#!/bin/sh
# can improve by passing $@ to functions, but seems need bashism, or abandon functions
# maybe seperate find extension part and output names as another script with options of recursive or not
# 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
# not sure if find here need -depth, not sure if mv here need -n and -T

outdir ()
{ 
	find . -type f -exec mv -nt "$PWD" -- '{}' \+ 
	find . -mindepth 1 -maxdepth 1 -type d -delete
}

# 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
# maybe better if make all uppercase to lowercase, is it possible to use awk for that?
indir ()
{
	find . -maxdepth 1 -type f | awk -F. '!a[$NF]++{print $NF}' | xargs mkdir --
	find . -mindepth 1 -maxdepth 1 -type d -exec basename -az -- '{}' \+ | xargs -0 -I _ find . -maxdepth 1 -type f -name '*._' -exec mv -t '_' -- '{}' \+
}

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