local P = {}
local m, topic, cid
local active_subscriptions = {}
local pending_subscriptions = {}
local pending_subcsription

local function p(msg)
  print("MQTT: "..msg)
end

-- Subscribe to all registered subscriptions
-- TODO: subscriptions that are not successfull will remain in state = 1. Might not be a real problem if it happens, the server probably disallowed the subscription.
local function create_subscriptions()
  print("create_subscriptions, pending count "..table.getn(pending_subscriptions)..", pending: "..tostring(pending_subscription))

  if (pending_subscription) then
    return
  end

  pending_subcsription = table.remove(pending_subscriptions)

  -- The API claims that the callback has this signature: function(client, topic, message)
  -- but that doesn't seems right from the source code. The code doesn't
  -- remember the topics that is being subscribed to.
  m:subscribe(pending_subcsription, 0, function(client)
    print("success: "..pending_subcsription)
    table.insert(active_subscriptions, pending_subscription)
    pending_subscription = nil
    create_subscriptions()
  end)
end

local function mq_client_connected(con)
  p("connected")

  create_subscriptions()
end

local function disconnect()
  p("Lost wifi connection, disconnecting")
  m:close()
  m = nil

  -- append active_subscriptions to pending_subscriptions
  active_subscriptions = {}
end

function mq_on_timer()
  -- This crashes the module:
  -- local status = wifi.sta.status()
  -- p("checking status, status="..status)

  local status = wifi.sta.getip()

  if status and status ~= "0.0.0.0" then
    if not m then
      p("connecting")

      -- client id, keepalive, username, password
      m = mqtt.Client(cid, 120)
      -- m:on("connect", mq_connected)
      m:on("offline", function() m:close(); m = nil end)

      -- host, port, secure, auto_reconnect, function(client), ssl=8883
      m:connect("trygvis.io", 1883, 0, 0, mq_client_connected)
    end
  else
    if m then
	  disconnect()
    end
  end
end

function P.init(timer_id, client_id)
  cid = client_id

  topic = "/esp8266/"..client_id

  tmr.alarm(timer_id, 3 * 1000, 1, mq_on_timer)
end 

function P.subscribe(path, cb)
  subscription = subscriptions[path]
  if subscription then
    print("subscription on "..path.." already registered, state="..tostring(subscription.state))
    return
  end

  print("Registering subscription on "..path)

  pending_subscriptions[path] = true

  create_subscriptions()
end

function P.publish(path, payload)
  if not m then
	print("Not connected, dropping message to "..path)
	return false, 'not connected'
  end

  path = topic.."/"..path
  print("path="..path)
  m:publish(path, payload, 0, 0)

  return true, 'ok'
end

return P