(defvar *album*)

(defun quotient (x y)
  (/ (- x (mod x y)) y))

(defclass time-spec ()
  ((min :initform 0)
   (sec :initform 0)))

(defmethod t-min ((time-spec time-spec))
  (slot-value time-spec 'min))

(defmethod t-sec ((time-spec time-spec))
  (slot-value time-spec 'sec))

(defmethod set-min ((time-spec time-spec) min)
  (if (and (typep min 'integer)
           (>= min 0))
      (setf (slot-value time-spec 'min) min)
    (error "Value must be an integer, greater than 0"))
  time-spec)

(defmethod set-sec ((time-spec time-spec) sec)
  (if (and (typep sec 'integer)
           (>= sec 0))
      (setf (slot-value time-spec 'sec) sec)
    (error "Value must be an integer, greater than 0"))
  time-spec)

(defmethod time-in-seconds ((time-spec time-spec))
  (+ (* (t-min time-spec) 60) (t-sec time-spec)))

(defmethod set-time-in-seconds ((time-spec time-spec) time-in-sec)
  (let* ((sec (mod time-in-sec 60))
         (min (quotient time-in-sec 60)))
    (set-min time-spec min)
    (set-sec time-spec sec)
    time-spec))

(defun make-time (min sec)
  (let ((time-instance (make-instance 'time-spec)))
    (set-min time-instance min)
    (set-sec time-instance sec)
    time-instance))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defclass track ()
  ((name :initform nil)
   (len :initform (make-time 0 0))))

(defmethod name ((track track))
  (slot-value track 'name))

(defmethod len ((track track))
  (slot-value track 'len))

(defmethod set-name ((track track) name)
  (if (typep name 'string)
      (setf (slot-value track 'name) name)
    (error "Name of the track must be a string"))
  track)

(defmethod set-len ((track track) time-instance)
  (setf (slot-value track 'len) time-instance)
  track)

(defmethod print-track ((track track))
  (format t "~A~1,40T~2D:~2D~%" (name track) (t-min (len track)) (t-sec (len track)))
  track)

(defun make-track (name time)
  (let ((track-instance (make-instance 'track)))
    (set-name track-instance name)
    (set-len track-instance time)
    track-instance))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defclass album ()
  ((artist :initform nil)
   (title :initform nil)
   (tracks :initform nil)
   (year-of-release :initform 0)))

(defmethod artist ((album album))
  (slot-value album 'artist))

(defmethod title ((album album))
  (slot-value album 'title))

(defmethod tracks ((album album))
  (slot-value album 'tracks))

(defmethod year-of-release ((album album))
  (slot-value album 'year-of-release))

(defmethod set-artist ((album album) artist)
  (if (typep artist 'string)
      (setf (slot-value album 'artist) artist)
    (error "Name of the artist must be a string"))
  album)

(defmethod set-title ((album album) title)
  (if (typep title 'string)
      (setf (slot-value album 'title) title)
    (error "Name of the album must be a string"))
  album)

(defmethod set-tracks ((album album) tracks)
  (setf (slot-value album 'tracks) tracks)
  album)

(defmethod set-year-of-release ((album album) year)
  (if (typep year 'integer)
      (setf (slot-value album 'year-of-release) year)
    (error "Year must be an integer"))
  album)

(defmethod track-count ((album album))
  (length (slot-value album 'tracks)))

(defmethod album-length ((album album))
  (let* ((temp-sec (apply #'+ (mapcar (lambda (x) (t-sec (len x))) (slot-value album 'tracks))))
         (sec (mod temp-sec 60))
         (min (+ (apply #'+ (mapcar (lambda (x) (t-min (len x))) (slot-value album 'tracks)))
                 (quotient temp-sec 60))))
    (make-time min sec)))

(defun make-album (artist title tracks year-of-release)
  (let ((album (make-instance 'album)))
    (set-artist album artist)
    (set-title album title)
    (set-tracks album tracks)
    (set-year-of-release album year-of-release)
    album))

(defmethod print-headlines ((album album))
  (format t "Album ~D by ~D, released ~D~%~%"
          (title album)
          (artist album)
          (year-of-release album)))

(defmethod print-tracks ((album album))
  (dotimes (x (track-count album))
    (format t "~D. " (+ x 1))
    (print-track (nth x (tracks album)))))

(defmethod print-total-length ((album album))
  (format t "Total length: ~D:~D"
          (t-min (album-length album))
          (t-sec (album-length album))))

(defmethod print-album ((album album))
  (print-headlines album)
  (print-tracks album)
  (print-total-length album))


(setf *album* (make-album "Miles Davis"
                          "Bitches Brew"
                          (list (make-track "Pharaoh's Dance" (make-time 20 05))                                                       (make-track "Bitches Brew" (make-time 26 58))
                                (make-track "Spanish Key" (make-time 17 32))
                                (make-track "John McLaughlin" (make-time 4 22))
                                (make-track "Miles Runs the Voodoo Down" (make-time 14 01))
                                (make-track "Sanctuary" (make-time 10 56))
                                (make-track "Feio" (make-time 11 49)))
                          1969))