#!/bin/bash
# Usage: ./buildm3u
# buildm3u will build an m3u playlist for an entire directory tree.
# It will place an m3u file in each subdirectory containing music files.
# The paths to the music files are full paths.
#
# Thanks to Mendel Cooper for writing the "Advanced Bash-Scripting Guide"
# Thanks to IntnsRed (creator of DebianHelp.org) for calling for this functionality.

IFS=$'\n' # Input Field Separator
# Normally this internal bash variable includes
# any type of whitespace, but we want to avoid
# splitting up file names with spaces.
# \n means "new line".

#M3Ulist="`pwd`/M3UfileList.txt" # Look here to see where your
# M3U files were created.
# The backticks tell bash to execute
# the pwd command and insert its output.
# Since pwd returns the current working
# directory, the file M3UfileList.txt
# will be created in the directory from
# which buildm3u is launched (not necessarily
# the directory where buildm3u resides).
#rm -f $M3Ulist # Remove this file first.

# indexCurrDir is a function.
# I only call this function once,
# but I didn't know that would be the
# case when I started writing this script.
# Still it never hurts to group some core
# functionality into a function.
#
# indexCurrDir finds all music files in the current
# working directory (including those in subdirectories).
# The full paths to the files are written to an m3u file
# named after the current working directory.
indexCurrDir ()
{
FileList="" # initialize empty variable FileList
for FileTypes in "ogg" "mp3" "flac" "wav" # loop over file types.
# the user can add file types here.
# FileTypes is a variable that cycles
# through ogg, mp3, flac, and wav
# inside the for loop.
do # the next line of a for loop is do (bash syntax for a for loop)
FindFiles=$(find $(pwd) -type f -iname "*.$FileTypes" -printf '%f\n'| sort)
# $(command) is equivalent to `command` (another way to do command substitution)
# This is mainly useful because you can have nested command substitutions using $(),
# which does not work with backquotes.
# The above command finds files with an extension corresponding to
# the the value of $FileType (FileType="ogg" the first time through, then "mp3",
# then "flac", then "wav"). In bash, $ preceding a variable gets the value
# of the variable. The results of the find command is piped to sort so that
# your songs play in a sorted order (which is hopefully the intended order).
# "i" in -iname specifies that the file types are case insensitive.
FileList=$FileList$FindFiles
# Each time through the for loop, the files found are appended to the list of files.
# After exiting the loop, you have a single list of files for all extensions.
# The find command above puts a \n (new line) after each file, so you are
# building up a list of files with one file per line.
done # end the loop with done (bash syntax for a for loop)

if [ "${#FileList}" != "0" ] # do not write m3u file if file list is empty
# The ${} is the most fool proof way of accessing
# the value of a variable. The # before #FileList
# means "get the length of the variable FileList".
# Note that this means the total number of characters
# summed over all file paths.
# FileList is one big long variable, not an array.
# Before I read about the IFS=$'\n' trick,
# I was thinking of dumping the file names to a file, and
# then reading them back into an array.
then
CurrDir=$(pwd) # get the current directory
echo "$CurrDir" # Show the user where the script is finding music files.
m3uName=$(basename $CurrDir) # basename is a command that strips off the parent
# directories of a path.

echo "Writing m3u playlist." # Tell the user that an m3u playlist is being created
echo "$FileList" > "${m3uName}.m3u" # write the list of music files to the m3u file
#echo "$CurrDir/${m3uName}.m3u" >> "$M3Ulist" # Add the m3u file to the list of m3u files.
# -- disabled. I didn't want this feature
# I have music scattered about,
# and need to be reminded where the music is!
fi
}

# This is the body of the script (like Main in a C program)
AllDirs=$(find $(pwd) -type d | sort) # Get a complete list of full paths to subdirectories,
# including the top level directory. This list
# includes directories without music. They are skipped
# inside the indexCurrDir function if no music is found.
for Directory in $AllDirs # loop over the top level directory and all subdirectories
# This didn't have to be recursive because the find command does the work.
do
cd "$Directory" # cd to each directory in turn
indexCurrDir # Here, the function indexCurrDir is called
# inside each directory. If there is music inside $Directory
# (or in the subdirectories of $Directory),
# then an m3u file for that directory will be created in $Directory.
done

exit 0 # an exit value of zero in bash means a successful exit