#!/usr/bin/env bash

set -euo pipefail

warn=''
crit=''
url=''
query='.'
title=''
netrc=''
name='value'
unit=''

usage() {
  cat <<USAGE

$0: reduce JSON response to an integer, check against thresholds.

This script uses:
  jq   - https://stedolan.github.io/jq/
  cURL - https://curl.haxx.se/

Usage:
  $0 [options]

Options:

  -q <expression>    jq query, must return an integer (default: $query)
  -u <url>           URL to fetch

  -t <title>         short description of the parameter
  -p <name>          name of the parameter (default: $name)
  -m <unit>          unit of measure (default: $unit)

  -n <file>          netrc file with credentials

  -w <spec>          warning threshold
  -c <spec>          critical threshold

Examples:

  $0 -u example.com/errors_list -w 1 -c 4 -q '. | length'
  $0 -u example.net/counter -w 1:4 -m c

USAGE
}

die () {
  echo "$0: " "$@" >&2
  exit 1
}

while [ $# -gt 0 ]; do
  case "$1" in
    -q) query="$2"; shift 2;;
    -u) url="$2"; shift 2;;
    -t) title="$2"; shift 2;;
    -p) name="$2"; shift 2;;
    -m) unit="$2"; shift 2;;
    -n) netrc="$2"; shift 2;;
    -w) warn="$2"; shift 2;;
    -c) crit="$2"; shift 2;;
    -h|--help) usage; exit 1;;
    *) die "unsupported argument: $1";;
  esac
done

inrange () {
  local r v
  local v1 v2
  local outter
  local sIFS

  r="$1"
  v="$2"

  case "$r" in
    @*) outter=true; r="${r/@/}";;
    *) outter=false;;
  esac

  sIFS=$IFS

  IFS=:
  set -- $r
  v1=${1-}
  v2=${2-}
  IFS=$sIFS

  case "$v1" in
    $r) v2=$v1; v1=0;;
    ~*)  v1=;;
  esac

  if $outter; then
    { [ -n "$v1" ] && [ "$v" -le "$v1" ]; } || { [ -n "$v2" ] && [ "$v" -ge "$v2" ]; }
  else
    { [ -z "$v1" ] || [ "$v" -ge "$v1" ]; } && { [ -z "$v2" ] || [ "$v" -le "$v2" ]; }
  fi
}

[ -n "$url" ] || die "missing url"

cmd=(curl --fail --silent --show-error --location)
if [ -n "$netrc" ]; then
  cmd+=(--netrc-file "$netrc")
fi
cmd+=("$url")

if ! out=$("${cmd[@]}" 2>&1); then
  printf 'UNKNOWN: %s\n' "$(echo "$out" | grep . | head -n 1)"
  exit 3
fi

json=$out

if ! value=$(echo "$json" | jq -c -r "$query" 2>&1); then
  printf 'UNKNOWN: %s\n' "$(echo "$value" | grep . | head -n 1)"
  exit 3
fi

if [[ ! "$value" =~ ^[-+]?[0-9]+$ ]]; then
  echo "UNKNOWN: not an integer: $value"
  exit 3
fi

stat="$name=$value$unit;$warn;$crit"

[ -n "$title" ] || title="some $name"
text="$value - $title|$stat"

if [ -n "$crit" ] && ! inrange "$crit" "$value"; then
  echo "CRITICAL: $text"
  exit 2
fi

if [ -n "$warn" ] && ! inrange "$warn" "$value"; then
  echo "WARNING: $text"
  exit 1
fi

echo "OK: $text"
exit 0