#!/bin/sh

if [ "$#" -ne 3 ]; then
    echo "Usage:"
    echo "  sha256-file-to SHA256 http://FETCH/FROM DST"
    echo
    echo "SHA256 is the sha256sum of the file fetched; the file is"
    echo "placed in DST."
    exit 1
fi

set -e
set -x

SHA256="$1"
URL="$2"
DST="$3"

# Work in a tmpdir which we clean up at the end
tmpdir="$(mktemp -d)"
trap 'rm -r "$tmpdir"' EXIT
cd "$tmpdir"

# Fetch to a predictable name, not whatever curl guesses from the URL
LOCALFILE="output"
curl -fL --retry 3 -o "$LOCALFILE" "$URL"

# Check the hash against what was passed in
echo "$SHA256  $LOCALFILE" >"$LOCALFILE.sha256"
sha256sum -c "$LOCALFILE.sha256"

mv "$LOCALFILE" "$DST"