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/*
* Copyright 2019-2024 John A. De Goes and the ZIO Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package zio.test
import zio.stacktracer.TracingImplicits.disableAutoTrace
import zio.stream.ZStream
import zio.{ZIO, Zippable, Trace}
/**
* A sample is a single observation from a random variable, together with a tree
* of "shrinkings" used for minimization of "large" failures.
*/
final case class Sample[-R, +A](value: A, shrink: ZStream[R, Nothing, Sample[R, A]]) { self =>
/**
* A symbolic alias for `zip`.
*/
def <*>[R1 <: R, B](
that: Sample[R1, B]
)(implicit zippable: Zippable[A, B], trace: Trace): Sample[R1, zippable.Out] =
self.zip(that)
/**
* Filters this sample by replacing it with its shrink tree if the value does
* not meet the specified predicate and recursively filtering the shrink tree.
*/
def filter(f: A => Boolean)(implicit trace: Trace): ZStream[R, Nothing, Sample[R, A]] =
if (f(value)) ZStream(Sample(value, shrink.flatMap(_.filter(f))))
else shrink.flatMap(_.filter(f))
def flatMap[R1 <: R, B](f: A => Sample[R1, B])(implicit trace: Trace): Sample[R1, B] = {
val sample = f(value)
Sample(sample.value, sample.shrink ++ shrink.map(_.flatMap(f)))
}
def foreach[R1 <: R, B](f: A => ZIO[R1, Nothing, B])(implicit trace: Trace): ZIO[R1, Nothing, Sample[R1, B]] =
f(value).map(Sample(_, shrink.mapZIO(_.foreach(f))))
def map[B](f: A => B)(implicit trace: Trace): Sample[R, B] =
Sample(f(value), shrink.map(_.map(f)))
/**
* Converts the shrink tree into a stream of shrinkings by recursively
* searching the shrink tree, using the specified function to determine
* whether a value is a failure. The resulting stream will contain all values
* explored, regardless of whether they are successes or failures.
*/
def shrinkSearch(f: A => Boolean)(implicit trace: Trace): ZStream[R, Nothing, A] =
if (!f(value))
ZStream(value)
else
ZStream(value) ++ shrink.takeUntil(v => f(v.value)).flatMap(_.shrinkSearch(f))
/**
* Composes this sample with the specified sample to create a cartesian
* product of values and shrinkings.
*/
def zip[R1 <: R, B](
that: Sample[R1, B]
)(implicit zippable: Zippable[A, B], trace: Trace): Sample[R1, zippable.Out] =
self.zipWith(that)(zippable.zip(_, _))
/**
* Composes this sample with the specified sample to create a cartesian
* product of values and shrinkings with the specified function.
*/
def zipWith[R1 <: R, B, C](that: Sample[R1, B])(f: (A, B) => C)(implicit trace: Trace): Sample[R1, C] =
self.flatMap(a => that.map(b => f(a, b)))
}
object Sample {
/**
* A sample without shrinking.
*/
def noShrink[A](a: A)(implicit trace: Trace): Sample[Any, A] =
Sample(a, ZStream.empty)
def shrinkFractional[A](smallest: A)(a: A)(implicit F: Fractional[A], trace: Trace): Sample[Any, A] =
Sample.unfold(a) { max =>
(
max,
ZStream.unfold(smallest) { min =>
val mid = F.plus(min, F.div(F.minus(max, min), F.fromInt(2)))
if (mid == max) None
else if (F.toDouble(F.abs(F.minus(max, mid))) < 0.001) Some((min, max))
else Some((mid, mid))
}
)
}
def shrinkIntegral[A](smallest: A)(a: A)(implicit I: Integral[A], trace: Trace): Sample[Any, A] =
Sample.unfold(a) { max =>
(
max,
ZStream.unfold(smallest) { min =>
val mid = I.plus(min, I.quot(I.minus(max, min), I.fromInt(2)))
if (mid == max) None
else if (I.equiv(I.abs(I.minus(max, mid)), I.one)) Some((mid, max))
else Some((mid, mid))
}
)
}
def unfold[R, A, S](s: S)(f: S => (A, ZStream[R, Nothing, S]))(implicit trace: Trace): Sample[R, A] = {
val (value, shrink) = f(s)
Sample(value, shrink.map(unfold(_)(f)))
}
}
