;;; ob-svgbob.el --- Babel Functions for SVGBob -*- lexical-binding: t; -*-

;; Copyright (C) 2021 Free Software Foundation, Inc.

;; Authors: Steven vanZyl <rushsteve1@rushsteve1.us>
;;          TEC <tec@tecosaur.net>
;; Maintainer: Timothy <tec@tecosaur.net>
;; Keywords: literate programming, reproducible research
;; Homepage: https://git.tecosaur.net/tec/ob-svgbob

;; This file is not part of GNU Emacs.

;; ob-svgbob 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.

;; ob-svgbob 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 ob-svgbob.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Org-Babel support for evaluating and SVGBob diagrams.
;; https://github.com/ivanceras/svgbob

;; This is very similar to ob-dot.el with a similar list of caveats:

;; * There are no sessions
;; * We are generally only going to return results of type "file graphics"
;; * The "file" header argument is required
;; * SVGBob has no definite syntax

;; This file also includes some additional utility functions and a simple
;; derived major-mode for SVGBob

;;; Code:

(require 'ob)

(eval-when-compile
  (require 'cl-lib))

(defcustom org-svgbob-executable "svgbob"
  "The path to the SVGBob binary.
This can be installed from source using `cargo install svgbob_cli'"
  :group 'org-babel
  :type 'file)

(defcustom org-svgbob-buffer-name "*svgbob-output*"
  "The name of the buffer that SVGBob will output to."
  :group 'org-babel
  :type 'string)

(defconst org-babel-svgbob--parameters
  '(:background :fill-color :font-family :font-size :scale :stroke-width)
  "Recognised SVGBob parameter keys.")

;; So `org-edit-special' works.
(unless (fboundp 'svgbob-mode)
  (add-to-list 'org-src-lang-modes (cons "svgbob" 'fundamental)))

(defun ob-svgbob-string-to-svg (str &optional parameters)
  "Convert STR to SVG text and return a string of that.
PARAMETERS should be a plist of svgbob parameters, and only keys
that are members of `org-babel-svgbob--parameters' will be used."
  (with-temp-buffer
    (insert
     (org-babel-eval
      (concat org-svgbob-executable
              (cl-loop for (key . val)
                       in parameters
                       when (memq key org-babel-svgbob--parameters)
                       concat (format " --%s %S"
                                      (substring (symbol-name key) 1)
                                      val)))
      str))
    (when-let ((stroke-color (alist-get :stroke-color parameters)))
      (goto-char (point-min))
      (re-search-forward "^[ \t]*stroke: \\(black\\);\n")
      (replace-match stroke-color t t nil 1))
    (when-let ((text-color (alist-get :text-color parameters)))
      (goto-char (point-min))
      (search-forward "text {")
      (re-search-forward "^[ \t]*fill: \\(black\\);\n")
      (replace-match text-color t t nil 1))
    (when-let ((file (alist-get :file parameters)))
      (write-region nil nil file))
    (buffer-string)))

(defun ob-svgbob-region-to-svg (start end)
  "Convert a region to SVG text in a new buffer.
The region is given by the range START to END."
  (interactive "r")
  (let ((str (ob-svgbob-string-to-svg (buffer-substring-no-properties start end))))
    (with-current-buffer (get-buffer-create org-svgbob-buffer-name)
      (read-only-mode 0) ; Disable read-only
      (fundamental-mode) ; Required to erase the buffer
      (erase-buffer)
      (insert str)
      (image-mode)
      (read-only-mode)
      (display-buffer-in-side-window (current-buffer) '((side . right))))))

(defun ob-svgbob-buffer-to-svg ()
  "Convert a buffer to SVG text in a new buffer.
See `svgbob-region-to-svg' for more"
  (interactive)
  (ob-svgbob-region-to-svg (point-min) (point-max)))

(defvar org-babel-default-header-args:svgbob
  '((:results . "file graphics")
    (:exports . "results")
    (:background . "transparent"))
  "Default arguments to use when evaluating a dot source block.")

(defun org-babel-execute:svgbob (body params)
  "Execute a block of svgbob with org-babel.
Specifically, svgbob is called on BODY with PARAMS."
  (if (alist-get :file params)
      (ob-svgbob-string-to-svg body params)
    (user-error "You need to specify a :file parameter")))

(defun org-babel-prep-session:svgbob (_session _params)
  "Return an error because SVGBob does not support sessions."
  (user-error "SVGBob does not support sessions"))

(provide 'ob-svgbob)

;;; ob-svgbob.el ends here