113 lines
3.0 KiB
Nim
113 lines
3.0 KiB
Nim
import std/sugar
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import pkg/questionable
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import pkg/chronos
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import pkg/chronicles
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import pkg/upraises
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import ./trackedfutures
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import ./then
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push: {.upraises:[].}
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type
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Machine* = ref object of RootObj
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state: State
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running: Future[void]
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scheduled: AsyncQueue[Event]
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started: bool
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trackedFutures: TrackedFutures
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State* = ref object of RootObj
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Query*[T] = proc(state: State): T
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Event* = proc(state: State): ?State {.gcsafe, upraises:[].}
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logScope:
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topics = "statemachine"
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proc new*[T: Machine](_: type T): T =
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T(trackedFutures: TrackedFutures.new())
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method `$`*(state: State): string {.base.} =
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raiseAssert "not implemented"
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proc transition(_: type Event, previous, next: State): Event =
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return proc (state: State): ?State =
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if state == previous:
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return some next
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proc query*[T](machine: Machine, query: Query[T]): ?T =
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if machine.state.isNil:
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none T
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else:
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some query(machine.state)
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proc schedule*(machine: Machine, event: Event) =
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if not machine.started:
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return
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try:
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machine.scheduled.putNoWait(event)
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except AsyncQueueFullError:
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raiseAssert "unlimited queue is full?!"
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method run*(state: State, machine: Machine): Future[?State] {.base, async.} =
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discard
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method onError*(state: State, error: ref CatchableError): ?State {.base.} =
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raise (ref Defect)(msg: "error in state machine: " & error.msg, parent: error)
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proc onError(machine: Machine, error: ref CatchableError): Event =
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return proc (state: State): ?State =
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state.onError(error)
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proc run(machine: Machine, state: State) {.async.} =
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try:
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if next =? await state.run(machine):
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machine.schedule(Event.transition(state, next))
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except CancelledError:
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discard
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proc scheduler(machine: Machine) {.async.} =
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var running: Future[void]
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try:
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while machine.started:
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let event = await machine.scheduled.get().track(machine)
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if next =? event(machine.state):
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if not running.isNil and not running.finished:
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await running.cancelAndWait()
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let fromState = if machine.state.isNil: "<none>" else: $machine.state
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machine.state = next
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debug "enter state", state = machine.state, fromState
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running = machine.run(machine.state)
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running
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.track(machine)
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.catch((err: ref CatchableError) =>
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machine.schedule(machine.onError(err))
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)
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except CancelledError:
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discard
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proc start*(machine: Machine, initialState: State) =
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if machine.started:
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return
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if machine.scheduled.isNil:
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machine.scheduled = newAsyncQueue[Event]()
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machine.started = true
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machine.scheduler()
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.track(machine)
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.catch((err: ref CatchableError) =>
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error("Error in scheduler", error = err.msg)
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)
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machine.schedule(Event.transition(machine.state, initialState))
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proc stop*(machine: Machine) {.async.} =
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if not machine.started:
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return
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trace "stopping state machine"
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machine.started = false
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await machine.trackedFutures.cancelTracked()
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machine.state = nil
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