# SPDX-FileCopyrightText: ☭ Emery Hemingway
# SPDX-License-Identifier: Unlicense

# Use procedures to call into SAM,
# use continuations to call within SAM.

import std/[deques, hashes, options, tables, times]
import pkg/cps
import preserves
import ./protocols/[protocol, sturdy]

# const traceSyndicate {.booldefine.}: bool = true
const traceSyndicate* = true

when traceSyndicate:
  import std/streams
  from std/os import getEnv
  import ./protocols/trace

export protocol.Handle

type
  Cont* = ref object of Continuation
    facet: Facet

  PublishProc* = proc (e: Entity; v: Value; h: Handle) {.cps: Cont.}
  RetractProc* = proc (e: Entity; h: Handle) {.cps: Cont.}
  MessageProc* = proc (e: Entity; v: Value) {.cps: Cont.}
  SyncProc* = proc (e: Entity; peer: Cap) {.cps: Cont.}

  Handler* = proc() {.closure.}

  Work = Deque[Cont]
  HandlerDeque = seq[ContinuationProc[Continuation]]

  FacetState = enum fFresh, fRunning, fEnded

  Callback* = proc () {.closure.}

  OutboundTable = Table[Handle, OutboundAssertion]
  OutboundAssertion = ref object
    handle: Handle
    peer: Cap
    established: bool

  Facet* = ref object
    ## https://synit.org/book/glossary.html#facet
    actor: Actor
    parent: Facet
    children: seq[Facet]
    outbound: OutboundTable
    stopHandlers: HandlerDeque
    stopCallbacks: seq[Callback]
    state: FacetState
    id: FacetId

  FacetProc* = proc (f: Facet) {.closure.}
    ## Type for callbacks to be called within a turn.
    ## The `Facet` parameter is the owning facet.

  Turn {.byref.} = object
    ## https://synit.org/book/glossary.html#turn
    facet: Facet
    work: Work
    actions: seq[Cont]
    event: Option[protocol.Event]
    when traceSyndicate:
      desc: TurnDescription

  Entity* = ref object of RootObj
    ## https://synit.org/book/glossary.html#entity
    publishImpl: PublishProc
    retractImpl: RetractProc
    messageImpl: MessageProc
    syncImpl: SyncProc
    facet*: Facet
      # This implementation associates Entities to
      # Facets, which is not to be taken as a SAM
      # axiom.
    oid*: sturdy.Oid # oid is how Entities are identified over the wire

  Cap* {.final, preservesEmbedded.} = ref object of EmbeddedObj
    target*: Entity
    attenuation*: seq[sturdy.Caveat]

  Actor* = ref object
    ## https://synit.org/book/glossary.html#actor
    # TODO: run on a seperate thread.
    # crashHandlers: HandlerDeque
    root: Facet
    handleAllocator: Handle
    facetIdAllocator: int
    id: ActorId
    turn: Turn
    when traceSyndicate:
      traceStream: FileStream
    stopped: bool

template turnWork*(prc: typed): untyped =
  cps(Cont, prc)

proc activeFacet(c: Cont): Facet {.cpsVoodoo.} =
  ## Return the active `Facet` within a `{.syndicate.}` context.
  assert not c.facet.isNil
  c.facet

using
  actor: Actor
  facet: Facet
  entity: Entity
  cap: Cap
  turn: Turn

proc `$`*(facet): string = $facet.id
proc `$`*(cap): string = "#:…"

proc hash*(facet): Hash = facet.unsafeAddr.hash
proc hash*(cap): Hash = cap.unsafeAddr.hash

proc relay*(cap): Facet =
  assert not cap.target.facet.isNil
  cap.target.facet

proc collectPath(result: var seq[FacetId]; facet) =
  if not facet.parent.isNil:
    collectPath(result, facet.parent)
  result.add(facet.id)

proc newFacet(actor; parent: Facet): Facet =
  inc(actor.facetIdAllocator)
  result = Facet(
      actor: actor,
      parent: parent,
      id: actor.facetIdAllocator.toPreserves,
    )
  if not parent.isNil:
    parent.children.add result
  when traceSyndicate:
    var act = ActionDescription(orKind: ActionDescriptionKind.facetstart)
    collectPath(act.facetstart.path, result)
    actor.turn.desc.actions.add act
    echo actor.turn.desc

proc stopped*(facet): bool = facet.state != fRunning

proc newActor(parent: Facet; name: string): Actor =
  result = Actor(id: name.toPreserves)
  result.root = newFacet(result, parent)
  when traceSyndicate:
    if parent.isNil:
      let path = getEnv("SYNDICATE_TRACE_FILE", "")
      case path
      of "": discard
      of "-": result.traceStream = newFileStream(stderr)
      else: result.traceStream = openFileStream(path, fmWrite)
    else:
      result.traceStream = parent.actor.traceStream

when traceSyndicate:
  proc traceFlush(actor) =
    if not actor.traceStream.isNil:
      actor.traceStream.flush()

  proc trace(actor; act: ActorActivation) =
    if not actor.traceStream.isNil:
      var entry = TraceEntry(
          timestamp: getTime().toUnixFloat(),
          actor: actor.id,
          item: act,
        )
      actor.traceStream.writeLine($entry.toPreserves)

  proc traceTurn(actor) =
    if not actor.traceStream.isNil:
      actor.trace(ActorActivation(
          orKind: ActorActivationKind.turn,
          turn: actor.turn.desc,
        ))
    actor.traceFlush()
    reset actor.turn.desc

  proc traceTarget(facet): trace.Target =
    Target(
        actor: facet.actor.id,
        facet: facet.id,
      )

  proc traceTarget(cap): trace.Target =
    let facet = cap.relay
    Target(
        actor: facet.actor.id,
        facet: facet.id,
        oid: cap.target.oid.toPreserves,
      )

  proc traceEnqueue(actor; e: TargetedTurnEvent) =
    actor.turn.desc.actions.add ActionDescription(
        orKind: ActionDescriptionKind.enqueue,
        enqueue: ActionDescriptionEnqueue(event: e),
      )

  proc traceDequeue(actor; e: TargetedTurnEvent) =
    actor.turn.desc.actions.add ActionDescription(
        orKind: ActionDescriptionKind.dequeue,
        dequeue: ActionDescriptionDequeue(event: e),
      )

proc pass*(a, b: Cont): Cont =
  assert not a.facet.isNil
  b.facet = a.facet
  b

proc queueWork(facet; c: Cont) =
  c.facet = facet
  facet.actor.turn.work.addLast(c)

proc yieldWork(c: Cont): Cont {.cpsMagic.} =
  ## Suspend and enqueue the caller until later in the turn.
  assert not c.facet.isNil
  c.facet.queueWork(c)
  nil

proc yieldToActions(c: Cont): Cont {.cpsMagic.} =
  assert not c.facet.isNil
  c.facet.actor.turn.actions.add(c)
  nil

proc startExternalTurn(facet) =
  let actor = facet.actor
  assert actor.turn.work.len == 0
  assert actor.turn.actions.len == 0
  actor.turn.facet = facet
  when traceSyndicate:
    actor.turn.desc = TurnDescription(cause: TurnCause(orKind: TurnCauseKind.external))

proc terminate(actor; err: ref Exception) =
  when traceSyndicate:
    actor.traceTurn()
  raise err

proc terminate(facet; err: ref Exception) =
  terminate(facet.actor, err)

proc complete(c: Cont) =
  var c = c
  try:
    while not c.isNil and not c.fn.isNil:
      var y = c.fn
      var x = y(c)
      c = Cont(x)
  except CatchableError as err:
    if not c.dismissed:
      writeStackFrames c
      terminate(c.facet, err)

proc runTurn*(actor): bool =
  if actor.stopped: return
  try:
    result = actor.turn.work.len > 0
    while actor.turn.work.len > 0:
      actor.turn.work.popFirst().complete()
    var i: int
    echo actor.turn.actions.len, " items in pending action queue"
    while i < actor.turn.actions.len:
      complete(move actor.turn.actions[i])
      inc i
    echo i, " items completed from action queue"
    actor.turn.actions.setLen(0)
    when traceSyndicate:
      actor.traceTurn()
      if actor.stopped:
        trace(actor, ActorActivation(orkind: ActorActivationKind.stop))
  except Exception as err:
    actor.terminate(err)

proc runChildren(facet): bool =
  var i = 0
  for child in facet.children:
    inc(i)
    if child.actor != facet.actor:
      result = result or
        runTurn(child.actor) or
          runChildren(child)

proc runActors*(actor): bool =
  runTurn(actor) or runChildren(actor.root)

proc start(actor; cont: Cont) =
  when traceSyndicate:
    var act = ActorActivation(orkind: ActorActivationKind.start)
    trace(actor, act)
  actor.root.state = fRunning
  actor.root.startExternalTurn()
  actor.root.queueWork(cont)

proc stop*(actor)

proc runNextStop(c: Cont; facet: Facet): Cont {.cpsMagic.} =
  c.fn = facet.stopHandlers.pop()
  result = c

proc runNextFacetStop() {.cps: Cont.} =
  activeFacet().runNextStop()

proc stop(facet; reason: FacetStopReason) =
  let actor = facet.actor
  while facet.stopHandlers.len > 0:
    var c = whelp runNextFacetStop()
    c.facet = facet
    complete(c)
  while facet.stopCallbacks.len > 0:
    var cb =  facet.stopCallbacks.pop()
    cb()
  while facet.children.len > 0:
    stop(facet.children.pop(), FacetStopReason.parentStopping)
  when traceSyndicate:
    var act = ActionDescription(orKind: ActionDescriptionKind.facetstop)
    collectPath(act.facetstop.path, facet)
    act.facetStop.reason = reason
    actor.turn.desc.actions.add act
  if facet.parent.isNil:
    actor.root = nil
    stop(actor)

proc stop*(actor) =
  if not actor.root.isNil:
    stop(actor.root, FacetStopReason.actorStopping)
  actor.stopped = true


# proc stopFacetAction(reason: FacetStopReason) {.syndicate.} =
#  stop(c.facet, reason)

proc stopActorAction() {.cps: Cont.} =
  yieldToActions()
  activeFacet().actor.stop()

proc stopActor*(facet) =
  let c = whelp stopActorAction()
  c.facet = facet
  facet.actor.turn.actions.add(c)

proc stopActor*(cap) =
  ## Stop an `Actor` from a `Cap`.
  stopActor(cap.relay)

type
  AssertionRef* = ref object
    value*: Value
      # if the Enity methods take a Value object then the generated
      # C code has "redefinition of struct" problems when orc is enabled

proc newCap*(facet; entity): Cap =
  doAssert entity.facet.isNil
  entity.facet = facet
  Cap(target: entity)

proc nextHandle(facet: Facet): Handle =
  inc(facet.actor.handleAllocator)
  facet.actor.handleAllocator

proc actor(cap): Actor = cap.relay.actor

type Bindings = Table[Value, Value]

proc attenuate(cap; att: seq[Caveat]): Cap =
  if att.len == 0: cap
  else: Cap(
    target: cap.target,
    attenuation: att & cap.attenuation)

proc match(bindings: var Bindings; p: Pattern; v: Value): bool =
  case p.orKind
  of PatternKind.Pdiscard: result = true
  of PatternKind.Patom:
    result = case p.patom
      of PAtom.Boolean: v.isBoolean
      of PAtom.Double: v.isDouble
      of PAtom.Signedinteger: v.isInteger
      of PAtom.String: v.isString
      of PAtom.Bytestring: v.isByteString
      of PAtom.Symbol: v.isSymbol
  of PatternKind.Pembedded:
    result = v.isEmbedded
  of PatternKind.Pbind:
    if match(bindings, p.pbind.pattern, v):
      bindings[p.pbind.pattern.toPreserves] = v
      result = true
  of PatternKind.Pand:
    for pp in p.pand.patterns:
      result = match(bindings, pp, v)
      if not result: break
  of PatternKind.Pnot:
    var b: Bindings
    result = not match(b, p.pnot.pattern, v)
  of PatternKind.Lit:
    result = p.lit.value == v
  of PatternKind.PCompound:
    case p.pcompound.orKind
    of PCompoundKind.rec:
      if v.isRecord and
          p.pcompound.rec.label == v.label and
          p.pcompound.rec.fields.len == v.arity:
        result = true
        for i, pp in p.pcompound.rec.fields:
          if not match(bindings, pp, v[i]):
            result = false
            break
    of PCompoundKind.arr:
      if v.isSequence and p.pcompound.arr.items.len == v.sequence.len:
        result = true
        for i, pp in p.pcompound.arr.items:
          if not match(bindings, pp, v[i]):
            result = false
            break
    of PCompoundKind.dict:
      if v.isDictionary:
        result = true
        for key, pp in p.pcompound.dict.entries:
          let vv = step(v, key)
          if vv.isNone or not match(bindings, pp, get vv):
            result = true
            break

proc match(p: Pattern; v: Value): Option[Bindings] =
  var b: Bindings
  if match(b, p, v):
    result = some b

proc instantiate(t: Template; bindings: Bindings): Value =
  case t.orKind
  of TemplateKind.Tattenuate:
    let v = instantiate(t.tattenuate.template, bindings)
    let cap = v.unembed(Cap)
    if cap.isNone:
      raise newException(ValueError, "Attempt to attenuate non-capability")
    result = attenuate(get cap, t.tattenuate.attenuation).embed
  of TemplateKind.TRef:
    let n = $t.tref.binding.int
    try: result = bindings[n.toPreserves]
    except KeyError:
      raise newException(ValueError, "unbound reference: " & n)
  of TemplateKind.Lit:
    result = t.lit.value
  of TemplateKind.Tcompound:
    case t.tcompound.orKind
    of TCompoundKind.rec:
      result = initRecord(t.tcompound.rec.label, t.tcompound.rec.fields.len)
      for i, tt in t.tcompound.rec.fields:
        result[i] = instantiate(tt, bindings)
    of TCompoundKind.arr:
      result = initSequence(t.tcompound.arr.items.len)
      for i, tt in t.tcompound.arr.items:
        result[i] = instantiate(tt, bindings)
    of TCompoundKind.dict:
      result = initDictionary()
      for key, tt in t.tcompound.dict.entries:
        result[key] = instantiate(tt, bindings)

proc rewrite(r: Rewrite; v: Value): Value =
  let bindings = match(r.pattern, v)
  if bindings.isSome:
    result = instantiate(r.template, get bindings)

proc examineAlternatives(cav: Caveat; v: Value): Value =
  case cav.orKind
  of CaveatKind.Rewrite:
    result = rewrite(cav.rewrite, v)
  of CaveatKind.Alts:
    for r in cav.alts.alternatives:
      result = rewrite(r, v)
      if not result.isFalse: break
  of CaveatKind.Reject: discard
  of CaveatKind.unknown: discard

proc runRewrites(v: Value; a: openarray[Caveat]): Value =
  result = v
  for stage in a:
    result = examineAlternatives(stage, result)
    if result.isFalse: break

proc setActions*(entity;
      publish = PublishProc();
      retract = RetractProc();
      message = MessageProc();
      sync = SyncProc();
    ): Entity {.discardable} =
  ## Set the action handlers for an `Entity`.
  result = entity
  result.publishImpl = publish
  result.retractImpl = retract
  result.messageImpl = message
  result.syncImpl = sync

proc publish(c: Cont; e: Entity; v: Value; h: Handle): Cont {.cpsMagic.} =
  if not e.publishImpl.fn.isNil:
    result = pass(c, e.publishImpl.call(e, v, h))

proc retract(c: Cont; e: Entity; h: Handle): Cont {.cpsMagic.} =
  if not e.retractImpl.fn.isNil:
    result = pass(c, e.retractImpl.call(e, h))

proc message(c: Cont; e: Entity; v: Value): Cont {.cpsMagic.} =
  if not e.messageImpl.fn.isNil:
    result = pass(c, e.messageImpl.call(e, v))

proc sync(c: Cont; e: Entity; p: Cap): Cont {.cpsMagic.} =
  if not e.syncImpl.fn.isNil:
    result = pass(c, e.syncImpl.call(e, p))

proc turnPublish(cap: Cap; val: Value; h: Handle) {.turnWork.} =
  when traceSyndicate:
    var traceEvent = TargetedTurnEvent(
        target: cap.traceTarget,
        detail: trace.TurnEvent(orKind: trace.TurnEventKind.assert)
      )
    traceEvent.detail = trace.TurnEvent(orKind: TurnEventKind.assert)
    traceEvent.detail.assert = TurnEventAssert(
        assertion: AssertionDescription(orKind: AssertionDescriptionKind.value),
        handle: h,
      )
    traceEvent.detail.assert.assertion.value.value = val
    cap.actor.traceEnqueue(traceEvent)
  cap.relay.outbound[h] = OutboundAssertion(handle: h, peer: cap)
  yieldToActions()
  when traceSyndicate:
    cap.actor.traceDequeue(traceEvent)
  cap.target.publish(val, h)
  cap.relay.outbound[h].established = true

proc turnRetract(cap: Cap; h: Handle) {.turnWork.} =
  when traceSyndicate:
    var traceEvent = TargetedTurnEvent(
        target: cap.traceTarget,
        detail: trace.TurnEvent(orKind: trace.TurnEventKind.retract)
      )
    traceEvent.detail.retract.handle = h
    cap.actor.traceEnqueue(traceEvent)
  yieldToActions()
  when traceSyndicate:
    cap.actor.traceDequeue(traceEvent)
  cap.target.retract(h)

proc turnMessage(cap: Cap; val: Value) {.turnWork.} =
  var val = runRewrites(val, cap.attenuation)
  when traceSyndicate:
    var traceEvent = TargetedTurnEvent(
        target: cap.traceTarget,
        detail: trace.TurnEvent(orKind: trace.TurnEventKind.message)
      )
    traceEvent.detail.message.body.value.value = val
    cap.actor.traceEnqueue(traceEvent)
  yieldToActions()
  when traceSyndicate:
    cap.actor.traceDequeue(traceEvent)
  cap.target.message(val)

proc turnSync(cap: Cap; peer: Cap) {.turnWork.} =
  when traceSyndicate:
    var traceEvent = TargetedTurnEvent(
        target: cap.traceTarget,
        detail: trace.TurnEvent(orKind: trace.TurnEventKind.sync)
      )
    traceEvent.detail.sync.peer = peer.traceTarget
    cap.actor.traceEnqueue(traceEvent)
  yieldToActions()
  when traceSyndicate:
    cap.actor.traceDequeue(traceEvent)
  cap.target.sync(peer)

proc publish*(cap; val: Value): Handle =
  ## Publish a `Value` to a `Cap` returning `Handle`
  ## for later retraction.
  # The publish action on an Entity always goes through
  # here first.
  var val = runRewrites(val, cap.attenuation)
    # TODO: attenuation to nothing?
  result = cap.relay.nextHandle()
  cap.relay.queueWork(whelp turnPublish(cap, val, result))

proc publish*[T](cap; x: T): Handle =
  ## Publish Preserves-convertable value to a `Cap`
  ## returning `Handle` for later retraction.
  publish(cap, x.toPreserves)

proc retract*(cap; h: Handle) =
  ## Retract a `Handle` from a `Cap`.
  cap.relay.queueWork(whelp turnRetract(cap, h))

proc message*(cap; val: Value) =
  var val = runRewrites(val, cap.attenuation)
  cap.relay.queueWork(whelp turnMessage(cap, val))

proc message*[T](cap; x: T) =
  message(cap, x.toPreserves)

proc sync*(cap, peer: Cap) =
  cap.relay.queueWork(whelp turnSync(cap, peer))

proc installStopHook(c: Cont, facet: Facet): Cont {.cpsMagic.} =
  facet.stopHandlers.add(c.fn)
  return c

proc addOnStopHandler(c: Cont; cb: Callback): Cont {.cpsMagic.} =
  c.facet.stopCallbacks.add(cb)
  result = c

proc onStop*(facet; cb: proc () {.closure.}) =
  facet.stopCallbacks.add(cb)

proc facetCall(prc: FacetProc) {.cps: Cont.} =
  prc(activeFacet())

proc bootActor*(name: string; bootProc: FacetProc): Actor =
  result = newActor(nil, name)
  result.root.startExternalTurn()
  result.root.queueWork(whelp facetCall(bootProc))

proc spawnActor*(parent: Facet; name: string; bootProc: FacetProc): Actor {.discardable.} =
  result = newActor(parent, name)
  result.root.startExternalTurn()
  result.root.queueWork(whelp facetCall(bootProc))