;;;  (c) copyright 2003 by Mathieu Chabanne, Camille Constant,
;;;                        Emmanuel Necibar and Stephanie Recco
;;;
;;;  (c) copyright 2003 by Robert Strandh (strandh@labri.fr)
;;;
;;;  (c) copyright 2007 by David Lewis, Marcus Pearce, Christophe
;;;                        Rhodes and contributors
;;;
;;; This library is free software; you can redistribute it and/or
;;; modify it under the terms of version 2 of the GNU Lesser General
;;; Public License as published by the Free Software Foundation.
;;;
;;; This library 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
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this library; if not, write to the 
;;; Free Software Foundation, Inc., 59 Temple Place - Suite 330, 
;;; Boston, MA  02111-1307  USA.
;;;
;;; This file contains library for MIDI and Midifiles. Messages are
;;; represented as CLOS class instances in a class hierarchy that
;;; reflects interesting aspects of the messages themselves. 

(defpackage :midi
  (:use :common-lisp)
  (:export #:read-midi-file #:write-midi-file
	   #:midifile
	   #:midifile-format #:midifile-tracks #:midifile-division
	   #:message #:note-off-message #:note-on-message #:tempo-message
	   #:program-change-message #:pitch-bend-message
	   #:key-signature-message #:time-signature-message
	   #:smpte-offset-message
           #:sequence/track-name-message
	   #:message-channel #:message-key #:message-time
	   #:message-velocity #:message-numerator #:message-denominator
	   #:message-sf #:message-mi #:message-tempo #:message-program
	   #:message-value
	   #:header #:header-type
	   #:unknown-event #:status #:data-byte))

(in-package :midi)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; Midifile protocol

(defgeneric midifile-format (midifile))
(defgeneric (setf midifile-format) (format midifile))
(defgeneric midifile-division (midifile))
(defgeneric midifile-tracks (midifile))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; Message protocol

(defgeneric message-time (message))
(defgeneric (setf message-time) (time message))
(defgeneric message-status (message))
(defgeneric message-channel (message))
(defgeneric message-key (message))
(defgeneric message-velocity (message))
(defgeneric message-tempo (message))
(defgeneric message-numerator (message))
(defgeneric message-denominator (message))
(defgeneric message-sf (message))
(defgeneric message-mi (message))
;; added 03-05-07
(defgeneric message-program (message))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; File support

(eval-when (:compile-toplevel)
  (defun string-code (s)
    "compute the ASCII-based numerical value of the string [warning:
works only if the chars are coded in ASCII]"
    (let ((v 0))
      (loop for i from 0 to (1- (length s))
	    do (setf v (+ (* v 256) (char-code (aref s i)))))
      v)))

(defconstant +header-mthd+ #.(string-code "MThd"))
(defconstant +header-mtrk+ #.(string-code "MTrk"))
(defconstant +header-mthd-length+ 6 "value of the header MThd data's length")

(defparameter *midi-input* nil "stream for reading a Midifile")
(defparameter *input-buffer* '() "used for unreading bytes from *midi-input")
(defparameter *midi-output* nil "stream for writing a Midifile")

(define-condition unknown-event ()
  ((status :initarg :status :reader status)
   (data-byte :initform "" :initarg :data-byte :reader data-byte))
  (:documentation "condition when the event does not exist in the library"))

(define-condition header ()
  ((header-type :initarg :header :reader header-type))
  (:documentation "condition when the header is not correct"))

(defun read-next-byte ()
  "read an unsigned 8-bit byte from *midi-input* checking for unread bytes"
  (if *input-buffer*
      (pop *input-buffer*)
      (read-byte *midi-input*)))

(defun unread-byte (byte)
  "unread a byte from *midi-input*"
  (push byte *input-buffer*))

(defun write-bytes (&rest bytes)
  "write an arbitrary number of bytes to *midi-output*"
  (mapc #'(lambda (byte) (write-byte byte *midi-output*)) bytes))

(defun read-fixed-length-quantity (nb-bytes)
  "read an unsigned integer of nb-bytes bytes from *midi-input*"
  (loop with result = 0
	for i from 1 to nb-bytes
	do (setf result (logior (ash result 8) (read-next-byte)))
	finally (return result)))

(defun write-fixed-length-quantity (quantity nb-bytes)
  "write an unsigned integer of nb-bytes bytes to *midi-output*"
  (unless (zerop nb-bytes)
    (write-fixed-length-quantity (ash quantity -8) (1- nb-bytes))
    (write-bytes (logand quantity #xff))))

(defmacro with-midi-input ((pathname &rest open-args &key &allow-other-keys) &body body)
  "execute body with *midi-input* assigned to a stream from pathname"
  `(with-open-file (*midi-input* ,pathname
		    :direction :input :element-type '(unsigned-byte 8)
		    ,@open-args)
    ,@body))

(defmacro with-midi-output ((pathname &rest open-args &key &allow-other-keys) &body body)
  "execute body with *midi-output* assigned to a stream from pathname"
  `(with-open-file (*midi-output* ,pathname
		    :direction :output :element-type '(unsigned-byte 8)
		    ,@open-args)
    ,@body))

(defun read-variable-length-quantity ()
  "read a MIDI variable length quantity from *midi-input*"
  (loop with result = 0
	with byte
	do (setf byte (read-next-byte)
		 result (logior (ash result 7) (logand byte #x7f)))
	until (< byte #x80)
	finally (return result)))

(defun write-variable-length-quantity (quantity &optional (termination 0))
  (when (> quantity 127)
    (write-variable-length-quantity (ash quantity -7) #x80))
  (write-bytes (logior (logand quantity #x7f) termination)))

(defun length-of-variables-length-quantity (quantity)
  (1+ (if (< quantity 128)
	  0
	  (length-of-variables-length-quantity (ash quantity -7)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; MIDI file representation

(defclass midifile ()
  ((format :initarg :format :reader midifile-format)
   (division :initarg :division :reader midifile-division)
   (tracks :initarg :tracks :reader midifile-tracks))
  (:documentation "the class that represents a Midifile in core"))

(defparameter *status* nil "the status while reading an event")
(defparameter *running-status* nil "the running status while reading an event")
(defparameter *dispatch-table* (make-array 256 :initial-element nil)
  "given values of status (and perhaps data1), find a class to create")

(defun read-message ()
  "read a message without time indication from *midi-input*"
  (let ((classname-or-subtype (aref *dispatch-table* *status*)))
    (unless classname-or-subtype 
      (error (make-condition 'unknown-event 
			     :status *status*)))
    (if (symbolp classname-or-subtype)
	(make-instance classname-or-subtype)
	(let* ((data-byte (read-next-byte))
	       (classname (aref classname-or-subtype data-byte)))
	  (unless classname
	    (error (make-condition 'unknown-event 
				   :status *status*
				   :data-byte data-byte)))
	  (unread-byte data-byte)
	  (make-instance classname)))))

(defparameter *time* 0 "accumulated time from the start of the track")

(defun read-timed-message ()
  "read a message preceded with a delta-time indication"
  (let ((delta-time (read-variable-length-quantity))
	(status-or-data (read-next-byte)))
    (if (>= status-or-data #x80)
	(progn (setf *status* status-or-data)
	       (when (<= *status* #xef)
		 (setf *running-status* *status*)))
	(progn (unread-byte status-or-data)
	       (setf *status* *running-status*)))
    (let ((message (read-message)))
      (fill-message message)
      (setf (message-time message) (incf *time* delta-time))
      message)))

(defun write-timed-message (message)
  "write a message preceded with a delta-time indication"
  (write-variable-length-quantity (- (message-time message) *time*))
  (setf *time* (message-time message))
  (write-message message))

(defun read-track ()
  "read a track as a list of timed messages, excluding the end-of-track message"
  (let ((type (read-fixed-length-quantity 4))
	(length (read-fixed-length-quantity 4)))
    (declare (ignore length))
    (unless (= type +header-mtrk+)
      (error (make-condition 'header :header "MTrk")))
    (loop with message = nil
	  do (setf message (read-timed-message))
	  until (typep message 'end-of-track-message)
	  collect message)))

(defun write-track (track)
  "write a track (which does not contain the end-of-track message"
  (write-fixed-length-quantity  +header-mtrk+ 4)
  (let ((end-of-track-message (make-instance 'end-of-track-message)))
    ;; write the length of the track
    (write-fixed-length-quantity
     (+ (reduce #'+ track :key #'length-message)
	(length-message end-of-track-message)
	(loop with time = *time*
	      for message in track
	      sum (prog1 (length-of-variables-length-quantity
			  (- (message-time message) time))
		    (setf time (message-time message))))
	1) ; the delta time of the end-of-track message
     4)
    (dolist (message track)
      (write-timed-message message))
    (setf (message-time end-of-track-message) *time*)
    (write-timed-message end-of-track-message)))

(defun read-midi-file (filename)
  "read an entire Midifile from the file with name given as argument"
  (setf *time* 0)
  (with-midi-input (filename)
    (let ((type (read-fixed-length-quantity 4))
	  (length (read-fixed-length-quantity 4))
	  (format (read-fixed-length-quantity 2))
	  (nb-tracks (read-fixed-length-quantity 2))
	  (division (read-fixed-length-quantity 2)))
      (unless (and (= length +header-mthd-length+) (= type +header-mthd+)) 
	(error (make-condition 'header :header "MThd")))
      (make-instance 'midifile
	:format format
	:division division
	:tracks (loop repeat nb-tracks
		      do (when (= format 1) (setf *time* 0))
		      collect (read-track))))))

(defun write-midi-file (midifile filename)
  (with-midi-output (filename :if-exists :supersede)
    (write-fixed-length-quantity +header-mthd+ 4)
    (write-fixed-length-quantity +header-mthd-length+ 4)
    (with-slots (format division tracks) midifile
      (write-fixed-length-quantity format 2)
      (write-fixed-length-quantity (length tracks) 2)
      (write-fixed-length-quantity division 2)
      (setf *time* 0)
      (loop for track in tracks do
	    (write-track track)
	    (when (= (slot-value midifile 'format) 1)
	      (setf *time* 0))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; Conversion routines

(defun format1-tracks-to-format0-tracks (tracks)
  (list (reduce (lambda (t1 t2) (merge 'list t1 t2 #'< :key #'message-time))
		(copy-tree tracks))))

(defun format0-tracks-to-format1-tracks (tracks)
  (assert (null (cdr tracks)))
  (let (tempo-map track)
    (dolist (message (car tracks) (list (nreverse tempo-map) (nreverse track)))
      (if (typep message 'tempo-map-message)
	  (push message tempo-map)
	  (push message track)))))

(defun change-to-format-0 (midifile)
  (assert (= (midifile-format midifile) 1))
  (setf (slot-value midifile 'format) 0
	(slot-value midifile 'tracks) (format1-tracks-to-format0-tracks (midifile-tracks midifile))))

(defun change-to-format-1 (midifile)
  (assert (= (midifile-format midifile) 0))
  (setf (slot-value midifile 'format) 1
	(slot-value midifile 'tracks) (format0-tracks-to-format1-tracks (midifile-tracks midifile))))

(defmethod (setf midifile-format) (new-value midifile)
  (cond
    ((= (midifile-format midifile) new-value) new-value)
    ((and (= new-value 0) (= (midifile-format midifile) 1))
     (change-to-format-0 midifile)
     new-value)
    ((and (= new-value 1) (= (midifile-format midifile) 0))
     (change-to-format-1 midifile)
     new-value)
    (t (error "Unsupported conversion from format ~S to format ~S"
	      (midifile-format midifile) new-value))))
	  
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; Macro for defining midi messages

(defparameter *status-min* (make-hash-table :test #'eq)
  "given a class name, find the minimum status value for the type of message")
(defparameter *status-max* (make-hash-table :test #'eq)
  "given a class name, find the maximum status value for the type of message")
(defparameter *data-min* (make-hash-table :test #'eq)
  "given a class name, find the minimum data1 value for the type of message")
(defparameter *data-max* (make-hash-table :test #'eq)
  "given a class name, find the maximum data1 value for the type of message")

(defun register-class (class superclass status-min status-max data-min data-max)
  (unless status-min
    (setf status-min (gethash superclass *status-min*)))
  (unless status-max
    (setf status-max (gethash superclass *status-max*)))
  (unless data-min
    (setf data-min (gethash superclass *data-min*)))
  (unless data-max
    (setf data-max (gethash superclass *data-max*)))
  ;; set status values for this class
  (setf (gethash class *status-min*) status-min)
  (setf (gethash class *status-max*) status-max)
  (setf (gethash class *data-min*) data-min)
  (setf (gethash class *data-max*) data-max)
  ;; update the dispatch table
  (when status-min
    (if data-min
	(progn (unless (arrayp (aref *dispatch-table* status-min))
		 (let ((secondary-dispatch (make-array 256
						       :initial-element nil)))
		   (loop for i from status-min to status-max do
			 (setf (aref *dispatch-table* i) secondary-dispatch))))
	       (loop for i from data-min to data-max do
		     (setf (aref (aref *dispatch-table* status-min) i)
			   class)))
	(loop for i from status-min to status-max do
	      (setf (aref *dispatch-table* i)
		    class)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; main filler, length, and writer methods

(defgeneric fill-message (message))
(defgeneric write-message (message))
(defgeneric length-message (message)
  (:method-combination +))

(defmethod fill-message (message)
  (declare (ignore message))
  nil)

(defmethod length-message + (message)
  (declare (ignore message))
  0)

(defmethod write-message (message)
  (declare (ignore message))
  nil)

(defmacro define-midi-message (name superclasses
			       &key slots filler (length 0) writer
			       status-min status-max data-min data-max)
  `(progn

    (register-class ',name ',(car superclasses)
     ,status-min ,status-max ,data-min ,data-max)

    (defclass ,name ,superclasses
      ((status-min :initform ,status-min :allocation :class)
       (status-max :initform ,status-max :allocation :class)
       (data-min :initform ,data-min :allocation :class)
       (data-max :initform ,data-max :allocation :class)
       ,@slots))

    (defmethod fill-message :after ((message ,name))
      (with-slots ,(mapcar #'car slots) message
	(symbol-macrolet ((next-byte (read-next-byte)))
	    ,filler)))
    
    (defmethod length-message + ((message ,name))
      (with-slots (status-min status-max data-min data-max ,@(mapcar #'car slots))
	  message
	,length))

    (defmethod write-message :after ((message ,name))
      (with-slots (status-min status-max data-min data-max ,@(mapcar #'car slots))
	  message
	,writer))))
    
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; midi messages

(define-midi-message message ()
  :slots ((time :initarg :time :accessor message-time)
	  (status :initarg :status :reader message-status))
  :length 1
  :filler (setf status *status*)
  :writer (write-bytes status))

(define-midi-message channel-message (message)
  :slots ((channel :reader message-channel))
  :filler (setf channel (logand *status* #x0f)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; voice messages

(define-midi-message voice-message (channel-message))

(define-midi-message note-off-message (voice-message)
  :status-min #x80 :status-max #x8f
  :slots ((key :initarg :key :reader message-key)
	  (velocity :initarg :velocity :reader message-velocity))
  :filler (setf key next-byte
		velocity next-byte)
  :length 2
  :writer (write-bytes key velocity))

(define-midi-message note-on-message (voice-message)
  :status-min #x90 :status-max #x9f
  :slots ((key :initarg :key :reader message-key)
	  (velocity :initarg :velocity :reader message-velocity))
  :filler (setf key next-byte
		velocity next-byte)
  :length 2
  :writer (write-bytes key velocity))

(define-midi-message polyphonic-key-pressure-message (voice-message)
  :status-min #xa0 :status-max #xaf
  :slots ((key)
	  (pressure))
  :filler (setf key next-byte
		pressure next-byte)
  :length 2
  :writer (write-bytes key pressure))

(define-midi-message control-change-message (voice-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x00 :data-max #x78
  :slots ((controller :initarg :controller)
	  (value :initarg value))
  :filler (setf controller next-byte
		value next-byte)
  :length 2
  :writer (write-bytes controller value))

(define-midi-message program-change-message (voice-message)
  :status-min #xc0 :status-max #xcf
  :slots ((program :initarg :program :reader message-program))
  :filler (setf program next-byte)
  :length 1
  :writer (write-bytes program))

(define-midi-message channel-pressure-message (voice-message)
  :status-min #xd0 :status-max #xdf
  :slots ((pressure))
  :filler (setf pressure next-byte)
  :length 1
  :writer (write-bytes pressure))

(define-midi-message pitch-bend-message (voice-message)
  :status-min #xe0 :status-max #xef
  :slots ((value :initarg :value :reader message-value))
  :filler (setf value (logior next-byte (ash next-byte 7)))
  :length 2
  :writer (write-bytes (logand value #x7f) (logand (ash value -7) #x7f)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; mode messages

(define-midi-message mode-message (channel-message)
  :filler next-byte) ; consume data byte

(define-midi-message reset-all-controllers-message (mode-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x79 :data-max #x79
  :filler next-byte ; consume unused byte
  :length 2
  :writer (write-bytes #x79 0))

(define-midi-message local-control-message (mode-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x7a :data-max #x7a
  :slots ((mode))
  :filler (setf mode (if (= next-byte 0) :off :on))
  :length 2
  :writer (write-bytes #x7a (if (eq mode :off) 0 127)))

(define-midi-message all-notes-off-message (mode-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x7b :data-max #x7b
  :filler next-byte ; consume unused byte
  :length 2
  :writer (write-bytes #x7b 0))

(define-midi-message omni-mode-off-message (mode-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x7c :data-max #x7c
  :filler next-byte ; consume unused byte
  :length 2
  :writer (write-bytes #x7c 0))

(define-midi-message omni-mode-on-message (mode-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x7d :data-max #x7d
  :filler next-byte ; consume unused byte
  :length 2
  :writer (write-bytes #x7d 0))

(define-midi-message mono-mode-on-message (mode-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x7e :data-max #x7e
  :slots ((nb-channels))
  :filler (setf nb-channels next-byte)
  :length 2
  :writer (write-bytes #x7e nb-channels))

(define-midi-message poly-mode-on-message (mode-message)
  :status-min #xb0 :status-max #xbf
  :data-min #x7f :data-max #x7f
  :filler next-byte ; consume unused byte
  :length 2
  :writer (write-bytes #x7f 0))

(define-midi-message system-message (message))

(define-midi-message tempo-map-message (message))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; system common messages

(define-midi-message common-message (system-message))

(define-midi-message timing-code-message (common-message)
  :status-min #xf1 :status-max #xf1
  :slots ((code))
  :filler (setf code next-byte)
  :length 1
  :writer (write-bytes code))

(define-midi-message song-position-pointer-message (common-message)
  :status-min #xf2 :status-max #xf2
  :slots ((pointer))
  :filler (setf pointer (logior next-byte (ash next-byte 7)))
  :length 2
  :writer (write-bytes (logand pointer #x7f) (logand (ash pointer -7) #x7f)))

(define-midi-message song-select-message (common-message)
  :status-min #xf3 :status-max #xf3
  :slots ((song))
  :filler (setf song next-byte)
  :length 1
  :writer (write-bytes song))

(define-midi-message tune-request-message (common-message)
  :status-min #xf6 :status-max #xf6)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; system real-time messages

(define-midi-message real-time-message (system-message))

(define-midi-message timing-clock-message (real-time-message)
  :status-min #xf8 :status-max #xf8)

(define-midi-message start-sequence-message (real-time-message)
  :status-min #xfa :status-max #xfa)

(define-midi-message continue-sequence-message (real-time-message)
  :status-min #xfb :status-max #xfb)

(define-midi-message stop-sequence-message (real-time-message)
  :status-min #xfc :status-max #xfc)

(define-midi-message active-sensing-message (real-time-message)
  :status-min #xfe :status-max #xfe)

;; (define-midi-message tune-request-message (real-time-message)
;;  :status-min #xf6 :status-max #xf6)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; system exclusive messages

(define-midi-message system-exclusive-message (system-message)
  :status-min #xf0 :status-max #xf0
  :slots ((data))
  :filler (loop with len = (read-variable-length-quantity)
	        initially (setf data (make-array
				      len :element-type '(unsigned-byte 8)))
	        for i from 0 below len
	        do (setf (aref data i) next-byte))
  :length (+ (length-of-variables-length-quantity (length data))
	   (length data))
  :writer (progn (write-variable-length-quantity (length data))
		 (loop for elem across data do (write-bytes elem))))

(define-midi-message authorization-system-exclusive-message (system-message)
  :status-min #xf7 :status-max #xf7  
  :slots ((data))
  :filler (loop with len = (read-variable-length-quantity)
	        initially (setf data (make-array
				      len :element-type '(unsigned-byte 8)))
	        for i from 0 below len
	        do (setf (aref data i) next-byte))
  :length (+ (length-of-variables-length-quantity (length data))
	   (length data))
  :writer (progn (write-variable-length-quantity (length data))
		 (loop for elem across data do (write-bytes elem))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;; meta messages

(define-midi-message meta-message (message)
  :status-min #xff :status-max #xff
  :length 2 ; the first data byte and the length byte
  :filler next-byte ; the first data byte which gives the type of meta message
  :writer (write-bytes data-min))

(define-midi-message sequence-number-message (meta-message tempo-map-message)
  :data-min #x00 :data-max #x00
  :slots ((sequence))
  :filler (let ((data2 next-byte))
	    (setf sequence (if (zerop data2)
			       0
			       (logior (ash next-byte 8) next-byte))))
  :length (if (zerop sequence) 0 2)
  :writer (unless (zerop sequence)
	    (write-bytes (ash sequence -8) (logand sequence #xf))))

(define-midi-message text-message (meta-message)
  :slots ((text))
  :filler (setf text (loop with len = next-byte
			   with str = (make-string len)
			   for i from 0 below len
			   do (setf (aref str i)
				    (code-char next-byte))
			   finally (return str)))
  :length (length text)
  :writer (progn (write-bytes (length text))
		 (loop for char across text do
		       (write-bytes (char-code char)))))

(define-midi-message general-text-message (text-message)
  :data-min #x01 :data-max #x01)
  
(define-midi-message copyright-message (text-message)
  :data-min #x02 :data-max #x02)
  
(define-midi-message sequence/track-name-message (text-message tempo-map-message)
  :data-min #x03 :data-max #x03)
  
(define-midi-message instrument-message (text-message)
  :data-min #x04 :data-max #x04)
  
(define-midi-message lyric-message (text-message)
  :data-min #x05 :data-max #x05)
  
(define-midi-message marker-message (text-message tempo-map-message)
  :data-min #x06 :data-max #x06)
  
(define-midi-message cue-point-message (text-message)
  :data-min #x07 :data-max #x07)
  
(define-midi-message program-name-message (text-message)
  :data-min #x08 :data-max #x08)

(define-midi-message device-name-message (text-message)
  :data-min #x09 :data-max #x09)

(define-midi-message channel-prefix-message (meta-message)
  :data-min #x20 :data-max #x20
  :slots ((channel))
  :length 1
  :filler (progn next-byte (setf channel next-byte))
  :writer (write-bytes 1 channel))

(define-midi-message midi-port-message (meta-message)
  :data-min #x21 :data-max #x21
  :slots ((port))
  :length 1
  :filler (progn next-byte (setf port next-byte))
  :writer (write-bytes 1 port))

(define-midi-message end-of-track-message (meta-message)
  :data-min #x2f :data-max #x2f
  :slots ((status :initform #xff))
  :filler next-byte
  :length 0
  :writer (write-bytes 0))

(define-midi-message tempo-message (meta-message tempo-map-message)
  :data-min #x51 :data-max #x51
  :slots ((tempo :initarg :tempo :reader message-tempo))
  :filler (progn next-byte (setf tempo (read-fixed-length-quantity 3)))
  :length 3
  :writer (progn (write-bytes 3) (write-fixed-length-quantity tempo 3)))

(define-midi-message smpte-offset-message (meta-message tempo-map-message)
  :data-min #x54 :data-max #x54
  :slots ((hr) (mn) (se) (fr) (ff))
  :filler (progn next-byte (setf hr next-byte mn next-byte se next-byte
				 fr next-byte ff next-byte))
  :length 5
  :writer (write-bytes 5 hr mn se fr ff))

(define-midi-message time-signature-message (meta-message tempo-map-message)
  :data-min #x58 :data-max #x58
  :slots ((nn :reader message-numerator) 
	  (dd :reader message-denominator) 
	  (cc) (bb))
  :filler (progn next-byte (setf nn next-byte dd next-byte
				 cc next-byte bb next-byte))
  :length 4
  :writer (write-bytes 4 nn dd cc bb))

(define-midi-message key-signature-message (meta-message)
  :data-min #x59 :data-max #x59
  :slots ((sf :reader message-sf)
	  (mi :reader message-mi))
  :filler (progn next-byte (setf sf (let ((temp-sf next-byte))
				      (if (> temp-sf 127) 
					  (- temp-sf 256)
					  temp-sf))
				 mi next-byte))
  :length 2
  :writer (write-bytes 2 (if (< sf 0) (+ sf 256) sf) mi))

(define-midi-message proprietary-event (meta-message)
  :data-min #x7f :data-max #x7f
  :slots ((data))
  :filler (setf data (loop with len = (read-variable-length-quantity)
			   with vec = (make-array 
				       len 
				       :element-type '(unsigned-byte 8))
			   for i from 0 below len
			   do (setf (aref vec i) next-byte)
			   finally (return vec)))
  :writer (map nil (lambda (byte) (write-bytes byte))
	       data)) ; FIXME