Add cost estimation wrapper

core/src/main/scala/caliban/wrappers/CostEstimation.scala

@@ -0,0 +1,257 @@
+package caliban.wrappers
+
+import caliban.CalibanError.ValidationError
+import caliban.InputValue.ListValue
+import caliban.ResponseValue.ObjectValue
+import caliban.Value.{ FloatValue, IntValue, StringValue }
+import caliban.execution.{ ExecutionRequest, Field }
+import caliban.parsing.adt.{ Directive, Document }
+import caliban.schema.Types
+import caliban.wrappers.Wrapper.{ EffectfulWrapper, OverallWrapper, ValidationWrapper }
+import caliban.{ CalibanError, GraphQLRequest, GraphQLResponse, ResponseValue }
+import zio.{ IO, Ref, UIO, URIO, ZIO }
+
+import scala.annotation.tailrec
+
+object CostEstimation {
+
+  final val COST_DIRECTIVE_NAME = "cost"
+  final val COST_EXTENSION_NAME = "queryCost"
+
+  /**
+   * A directive that can be applied to both fields and types to flag them as targets for cost analysis.
+   * This allows a simple estimation to be applied which can be used to prevent overly expensive queries from being executed
+   */
+  object CostDirective {
+    def apply(cost: Double): Directive =
+      Directive(COST_DIRECTIVE_NAME, arguments = Map("weight" -> FloatValue(cost)))
+
+    def apply(cost: Double, multipliers: List[String]): Directive =
+      Directive(
+        COST_DIRECTIVE_NAME,
+        arguments = Map("weight" -> FloatValue(cost), "multipliers" -> ListValue(multipliers.map(StringValue.apply)))
+      )
+  }
+
+  /**
+   * Computes field cost by examining the @cost directive. This can be used in conjunction with [[queryCost]] or [[maxCost]]
+   * In order to compute the estimated cost of executing a query.
+   *
+   * @note This will be executed *before* the actual resolvers are called, which allows you to stop potentially expensive queries
+   *       from being run, but may also require more work on the developer part to determine the correct heuristic for estimating field cost.
+   */
+  val costDirective = (f: Field) => {
+    def computeDirectiveCost(directives: List[Directive]) =
+      directives.collectFirst {
+        case d if d.name == COST_DIRECTIVE_NAME =>
+          // TODO should we support string backed formulas?
+          // TODO Support list arguments / multipliers
+          val weight = d.arguments
+            .get("weight")
+            .collect {
+              case i: IntValue   => i.toInt.toDouble
+              case f: FloatValue => f.toDouble
+            }
+            .getOrElse(1.0)
+
+          val multipliers = d.arguments
+            .get("multipliers")
+            .toList
+            .collect { case ListValue(values) =>
+              values.collect {
+                case StringValue(name) =>
+                  f.arguments.get(name).collectFirst {
+                    case i: IntValue   => i.toInt.toDouble
+                    case d: FloatValue => d.toDouble
+                  }
+                case _                 => None
+              }.flatten
+            }
+            .flatten
+            .sum[Double]
+            .max(1.0)
+
+          weight * multipliers
+      }
+
+    val directiveCost = computeDirectiveCost(f.directives)
+
+    val typeCost = Types
+      .innerType(f.fieldType)
+      .directives
+      .flatMap(computeDirectiveCost)
+
+    (directiveCost orElse typeCost).getOrElse(1.0)
+  }
+
+  /**
+   * Computes the estimated cost of the query based on the provided field cost function and adds it as an extension to the GraphQLResponse.
+   * This is useful for tracking the overall cost of a query either when you are trying to dial in a correct heuristic or when you
+   * want to inform users of your graph how expensive their queries are.
+   *
+   * @see queryCostWith, queryCostZIO
+   */
+  def queryCost(f: Field => Double): Wrapper[Any] = EffectfulWrapper(
+    Ref.make(0.0).map { cost =>
+      costWrapper(cost)(f) |+| costOverall(addCostToExtensions(cost))
+    }
+  )
+
+  /**
+   * Computes the estimated cost of the query based on the provided field cost function and passes it to the second function
+   * which can run an arbitrary side effect with the result.
+   *
+   * @see queryCost
+   */
+  def queryCostWith[R](f: Field => Double)(p: Double => URIO[R, Any]): Wrapper[R] = EffectfulWrapper(
+    Ref.make(0.0).map { cost =>
+      costWrapper(cost)(f) |+| costOverall(cost.get.flatMap(p) as _)
+    }
+  )
+
+  /**
+   * A more powerful version of [[queryCost]] which allows the field cost computation to return an effect instead of a plain value
+   * when computing the cost estimate.
+   * @param f The field cost estimate function
+   *
+   * @see queryCostZIOWith for a more powerful version
+   */
+  def queryCostZIO[R](f: Field => URIO[R, Double]): Wrapper[R] = EffectfulWrapper(
+    Ref.make(0.0).map { cost =>
+      costWrapperZIO(cost)(f) |+| costOverall[Any](addCostToExtensions(cost))
+    }
+  )
+
+  /**
+   * A more powerful version of [[queryCostZIO]] that allows the total result of the query to be pushed into a separate effect.
+   * This is useful when you want to compute the cost of the query but you already have your own system for recording the cost.
+   * @param f The field cost estimate function
+   * @param p A function which receives the total estimated cost of executing the query and can
+   */
+  def queryCostZIOWith[R](f: Field => URIO[R, Double])(p: Double => URIO[R, Any]): Wrapper[R] = EffectfulWrapper(
+    Ref.make(0.0).map { cost =>
+      costWrapperZIO(cost)(f) |+| costOverall(cost.get.flatMap(p) as _)
+    }
+  )
+
+  /**
+   * Computes the estimated cost of executing the query using the provided function and compares it to
+   * the `maxCost` parameter which determines the maximum allowable cost for a query.
+   *
+   * @param maxCost The maximum allowable cost for executing a query
+   * @param f The field cost estimate function
+   */
+  def maxCost(maxCost: Double)(f: Field => Double): ValidationWrapper[Any] =
+    maxCostOrError(maxCost)(f)(cost => ValidationError(s"Query costs too much: $cost. Max cost: $maxCost.", ""))
+
+  /**
+   * More powerful version of [[maxCost]] which allow you to also specify the error that is returned when the cost exceeds the maximum cost.
+   * @param maxCost The total cost allowed for any one query
+   * @param f The function used to evaluate the cost of a single field
+   * @param error A function that will be provided the total estimated cost and must return the error that will be returned
+   */
+  def maxCostOrError(maxCost: Double)(f: Field => Double)(error: Double => ValidationError): ValidationWrapper[Any] =
+    new ValidationWrapper[Any] {
+      override def wrap[R1 <: Any](
+        process: Document => ZIO[R1, ValidationError, ExecutionRequest]
+      ): Document => ZIO[R1, ValidationError, ExecutionRequest] =
+        (doc: Document) =>
+          for {
+            req <- process(doc)
+            cost = computeCost(req.field)(f)
+            _   <- IO.when(cost > maxCost)(IO.fail(error(cost)))
+          } yield req
+    }
+
+  /**
+   * More powerful version of [[maxCost]] which allows the field computation function to specify a function which returns an effectful computation
+   * for the cost of a field.
+   * @param maxCost The total cost allowed for any one query
+   * @param f The function used to evaluate the cost of a single field returning an effect which will result in the field cost as a double
+   */
+  def maxCostZIO[R](maxCost: Double)(f: Field => URIO[R, Double]): ValidationWrapper[R] =
+    new ValidationWrapper[R] {
+      override def wrap[R1 <: R](
+        process: Document => ZIO[R1, ValidationError, ExecutionRequest]
+      ): Document => ZIO[R1, ValidationError, ExecutionRequest] =
+        (doc: Document) =>
+          for {
+            req  <- process(doc)
+            cost <- computeCostZIO(req.field)(f)
+            _    <- IO.when(cost > maxCost)(
+                      IO.fail(ValidationError(s"Query costs too much: $cost. Max cost: $maxCost.", ""))
+                    )
+          } yield req
+    }
+
+  private def costWrapper(total: Ref[Double])(f: Field => Double): ValidationWrapper[Any] =
+    new ValidationWrapper[Any] {
+      override def wrap[R1 <: Any](
+        process: Document => ZIO[R1, ValidationError, ExecutionRequest]
+      ): Document => ZIO[R1, ValidationError, ExecutionRequest] =
+        (doc: Document) =>
+          for {
+            req <- process(doc)
+            _   <- total.set(computeCost(req.field)(f))
+          } yield req
+    }
+
+  private def costWrapperZIO[R](total: Ref[Double])(f: Field => URIO[R, Double]): ValidationWrapper[R] =
+    new ValidationWrapper[R] {
+      override def wrap[R1 <: R](
+        process: Document => ZIO[R1, ValidationError, ExecutionRequest]
+      ): Document => ZIO[R1, ValidationError, ExecutionRequest] =
+        (doc: Document) =>
+          for {
+            req <- process(doc)
+            _   <- computeCostZIO(req.field)(f) >>= total.set
+          } yield req
+    }
+
+  private def addCostToExtensions(
+    cost: Ref[Double]
+  )(resp: GraphQLResponse[CalibanError]): UIO[GraphQLResponse[CalibanError]] =
+    cost.get.map { total =>
+      resp.copy(
+        extensions = Some(
+          ObjectValue(
+            resp.extensions.foldLeft[List[(String, ResponseValue)]](
+              List(COST_EXTENSION_NAME -> FloatValue(total))
+            )(_ ++ _.fields)
+          )
+        )
+      )
+    }
+
+  private def costOverall[R](
+    f: GraphQLResponse[CalibanError] => URIO[R, GraphQLResponse[CalibanError]]
+  ): OverallWrapper[R] =
+    new OverallWrapper[R] {
+      override def wrap[R1 <: R](
+        process: GraphQLRequest => ZIO[R1, Nothing, GraphQLResponse[CalibanError]]
+      ): GraphQLRequest => ZIO[R1, Nothing, GraphQLResponse[CalibanError]] =
+        (req: GraphQLRequest) => process(req).flatMap(f)
+    }
+
+  private def computeCost(field: Field)(f: Field => Double): Double = {
+    @tailrec
+    def go(fields: List[Field], total: Double): Double = fields match {
+      case Nil          => total
+      case head :: tail => go(head.fields ++ tail, f(head) + total)
+    }
+
+    go(List(field), 0.0)
+  }
+
+  private def computeCostZIO[R](field: Field)(f: Field => URIO[R, Double]): URIO[R, Double] = {
+    @tailrec
+    def go(fields: List[Field], result: List[URIO[R, Double]]): List[URIO[R, Double]] = fields match {
+      case Nil          => result
+      case head :: tail =>
+        go(head.fields ++ tail, f(head) :: result)
+    }
+
+    URIO.mergeAllPar(go(List(field), Nil))(0.0)(_ + _)
+  }
+
+}