;;; -*- Mode: Lisp;  show-trailing-whitespace: t; Base: 10; indent-tabs: nil; Syntax: ANSI-Common-Lisp; Package: M4A; -*-
;;; Copyright (c) 2013, Mark VandenBrink. All rights reserved.
(in-package #:m4a)

;;;; ATOMS
;;;
;;; A word about atoms (aka "boxes").  There are three kinds of atoms: ones that
;;; are containers, ones that are data, and ones that are both. A lot of the
;;; taggers out there mostly ignore third class and treat "container atoms that
;;; also have data" as a big blob of data that they rummage around in via
;;; indices.  Seems sort of broken, IMHO, so we'll try to handle all three if
;;; at all possible.
;;;

(defun mk-atom-class-name (name)
  "Create an atom class name by concatenating ATOM- with NAME"
  (declare #.utils:*standard-optimize-settings*)
  (string-upcase (concatenate 'string "atom-" name)))
(memoize 'mk-atom-class-name)

(eval-when (:compile-toplevel :load-toplevel :execute)
  (defun as-string (atom-type)
    "Given an integer, return the string representation"
    (declare #.utils:*standard-optimize-settings*)

    (with-output-to-string (s nil)
      (write-char (code-char (ldb (byte 8 24) atom-type)) s)
      (write-char (code-char (ldb (byte 8 16) atom-type)) s)
      (write-char (code-char (ldb (byte 8 8)  atom-type)) s)
      (write-char (code-char (ldb (byte 8 0)  atom-type)) s)))

  (defun as-octet (c)
    "Used below so that we can create atom 'types' from char/ints"
    (declare #.utils:*standard-optimize-settings*)

    (cond ((typep c 'standard-char) (coerce (char-code c) '(unsigned-byte 8)))
          ((typep c 'integer) (coerce c '(unsigned-byte 8)))
          (t (error "can only handle characters and integers"))))

  (defmacro mk-mp4-atom-type (l1 l2 l3 l4)
    "Given 4 chars/ints, create a string for the name"
    `(with-output-to-string (s nil)
       (write-char (code-char ,(as-octet l1)) s)
       (write-char (code-char ,(as-octet l2)) s)
       (write-char (code-char ,(as-octet l3)) s)
       (write-char (code-char ,(as-octet l4)) s))))

;;;; Atom names/ids. Each one of these has an associated "value"(nee data) atom under it
(defconstant* +root+                  (mk-mp4-atom-type #\R #\O #\O #\T)  "fake root for atom tree")

(defconstant* +itunes-ilst-data+      (mk-mp4-atom-type #\d #\a #\t #\a)  "carries the actual data under an ilst atom")

(defconstant* +m4-ftyp+               (mk-mp4-atom-type #\f #\t #\y #\p) "This should be the first atom type found in file")

(defconstant* +mp4-atom-hdlr+         (mk-mp4-atom-type #\h #\d #\l #\r) "Found under trak.mdia and tells what kind of handler it is")

(defconstant* +audioprop-mdhd+        (mk-mp4-atom-type #\m #\d #\h #\d) "Found under trak.mdia and holds data to calculate length of audio")
(defconstant* +audioprop-stsd+        (mk-mp4-atom-type #\s #\t #\s #\d) "Container atom: found under trak.mdia.minf.stbl and holds bit-rate, etc")
(defconstant* +audioprop-mp4a+        (mk-mp4-atom-type #\m #\p #\4 #\a) "Found under trak.mdia.minf.stbl")
(defconstant* +audioprop-esds+        (mk-mp4-atom-type #\e #\s #\d #\s) "Found under trak.mdia.minf.stbl.mp4a")

(defconstant* +mp4-atom-ilst+         (mk-mp4-atom-type #\i #\l #\s #\t))
(defconstant* +mp4-atom-mdia+         (mk-mp4-atom-type #\m #\d #\i #\a))
(defconstant* +mp4-atom-meta+         (mk-mp4-atom-type #\m #\e #\t #\a))
(defconstant* +mp4-atom-minf+         (mk-mp4-atom-type #\m #\i #\n #\f))
(defconstant* +mp4-atom-moov+         (mk-mp4-atom-type #\m #\o #\o #\v))
(defconstant* +mp4-atom-stbl+         (mk-mp4-atom-type #\s #\t #\b #\l))
(defconstant* +mp4-atom-trak+         (mk-mp4-atom-type #\t #\r #\a #\k))
(defconstant* +mp4-atom-udta+         (mk-mp4-atom-type #\u #\d #\t #\a))

(defparameter *in-progress* nil "the node currently being worked upon")
(defparameter *tree*        nil "the root of the atom tree being constructed")

;;;; Atoms
(defclass mp4-atom ()
  ((atom-file-pos :accessor atom-file-pos :initarg :atom-file-pos :initform nil)
   (atom-size     :accessor atom-size     :initarg :atom-size     :initform nil)
   (atom-type     :accessor atom-type     :initarg :atom-type     :initform nil))
  (:documentation "The minimal mp4-atom."))

(defmethod initialize-instance :around ((me mp4-atom) &key &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

  (let* ((old *in-progress*)
         (*in-progress* (tree:make-node me)))
    (if old
        (progn
          (tree:add-child old *in-progress*)
          (call-next-method))
        (let ((*tree* *in-progress*)) ; must use dynamic binding for multi-threading
          (call-next-method)
          ;; HACK ALERT: this is the top of the tree, so stuff the root
          ;; in the TREE slot of a container atom
          (setf (tree me) *tree*)))))

(defmacro with-mp4-atom-slots ((instance) &body body)
  `(with-slots (atom-file-pos atom-size atom-type) ,instance
     ,@body))

;;;; Concrete atoms
(defclass atom-skip (mp4-atom) ())

(defmethod initialize-instance :after ((me atom-skip) &key mp4-file &allow-other-keys)
  "The 'skip' atom.  Used when we want to capture the header of atom, but don't want/need
to read the payload of an atom."
  (declare #.utils:*standard-optimize-settings*)

  (with-mp4-atom-slots (me)
    (stream-seek mp4-file (- atom-size 8) :current)))

;;; For atoms we don't implement yet, subclass atom-skip
(defclass atom----- (atom-skip) ())
(defclass atom-cmID (atom-skip) ()) ; ???
(defclass atom-dinf (atom-skip) ())
(defclass atom-drms (atom-skip) ())
(defclass atom-edts (atom-skip) ())
(defclass atom-flvr (atom-skip) ())
(defclass atom-free (atom-skip) ())
(defclass atom-ftyp (atom-skip) ())
(defclass atom-iods (atom-skip) ())
(defclass atom-mdat (atom-skip) ())
(defclass atom-mvhd (atom-skip) ())
(defclass atom-name (atom-skip) ())
(defclass atom-pinf (atom-skip) ())
(defclass atom-plID (atom-skip) ())
(defclass atom-sbtd (atom-skip) ())
(defclass atom-smhd (atom-skip) ())
(defclass atom-stco (atom-skip) ())
(defclass atom-stsc (atom-skip) ())
(defclass atom-stsz (atom-skip) ())
(defclass atom-stts (atom-skip) ())
(defclass atom-tkhd (atom-skip) ())
(defclass atom-xid  (atom-skip) ()) ; NOTE: it's actually "xid#\Space"

(defclass mp4-container-atom (mp4-atom)
  ((tree :accessor tree :documentation "Note: this is ONLY set for the ROOT atom"))
  (:documentation "An atom that 'contains' other atoms"))

(defmethod initialize-instance :after ((me mp4-container-atom) &key mp4-file &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

  (with-mp4-atom-slots (me)
    (loop for end = (+ atom-file-pos atom-size)
          for current = (stream-seek mp4-file) then (stream-seek mp4-file)
          while (< current end) do
            (make-mp4-atom mp4-file me))))

;;;; ILST ATOMS (ie atoms related to tagging)
(defclass atom-ilst (mp4-container-atom) ())

(eval-when (:compile-toplevel :load-toplevel :execute)
  (defparameter *ilst-atoms*
    '(("account-type"      "akID")
      ("album"             "©alb")
      ("album-artist"      "aART")
      ("artist"            "©art")
      ("at-id"             "atID")
      ("cn-id"             "cnID")
      ("comment"           "©cmt")
      ("compilation"       "cpil")
      ("composer"          "©com")
      ("content-rating"    "rtng")
      ("copyright"         "cprt")
      ("cover-art"         "covr")
      ("disk"              "disk")
      ("encoder"           "©enc")
      ("gapless-playback"  "pgap")
      ("ge-id"             "geID")
      ("genre"             "gnre")
      ("genre-x"           "©gen")
      ("groups"            "©grp")
      ("lyrics"            "©lyr")
      ("media-type"        "stik")
      ("purchase-account"  "apID")
      ("purchased-date"    "purd")
      ("sort-album"        "soal")
      ("sort-album-artist" "soaa")
      ("sort-artist"       "soar")
      ("sort-composer"     "soco")
      ("sort-name"         "sonm")
      ("store"             "sfID")
      ("tempo"             "tmpo")
      ("title"             "©nam")
      ("tool"              "©too")
      ("track"             "©trk")
      ("track-n"           "trkn")
      ("writer"            "©wrt")
      ("year"              "©day"))
    "This is the list of ILST atoms we handle. Each entry is constant-name/class-name")

  (defmacro mk-ilst-atoms-constants ()
    `(progn
       ,@(loop for e in *ilst-atoms*
               collect
               `(progn
                  (defclass ,(mksym "atom-" (second e)) (atom-ilst) ())
                  (defconstant* ,(mksym "+itunes-" (first e) "+") ,(second e))
                  (export ',(mksym "+itunes-" (first e) "+")))))))

;;; generate the ilst atoms/constants/exports
(mk-ilst-atoms-constants)


(defclass atom-data (mp4-atom)
  ((atom-version :accessor atom-version :initarg :atom-version :initform nil)
   (atom-flags   :accessor atom-flags   :initarg :atom-flags   :initform nil)
   (atom-locale  :accessor atom-locale  :initarg :atom-locale  :initform nil)
   (atom-value   :accessor atom-value   :initarg :atom-value   :initform nil))
  (:documentation "Represents the 'data' portion of ilst data atom"))

(defmethod initialize-instance :after ((me atom-data) &key mp4-file parent &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

  (with-slots (atom-size atom-type atom-version atom-flags atom-value atom-locale) me
    (setf atom-version (stream-read-u8 mp4-file)
          atom-flags   (stream-read-u24 mp4-file)
          atom-locale  (stream-read-u32 mp4-file))

    ;; Ideally, we would be able to read the atom's value by looking
    ;; solely at the atom-flags; however, when atom-flags == 0, then
    ;; things get crazy---I can NOT for the life of me figure out
    ;; the trck/trkn/disk integer format, hence the mess below.
    (setf atom-value
          (ecase atom-flags
            (1
             (stream-read-utf-8-string mp4-file (- atom-size 16)))

            ((13 14)
             (stream-read-sequence mp4-file (- atom-size 16)))

            ((0 21)
             (cond      ; messy!
               ((member (atom-type parent)
                        (list +itunes-track+ +itunes-track-n+ +itunes-disk+)
                        :test #'string=)
                (stream-read-u16 mp4-file) ; throw away
                (let* ((a (stream-read-u16 mp4-file))
                       (b (stream-read-u16 mp4-file)))
                  (stream-seek mp4-file (- atom-size 16 6) :current)
                  (list a b)))

               (t (ecase (- atom-size 16)
                    (2 (stream-read-u16 mp4-file))
                    (1 (stream-read-u8 mp4-file))))))))))

;;;; Audio Property Atoms
(defclass atom-trak (mp4-container-atom) ())
(defclass atom-minf (mp4-container-atom) ())
(defclass atom-moov (mp4-container-atom) ())
(defclass atom-udta (mp4-container-atom) ())
(defclass atom-mdia (mp4-container-atom) ())
(defclass atom-stbl (mp4-container-atom) ())

(defclass atom-hdlr (mp4-atom)
  ((version :accessor version) ; 1 byte
   (flags   :accessor flags)   ; 3 bytes
   (qtype   :accessor qtype)   ; 4 bytes
   (mtype   :accessor mtype)   ; 4 bytes
   (resv    :accessor resv)    ; 4 bytes
   (rflag   :accessor rflag)   ; 4 bytes
   (rmask   :accessor rmask)   ; 4 bytes
   (mhdlr   :accessor mhdlr))) ; null-terminated string (but we're reading it as octets)

(defmethod initialize-instance :after ((me atom-hdlr) &key mp4-file &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

  (with-slots (version flags qtype mtype resv rflag rmask mhdlr atom-size) me
    (setf version  (stream-read-u8 mp4-file)
          flags    (stream-read-u24 mp4-file)
          qtype    (stream-read-u32 mp4-file)
          mtype    (stream-read-u32 mp4-file)
          resv     (stream-read-u32 mp4-file)
          rflag    (stream-read-u32 mp4-file)
          rmask    (stream-read-u32 mp4-file)
          mhdlr    (stream-read-sequence mp4-file (- atom-size 32))) ; 32 is 8-bytes of header plus fields above
    ))

(defclass atom-mdhd (mp4-atom)
  ((version  :accessor version)
   (flags    :accessor flags)
   (c-time   :accessor c-time)
   (m-time   :accessor m-time)
   (scale    :accessor scale)
   (duration :accessor duration)
   (lang     :accessor lang)
   (quality  :accessor quality)))

(defmethod initialize-instance :after ((me atom-mdhd) &key mp4-file &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

  (with-slots (version flags c-time m-time scale duration lang quality) me
    (setf version  (stream-read-u8 mp4-file)
          flags    (stream-read-u24 mp4-file)
          c-time   (stream-read-u32 mp4-file)
          m-time   (stream-read-u32 mp4-file)
          scale    (stream-read-u32 mp4-file)
          duration (if (= 0 version) (stream-read-u32 mp4-file) (stream-read-u64 mp4-file))
          lang     (stream-read-u16 mp4-file)
          quality  (stream-read-u16 mp4-file))))

(defclass atom-esds (mp4-atom)
  ((version      :accessor version)       ; 1 byte
   (flags        :accessor flags)         ; 3 bytes
   (esid         :accessor esid)          ; 2 bytes
   (s-priority   :accessor s-priority)    ; 1 byte
   (obj-id       :accessor obj-id)        ; 1 byte
   (s-type       :accessor s-type)        ; 1 byte (1 bit up-stream, 1-but reservered, 6-bits stream type
   (buf-size     :accessor buf-size)      ; 3 bytes
   (max-bit-rate :accessor max-bit-rate)  ; 4 bytes
   (avg-bit-rate :accessor avg-bit-rate)) ; 4 bytes
  (:documentation "XXX-partial definition for Elementary Stream Descriptors (ESDs)"))

;;; 3 bytes extended descriptor type tag string = 3 * 8-bit hex value
;;; types are Start = 0x80 ; End = 0xFE
;;; then, one byte of length
;;; Note: start types are optional
(defun read-descriptor-len (instream)
  "Get the ES descriptor's length."
  (declare #.utils:*standard-optimize-settings*)

  (let* ((tmp (stream-read-u8 instream))
         (len (logand tmp #x7f)))
    (declare (type (unsigned-byte 8) tmp))
    (while (not (zerop (logand #x80 tmp)))
      (setf tmp (stream-read-u8 instream)
            len (logior (ash len 7) (logand tmp #x7f))))
    len))

;;; one-byte descriptor tags
(defconstant* +mp4-odescrtag+               #x01)
(defconstant* +mp4-iodescrtag+              #x02)
(defconstant* +mp4-esdescrtag+              #x03)
(defconstant* +mp4-decconfigdescrtag+       #x04)
(defconstant* +mp4-decspecificdescrtag+     #x05)
(defconstant* +mp4-slconfigdescrtag+        #x06)
(defconstant* +mp4-contentiddescrtag+       #x07)
(defconstant* +mp4-supplcontentiddescrtag+  #x08)
(defconstant* +mp4-ipiptrdescrtag+          #x09)
(defconstant* +mp4-ipmpptrdescrtag+         #x0a)
(defconstant* +mp4-ipmpdescrtag+            #x0b)
(defconstant* +mp4-registrationdescrtag+    #x0d)
(defconstant* +mp4-esidincdescrtag+         #x0e)
(defconstant* +mp4-esidrefdescrtag+         #x0f)
(defconstant* +mp4-fileiodescrtag+          #x10)
(defconstant* +mp4-fileodescrtag+           #x11)
(defconstant* +mp4-extprofileleveldescrtag+ #x13)
(defconstant* +mp4-extdescrtagsstart+       #x80)
(defconstant* +mp4-extdescrtagsend+         #xfe)

(defmethod initialize-instance :after ((me atom-esds) &key mp4-file &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

  (with-slots (version flags esid s-priority obj-id s-type buf-size max-bit-rate avg-bit-rate) me
    (setf version (stream-read-u8 mp4-file)
          flags   (stream-read-u24 mp4-file))

    (assert (= +MP4-ESDescrTag+ (stream-read-u8 mp4-file)) () "Expected description tag of ESDescrTag")

    (let* ((len         (read-descriptor-len mp4-file))
           (end-of-atom (+ (stream-seek mp4-file) len)))
      (setf esid       (stream-read-u16 mp4-file)
            s-priority (stream-read-u8 mp4-file))

      (assert (= +MP4-DecConfigDescrTag+ (stream-read-u8 mp4-file)) () "Expected tag type of DecConfigDescrTag")

      (setf len          (read-descriptor-len mp4-file)
            obj-id       (stream-read-u8 mp4-file)
            s-type       (stream-read-u8 mp4-file)
            buf-size     (stream-read-u24 mp4-file)
            max-bit-rate (stream-read-u32 mp4-file)
            avg-bit-rate (stream-read-u32 mp4-file))

      ;; Should do checking here and/or read rest of atom,
      ;; but for now, we have what we want, so just seek to end of atom
      (stream-seek mp4-file end-of-atom :start))))

(defclass atom-stsd (mp4-atom)
  ((flags       :accessor flags)
   (version     :accessor version)
   (num-entries :accessor num-entries)))

(defmethod initialize-instance :after ((me atom-stsd) &key mp4-file &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

  (with-slots (flags version num-entries) me
    (setf version     (stream-read-u8 mp4-file)
          flags       (stream-read-u24 mp4-file)
          num-entries (stream-read-u32 mp4-file))))

(defclass atom-mp4a (mp4-container-atom)
  ((reserved    :accessor reserved)    ; 6 bytes
   (d-ref-idx   :accessor d-ref-idx)   ; 2 bytes
   (version     :accessor version)     ; 2 bytes
   (revision    :accessor revision)    ; 2 bytes
   (vendor      :accessor vendor)      ; 4 bytes
   (num-chans   :accessor num-chans)   ; 2 bytes
   (samp-size   :accessor samp-size)   ; 2 bytes
   (comp-id     :accessor comp-id)     ; 2 bytes
   (packet-size :accessor packet-size) ; 2 bytes
   (samp-rate   :accessor samp-rate))) ; 4 bytes

(defmethod initialize-instance :around ((me atom-mp4a) &key mp4-file &allow-other-keys)
  "Note: this MUST be an AROUND method so that the atom's data can be read in before
reading the container atoms"
  (declare #.utils:*standard-optimize-settings*)
  (with-slots (reserved d-ref-idx version revision vendor num-chans samp-size comp-id packet-size samp-rate) me
    (setf reserved    (stream-read-sequence mp4-file 6)
          d-ref-idx   (stream-read-u16 mp4-file)
          version     (stream-read-u16 mp4-file)
          revision    (stream-read-u16 mp4-file)
          vendor      (stream-read-u32 mp4-file)
          num-chans   (stream-read-u16 mp4-file)
          samp-size   (stream-read-u16 mp4-file)
          comp-id     (stream-read-u16 mp4-file)
          packet-size (stream-read-u16 mp4-file)
          samp-rate   (stream-read-u32 mp4-file))) ; fixed 16.16 floating point number
  (call-next-method))

(defclass atom-meta (mp4-container-atom)
  ((version  :accessor version)
   (flags    :accessor flags)))

(defmethod initialize-instance :around ((me atom-meta) &key mp4-file &allow-other-keys)
  (declare #.utils:*standard-optimize-settings*)

   (with-slots (version flags) me
     (setf version (stream-read-u8 mp4-file)
           flags   (stream-read-u24 mp4-file)))
  (call-next-method))

(defun find-atom-class (id)
  "Search by concatenating 'atom-' with ID and look for that symbol in this package"
  (declare #.utils:*standard-optimize-settings*)

  (let ((found-class-symbol (find-symbol (mk-atom-class-name id) :M4A)))

    ;; if we found the class name, return the class (to be used for MAKE-INSTANCE)
    (when found-class-symbol
      (return-from find-atom-class (find-class found-class-symbol)))

    ;; didn't find a class, so return ATOM-SKIP class
    (warn-user "file ~a~%Unknown atom type <~a> encountered~%"
               audio-streams:*current-file* id)
    'atom-skip))
(memoize 'find-atom-class)

(defun make-mp4-atom (mp4-file parent)
  "Get current file position, read in size/type, then construct the correct atom."
  (declare #.utils:*standard-optimize-settings*)

  (let* ((pos (stream-seek mp4-file))
         (siz (stream-read-u32 mp4-file))
         (typ (string-right-trim '(#\Space)
                                 (as-string (stream-read-u32 mp4-file))))
         (atom))
    (declare (fixnum pos siz))

    (when (= 0 siz)
      (error "trying to make an atom ~a with size of 0 at offset ~:d in file ~a"
             typ pos (stream-filename mp4-file)))

    (setf atom (make-instance (find-atom-class typ)
                              :atom-size siz
                              :atom-type typ
                              :atom-file-pos pos
                              :parent parent
                              :mp4-file mp4-file))
    atom))

(defmethod vpprint ((me mp4-atom) stream)
  (declare #.utils:*standard-optimize-settings*)

  (format stream "~a"
          (with-output-to-string (s)
            (with-mp4-atom-slots (me)
              (format s "atom:: type: <~a> @ ~:d of size ~:d"
                      atom-type atom-file-pos atom-size))
            (if (typep me 'atom-data)
                (with-slots (atom-version atom-flags atom-value atom-type) me
                  (format s ", ilst fields: verison = ~d, flags = ~x, data = ~a"
                          atom-version atom-flags
                          (if (typep atom-value 'octets)
                              (printable-array atom-value)
                              atom-value)))))))

(defun is-valid-m4-file (mp4-file)
  "Make sure this is an MP4 file.  Quick check: is first atom (at file-offset 4) == FSTYP?
Written in this fashion so as to be 'crash-proof' when passed an arbitrary file."
  (declare #.utils:*standard-optimize-settings*)

  (let ((valid)
        (size)
        (header))
    (when (> (stream-size mp4-file) 8)
      (stream-seek mp4-file 0 :start)
      (setf size   (stream-read-u32 mp4-file)
            header (as-string (stream-read-u32 mp4-file))
            valid  (and (<= size (stream-size mp4-file))
                        (string= header +m4-ftyp+))))
    (stream-seek mp4-file 0 :start)
    valid))

(defclass mp4-file ()
  ((filename   :accessor filename :initform nil :initarg :filename
               :documentation "filename that was parsed")
   (mp4-atoms  :accessor mp4-atoms  :initform nil
               :documentation "holds tree of parsed MP4 atoms/boxes")
   (audio-info :accessor audio-info :initform nil
               :documentation "holds the bit-rate, etc info"))
  (:documentation "Stream for parsing MP4 audio files"))

(defun parse-audio-file (instream &optional (get-audio-info nil))
  "Given a valid MP4 file, look for the 'right' atoms and return them."
  (declare #.utils:*standard-optimize-settings*)

  (stream-seek instream 0 :start)

  (let* ((*in-progress* nil)          ; dynamic binding for multi-threading
         (parsed-info (make-instance 'mp4-file
                                     :filename (stream-filename instream))))
    (setf (mp4-atoms parsed-info)
          (tree      (make-instance 'mp4-container-atom
                                    :atom-type +root+
                                    :atom-file-pos 0
                                    :atom-size (stream-size instream)
                                    :mp4-file instream)))
    (when get-audio-info
      (setf (audio-info parsed-info) (get-mp4-audio-info parsed-info)))

    parsed-info))

(defparameter *ilst-data* (list +root+ +mp4-atom-moov+ +mp4-atom-udta+
                                +mp4-atom-meta+ +mp4-atom-ilst+ nil)
  "iTunes artist/album/etc path. The 5th element should be set to
one of the +iTunes- constants")

(defun tag-get-value (mp4-file atom-type)
  "Helper function to extract text from ILST atom's data atom"
  (declare #.utils:*standard-optimize-settings*)

  (setf (nth 5 *ilst-data*) atom-type)
  (aif (tree:at-path (mp4-atoms mp4-file) *ilst-data*
                     (lambda (x y)
                       (string= (atom-type (tree:data x)) y)))

       (let ((ret))
         ;; NB: only the COVR atom can have more than one data atom,
         ;; and it can be "data", "name", or "itif"(???).
         (loop for e = (tree:first-child it)
                 then (tree:next-sibling e)
               until (null e) do
                 (when (typep (tree:data e) 'atom-data)
                   (push (atom-value (tree:data e)) ret)))
         (nreverse ret))
       nil))

(defun mp4-show-raw-tag-atoms (mp4-file-stream out-stream)
  "Show all the iTunes data atoms"
  (declare #.utils:*standard-optimize-settings*)

  (let ((top-node
          (tree:at-path (mp4-atoms mp4-file-stream)
                        (list +root+ +mp4-atom-moov+ +mp4-atom-udta+
                              +mp4-atom-meta+ +mp4-atom-ilst+)
                        (lambda (x y)
                          (string= (atom-type (tree:data x)) y)))))

    (loop for node = (tree:first-child top-node)
            then (tree:next-sibling node) until (null node) do
              (format out-stream "~2t~a" (vpprint (tree:data node) nil))
              (aif (tree:first-child node)
                   (format out-stream ", Data ~a~%" (vpprint (tree:data it) nil))
                   (format out-stream "~%")))))

(defun get-audio-properties-atoms (mp4-file)
  "Get the audio property atoms from MP4-FILE.
MP4A audio info is held in under root.moov.trak.mdia.mdhd,
root.moov.trak.mdia.minf.stbl.mp4a, and root.moov.trak.mdia.minf.stbl.mp4a.esds"
  (declare #.utils:*standard-optimize-settings*)

  (let ((mdhd
          (tree:find-tree
           (mp4-atoms mp4-file)
           (lambda (x)
             (string= (atom-type (tree:data x)) +audioprop-mdhd+))))
        (mp4a (tree:find-tree
               (mp4-atoms mp4-file)
               (lambda (x)
                 (string= (atom-type (tree:data x)) +audioprop-mp4a+))))
        (esds (tree:find-tree
               (mp4-atoms mp4-file)
               (lambda (x)
                 (string= (atom-type (tree:data x)) +audioprop-esds+)))))

    (if (and mdhd mp4a esds)
        (values (tree:data (first mdhd))
                (tree:data (first mp4a))
                (tree:data (first esds)))
        nil)))

(defclass audio-info ()
  ((seconds         :accessor seconds         :initform nil)
   (channels        :accessor channels        :initform nil)
   (bits-per-sample :accessor bits-per-sample :initform nil)
   (sample-rate     :accessor sample-rate     :initform nil)
   (max-bit-rate    :accessor max-bit-rate    :initform nil)
   (avg-bit-rate    :accessor avg-bit-rate    :initform nil))
  (:documentation "Holds extracted audio information about an MP4 file."))

(defmethod vpprint ((me audio-info) stream)
  (declare #.utils:*standard-optimize-settings*)

  (with-slots (seconds channels bits-per-sample sample-rate max-bit-rate avg-bit-rate) me
    (format stream "sample rate: ~:d Hz, # channels: ~d, bits-per-sample: ~:d, max bit-rate: ~:d Kbps, avg bit-rate: ~:d Kbps, duration: ~:d:~2,'0d"
            (if sample-rate sample-rate 0)
            (if channels channels 0)
            (if bits-per-sample bits-per-sample 0)
            (if max-bit-rate (round (/ max-bit-rate 1000)) 0)
            (if avg-bit-rate (round (/ avg-bit-rate 1000)) 0)
            (if seconds (floor (/ seconds 60)) 0)
            (if seconds (round (mod seconds 60)) 0))))

(defun get-mp4-audio-info (mp4-file)
  "Find and parse the audio information in MP4-FILE"
  (declare #.utils:*standard-optimize-settings*)

  (let ((info (make-instance 'audio-info)))
    (multiple-value-bind (mdhd mp4a esds) (get-audio-properties-atoms mp4-file)
      (with-slots (seconds channels bits-per-sample sample-rate max-bit-rate avg-bit-rate) info
        (when mdhd
          (setf seconds (/ (float (duration mdhd)) (float (scale mdhd)))))
        (when mp4a
          (setf channels        (num-chans mp4a)
                bits-per-sample (samp-size mp4a))
          (let* ((upper (ash (samp-rate mp4a) -16))
                 (lower (logand (samp-rate mp4a) #xffff)))
            (setf sample-rate (+ (float upper) (/ (float lower) 1000))))
        (when esds
          (setf avg-bit-rate (avg-bit-rate esds)
                max-bit-rate (max-bit-rate esds))))))
    info))

(defun map-mp4-atoms (m4a &key (func (constantly t)))
  "Visit each atom we found in M4A"
  (declare #.utils:*standard-optimize-settings*)

  (tree:traverse
   (m4a:mp4-atoms m4a)
   (lambda (node depth)
     (declare (ignore depth))
     (funcall func (tree:data node)))))