# SPDX-License-Identifier: ISC

import preserves, preserves/records

import ./assertions, ./dataspaces, ./events, ./skeletons
import std/[asyncdispatch, macros, options]

export assertions.Capture
export assertions.Discard
export assertions.Observe
export dataspaces.Facet
export dataspaces.FieldId
export dataspaces.Fields
export dataspaces.addEndpoint
export dataspaces.defineObservableProperty
export dataspaces.generateId
export dataspaces.hash
export dataspaces.recordDamage
export dataspaces.recordObservation
export dataspaces.scheduleScript
export events.EventKind
export skeletons.Analysis

export asyncdispatch.`callback=`

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

proc newLit(p: pointer): NimNode = ident"nil"
  ## Hack to make `newLit` work on `Presevere`.

proc getCurrentFacet*(): Facet =
  ## Return the current `Facet` for this context.
  raiseAssert "getCurrentFacet called outside of a Syndicate context"

template stopIf*(cond, body: untyped): untyped =
  ## Stop the current facet if `cond` is true and
  ## invoke `body` after the facet has stopped.
  mixin getCurrentFacet
  discard getCurrentFacet().addDataflow do (facet: Facet):
    if cond:
      facet.stop do (facet: Facet):
        body

template send*(class: RecordClass; fields: varargs[Preserve,
    toPreserve]): untyped =
  mixin getCurrentFacet
  send(getCurrentFacet(), init(class, fields))

proc assertionForRecord(class: RecordClass; doHandler: NimNode): NimNode =
  ## Generate an assertion that captures or discards the items of record `class`
  ## according to the parameters of `doHandler`. `_` parameters are discarded.
  let formalArgs = doHandler[3]
  if formalArgs.len.pred != class.arity:
    error($formalArgs.repr & " does not match record class " & $class, doHandler)
  result = newCall("init", newLit(class))
  for i, arg in formalArgs:
    if i > 0:
      arg.expectKind nnkIdentDefs
      if arg[0] == ident"_":
        result.add newCall("init", ident"Discard")
      else:
        result.add newCall("init", ident"Capture", newCall("init",
            ident"Discard"))

proc callbackForEvent(event: EventKind; class: RecordClass; doHandler: NimNode;
    assertion: NimNode): NimNode =
  ## Generate a procedure that checks an event kind, unpacks the fields of `class` to match the
  ## parameters of `doHandler`, and calls the body of `doHandler`.
  # TODO: the assertion parameter is just for tracing.
  let formalArgs = doHandler[3]
  if formalArgs.len.pred != class.arity:
    error($formalArgs.repr & " does not match record class " & $class, doHandler)
  doHandler.expectKind nnkDo
  let
    cbFacetSym = genSym(nskParam, "facet")
    scriptFacetSym = genSym(nskParam, "facet")
    eventSym = genSym(nskParam, "event")
    recSym = genSym(nskParam, "record")
  var
    letSection = newNimNode(nnkLetSection, doHandler)
    captureCount: int
  for i, arg in formalArgs:
    if i > 0:
      arg.expectKind nnkIdentDefs
      if arg[0] == ident"_" or arg[0] == ident"*":
        if arg[1].kind != nnkEmpty:
          error("placeholders may not be typed", arg)
      else:
        if arg[1].kind == nnkEmpty:
          error("type required for capture", arg)
        var letDef = newNimNode(nnkIdentDefs, arg)
        arg.copyChildrenTo letDef
        letDef[2] = newCall("preserveTo",
            newNimNode(nnkBracketExpr).add(recSym, newLit(pred i)),
            letDef[1])
        letSection.add(letDef)
        inc(captureCount)
  let script = newProc(
    # the script scheduled by the callback when the event is matched
    name = genSym(nskProc, "script"),
    params = [
      newEmptyNode(),
        newIdentDefs(scriptFacetSym, ident"Facet"),
    ],
    body = newStmtList(
      newCall("assert",
          infix(newCall("len", recSym), "==", newLit(captureCount))),
      letSection,
      doHandler[6]
    )
  )
  newProc(
    # the event handler that is called when an assertion matches
    name = genSym(nskProc, "event_handler"),
    params = [
      newEmptyNode(),
      newIdentDefs(cbFacetSym, ident"Facet"),
      newIdentDefs(eventSym, ident"EventKind"),
      newIdentDefs(recSym, newNimNode(nnkBracketExpr).add(ident"seq",
          ident"Preserve")),
    ],
    body = newStmtList(
      newIfStmt((cond: infix(eventSym, "==", newLit(event)), body:
      newStmtList(
          script,
          newCall("scheduleScript", cbFacetSym, script[0])
        )))))
      # TODO: this proc just checks the event type and then schedules a script,
      # should the event check be done in skeletons instead?

proc onEvent(event: EventKind; class: RecordClass; doHandler: NimNode): NimNode =
  let
    assertion = assertionForRecord(class, doHandler)
    handler = callbackForEvent(event, class, doHandler, assertion)
    handlerSym = handler[0]
  result = quote do:
    `handler`
    mixin getCurrentFacet
    discard getCurrentFacet().addEndpoint do (facet: Facet) -> EndpointSpec:
      let a = `assertion`
      result.assertion = some(init(Observe, a))
      result.analysis = some(analyzeAssertion(a))
      result.analysis.get.callback = wrap(facet, `handlerSym`)

macro onAsserted*(class: static[RecordClass]; doHandler: untyped) =
  onEvent(addedEvent, class, doHandler)

macro onRetracted*(class: static[RecordClass]; doHandler: untyped) =
  onEvent(removedEvent, class, doHandler)

macro onMessage*(class: static[RecordClass]; doHandler: untyped) =
  onEvent(messageEvent, class, doHandler)

template assert*(class: RecordClass; field: untyped): untyped =
  mixin getCurrentFacet
  let facet = getCurrentFacet()
  discard facet.addEndpoint do (facet: Facet) -> EndpointSpec:
    let a = init(class, getPreserve(field))
    result.assertion = some(a)

template field*(F: untyped; T: typedesc; initial: T): untyped =
  ## Declare a field. The identifier `F` shall be a value with
  ## `get` and `set` procs.
  mixin getCurrentFacet
  declareField(getCurrentFacet(), F, T, initial)
    # use the template defined in dataspaces

template spawn*(name: string; spawnBody: untyped): untyped =
  mixin getCurrentFacet
  spawn(getCurrentFacet(), name) do (spawnFacet: Facet):
    proc getCurrentFacet(): Facet {.inject.} = spawnFacet
    spawnBody

template syndicate*(name: string; dataspaceBody: untyped): untyped =
  proc bootProc(rootFacet: Facet) =
    proc getCurrentFacet(): Facet {.inject.} = rootFacet
    dataspaceBody
  waitFor bootModule(name, bootProc)