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+;;; jao-pdf.el --- utilities for pdf files           -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2022  jao
+
+;; Author: jao <mail@jao.io>
+;; Keywords: docs
+
+;; 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:
+
+;; Some niceties for PDFs:
+;;
+;;   - Using mutools, we can extract the outline of PDFs, and tell back the
+;;     section title of a given page.
+;;   - Interoperability with zathura.
+
+(require 'jao-doc-session)
+
+;;; PDF info
+
+(declare-function 'pdf-info-outline "pdf-info")
+
+(defvar-local jao-pdf--outline nil)
+
+(defun jao-pdf-is-pdf-file (file)
+  "Simply checks the FILE extension."
+  (string-match-p ".*\\.pdf$" file))
+
+(defun jao-pdf-title-to-file-name (title)
+  "Convert a title, possibly with embedded spaces, to a PDF filename."
+  (concat (mapconcat 'downcase (split-string title nil t) "-") ".pdf"))
+
+(defun jao-pdf-title (&optional fname)
+  (if (or fname (not (derived-mode-p 'doc-view-mode 'pdf-view-mode)))
+      (let ((base (file-name-base (or fname (buffer-file-name)))))
+        (capitalize (replace-regexp-in-string "-" " " base)))
+    (or (jao-pdf-section-title)
+        (when buffer-file-name (jao-pdf-title buffer-file-name)))))
+
+(defvar-local jao-pdf--outline nil)
+
+(defun jao-pdf-section-title (&optional page file-name)
+  (when (not jao-pdf--outline)
+    (setq-local jao-pdf--outline (doc-view--pdf-outline file-name)))
+  (let ((page (or page
+                  (and (derived-mode-p 'doc-view-mode) (doc-view-current-page))
+                  (and (derived-mode-p 'pdf-view) (pdf-view-current-page))))
+        (outline jao-pdf--outline)
+        (cur-page 0)
+        (cur-title (jao-pdf-title (or file-name buffer-file-name "title"))))
+    (while (and (car outline) page (< cur-page page))
+      (setq cur-page (cdr (assoc 'page (car outline))))
+      (when (<= cur-page page)
+        (setq cur-title (cdr (assoc 'title (car outline)))))
+      (setq outline (cdr outline)))
+    (replace-regexp-in-string "[[:blank:]]+" " " cur-title)))
+
+;;; zathura interop
+(defun jao-pdf-zathura-open-cmd (file page &optional suffix)
+  (let ((page (if page (format "-P %s" page) "")))
+    (format "zathura %s %s %s" file page (or suffix ""))))
+
+(defun jao-pdf-zathura-title-rx (file)
+  (concat (file-name-nondirectory file) " \\[.+\\]"))
+
+;; e.g.  "~/org/doc/write-yourself-a-scheme-in-48-hours.pdf [96 (96/138)]"
+(defun jao-pdf-zathura-file-info (title)
+  (when (string-match "\\(.+\\) \\[\\(.+\\) (\\([0-9]+\\)/\\([0-9]+\\))\\]"
+                      title)
+    (list (expand-file-name (match-string 1 title))
+          (string-to-number (match-string 3 title))
+          (string-to-number (match-string 4 title))
+          (match-string 2 title))))
+
+(defun jao-pdf--zathura-link (info)
+  (when-let* ((file (car info))
+              (page (cadr info))
+              (no (or (car (last info)) page))
+              (fn (file-name-nondirectory file))
+              (lnk (format "doc:%s::%s" fn page))
+              (desc (format "%s (p. %s)" (jao-pdf-section-title page file) no)))
+    (org-make-link-string lnk desc)))
+
+(defun jao-pdf-zathura-org-link (title)
+  (jao-pdf--zathura-link (jao-pdf-zathura-file-info title)))
+
+(provide 'jao-pdf)
+;;; jao-pdf.el ends here