#!/usr/bin/lua5.1

local sys_stat = require "posix.sys.stat"
local state_filename = '/run/prometheus-node-exporter_sensors/state'

local sensors = require "sensors"
local units = {
    temperature = "celsius",
    humidity = "percent",
    pressure = "pascals",
    gpio = "status",
}

local _typestring_printed = {}

local function metric(name, mtype, labels, value)
  if nil == _typestring_printed[name] then
    print("# TYPE " .. name .. " " .. mtype)
    _typestring_printed[name] = 1
  end

  local label_string = ""
  if labels then
    for label,value in pairs(labels) do
      label_string =  label_string .. label .. '="' .. value .. '",'
    end
    label_string = "{" .. string.sub(label_string, 1, -2) .. "}"
  end
  print(string.format("%s%s %s", name, label_string, value))
end

local function scrape(config, num_sensors)
    local readings, err = sensors.read(config)
    if not readings then return end

    metric("sensors_count_total", "gauge", nil, num_sensors)
    for name, values in pairs(readings) do
        labels = { name = name, kind = values._kind_ }
        for t, v in pairs(values) do
            local unit = units[t]
            if unit ~= nil then
                metric("sensors_" .. t .. "_" .. unit, "gauge", labels, v)
            end
        end
    end
end

local function _setup(config)
    local num_sensors, err = sensors.setup(config)
    if num_sensors == nil then error(err) end
    io.stderr:write(string.format("setup: %d sensors found.\n", num_sensors))

    local f, err = io.open(state_filename, "w")
    if not f then error(err) end
    local ret, err = f:write(string.format("%d\n", num_sensors))
    f:close()
    if not ret then error(err) end

    return num_sensors
end

local function setup(config)
    local s, _ = sys_stat.stat(state_filename)
    if s == nil then
        return _setup(config)
    end

    local f, err = io.open(state_filename, "r")
    if not f then error(err) end
    local data, err = f:read("*l")
    f:close()
    if not data then
        return _setup(config)
    end

    local num_sensors, err = tonumber(data)
    if num_sensors == nil then
        return _setup(config)
    end
    return num_sensors
end

function main()
    local config, err = sensors.read_config('/etc/prometheus/exporter/node/sensors.json')
    if config == nil then error(err) end

    local num_sensors = setup(config)
    scrape(config, num_sensors, units)
end

main()