#! /usr/bin/perl
#
#        name: m4a2mp3.pl
# description: Convert m4a file to mp3 format. Attempts to convert tags.
#   developer: Nathan G. Marley <nathan.marley@gmail.com>
#        date: 2011Sep10
#
# change history:
# ========================================================================
# description: change description placeholder
#   developer: developer name goes here
#        date: YYYYMmmDD
# ========================================================================

use strict;
use Data::Dumper;
use File::Basename;
use Carp;

use MP4::Info;
use MP3::Tag;
use Getopt::Long;

sub get_m4a_tags;
sub convert_m4a_2_mp3;
sub tag_mp3_file;
sub app_abort;


# boilerplate
my $progname = basename($0);
my $usage    = "usage: $progname <arg1> <arg2> ...";

if ( 0 == scalar(@ARGV) ) {
    print "$usage\n";
    exit 2;
}


my @m4atags = qw ( YEAR ARTIST GENRE TRACKNUM TIME
                   TITLE ALBUM ENCODING BITRATE );

sub main() {

    my @files; 
    for my $arg ( @ARGV ) {
        push @files, $arg;
    }

    for my $file ( @files ) {
        my $m4atags = &get_m4a_tags( $file );
        my $mp3file = &convert_m4a_2_mp3( $file );
        my $rc = &tag_mp3_file( $mp3file , $m4atags );
    }

}

&main();


sub get_m4a_tags($) {
    my $filename = shift;
    my $taginfo;

    my $tag = get_mp4tag($filename)
        or die "No TAG info";

    for my $t ( @m4atags ) {
        $taginfo->{ $t } = $tag->{$t};
    }

    return $taginfo;
}


sub convert_m4a_2_mp3($) {
    my $m4afile = shift;
    my $mp3file;

    ($mp3file = $m4afile) =~ s/\.m4a$/.mp3/;

    if ( -e $mp3file ) {
        &app_abort("error: MP3 file '$mp3file' already exists.");
    }

    my $faad_opts = "-q -o -";
    my $lame_opts = "-S -v -V 0";
    my $cmd = "faad $faad_opts \"$m4afile\" | lame $lame_opts - \"$mp3file\"";

    my $rc = system($cmd) >> 8;
    if ( 0 != $rc ) {
        die "error: Couldn't convert m4a file to mp3 format";
    }

    return $mp3file;
}



sub tag_mp3_file($$) {
    my ( $mp3file , $tags ) = (@_)[0,1];

    my $mp3 = MP3::Tag->new($mp3file);

    # scan file for existing tags
    $mp3->get_tags;

    if (exists $mp3->{ID3v1}) {
        $mp3->{ID3v1}->remove_tag;
        $mp3->new_tag("ID3v1");
    }

    if (exists $mp3->{ID3v2}) {
        $mp3->{ID3v2}->remove_tag;
        $mp3->new_tag("ID3v2");
    }

    $mp3->title_set( $tags->{TITLE} );
    $mp3->artist_set( $tags->{ARTIST} );
    $mp3->album_set( $tags->{ALBUM} );
    $mp3->year_set( $tags->{YEAR} );
    $mp3->genre_set( $tags->{GENRE} );
    $mp3->track_set( $tags->{TRACKNUM} );

    $mp3->update_tags();                  # Commit to file
    $mp3->close();

    return;
}

sub app_abort($) {
    my $msg = shift;
    print "$msg Aborting...\n";
    exit 2;
}

__END__