#!/bin/sh
URL="$1"
SELECTORS="$2"

if ! command -v pup >/dev/null 2>&1; then
	printf "Can not find dependency: pup\n"
	exit 1
fi

if ! command -v curl >/dev/null 2>&1; then
	printf "Can not find dependency: curl\n"
	exit 1
fi

if test -z "$URL" || test -z "$SELECTORS"; then
	printf "$0 <URL> <SELECTORS>\n"
	exit 1
fi

VERSION1="$(mktemp)"
VERSION2="$(mktemp)"

curl -s "$URL" | pup "$SELECTORS" > "$VERSION1"

while true; do
	sleep "${SLEEP:-60}"

	curl -s "$URL" | pup "$SELECTORS" > "$VERSION2"

	DIFF="$(diff "$VERSION1" "$VERSION2")"

	if test $? -ne 0; then
		printf "Change detected $(date)\n"
		printf "$DIFF\n\n"
	fi

	cat "$VERSION2" > "$VERSION1"
done