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

import std/[hashes, monotimes, options, sets, tables, times]
import preserves
import ../syndicate/protocols/[protocol, sturdy]

const tracing = defined(traceSyndicate)

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

export Handle

template generateIdType(typ: untyped) =
  type typ* = distinct Natural
  proc `==`*(x, y: typ): bool {.borrow.}
  proc `$`*(id: typ): string {.borrow.}

generateIdType(ActorId)
generateIdType(FacetId)
generateIdType(EndpointId)
generateIdType(FieldId)
generateIdType(TurnId)

type
  Oid = sturdy.Oid
  Caveat = sturdy.Caveat
  Attenuation = seq[Caveat]
  Rewrite = sturdy.Rewrite

  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

  Entity* = ref object of RootObj
    oid*: Oid # oid is how Entities are identified over the wire

  Cap* {.preservesEmbedded.} = ref object of EmbeddedObj
    relay*: Facet
    target*: Entity
    attenuation*: Attenuation

  Ref* {.deprecated: "Ref was renamed to Cap".} = Cap

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

  Actor* = ref object
    name: string
    handleAllocator: ref Handle
      # a fresh actor gets a new ref Handle and
      # all actors spawned from it get the same ref.
    root: Facet
    exitReason: ref Exception
    exitHooks: seq[TurnAction]
    id: ActorId
    exiting, exited: bool
    when tracing:
      turnIdAllocator: ref TurnId
      traceStream: FileStream

  TurnAction* = proc (t: var Turn) {.closure.}

  Queues = TableRef[Facet, seq[TurnAction]]

  Turn* = object # an object that should remain on the stack
    facet: Facet
    queues: Queues # a ref object that can outlive Turn
    when tracing:
      desc: TurnDescription

  Facet* = ref FacetObj
  FacetObj = object
    actor*: Actor
    parent: Facet
    children: HashSet[Facet]
    outbound: OutboundTable
    shutdownActions: seq[TurnAction]
    inertCheckPreventers: int
    id: FacetId
    isAlive: bool

when tracing:

  proc nextTurnId(facet: Facet): TurnId =
    result = succ(facet.actor.turnIdAllocator[])
    facet.actor.turnIdAllocator[] = result

  proc trace(actor: Actor; act: ActorActivation) =
    if not actor.traceStream.isNil:
      var entry = TraceEntry(
          timestamp: getTime().toUnixFloat(),
          actor: initRecord("named", actor.name.toPreserves),
          item: act)
      actor.traceStream.writeText entry.toPreserves
      actor.traceStream.writeLine()

  proc path(facet: Facet): seq[trace.FacetId] =
    var f = facet
    while not f.isNil:
      result.add f.id.toPreserves
      f = f.parent

method publish*(e: Entity; turn: var Turn; v: AssertionRef; h: Handle) {.base.} = discard
method retract*(e: Entity; turn: var Turn; h: Handle) {.base.} = discard
method message*(e: Entity; turn: var Turn; v: AssertionRef) {.base.} = discard
method sync*(e: Entity; turn: var Turn; peer: Cap) {.base.} = discard

using
  actor: Actor
  facet: Facet
  turn: var Turn
  action: TurnAction

proc labels(f: Facet): string =
  proc catLabels(f: Facet; labels: var string) =
    labels.add ':'
    if not f.parent.isNil:
      catLabels(f.parent, labels)
      labels.add ':'
    when tracing:
      labels.add $f.id
  result.add f.actor.name
  catLabels(f, result)

proc `$`*(f: Facet): string =
  "<Facet:" & f.labels & ">"

proc `$`*(r: Cap): string =
  "<Ref:" & r.relay.labels & ">"

proc `$`*(actor: Actor): string =
  "<Actor:" & actor.name & ">" # TODO: ambigous

proc attenuate(r: Cap; a: Attenuation): Cap =
  if a.len == 0: result = r
  else: result = Cap(
    relay: r.relay,
    target: r.target,
    attenuation: a & r.attenuation)

proc hash*(facet): Hash =
  facet.id.hash

proc hash*(r: Cap): Hash = !$(r.relay.hash !& r.target.unsafeAddr.hash)

proc nextHandle(facet: Facet): Handle =
  result = succ(facet.actor.handleAllocator[])
  facet.actor.handleAllocator[] = result

proc facet*(turn: var Turn): Facet = turn.facet

proc enqueue(turn: var Turn; target: Facet; action: TurnAction) =
  if target in turn.queues:
    turn.queues[target].add action
  else:
    turn.queues[target] = @[action]

type Bindings = Table[Value, Value]

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.isFloat
      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*(a: Attenuation; v: Value): Value =
  result = v
  for stage in a:
    result = examineAlternatives(stage, result)
    if result.isFalse: break

proc publish(turn: var Turn; r: Cap; v: Value; h: Handle) =
  var a = runRewrites(r.attenuation, v)
  if not a.isFalse:
    let e = OutboundAssertion(handle: h, peer: r)
    turn.facet.outbound[h] = e
    enqueue(turn, r.relay) do (turn: var Turn):
      e.established = true
      publish(r.target, turn, AssertionRef(value: a), e.handle)
  when tracing:
    var act = ActionDescription(orKind: ActionDescriptionKind.enqueue)
    act.enqueue.event.target.actor = turn.facet.actor.id.toPreserves
    act.enqueue.event.target.facet = turn.facet.id.toPreserves
    act.enqueue.event.target.oid = r.target.oid.toPreserves
    act.enqueue.event.detail = trace.TurnEvent(orKind: TurnEventKind.assert)
    act.enqueue.event.detail.assert.assertion.value.value =
      mapEmbeds(v) do (cap: Value) -> Value: discard
    act.enqueue.event.detail.assert.handle = h
    turn.desc.actions.add act

proc publish*(turn: var Turn; r: Cap; a: Value): Handle {.discardable.} =
  result = turn.facet.nextHandle()
  publish(turn, r, a, result)

proc publish*[T](turn: var Turn; r: Cap; a: T): Handle {.discardable.} =
  publish(turn, r, a.toPreserves)

proc retract(turn: var Turn; e: OutboundAssertion) =
  enqueue(turn, e.peer.relay) do (turn: var Turn):
    if e.established:
      e.established = false
      e.peer.target.retract(turn, e.handle)

proc retract*(turn: var Turn; h: Handle) =
  var e: OutboundAssertion
  if turn.facet.outbound.pop(h, e):
    turn.retract(e)

proc message*(turn: var Turn; r: Cap; v: Value) =
  var a = runRewrites(r.attenuation, v)
  if not a.isFalse:
    enqueue(turn, r.relay) do (turn: var Turn):
      r.target.message(turn, AssertionRef(value: a))

proc message*[T](turn: var Turn; r: Cap; v: T) =
  message(turn, r, v.toPreserves)

proc sync(turn: var Turn; e: Entity; peer: Cap) =
  e.sync(turn, peer)

proc sync*(turn: var Turn; r, peer: Cap) =
  enqueue(turn, r.relay) do (turn: var Turn):
    sync(turn, r.target, peer)

proc replace*[T](turn: var Turn; cap: Cap; h: Handle; v: T): Handle =
  result = publish(turn, cap, v)
  if h != default(Handle):
    retract(turn, h)

proc replace*[T](turn: var Turn; cap: Cap; h: var Handle; v: T): Handle {.discardable.} =
  var old = h
  h = publish(turn, cap, v)
  if old != default(Handle):
    retract(turn, old)
  h

proc stop*(turn: var Turn)

proc run*(facet; action: TurnAction; zombieTurn = false)

proc newFacet(actor; parent: Facet; initialAssertions: OutboundTable): Facet =
  result = Facet(
    id: getMonoTime().ticks.FacetId,
    actor: actor,
    parent: parent,
    outbound: initialAssertions,
    isAlive: true)
  if not parent.isNil: parent.children.incl result

proc newFacet(actor; parent: Facet): Facet =
  var initialAssertions: OutboundTable
  newFacet(actor, parent, initialAssertions)

proc isInert(facet): bool =
  result = facet.children.len == 0 and
    (facet.outbound.len == 0 or facet.parent.isNil) and
    facet.inertCheckPreventers == 0

proc preventInertCheck*(facet): (proc()) {.discardable.} =
  var armed = true
  inc facet.inertCheckPreventers
  proc disarm() =
    if armed:
      armed = false
      dec facet.inertCheckPreventers
  result = disarm

proc inFacet(turn: var Turn; facet; act: TurnAction) =
  ## Call an action with a facet using a temporary `Turn`
  ## that shares the `Queues` of the calling `Turn`.
  var t = Turn(facet: facet, queues: turn.queues)
  act(t)

proc terminate(actor; turn; reason: ref Exception)

proc terminate(facet; turn: var Turn; orderly: bool) =
  if facet.isAlive:
    facet.isAlive = false
    let parent = facet.parent
    if not parent.isNil:
      parent.children.excl facet
    block:
      var turn = Turn(facet: facet, queues: turn.queues)
      while facet.children.len > 0:
        facet.children.pop.terminate(turn, orderly)
      if orderly:
        for act in facet.shutdownActions:
          act(turn)
      for a in facet.outbound.values: turn.retract(a)
      if orderly:
        if not parent.isNil:
          if parent.isInert:
            parent.terminate(turn, true)
        else:
          terminate(facet.actor, turn, nil)
    when tracing:
      var act = ActionDescription(orKind: ActionDescriptionKind.facetStop)
      act.facetstop.path = facet.path
      turn.desc.actions.add act

proc stopIfInertAfter(action: TurnAction): TurnAction =
  proc wrapper(turn: var Turn) =
    action(turn)
    enqueue(turn, turn.facet) do (turn: var Turn):
      if (not turn.facet.parent.isNil and
            (not turn.facet.parent.isAlive)) or
          turn.facet.isInert:
        stop(turn)
  wrapper

proc newFacet*(turn: var Turn): Facet = newFacet(turn.facet.actor, turn.facet)

proc inFacet*(turn: var Turn; bootProc: TurnAction): Facet =
  result = newFacet(turn)
  when tracing:
    var act = ActionDescription(orKind: ActionDescriptionKind.facetstart)
    act.facetstart.path.add result.path
    turn.desc.actions.add act
  inFacet(turn, result, stopIfInertAfter(bootProc))

proc facet*(turn: var Turn; bootProc: TurnAction): Facet {.deprecated.} = inFacet(turn, bootProc)

proc newActor(name: string; handleAlloc: ref Handle): Actor =
  let
    now = getTime()
    seed = now.toUnix * 1_000_000_000 + now.nanosecond
  result = Actor(
    name: name,
    id: ActorId(seed),
    handleAllocator: handleAlloc,
  )
  result.root = newFacet(result, nil)
  when tracing:
    var act = ActorActivation(orKind: ActorActivationKind.start)
    act.start.actorName = Name(orKind: NameKind.named)
    act.start.actorName.named.name = name.toPreserves
    trace(result, act)

proc run(actor; bootProc: TurnAction; initialAssertions: OutboundTable) =
  run(newFacet(actor, actor.root, initialAssertions), stopIfInertAfter(bootProc))

proc bootActor*(name: string; bootProc: TurnAction): Actor =
  var initialAssertions: OutboundTable
  result = newActor(name, new(ref Handle))
  when tracing:
    new result.turnIdAllocator
    let path = getEnv("SYNDICATE_TRACE_FILE", "/tmp/" & name & ".trace.pr")
    case path
    of "": stderr.writeLine "$SYNDICATE_TRACE_FILE unset, not tracing actor ", name
    of "-": result.traceStream = newFileStream(stderr)
    else: result.traceStream = openFileStream(path, fmWrite)
  run(result, bootProc, initialAssertions)

proc spawnActor*(name: string; turn: var Turn; bootProc: TurnAction; initialAssertions = initHashSet[Handle]()): Actor {.discardable.} =
  let actor = newActor(name, turn.facet.actor.handleAllocator)
  enqueue(turn, turn.facet) do (turn: var Turn):
    var newOutBound: Table[Handle, OutboundAssertion]
    for key in initialAssertions:
      discard turn.facet.outbound.pop(key, newOutbound[key])
    when tracing:
      actor.turnIdAllocator = turn.facet.actor.turnIdAllocator
      actor.traceStream = turn.facet.actor.traceStream
      var act = ActionDescription(orKind: ActionDescriptionKind.spawn)
      act.spawn.id = actor.id.toPreserves
      turn.desc.actions.add act
    run(actor, bootProc, newOutBound)
  actor

proc spawn*(name: string; turn: var Turn; bootProc: TurnAction; initialAssertions = initHashSet[Handle]()): Actor {.discardable.} =
  spawnActor(name, turn, bootProc, initialAssertions)

proc newInertCap*(): Cap =
  let a = bootActor("inert") do (turn: var Turn): turn.stop()
  Cap(relay: a.root)

proc atExit*(actor; action) = actor.exitHooks.add action

proc terminate(actor; turn; reason: ref Exception) =
  if not actor.exiting:
    actor.exiting = true
    actor.exitReason = reason
    when tracing:
      var act = ActorActivation(orKind: ActorActivationKind.stop)
      if not reason.isNil:
        act.stop.status = ExitStatus(orKind: ExitStatusKind.Error)
        act.stop.status.error.message = reason.msg
      trace(actor, act)
    for hook in actor.exitHooks: hook(turn)
    proc finish(turn: var Turn) =
      actor.root.terminate(turn, reason.isNil)
      actor.exited = true
    block:
      run(actor.root, finish, true)

proc terminate*(facet; e: ref Exception) =
  run(facet.actor.root) do (turn: var Turn):
    facet.actor.terminate(turn, e)

#[
proc asyncCheck*(facet: Facet; fut: FutureBase) =
  ## Sets a callback on `fut` which propagates exceptions to `facet`.
  addCallback(fut) do ():
    if fut.failed: terminate(facet, fut.error)

proc asyncCheck*(turn; fut: FutureBase) =
  ## Sets a callback on `fut` which propagates exceptions to the facet of `turn`.
  asyncCheck(turn.facet, fut)
]#

template tryFacet(facet; body: untyped) =
  try: body
  except CatchableError as err: terminate(facet, err)

proc run*(facet; action: TurnAction; zombieTurn = false) =
  if true and zombieTurn or (facet.actor.exitReason.isNil and facet.isAlive):
    tryFacet(facet):
      var queues = newTable[Facet, seq[TurnAction]]()
      block:
        var turn = Turn(facet: facet, queues: queues)
        action(turn)
        when tracing:
          turn.desc.id = facet.nextTurnId.toPreserves
          facet.actor.trace ActorActivation(
              orKind: ActorActivationKind.turn, turn: turn.desc)
      for facet, queue in queues:
        for action in queue: run(facet, action)

proc run*(cap: Cap; action: TurnAction) =
  ## Convenience proc to run a `TurnAction` in the scope of a `Cap`.
  run(cap.relay, action)

#[
proc addCallback*(fut: FutureBase; facet: Facet; act: TurnAction) =
  ## Add a callback to a `Future` that will be called at a later `Turn`
  ## within the context of `facet`.
  addCallback(fut) do ():
    if fut.failed: terminate(facet, fut.error)
    else:
      when tracing:
        run(facet) do (turn: var Turn):
          turn.desc.cause = TurnCause(orKind: TurnCauseKind.external)
          turn.desc.cause.external.description = "Future".toPreserves
          act(turn)
      else:
        run(facet, act)

proc addCallback*(fut: FutureBase; turn: var Turn; act: TurnAction) =
  ## Add a callback to a `Future` that will be called at a later `Turn`
  ## with the same context as the current.
  if fut.failed:
    terminate(turn.facet, fut.error)
  elif fut.finished:
    enqueue(turn, turn.facet, act)
  else:
    addCallback(fut, turn.facet, act)

proc addCallback*[T](fut: Future[T]; turn: var Turn; act: proc (t: var Turn, x: T) {.closure.}) =
  addCallback(fut, turn) do (turn: var Turn):
    if fut.failed: terminate(turn.facet, fut.error)
    else:
      when tracing:
        turn.desc.cause = TurnCause(orKind: TurnCauseKind.external)
        turn.desc.cause.external.description = "Future".toPreserves
      act(turn, read fut)
]#

proc stop*(turn: var Turn, facet: Facet) =
  if facet.parent.isNil:
      facet.terminate(turn, true)
  else:
    enqueue(turn, facet.parent) do (turn: var Turn):
      facet.terminate(turn, true)

proc stop*(turn: var Turn) =
  stop(turn, turn.facet)

proc onStop*(facet: Facet; act: TurnAction) =
  ## Add a `proc (turn: var Turn)` action to `facet` to be called as it stops.
  add(facet.shutdownActions, act)

proc stopActor*(facet: Facet) =
  run(facet) do (turn: var Turn):
    let actor = facet.actor
    enqueue(turn, actor.root) do (turn: var Turn):
      terminate(actor, turn, nil)

proc stopActor*(turn: var Turn) =
  stopActor(turn.facet)

proc stop*(actor: Actor) =
  stopActor(actor.root)

proc freshen*(turn: var Turn, act: TurnAction) =
  assert(turn.queues.len == 0, "Attempt to freshen a non-stale Turn")
  run(turn.facet, act)

proc newCap*(relay: Facet; e: Entity): Cap =
  Cap(relay: relay, target: e)

proc newCap*(turn; e: Entity): Cap =
  Cap(relay: turn.facet, target: e)

proc newCap*(e: Entity; turn): Cap =
  Cap(relay: turn.facet, target: e)

type SyncContinuation {.final.} = ref object of Entity
  action: TurnAction

method message(entity: SyncContinuation; turn: var Turn; v: AssertionRef) =
  entity.action(turn)

proc sync*(turn: var Turn; refer: Cap; act: TurnAction) =
  sync(turn, refer, newCap(turn, SyncContinuation(action: act)))

proc running*(actor): bool =
  result = not actor.exited
  if not (result or actor.exitReason.isNil):
    raise actor.exitReason