oc-natbib: Implement `natbib' citation processor

* lisp/oc-natbib.el: New file.

lisp/oc-natbib.el

@@ -0,0 +1,189 @@
+;;; oc-natbib.el --- Citation processor using natbib LaTeX package  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2021 Free Software Foundation, Inc.
+
+;; Author: Nicolas Goaziou <mail@nicolasgoaziou.fr>
+
+;; 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:
+
+;; This library registers the `natbib' citation processor, which provides the
+;; "export" capability for citations.
+
+;; The processor relies on "natbib" LaTeX package.  As such it ensures that the
+;; package is properly required in the document's preamble.  More accurately, it
+;; will use any "\\usepackage{natbib}" command already present in the document
+;; (e.g., through `org-latex-packages-alist'), or insert one using options
+;; defined in `org-cite-natbib-options'.
+
+;; It supports the following citation styles:
+;;
+;; - author (a), including caps (c), and full (f) variants,
+;; - noauthor (na), including bare (b) variant,
+;; - text (t), including bare (b), caps (c), full (f), bare-caps (bc),
+;;   bare-full (bf), caps-full (cf), and bare-caps-full (bcf) variants,
+;; - default, including bare (b), caps (c), full (f), bare-caps (bc),
+;;   bare-full (bf), caps-full (cf), and bare-caps-full (bcf) variants.
+
+;; Bibliography accepts any style supported by "natbib" package.
+
+;;; Code:
+(require 'oc)
+
+(declare-function org-element-property "org-element" (property element))
+
+(declare-function org-export-data "org-export" (data info))
+
+
+;;; Customization
+(defcustom org-cite-natbib-options nil
+  "List of options added to \"natbib\" package.
+If \"natbib\" package is already required in the document, e.g., through
+`org-latex-packages-alist' variable, these options are ignored."
+  :group 'org-cite
+  :package-version '(Org . "9.5")
+  :type
+  '(set
+    (const :tag "use round parentheses (default)" round)
+    (const :tag "use square brackets" square)
+    (const :tag "use curly braces" curly)
+    (const :tag "use angle brackets" angle)
+    (const :tag "separate multiple citations with colons (default)" colon)
+    (const :tag "separate multiple citations with comas" comma)
+    (const :tag "generate author-year citations" authoryear)
+    (const :tag "generate numerical citations" numbers)
+    (const :tag "generate superscripted numerical citations" super)
+    (const :tag "order multiple citations according to the list of references" sort)
+    (const :tag "order as above, but numerical citations are compressed if possible" sort&compress)
+    (const :tag "display full author list on first citation, abbreviate the others" longnamesfirst)
+    (const :tag "redefine \\thebibliography to issue \\section* instead of \\chapter*" sectionbib)
+    (const :tag "keep all the authors' names in a citation on one line" nonamebreak))
+  :safe t)
+
+
+;;; Internal functions
+(defun org-cite-natbib--style-to-command (style)
+  "Return command name to use according to STYLE pair."
+  (pcase style
+    ;; "author" style.
+    (`(,(or "author" "a") . ,(or "caps" "c"))           "\\Citeauthor")
+    (`(,(or "author" "a") . ,(or "full" "f"))           "\\citeauthor*")
+    (`(,(or "author" "a") . ,_)                         "\\citeauthor")
+    ;; "noauthor" style.
+    (`(,(or "noauthor" "na") . ,(or "bare" "b"))        "\\citeyear")
+    (`(,(or "noauthor" "na") . ,_)                      "\\citeyearpar")
+    ;; "nocite" style.
+    (`(,(or "nocite" "n") . ,_)                         "\\nocite")
+    ;; "text" style.
+    (`(,(or "text" "t") . ,(or "bare" "b"))             "\\citealt")
+    (`(,(or "text" "t") . ,(or "caps" "c"))             "\\Citet")
+    (`(,(or "text" "t") . ,(or "full" "f"))             "\\citet*")
+    (`(,(or "text" "t") . ,(or "bare-caps" "bc"))       "\\Citealt")
+    (`(,(or "text" "t") . ,(or "bare-full" "bf"))       "\\citealt*")
+    (`(,(or "text" "t") . ,(or "caps-full" "cf"))       "\\Citet*")
+    (`(,(or "text" "t") . ,(or "bare-caps-full" "bcf")) "\\Citealt*")
+    (`(,(or "text" "t") . ,_)                           "\\citet")
+    ;; Default ("nil") style.
+    (`(,_ . ,(or "bare" "b"))                           "\\citealp")
+    (`(,_ . ,(or "caps" "c"))                           "\\Citep")
+    (`(,_ . ,(or "full" "f"))                           "\\citep*")
+    (`(,_ . ,(or "bare-caps" "bc"))                     "\\Citealp")
+    (`(,_ . ,(or "bare-full" "bf"))                     "\\citealp*")
+    (`(,_ . ,(or "caps-full" "cf"))                     "\\Citep*")
+    (`(,_ . ,(or "bare-caps-full" "bcf"))               "\\Citealp*")
+    (`(,_ . ,_)                                         "\\citep")
+    ;; This should not happen.
+    (_ (error "Invalid style: %S" style))))
+
+(defun org-cite-natbib--build-optional-arguments (citation info)
+  "Build optional arguments for citation command.
+CITATION is the citation object.  INFO is the export state, as a property list."
+  (let* ((origin (pcase (org-cite-get-references citation)
+                   (`(,reference) reference)
+                   (_ citation)))
+         (suffix (org-element-property :suffix origin))
+         (prefix (org-element-property :prefix origin)))
+    (concat (and prefix (format "[%s]" (org-trim (org-export-data prefix info))))
+            (cond
+             (suffix (format "[%s]" (org-trim (org-export-data suffix info))))
+             (prefix "[]")
+             (t nil)))))
+
+(defun org-cite-natbib--build-arguments (citation)
+  "Build arguments for citation command for CITATION object."
+  (format "{%s}"
+          (mapconcat #'identity
+                     (org-cite-get-references citation t)
+                     ",")))
+
+
+;;; Export capability
+(defun org-cite-natbib-export-bibliography (_keys files style &rest _)
+  "Print references from bibliography FILES.
+FILES is a list of absolute file names.  STYLE is the bibliography style, as
+a string or nil."
+  (concat (and style (format "\\bibliographystyle{%s}\n" style))
+          (format "\\bibliography{%s}"
+                  (mapconcat #'file-name-sans-extension
+                             files
+                             ","))))
+
+(defun org-cite-natbib-export-citation (citation style _ info)
+  "Export CITATION object.
+STYLE is the citation style, as a pair of strings or nil.  INFO is the export
+state, as a property list."
+  (concat (org-cite-natbib--style-to-command style)
+          (org-cite-natbib--build-optional-arguments citation info)
+          (org-cite-natbib--build-arguments citation)))
+
+(defun org-cite-natbib-use-package (output &rest _)
+  "Ensure output requires \"natbib\" package.
+OUTPUT is the final output of the export process."
+  (with-temp-buffer
+    (save-excursion (insert output))
+    (when (search-forward "\\begin{document}" nil t)
+      ;; Ensure there is a \usepackage{natbib} somewhere or add one.
+      (goto-char (match-beginning 0))
+      (let ((re (rx "\\usepackage" (opt "[" (*? nonl) "]") "{natbib}")))
+        (unless (re-search-backward re nil t)
+          (insert
+           (format "\\usepackage%s{natbib}\n"
+                   (if (null org-cite-natbib-options)
+                       ""
+                     (format "[%s]"
+                             (mapconcat #'symbol-name
+                                        org-cite-natbib-options
+                                        ","))))))))
+    (buffer-string)))
+
+
+;;; Register `natbib' processor
+(org-cite-register-processor 'natbib
+  :export-bibliography #'org-cite-natbib-export-bibliography
+  :export-citation #'org-cite-natbib-export-citation
+  :export-finalizer #'org-cite-natbib-use-package
+  :cite-styles
+  '((("author" "a") ("caps" "a") ("full" "f"))
+    (("noauthor" "na") ("bare" "b"))
+    (("text" "t")
+     ("bare" "b") ("caps" "c") ("full" "f") ("bare-caps" "bc")
+     ("bare-full" "bf") ("caps-full" "cf") ("bare-caps-full" "bcf"))
+    (("nil")
+     ("bare" "b") ("caps" "c") ("full" "f") ("bare-caps" "bc")
+     ("bare-full" "bf") ("caps-full" "cf") ("bare-caps-full" "bcf"))))
+
+(provide 'org-cite-natbib)
+(provide 'oc-natbib)
+;;; oc-natbib.el ends here