(.module: {#.doc "The actor model of concurrency."}
  [lux #*
   [control monad
    ["p" parser]
    ["ex" exception (#+ exception:)]]
   [io (#- run) ("io/" Monad<IO>)]
   [data
    [product]
    ["e" error]
    text/format
    [collection [list ("list/" Monoid<List> Monad<List> Fold<List>)]]]
   [macro (#+ with-gensyms Monad<Meta>)
    [code]
    ["s" syntax (#+ syntax: Syntax)]
    [syntax
     ["cs" common]
     [common
      ["csr" reader]
      ["csw" writer]]]]
   [type
    abstract]]
  [//
   [atom (#+ Atom atom)]
   [promise (#+ Promise promise) ("promise/" Monad<Promise>)]
   [task (#+ Task)]])

(exception: #export poisoned)

(exception: #export (dead {actor-name Text}
                          {message-name Text})
  (format "  Actor: " actor-name "\n"
          "Message: " message-name "\n"))

## [Types]
(with-expansions
  [<Message> (as-is (-> s (Actor s) (Task s)))
   <Obituary> (as-is [Text s (List <Message>)])
   <Mailbox> (as-is (Rec Mailbox (Promise [<Message> Mailbox])))]

  (def: (obituary mailbox)
    (All [a] (-> (Rec Mailbox (Promise [a Mailbox])) (List a)))
    (case (promise.poll mailbox)
      (#.Some [head tail])
      (#.Cons head (obituary tail))
      
      #.None
      #.Nil))
  
  (abstract: #export (Actor s)
    {#.doc "An actor, defined as all the necessities it requires."}
    {#mailbox (Atom <Mailbox>)
     #obituary (Promise <Obituary>)}

    ## TODO: Delete after new-luxc becomes the new standard compiler.
    (def: (actor mailbox obituary)
      (All [s] (-> (Atom <Mailbox>) (Promise <Obituary>) (Actor s)))
      (:abstraction {#mailbox mailbox
                     #obituary obituary}))

    (type: #export (Message s)
      <Message>)

    (type: #export (Obituary s)
      <Obituary>)

    (type: #export (Behavior s)
      {#.doc "An actor's behavior when messages are received."}
      {#handle (-> (Message s) s (Actor s) (Task s))
       #end (-> Text s (Promise Any))})

    (def: #export (spawn behavior init)
      {#.doc "Given a behavior and initial state, spawns an actor and returns it."}
      (All [s] (-> (Behavior s) s (IO (Actor s))))
      (io (let [[handle end] behavior
                self (actor (atom (promise #.None))
                            (promise #.None))
                process (loop [state init
                               |mailbox| (io.run (atom.read (get@ #mailbox (:representation self))))]
                          (do promise.Monad<Promise>
                            [[head tail] |mailbox|
                             ?state' (handle head state self)]
                            (case ?state'
                              (#e.Error error)
                              (do @
                                [_ (end error state)]
                                (exec (io.run (promise.resolve [error state (#.Cons head (obituary tail))]
                                                               (get@ #obituary (:representation self))))
                                  (wrap [])))

                              (#e.Success state')
                              (recur state' tail))))]
            self)))

    (def: #export (alive? actor)
      (All [s] (-> (Actor s) Bit))
      (case (promise.poll (get@ #obituary (:representation actor)))
        #.None
        true

        _
        false))

    (def: #export (send message actor)
      {#.doc "Communicate with an actor through message passing."}
      (All [s] (-> (Message s) (Actor s) (IO Bit)))
      (if (alive? actor)
        (let [entry [message (promise #.None)]]
          (do Monad<IO>
            [|mailbox| (atom.read (get@ #mailbox (:representation actor)))]
            (loop [|mailbox| |mailbox|]
              (case (promise.poll |mailbox|)
                #.None
                (do @
                  [resolved? (promise.resolve entry |mailbox|)]
                  (if resolved?
                    (do @
                      [_ (atom.write (product.right entry) (get@ #mailbox (:representation actor)))]
                      (wrap true))
                    (recur |mailbox|)))
                
                (#.Some [_ |mailbox|'])
                (recur |mailbox|')))))
        (io/wrap false)))
    ))

## [Values]
(def: (default-handle message state self)
  (All [s] (-> (Message s) s (Actor s) (Task s)))
  (message state self))

(def: (default-end cause state)
  (All [s] (-> Text s (Promise Any)))
  (promise/wrap []))

(def: #export default-behavior
  (All [s] (Behavior s))
  {#handle default-handle
   #end default-end})

(def: #export (poison actor)
  {#.doc "Kills the actor by sending a message that will kill it upon processing,
          but allows the actor to handle previous messages."}
  (All [s] (-> (Actor s) (IO Bit)))
  (send (function (_ state self)
          (task.throw poisoned []))
        actor))

## [Syntax]
(do-template [<with> <resolve> <tag> <desc>]
  [(def: #export (<with> name)
     (-> Ident cs.Annotations cs.Annotations)
     (|>> (#.Cons [(ident-for <tag>)
                   (code.tag name)])))
   
   (def: #export (<resolve> name)
     (-> Ident (Meta Ident))
     (do Monad<Meta>
       [[_ annotations _] (macro.find-def name)]
       (case (macro.get-tag-ann (ident-for <tag>) annotations)
         (#.Some actor-name)
         (wrap actor-name)

         _
         (macro.fail (format "Definition is not " <desc> ".")))))]

  [with-actor   resolve-actor   #..actor   "an actor"]
  [with-message resolve-message #..message "a message"]
  )

(def: actor-decl^
  (Syntax [Text (List Text)])
  (p.either (s.form (p.seq s.local-symbol (p.some s.local-symbol)))
            (p.seq s.local-symbol (:: p.Monad<Parser> wrap (list)))))

(do-template [<name> <desc>]
  [(def: #export <name>
     (-> Text Text)
     (|>> (format <desc> "@")))]

  [state-name    "State"]
  [behavior-name "Behavior"]
  [new-name      "new"]
  )

(type: HandleC
  [[Text Text Text] Code])

(type: StopC
  [[Text Text] Code])

(type: BehaviorC
  [(Maybe HandleC) (Maybe StopC)])

(def: behavior^
  (s.Syntax BehaviorC)
  (let [handle-args ($_ p.seq s.local-symbol s.local-symbol s.local-symbol)
        stop-args ($_ p.seq s.local-symbol s.local-symbol)]
    (p.seq (p.maybe (s.form (p.seq (s.form (p.after (s.this (' handle)) handle-args))
                                   s.any)))
           (p.maybe (s.form (p.seq (s.form (p.after (s.this (' stop)) stop-args))
                                   s.any))))))

(syntax: #export (actor:
                   {export csr.export}
                   {[_name _vars] actor-decl^}
                   {annotations (p.default cs.empty-annotations csr.annotations)}
                   state-type
                   {[?handle ?stop] behavior^})
  {#.doc (doc "Defines an actor, with its behavior and internal state."
              (actor: #export Counter
                Nat
                
                ((stop cause state)
                 (:: promise.Monad<Promise> wrap
                     (log! (if (ex.match? ..poisoned cause)
                             (format "Counter was poisoned: " (%n state))
                             cause)))))
              
              (actor: #export (Stack a)
                (List a)
                
                ((handle message state self)
                 (do task.Monad<Task>
                   [#let [_ (log! "BEFORE")]
                    output (message state self)
                    #let [_ (log! "AFTER")]]
                   (wrap output)))))}
  (with-gensyms [g!_ g!init]
    (do @
      [module macro.current-module-name
       #let [g!type (code.local-symbol (state-name _name))
             g!behavior (code.local-symbol (behavior-name _name))
             g!actor (code.local-symbol _name)
             g!new (code.local-symbol (new-name _name))
             g!vars (list/map code.local-symbol _vars)]]
      (wrap (list (` (type: (~+ (csw.export export)) ((~ g!type) (~+ g!vars))
                       (~ state-type)))
                  (` (type: (~+ (csw.export export)) ((~ g!actor) (~+ g!vars))
                       (~ (|> annotations
                              (with-actor [module _name])
                              csw.annotations))
                       (..Actor ((~ g!type) (~+ g!vars)))))
                  (` (def: (~+ (csw.export export)) (~ g!behavior)
                       (All [(~+ g!vars)]
                         (..Behavior ((~ g!type) (~+ g!vars))))
                       {#..handle (~ (case ?handle
                                       #.None
                                       (` (~! ..default-handle))

                                       (#.Some [[messageN stateN selfN] bodyC])
                                       (` (function ((~ g!_)
                                                     (~ (code.local-symbol messageN))
                                                     (~ (code.local-symbol stateN))
                                                     (~ (code.local-symbol selfN)))
                                            (do task.Monad<Task>
                                              []
                                              (~ bodyC))))))
                        #..end (~ (case ?stop
                                    #.None
                                    (` (~! ..default-end))

                                    (#.Some [[causeN stateN] bodyC])
                                    (` (function ((~ g!_)
                                                  (~ (code.local-symbol causeN))
                                                  (~ (code.local-symbol stateN)))
                                         (do promise.Monad<Promise>
                                           []
                                           (~ bodyC))))))}))
                  (` (def: (~+ (csw.export export)) ((~ g!new) (~ g!init))
                       (All [(~+ g!vars)]
                         (-> ((~ g!type) (~+ g!vars)) (io.IO ((~ g!actor) (~+ g!vars)))))
                       (..spawn (~ g!behavior) (~ g!init))))))
      )))

(type: Signature
  {#vars (List Text)
   #name Text
   #inputs (List cs.Typed-Input)
   #state Text
   #self Text
   #output Code})

(def: signature^
  (s.Syntax Signature)
  (s.form ($_ p.seq
              (p.default (list) (s.tuple (p.some s.local-symbol)))
              s.local-symbol
              (p.some csr.typed-input)
              s.local-symbol
              s.local-symbol
              s.any)))

(def: reference^
  (s.Syntax [Ident (List Text)])
  (p.either (s.form (p.seq s.symbol (p.some s.local-symbol)))
            (p.seq s.symbol (:: p.Monad<Parser> wrap (list)))))

(syntax: #export (message:
                   {export csr.export}
                   {[actor-name actor-vars] reference^}
                   {signature signature^}
                   {annotations (p.default cs.empty-annotations csr.annotations)}
                   body)
  {#.doc (doc "A message can access the actor's state through the state parameter."
              "A message can also access the actor itself through the self parameter."
              "A message's output must be a task containing a 2-tuple with the updated state and a return value."
              "A message may succeed or fail (in case of failure, the actor dies)."

              (message: #export Counter
                (count! [increment Nat] state self Nat)
                (let [state' (n/+ increment state)]
                  (task.return [state' state'])))

              (message: #export (Stack a)
                (push [value a] state self (List a))
                (let [state' (#.Cons value state)]
                  (task.return [state' state']))))}
  (with-gensyms [g!_ g!return g!error g!task g!sent?]
    (do @
      [current-module macro.current-module-name
       actor-name (resolve-actor actor-name)
       #let [message-name [current-module (get@ #name signature)]
             g!type (code.symbol (product.both id state-name actor-name))
             g!message (code.local-symbol (get@ #name signature))
             g!actor-vars (list/map code.local-symbol actor-vars)
             actorC (` ((~ (code.symbol actor-name)) (~+ g!actor-vars)))
             g!all-vars (|> (get@ #vars signature) (list/map code.local-symbol) (list/compose g!actor-vars))
             g!inputsC (|> (get@ #inputs signature) (list/map product.left))
             g!inputsT (|> (get@ #inputs signature) (list/map product.right))
             g!state (|> signature (get@ #state) code.local-symbol)
             g!self (|> signature (get@ #self) code.local-symbol)
             g!actor-refs (: (List Code)
                             (if (list.empty? actor-vars)
                               (list)
                               (|> actor-vars list.size dec
                                   (list.n/range +0) (list/map (|>> code.nat (~) ($) (`))))))
             ref-replacements (|> (if (list.empty? actor-vars)
                                    (list)
                                    (|> actor-vars list.size dec
                                        (list.n/range +0) (list/map (|>> code.nat (~) ($) (`)))))
                                  (: (List Code))
                                  (list.zip2 g!all-vars)
                                  (: (List [Code Code])))
             g!outputT (list/fold (function (_ [g!var g!ref] outputT)
                                    (code.replace g!var g!ref outputT))
                                  (get@ #output signature)
                                  ref-replacements)]]
      (wrap (list (` (def: (~+ (csw.export export)) ((~ g!message) (~+ g!inputsC) (~ g!self))
                       (~ (|> annotations
                              (with-message actor-name)
                              csw.annotations))
                       (All [(~+ g!all-vars)] (-> (~+ g!inputsT) (~ actorC) (Task (~ (get@ #output signature)))))
                       (let [(~ g!task) (task.task (~ g!outputT))]
                         (io.run (do io.Monad<IO>
                                   [(~ g!sent?) (..send (function ((~ g!_) (~ g!state) (~ g!self))
                                                          (do promise.Monad<Promise>
                                                            [(~ g!return) (: (Task [((~ g!type) (~+ g!actor-refs))
                                                                                    (~ g!outputT)])
                                                                             (do task.Monad<Task>
                                                                               []
                                                                               (~ body)))]
                                                            (case (~ g!return)
                                                              (#.Right [(~ g!state) (~ g!return)])
                                                              (exec (io.run (promise.resolve (#.Right (~ g!return)) (~ g!task)))
                                                                (task.return (~ g!state)))
                                                              
                                                              (#.Left (~ g!error))
                                                              (exec (io.run (promise.resolve (#.Left (~ g!error)) (~ g!task)))
                                                                (task.fail (~ g!error))))
                                                            ))
                                                        (~ g!self))]
                                   (if (~ g!sent?)
                                     ((~' wrap) (~ g!task))
                                     ((~' wrap) (task.throw ..dead [(~ (code.text (%ident actor-name)))
                                                                    (~ (code.text (%ident message-name)))]))))))))
                  ))
      )))