#!/usr/bin/env bash
# Redirect Chain Checker (v1.0.0) - from srvScripts.com
# Source, docs and updates: https://srvscripts.com/scripts/redirect-tester/
# Copyright (c) 2026 srvScripts.com. MIT licence: if you copy, share or adapt this script, keep this notice and credit srvScripts.com.
# redirect-tester.sh — follow redirect chains hop by hop and flag loops, long chains, 302s, HTTPS downgrades and bad endings
# https://srvscripts.com/scripts/redirect-tester/   License: MIT
#
# Read-only: it only sends GET requests with curl, one hop at a time, and prints every hop.
#   bash redirect-tester.sh http://example.com/old-page https://example.com/blog
#   bash redirect-tester.sh --file urls.txt -q          # only URLs with problems
#   bash redirect-tester.sh --variants example.com      # http/https x www/non-www
set -uo pipefail
export LC_ALL=C

usage() {
  cat <<'EOF'
Usage: redirect-tester.sh [options] URL|DOMAIN ...

Options:
  --file FILE         read URLs from FILE (one per line, # comments allowed)
  --variants          for each domain, test http/https x www/non-www and check
                      that all four end on the same URL
  --max-hops=N        give up after N redirects (default 10)
  --timeout=SEC       per-request timeout (default 10)
  --user-agent=STR    User-Agent header to send
  -q, --quiet         print only URLs that have a problem
  --no-color          plain output even on a terminal
  -h, --help          show this help

A bare domain (example.com) is tested as http://example.com/.
Exit codes: 0 all OK, 1 at least one WARN/FAIL, 2 usage or dependency error
EOF
}

MAXHOPS=10; TIMEOUT=10; UA='srvscripts-redirect-tester/1.0'; VARIANTS=0; QUIET=0; COLOR=1
TARGETS=()
read_list() {
  [[ -r $1 ]] || { echo "Cannot read $1" >&2; exit 2; }
  local l
  while IFS= read -r l; do l=${l%%#*}; l=${l//[[:space:]]/}; [[ -n $l ]] && TARGETS+=("$l"); done < "$1"
}
while (( $# )); do
  case $1 in
    --file) read_list "${2:-}"; shift ;;
    --file=*) read_list "${1#*=}" ;;
    --variants) VARIANTS=1 ;;
    --max-hops=*) MAXHOPS=${1#*=} ;;
    --max-hops) MAXHOPS=${2:-}; shift ;;
    --timeout=*) TIMEOUT=${1#*=} ;;
    --timeout) TIMEOUT=${2:-}; shift ;;
    --user-agent=*) UA=${1#*=} ;;
    --user-agent) UA=${2:-}; shift ;;
    -q|--quiet) QUIET=1 ;;
    --no-color) COLOR=0 ;;
    -h|--help) usage; exit 0 ;;
    -*) echo "Unknown option: $1 (see --help)" >&2; exit 2 ;;
    *) TARGETS+=("$1") ;;
  esac
  shift
done
[[ $MAXHOPS =~ ^[0-9]+$ && $TIMEOUT =~ ^[0-9]+$ ]] || { echo "--max-hops and --timeout need a number" >&2; exit 2; }
(( ${#TARGETS[@]} )) || { usage >&2; exit 2; }
command -v curl >/dev/null 2>&1 || { echo "curl is required and was not found." >&2; exit 2; }

C_OK=''; C_WARN=''; C_FAIL=''; C_OFF=''
if [[ -t 1 && $COLOR -eq 1 ]]; then C_OK=$'\e[32m'; C_WARN=$'\e[33m'; C_FAIL=$'\e[31m'; C_OFF=$'\e[0m'; fi
ERRF=$(mktemp) || exit 2
trap 'rm -f "$ERRF"' EXIT

OUT=''                                    # output of the current check, printed at the end
add()  { OUT+="$*"$'\n'; }
flag() {                                  # flag OK|WARN|FAIL message
  local c=$C_OK; [[ $1 == WARN ]] && c=$C_WARN; [[ $1 == FAIL ]] && c=$C_FAIL
  add "$(printf '  %s%-4s%s  %s' "$c" "$1" "$C_OFF" "$2")"
  [[ $1 != OK ]] && ISSUES=$((ISSUES + 1))
}
normalize() { [[ $1 == *://* ]] && printf '%s' "$1" || printf 'http://%s/' "$1"; }

# Follow one URL. Sets FINAL_URL and FINAL_CODE; adds hop lines and verdicts to OUT.
follow() {
  local url=$1 hop=0 code next reason redirects=0 temp=0 downgrade=0
  local -A seen=()
  FINAL_URL=$url; FINAL_CODE=000; ISSUES=0
  add "== $url =="
  while :; do
    seen[$url]=1
    reason=$(curl -sS -o /dev/null --max-time "$TIMEOUT" -A "$UA" -w '%{http_code} %{redirect_url}' -- "$url" 2>"$ERRF")
    code=${reason%% *}; next=${reason#* }; [[ $next == "$reason" ]] && next=''
    hop=$((hop + 1)); FINAL_URL=$url; FINAL_CODE=$code
    if [[ $code == 000 ]]; then
      add "$(printf '  %2d  ERR  %s' "$hop" "$url")"
      flag FAIL "request failed: $(head -n1 "$ERRF" | sed 's/^curl: ([0-9]*) //')"
      break
    fi
    if [[ $code =~ ^3 && -n $next ]]; then
      add "$(printf '  %2d  %s  %s -> %s' "$hop" "$code" "$url" "$next")"
      redirects=$((redirects + 1))
      [[ $code == 302 || $code == 303 || $code == 307 ]] && temp=$((temp + 1))
      [[ $url == https://* && $next == http://* ]] && downgrade=1
      if [[ -n ${seen[$next]:-} ]]; then flag FAIL "redirect loop: $next was already visited"; FINAL_CODE=loop; break; fi
      if (( redirects >= MAXHOPS )); then flag FAIL "gave up after $MAXHOPS redirects (--max-hops)"; FINAL_CODE=toolong; break; fi
      url=$next
      continue
    fi
    add "$(printf '  %2d  %s  %s' "$hop" "$code" "$url")"
    [[ $code =~ ^3 ]] && flag FAIL "$code response without a Location header"
    break
  done

  (( downgrade )) && flag WARN "redirects from HTTPS down to plain HTTP"
  [[ $FINAL_CODE == 200 && $FINAL_URL == http://* ]] && flag WARN "ends on plain HTTP: $FINAL_URL"
  (( redirects > 2 )) && flag WARN "chain of $redirects redirects (more than 2 costs time and crawl budget)"
  (( temp > 0 )) && flag WARN "$temp temporary redirect(s) (302/303/307); a permanent move should be 301 or 308"
  if [[ $FINAL_CODE =~ ^[0-9]+$ && $FINAL_CODE != 200 && $FINAL_CODE != 000 && ! $FINAL_CODE =~ ^3 ]]; then flag FAIL "final status $FINAL_CODE (expected 200)"; fi
  (( ISSUES == 0 )) && flag OK "$redirects redirect(s), ends 200 on $FINAL_URL"
  return 0
}

# Print OUT unless quiet mode is on and the check had no issues.
emit() { if (( ! QUIET || ISSUES > 0 )); then printf '%s\n' "$OUT"; fi; OUT=''; }

TOTAL_ISSUES=0; CHECKED=0
for t in "${TARGETS[@]}"; do
  if (( VARIANTS )); then
    host=${t#*://}; path=/
    [[ $host == */* ]] && path="/${host#*/}"
    host=${host%%/*}; base=${host#www.}
    finals=(); vissues=0
    vlist=("http://$base$path" "http://www.$base$path" "https://$base$path" "https://www.$base$path")
    for v in "${vlist[@]}"; do
      follow "$v"; emit
      CHECKED=$((CHECKED + 1)); vissues=$((vissues + ISSUES)); finals+=("$FINAL_CODE $FINAL_URL")
    done
    ISSUES=0
    add "== Variants of $base$path =="
    for i in 0 1 2 3; do add "$(printf '  %-40s -> %s' "${vlist[i]}" "${finals[i]}")"; done
    distinct=$(printf '%s\n' "${finals[@]}" | sort -u | wc -l)
    if (( distinct > 1 )); then flag FAIL "the four variants end on $distinct different URLs; pick one canonical URL and 301 the rest to it"
    else flag OK "all four variants end on ${finals[0]#* }"; fi
    emit
    TOTAL_ISSUES=$((TOTAL_ISSUES + vissues + ISSUES))
  else
    follow "$(normalize "$t")"; emit
    CHECKED=$((CHECKED + 1)); TOTAL_ISSUES=$((TOTAL_ISSUES + ISSUES))
  fi
done

echo "Checked $CHECKED URL(s); $TOTAL_ISSUES problem(s)."
(( TOTAL_ISSUES > 0 )) && exit 1
exit 0