#!/usr/bin/env bash
# cachecheck.sh <url> — did the purge actually evict anything?
#
# THE TRAP THIS EXISTS FOR: a PURGE request that returns 200 has proved that
# SOMETHING answered, not that a cache dropped anything. On a Cloudways app,
# a PURGE aimed at the public URL sails past the cache tier and WordPress
# answers it with a normal page — 200, every time, evicting nothing. Four
# "successful" purges in a row cleared exactly zero objects.
#
# The only honest test is a differential one: ask for the bare URL, then ask
# for the same page with a cache-busting query string. The bare URL is what a
# visitor and a crawler receive. The busted URL is what the origin generates
# right now. IF THEY DISAGREE, A CACHE IS SERVING A DOCUMENT YOUR SERVER NO
# LONGER PRODUCES — and no status code anywhere will tell you that.
set -u
URL="${1:?usage: cachecheck.sh <url>}"
UA='Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 Chrome/126 Safari/537.36'
T=$(mktemp -d); trap 'rm -rf "$T"' EXIT
sep="${URL#*\?}"; q="?"; [ "$sep" != "$URL" ] && q="&"

curl -s -A "$UA" -D "$T/h1" -o "$T/bare" "$URL"
curl -s -A "$UA" -D "$T/h2" -o "$T/bust" "${URL}${q}cachecheck=$(date +%s)"
b=$(wc -c < "$T/bare" | tr -d ' '); f=$(wc -c < "$T/bust" | tr -d ' ')
age=$(grep -i '^age:' "$T/h1" | tr -d '\r' | awk '{print $2}')
xc=$(grep -i '^x-cache:' "$T/h1" | tr -d '\r' | awk '{print $2}')
prov=$(grep -i '^cache-provider:' "$T/h1" | tr -d '\r' | cut -d' ' -f2-)

echo "  $URL"
echo "  bare: ${b}B   origin-now: ${f}B   age=${age:-none}  x-cache=${xc:-none}  ${prov:+provider=$prov}"

# ⚠️ THE TOOL'S OWN FIRST RUN PRODUCED A FALSE POSITIVE: the cache-busted
# request was challenged and came back 163 bytes, so the script reported the
# cached copy as 36,504% stale. A comparison is only valid when BOTH sides are
# real pages — guarding one side and trusting the other is the same mistake as
# trusting a 200.
for side in bare bust; do
  n=$(wc -c < "$T/$side" | tr -d ' ')
  if [ "$n" -lt 2000 ] || { [ "$n" -lt 20000 ] && grep -qiE 'one moment, please|being verified|checking your browser' "$T/$side"; }; then
    echo "  X the $side reading is ${n}B — a challenge or an error page, not the site."
    echo "    Cannot compare. This vantage point is being refused; measure elsewhere."
    exit 3
  fi
done

# A few bytes of nonce differ between any two renders; a stale cache differs by
# whole blocks. 2% is the line between noise and a different document.
diff=$(( b > f ? b - f : f - b ))
pct=$(( f > 0 ? diff * 100 / f : 0 ))
if [ "$pct" -le 2 ]; then
  echo "  OK cache is serving what the origin generates (${pct}% apart)"
  [ -n "${age:-}" ] && [ "${age:-0}" -gt 3600 ] 2>/dev/null && \
    echo "  ! but age=${age}s — every change you make stays invisible that long"
  exit 0
fi
echo "  X STALE: ${pct}% apart. A cache is serving a document the origin no longer produces."
echo "    A purge that returned 200 did not evict this. Flush the OBJECT cache and the"
echo "    hosting cache from wp-admin, not by sending PURGE to the public URL."
exit 1