#!/usr/bin/env bash

set -ueo pipefail

# Related: https://joeyh.name/code/moreutils/ sponge

usage()
{
    echo 'Usage: refresh [-a] [-v] DEST'
    echo '       refresh [-a] [-v] -- DEST'
}

append=''
verbose=''

while test $# -gt 0; do
    case $1 in
        -a) append=true; shift;;
        -v) verbose=true; shift;;
        --)
            if test "$#" -ne 2; then
                usage 1>&2
                exit 2
            fi
            dest="$2"
            shift 2
            ;;
        -*)
            usage 1>&2
            exit 2
            ;;
        *)
            if test "$#" -ne 1; then
                usage 1>&2
                exit 2
            fi
            dest="$1"
            shift
            ;;
    esac
done

tmpfile="$(mktemp "$dest.sponge-XXXXXXX")"

clean-up()
{
    rm -f "$tmpfile"
}

trap clean-up EXIT

# Inefficient, but should clone the permissions
if test -e "$dest"; then
   cp -Lp "$dest" "$tmpfile"
fi

if test "$append"; then
    cat >> "$tmpfile"
else
    cat > "$tmpfile"
fi

if ! cmp -s "$tmpfile" "$dest"; then
    if test "$verbose"; then
        echo "Refreshed $dest" 1>&2
    fi
    mv "$tmpfile" "$dest"
fi