Align a vector of Clojure maps so that keys line up across maps like columns

clojure-align.el

(defun clojure-align--current-indent (pos)
  "Return indentation (string of spaces) at POS."
  (save-excursion
    (goto-char pos)
    (back-to-indentation)
    (buffer-substring (line-beginning-position) (point))))

(defun clojure-align--lines (beg end)
  "Return list of lines from region between BEG and END."
  (split-string (buffer-substring-no-properties beg end) "\n"))

(defun clojure-align--extract-rows (lines)
  "Extract rows of key-value pairs from map LINES."
  (mapcar (lambda (line)
            (let ((row '())
                  (pos 0))
              (while (string-match ":\\(\\w+\\)\\s-*\\([^:}\n ]+\\)?" line pos)
                (let ((key (match-string 1 line))
                      (val (match-string 2 line)))
                  (push (cons key (or val "")) row)
                  (setq pos (match-end 0))))
              (reverse row)))
          lines))

(defun clojure-align--all-keys (rows)
  "Return list of all unique keys in ROWS, in order of appearance."
  (let ((keys '()))
    (dolist (row rows)
      (dolist (entry row)
        (let ((k (car entry)))
          (unless (member k keys)
            (push k keys)))))
    (reverse keys)))

(defun clojure-align--column-widths (all-keys rows)
  "Calculate maximum value widths for ALL-KEYS in ROWS."
  (mapcar
   (lambda (k)
     (apply #'max
            (length k)
            (mapcar (lambda (row)
                      (length (or (cdr (assoc k row)) "")))
                    rows)))
   all-keys))

(defun clojure-align--format-rows (rows all-keys col-widths indent)
  "Format ROWS into aligned strings using ALL-KEYS and COL-WIDTHS.

   It also preserves INDENT."
  (mapcar
   (lambda (row)
     (let ((parts '()))
       (cl-mapcar
        (lambda (k w)
          (let ((v (or (cdr (assoc k row)) "")))
            (push (format ":%s %s"
                          (format (format "%%-%ds" (length k)) k)
                          (format (format "%%-%ds" w) v))
                  parts)))
        all-keys col-widths)
       (concat indent " {" (string-join (reverse parts) " ") "}")))
   rows))

(defun clojure-align-maps-in-vector (beg end)
  "Align a vector of Clojure maps so that keys line up across maps like columns.

If a region is active, align from BEG to END.  Otherwise, align the top-level form at point."
  (interactive
   (if (use-region-p)
       (list (region-beginning) (region-end))
     (let ((bounds (bounds-of-thing-at-point 'sexp)))
       (list (car bounds) (cdr bounds)))))
  (save-excursion
    (let* ((indent (clojure-align--current-indent beg))
           (lines (clojure-align--lines beg end))
           (rows (clojure-align--extract-rows lines))
           (all-keys (clojure-align--all-keys rows))
           (col-widths (clojure-align--column-widths all-keys rows))
           (result-lines (clojure-align--format-rows rows all-keys col-widths indent)))
      (delete-region beg end)
      (insert (concat indent "[\n"
                      (mapconcat #'identity result-lines "\n")
                      "\n" indent "]")))))