;;; lyrics-fetcher-genius.el --- fetch lyrics from genius.com -*- lexical-binding: t -*-

;; Copyright (C) 2021 Korytov Pavel

;; Author: Korytov Pavel <thexcloud@gmail.com>
;; Maintainer: Korytov Pavel <thexcloud@gmail.com>
;; Version: 0.1.0
;; Package-Requires: ((emacs "27") (request "0.3.2"))
;; Homepage: https://github.com/SqrtMinusOne/lyrics-fetcher.el

;; This file is NOT part of GNU Emacs.

;; 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:

;; Fetch song lyrics from genius.com.

;;; Code:
(require 'request)
(require 'json)
(require 'seq)
(require 'shr)

(defcustom lyrics-fetcher-genius-access-token nil
  "Genius access token.  Get one at https://genius.com."
  :type '(string nil)
  :group 'lyrics-fetcher)

(defun lyrics-fetcher-genius-do-search (query callback &optional sync)
  "Perform a lyrics search on 'genius.com'.

Requies ‘lyrics-fetcher-genius-access-token’ to be set.

QUERY should be a string which contains the requied information
about the song, e.g. \"Queen The Show Must Go On\". If the search
is successful, CALLBACK will be called with the resulting lyrics
text.

If SYNC is non-nil, perform request synchronously and ask the
user to pick the matching search result."
  (if (string-empty-p lyrics-fetcher-genius-access-token)
      (message "Genius client access token not set!")
    (message "Sending a query to genius API...")
    (request "https://api.genius.com/search"
      :params `(("q" . ,query) ("access_token" . ,lyrics-fetcher-genius-access-token))
      :parser 'json-read
      :sync sync
      :success (cl-function
                (lambda (&key data &allow-other-keys)
                  (lyrics-fetcher--genius-fetch-lyrics
                   (lyrics-fetcher--genius-get-url-from-response data sync)
                   callback
                   sync)))
      :error (cl-function
              (lambda (&&key error-thrown &allow-other-keys)
                (message "Error!: %S" error-thrown))))))

(defun lyrics-fetcher--genius-format-song-title (entry)
  "Convert a Genius search ENTRY to a string, which can be used in selection."
  (let ((result (assoc 'result entry)))
    (format "%-40s [lyrics: %s]"
            (cdr (assoc 'full_title result))
            (cdr (assoc 'lyrics_state result)))))

(defun lyrics-fetcher--genius-get-url-from-response (data &optional ask)
  "Retrive a song URL from the Genius response DATA.

If ASK is non-nil, prompt user for a choice, otherwise select the
first song."
  (if (not (= (cdr (assoc 'status (assoc 'meta data))) 200))
      (message "Error: %" (cdr (assoc 'message (assoc 'meta data))))
    (let* ((results (cdr (assoc 'hits (assoc 'response data))))
           (results-songs (seq-filter
                           (lambda (entry)
                             (string-equal (cdr (assoc 'type entry)) "song"))
                           results)))
      (if (seq-empty-p results-songs)
          (message "Error: no results!")
        (cdr
         (if ask
             (let ((results-songs-for-select
                    (mapcar
                     (lambda (entry)
                       (cons (lyrics-fetcher--genius-format-song-title entry)
                             (assoc 'url (assoc 'result entry))))
                     results-songs)))
               (cdr
                (assoc
                 (completing-read
                  "Pick a result: "
                  results-songs-for-select
                  nil t)
                 results-songs-for-select)))
           (assoc 'url (assoc 'result (car results-songs)))))))))

(defun lyrics-fetcher--genius-fetch-lyrics (url callback &optional sync)
  "Fetch lyrics from genius.com page at URL and call CALLBACK with result.

If SYNC is non-nil, the request will be performed synchronously, but
the function will still make Emacs lags, as HTML parsing is pretty
expensive."
  (message "Getting lyrics from %s" url)
  (request url
    :parser 'buffer-string
    :sync sync
    :success (cl-function
              (lambda (&key data &allow-other-keys)
                (let* ((html (with-temp-buffer
                               (insert data)
                               (libxml-parse-html-region (point-min) (point-max))))
                       (lyrics-div (dom-by-class html (rx bos "lyrics" eos))))
                  (with-temp-buffer
                    (dom-print lyrics-div)
                    (shr-render-region (point-min) (point-max))
                    (funcall callback
                             (buffer-substring-no-properties
                              (point-min)
                              (point-max)))))))
    (cl-function
     (lambda (&&key error-thrown &allow-other-keys)
       (message "Error!: %S" error-thrown)))))

(provide 'lyrics-fetcher-genius)
;;; lyrics-fetcher-genius.el ends here