#lang racket/base

(require racket/file
         racket/list
         racket/path
         racket/string
         "util.rkt")

(provide convert-flac-to-opus)

(define conversion-note "Converted from FLAC to Opus by flac2opus-manager")

(define (temp-output-path output-path)
  (define-values (base name dir?) (split-path output-path))
  (define name-str (if (path? name) (path->string name) "output.opus"))
  (build-path base (format ".~a.tmp-~a.opus" name-str (current-inexact-milliseconds))))

(define (delete-file/quiet! p)
  (with-handlers ([exn:fail? (lambda (_) (void))])
    (when (file-exists? p) (delete-file p))))

(define (list-of-strings? v)
  (and (list? v) (andmap string? v)))

(define (property-key-symbol k)
  (cond [(symbol? k) k]
        [(string? k) (string->symbol (string-downcase k))]
        [else (string->symbol (string-downcase (format "~a" k)))]))

(define (first-comment-value v)
  (cond [(and (pair? v) (string? (car v))) (car v)]
        [(string? v) v]
        [else #f]))

(define (source-tags-data input-file)
  (define call-with-id3-tags (dynamic-require 'racket-audio/taglib 'call-with-id3-tags))
  (define tags-valid? (dynamic-require 'racket-audio/taglib 'tags-valid?))
  (define tags-keys (dynamic-require 'racket-audio/taglib 'tags-keys))
  (define tags-ref (dynamic-require 'racket-audio/taglib 'tags-ref))
  (define tags-picture (dynamic-require 'racket-audio/taglib 'tags-picture))
  (call-with-id3-tags
   input-file
   (lambda (tags)
     (if (not (tags-valid? tags))
         (list (cons 'properties '()) (cons 'picture #f))
         (let* ((keys (sort (tags-keys tags) string<? #:key (lambda (x) (format "~a" x))))
                (properties (for/list ([k (in-list keys)])
                              (cons (property-key-symbol k) (tags-ref tags k)))))
           (list (cons 'properties properties)
                 (cons 'picture (tags-picture tags))))))
   #:mode 'read))

(define (source-tags->settings input-file kbps)
  (define data (source-tags-data input-file))
  (define properties (alist-ref/default data 'properties '()))
  (define picture (alist-ref/default data 'picture #f))
  (define comments (make-hash))
  (for ([kv (in-list properties)])
    (define v (first-comment-value (cdr kv)))
    (when v (hash-set! comments (car kv) v)))
  (hash-set! comments 'flac2opus conversion-note)
  (define settings (make-hash))
  (hash-set! settings 'bitrate (* kbps 1000))
  (hash-set! settings 'vbr? #t)
  (hash-set! settings 'comments comments)
  ;; Do not put the id3-picture struct in settings.  It makes the encoder result
  ;; harder to store or serialize, and the picture is copied explicitly below.
  (values settings properties picture))

(define (copy-all-tag-properties! output-file properties picture)
  (define call-with-id3-tags (dynamic-require 'racket-audio/taglib 'call-with-id3-tags))
  (define tags-valid? (dynamic-require 'racket-audio/taglib 'tags-valid?))
  (define tags-set-values! (dynamic-require 'racket-audio/taglib 'tags-set-values!))
  (define tags-set! (dynamic-require 'racket-audio/taglib 'tags-set!))
  (define tags-picture! (dynamic-require 'racket-audio/taglib 'tags-picture!))
  (define tags-save! (dynamic-require 'racket-audio/taglib 'tags-save!))
  (call-with-id3-tags
   output-file
   (lambda (tags)
     (when (tags-valid? tags)
       (for ([kv (in-list properties)])
         (define v (cdr kv))
         (cond [(list-of-strings? v) (tags-set-values! tags (car kv) v)]
               [(string? v) (tags-set! tags (car kv) v)]
               [else (void)]))
       (tags-set! tags 'flac2opus conversion-note)
       (unless (eq? picture #f) (tags-picture! tags picture))
       (tags-save! tags)))
   #:mode 'read-write))

(define (call-audio-encode audio-encode in-file out-file settings progress-callback)
  (if progress-callback
      (audio-encode in-file out-file settings
                    #:encoder 'opus
                    #:copy-tags? #f
                    #:progress-callback progress-callback)
      (audio-encode in-file out-file settings
                    #:encoder 'opus
                    #:copy-tags? #f)))

(define (convert-flac-to-opus input-path output-path kbps #:progress-callback [progress-callback #f])
  (define tmp-path (temp-output-path output-path))
  (ensure-parent-directory! tmp-path)
  (with-handlers ([exn:break? (lambda (e) (delete-file/quiet! tmp-path) (raise e))]
                  [exn:fail? (lambda (e) (delete-file/quiet! tmp-path) (raise e))])
    (define-values (settings properties picture) (source-tags->settings input-path kbps))
    (define audio-encode (dynamic-require 'racket-audio/audio-encoder 'audio-encode))
    (define result (call-audio-encode audio-encode input-path tmp-path settings progress-callback))
    (copy-all-tag-properties! tmp-path properties picture)
    (ensure-parent-directory! output-path)
    (rename-file-or-directory tmp-path output-path #t)
    result))