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64module Duets.Agents.State
open Duets.Entities
type Handler = State -> unit
type StateMessage =
| Get of AsyncReplyChannel<State>
| Set of State
| Subscribe of id: Identity * handler: Handler
| Unsubscribe of id: Identity
type StateAgent() =
let state =
MailboxProcessor.Start
<| fun inbox ->
let rec loop (state, listeners) =
async {
let! msg = inbox.Receive()
let notifyAll value =
listeners |> Map.iter (fun _ handler -> handler value)
match msg with
| Get channel ->
channel.Reply state
return! loop (state, listeners)
| Set value ->
notifyAll value
return! loop (value, listeners)
| Subscribe(id, handler) ->
let updated = listeners |> Map.add id handler
handler state
return! loop (state, updated)
| Unsubscribe id ->
let updated = listeners |> Map.remove id
return! loop (state, updated)
}
loop (State.empty, Map.empty)
member this.Agent = state
let private staticAgent = StateAgent()
type private Subscription(id: Identity) =
interface System.IDisposable with
member this.Dispose() =
Unsubscribe id |> staticAgent.Agent.Post
/// Returns the state of the game.
let get () = staticAgent.Agent.PostAndReply Get
/// Sets the state of the game.
let set value = Set value |> staticAgent.Agent.Post
/// Subscribes to changes on the state and returns the ID that identifies the
/// subscription.
let subscribe handler : System.IDisposable =
let id = Identity.create ()
Subscribe(id, handler) |> staticAgent.Agent.Post
new Subscription(id)