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+;;; emms-playlist-limit.el --- Limit playlist by various info
+
+;; Copyright (C) 2007 William Xu
+
+;; Author: William Xu <william.xwl@gmail.com>
+;; Keywords: emms, limit
+
+;; EMMS 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, or (at your option)
+;; any later version.
+
+;; EMMS 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 EMMS; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+;; Boston, MA 02110-1301, USA.
+
+;;; Code:
+
+(require 'emms-playlist-mode)
+
+;;; User Interfaces
+
+(defgroup emms-playlist-limit nil
+  "Playlist limit module for EMMS."
+  :group 'emms)
+
+(defcustom emms-playlist-limit-hook nil
+  "Hooks to run after each limit operations."
+  :type 'symbol
+  :group 'emms-playing-limit)
+
+(defvar emms-playlist-limit-enabled-p nil
+  "If non-nil, emms playlist limit is enabled.")
+
+(defun emms-playlist-limit (arg)
+  "Turn on emms playlist limit if ARG is positive, off otherwise."
+  (interactive "p")
+  (if (and arg (> arg 0))
+      (progn
+        (setq emms-playlist-limit-enabled-p t)
+        (add-hook 'emms-playlist-source-inserted-hook
+                  'emms-playlist-limit-insert))
+    (setq emms-playlist-limit-enabled-p nil)
+    (remove-hook 'emms-playlist-source-inserted-hook
+                 'emms-playlist-limit-insert)))
+
+;;;###autoload
+(defun emms-playlist-limit-enable ()
+  "Turn on emms playlist limit."
+  (interactive)
+  (emms-playlist-limit 1)
+  (message "emms playlist limit enabled"))
+
+;;;###autoload
+(defun emms-playlist-limit-disable ()
+  "Turn off emms playlist limit."
+  (interactive)
+  (emms-playlist-limit -1)
+  (message "emms playlist limit disabled"))
+
+;;;###autoload
+(defun emms-playlist-limit-toggle ()
+  "Toggle emms playlist limit."
+  (interactive)
+  (if emms-playlist-limit-enabled-p
+      (emms-playlist-limit-disable)
+    (emms-playlist-limit-enable)))
+
+(defmacro define-emms-playlist-limit (attribute)
+  "Macro for defining emms playlist limit functions."
+  `(defun ,(intern (format "emms-playlist-limit-to-%s" attribute)) (regexp)
+     ,(format "Limit to playlists that have %s that matches REGEXP." attribute)
+     (interactive
+      (list
+       (let* ((curr
+               (or (emms-track-get
+                    (emms-playlist-track-at) (quote ,attribute))
+                   (emms-track-get
+                    (emms-playlist-selected-track) (quote ,attribute))))
+              (attr-name ,(emms-replace-regexp-in-string
+                           "info-" "" (symbol-name attribute)))
+              (fmt (if curr
+                       (format "Limit to %s (regexp = %s): " attr-name curr)
+                     (format "Limit to %s (regexp): " attr-name))))
+         (read-string fmt))))
+     (when (string= regexp "")
+       (setq regexp (emms-track-get (emms-playlist-track-at) (quote ,attribute))))
+     (emms-playlist-limit-do (quote ,attribute) regexp)))
+
+(define-emms-playlist-limit info-artist)
+(define-emms-playlist-limit info-composer)
+(define-emms-playlist-limit info-performer)
+(define-emms-playlist-limit info-title)
+(define-emms-playlist-limit info-album)
+(define-emms-playlist-limit info-year)
+(define-emms-playlist-limit info-genre)
+(define-emms-playlist-limit name)
+
+(defun emms-playlist-limit-to-all ()
+  "Show all tracks again."
+  (interactive)
+  (emms-playlist-limit-do nil nil))
+
+(define-key emms-playlist-mode-map (kbd "/ n") 'emms-playlist-limit-to-name)
+(define-key emms-playlist-mode-map (kbd "/ a") 'emms-playlist-limit-to-info-artist)
+(define-key emms-playlist-mode-map (kbd "/ c") 'emms-playlist-limit-to-info-composer)
+(define-key emms-playlist-mode-map (kbd "/ p") 'emms-playlist-limit-to-info-performer)
+(define-key emms-playlist-mode-map (kbd "/ t") 'emms-playlist-limit-to-info-title)
+(define-key emms-playlist-mode-map (kbd "/ b") 'emms-playlist-limit-to-info-album)
+(define-key emms-playlist-mode-map (kbd "/ y") 'emms-playlist-limit-to-info-year)
+(define-key emms-playlist-mode-map (kbd "/ g") 'emms-playlist-limit-to-info-genre)
+(define-key emms-playlist-mode-map (kbd "/ /") 'emms-playlist-limit-to-all)
+
+
+;;; Low Level Functions
+
+(defvar emms-playlist-limit-tracks nil
+  "All tracks in playlist buffer(unlimited).")
+
+(defun emms-playlist-limit-insert ()
+  "Run in `emms-playlist-source-inserted-hook'."
+  (with-current-emms-playlist
+    (emms-playlist-ensure-playlist-buffer)
+    (setq emms-playlist-limit-tracks
+          (emms-with-widened-buffer
+           (emms-playlist-tracks-in-region (point-min) (point-max))))))
+
+;; FIXME: When user deletes some tracks, `emms-playlist-limit-tracks'
+;; should be updated.
+;; (defun emms-playlist-limit-clear ()
+;;   "Run in `emms-playlist-cleared-hook'."
+;;   (setq emms-playlist-limit-tracks
+;;         (append emms-playlist-limit-tracks
+;;                 (emms-playlist-tracks-in-region
+;;                  (point-min) (point-max)))))
+
+(defun emms-playlist-limit-do (name value)
+  "Limit by NAME with VALUE.
+e.g.,
+    (emms-playlist-limit-do 'info-artist \"Jane Zhang\")
+
+When NAME is nil, show all tracks again.
+
+See `emms-info-mp3find-arguments' for possible options for NAME."
+  (with-current-emms-playlist
+    (emms-playlist-ensure-playlist-buffer)
+    (let ((curr (emms-playlist-current-selected-track))
+          (tracks (emms-playlist-tracks-in-region (point-min) (point-max))))
+      (erase-buffer)
+      (run-hooks 'emms-playlist-cleared-hook)
+      (if name
+          (mapc (lambda (track)
+                  (let ((track-value (emms-track-get track name)))
+                    (when (and track-value (string-match value track-value))
+                      (emms-playlist-insert-track track))))
+                tracks)
+        (mapc (lambda (track)
+                (emms-playlist-insert-track track))
+              emms-playlist-limit-tracks))
+      (let ((pos (text-property-any (point-min) (point-max)
+                                    'emms-track curr)))
+        (if pos
+            (emms-playlist-select pos)
+          (emms-playlist-first)))
+      (run-hooks 'emms-playlist-limit-hook)
+      (emms-playlist-mode-center-current))))
+
+
+(provide 'emms-playlist-limit)
+
+;;; emms-playlist-limit.el ends here