mlc

#!/usr/bin/env zsh

# mlc - Media Length Cache
# store length with timestamps in a cache
#
# functions that end in _ are dangerous and
# intended for internal use only
#
# normally, the only thing you need to do is 
# import,
#  . mlc
# then run,
#  mlcLookup $path
# which yields the duration in seconds of a
# media file.
# 
# media files can be in any format supported
# by mplayer; any file that mplayer cannot 
# determine the length of will appear as zero

MLC_POLL_DUR="0.1"
[ -e ~/.mlc ] || touch ~/.mlc

function mlcGetLength() {
	(mplayer -vo null -ao null -identify -frames 0 "$@" | (grep '^ID_LENGTH=[0-9\.]*$' || echo 0) | sed 's/^ID_LENGTH*=//' )2>/dev/null
}

function mlcPath2Key_() {
	path="$@"
	echo $path | md5sum | cut -d ' ' -f 1
}

function mlcLockEngage_() {
	while [ -e ~/.mlc.lock ] ; do
		sleep $MLC_POLL_DUR
	done
	touch ~/.mlc.lock
}

function mlcLockDisengage_() {
	rm ~/.mlc.lock
}

function mlcReplaceDB_() {
	cat > ~/.mlc.bak
	mv ~/.mlc{.bak,}
}

function mlcEvict_() {
	mlcLockEngage_
	grep -v "^$2 " ~/.mlc | mlcReplaceDB_
	mlcLockDisengage_
}

function mlcEvict() {
	path=$(realpath "$@")
	mlcEvict_ "$path" `mlcPath2Pat "$path"`	
}

function mlcLookupCache_() {
	grep "^$1 " ~/.mlc
}

function mlcEnter_() {
	path="$1"
	pat="$2"
	mlcLockEngage_
	date=`stat -c '%Y' "$path"`
	length=`mlcGetLength "$path"`
	(
		echo "$pat $date $length"
		cat ~/.mlc
	) | mlcReplaceDB_
	mlcLockDisengage_ 
}

function mlcLookup_() {
	path="$1"
	pat="$2"
	cached="$(mlcLookupCache_ $pat)"
	[ -z "$cached" ] || {
		date=$(echo "$cached" | cut -d\  -f 2)
		date2=`stat -c '%Y' "$path"`
		([ -z "$date" ] || [ $date -lt $date2 ] ) && {
			mlcEvict_ "$path" "$pat"
			cached="$(mlcLookupCache_ $pat)"
		}
	}
	[ -z "$cached" ] && {
		mlcEnter_ "$path" "$pat"
		cached="$(mlcLookupCache_ $pat)"
	}
	echo "$cached" | cut -d\  -f 3
}

function mlcLookup() {
	[ -e ~/.mlc ] || touch ~/.mlc
	path="$@"
	[ -e "$path" ] && {
		path=`realpath "$path"`
		mlcLookup_ "$path" "$(mlcPath2Key_ $path)"
	} || echo 0
}