Merge branch 'maint'

[org-mode.git] / lisp / ox-beamer.el

;;; ox-beamer.el --- Beamer Back-End for Org Export Engine

;; Copyright (C) 2007-2013  Free Software Foundation, Inc.

;; Author: Carsten Dominik <carsten.dominik AT gmail DOT com>
;;         Nicolas Goaziou <n.goaziou AT gmail DOT com>
;; Keywords: org, wp, tex

;; 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 <http://www.gnu.org/licenses/>.

;;; Commentary:
;;
;; This library implements both a Beamer back-end, derived from the
;; LaTeX one and a minor mode easing structure edition of the
;; document.
;;
;; Depending on the desired output format, three commands are provided
;; for export: `org-beamer-export-as-latex' (temporary buffer),
;; `org-beamer-export-to-latex' ("tex" file) and
;; `org-beamer-export-to-pdf' ("pdf" file).
;;
;; This back-end supports every buffer keyword, attribute and options
;; items (see `org-latex-options-alist') already supported by `latex'
;; back-end.  As such, it is suggested to add an entry in
;; `org-latex-classes' variable which is appropriate for Beamer
;; export.
;;
;; On top of this, the `beamer' back-end also introduces the following
;; keywords: "BEAMER_THEME", "BEAMER_COLOR_THEME",
;; "BEAMER_FONT_THEME", "BEAMER_INNER_THEME", "BEAMER_OUTER_THEME" and
;; "BEAMER_HEADER".  All but the latter accept options in square
;; brackets.
;;
;; Moreover, headlines now fall into three categories: sectioning
;; elements, frames and blocks.
;;
;; - Headlines become frames when their level is equal to
;;   `org-beamer-frame-level' (or "H" value in the OPTIONS line).
;;   Though, if a headline in the current tree has a "BEAMER_env"
;;   (see below) property set to either "frame" or "fullframe", its
;;   level overrides the variable.  A "fullframe" is a frame with an
;;   empty (ignored) title.
;;
;; - All frames' children become block environments.  Special block
;;   types can be enforced by setting headline's "BEAMER_env" property
;;   to an appropriate value (see `org-beamer-environments-default'
;;   for supported value and `org-beamer-environments-extra' for
;;   adding more).
;;
;; - As a special case, if the "BEAMER_env" property is set to either
;;   "appendix", "note", "noteNH" or "againframe", the headline will
;;   become, respectively, an appendix, a note (within frame or
;;   between frame, depending on its level), a note with its title
;;   ignored or an againframe command.  In the latter case,
;;   a "BEAMER_ref" property is mandatory in order to refer to the
;;   frame being resumed, and contents are ignored.
;;
;;   Also, a headline with an "ignoreheading" environment will have
;;   its contents only inserted in the output.  This special value is
;;   useful to have data between frames, or to properly close
;;   a "column" environment.
;;
;; Along with "BEAMER_env", headlines also support the "BEAMER_act"
;; and "BEAMER_opt" properties.  The former is translated as an
;; overlay/action specification (or a default overlay specification
;; when enclosed within square brackets) whereas the latter specifies
;; options for the current frame ("fragile" option is added
;; automatically, though).
;;
;; Moreover, headlines handle the "BEAMER_col" property.  Its value
;; should be a decimal number representing the width of the column as
;; a fraction of the total text width.  If the headline has no
;; specific environment, its title will be ignored and its contents
;; will fill the column created.  Otherwise, the block will fill the
;; whole column and the title will be preserved.  Two contiguous
;; headlines with a non-nil "BEAMER_col" value share the same
;; "columns" LaTeX environment.  It will end before the next headline
;; without such a property.  This environment is generated
;; automatically.  Although, it can also be explicitly created, with
;; a special "columns" value for "BEAMER_env" property (if it needs to
;; be set up with some specific options, for example).
;;
;; Every plain list has support for `:environment', `:overlay' and
;; `:options' attributes (through ATTR_BEAMER affiliated keyword).
;; The first one allows to use a different environment, the second
;; sets overlay specifications and the last one inserts optional
;; arguments in current list environment.
;;
;; Table of contents generated from "toc:t" option item are wrapped
;; within a "frame" environment.  Those generated from a TOC keyword
;; aren't.  TOC keywords accept options enclosed within square
;; brackets (e.g. #+TOC: headlines [currentsection]).
;;
;; Eventually, an export snippet with a value enclosed within angular
;; brackets put at the beginning of an element or object whose type is
;; among `bold', `item', `link', `radio-target' and `target' will
;; control its overlay specifications.
;;
;; On the minor mode side, `org-beamer-select-environment' (bound by
;; default to "C-c C-b") and `org-beamer-insert-options-template' are
;; the two entry points.

;;; Code:

(eval-when-compile (require 'cl))
(require 'ox-latex)

;; Install a default set-up for Beamer export.
(unless (assoc "beamer" org-latex-classes)
  (add-to-list 'org-latex-classes
               '("beamer"
                 "\\documentclass[presentation]{beamer}
     \[DEFAULT-PACKAGES]
     \[PACKAGES]
     \[EXTRA]"
                 ("\\section{%s}" . "\\section*{%s}")
                 ("\\subsection{%s}" . "\\subsection*{%s}")
                 ("\\subsubsection{%s}" . "\\subsubsection*{%s}"))))


\f
;;; User-Configurable Variables

(defgroup org-export-beamer nil
  "Options specific for using the beamer class in LaTeX export."
  :tag "Org Beamer"
  :group 'org-export
  :version "24.2")

(defcustom org-beamer-frame-level 1
  "The level at which headlines become frames.

Headlines at a lower level will be translated into a sectioning
structure.  At a higher level, they will be translated into
blocks.

If a headline with a \"BEAMER_env\" property set to \"frame\" is
found within a tree, its level locally overrides this number.

This variable has no effect on headlines with the \"BEAMER_env\"
property set to either \"ignoreheading\", \"appendix\", or
\"note\", which will respectively, be invisible, become an
appendix or a note.

This integer is relative to the minimal level of a headline
within the parse tree, defined as 1."
  :group 'org-export-beamer
  :type 'integer)

(defcustom org-beamer-frame-default-options ""
  "Default options string to use for frames.
For example, it could be set to \"allowframebreaks\"."
  :group 'org-export-beamer
  :type '(string :tag "[options]"))

(defcustom org-beamer-column-view-format
  "%45ITEM %10BEAMER_env(Env) %10BEAMER_act(Act) %4BEAMER_col(Col) %8BEAMER_opt(Opt)"
  "Column view format that should be used to fill the template."
  :group 'org-export-beamer
  :version "24.4"
  :package-version '(Org . "8.0")
  :type '(choice
          (const  :tag "Do not insert Beamer column view format" nil)
          (string :tag "Beamer column view format")))

(defcustom org-beamer-theme "default"
  "Default theme used in Beamer presentations."
  :group 'org-export-beamer
  :version "24.4"
  :package-version '(Org . "8.0")
  :type '(choice
          (const :tag "Do not insert a Beamer theme" nil)
          (string :tag "Beamer theme")))

(defcustom org-beamer-environments-extra nil
  "Environments triggered by tags in Beamer export.
Each entry has 4 elements:

name    Name of the environment
key     Selection key for `org-beamer-select-environment'
open    The opening template for the environment, with the following escapes
        %a   the action/overlay specification
        %A   the default action/overlay specification
        %o   the options argument of the template
        %h   the headline text
        %H   if there is headline text, that text in {} braces
        %U   if there is headline text, that text in [] brackets
close   The closing string of the environment."
  :group 'org-export-beamer
  :version "24.4"
  :package-version '(Org . "8.0")
  :type '(repeat
          (list
           (string :tag "Environment")
           (string :tag "Selection key")
           (string :tag "Begin")
           (string :tag "End"))))

(defcustom org-beamer-outline-frame-title "Outline"
  "Default title of a frame containing an outline."
  :group 'org-export-beamer
  :type '(string :tag "Outline frame title"))

(defcustom org-beamer-outline-frame-options ""
  "Outline frame options appended after \\begin{frame}.
You might want to put e.g. \"allowframebreaks=0.9\" here."
  :group 'org-export-beamer
  :type '(string :tag "Outline frame options"))


\f
;;; Internal Variables

(defconst org-beamer-column-widths
  "0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.0 :ETC"
"The column widths that should be installed as allowed property values.")

(defconst org-beamer-environments-special
  '(("againframe"     "A")
    ("appendix"       "x")
    ("column"         "c")
    ("columns"        "C")
    ("frame"          "f")
    ("fullframe"      "F")
    ("ignoreheading"  "i")
    ("note"           "n")
    ("noteNH"         "N"))
  "Alist of environments treated in a special way by the back-end.
Keys are environment names, as strings, values are bindings used
in `org-beamer-select-environment'.  Environments listed here,
along with their binding, are hard coded and cannot be modified
through `org-beamer-environments-extra' variable.")

(defconst org-beamer-environments-default
  '(("block"          "b" "\\begin{block}%a{%h}"          "\\end{block}")
    ("alertblock"     "a" "\\begin{alertblock}%a{%h}"     "\\end{alertblock}")
    ("verse"          "v" "\\begin{verse}%a %% %h"        "\\end{verse}")
    ("quotation"      "q" "\\begin{quotation}%a %% %h"    "\\end{quotation}")
    ("quote"          "Q" "\\begin{quote}%a %% %h"        "\\end{quote}")
    ("structureenv"   "s" "\\begin{structureenv}%a %% %h" "\\end{structureenv}")
    ("theorem"        "t" "\\begin{theorem}%a%U"          "\\end{theorem}")
    ("definition"     "d" "\\begin{definition}%a%U"       "\\end{definition}")
    ("example"        "e" "\\begin{example}%a%U"          "\\end{example}")
    ("exampleblock"   "E" "\\begin{exampleblock}%a{%h}"   "\\end{exampleblock}")
    ("proof"          "p" "\\begin{proof}%a%U"            "\\end{proof}")
    ("beamercolorbox" "o" "\\begin{beamercolorbox}%o{%h}" "\\end{beamercolorbox}"))
  "Environments triggered by properties in Beamer export.
These are the defaults - for user definitions, see
`org-beamer-environments-extra'.")

(defconst org-beamer-verbatim-elements
  '(code example-block fixed-width inline-src-block src-block verbatim)
  "List of element or object types producing verbatim text.
This is used internally to determine when a frame should have the
\"fragile\" option.")


\f
;;; Internal functions

(defun org-beamer--normalize-argument (argument type)
  "Return ARGUMENT string with proper boundaries.

TYPE is a symbol among the following:
`action'    Return ARGUMENT within angular brackets.
`defaction' Return ARGUMENT within both square and angular brackets.
`option'    Return ARGUMENT within square brackets."
  (if (not (string-match "\\S-" argument)) ""
    (case type
      (action (if (string-match "\\`<.*>\\'" argument) argument
                (format "<%s>" argument)))
      (defaction (cond
                  ((string-match "\\`\\[<.*>\\]\\'" argument) argument)
                  ((string-match "\\`<.*>\\'" argument)
                   (format "[%s]" argument))
                  ((string-match "\\`\\[\\(.*\\)\\]\\'" argument)
                   (format "[<%s>]" (match-string 1 argument)))
                  (t (format "[<%s>]" argument))))
      (option (if (string-match "\\`\\[.*\\]\\'" argument) argument
                (format "[%s]" argument)))
      (otherwise argument))))

(defun org-beamer--element-has-overlay-p (element)
  "Non-nil when ELEMENT has an overlay specified.
An element has an overlay specification when it starts with an
`beamer' export-snippet whose value is between angular brackets.
Return overlay specification, as a string, or nil."
  (let ((first-object (car (org-element-contents element))))
    (when (eq (org-element-type first-object) 'export-snippet)
      (let ((value (org-element-property :value first-object)))
        (and (string-match "\\`<.*>\\'" value) value)))))


\f
;;; Define Back-End

(org-export-define-derived-backend 'beamer 'latex
  :export-block "BEAMER"
  :menu-entry
  '(?l 1
       ((?B "As LaTeX buffer (Beamer)" org-beamer-export-as-latex)
        (?b "As LaTeX file (Beamer)" org-beamer-export-to-latex)
        (?P "As PDF file (Beamer)" org-beamer-export-to-pdf)
        (?O "As PDF file and open (Beamer)"
            (lambda (a s v b)
              (if a (org-beamer-export-to-pdf t s v b)
                (org-open-file (org-beamer-export-to-pdf nil s v b)))))))
  :options-alist
  '((:beamer-theme "BEAMER_THEME" nil org-beamer-theme)
    (:beamer-color-theme "BEAMER_COLOR_THEME" nil nil t)
    (:beamer-font-theme "BEAMER_FONT_THEME" nil nil t)
    (:beamer-inner-theme "BEAMER_INNER_THEME" nil nil t)
    (:beamer-outer-theme "BEAMER_OUTER_THEME" nil nil t)
    (:beamer-header-extra "BEAMER_HEADER" nil nil newline)
    ;; Modify existing properties.
    (:headline-levels nil "H" org-beamer-frame-level)
    (:latex-class "LATEX_CLASS" nil "beamer" t))
  :translate-alist '((bold . org-beamer-bold)
                     (export-block . org-beamer-export-block)
                     (export-snippet . org-beamer-export-snippet)
                     (headline . org-beamer-headline)
                     (item . org-beamer-item)
                     (keyword . org-beamer-keyword)
                     (link . org-beamer-link)
                     (plain-list . org-beamer-plain-list)
                     (radio-target . org-beamer-radio-target)
                     (target . org-beamer-target)
                     (template . org-beamer-template)))


\f
;;; Transcode Functions

;;;; Bold

(defun org-beamer-bold (bold contents info)
  "Transcode BLOCK object into Beamer code.
CONTENTS is the text being bold.  INFO is a plist used as
a communication channel."
  (format "\\alert%s{%s}"
          (or (org-beamer--element-has-overlay-p bold) "")
          contents))


;;;; Export Block

(defun org-beamer-export-block (export-block contents info)
  "Transcode an EXPORT-BLOCK element into Beamer code.
CONTENTS is nil.  INFO is a plist used as a communication
channel."
  (when (member (org-element-property :type export-block) '("BEAMER" "LATEX"))
    (org-remove-indentation (org-element-property :value export-block))))


;;;; Export Snippet

(defun org-beamer-export-snippet (export-snippet contents info)
  "Transcode an EXPORT-SNIPPET object into Beamer code.
CONTENTS is nil.  INFO is a plist used as a communication
channel."
  (let ((backend (org-export-snippet-backend export-snippet))
        (value (org-element-property :value export-snippet)))
    ;; Only "latex" and "beamer" snippets are retained.
    (cond ((eq backend 'latex) value)
          ;; Ignore "beamer" snippets specifying overlays.
          ((and (eq backend 'beamer)
                (or (org-export-get-previous-element export-snippet info)
                    (not (string-match "\\`<.*>\\'" value))))
           value))))


;;;; Headline
;;
;; The main function to translate a headline is
;; `org-beamer-headline'.
;;
;; Depending on the level at which a headline is considered as
;; a frame (given by `org-beamer--frame-level'), the headline is
;; either a section (`org-beamer--format-section'), a frame
;; (`org-beamer--format-frame') or a block
;; (`org-beamer--format-block').
;;
;; `org-beamer-headline' also takes care of special environments
;; like "ignoreheading", "note", "noteNH", "appendix" and
;; "againframe".

(defun org-beamer--get-label (headline info)
  "Return label for HEADLINE, as a string.

INFO is a plist used as a communication channel.

The value is either the label specified in \"BEAMER_opt\"
property, or a fallback value built from headline's number.  This
function assumes HEADLINE will be treated as a frame."
  (let ((opt (org-element-property :BEAMER_OPT headline)))
    (if (and (org-string-nw-p opt)
             (string-match "\\(?:^\\|,\\)label=\\(.*?\\)\\(?:$\\|,\\)" opt))
        (match-string 1 opt)
      (format "sec-%s"
              (mapconcat 'number-to-string
                         (org-export-get-headline-number headline info)
                         "-")))))

(defun org-beamer--frame-level (headline info)
  "Return frame level in subtree containing HEADLINE.
INFO is a plist used as a communication channel."
  (or
   ;; 1. Look for "frame" environment in parents, starting from the
   ;;    farthest.
   (catch 'exit
     (mapc (lambda (parent)
             (let ((env (org-element-property :BEAMER_ENV parent)))
               (when (and env (member-ignore-case env '("frame" "fullframe")))
                 (throw 'exit (org-export-get-relative-level parent info)))))
           (nreverse (org-export-get-genealogy headline)))
     nil)
   ;; 2. Look for "frame" environment in HEADLINE.
   (let ((env (org-element-property :BEAMER_ENV headline)))
     (and env (member-ignore-case env '("frame" "fullframe"))
          (org-export-get-relative-level headline info)))
   ;; 3. Look for "frame" environment in sub-tree.
   (org-element-map headline 'headline
     (lambda (hl)
       (let ((env (org-element-property :BEAMER_ENV hl)))
         (when (and env (member-ignore-case env '("frame" "fullframe")))
           (org-export-get-relative-level hl info))))
     info 'first-match)
   ;; 4. No "frame" environment in tree: use default value.
   (plist-get info :headline-levels)))

(defun org-beamer--format-section (headline contents info)
  "Format HEADLINE as a sectioning part.
CONTENTS holds the contents of the headline.  INFO is a plist
used as a communication channel."
  ;; Use `latex' back-end output, inserting overlay specifications
  ;; if possible.
  (let ((latex-headline (org-export-with-backend 'latex headline contents info))
        (mode-specs (org-element-property :BEAMER_ACT headline)))
    (if (and mode-specs
             (string-match "\\`\\\\\\(.*?\\)\\(?:\\*\\|\\[.*\\]\\)?{"
                           latex-headline))
        (replace-match (concat (match-string 1 latex-headline)
                               (format "<%s>" mode-specs))
                       nil nil latex-headline 1)
      latex-headline)))

(defun org-beamer--format-frame (headline contents info)
  "Format HEADLINE as a frame.
CONTENTS holds the contents of the headline.  INFO is a plist
used as a communication channel."
  (let ((fragilep
         ;; FRAGILEP is non-nil when HEADLINE contains an element
         ;; among `org-beamer-verbatim-elements'.
         (org-element-map headline org-beamer-verbatim-elements 'identity
                          info 'first-match)))
    (concat "\\begin{frame}"
            ;; Overlay specification, if any. When surrounded by
            ;; square brackets, consider it as a default
            ;; specification.
            (let ((action (org-element-property :BEAMER_ACT headline)))
              (cond
               ((not action) "")
               ((string-match "\\`\\[.*\\]\\'" action )
                (org-beamer--normalize-argument action 'defaction))
               (t (org-beamer--normalize-argument action 'action))))
            ;; Options, if any.
            (let* ((beamer-opt (org-element-property :BEAMER_OPT headline))
                   (options
                    ;; Collect options from default value and headline's
                    ;; properties.  Also add a label for links.
                    (append
                     (org-split-string org-beamer-frame-default-options ",")
                     (and beamer-opt
                          (org-split-string
                           ;; Remove square brackets if user provided
                           ;; them.
                           (and (string-match "^\\[?\\(.*\\)\\]?$" beamer-opt)
                                (match-string 1 beamer-opt))
                           ","))
                     ;; Provide an automatic label for the frame
                     ;; unless the user specified one.
                     (unless (and beamer-opt
                                  (string-match "\\(^\\|,\\)label=" beamer-opt))
                       (list
                        (format "label=%s"
                                (org-beamer--get-label headline info)))))))
              ;; Change options list into a string.
              (org-beamer--normalize-argument
               (mapconcat
                'identity
                (if (or (not fragilep) (member "fragile" options)) options
                  (cons "fragile" options))
                ",")
               'option))
            ;; Title.
            (let ((env (org-element-property :BEAMER_ENV headline)))
              (format "{%s}"
                      (if (and env (equal (downcase env) "fullframe")) ""
                        (org-export-data
                         (org-element-property :title headline) info))))
            "\n"
            ;; The following workaround is required in fragile frames
            ;; as Beamer will append "\par" to the beginning of the
            ;; contents.  So we need to make sure the command is
            ;; separated from the contents by at least one space.  If
            ;; it isn't, it will create "\parfirst-word" command and
            ;; remove the first word from the contents in the PDF
            ;; output.
            (if (not fragilep) contents
              (replace-regexp-in-string "\\`\n*" "\\& " (or contents "")))
            "\\end{frame}")))

(defun org-beamer--format-block (headline contents info)
  "Format HEADLINE as a block.
CONTENTS holds the contents of the headline.  INFO is a plist
used as a communication channel."
  (let* ((column-width (org-element-property :BEAMER_COL headline))
         ;; ENVIRONMENT defaults to "block" if none is specified and
         ;; there is no column specification.  If there is a column
         ;; specified but still no explicit environment, ENVIRONMENT
         ;; is "column".
         (environment (let ((env (org-element-property :BEAMER_ENV headline)))
                        (cond
                         ;; "block" is the fallback environment.
                         ((and (not env) (not column-width)) "block")
                         ;; "column" only.
                         ((not env) "column")
                         ;; Use specified environment.
                         (t env))))
         (env-format (unless (member environment '("column" "columns"))
                       (assoc environment
                              (append org-beamer-environments-special
                                      org-beamer-environments-extra
                                      org-beamer-environments-default))))
         (title (org-export-data (org-element-property :title headline) info))
         (options (let ((options (org-element-property :BEAMER_OPT headline)))
                    (if (not options) ""
                      (org-beamer--normalize-argument options 'option))))
         ;; Start a "columns" environment when explicitly requested or
         ;; when there is no previous headline or the previous
         ;; headline do not have a BEAMER_column property.
         (parent-env (org-element-property
                      :BEAMER_ENV (org-export-get-parent-headline headline)))
         (start-columns-p
          (or (equal environment "columns")
              (and column-width
                   (not (and parent-env
                             (equal (downcase parent-env) "columns")))
                   (or (org-export-first-sibling-p headline info)
                       (not (org-element-property
                             :BEAMER_COL
                             (org-export-get-previous-element
                              headline info)))))))
         ;; End the "columns" environment when explicitly requested or
         ;; when there is no next headline or the next headline do not
         ;; have a BEAMER_column property.
         (end-columns-p
          (or (equal environment "columns")
              (and column-width
                   (not (and parent-env
                             (equal (downcase parent-env) "columns")))
                   (or (org-export-last-sibling-p headline info)
                       (not (org-element-property
                             :BEAMER_COL
                             (org-export-get-next-element headline info))))))))
    (concat
     (when start-columns-p
       ;; Column can accept options only when the environment is
       ;; explicitly defined.
       (if (not (equal environment "columns")) "\\begin{columns}\n"
         (format "\\begin{columns}%s\n" options)))
     (when column-width
       (format "\\begin{column}%s{%s}\n"
               ;; One can specify placement for column only when
               ;; HEADLINE stands for a column on its own.
               (if (equal environment "column") options "")
               (format "%s\\textwidth" column-width)))
     ;; Block's opening string.
     (when env-format
       (concat
        (org-fill-template
         (nth 2 env-format)
         (nconc
          ;; If BEAMER_act property has its value enclosed in square
          ;; brackets, it is a default overlay specification and
          ;; overlay specification is empty.  Otherwise, it is an
          ;; overlay specification and the default one is nil.
          (let ((action (org-element-property :BEAMER_ACT headline)))
            (cond
             ((not action) (list (cons "a" "") (cons "A" "")))
             ((string-match "\\`\\[.*\\]\\'" action)
              (list
               (cons "A" (org-beamer--normalize-argument action 'defaction))
               (cons "a" "")))
             (t
              (list (cons "a" (org-beamer--normalize-argument action 'action))
                    (cons "A" "")))))
          (list (cons "o" options)
                (cons "h" title)
                (cons "H" (if (equal title "") "" (format "{%s}" title)))
                (cons "U" (if (equal title "") "" (format "[%s]" title))))))
        "\n"))
     contents
     ;; Block's closing string.
     (when environment (concat (nth 3 env-format) "\n"))
     (when column-width "\\end{column}\n")
     (when end-columns-p "\\end{columns}"))))

(defun org-beamer-headline (headline contents info)
  "Transcode HEADLINE element into Beamer code.
CONTENTS is the contents of the headline.  INFO is a plist used
as a communication channel."
  (unless (org-element-property :footnote-section-p headline)
    (let ((level (org-export-get-relative-level headline info))
          (frame-level (org-beamer--frame-level headline info))
          (environment (let ((env (org-element-property :BEAMER_ENV headline)))
                         (or (org-string-nw-p env) "block"))))
      (cond
       ;; Case 1: Resume frame specified by "BEAMER_ref" property.
       ((equal environment "againframe")
        (let ((ref (org-element-property :BEAMER_REF headline)))
          ;; Reference to frame being resumed is mandatory.  Ignore
          ;; the whole headline if it isn't provided.
          (when (org-string-nw-p ref)
            (concat "\\againframe"
                    ;; Overlay specification.
                    (let ((overlay (org-element-property :BEAMER_ACT headline)))
                      (when overlay
                        (org-beamer--normalize-argument
                         overlay
                         (if (string-match "^\\[.*\\]$" overlay) 'defaction
                           'action))))
                    ;; Options.
                    (let ((options (org-element-property :BEAMER_OPT headline)))
                      (when options
                        (org-beamer--normalize-argument options 'option)))
                    ;; Resolve reference provided by "BEAMER_ref"
                    ;; property.  This is done by building a minimal fake
                    ;; link and calling the appropriate resolve function,
                    ;; depending on the reference syntax.
                    (let* ((type
                            (progn
                              (string-match "^\\(id:\\|#\\|\\*\\)?\\(.*\\)" ref)
                              (cond
                               ((or (not (match-string 1 ref))
                                    (equal (match-string 1 ref) "*")) 'fuzzy)
                               ((equal (match-string 1 ref) "id:") 'id)
                               (t 'custom-id))))
                           (link (list 'link (list :path (match-string 2 ref))))
                           (target (if (eq type 'fuzzy)
                                       (org-export-resolve-fuzzy-link link info)
                                     (org-export-resolve-id-link link info))))
                      ;; Now use user-defined label provided in TARGET
                      ;; headline, or fallback to standard one.
                      (format "{%s}" (org-beamer--get-label target info)))))))
       ;; Case 2: Creation of an appendix is requested.
       ((equal environment "appendix")
        (concat "\\appendix"
                (org-element-property :BEAMER_ACT headline)
                "\n"
                (make-string (org-element-property :pre-blank headline) ?\n)
                contents))
       ;; Case 3: Ignore heading.
       ((equal environment "ignoreheading")
        (concat (make-string (org-element-property :pre-blank headline) ?\n)
                contents))
       ;; Case 4: HEADLINE is a note.
       ((member environment '("note" "noteNH"))
        (format "\\note{%s}"
                (concat (and (equal environment "note")
                             (concat
                              (org-export-data
                               (org-element-property :title headline) info)
                              "\n"))
                        (org-trim contents))))
       ;; Case 5: HEADLINE is a frame.
       ((= level frame-level)
        (org-beamer--format-frame headline contents info))
       ;; Case 6: Regular section, extracted from
       ;; `org-latex-classes'.
       ((< level frame-level)
        (org-beamer--format-section headline contents info))
       ;; Case 7: Otherwise, HEADLINE is a block.
       (t (org-beamer--format-block headline contents info))))))


;;;; Item

(defun org-beamer-item (item contents info)
  "Transcode an ITEM element into Beamer code.
CONTENTS holds the contents of the item.  INFO is a plist holding
contextual information."
  (let ((action (let ((first-element (car (org-element-contents item))))
                  (and (eq (org-element-type first-element) 'paragraph)
                       (org-beamer--element-has-overlay-p first-element))))
        (output (org-export-with-backend 'latex item contents info)))
    (if (not action) output
      ;; If the item starts with a paragraph and that paragraph starts
      ;; with an export snippet specifying an overlay, insert it after
      ;; \item command.
      (replace-regexp-in-string "\\\\item" (concat "\\\\item" action) output))))


;;;; Keyword

(defun org-beamer-keyword (keyword contents info)
  "Transcode a KEYWORD element into Beamer code.
CONTENTS is nil.  INFO is a plist used as a communication
channel."
  (let ((key (org-element-property :key keyword))
        (value (org-element-property :value keyword)))
    ;; Handle specifically BEAMER and TOC (headlines only) keywords.
    ;; Otherwise, fallback to `latex' back-end.
    (cond
     ((equal key "BEAMER") value)
     ((and (equal key "TOC") (string-match "\\<headlines\\>" value))
      (let ((depth (or (and (string-match "[0-9]+" value)
                            (string-to-number (match-string 0 value)))
                       (plist-get info :with-toc)))
            (options (and (string-match "\\[.*?\\]" value)
                          (match-string 0 value))))
        (concat
         (when (wholenump depth) (format "\\setcounter{tocdepth}{%s}\n" depth))
         "\\tableofcontents" options)))
     (t (org-export-with-backend 'latex keyword contents info)))))


;;;; Link

(defun org-beamer-link (link contents info)
  "Transcode a LINK object into Beamer code.
CONTENTS is the description part of the link.  INFO is a plist
used as a communication channel."
  (let ((type (org-element-property :type link))
        (path (org-element-property :path link)))
    ;; Use \hyperlink command for all internal links.
    (cond
     ((equal type "radio")
      (let ((destination (org-export-resolve-radio-link link info)))
        (when destination
          (format "\\hyperlink%s{%s}{%s}"
                  (or (org-beamer--element-has-overlay-p link) "")
                  (org-export-solidify-link-text path)
                  (org-export-data (org-element-contents destination) info)))))
     ((and (member type '("custom-id" "fuzzy" "id"))
           (let ((destination (if (string= type "fuzzy")
                                  (org-export-resolve-fuzzy-link link info)
                                (org-export-resolve-id-link link info))))
             (case (org-element-type destination)
               (headline
                (let ((label
                       (format "sec-%s"
                               (mapconcat
                                'number-to-string
                                (org-export-get-headline-number
                                 destination info)
                                "-"))))
                  (if (and (plist-get info :section-numbers) (not contents))
                      (format "\\ref{%s}" label)
                    (format "\\hyperlink%s{%s}{%s}"
                            (or (org-beamer--element-has-overlay-p link) "")
                            label
                            contents))))
               (target
                (let ((path (org-export-solidify-link-text path)))
                  (if (not contents) (format "\\ref{%s}" path)
                    (format "\\hyperlink%s{%s}{%s}"
                            (or (org-beamer--element-has-overlay-p link) "")
                            path
                            contents))))))))
     ;; Otherwise, use `latex' back-end.
     (t (org-export-with-backend 'latex link contents info)))))


;;;; Plain List
;;
;; Plain lists support `:environment', `:overlay' and `:options'
;; attributes.

(defun org-beamer-plain-list (plain-list contents info)
  "Transcode a PLAIN-LIST element into Beamer code.
CONTENTS is the contents of the list.  INFO is a plist holding
contextual information."
  (let* ((type (org-element-property :type plain-list))
         (attributes (org-combine-plists
                      (org-export-read-attribute :attr_latex plain-list)
                      (org-export-read-attribute :attr_beamer plain-list)))
         (latex-type (let ((env (plist-get attributes :environment)))
                       (cond (env)
                             ((eq type 'ordered) "enumerate")
                             ((eq type 'descriptive) "description")
                             (t "itemize")))))
    (org-latex--wrap-label
     plain-list
     (format "\\begin{%s}%s%s\n%s\\end{%s}"
             latex-type
             ;; Default overlay specification, if any.
             (org-beamer--normalize-argument
              (or (plist-get attributes :overlay) "")
              'defaction)
             ;; Second optional argument depends on the list type.
             (org-beamer--normalize-argument
              (or (plist-get attributes :options) "")
              'option)
             ;; Eventually insert contents and close environment.
             contents
             latex-type))))


;;;; Radio Target

(defun org-beamer-radio-target (radio-target text info)
  "Transcode a RADIO-TARGET object into Beamer code.
TEXT is the text of the target.  INFO is a plist holding
contextual information."
  (format "\\hypertarget%s{%s}{%s}"
          (or (org-beamer--element-has-overlay-p radio-target) "")
          (org-export-solidify-link-text
           (org-element-property :value radio-target))
          text))


;;;; Target

(defun org-beamer-target (target contents info)
  "Transcode a TARGET object into Beamer code.
CONTENTS is nil.  INFO is a plist holding contextual
information."
  (format "\\hypertarget{%s}{}"
          (org-export-solidify-link-text (org-element-property :value target))))


;;;; Template
;;
;; Template used is similar to the one used in `latex' back-end,
;; excepted for the table of contents and Beamer themes.

(defun org-beamer-template (contents info)
  "Return complete document string after Beamer conversion.
CONTENTS is the transcoded contents string.  INFO is a plist
holding export options."
  (let ((title (org-export-data (plist-get info :title) info)))
    (concat
     ;; 1. Time-stamp.
     (and (plist-get info :time-stamp-file)
          (format-time-string "%% Created %Y-%m-%d %a %H:%M\n"))
     ;; 2. Document class and packages.
     (let ((class (plist-get info :latex-class))
           (class-options (plist-get info :latex-class-options)))
       (org-element-normalize-string
        (let* ((header (nth 1 (assoc class org-latex-classes)))
               (document-class-string
                (and (stringp header)
                     (if (not class-options) header
                       (replace-regexp-in-string
                        "^[ \t]*\\\\documentclass\\(\\(\\[[^]]*\\]\\)?\\)"
                        class-options header t nil 1)))))
          (if (not document-class-string)
              (user-error "Unknown LaTeX class `%s'" class)
            (org-latex-guess-babel-language
             (org-latex-guess-inputenc
              (org-splice-latex-header
               document-class-string
               org-latex-default-packages-alist
               org-latex-packages-alist nil
               (concat (plist-get info :latex-header)
                       (plist-get info :latex-header-extra)
                       (plist-get info :beamer-header-extra))))
             info)))))
     ;; 3. Insert themes.
     (let ((format-theme
            (function
             (lambda (prop command)
               (let ((theme (plist-get info prop)))
                 (when theme
                   (concat command
                           (if (not (string-match "\\[.*\\]" theme))
                               (format "{%s}\n" theme)
                             (format "%s{%s}\n"
                                     (match-string 0 theme)
                                     (org-trim
                                      (replace-match "" nil nil theme)))))))))))
       (mapconcat (lambda (args) (apply format-theme args))
                  '((:beamer-theme "\\usetheme")
                    (:beamer-color-theme "\\usecolortheme")
                    (:beamer-font-theme "\\usefonttheme")
                    (:beamer-inner-theme "\\useinnertheme")
                    (:beamer-outer-theme "\\useoutertheme"))
                  ""))
     ;; 4. Possibly limit depth for headline numbering.
     (let ((sec-num (plist-get info :section-numbers)))
       (when (integerp sec-num)
         (format "\\setcounter{secnumdepth}{%d}\n" sec-num)))
     ;; 5. Author.
     (let ((author (and (plist-get info :with-author)
                        (let ((auth (plist-get info :author)))
                          (and auth (org-export-data auth info)))))
           (email (and (plist-get info :with-email)
                       (org-export-data (plist-get info :email) info))))
       (cond ((and author email (not (string= "" email)))
              (format "\\author{%s\\thanks{%s}}\n" author email))
             (author (format "\\author{%s}\n" author))
             (t "\\author{}\n")))
     ;; 6. Date.
     (let ((date (and (plist-get info :with-date) (org-export-get-date info))))
       (format "\\date{%s}\n" (org-export-data date info)))
     ;; 7. Title
     (format "\\title{%s}\n" title)
     ;; 8. Hyperref options.
     (when (plist-get info :latex-hyperref-p)
       (format "\\hypersetup{\n  pdfkeywords={%s},\n  pdfsubject={%s},\n  pdfcreator={%s}}\n"
               (or (plist-get info :keywords) "")
               (or (plist-get info :description) "")
               (if (not (plist-get info :with-creator)) ""
                 (plist-get info :creator))))
     ;; 9. Document start.
     "\\begin{document}\n\n"
     ;; 10. Title command.
     (org-element-normalize-string
      (cond ((string= "" title) nil)
            ((not (stringp org-latex-title-command)) nil)
            ((string-match "\\(?:[^%]\\|^\\)%s"
                           org-latex-title-command)
             (format org-latex-title-command title))
            (t org-latex-title-command)))
     ;; 11. Table of contents.
     (let ((depth (plist-get info :with-toc)))
       (when depth
         (concat
          (format "\\begin{frame}%s{%s}\n"
                  (org-beamer--normalize-argument
                   org-beamer-outline-frame-options 'option)
                  org-beamer-outline-frame-title)
          (when (wholenump depth)
            (format "\\setcounter{tocdepth}{%d}\n" depth))
          "\\tableofcontents\n"
          "\\end{frame}\n\n")))
     ;; 12. Document's body.
     contents
     ;; 13. Creator.
     (let ((creator-info (plist-get info :with-creator)))
       (cond
        ((not creator-info) "")
        ((eq creator-info 'comment)
         (format "%% %s\n" (plist-get info :creator)))
        (t (concat (plist-get info :creator) "\n"))))
     ;; 14. Document end.
     "\\end{document}")))


\f
;;; Minor Mode


(defvar org-beamer-mode-map (make-sparse-keymap)
  "The keymap for `org-beamer-mode'.")
(define-key org-beamer-mode-map "\C-c\C-b" 'org-beamer-select-environment)

;;;###autoload
(define-minor-mode org-beamer-mode
  "Support for editing Beamer oriented Org mode files."
  nil " Bm" 'org-beamer-mode-map)

(when (fboundp 'font-lock-add-keywords)
  (font-lock-add-keywords
   'org-mode
   '((":\\(B_[a-z]+\\|BMCOL\\):" 1 'org-beamer-tag prepend))
   'prepend))

(defface org-beamer-tag '((t (:box (:line-width 1 :color grey40))))
  "The special face for beamer tags."
  :group 'org-export-beamer)

(defun org-beamer-property-changed (property value)
  "Track the BEAMER_env property with tags.
PROPERTY is the name of the modified property.  VALUE is its new
value."
  (cond
   ((equal property "BEAMER_env")
    (save-excursion
      (org-back-to-heading t)
      ;; Filter out Beamer-related tags and install environment tag.
      (let ((tags (org-remove-if (lambda (x) (string-match "^B_" x))
                                 (org-get-tags)))
            (env-tag (and (org-string-nw-p value) (concat "B_" value))))
        (org-set-tags-to (if env-tag (cons env-tag tags) tags))
        (when env-tag (org-toggle-tag env-tag 'on)))))
   ((equal property "BEAMER_col")
    (org-toggle-tag "BMCOL" (if (org-string-nw-p value) 'on 'off)))))

(add-hook 'org-property-changed-functions 'org-beamer-property-changed)

(defun org-beamer-allowed-property-values (property)
  "Supply allowed values for PROPERTY."
  (cond
   ((and (equal property "BEAMER_env")
         (not (org-entry-get nil (concat property "_ALL") 'inherit)))
    ;; If no allowed values for BEAMER_env have been defined,
    ;; supply all defined environments
    (mapcar 'car (append org-beamer-environments-special
                         org-beamer-environments-extra
                         org-beamer-environments-default)))
   ((and (equal property "BEAMER_col")
         (not (org-entry-get nil (concat property "_ALL") 'inherit)))
    ;; If no allowed values for BEAMER_col have been defined,
    ;; supply some
    (org-split-string org-beamer-column-widths " "))))

(add-hook 'org-property-allowed-value-functions
          'org-beamer-allowed-property-values)


\f
;;; Commands

;;;###autoload
(defun org-beamer-export-as-latex
  (&optional async subtreep visible-only body-only ext-plist)
  "Export current buffer as a Beamer buffer.

If narrowing is active in the current buffer, only export its
narrowed part.

If a region is active, export that region.

A non-nil optional argument ASYNC means the process should happen
asynchronously.  The resulting buffer should be accessible
through the `org-export-stack' interface.

When optional argument SUBTREEP is non-nil, export the sub-tree
at point, extracting information from the headline properties
first.

When optional argument VISIBLE-ONLY is non-nil, don't export
contents of hidden elements.

When optional argument BODY-ONLY is non-nil, only write code
between \"\\begin{document}\" and \"\\end{document}\".

EXT-PLIST, when provided, is a property list with external
parameters overriding Org default settings, but still inferior to
file-local settings.

Export is done in a buffer named \"*Org BEAMER Export*\", which
will be displayed when `org-export-show-temporary-export-buffer'
is non-nil."
  (interactive)
  (if async
      (org-export-async-start
          (lambda (output)
            (with-current-buffer (get-buffer-create "*Org BEAMER Export*")
              (erase-buffer)
              (insert output)
              (goto-char (point-min))
              (LaTeX-mode)
              (org-export-add-to-stack (current-buffer) 'beamer)))
        `(org-export-as 'beamer ,subtreep ,visible-only ,body-only
                        ',ext-plist))
    (let ((outbuf (org-export-to-buffer
                   'beamer "*Org BEAMER Export*"
                   subtreep visible-only body-only ext-plist)))
      (with-current-buffer outbuf (LaTeX-mode))
      (when org-export-show-temporary-export-buffer
        (switch-to-buffer-other-window outbuf)))))

;;;###autoload
(defun org-beamer-export-to-latex
  (&optional async subtreep visible-only body-only ext-plist)
  "Export current buffer as a Beamer presentation (tex).

If narrowing is active in the current buffer, only export its
narrowed part.

If a region is active, export that region.

A non-nil optional argument ASYNC means the process should happen
asynchronously.  The resulting file should be accessible through
the `org-export-stack' interface.

When optional argument SUBTREEP is non-nil, export the sub-tree
at point, extracting information from the headline properties
first.

When optional argument VISIBLE-ONLY is non-nil, don't export
contents of hidden elements.

When optional argument BODY-ONLY is non-nil, only write code
between \"\\begin{document}\" and \"\\end{document}\".

EXT-PLIST, when provided, is a property list with external
parameters overriding Org default settings, but still inferior to
file-local settings.

Return output file's name."
  (interactive)
  (let ((outfile (org-export-output-file-name ".tex" subtreep)))
    (if async
        (org-export-async-start
            (lambda (f) (org-export-add-to-stack f 'beamer))
          `(expand-file-name
            (org-export-to-file
             'beamer ,outfile ,subtreep ,visible-only ,body-only
             ',ext-plist)))
      (org-export-to-file
       'beamer outfile subtreep visible-only body-only ext-plist))))

;;;###autoload
(defun org-beamer-export-to-pdf
  (&optional async subtreep visible-only body-only ext-plist)
  "Export current buffer as a Beamer presentation (PDF).

If narrowing is active in the current buffer, only export its
narrowed part.

If a region is active, export that region.

A non-nil optional argument ASYNC means the process should happen
asynchronously.  The resulting file should be accessible through
the `org-export-stack' interface.

When optional argument SUBTREEP is non-nil, export the sub-tree
at point, extracting information from the headline properties
first.

When optional argument VISIBLE-ONLY is non-nil, don't export
contents of hidden elements.

When optional argument BODY-ONLY is non-nil, only write code
between \"\\begin{document}\" and \"\\end{document}\".

EXT-PLIST, when provided, is a property list with external
parameters overriding Org default settings, but still inferior to
file-local settings.

Return PDF file's name."
  (interactive)
  (if async
      (let ((outfile (org-export-output-file-name ".tex" subtreep)))
        (org-export-async-start
            (lambda (f) (org-export-add-to-stack f 'beamer))
          `(expand-file-name
            (org-latex-compile
             (org-export-to-file
              'beamer ,outfile ,subtreep ,visible-only ,body-only
              ',ext-plist)))))
    (org-latex-compile
     (org-beamer-export-to-latex
      nil subtreep visible-only body-only ext-plist))))

;;;###autoload
(defun org-beamer-select-environment ()
  "Select the environment to be used by beamer for this entry.
While this uses (for convenience) a tag selection interface, the
result of this command will be that the BEAMER_env *property* of
the entry is set.

In addition to this, the command will also set a tag as a visual
aid, but the tag does not have any semantic meaning."
  (interactive)
  ;; Make sure `org-beamer-environments-special' has a higher
  ;; priority than `org-beamer-environments-extra'.
  (let* ((envs (append org-beamer-environments-special
                       org-beamer-environments-extra
                       org-beamer-environments-default))
         (org-tag-alist
          (append '((:startgroup))
                  (mapcar (lambda (e) (cons (concat "B_" (car e))
                                       (string-to-char (nth 1 e))))
                          envs)
                  '((:endgroup))
                  '(("BMCOL" . ?|))))
         (org-fast-tag-selection-single-key t))
    (org-set-tags)
    (let ((tags (or (ignore-errors (org-get-tags-string)) "")))
      (cond
       ;; For a column, automatically ask for its width.
       ((eq org-last-tag-selection-key ?|)
        (if (string-match ":BMCOL:" tags)
            (org-set-property "BEAMER_col" (read-string "Column width: "))
          (org-delete-property "BEAMER_col")))
       ;; For an "againframe" section, automatically ask for reference
       ;; to resumed frame and overlay specifications.
       ((eq org-last-tag-selection-key ?A)
        (if (equal (org-entry-get nil "BEAMER_env") "againframe")
            (progn (org-entry-delete nil "BEAMER_env")
                   (org-entry-delete nil "BEAMER_ref")
                   (org-entry-delete nil "BEAMER_act"))
          (org-entry-put nil "BEAMER_env" "againframe")
          (org-set-property
           "BEAMER_ref"
           (read-string "Frame reference (*Title, #custom-id, id:...): "))
          (org-set-property "BEAMER_act"
                            (read-string "Overlay specification: "))))
       ((string-match (concat ":B_\\(" (mapconcat 'car envs "\\|") "\\):") tags)
        (org-entry-put nil "BEAMER_env" (match-string 1 tags)))
       (t (org-entry-delete nil "BEAMER_env"))))))

;;;###autoload
(defun org-beamer-insert-options-template (&optional kind)
  "Insert a settings template, to make sure users do this right."
  (interactive (progn
                 (message "Current [s]ubtree or [g]lobal?")
                 (if (eq (read-char-exclusive) ?g) (list 'global)
                   (list 'subtree))))
  (if (eq kind 'subtree)
      (progn
        (org-back-to-heading t)
        (org-reveal)
        (org-entry-put nil "EXPORT_LaTeX_CLASS" "beamer")
        (org-entry-put nil "EXPORT_LaTeX_CLASS_OPTIONS" "[presentation]")
        (org-entry-put nil "EXPORT_FILE_NAME" "presentation.pdf")
        (when org-beamer-column-view-format
          (org-entry-put nil "COLUMNS" org-beamer-column-view-format))
        (org-entry-put nil "BEAMER_col_ALL" org-beamer-column-widths))
    (insert "#+LaTeX_CLASS: beamer\n")
    (insert "#+LaTeX_CLASS_OPTIONS: [presentation]\n")
    (when org-beamer-theme (insert "#+BEAMER_THEME: " org-beamer-theme "\n"))
    (when org-beamer-column-view-format
      (insert "#+COLUMNS: " org-beamer-column-view-format "\n"))
    (insert "#+PROPERTY: BEAMER_col_ALL " org-beamer-column-widths "\n")))

;;;###autoload
(defun org-beamer-publish-to-latex (plist filename pub-dir)
  "Publish an Org file to a Beamer presentation (LaTeX).

FILENAME is the filename of the Org file to be published.  PLIST
is the property list for the given project.  PUB-DIR is the
publishing directory.

Return output file name."
  (org-publish-org-to 'beamer filename ".tex" plist pub-dir))

;;;###autoload
(defun org-beamer-publish-to-pdf (plist filename pub-dir)
  "Publish an Org file to a Beamer presentation (PDF, via LaTeX).

FILENAME is the filename of the Org file to be published.  PLIST
is the property list for the given project.  PUB-DIR is the
publishing directory.

Return output file name."
  ;; Unlike to `org-beamer-publish-to-latex', PDF file is generated in
  ;; working directory and then moved to publishing directory.
  (org-publish-attachment
   plist
   (org-latex-compile (org-publish-org-to 'beamer filename ".tex" plist))
   pub-dir))


(provide 'ox-beamer)

;; Local variables:
;; generated-autoload-file: "org-loaddefs.el"
;; End:

;;; ox-beamer.el ends here