(defun my-queens-chess-position (variable size)
  "Return a file-rank string for SOLUTION."
  (let ((file (+ ?a (mod (1- variable) size)))
        (rank (- size (/ (1- variable) size))))
    (format "%c%d" file rank)))

(defun my-queens-chess-pieces (solution)
  "Return a list of piece-file-rank strings for SOLUTION."
  (let ((size (truncate (sqrt (length solution)))))
    (mapcan (pcase-lambda (`(,variable . ,value))
              (when (= value 1)
                (list (concat "q" (my-queens-chess-position variable size)))))
            solution)))

(defun my-queens-render-solution (solution)
  "Return LaTeX source code that renders SOLUTION."
  (let ((size (truncate (sqrt (length solution)))))
    (format "\\chessboard[smallboard, maxfield=%s, setpieces={%s}]"
            (my-queens-chess-position size size)
            (string-join (sort (my-queens-chess-pieces solution)) ", "))))

(defun my-queens-render-solutions (solutions)
  "Return LaTeX source code that renders SOLUTIONS."
  (string-join
   (append '("\\begin{flushleft}")
           (mapcar (lambda (solution)
                     (concat "  " (my-queens-render-solution solution)))
                   solutions)
           '("\\end{flushleft}"))
   "\n"))

(ert-deftest my-queens-render-solutions/size-2 ()
  (should (equal (my-queens-render-solutions '(((1 . 1) (2 . 0)
                                                (3 . 0) (4 . 1))))
                 "\\begin{flushleft}
  \\chessboard[smallboard, maxfield=b2, setpieces={qa2, qb1}]
\\end{flushleft}")))

(ert-deftest my-queens-render-solutions/size-2/different ()
  (should (equal (my-queens-render-solutions '(((1 . 0) (2 . 1)
                                                (3 . 1) (4 . 0))))
                 "\\begin{flushleft}
  \\chessboard[smallboard, maxfield=b2, setpieces={qa1, qb2}]
\\end{flushleft}")))

(ert-deftest my-queens-render-solutions/size-2/multiple ()
  (should (equal (my-queens-render-solutions '(((1 . 1) (2 . 0)
                                                (3 . 0) (4 . 1))
                                               ((1 . 0) (2 . 1)
                                                (3 . 1) (4 . 0))))
                 "\\begin{flushleft}
  \\chessboard[smallboard, maxfield=b2, setpieces={qa2, qb1}]
  \\chessboard[smallboard, maxfield=b2, setpieces={qa1, qb2}]
\\end{flushleft}")))

(ert-deftest my-queens-render-solutions/size-3 ()
  (should (equal (my-queens-render-solutions '(((1 . 0) (2 . 0) (3 . 0)
                                                (4 . 0) (5 . 0) (6 . 0)
                                                (7 . 0) (8 . 0) (9 . 1))))
                 "\\begin{flushleft}
  \\chessboard[smallboard, maxfield=c3, setpieces={qc1}]
\\end{flushleft}")))