#!/bin/bash

# Configuration.
STORAGE_PREFIX="/storage/md0"
LOCATE_DB="/tmp/mirrors.db"
DEF_RESULTS=500
MAX_RESULTS=3000
MAX_CONCURRENT=10
IGNORE_REGEXES=('^/\.sandbox.*' '^/\.lftp.*' '^/dead\.letter' '.*\.rsync-tmp.*')

# Extglob is required.
shopt -s extglob

# Output an error in processing.
die() {
  # $1 = The error code to output.
  #		0 = Success.
  #		1 = Temporary error (eg, max concurrent).
  #		2 = Perminant error.
  # $2 = The error message to output (if any).
  printf "%s: %s\\n" "Status" "${1:-2}"
  [[ -n "$2" ]] && printf "%s: %s\\n" "Error" "$2"
  exit 1
}

# Initial headers.
printf "%s: %s\\n" "Content-type" "text/plain"
printf "%s: %s\\n" "Cache-Control" "no-cache, no-store, must-revalidate"
printf "%s: %s\\n" "Pragma" "no-cache"
printf "%s: %s\\n\\n" "Expires" "1"

# Limit the number of concurrent searches to avoid DoS.
if (( $(lsof -t "$LOCATE_DB" | wc -l) > (MAX_CONCURRENT - 1) )); then
  die "1" "Too many concurrent searches"
else
  # Lock the DB for the lsof count above.
  # shellcheck disable=SC2015
  exec 9<"$LOCATE_DB" && flock -s -E 10 -w 2 9 || die "1" "Too many concurrent searches"

  # shellcheck disable=SC2154
  while read -r -d '&' QUERY; do
    # If the read returned an empty string, skip.
    [[ -z "$QUERY" ]] && continue

    # Extract the key and value to temporary variables.
    KEY="${QUERY%%=*}"
    VALUE="${QUERY#*=}"

    # Check the key is valid as a variable name.
    [[ ! "$KEY" =~ ^[[:digit:]_]*[[:alnum:]_]*$ ]] && die "2" "Invalid query - don't try to be clever :)"

    # Remove spaces from beginning and end of value.
    : "${VALUE/#+(+)}"
    : "${_/%+(+)}"

    # Squash multiple spaces in value.
    : "${_//+(+)/+}"

    # Convert values from %-encoded form.
    : "${_//%/\\x}"

    # Define the variable from the key name.
    declare "QS_$KEY"="$(printf "%b" "${_//+/ }")"
  done <<<"${QUERY_STRING,,}&"	# The & at the end is required.

  # Adjust 'QS_q' for the locate command by wrapping search elements in *.
  : "*${QS_q// /* *}*"
  QS_q="${_//\/*/*}"

  # Adjust 'QS_l' to not go over maximum limit of results or use default if not supplied.
  [[ -z "$QS_l" ]] && QS_l="$DEF_RESULTS"
  (( QS_l > MAX_RESULTS )) && QS_l="$MAX_RESULTS"

  # Give success status as checks have passed.
  printf "%s: %s\\n" "Status" "0"

  I=1
  # shellcheck disable=SC2154
  while read -r ITEM; do
    # Only show specified number of items.
    (( I == (QS_l + 1) )) && break

    # Remove paths we don't want the user to see.
    while read -r -d " " REGEX; do
      [[ "${ITEM/$STORAGE_PREFIX}" =~  $REGEX ]] && continue 2
    done <<<"${IGNORE_REGEXES[@]}"

    # List the item.
    printf "%s\\n" "${ITEM/$STORAGE_PREFIX}"

    (( I++ ))
  done < <(locate -A -d "$LOCATE_DB" -i -l "$(( QS_l * 2 ))" "$STORAGE_PREFIX/${QS_p##/}" "$QS_q" | sort)
fi