in this challenge.

Examples

chess([
  [" ", " ", " ", " ", " ", "r", " ", " "],
  [" ", " ", " ", " ", " ", " ", " ", "q"],
  [" ", " ", " ", " ", " ", " ", "N", " "],
  ["k", " ", " ", " ", " ", " ", " ", " "],
  [" ", "P", " ", "P", " ", " ", " ", " "],
  [" ", " ", "P", " ", " ", "Q", " ", " "],
  ["B", " ", " ", " ", " ", " ", " ", " "],
  [" ", " ", " ", "R", " ", " ", "K", " "],
])
  ➞ "The black king is checked. Possible escape positions: [(2, 0), (2, 1), (3, 1), (4, 0)]"

chess([
  [" ", " ", " ", " ", " ", "r", " ", " "],
  [" ", " ", " ", " ", " ", " ", "k", "q"],
  [" ", " ", " ", " ", " ", " ", "N", " "],
  [" ", " ", " ", " ", " ", " ", " ", " "],
  [" ", "P", " ", " ", " ", " ", " ", " "],
  [" ", " ", " ", " ", " ", "Q", " ", " "],
  ["B", " ", " ", " ", " ", " ", " ", " "],
  [" ", " ", " ", "R", " ", " ", "K", " "],
])
  ➞ "The black king is safe."

chess([
  [" ", " ", " ", " ", " ", "r", " ", " "],
  [" ", " ", " ", " ", " ", " ", " ", "q"],
  [" ", " ", " ", " ", " ", " ", "N", " "],
  [" ", " ", " ", " ", " ", " ", " ", " "],
  [" ", "P", " ", "k", " ", " ", " ", " "],
  [" ", " ", " ", " ", " ", "Q", " ", " "],
  ["B", " ", " ", " ", " ", " ", " ", " "],
  [" ", " ", " ", "R", " ", " ", "K", " "],
])
  ➞ "The black king is checkmated."

chess([
  [" ", " ", " ", " ", " ", " ", " ", " "],
  [" ", " ", " ", " ", " ", " ", "k", " "],
  [" ", " ", " ", " ", " ", " ", " ", " "],
  [" ", " ", " ", " ", "B", "p", " ", " "],
  [" ", " ", " ", "q", " ", " ", " ", " "],
  [" ", " ", " ", " ", " ", " ", " ", " "],
  ["p", " ", " ", " ", " ", " ", " ", " "],
  [" ", " ", " ", " ", " ", "K", "R", " "],
])
  ➞ "The black king is double-checked. Possible escape positions: [(0, 5), (1, 5), (1, 7), (2, 7)]"

Notes

N/A