markdown-join.el

;;; markdown-join.el --- Join markdown tables based on cell contents  -*- lexical-binding: t; -*-

;; Copyright (C) 2023  Tony Garnock-Jones

;; Author: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
;; Keywords: data, convenience, matching
;; Version: 0.0.1
;; Package-Requires: ((markdown-mode "2.6") (emacs "25.1"))
;; Homepage: https://gist.github.com/tonyg/c951be93656b45027ed7d15e79f07c01

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; When working on Markdown files containing tables, occasionally one will wish to bring in
;; information from another table nearby. This package offers one way to accomplish this, if
;; the source table is in a separate buffer: use `M-x markdown-join`.

;;; Code:

(require 'markdown-mode)

(defun markdown-join-get-row ()
  "Retrieves all cells in the row at point."
  ;; Cribs from markdown-table-get-column and markdown-table-get-cell.
  (let ((acc '()))
    (save-excursion
      (beginning-of-line)
      (while (search-forward "|" (line-end-position) t)
        (when (and (not (looking-back "\\\\|" (line-beginning-position)))
                   (not (markdown--thing-at-wiki-link (match-beginning 0))))
	  (setq acc (cons (progn
			    (skip-chars-backward "^|\n") (backward-char 1)
			    (if (looking-at "|[^|\r\n]*")
				(let* ((pos (match-beginning 0))
				       (val (buffer-substring (1+ pos) (match-end 0))))
				  (goto-char (min (line-end-position) (+ 2 pos)))
				  ;; Trim whitespaces
				  (setq val (replace-regexp-in-string "\\`[ \t]+" "" val)
					val (replace-regexp-in-string "[ \t]+\\'" "" val)))
			      (forward-char 1) ""))
			  acc)))))
    (reverse acc)))

;;;###autoload
(defun markdown-join (source-buffer)
  "Copies cells from another Markdown table into the row in the table at point.
This function requires point to be in a cell in a table.

Requests a buffer containing the table to pull values
from (SOURCE-BUFFER). Point in that buffer should be in a cell of
a Markdown table.

The contents of the cell under point in the current (``target'')
buffer is compared with cells in the column selected by point in
SOURCE-BUFFER. The first matching row is copied, cell by cell, to
the row at point in the target buffer, excepting the column under
point in SOURCE-BUFFER (since its contents are the same as the
cell under point in the target).

To join two whole tables, try using a keyboard macro to repeat
markdown-join for each row in the target table."
  (interactive "bBuffer containing table to pull values from: ")
  (save-excursion
    (let ((target-buffer (current-buffer)))
      (unless (with-current-buffer target-buffer (markdown-table-at-point-p))
	(user-error "Please select a target markdown table and column in %s" target-buffer))
      (let* ((target-join-value (markdown--remove-invisible-markup (markdown-table-get-cell)))
	     (source-columns
	      (with-current-buffer source-buffer
		(unless (markdown-table-at-point-p)
		  (user-error "Please select a source markdown table and column in %s" (current-buffer)))
		(let ((source-column (markdown-table-get-column)))
		  (save-restriction
		    ;; Select current hline-separated table region, else the whole table
		    (let ((start (markdown-table-begin))
			  (end (markdown-table-end)))
		      (narrow-to-region
		       (save-excursion
			 (if (re-search-backward
			      markdown-table-hline-regexp start t)
			     (line-beginning-position 2)
			   start))
		       (if (save-excursion (re-search-forward
					    markdown-table-hline-regexp end t))
			   (match-beginning 0)
			 end)))
		    ;; Find a matching row
		    (let ((source-columns
			   (with-temp-message "Searching for matching row..."
			     (catch 'join-successful
			       (save-excursion
				 (goto-char (markdown-table-begin))
				 (while (re-search-forward markdown-table-dline-regexp (point-max) t)
				   (when (string-equal (markdown-table-get-cell source-column) target-join-value)
				     (throw 'join-successful (markdown-join-get-row)))))))))
		      (when source-columns
			(append (seq-take source-columns (1- source-column))
				(seq-drop source-columns source-column)))))))))
	(if source-columns
	    (progn (save-excursion
		     (end-of-line)
		     (dolist (v source-columns)
		       (insert " ")
		       (insert v)
		       (insert " |")))
		   "Join successful.")
	  "No matching row found.")))))

(provide 'markdown-join)
;;; markdown-join.el ends here