#!/bin/sh
#
# Analyse an audio file and add BPM metadata
#

set -e

usage()
{
	cat <<END
bpm-tag 0.0-beta (C) Copyright 2011 Mark Hills <mark@pogo.org.uk>

Usage: bpm-tag [options] <file>
Tag an audio file with tempo (in beats-per-minute, BPM)

  -f   Ignore existing BPM value
  -n   Display BPM only, don't tag
  -h   Display this help message and exit

END
}

# Parse command line arguments

FORCE=false
WRITE=true

while getopts "fhn" OPT; do
	case "$OPT" in
	f)
		FORCE=true
		;;
	n)
		WRITE=false
		;;
	h)
		usage
		exit 0
		;;
	?)
		exit 1
	esac
done
shift $((OPTIND - 1))

if [ -n "$1" ]; then
	usage >&2
	exit 1
fi

set -u

FILE="$1"
shift

# Don't overwrite an existing BPM tag

case "$FILE" in
*.flac)
	BPM=`metaflac --show-tag=BPM "$FILE" | sed -e 's/BPM=//'`
	;;
*.mp3)
	BPM=`id3v2 -R "$FILE" | sed -n 's/^TBPM.*: \([0-9\.]\+\)/\1/p'`
	;;
*.ogg)
	BPM=`vorbiscomment "$FILE" | sed -n 's/^BPM=//p'`
	;;
*)
	echo "$FILE: file extension not known" >&2
	exit 1
	;;
esac

if [ -n "$BPM" ] && ! $FORCE; then
	echo "$FILE: already tagged, $BPM BPM" >&2
	exit 1
fi

# Analyse the BPM

BPM=`sox -V1 "$FILE" -r 44100 -e float -c 1 -t raw - | bpm`
if [ -z "$BPM" ]; then
	exit 1
fi

if ! $WRITE; then
	echo "$FILE: $BPM BPM" >&2
	exit 0
fi

# Write a BPM tag

case "$FILE" in
*.flac)
	metaflac --remove-tag=BPM --set-tag="BPM=$BPM" "$FILE"
	;;
*.mp3)
	id3v2 --TBPM "$BPM" "$FILE"
	;;
*.ogg)
	vorbiscomment -at "BPM=$BPM" "$FILE"
	;;
*)
	echo "$FILE: don't know how to tag this type of file" >&2
	exit 1
esac

echo "$FILE: $BPM BPM" >&2