path: root/lisp/emms-lastfm-client.el

;;; -*- show-trailing-whitespace: t -*-
;;; emms-lastfm-client.el --- Last.FM Music API

;; Copyright (C) 2009  Free Software Foundation, Inc.

;; Author: Yoni Rabkin <yonirabkin@member.fsf.org>

;; Keywords: emms, lastfm

;; 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 Street, Fifth Floor, Boston,
;; MA 02110-1301, USA.

;;; Commentary:
;;
;; There are restrictions on the use of this service. Quoting from
;; [http://www.last.fm/api/radio]: "Who can I stream radio to? Any API
;; account can only stream radio to Last.fm's paid subscribers".
;;
;; We've spoken to representatives from Last.fm and arrived at the
;; following agreement: In order to be able to use the service while
;; preserving the essential freedoms of the GPL each client must apply
;; for their own API key from Last.fm.

;;; Installation:
;;
;; Here is how to get authorization from Last.fm to stream
;; music. Thankfully this only needs to be done _once_:
;;
;; 1. Complete steps 1 and 2 from
;;    [http://www.last.fm/api/authentication] to get an API key and a
;;    secret key. Set `emms-lastfm-client-api-key' and
;;    `emms-lastfm-client-api-secret-key' accordingly.
;;
;; 2. M-x emms-lastfm-client-user-authorization
;;
;;    If this completes successfully a browser window will open asking
;;    for confirmation to allow this application to access the Last.fm
;;    account. Confirm and close the browser.
;;
;; 3. M-x emms-lastfm-client-get-session
;;
;;    After this last step the permanent session key will be stored in
;;    `emms-lastfm-client-session-key-file'. As long as this key value
;;    is accessible the authentication process need never be repeated.

;;; Use:
;;
;; M-x emms-lastfm-client-play-similar-artists
;;
;; Call the ...-play- family of interactive functions, such the above,
;; to start streaming music.
;;
;; To show the currently playing track: M-x emms-lastfm-client-show
;;
;; To skip to the next track: M-x emms-lastfm-client-track-advance
;;
;; ...more Last.fm functionality to come, so stay tuned.

;;; Code:

(require 'md5)
(require 'xml)

(defvar emms-lastfm-client-api-key nil
  "Key for the Last.fm API.")

(defvar emms-lastfm-client-api-secret-key nil
  "Secret key for the Last.fm API.")

(defvar emms-lastfm-client-api-session-key nil
  "Session key for the Last.fm API.")

(defvar emms-lastfm-client-token nil
  "Authorization token for API.")

(defvar emms-lastfm-client-api-base-url
  "http://ws.audioscrobbler.com/2.0/"
  "URL for API calls.")

(defvar emms-lastfm-client-session-key-file
  (concat (file-name-as-directory emms-directory)
	  "emms-lastfm-client-sessionkey")
  "File for storing the Last.fm API session key.")

(defvar emms-lastfm-client-playlist-valid nil
  "True if the playlist hasn't expired.")

(defvar emms-lastfm-client-playlist-timer nil
  "Playlist timer object.")

(defvar emms-lastfm-client-playlist nil
  "Latest Last.fm playlist.")

(defvar emms-lastfm-client-track nil
  "Latest Last.fm track.")

(defvar emms-lastfm-client-original-next-function nil
  "Original `-next-function' to be restored.")

(defvar emms-lastfm-client-playlist-buffer-name "*Emms Last.fm*"
  "Name for non-interactive Emms Last.fm buffer.")

(defvar emms-lastfm-client-playlist-buffer nil
  "Non-interactive Emms Last.fm buffer.")

(defvar emms-lastfm-client-api-method-dict
  '((auth-get-token    . ("auth.gettoken"
			  emms-lastfm-client-auth-get-token-ok
			  emms-lastfm-client-auth-get-token-failed))
    (auth-get-session  . ("auth.getsession"
			  emms-lastfm-client-auth-get-session-ok
			  emms-lastfm-client-auth-get-session-failed))
    (radio-tune        . ("radio.tune"
			  emms-lastfm-client-radio-tune-ok
			  emms-lastfm-client-radio-tune-failed))
    (radio-getplaylist . ("radio.getplaylist"
			  emms-lastfm-client-radio-getplaylist-ok
			  emms-lastfm-client-radio-getplaylist-failed)))
  "Mapping symbols to method calls. This is a list of cons pairs
  where the CAR is the symbol name of the method and the CDR is a
  list whose CAR is the method call string, CADR is the function
  to call on a success and CADDR is the function to call on
  failure.")

;;; ------------------------------------------------------------------
;;; API method call
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-get-method (method)
  "Return the associated method cons for the symbol METHOD."
  (let ((m (cdr (assoc method emms-lastfm-client-api-method-dict))))
    (if (not m)
	(error "method not in dictionary: %s" method)
      m)))

(defun emms-lastfm-client-get-method-name (method)
  "Return the associated method string for the symbol METHOD."
  (let ((this (nth 0 (emms-lastfm-client-get-method method))))
    (if (not this)
	(error "no name string registered for method: %s" method)
      this)))

(defun emms-lastfm-client-get-method-ok (method)
  "Return the associated OK function for METHOD.

This function is called when the method call returns
successfully."
  (let ((this (nth 1 (emms-lastfm-client-get-method method))))
    (if (not this)
	(error "no OK function registered for method: %s" method)
      this)))

(defun emms-lastfm-client-get-method-fail (method)
  "Return the associated fail function for METHOD.

This function is called when the method call returns a failure
status message."
  (let ((this (nth 2 (emms-lastfm-client-get-method method))))
    (if (not this)
	(error "no fail function registered for method: %s" method)
      this)))

(defun emms-lastfm-client-encode-arguments (arguments)
  "Encode ARGUMENTS in UTF-8 for the Last.fm API."
  (let ((result nil))
    (while arguments
      (setq result
	    (append result
		    (list
		     (cons
		      (encode-coding-string (caar arguments) 'utf-8)
		      (encode-coding-string (cdar arguments) 'utf-8)))))
      (setq arguments (cdr arguments)))
    result))

(defun emms-lastfm-client-construct-arguments (str arguments)
  "Return a concatenation of arguments for the URL."
  (cond ((not arguments) str)
	(t (emms-lastfm-client-construct-arguments
	    (concat str "&" (caar arguments) "=" (url-hexify-string (cdar arguments)))
	    (cdr arguments)))))

(defun emms-lastfm-client-construct-method-call (method arguments)
  "Return a complete URL method call for METHOD with ARGUMENTS.

This function includes the cryptographic signature."
  (concat emms-lastfm-client-api-base-url "?"
	  "method=" (emms-lastfm-client-get-method-name method)
	  (emms-lastfm-client-construct-arguments
	   "" arguments)
	  "&api_sig="
	  (emms-lastfm-client-construct-signature method arguments)))

(defun emms-lastfm-client-construct-write-method-call (method arguments)
  "Return a complete POST body method call for METHOD with ARGUMENTS.

This function includes the cryptographic signature."
  (concat "method=" (emms-lastfm-client-get-method-name method)
	  (emms-lastfm-client-construct-arguments
	   "" arguments)
	  "&api_sig="
	  (emms-lastfm-client-construct-signature method arguments)))

;;; ------------------------------------------------------------------
;;; Response handler
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-handle-response (method xml-response)
  "Dispatch the handler functions of METHOD for XML-RESPONSE."
  (let ((status (cdr (assoc 'status (nth 1 (car xml-response)))))
	(data (cddar xml-response)))
    (when (not status)
      (error "error parsing status from: %s" xml-response))
    (cond ((string= status "failed")
	   (funcall (emms-lastfm-client-get-method-fail method) data))
	  ((string= status "ok")
	   (funcall (emms-lastfm-client-get-method-ok method) data))
	  (t (error "unknown response status %s" status)))))

;;; ------------------------------------------------------------------
;;; Unathorized request token for an API account
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-construct-urt ()
  "Return a request for an Unauthorized Request Token."
  (let ((arguments
	 (emms-lastfm-client-encode-arguments
	  `(("api_key" . ,emms-lastfm-client-api-key)))))
    (emms-lastfm-client-construct-method-call
     'auth-get-token arguments)))

(defun emms-lastfm-client-make-call-urt ()
  "Make method call for Unauthorized Request Token."
  (let* ((url-request-method "POST"))
    (let ((response
	   (url-retrieve-synchronously
	    (emms-lastfm-client-construct-urt))))
      (emms-lastfm-client-handle-response
       'auth-get-token
       (with-current-buffer response
	 (xml-parse-region (point-min) (point-max)))))))

;; example response: ((lfm ((status . \"ok\")) \"\" (token nil
;; \"31cab3398a9b46cf7231ef84d73169cf\")))

;;; ------------------------------------------------------------------
;;; Signatures
;;; ------------------------------------------------------------------
;;
;; From [http://www.last.fm/api/desktopauth]:
;;
;; Construct your api method signatures by first ordering all the
;; parameters sent in your call alphabetically by parameter name and
;; concatenating them into one string using a <name><value>
;; scheme. So for a call to auth.getSession you may have:
;;
;;   api_keyxxxxxxxxmethodauth.getSessiontokenxxxxxxx
;;
;; Ensure your parameters are utf8 encoded. Now append your secret
;; to this string. Finally, generate an md5 hash of the resulting
;; string. For example, for an account with a secret equal to
;; 'mysecret', your api signature will be:
;;
;;   api signature = md5("api_keyxxxxxxxxmethodauth.getSessiontokenxxxxxxxmysecret")
;;
;; Where md5() is an md5 hashing operation and its argument is the
;; string to be hashed. The hashing operation should return a
;; 32-character hexadecimal md5 hash.

(defun emms-lastfm-client-construct-lexi (arguments)
  "Return ARGUMENTS sorted in lexicographic order."
  (let ((lexi (sort arguments
		    '(lambda (a b) (string< (car a) (car b)))))
	(out ""))
    (while lexi
      (setq out (concat out (caar lexi) (cdar lexi)))
      (setq lexi (cdr lexi)))
    out))

(defun emms-lastfm-client-construct-signature (method arguments)
  "Return request signature for METHOD and ARGUMENTS."
  (let ((complete-arguments
	 (append arguments
		 `(("method" .
		    ,(emms-lastfm-client-get-method-name method))))))
    (md5
     (concat (emms-lastfm-client-construct-lexi complete-arguments)
	     emms-lastfm-client-api-secret-key))))

;;; ------------------------------------------------------------------
;;; General error handling
;;; ------------------------------------------------------------------

;; Each method call provides its own error codes, but if we don't want
;; to code a handler for a method we call this instead:
(defun emms-lastfm-client-default-error-handler (data)
  "Default method failure handler."
  (let ((errorcode (cdr (assoc 'code (nth 1 (cadr data)))))
	(message (nth 2 (cadr data))))
    (when (not (and errorcode message))
      (error "failed to read errorcode or message: %s %s"
	     errorcode message))
    (error "method call failed with code %s: %s"
	   errorcode message)))

;;; ------------------------------------------------------------------
;;; Request authorization from the user
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-ask-for-auth ()
  "Open a Web browser for authorizing the application."
  (when (not (and emms-lastfm-client-api-key
		  emms-lastfm-client-token))
    (error "API key and authorization token needed."))
  (browse-url
   (format "http://www.last.fm/api/auth/?api_key=%s&token=%s"
	   emms-lastfm-client-api-key
	   emms-lastfm-client-token)))

;;; ------------------------------------------------------------------
;;; Parse XSPF
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-xspf-header (data)
  "Return an alist representing the XSPF header of DATA."
  (let (out
	(orig data))
    (setq data (cadr data))
    (while data
      (when (and (car data)
		 (listp (car data))
		 (= (length (car data)) 3))
	(setq out (append out (list (cons (nth 0 (car data))
					  (nth 2 (car data)))))))
      (setq data (cdr data)))
    (if (not out)
	(error "failed to parse XSPF header from: %s" orig)
      out)))

(defun emms-lastfm-client-xspf-tracklist (data)
  "Return the start of the track-list in DATE."
  (nthcdr 3 (nth 11 (cadr data))))

(defun emms-lastfm-client-xspf-header-date (header-alist)
  "Return the date parameter from HEADER-ALIST."
  (let ((out (cdr (assoc 'date header-alist))))
    (if (not out)
	(error "could not read date from header alist: %s"
	       header-alist)
      out)))

(defun emms-lastfm-client-xspf-header-expiry (header-alist)
  "Return the expiry parameter from HEADER-ALIST."
  (let ((out (cdr (assoc 'link header-alist))))
    (if (not out)
	(error "could not read expiry from header alist: %s"
	       header-alist)
      out)))

(defun emms-lastfm-client-xspf-header-creator (header-alist)
  "Return the creator parameter from HEADER-ALIST."
  (let ((out (cdr (assoc 'creator header-alist))))
    (if (not out)
	(error "could not read creator from header alist: %s"
	       header-alist)
      out)))

(defun emms-lastfm-client-xspf-playlist (data)
  "Return the playlist from the XSPF DATA."
  (let ((playlist (car (nthcdr 11 data))))
    (if (not playlist)
	(error "could not read playlist from: %s" data)
      playlist)))

(defun emms-lastfm-client-xspf-get (node track)
  "Return data associated with NODE in TRACK."
  (let ((result nil))
    (while track
      (when (consp track)
	(let ((this (car track)))
	  (when (and (consp this)
		     (= (length this) 3)
		     (symbolp (nth 0 this))
		     (stringp (nth 2 this))
		     (equal (nth 0 this) node))
	    (setq result (nth 2 this)))))
      (setq track (cdr track)))
    (if (not result)
	nil
      result)))

;;; ------------------------------------------------------------------
;;; Timers
;;; ------------------------------------------------------------------

;; timed playlist invalidation is a part of the Last.fm API
(defun emms-lastfm-client-set-timer (header)
  "Start timer countdown to playlist invalidation"
  (when (not header)
    (error "can't set timer with no header data"))
  (let ((expiry (parse-integer
		 (emms-lastfm-client-xspf-header-expiry header))))
    (setq emms-lastfm-client-playlist-valid t)
    (setq emms-lastfm-client-playlist-timer
	  (run-at-time
	   expiry nil
	   '(lambda () (setq emms-lastfm-client-playlist-valid
			     nil))))))

;;; ------------------------------------------------------------------
;;; Player
;;; ------------------------------------------------------------------

;; this should return `nil' to the track-manager when the playlist has
;; been exhausted
(defun emms-lastfm-client-consume-next-track ()
  "Pop and return the next track from the playlist or nil."
  (when emms-lastfm-client-playlist
    (if emms-lastfm-client-playlist-valid
	(let ((track (car emms-lastfm-client-playlist)))
	  ;; we can only request each track once so we pop it off the
	  ;; playlist
	  (setq emms-lastfm-client-playlist
		(if (stringp (cdr emms-lastfm-client-playlist))
		    (cddr emms-lastfm-client-playlist)
		  (cdr emms-lastfm-client-playlist)))
	  track)
      (error "playlist invalid"))))

(defun emms-lastfm-client-set-lastfm-playlist-buffer ()
  (when (not (buffer-live-p emms-lastfm-client-playlist-buffer))
    (setq emms-lastfm-client-playlist-buffer
	  (emms-playlist-new
	   emms-lastfm-client-playlist-buffer-name))
    (setq emms-playlist-buffer emms-lastfm-client-playlist-buffer)))

(defun emms-lastfm-client-load-next-track ()
  (with-current-buffer emms-lastfm-client-playlist-buffer
    (emms-playlist-clear)
    (if emms-lastfm-client-playlist
	(let ((track (emms-lastfm-client-consume-next-track)))
	  (setq emms-lastfm-client-track track)
	  (when emms-player-playing-p
	    (emms-stop))
	  (emms-play-url
	   (emms-lastfm-client-xspf-get 'location track)))
      (emms-lastfm-client-make-call-radio-getplaylist)
      (emms-lastfm-client-load-next-track))))

;; call this `-track-advance' to avoid confusion with Emms'
;; `-next-track-' mechanism
(defun emms-lastfm-client-track-advance ()
  (interactive)
  (when (equal emms-playlist-buffer
	       emms-lastfm-client-playlist-buffer)
    (emms-lastfm-client-load-next-track)))

(defun emms-lastfm-client-play-playlist ()
  "Entry point to play tracks from Last.fm."
  (emms-lastfm-client-set-lastfm-playlist-buffer)
  (add-hook 'emms-player-finished-hook
	    'emms-lastfm-client-track-advance)
  (emms-lastfm-client-track-advance))

;; stolen from Tassilo Horn's original emms-lastfm.el
(defun emms-lastfm-client-read-artist ()
  "Read an artist name from the user."
  (let ((artists nil))
    (when (boundp 'emms-cache-db)
      (maphash
       #'(lambda (file track)
	   (let ((artist (emms-track-get track 'info-artist)))
	     (when artist
	       (add-to-list 'artists artist))))
       emms-cache-db))
    (if artists
	(emms-completing-read "Artist: " artists)
      (read-string "Artist: "))))

(defun emms-lastfm-client-play-similar-artists (artist)
  "Play a Last.fm station with music similar to ARTIST."
  (interactive (list (emms-lastfm-client-read-artist)))
  (when (not (stringp artist))
    (error "not a string: %s" artist))
  (emms-lastfm-client-check-session-key)
  (emms-lastfm-client-make-call-radio-tune
   (format "lastfm://artist/%s/similarartists" artist))
  (emms-lastfm-client-make-call-radio-getplaylist)
  (emms-lastfm-client-play-playlist))

;;; ------------------------------------------------------------------
;;; Information
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-convert-track (track)
  "Convert a Last.fm track to an Emms track."
  (let ((emms-track (emms-dictionary '*track*)))
    (emms-track-set emms-track 'name
		    (emms-lastfm-client-xspf-get 'location track))
    (emms-track-set emms-track 'info-artist
		    (emms-lastfm-client-xspf-get 'creator track))
    (emms-track-set emms-track 'info-title
		    (emms-lastfm-client-xspf-get 'title track))
    (emms-track-set emms-track 'info-album
		    (emms-lastfm-client-xspf-get 'album track))
    (emms-track-set emms-track 'info-playing-time
		    (/
		     (parse-integer
		      (emms-lastfm-client-xspf-get 'duration track))
		     1000))
    emms-track))

(defun emms-lastfm-client-show-track (track)
  "Return description of TRACK."
  (decode-coding-string
   (format emms-show-format
	   (emms-track-description
	    (emms-lastfm-client-convert-track track)))
   'utf-8))

(defun emms-lastfm-client-show ()
  "Display a description of the current track."
  (interactive)
  (if emms-player-playing-p
      (message
       (emms-lastfm-client-show-track emms-lastfm-client-track))
    nil))

;;; ------------------------------------------------------------------
;;; Desktop application authorization [http://www.last.fm/api/desktopauth]
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-user-authorization ()
  "Ask user to authorize the application."
  (interactive)
  (emms-lastfm-client-make-call-urt)
  (emms-lastfm-client-ask-for-auth))

(defun emms-lastfm-client-get-session ()
  "Retrieve and store session key."
  (interactive)
  (emms-lastfm-client-make-call-get-session)
  (emms-lastfm-client-save-session-key
   emms-lastfm-client-api-session-key))

;;; ------------------------------------------------------------------
;;; method: auth.getToken [http://www.last.fm/api/show?service=265]
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-auth-get-token-ok (data)
  "Function called when auth.getToken succeeds."
  (setq emms-lastfm-client-token
	(nth 2 (cadr data)))
  (if (or (not emms-lastfm-client-token)
	  (not (= (length emms-lastfm-client-token) 32)))
      (error "could not read token from response %s" data)
    (message "Emms Last.FM auth.getToken method call success.")))

(defun emms-lastfm-client-auth-get-token-failed (data)
  "Function called when auth.getToken fails."
  (emms-lastfm-client-default-error-handler data))

;;; ------------------------------------------------------------------
;;; method: auth.getSession [http://www.last.fm/api/show?service=125]
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-construct-get-session ()
  "Return an auth.getSession request string."
  (let ((arguments
	 (emms-lastfm-client-encode-arguments
	  `(("token"   . ,emms-lastfm-client-token)
	    ("api_key" . ,emms-lastfm-client-api-key)))))
    (emms-lastfm-client-construct-method-call
     'auth-get-session arguments)))

(defun emms-lastfm-client-make-call-get-session ()
  "Make auth.getSession call."
  (let* ((url-request-method "POST"))
    (let ((response
	   (url-retrieve-synchronously
	    (emms-lastfm-client-construct-get-session))))
      (emms-lastfm-client-handle-response
       'auth-get-session
       (with-current-buffer response
	 (xml-parse-region (point-min) (point-max)))))))

(defun emms-lastfm-client-save-session-key (key)
  "Store KEY."
  (let ((buffer (find-file-noselect
		 emms-lastfm-client-session-key-file)))
    (set-buffer buffer)
    (erase-buffer)
    (insert key)
    (save-buffer)
    (kill-buffer buffer)))

(defun emms-lastfm-client-load-session-key ()
  "Return stored session key."
  (let ((file (expand-file-name emms-lastfm-client-session-key-file)))
    (setq emms-lastfm-client-api-session-key
	  (if (file-readable-p file)
	      (with-temp-buffer
		(emms-insert-file-contents file)
		(goto-char (point-min))
		(buffer-substring-no-properties
		 (point) (point-at-eol)))
	    nil))))

(defun emms-lastfm-client-check-session-key ()
  "Signal an error condition if there is no session key."
  (if emms-lastfm-client-api-session-key
      emms-lastfm-client-api-session-key
    (if (emms-lastfm-client-load-session-key)
	emms-lastfm-client-api-session-key
      (error "no session key for API access"))))

(defun emms-lastfm-client-auth-get-session-ok (data)
  "Function called on DATA if auth.getSession succeeds."
  (let ((session-key (nth 2 (nth 5 (cadr data)))))
    (cond (session-key
	   (setq emms-lastfm-client-api-session-key
		 session-key)
	   (message "Emms Last.fm session key retrieval successful"
		    session-key))
	  (t (error "failed to parse session key data %s" data)))))

(defun emms-lastfm-client-auth-get-session-failed (data)
  "Function called on DATA if auth.getSession fails."
  (emms-lastfm-client-default-error-handler data))

;;; ------------------------------------------------------------------
;;; method: radio.tune [http://www.last.fm/api/show?service=160]
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-construct-radio-tune (station)
  "Return a request to tune to STATION."
  (let ((arguments
	 (emms-lastfm-client-encode-arguments
	  `(("sk"   . ,emms-lastfm-client-api-session-key)
	    ("station" . ,station)
	    ("api_key" . ,emms-lastfm-client-api-key)))))
    (emms-lastfm-client-construct-write-method-call
     'radio-tune arguments)))

(defun emms-lastfm-client-make-call-radio-tune (station)
  "Make call to tune to STATION."
  (let ((url-request-method "POST")
	(url-request-extra-headers
	 `(("Content-type" . "application/x-www-form-urlencoded")))
	(url-request-data
	 (emms-lastfm-client-construct-radio-tune station)))
    (let ((response
	   (url-retrieve-synchronously
	    emms-lastfm-client-api-base-url)))
      (emms-lastfm-client-handle-response
       'radio-tune
       (with-current-buffer response
	 (xml-parse-region (point-min) (point-max)))))))

(defun emms-lastfm-client-radio-tune-failed (data)
  "Function called on DATA when tuning fails."
  (emms-lastfm-client-default-error-handler data))

(defun emms-lastfm-client-radio-tune-ok (data)
  "Set the current radio station according to DATA."
  (let ((response (cdr (cadr data)))
	data)
    (while response
      (when (and (listp (car response))
		 (car response)
		 (= (length (car response)) 3))
	(add-to-list 'data (cons (caar response)
				 (caddr (car response)))))
      (setq response (cdr response)))
    (when (not data)
      (error "could not parse station information %s" data))
    (setq emms-lastfm-client-tuned-station-alist data)))

;;; ------------------------------------------------------------------
;;; method: radio.getPlaylist [http://www.last.fm/api/show?service=256]
;;; ------------------------------------------------------------------

(defun emms-lastfm-client-construct-radio-getplaylist ()
  "Return a request for a playlist from the tuned station."
  (let ((arguments
	 (emms-lastfm-client-encode-arguments
	  `(("sk"   . ,emms-lastfm-client-api-session-key)
	    ("api_key" . ,emms-lastfm-client-api-key)))))
    (emms-lastfm-client-construct-write-method-call
     'radio-getplaylist arguments)))

(defun emms-lastfm-client-make-call-radio-getplaylist ()
  "Make call for playlist from the tuned station."
  (let ((url-request-method "POST")
	(url-request-extra-headers
	 `(("Content-type" . "application/x-www-form-urlencoded")))
	(url-request-data
	 (emms-lastfm-client-construct-radio-getplaylist)))
    (let ((response
	   (url-retrieve-synchronously
	    emms-lastfm-client-api-base-url)))
      (emms-lastfm-client-handle-response
       'radio-getplaylist
       (with-current-buffer response
	 (xml-parse-region (point-min) (point-max)))))))

(defun emms-lastfm-client-radio-getplaylist-failed (data)
  "Function called on DATA when retrieving a playlist fails."
  'stub-needs-to-handle-playlist-issues
  (emms-lastfm-client-default-error-handler data))

(defun emms-lastfm-client-list-filter (l)
  "Remove strings from the roots of list L."
  (let (acc)
    (while l
      (when (listp (car l))
	(push (car l) acc))
      (setq l (cdr l)))
    (reverse acc)))

(defun emms-lastfm-client-radio-getplaylist-ok (data)
  "Function called on DATA when retrieving a playlist succeeds."
  (let ((header (emms-lastfm-client-xspf-header data))
	(tracklist (emms-lastfm-client-xspf-tracklist data)))
    (emms-lastfm-client-set-timer header)
    (setq emms-lastfm-client-playlist
	  (emms-lastfm-client-list-filter tracklist))))

(provide 'emms-lastfm-client)

;;; emms-lastfm-client.el ends here