#!/bin/sh
# dirsum PATHS... - compute order-invariant hash for given files/directory

# Only takes file names and contents into account.

export LC_ALL=C

if command -v sha256sum >/dev/null; then
	SUM="sha256sum --tag"
elif command -v sha256 >/dev/null; then
	SUM="sha256"
else
        echo "no hash tool found" 1>&2
        exit 2
fi

if xargs -P0 </dev/null 2>/dev/null 1>&2; then
	XARGS=-P0
fi

for arg; do
	(
	set -e
	if [ -d "$arg" ]; then
		cd "$arg"
		arg=./
	else
		dir=$(dirname "$arg")
		arg=./$(basename "$arg")
		cd "$dir"
	fi
	find $arg -type f -print0 |
		xargs -0 -n1 $XARGS $SUM --
	)
done | sort | $SUM /dev/stdin | cut -d' ' -f4