#!/bin/bash


usage() {
cat << 'EOF'
    gdh - git diff helper

    Usage:

    gdh
        show diff HEAD^1 HEAD

    gdh <number>
        show diff HEAD^<number> HEAD

    gdh <number1> <number2>
        show diff HEAD^<number1> HEAD^<number2>

    gdh -h/--help
        show usage
EOF
}


main() {
    if [[ "$1" == "-h" || "$1" == "--help" ]]; then
        usage
    else
        if [[ -z "$1" ]]; then
            git diff HEAD^1 HEAD
        elif [[ -z "$2" ]]; then
            git diff "HEAD^$1" HEAD
        else
            git diff "HEAD^$1" "HEAD^$2"
        fi
    fi
}

main "$@"
