# SPDX-FileCopyrightText: ☭ 2021 Emery Hemingway
# SPDX-License-Identifier: Unlicense

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

export Handle

# proc `==`*(x, y: Handle): bool {.borrow.}

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

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

#[
proc genId(T: type): T =
  getMonotime().ticks.T
]#

type
  Attenuation = sturdy.Attenuation[Ref]
  Oid = sturdy.Oid
  Assertion* = protocol.Assertion[Ref]
  Caveat = sturdy.Caveat[Ref]
  Rewrite = sturdy.Rewrite[Ref]

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

  Ref* {.unpreservable.} = ref object # TODO: rename
    relay*: Facet
    target*: Entity
    attenuation*: Attenuation

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

  Actor* = ref object
    future: Future[void]
    name: string
    id: ActorId
    handleAllocator: Handle
    root: Facet
    exitReason: ref Exception
    exitHooks: seq[TurnAction]
    exiting: bool

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

  Queues = TableRef[Facet, seq[TurnAction]]

  Turn* = object # an object that should remain on the stack
    id: TurnId
    facet: Facet
    queues: Queues # a ref object that can outlive Turn

  ParentFacet = Option[Facet]

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

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

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

proc labels(f: Facet): string =
  proc catLabels(f: Facet; labels: var string) =
    labels.add ':'
    if f.parent.isSome:
      catLabels(f.parent.get, labels)
      labels.add ':'
    labels.add $f.id
  result.add f.actor.name
  catLabels(f, result)

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

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

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

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

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

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

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

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[Preserve[Ref], Preserve[Ref]]

proc match(bindings: var Bindings; p: Pattern; v: Assertion): bool =
  case p.orKind
  of PatternKind.Pdiscard: result = true
  of PatternKind.Patom:
    result = case p.patom
      of PAtom.Boolean: v.isBoolean
      of PAtom.Float: v.isFloat
      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[toPreserve(p.pbind.pattern, Ref)] = 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 = v[key]
          if vv.isFalse or not match(bindings, pp, vv):
            result = true
            break

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

proc instantiate(t: Template; bindings: Bindings): Assertion =
  case t.orKind
  of TemplateKind.Tattenuate:
    let v = instantiate(t.tattenuate.template, bindings)
    if not v.isEmbedded:
      raise newException(ValueError, "Attempt to attenuate non-capability")
    result = embed(attenuate(v.embed, t.tattenuate.attenuation))
  of TemplateKind.TRef:
    let n = $t.tref.binding
    try: result = bindings[toPreserve(n, Ref)]
    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[Ref](t.tcompound.arr.items.len)
      for i, tt in t.tcompound.arr.items:
        result[i] = instantiate(tt, bindings)
    of TCompoundKind.dict:
      result = initDictionary[Ref]()
      for key, tt in t.tcompound.dict.entries:
        result[key] = instantiate(tt, bindings)

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

proc examineAlternatives(cav: Caveat; v: Assertion): Assertion =
  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

proc runRewrites*(a: Attenuation; v: Assertion): Assertion =
  result = v
  for stage in a:
    result = examineAlternatives(stage, result)
    if result.isFalse: break

proc publish(turn: var Turn; r: Ref; v: Assertion; h: Handle) =
  let a = runRewrites(r.attenuation, v)
  if not a.isFalse:
    let e = OutboundAssertion(
      handle: h, peer: r, established: false)
    turn.facet.outbound[h] = e
    enqueue(turn, r.relay) do (turn: var Turn):
      e.established = true
      publish(r.target, turn, a, e.handle)

proc publish*(turn: var Turn; r: Ref; a: Assertion): Handle =
  result = turn.facet.nextHandle()
  publish(turn, r, a, result)

proc publish*[T](turn: var Turn; r: Ref; a: T): Handle =
  publish(turn, r, toPreserve(a, Ref))

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: Ref; v: Assertion) =
  let a = runRewrites(r.attenuation, v)
  if not a.isFalse:
    enqueue(turn, r.relay) do (turn: var Turn):
      r.target.message(turn, a)

proc message*[T](turn: var Turn; r: Ref; v: T) =
  message(turn, r, toPreserve(v, Ref))

proc sync(turn: var Turn; e: Entity; peer: Ref) =
  e.sync(turn, peer)
  # or turn.message(peer, true) ?

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

proc replace*[T](turn: var Turn; `ref`: Ref; h: Handle; v: T): Handle =
  result = publish(turn, `ref`, v)
  retract(turn, h)

proc stop*(turn: var Turn) {.gcsafe.}

proc run*(facet; action: TurnAction; zombieTurn = false) {.gcsafe.}

proc newFacet(actor; parent: ParentFacet; initialAssertions: OutboundTable): Facet =
  result = Facet(
    id: getMonoTime().ticks.FacetId,
    actor: actor,
    parent: parent,
    outbound: initialAssertions,
    isAlive: true)
  if parent.isSome: parent.get.children.incl result

proc newFacet(actor; parent: ParentFacet): 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.isNone) and
    facet.inertCheckPreventers == 0

proc preventInertCheck*(facet): (proc() {.gcsafe.}) {.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) {.gcsafe.}

proc terminate(facet; turn: var Turn; orderly: bool) {.gcsafe.} =
  if facet.isAlive:
    facet.isAlive = false
    let parent = facet.parent
    if parent.isSome:
      parent.get.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 parent.isSome:
          if parent.get.isInert:
            parent.get.terminate(turn, true)
        else:
          terminate(facet.actor, turn, nil)

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

proc facet*(turn: var Turn; bootProc: TurnAction): Facet =
  result = newFacet(turn.facet.actor, some turn.facet)
  inFacet(turn, result, stopIfInertAfter(bootProc))

proc newActor(name: string; bootProc: TurnAction; initialAssertions: OutboundTable): Actor =
  let
    now = getTime()
    seed = now.toUnix * 1_000_000_000 + now.nanosecond
  result = Actor(
    name: name,
    id: ActorId(seed))
  result.root = newFacet(result, none Facet)
  result.future = newFuture[void]($result)
  run(
    newFacet(result, some result.root, initialAssertions),
    stopIfInertAfter(bootProc))

proc bootActor*(name: string; bootProc: TurnAction): Actor =
  var initialAssertions: OutboundTable
  newActor(name, bootProc, initialAssertions)

proc spawn*(name: string; turn: var Turn; bootProc: TurnAction; initialAssertions = initHashSet[Handle]()) =
  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])
    callSoon:
      discard newActor(name, bootProc, newOutBound)

proc newInertRef*(): Ref =
  let a = bootActor("inert") do (turn: var Turn): turn.stop()
  Ref(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
    for hook in actor.exitHooks: hook(turn)
    proc finish(turn: var Turn) =
      actor.root.terminate(turn, not reason.isNil)
      if reason.isNil:
        actor.future.complete()
      else:
        actor.future.fail reason
    callSoon:
      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*(turn; fut: FutureBase) =
  let facet = turn.facet
  fut.addCallback do ():
    if fut.failed: terminate(facet, fut.error)

template tryFacet(facet; body: untyped) =
  body
  # TODO
  #try: body
  #except: terminate(facet, getCurrentException())

proc run(queues: Queues) =
  callSoon:
    for facet, queue in queues:
      for action in queue: run(facet, action)

proc run*(facet; action: TurnAction; zombieTurn = false) =
  if not zombieTurn:
    if not facet.actor.exitReason.isNil: return
    if not facet.isAlive: return
    # TODO: not Nim idiom
  tryFacet(facet):
    var turn = Turn(
      facet: facet,
      queues: newTable[Facet, seq[TurnAction]]())
    action(turn)
    run(turn.queues)

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

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

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

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

proc newRef*(relay: Facet; e: Entity): Ref =
  Ref(relay: relay, target: e)

proc newRef*(turn; e: Entity): Ref =
  Ref(relay: turn.facet, target: e)

proc sync*(turn, refer: Ref, cb: proc(t: Turn) {.gcsafe.}) =
  discard # TODO

proc runActor*(name: string; bootProc: TurnAction): Future[void] =
  bootActor(name, bootProc).future