.preload

-- A simple MQTT Sparkplug Explorer

-- The broker. The public HiveMQ broker typically has many connected Sparkplug clients
local mqttServer = "broker.hivemq.com"

local mqttVer="mqttc" -- V5
--local mqttVer="mqtt3c" -- V3

local username,password="admin","admin"

local mqtt,sp,serpent -- forward declarations, see runExplorer()
local fmt=string.format

-- MQTT connect/disconnect callback
local function onstatus(type,code,status)
   -- If a successful MQTT connect
   if "mqtt" == type and "connect" == code and 0 == status.reasoncode then
      -- Subscribe to the Sparkplug wildcard topic 'spBv1.0/#'
      mqtt:subscribe"spBv1.0/#"
      tracep(false,0,"MQTT connection established; Waiting for messages")
      return true -- Accept connection
   end
   tracep(false,0,"MQTT broker disconnected or connect failed:",type,code)
   return 0 -- reconnect with zero timeout
end

-- MQTT on publish callback
local function onpublish(topic,payload,prop)
   tracep(false,0,fmt("Sparkplug topic: %s",topic))
   local t,err = sp.decode(payload)
   if t then
      tracep(false,0,serpent.block(t,{comment=false}),"\n")
   else
      trace("Decode err",err)
   end
end


-- Load the complete Sparkplug protobuf schema from the ZIP file mako.zip
local function loadSchema()
   -- Open the file mako.zip:.lua/sparkplug_b.proto
   local fp <close> = ba.openio"vm":open".lua/sparkplug_b.proto"
   assert(fp, "\nsparkplug_b.proto not found")
   return fp:read"*a" -- Return schema
end

-- The runExplorer function is the core of the script that sets up and
-- starts the Sparkplug Explorer.
local function runExplorer()
   local ok
   -- Load the 'protoc' Lua module, which is used for parsing the protobuf
   -- schema. If the module is not found, an error message is printed.
   local ok,protoc = pcall(require,"protoc")
   assert(ok, "\nThe Lua module 'protoc' is not included in the server's resource file")
   assert(protoc:load(loadSchema()), "Cannot parse schema")
   -- Load the Serpent Lua module, a Lua serializer and pretty
   -- printer. It is used for pretty printing Lua tables in
   -- onpublish() above.
   -- Docs: https://github.com/pkulchenko/serpent
   serpent=require"serpent"
   tracep(false,0,fmt("\nConnecting to broker %s",mqttServer))
   -- Load and create instance: https://realtimelogic.com/ba/doc/?url=MQTT.html
   mqtt=require(mqttVer).create(mqttServer,onstatus,onpublish,{recbta=false,username=username,password=password})
   sp=require"SparkplugB"
   tracep(false,0,"Sparkplug Explorer started")
end

ba.thread.run(runExplorer) -- Run after Mako completes the startup process