#!/bin/sh
# can improve by passing $@ to functions, but seems need bashism, or abandon functions
# maybe use $1 for getext and use getopts, maybe seperate getext as another script, maybe add option for using ln instead of mv
# references: 
# https://stackoverflow.com/questions/1842254/how-can-i-find-all-of-the-distinct-file-extensions-in-a-folder-hierarchy

outdir ()
{ 
	find . -type f -execdir mv -t "$PWD" '{}' \+ 
	find . -mindepth 1 -maxdepth 1 -type d -execdir rm -r '{}' \+ 
}

# may further optimize by output file extension names to a variable and use it for both mkdir and mv, current is fast enough for me
indir ()
{
	find . -maxdepth 1 -type f | awk -F. '!a[$NF]++{print $NF}' | xargs mkdir
	# don't know why -print0/-0 for find and xargs doesn't work here
	find . -mindepth 1 -maxdepth 1 -type d -execdir basename '{}' \; | xargs -I _ find . -maxdepth 1 -type f -name '*._' -execdir mv -t '_' '{}' \+
}

case "$1" in
	'-o') outdir;;
	'-i') indir;;
	*) outdir; indir;;
esac