id3.lisp

(defpackage :id3v1
  (:use :cl :alexandria :flexi-streams
        )
  (:export #:scan-id3
           #:take-bytes))
(defpackage :id3v2
  (:use :cl :alexandria :flexi-streams
        ))

(in-package :id3v1)


(defun as-string (barray)
  (map 'string (lambda (x) (code-char x))
       barray))

(defun id3p (barray)
  (string= "ID3"
           (as-string (take-bytes barray 0 3))))

(defun strip (barray)
  (remove-if (lambda (x)
               (= x 0)) barray))

(defun take-bytes (seq start &optional (end (length seq)) from-end)
  (if from-end
      (reverse (subseq (reverse seq) start (if (not end) (1- (length seq)) end)))
      (subseq seq start end)))

;;Partially generated by:
;; (mapcar (lambda (x)
;;                  `(,(intern (string-upcase (symbol-name x)) 'keyword)
;;                     (,x barray))) '(title artist album year comment track genre start-time end-time))
(defun scan-id3 (barray &optional (strict nil))
  "BARRAY is a full byte array of a music file. STRICT simply tells the function whether or not it should assert that it is indeed id3 complaint with ID3P"
  (let* ((tag-array (take-bytes barray 0 128 t)))
    (if strict (assert (id3p tag-array)))
    `((:TITLE ,(TITLE TAG-ARRAY)) (:ARTIST ,(ARTIST TAG-ARRAY)) (:ALBUM ,(ALBUM TAG-ARRAY))
     (:YEAR ,(YEAR TAG-ARRAY)) (:COMMENT ,(COMMENT TAG-ARRAY))
     (:GENRE ,(GENRE TAG-ARRAY)))))


(defun title (barray)
  (as-string (strip (take-bytes barray 3 30))))
(defun artist (barray)
  (as-string (strip (take-bytes barray 33 63))))
(defun album (barray)
  (as-string (strip (take-bytes barray 63 93))))
(defun year (barray)
  (as-string (strip (take-bytes barray 93 97))))
(defun comment (barray)
  (as-string (strip (take-bytes barray 97 127))))
(defun genre (barray)
  (aref (take-bytes barray 127 128) 0))

(defun track (barray)
  (declare (ignore barray)))
(defun start-time (barray) (declare (ignore barray)))
(defun end-time (barray) (declare (ignore barray)))


(in-package :id3v2)