seq.puml

@startuml
participant FacebookMessenger as fb
participant Ivanka as i
participant ContactCenter as cc
participant Agent as a

fb -> i : Hello/First message
i -> fb : Greeting
fb <-> i : Gather information about problem
i <-> cc : Check Agent Availability

alt agents available
i -> cc : Start/Inject a new chat
cc -> a : Assign chat to agent
a -> cc : Pick the chat
a -> i : send message
i -> fb : fwd message to user
fb -> i : send message/response
i -> a : fwd message/response to agent 

note over fb,a
This back and forth conversation repeats for each message 
sent by either Facebook user or contact center agent
end note

fb -> i : send Goodbye
i -> a : fwd goodbye and end chat
a -> cc : close the chat

else agents not available
i -> fb : Send agent unavailable message
i <-> fb : Ask permission to request callback

alt request callback
i <-> fb : Ask for phone number
i <-> cc : Inject new callback request
i -> fb : Confirm acceptance of request
else no request callback
i -> fb : Ask to retry later
end

end

@enduml