package sbt

	import Def.ScopedKey
	import Types.Id
	import Keys.sessionVars
	import sbinary.{Format, Operations}

object SessionVar
{
	val DefaultDataID = "data"

	// these are required because of inference+manifest limitations
	final case class Key[T](key: ScopedKey[Task[T]])
	final case class Map(map: IMap[Key, Id]) {
		def get[T](k: ScopedKey[Task[T]]): Option[T] = map get Key(k)
		def put[T](k: ScopedKey[Task[T]], v: T): Map = Map(map put (Key(k), v))
	}
	def emptyMap = Map(IMap.empty)

	def persistAndSet[T](key: ScopedKey[Task[T]], state: State, value: T)(implicit f: sbinary.Format[T]): State =
	{
		persist(key, state, value)(f)
		set(key, state, value)
	}

	def persist[T](key: ScopedKey[Task[T]], state: State, value: T)(implicit f: sbinary.Format[T]): Unit =
		Project.structure(state).streams(state).use(key)( s =>
			Operations.write(s.binary(DefaultDataID), value)(f)
		)

	def clear(s: State): State  =  s.put(sessionVars, SessionVar.emptyMap)

	def get[T](key: ScopedKey[Task[T]], state: State): Option[T] = orEmpty(state get sessionVars) get key

	def set[T](key: ScopedKey[Task[T]], state: State, value: T): State = state.update(sessionVars)(om => orEmpty(om) put (key, value))

	def orEmpty(opt: Option[Map]) = opt getOrElse emptyMap

	def transform[S](task: Task[S], f: (State, S) => State): Task[S] =
	{
		val g = (s: S, map: AttributeMap) => map.put(Keys.transformState, (state: State) => f(state, s))
		task.copy(info = task.info.postTransform(g))
	}

	def resolveContext[T](key: ScopedKey[Task[T]], context: Scope, state: State): ScopedKey[Task[T]] =
	{
		val subScope = Scope.replaceThis(context)(key.scope)
		val scope = Project.structure(state).data.definingScope(subScope, key.key) getOrElse subScope
		ScopedKey(scope, key.key)
	}

	def read[T](key: ScopedKey[Task[T]], state: State)(implicit f: Format[T]): Option[T] =
		Project.structure(state).streams(state).use(key) { s =>
			try { Some(Operations.read(s.readBinary(key, DefaultDataID))) }
			catch { case e: Exception => None }
		}

	def load[T](key: ScopedKey[Task[T]], state: State)(implicit f: Format[T]): Option[T] =
		get(key, state) orElse read(key, state)(f)

	def loadAndSet[T](key: ScopedKey[Task[T]], state: State, setIfUnset: Boolean = true)(implicit f: Format[T]): (State, Option[T]) =
		get(key, state) match {
			case s: Some[T] => (state, s)
			case None => read(key, state)(f) match {
				case s @ Some(t) =>
					val newState = if(setIfUnset && get(key, state).isDefined) state else set(key, state, t)
					(newState, s)
				case None => (state, None)
			}
		}
}
