const DEFAULT_NATS_URL = "nats://localhost:4222"

struct msgPayload_v1
  id::String                    # id of this payload
  dataname::String              # name of this payload
  type::String                  # "text | json | table | image | audio | video | binary"
  transport::String             # "direct | link"
  encoding::String              # "none | json | base64 | arrow-ipc"
  size::Integer                 # data size in bytes e.g. 15433
  data::Any                     # payload data in case of direct transport or URL in case of link
  metadata::Dict{String, Any}   # Dict("checksum=> "sha256_hash", ...)
end

# constructor
function msgPayload_v1(
  id::String = "";
  dataname::String = "",
  type::String = "text",
  transport::String = "direct",
  encoding::String = "none",
  size::Integer = 0,
  data::Any = nothing,
  metadata::Dict{String, Any} = Dict{String, Any}()
)
  return msgPayload_v1(
            id,
            dataname,
            type,
            transport,
            encoding,
            size,
            data,
            metadata
          )
end


struct msgEnvelope_v1
  correlationId::String       # Unique identifier to track messages across systems. Many senders can talk about the same topic.
  msgId::String               # this message id
  timestamp::String           # message published timestamp.  string(Dates.now())

  sendTo::String              # topic/subject the sender sends to e.g. "/agent/wine/api/v1/prompt"
  msgPurpose::String           # purpose of this message e.g. "ACK | NACK | updateStatus | shutdown | ..."
  senderName::String           # sender name (String) e.g. "agent-wine-web-frontend"
  senderId::String            # sender id e.g. uuid4snakecase()
  receiverName::String        # msg receiver name (String)  e.g. "agent-backend"
  receiverId::String          # msg receiver id, nothing means everyone in the topic e.g. uuid4snakecase()

  replyTo::String             # sender ask receiver to reply to this topic
  replyToMsgId::String        # the message id this message is replying to
  BrokerURL::String           # mqtt/NATS server address

  note::Dict{String, Any}     # used to store additional info
  payloads::AbstractArray{msgPayload_v1}     # multiple payload store here
end

# constructor
function msgEnvelope_v1(
  correlationId::String = "";
  msgId::String = "",
  timestamp::String = "",
  sendTo::String = "",
  msgPurpose::String = "",
  senderName::String = "",
  senderId::String = "",
  receiverName::String = "",
  receiverId::String = "",
  replyTo::String = "",
  replyToMsgId::String = "",
  BrokerURL::String = DEFAULT_NATS_URL,
  note::Dict{String, Any} = Dict{String, Any}(),
  payloads::AbstractArray{msgPayload_v1} = msgPayload_v1[]
)
  return  msgEnvelope_v1(
            correlationId,
            msgId,
            timestamp,
            sendTo,
            msgPurpose,
            senderName,
            senderId,
            receiverName,
            receiverId,
            replyTo,
            replyToMsgId,
            BrokerURL,
            note,
            payloads
          )
end