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+;;; calibredb-epub-config --- Functionality for Ebook Management and Display -*- lexical-binding: t; coding: utf-8; -*-
+;; author Craig Jennings <c@cjennings.net>
+
+;;; Commentary:
+
+;; This module provides a comprehensive ebook management and reading experience
+;; within Emacs, integrating CalibreDB for library management and Nov for EPUB
+;; reading.
+;;
+;; FEATURES:
+;; - CalibreDB integration for managing your Calibre ebook library
+;; - Nov mode for reading EPUB files with customized typography and layout
+;; - Seamless navigation between Nov reading buffers and CalibreDB entries
+;; - Image centering in EPUB documents without modifying buffer text
+;; - Quick filtering and searching within your ebook library
+;;
+;; KEY BINDINGS:
+;; - M-B: Open CalibreDB library browser
+;; - In CalibreDB search mode:
+;;   - l: Filter by tag
+;;   - L: Clear all filters
+;; - In Nov mode:
+;;   - z: Open current EPUB in external viewer (zathura)
+;;   - C-c C-b: Jump to CalibreDB entry for current book
+;;   - m: Set bookmark
+;;   - b: List bookmarks
+;;
+;; WORKFLOW:
+;; 1. Press M-B to browse your Calibre library
+;; 2. Use filters (l for tags, L to clear) to narrow results
+;; 3. Open an EPUB to read it in Nov with optimized typography
+;; 4. While reading, use C-c C-b to jump back to the book's metadata
+;; 5. Use z to open in external reader when needed
+;;
+;; CONFIGURATION NOTES:
+;; - Prefers EPUB format when available, falls back to PDF
+;; - Centers images in EPUB documents using display properties
+;; - Applies custom typography with larger fonts for comfortable reading
+;; - Uses visual-fill-column for centered text with appropriate margins
+
+;;; Code:
+
+(require 'user-constants)  ;; for books-dir
+
+;; -------------------------- CalibreDB Ebook Manager --------------------------
+
+(use-package calibredb
+  :defer 1
+  :commands calibredb
+  :bind
+  ("M-B" . calibredb)
+  ;; use built-in filter by tag, add clear-filters
+  (:map calibredb-search-mode-map
+		("l" . calibredb-filter-by-tag)
+		("L" . cj/calibredb-clear-filters))
+  :config
+  ;; basic config
+  (setq calibredb-root-dir books-dir)
+  (setq calibredb-db-dir (expand-file-name "metadata.db" calibredb-root-dir))
+  (setq calibredb-program "/usr/bin/calibredb")
+  (setq calibredb-preferred-format "epub")
+  (setq calibredb-search-page-max-rows 20000)
+
+  ;; search window display
+  (setq calibredb-size-show nil)
+  (setq calibredb-order "asc")
+  (setq calibredb-id-width 7))
+
+(defun cj/calibredb-clear-filters ()
+  "Clear active filters and show all results."
+  (interactive)
+  (setq calibredb-tag-filter-p nil
+		calibredb-favorite-filter-p nil
+		calibredb-author-filter-p nil
+		calibredb-date-filter-p nil
+		calibredb-format-filter-p nil
+		calibredb-search-current-page 1)
+  ;; empty string resets keyword filter and refreshes listing
+  (calibredb-search-keyword-filter ""))
+
+;; ------------------------------ Nov Epub Reader ------------------------------
+
+(use-package nov
+  :defer .5
+  :after visual-fill-column
+  :mode ("\\.epub\\'" . nov-mode)
+  :hook (nov-mode . cj/nov-apply-preferences)
+  :bind
+  (:map nov-mode-map
+		("m" . bookmark-set)
+		("b" . bookmark-bmenu-list)
+		("r" . nov-render-document)
+		("l" . recenter-top-bottom)
+		("d" . sdcv-search-input)
+		("." . cj/forward-paragraph-and-center)
+		("<" . nov-history-back)
+		(">" . nov-history-forward)
+		("," . backward-paragraph)
+		;; open current EPUB with zathura (same key in pdf-view)
+		("z" . (lambda () (interactive) (cj/open-file-with-command "zathura")))
+		("t" . nov-goto-toc)
+		("C-c C-b" . cj/nov-jump-to-calibredb)))
+
+(defun cj/forward-paragraph-and-center ()
+  "Forward one paragraph and center the page."
+  (interactive)
+  (forward-paragraph)
+  (recenter))
+
+(defun cj/nov-apply-preferences ()
+  "Apply preferences after nov-mode has launched."
+  (interactive)
+  (face-remap-add-relative 'variable-pitch :height 180)
+  (face-remap-add-relative 'fixed-pitch :height 180)
+  ;; Make this buffer-local so other Nov buffers can choose differently
+  (setq-local nov-text-width 115)
+  (when (require 'visual-fill-column nil t)
+	(setq-local visual-fill-column-center-text t
+				;; small cushion above nov-text-width prevents truncation
+				visual-fill-column-width (+ nov-text-width 10))
+	(hl-line-mode)
+	(visual-fill-column-mode 1))
+  (nov-render-document))
+
+(defun cj/nov-center-images ()
+  "Center images in the current Nov buffer without modifying text.
+
+Use line-prefix and wrap-prefix with a space display property aligned to a
+computed column based on the window text area width."
+  (let ((inhibit-read-only t))
+	;; Clear any prior centering prefixes first (fresh render usually makes this
+	;; unnecessary, but it makes the function idempotent).
+	(remove-text-properties (point-min) (point-max)
+							'(line-prefix nil wrap-prefix nil))
+	(save-excursion
+	  (goto-char (point-min))
+	  ;; Work in the selected window showing this buffer (if any).
+	  (when-let* ((win (get-buffer-window (current-buffer) t))
+				  (col-width (window-body-width win)) ;; columns
+				  (col-px (* col-width (window-font-width win))))
+		(while (let ((m (text-property-search-forward
+						 'display nil
+						 (lambda (_ p) (and (consp p) (eq (car-safe p) 'image))))))
+				 (when m
+				   (let* ((img (prop-match-value m))
+						  (img-px (car (image-size img t)))   ;; pixel width
+						  ;; Convert pixel image width to columns for alignment.
+						  (img-cols (max 1 (ceiling (/ (float img-px)
+													   (max 1 (window-font-width win))))))
+						  (pad-cols (max 0 (/ (- col-width img-cols) 2)))
+						  (prefix (propertize " " 'display `(space :align-to ,pad-cols))))
+					 (save-excursion
+					   (goto-char (prop-match-beginning m))
+					   (beginning-of-line)
+					   (let ((bol (point))
+							 (eol (line-end-position)))
+						 (add-text-properties bol eol
+											  `(line-prefix ,prefix
+															wrap-prefix ,prefix)))))
+				   t)))))))
+
+(add-hook 'nov-post-html-render-hook #'cj/nov-center-images)
+
+;; Jump from a Nov buffer to the corresponding CalibreDB entry.
+(defun cj/nov--metadata-get (key)
+  "Return a metadata value from nov-metadata trying KEY as symbol and string."
+  (let* ((v (or (and (boundp 'nov-metadata)
+					 (or (alist-get key nov-metadata nil nil #'equal)
+						 (alist-get (if (symbolp key) (symbol-name key) key)
+									nov-metadata nil nil #'equal)))
+				nil)))
+	(cond
+	 ((and (listp v) (= (length v) 1)) (car v))
+	 ((stringp v) v)
+	 (t v))))
+
+(defun cj/nov--file-path ()
+  "Return the current EPUB file path when in nov-mode, or nil."
+  (when (derived-mode-p 'nov-mode)
+	;; In nov, the buffer visits the .epub; buffer-file-name is usually the EPUB.
+	(or buffer-file-name
+		(and (boundp 'nov-epub-filename) nov-epub-filename)
+		(and (boundp 'nov-epub-file) nov-epub-file))))
+
+(defun cj/nov-jump-to-calibredb ()
+  "Open CalibreDB focused on the current EPUB's book entry.
+
+Try to use the Calibre book id from the parent folder name (for example,
+\"Title (123)\"). Fall back to a title or author search when no id exists."
+  (interactive)
+  (require 'calibredb)
+  (let* ((file (cj/nov--file-path))
+		 (title (or (cj/nov--metadata-get 'title)
+					(cj/nov--metadata-get "title")))
+		 (author (or (cj/nov--metadata-get 'creator)
+					 (cj/nov--metadata-get 'author)
+					 (cj/nov--metadata-get "creator")
+					 (cj/nov--metadata-get "author")))
+		 (id (when file
+			   (let* ((parent (file-name-nondirectory
+							   (directory-file-name (file-name-directory file)))))
+				 (when (string-match " (\\([0-9]+\\))\\'" parent)
+				   (match-string 1 parent))))))
+	(calibredb)
+	(with-current-buffer (calibredb-find-create-search-buffer)
+	  (setq calibredb-search-current-page 1)
+	  (cond
+	   (id
+		(calibredb-search-keyword-filter (format "id:%s" id))
+		(message "CalibreDB: focused by id:%s" id))
+	   ((or title author)
+		(let* ((q (string-join
+				   (delq nil (list (and title (format "title:\"%s\"" title))
+								   (and author (format "authors:\"%s\"" author))))
+				   " and ")))
+		  (calibredb-search-keyword-filter q)
+		  (message "CalibreDB: search %s" (if (string-empty-p q) "<all>" q))))
+	   (t
+		(calibredb-search-keyword-filter "")
+		(message "CalibreDB: no metadata; showing all"))))))
+
+(provide 'calibredb-epub-config)
+;;; calibredb-epub-config.el ends here