;;; oc-biblatex.el --- biblatex citation processor for Org  -*- lexical-binding: t; -*-

;; Copyright (C) 2021-2023 Free Software Foundation, Inc.

;; Author: Nicolas Goaziou <mail@nicolasgoaziou.fr>

;; This file is part of GNU Emacs.

;; GNU Emacs 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.

;; GNU Emacs 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 GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This library registers the `biblatex' citation processor, which provides
;; the "export" capability for citations.

;; The processor relies on "biblatex" LaTeX package.  As such it ensures that
;; the package is properly required in the document's preamble.  More
;; accurately, it will re-use any "\usepackage{biblatex}" already present in
;; the document (e.g., through `org-latex-packages-alist'), or insert one using
;; options defined in `org-cite-biblatex-options'.

;; In any case, the library will override style-related options with those
;; specified with the citation processor, in `org-cite-export-processors' or
;; "cite_export" keyword.  If you need to use different styles for bibliography
;; and citations, you can separate them with "bibstyle/citestyle" syntax.  E.g.,
;;
;;   #+cite_export: biblatex authortitle/authortitle-ibid

;; The library supports the following citation styles:
;;
;; - author (a), including caps (c), full (f) and caps-full (cf) variants,
;; - locators (l), including bare (b), caps (c) and bare-caps (bc) variants,
;; - noauthor (na), including bare (b) variant,
;; - nocite (n),
;; - text (t), including caps (c) variant,
;; - default style, including bare (b), caps (c) and bare-caps (bc) variants.

;; When citation and style permit, the library automatically generates
;; "multicite" versions of the commands above.

;; Bibliography is printed using "\printbibliography" command.  Additional
;; options may be passed to it through a property list attached to the
;; "print_bibliography" keyword.  E.g.,
;;
;;    #+print_bibliography: :section 2 :heading subbibliography
;;
;; Values including spaces must be surrounded with double quotes.  If you need
;; to use a key multiple times, you can separate its values with commas, but
;; without any space in-between:
;;
;;    #+print_bibliography: :keyword abc,xyz :title "Primary Sources"

;;; Code:

(require 'org-macs)
(org-assert-version)

(require 'map)
(require 'org-macs)
(require 'oc)

(declare-function org-element-property "org-element" (property element))
(declare-function org-export-data "org-export" (data info))

\f
;;; Customization
(defcustom org-cite-biblatex-options nil
  "Options added to \"biblatex\" package.
If \"biblatex\" 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 '(choice
          (string :tag "Options (key=value,key2=value2...)")
          (const :tag "No option" nil))
  :safe #'string-or-null-p)

(defcustom org-cite-biblatex-styles
  '(("author"   "caps"      "Citeauthor*" nil         nil)
    ("author"   "full"      "citeauthor"  nil         nil)
    ("author"   "caps-full" "Citeauthor"  nil         nil)
    ("author"   nil         "citeauthor*" nil         nil)
    ("locators" "bare"      "notecite"    nil         nil)
    ("locators" "caps"      "Pnotecite"   nil         nil)
    ("locators" "bare-caps" "Notecite"    nil         nil)
    ("locators" nil         "pnotecite"   nil         nil)
    ("noauthor" "bare"      "cite*"       nil         nil)
    ("noauthor" nil         "autocite*"   nil         nil)
    ("nocite"   nil         "nocite"      nil         t)
    ("text"     "caps"      "Textcite"    "Textcites" nil)
    ("text"     nil         "textcite"    "textcites" nil)
    (nil        "bare"      "cite"        "cites"     nil)
    (nil        "caps"      "Autocite"    "Autocites" nil)
    (nil        "bare-caps" "Cite"        "Cites"     nil)
    (nil        nil         "autocite"    "autocites" nil))
  "List of styles and variants, with associated BibLaTeX commands.

Each style follows the pattern

  (NAME VARIANT COMMAND MULTI-COMMAND NO-OPTION)

where:

  NAME is the name of the style, as a string, or nil.  The nil
  style is the default style.  As such, it must have an entry in
  the list.

  VARIANT is the name of the style variant, as a string or nil.
  The nil variant is the default variant for the current style.
  As such, each style name must be associated to a nil variant.

  COMMAND is the LaTeX command to use, as a string.  It should
  not contain the leading backslash character.

  MULTI-COMMAND is the LaTeX command to use when a multi-cite
  command is appropriate.  When nil, the style is deemed
  inappropriate for multi-cites.  The command should not contain
  the leading backslash character.

  NO-OPTION is a boolean.  When non-nil, no optional argument
  should be added to the LaTeX command.

Each NAME-VARIANT pair should be unique in the list.

It is also possible to provide shortcuts for style and variant
names.  See `org-cite-biblatex-style-shortcuts'."
  :group 'org-cite
  :package-version '(Org . "9.6")
  :type '(repeat
          (list :tag "Style/variant combination"
                ;; Name part.
                (choice :tag "Style"
                        (string :tag "Name")
                        (const :tag "Default style" nil))
                ;; Variant part.
                (choice :tag "Variant"
                        (string :tag "Name")
                        (const :tag "Default variant" nil))
                ;; Command part.
                (string :tag "Command name")
                (choice :tag "Multicite command"
                        (string :tag "Command name")
                        (const :tag "No multicite support" nil))
                (choice :tag "Skip optional arguments"
                        (const :tag "Yes" t)
                        (const :tag "No" nil)))))

(defcustom org-cite-biblatex-style-shortcuts
  '(("a"  . "author")
    ("b"  . "bare")
    ("bc" . "bare-caps")
    ("c"  . "caps")
    ("cf" . "caps-full")
    ("f"  . "full")
    ("l"  . "locators")
    ("n"  . "nocite")
    ("na" . "noauthor")
    ("t"  . "text"))
  "List of shortcuts associated to style or variant names.

Each entry is a pair (NAME . STYLE-NAME) where NAME is the name
of the shortcut, as a string, and STYLE-NAME is the name of
a style in `org-cite-biblatex-styles'."
  :group 'org-cite
  :package-version '(Org . "9.6")
  :type '(repeat
          (cons :tag "Shortcut"
                (string :tag "Name")
                (string :tag "Full name")))
  :safe t)

\f
;;; Internal functions
(defun org-cite-biblatex--package-options (initial style)
  "Return options string for \"biblatex\" package.

INITIAL is an initial style of comma-separated options, as a string or nil.
STYLE is the style definition as a string or nil.

Return a string."
  (let ((options-no-style
         (and initial
              (let ((re (rx string-start (or "bibstyle" "citestyle" "style"))))
                (seq-filter
                 (lambda (option) (not (string-match re option)))
                 (split-string (org-unbracket-string "[" "]" initial)
                               "," t " \t")))))
        (style-options
         (cond
          ((null style) nil)
          ((not (string-match "/" style)) (list (concat "style=" style)))
          (t
           (list (concat "bibstyle=" (substring style nil (match-beginning 0)))
                 (concat "citestyle=" (substring style (match-end 0))))))))
    (if (or options-no-style style-options)
        (format "[%s]"
                (mapconcat #'identity
                           (append options-no-style style-options)
                           ","))
      "")))

(defun org-cite-biblatex--multicite-p  (citation)
  "Non-nil when citation could make use of a \"multicite\" command."
  (let ((references (org-cite-get-references citation)))
    (and (< 1 (length references))
         (seq-some (lambda (r)
                     (or (org-element-property :prefix r)
                         (org-element-property :suffix r)))
                   references))))

(defun org-cite-biblatex--atomic-arguments (references info &optional no-opt)
  "Build argument for the list of citation REFERENCES.
When NO-OPT argument is non-nil, only provide mandatory arguments."
  (let ((mandatory
         (format "{%s}"
                 (mapconcat (lambda (r) (org-element-property :key r))
                            references
                            ","))))
    (if no-opt mandatory
      (let* ((origin (pcase references
                       (`(,reference) reference)
                       (`(,reference . ,_)
                        (org-element-property :parent reference))))
             (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))
                mandatory)))))

(defun org-cite-biblatex--multi-arguments (citation info)
  "Build \"multicite\" command arguments for CITATION object.
INFO is the export state, as a property list."
  (let ((global-prefix (org-element-property :prefix citation))
        (global-suffix (org-element-property :suffix citation)))
    (concat (and global-prefix
                 (format "(%s)"
                         (org-trim (org-export-data global-prefix info))))
            (cond
             ;; Global pre/post-notes.
             (global-suffix
              (format "(%s)"
                      (org-trim (org-export-data global-suffix info))))
             (global-prefix "()")
             (t nil))
            ;; All arguments.
            (mapconcat (lambda (r)
                         (org-cite-biblatex--atomic-arguments (list r) info))
                       (org-cite-get-references citation)
                       ""))))

(defun org-cite-biblatex--command (citation info name &optional multi no-opt)
  "Return BibLaTeX command NAME for CITATION object.

INFO is the export state, as a property list.

When optional argument MULTI is non-nil, use it as a multicite
command name when appropriate.  When optional argument NO-OPT is
non-nil, do not add optional arguments to the command."
  (if (and multi (org-cite-biblatex--multicite-p citation))
      (format "\\%s%s" multi (org-cite-biblatex--multi-arguments citation info))
    (format "\\%s%s"
            name
            (org-cite-biblatex--atomic-arguments
             (org-cite-get-references citation) info no-opt))))

(defun org-cite-biblatex--expand-shortcuts (style)
  "Return STYLE pair with shortcuts expanded."
  (pcase style
    (`(,style . ,variant)
     (cons (or (alist-get style org-cite-biblatex-style-shortcuts
                          nil nil #'equal)
               style)
           (or (alist-get variant org-cite-biblatex-style-shortcuts
                          nil nil #'equal)
               variant)))
    (_ (error "This should not happen"))))

(defun org-cite-biblatex-list-styles ()
  "List styles and variants supported in `biblatex' citation processor.
The output format is appropriate as a value for `:cite-styles' keyword
in `org-cite-register-processor', which see."
  (let ((shortcuts (make-hash-table :test #'equal))
        (variants (make-hash-table :test #'equal)))
    (pcase-dolist (`(,name . ,full-name) org-cite-biblatex-style-shortcuts)
      (push name (gethash full-name shortcuts)))
    (pcase-dolist (`(,name ,variant . ,_) org-cite-biblatex-styles)
      (unless (null variant) (push variant (gethash name variants))))
    (map-apply (lambda (style-name variants)
                 (cons (cons (or style-name "nil")
                             (gethash style-name shortcuts))
                       (mapcar (lambda (v)
                                 (cons v (gethash v shortcuts)))
                               variants)))
               variants)))

\f
;;; Export capability
(defun org-cite-biblatex-export-bibliography (_keys _files _style props &rest _)
  "Print references from bibliography.
PROPS is the local properties of the bibliography, as a property list."
  (concat "\\printbibliography"
          (and props
               (let ((key nil)
                     (results nil))
                 (dolist (datum props)
                   (cond
                    ((keywordp datum)
                     (when key (push key results))
                     (setq key (substring (symbol-name datum) 1)))
                    (t
                     ;; Comma-separated values are associated to the
                     ;; same keyword.
                     (push (mapconcat (lambda (v) (concat key "=" v))
                                      (split-string datum "," t)
                                      ",")
                           results)
                     (setq key nil))))
                 (format "[%s]"
                         (mapconcat #'identity (nreverse results) ","))))))

(defun org-cite-biblatex-export-citation (citation style _ info)
  "Export CITATION object.
STYLE is the citation style, as a pair of either strings or nil.
INFO is the export state, as a property list."
  (pcase-let* ((`(,name . ,variant) (org-cite-biblatex--expand-shortcuts style))
               (candidates nil)
               (style-match-flag nil))
    (catch :match
      ;; Walk `org-cite-biblatex-styles' and prioritize matching
      ;; candidates.  At the end of the process, the optimal candidate
      ;; should appear in front of CANDIDATES.
      (dolist (style org-cite-biblatex-styles)
        (pcase style
          ;; A matching style-variant pair trumps anything else.
          ;; Return it.
          (`(,(pred (equal name)) ,(pred (equal variant)) . ,_)
           (throw :match (setq candidates (list style))))
          ;; nil-nil style-variant is the fallback value.  Consider it
          ;; only if nothing else matches.
          (`(nil nil . ,_)
           (unless candidates (push style candidates)))
          ;; A matching style with default variant trumps a matching
          ;; variant without the adequate style.  Ensure the former
          ;; appears first in the list.
          (`(,(pred (equal name)) nil . ,_)
           (push style candidates)
           (setq style-match-flag t))
          (`(nil ,(pred (equal variant)) . ,_)
           (unless style-match-flag (push style candidates)))
          ;; Discard anything else.
          (_ nil))))
    (apply
     #'org-cite-biblatex--command citation info
     (pcase (seq-elt candidates 0) ;; `seq-first' is not available in Emacs 26.
       (`(,_ ,_ . ,command-parameters) command-parameters)
       ('nil
        (user-error
         "Missing default style or variant in `org-cite-biblatex-styles'"))
       (other
        (user-error "Invalid entry %S in `org-cite-biblatex-styles'" other))))))

(defun org-cite-biblatex--generate-latex-preamble (info)
  "Ensure that the biblatex package is loaded, and the necessary resources.
This is performed by extracting relevant information from the
INFO export plist, and modifying any existing
\\usepackage{biblatex} statement in the LaTeX header."
  (let ((style (org-cite-bibliography-style info))
        (files (plist-get info :bibliography))
        (usepackage-rx (rx "\\usepackage"
                           (opt (group "[" (*? anything) "]"))
                           "{biblatex}")))
    (concat
     (if (string-match usepackage-rx (plist-get info :latex-full-header))
         ;; "biblatex" package loaded, but with none (or different) options.
         ;; Replace with style-including command.
         (plist-put info :latex-full-header
                    (replace-match
                     (format "\\usepackage%s{biblatex}"
                             (save-match-data
                               (org-cite-biblatex--package-options nil style)))
                     t t
                     (plist-get info :latex-full-header)))
       ;; No "biblatex" package loaded.  Insert "usepackage" command
       ;; with appropriate options, including style.
       (format "\\usepackage%s{biblatex}\n"
               (org-cite-biblatex--package-options
                org-cite-biblatex-options style)))
     ;; Load resources.
     (mapconcat (lambda (f)
                  (format "\\addbibresource%s{%s}"
                          (if (org-url-p f) "[location=remote]" "")
                          f))
                files
                "\n"))))

\f
;;; Register `biblatex' processor
(org-cite-register-processor 'biblatex
  :export-bibliography #'org-cite-biblatex-export-bibliography
  :export-citation #'org-cite-biblatex-export-citation
  :cite-styles #'org-cite-biblatex-list-styles)

(provide 'oc-biblatex)
;;; oc-biblatex.el ends here