#!/bin/sh

function print_example() {
    echo "Example"
    echo "  git-diff develop master"
}

function print_usage() {
    echo "Usage"
    echo "  git-diff <branch|tag|commit> <branch|tag|commit>"
}

if [ "$1" = "--help" ] || [ "$1" = "-h" ] ; then
    print_usage
    exit 0
fi

FROM="$1"
TO="$2"
if [ -z "$FROM" ] || [ -z "$TO" ]; then
    echo "Error: missing arguments"
    echo ""
    print_usage
    echo ""
    print_example
    exit 1
fi

if ! [ -d .git ]; then # .git folder exists?
    echo "Error: current directory is not a git root directory"
    exit 1
fi

DIR=${TMPDIR%/}/gitdiff # `%/` removes trailing slash
rm -rf "$DIR"
for i in $(git diff --name-only $FROM $TO) ; do
    # Setup folder structure
    mkdir -p $DIR/"$FROM"/"$(dirname $i)";
    mkdir -p $DIR/"$TO"/"$(dirname $i)";

    # Get revision of files
    git show "$FROM":"$i" > "$DIR"/"$FROM"/$i;
    git show "$TO":"$i" > "$DIR"/"$TO"/$i;
done

# Use git's difftool or opendiff as alternative
DIFFTOOL=$(expr "$(git config --get diff.tool)" '|' "opendiff")

$($DIFFTOOL "$DIR"/"$FROM" "$DIR"/"$TO")