@effect-ts/system/_src/Cause/core.ts

Effect-TS is a zero dependency set of libraries to write highly productive, purely functional TypeScript at scale.

// ets_tracing: off

/* eslint-disable prefer-const */
import * as A from "../Collections/Immutable/Array/index.js"
import * as E from "../Either/index.js"
import type { FiberID } from "../Fiber/id.js"
import type { Trace } from "../Fiber/index.js"
import { identity, pipe } from "../Function/index.js"
import * as S from "../IO/index.js"
import * as O from "../Option/index.js"
import { Stack } from "../Stack/index.js"
import type { Both, Cause, Then, Traced } from "./cause.js"
import { combinePar, combineSeq, die, empty, fail, interrupt, traced } from "./cause.js"
import { InterruptedException } from "./errors.js"

export {
  combinePar,
  Cause,
  die,
  empty,
  fail,
  interrupt,
  combineSeq,
  traced,
  isEmpty
} from "./cause.js"

/**
 * Applicative's ap
 */
export function ap<A>(fa: Cause<A>): <B>(fab: Cause<(a: A) => B>) => Cause<B> {
  return chain((f) => pipe(fa, map(f)))
}

/**
 * Substitute the E in the cause
 */
export function as<E1>(e: E1) {
  return map(() => e)
}

/**
 * Builds a Cause depending on the result of another
 */
export function chain_<E, E1>(cause: Cause<E>, f: (_: E) => Cause<E1>): Cause<E1> {
  return S.run(chainSafe_(cause, f))
}

/**
 * Builds a Cause depending on the result of another
 */
export function chain<E, E1>(f: (_: E) => Cause<E1>) {
  return (cause: Cause<E>): Cause<E1> => chain_(cause, f)
}

/**
 * Builds a Cause depending on the result of another
 */
export function chainSafe_<E, E1>(
  cause: Cause<E>,
  f: (_: E) => Cause<E1>
): S.IO<Cause<E1>> {
  switch (cause._tag) {
    case "Empty": {
      return S.succeed(empty)
    }
    case "Fail": {
      return S.succeed(f(cause.value))
    }
    case "Die": {
      return S.succeed(cause)
    }
    case "Interrupt": {
      return S.succeed(cause)
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => chainSafe_(cause.left, f)),
        S.suspend(() => chainSafe_(cause.right, f)),
        (l, r) => combineSeq(l, r)
      )
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => chainSafe_(cause.left, f)),
        S.suspend(() => chainSafe_(cause.right, f)),
        (l, r) => combinePar(l, r)
      )
    }
    case "Traced": {
      return S.map_(chainSafe_(cause.cause, f), (x) => traced(x, cause.trace))
    }
  }
}

/**
 * Equivalent to chain((a) => Fail(f(a)))
 */
export function map_<E, E1>(cause: Cause<E>, f: (e: E) => E1) {
  return chain_(cause, (e: E) => fail(f(e)))
}

/**
 * Equivalent to chain((a) => Fail(f(a)))
 */
export function map<E, E1>(f: (e: E) => E1) {
  return (cause: Cause<E>) => map_(cause, f)
}

/**
 * Determines if this cause contains or is equal to the specified cause.
 */
export function contains<E, E1 extends E = E>(that: Cause<E1>) {
  return (cause: Cause<E>) => S.run(containsSafe(that)(cause))
}

/**
 * Determines if this cause contains or is equal to the specified cause.
 */
export function containsSafe<E, E1 extends E = E>(that: Cause<E1>) {
  return (cause: Cause<E>) =>
    S.gen(function* (_) {
      if (yield* _(cause.equalsSafe(that))) {
        return true
      }
      return yield* _(
        pipe(
          cause,
          reduceLeft(S.succeed(false))((_, c) =>
            O.some(S.chain_(_, (b) => (b ? S.succeed(b) : c.equalsSafe(that))))
          )
        )
      )
    })
}

/**
 * Extracts a list of non-recoverable errors from the `Cause`.
 */
export function defects<E>(cause: Cause<E>): readonly unknown[] {
  return pipe(
    cause,
    reduceLeft<readonly unknown[]>([])((a, c) =>
      c._tag === "Die" ? O.some([...a, c.value]) : O.none
    )
  )
}

/**
 * Returns the `Error` associated with the first `Die` in this `Cause` if
 * one exists.
 */
export function dieOption<E>(cause: Cause<E>) {
  return pipe(
    cause,
    find((c) => (c._tag === "Die" ? O.some(c.value) : O.none))
  )
}

/**
 * Returns if a cause contains a defect
 */
export function died<E>(cause: Cause<E>) {
  return pipe(
    cause,
    dieOption,
    O.map(() => true),
    O.getOrElse(() => false)
  )
}

/**
 * Returns the `E` associated with the first `Fail` in this `Cause` if one
 * exists.
 */
export function failureOption<E>(cause: Cause<E>) {
  return pipe(
    cause,
    find((c) => (c._tag === "Fail" ? O.some(c.value) : O.none))
  )
}

/**
 * Returns if the cause has a failure in it
 */
export function failed<E>(cause: Cause<E>) {
  return pipe(
    cause,
    failureOption,
    O.map(() => true),
    O.getOrElse(() => false)
  )
}

/**
 * Retrieve the first checked error on the `Left` if available,
 * if there are no checked errors return the rest of the `Cause`
 * that is known to contain only `Die` or `Interrupt` causes.
 * */
export function failureOrCause<E>(cause: Cause<E>): E.Either<E, Cause<never>> {
  return pipe(
    cause,
    failureOption,
    O.map(E.left),
    O.getOrElse(() => E.right(cause as Cause<never>)) // no E inside this cause, can safely cast
  )
}

/**
 * Produces a list of all recoverable errors `E` in the `Cause`.
 */
export function failures<E>(cause: Cause<E>) {
  return pipe(
    cause,
    reduceLeft<readonly E[]>([])((a, c) =>
      c._tag === "Fail" ? O.some([...a, c.value]) : O.none
    )
  )
}

/**
 * Remove all `Die` causes that the specified partial function is defined at,
 * returning `Some` with the remaining causes or `None` if there are no
 * remaining causes.
 */
export function stripSomeDefects(f: (_: unknown) => O.Option<unknown>) {
  return <E>(cause: Cause<E>): O.Option<Cause<E>> => {
    return S.run(stripSomeDefectsSafe(cause, f))
  }
}

/**
 * Remove all `Die` causes that the specified partial function is defined at,
 * returning `Some` with the remaining causes or `None` if there are no
 * remaining causes.
 */
export function stripSomeDefects_<E>(
  cause: Cause<E>,
  f: (_: unknown) => O.Option<unknown>
): O.Option<Cause<E>> {
  return S.run(stripSomeDefectsSafe(cause, f))
}

/**
 * Filter out all `Die` causes according to the specified function,
 * returning `Some` with the remaining causes or `None` if there are no
 * remaining causes.
 */
export function stripSomeDefectsSafe<E>(
  cause: Cause<E>,
  f: (_: unknown) => O.Option<unknown>
): S.IO<O.Option<Cause<E>>> {
  switch (cause._tag) {
    case "Empty": {
      return S.succeed(O.none)
    }
    case "Interrupt": {
      return S.succeed(O.some(cause))
    }
    case "Fail": {
      return S.succeed(O.some(cause))
    }
    case "Die": {
      return S.succeed(O.map_(f(cause.value), die))
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => stripSomeDefectsSafe(cause.left, f)),
        S.suspend(() => stripSomeDefectsSafe(cause.right, f)),
        (l, r) => {
          if (l._tag === "Some" && r._tag === "Some") {
            return O.some(combinePar(l.value, r.value))
          } else if (l._tag === "Some") {
            return l
          } else if (r._tag === "Some") {
            return r
          } else {
            return O.none
          }
        }
      )
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => stripSomeDefectsSafe(cause.left, f)),
        S.suspend(() => stripSomeDefectsSafe(cause.right, f)),
        (l, r) => {
          if (l._tag === "Some" && r._tag === "Some") {
            return O.some(combineSeq(l.value, r.value))
          } else if (l._tag === "Some") {
            return l
          } else if (r._tag === "Some") {
            return r
          } else {
            return O.none
          }
        }
      )
    }
    case "Traced": {
      return S.suspend(() => stripSomeDefectsSafe(cause.cause, f))
    }
  }
}

/**
 * Finds the first result matching f
 */
export function find<Z, E>(
  f: (cause: Cause<E>) => O.Option<Z>
): (cause: Cause<E>) => O.Option<Z> {
  return (cause) => S.run(findSafe(f)(cause))
}

/**
 * Finds the first result matching f
 */
export function findSafe<Z, E>(
  f: (cause: Cause<E>) => O.Option<Z>
): (cause: Cause<E>) => S.IO<O.Option<Z>> {
  return (cause) => {
    const apply = f(cause)

    if (apply._tag === "Some") {
      return S.succeed(apply)
    }

    switch (cause._tag) {
      case "Then": {
        return S.chain_(
          S.suspend(() => findSafe(f)(cause.left)),
          (isLeft) => {
            if (isLeft._tag === "Some") {
              return S.succeed(isLeft)
            } else {
              return findSafe(f)(cause.right)
            }
          }
        )
      }
      case "Traced": {
        return S.suspend(() => findSafe(f)(cause.cause))
      }
      case "Both": {
        return S.chain_(
          S.suspend(() => findSafe(f)(cause.left)),
          (isLeft) => {
            if (isLeft._tag === "Some") {
              return S.succeed(isLeft)
            } else {
              return findSafe(f)(cause.right)
            }
          }
        )
      }
      default: {
        return S.succeed(apply)
      }
    }
  }
}

/**
 * Equivalent to chain(identity)
 */
export const flatten: <E>(cause: Cause<Cause<E>>) => Cause<E> = chain(identity)

/**
 * Folds over a cause
 */
export function fold<E, Z>(
  empty: () => Z,
  failCase: (_: E) => Z,
  dieCase: (_: unknown) => Z,
  interruptCase: (_: FiberID) => Z,
  thenCase: (_: Z, __: Z) => Z,
  bothCase: (_: Z, __: Z) => Z,
  tracedCase: (_: Z, __: Trace) => Z
) {
  return (cause: Cause<E>): Z =>
    S.run(
      foldSafe(
        empty,
        failCase,
        dieCase,
        interruptCase,
        thenCase,
        bothCase,
        tracedCase
      )(cause)
    )
}

/**
 * Folds over a cause
 */
export function foldSafe<E, Z>(
  empty: () => Z,
  failCase: (_: E) => Z,
  dieCase: (_: unknown) => Z,
  interruptCase: (_: FiberID) => Z,
  thenCase: (_: Z, __: Z) => Z,
  bothCase: (_: Z, __: Z) => Z,
  tracedCase: (_: Z, __: Trace) => Z
) {
  return (cause: Cause<E>): S.IO<Z> => {
    switch (cause._tag) {
      case "Empty": {
        return S.succeedWith(empty)
      }
      case "Fail": {
        return S.succeed(failCase(cause.value))
      }
      case "Die": {
        return S.succeed(dieCase(cause.value))
      }
      case "Interrupt": {
        return S.succeed(interruptCase(cause.fiberId))
      }
      case "Traced": {
        return S.map_(
          S.suspend(() =>
            foldSafe(
              empty,
              failCase,
              dieCase,
              interruptCase,
              thenCase,
              bothCase,
              tracedCase
            )(cause.cause)
          ),
          (x) => tracedCase(x, cause.trace)
        )
      }
      case "Both": {
        return S.zipWith_(
          S.suspend(() =>
            foldSafe(
              empty,
              failCase,
              dieCase,
              interruptCase,
              thenCase,
              bothCase,
              tracedCase
            )(cause.left)
          ),
          S.suspend(() =>
            foldSafe(
              empty,
              failCase,
              dieCase,
              interruptCase,
              thenCase,
              bothCase,
              tracedCase
            )(cause.right)
          ),
          (l, r) => bothCase(l, r)
        )
      }
      case "Then": {
        return S.zipWith_(
          S.suspend(() =>
            foldSafe(
              empty,
              failCase,
              dieCase,
              interruptCase,
              thenCase,
              bothCase,
              tracedCase
            )(cause.left)
          ),
          S.suspend(() =>
            foldSafe(
              empty,
              failCase,
              dieCase,
              interruptCase,
              thenCase,
              bothCase,
              tracedCase
            )(cause.right)
          ),
          (l, r) => thenCase(l, r)
        )
      }
    }
  }
}

/**
 * Accumulates a state over a Cause
 */
export function reduceLeft<Z>(z: Z) {
  return <E>(f: (z: Z, cause: Cause<E>) => O.Option<Z>): ((cause: Cause<E>) => Z) => {
    return (cause) => {
      let causes: Stack<Cause<E>> | undefined = undefined
      let current: Cause<E> | undefined = cause
      let acc = z
      while (current) {
        const x = f(acc, current)
        acc = x._tag === "Some" ? x.value : acc

        switch (current._tag) {
          case "Then": {
            causes = new Stack(current.right, causes)
            current = current.left
            break
          }
          case "Both": {
            causes = new Stack(current.right, causes)
            current = current.left
            break
          }
          case "Traced": {
            current = current.cause
            break
          }
          default: {
            current = undefined
            break
          }
        }

        if (!current && causes) {
          current = causes.value
          causes = causes.previous
        }
      }
      return acc
    }
  }
}

/**
 * Returns if the cause contains an interruption in it
 */
export function interrupted<E>(cause: Cause<E>) {
  return pipe(
    cause,
    interruptOption,
    O.map(() => true),
    O.getOrElse(() => false)
  )
}

/**
 * Returns the `FiberID` associated with the first `Interrupt` in this `Cause` if one
 * exists.
 */
export function interruptOption<E>(cause: Cause<E>) {
  return pipe(
    cause,
    find((c) => (c._tag === "Interrupt" ? O.some(c.fiberId) : O.none))
  )
}

/**
 * Determines if the `Cause` contains only interruptions and not any `Die` or
 * `Fail` causes.
 */
export function interruptedOnly<E>(cause: Cause<E>) {
  return pipe(
    cause,
    find((c) => (c._tag === "Die" || c._tag === "Fail" ? O.some(false) : O.none)),
    O.getOrElse(() => true)
  )
}

/**
 * Returns a set of interruptors, fibers that interrupted the fiber described
 * by this `Cause`.
 */
export function interruptors<E>(cause: Cause<E>): readonly FiberID[] {
  return Array.from(
    pipe(
      cause,
      reduceLeft<Set<FiberID>>(new Set())((s, c) =>
        c._tag === "Interrupt" ? O.some(s.add(c.fiberId)) : O.none
      )
    )
  )
}

/**
 * Remove all `Fail` and `Interrupt` nodes from this `Cause`,
 * return only `Die` cause/finalizer defects.
 */
export function keepDefectsSafe<E>(cause: Cause<E>): S.IO<O.Option<Cause<never>>> {
  switch (cause._tag) {
    case "Empty": {
      return S.succeed(O.none)
    }
    case "Fail": {
      return S.succeed(O.none)
    }
    case "Interrupt": {
      return S.succeed(O.none)
    }
    case "Die": {
      return S.succeed(O.some(cause))
    }
    case "Traced": {
      return S.map_(
        S.suspend(() => keepDefectsSafe(cause.cause)),
        (x) => O.map_(x, (_) => traced(_, cause.trace))
      )
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => keepDefectsSafe(cause.left)),
        S.suspend(() => keepDefectsSafe(cause.right)),
        (l, r) => {
          if (l._tag === "Some" && r._tag === "Some") {
            return O.some(combineSeq(l.value, r.value))
          } else if (l._tag === "Some") {
            return l
          } else if (r._tag === "Some") {
            return r
          } else {
            return O.none
          }
        }
      )
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => keepDefectsSafe(cause.left)),
        S.suspend(() => keepDefectsSafe(cause.right)),
        (l, r) => {
          if (l._tag === "Some" && r._tag === "Some") {
            return O.some(combinePar(l.value, r.value))
          } else if (l._tag === "Some") {
            return l
          } else if (r._tag === "Some") {
            return r
          } else {
            return O.none
          }
        }
      )
    }
  }
}

/**
 * Remove all `Fail` and `Interrupt` nodes from this `Cause`,
 * return only `Die` cause/finalizer defects.
 */
export function keepDefects<E>(cause: Cause<E>): O.Option<Cause<never>> {
  return S.run(keepDefectsSafe(cause))
}

/**
 * Converts the specified `Cause<Either<E, A>>` to an `Either<Cause<E>, A>`.
 */
export function sequenceCauseEither<E, A>(
  c: Cause<E.Either<E, A>>
): E.Either<Cause<E>, A> {
  return S.run(sequenceCauseEitherSafe(c))
}

/**
 * Converts the specified `Cause<Either<E, A>>` to an `Either<Cause<E>, A>`.
 */
export function sequenceCauseEitherSafe<E, A>(
  c: Cause<E.Either<E, A>>
): S.IO<E.Either<Cause<E>, A>> {
  switch (c._tag) {
    case "Empty": {
      return S.succeed(E.left(empty))
    }
    case "Interrupt": {
      return S.succeed(E.left(c))
    }
    case "Fail": {
      return S.succeed(
        c.value._tag === "Left" ? E.left(fail(c.value.left)) : E.right(c.value.right)
      )
    }
    case "Traced": {
      return S.map_(
        S.suspend(() => sequenceCauseEitherSafe(c.cause)),
        (x) => E.mapLeft_(x, (_) => traced(_, c.trace))
      )
    }
    case "Die": {
      return S.succeed(E.left(c))
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => sequenceCauseEitherSafe(c.left)),
        S.suspend(() => sequenceCauseEitherSafe(c.right)),
        (l, r) => {
          if (l._tag === "Left") {
            if (r._tag === "Right") {
              return E.right(r.right)
            } else {
              return E.left(combineSeq(l.left, r.left))
            }
          } else {
            return E.right(l.right)
          }
        }
      )
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => sequenceCauseEitherSafe(c.left)),
        S.suspend(() => sequenceCauseEitherSafe(c.right)),
        (l, r) => {
          if (l._tag === "Left") {
            if (r._tag === "Right") {
              return E.right(r.right)
            } else {
              return E.left(combinePar(l.left, r.left))
            }
          } else {
            return E.right(l.right)
          }
        }
      )
    }
  }
}

/**
 * Converts the specified `Cause<Option<E>>` to an `Option<Cause<E>>` by
 * recursively stripping out any failures with the error `None`.
 */
export function sequenceCauseOptionSafe<E>(
  c: Cause<O.Option<E>>
): S.IO<O.Option<Cause<E>>> {
  switch (c._tag) {
    case "Empty": {
      return S.succeed(O.some(empty))
    }
    case "Interrupt": {
      return S.succeed(O.some(c))
    }
    case "Traced": {
      return S.map_(
        S.suspend(() => sequenceCauseOptionSafe(c.cause)),
        (x) => O.map_(x, (_) => traced(_, c.trace))
      )
    }
    case "Fail": {
      return S.succeed(O.map_(c.value, fail))
    }
    case "Die": {
      return S.succeed(O.some(c))
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => sequenceCauseOptionSafe(c.left)),
        S.suspend(() => sequenceCauseOptionSafe(c.right)),
        (l, r) => {
          if (l._tag === "Some" && r._tag === "Some") {
            return O.some(combineSeq(l.value, r.value))
          } else if (l._tag === "Some") {
            return O.some(l.value)
          } else if (r._tag === "Some") {
            return O.some(r.value)
          } else {
            return O.none
          }
        }
      )
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => sequenceCauseOptionSafe(c.left)),
        S.suspend(() => sequenceCauseOptionSafe(c.right)),
        (l, r) => {
          if (l._tag === "Some" && r._tag === "Some") {
            return O.some(combinePar(l.value, r.value))
          } else if (l._tag === "Some") {
            return O.some(l.value)
          } else if (r._tag === "Some") {
            return O.some(r.value)
          } else {
            return O.none
          }
        }
      )
    }
  }
}

/**
 * Converts the specified `Cause<Option<E>>` to an `Option<Cause<E>>` by
 * recursively stripping out any failures with the error `None`.
 */
export function sequenceCauseOption<E>(c: Cause<O.Option<E>>): O.Option<Cause<E>> {
  return S.run(sequenceCauseOptionSafe(c))
}

/**
 * Squashes a `Cause` down to a single `Throwable`, chosen to be the
 * "most important" `Throwable`.
 */
export function squash<E>(f: (e: E) => unknown) {
  return (cause: Cause<E>): unknown =>
    pipe(
      cause,
      failureOption,
      O.map(f),
      (o) =>
        o._tag === "Some"
          ? o
          : interrupted(cause)
          ? O.some<unknown>(
              new InterruptedException(
                "Interrupted by fibers: " +
                  Array.from(interruptors(cause))
                    .map((_) => _.seqNumber.toString())
                    .map((_) => "#" + _)
                    .join(", ")
              )
            )
          : O.none,
      (o) => (o._tag === "Some" ? o : A.head(defects(cause))),
      O.getOrElse(() => new InterruptedException())
    )
}

/**
 * Discards all typed failures kept on this `Cause`.
 */
export function stripFailures<E>(cause: Cause<E>): Cause<never> {
  switch (cause._tag) {
    case "Empty": {
      return empty
    }
    case "Fail": {
      return empty
    }
    case "Interrupt": {
      return cause
    }
    case "Die": {
      return cause
    }
    default: {
      return S.run(stripFailuresSafe(cause))
    }
  }
}

/**
 * Discards all typed failures kept on this `Cause`.
 */
export function stripFailuresSafe<E>(cause: Cause<E>): S.IO<Cause<never>> {
  switch (cause._tag) {
    case "Empty": {
      return S.succeed(empty)
    }
    case "Fail": {
      return S.succeed(empty)
    }
    case "Interrupt": {
      return S.succeed(cause)
    }
    case "Die": {
      return S.succeed(cause)
    }
    case "Traced": {
      return S.map_(
        S.suspend(() => stripFailuresSafe(cause.cause)),
        (x) => traced(x, cause.trace)
      )
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => stripFailuresSafe(cause.left)),
        S.suspend(() => stripFailuresSafe(cause.right)),
        (l, r) => combinePar(l, r)
      )
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => stripFailuresSafe(cause.left)),
        S.suspend(() => stripFailuresSafe(cause.right)),
        (l, r) => combineSeq(l, r)
      )
    }
  }
}

/**
 * Discards all typed failures kept on this `Cause`.
 */
export function stripInterrupts<E>(cause: Cause<E>): Cause<E> {
  switch (cause._tag) {
    case "Empty": {
      return empty
    }
    case "Fail": {
      return cause
    }
    case "Interrupt": {
      return empty
    }
    case "Die": {
      return cause
    }
    default: {
      return S.run(stripInterruptsSafe(cause))
    }
  }
}

/**
 * Discards all typed failures kept on this `Cause`.
 */
export function stripInterruptsSafe<E>(cause: Cause<E>): S.IO<Cause<E>> {
  switch (cause._tag) {
    case "Empty": {
      return S.succeed(empty)
    }
    case "Fail": {
      return S.succeed(cause)
    }
    case "Interrupt": {
      return S.succeed(empty)
    }
    case "Die": {
      return S.succeed(cause)
    }
    case "Traced": {
      return S.map_(
        S.suspend(() => stripInterruptsSafe(cause.cause)),
        (x) => traced(x, cause.trace)
      )
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => stripInterruptsSafe(cause.left)),
        S.suspend(() => stripInterruptsSafe(cause.right)),
        (l, r) => combinePar(l, r)
      )
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => stripInterruptsSafe(cause.left)),
        S.suspend(() => stripInterruptsSafe(cause.right)),
        (l, r) => combineSeq(l, r)
      )
    }
  }
}

/**
 * Returns a `Cause` that has been stripped of all tracing information.
 */
export function untraced<E>(cause: Cause<E>): Cause<E> {
  switch (cause._tag) {
    case "Die":
    case "Empty":
    case "Fail":
    case "Interrupt":
      return cause
    default:
      return S.run(untracedSafe(cause))
  }
}

/**
 * Returns a `Cause` that has been stripped of all tracing information.
 */
export function untracedSafe<E>(cause: Cause<E>): S.IO<Cause<E>> {
  switch (cause._tag) {
    case "Traced": {
      return S.suspend(() => untracedSafe(cause.cause))
    }
    case "Both": {
      return S.zipWith_(
        S.suspend(() => untracedSafe(cause.left)),
        S.suspend(() => untracedSafe(cause.right)),
        (l, r) => combinePar(l, r)
      )
    }
    case "Then": {
      return S.zipWith_(
        S.suspend(() => untracedSafe(cause.left)),
        S.suspend(() => untracedSafe(cause.right)),
        (l, r) => combineSeq(l, r)
      )
    }
    default: {
      return S.succeed(cause)
    }
  }
}

const FCOStackFrameDoneTypeId = Symbol()
class FCOStackFrameDone {
  readonly _typeId: typeof FCOStackFrameDoneTypeId = FCOStackFrameDoneTypeId
}
const FCOStackFrameTracedTypeId = Symbol()
class FCOStackFrameTraced<E> {
  readonly _typeId: typeof FCOStackFrameTracedTypeId = FCOStackFrameTracedTypeId

  constructor(readonly cause: Traced<O.Option<E>>) {}
}

const FCOStackFrameThenLeftTypeId = Symbol()
class FCOStackFrameThenLeft<E> {
  readonly _typeId: typeof FCOStackFrameThenLeftTypeId = FCOStackFrameThenLeftTypeId

  constructor(readonly cause: Then<O.Option<E>>) {}
}
const FCOStackFrameThenRightTypeId = Symbol()
class FCOStackFrameThenRight<E> {
  readonly _typeId: typeof FCOStackFrameThenRightTypeId = FCOStackFrameThenRightTypeId

  constructor(
    readonly cause: Then<O.Option<E>>,
    readonly leftResult: O.Option<Cause<E>>
  ) {}
}
const FCOStackFrameBothLeftTypeId = Symbol()
class FCOStackFrameBothLeft<E> {
  readonly _typeId: typeof FCOStackFrameBothLeftTypeId = FCOStackFrameBothLeftTypeId

  constructor(readonly cause: Both<O.Option<E>>) {}
}
const FCOStackFrameBothRightTypeId = Symbol()
class FCOStackFrameBothRight<E> {
  readonly _typeId: typeof FCOStackFrameBothRightTypeId = FCOStackFrameBothRightTypeId

  constructor(
    readonly cause: Both<O.Option<E>>,
    readonly leftResult: O.Option<Cause<E>>
  ) {}
}

type FCOStackFrame<E> =
  | FCOStackFrameDone
  | FCOStackFrameTraced<E>
  | FCOStackFrameThenLeft<E>
  | FCOStackFrameThenRight<E>
  | FCOStackFrameBothLeft<E>
  | FCOStackFrameBothRight<E>

/**
 * Converts the specified `Cause<Either<E, A>>` to an `Either<Cause<E>, A>` by
 * recursively stripping out any failures with the error `None`.
 */
export function flipCauseOption<E>(c: Cause<O.Option<E>>): O.Option<Cause<E>> {
  let stack: Stack<FCOStackFrame<E>> = new Stack(new FCOStackFrameDone())
  let result: O.Option<Cause<E>> | undefined

  recursion: while (stack) {
    // eslint-disable-next-line no-constant-condition
    pushing: while (true) {
      switch (c._tag) {
        case "Empty":
          result = O.some(empty)
          break pushing
        case "Traced":
          stack = new Stack(new FCOStackFrameTraced(c), stack)
          c = c.cause
          continue pushing
        case "Interrupt":
          result = O.some(interrupt(c.fiberId))
          break pushing
        case "Die":
          result = O.some(c)
          break pushing
        case "Fail":
          result = O.fold_(
            c.value,
            () => O.none,
            (r) => O.some(fail(r))
          )
          break pushing
        case "Then":
          stack = new Stack(new FCOStackFrameThenLeft(c), stack)
          c = c.left
          continue pushing
        case "Both":
          stack = new Stack(new FCOStackFrameBothLeft(c), stack)
          c = c.left
          continue pushing
      }
    }

    // eslint-disable-next-line no-constant-condition
    popping: while (true) {
      const top = stack.value

      stack = stack.previous!

      switch (top._typeId) {
        case FCOStackFrameDoneTypeId:
          return result
        case FCOStackFrameTracedTypeId:
          result = O.map_(result, (_) => traced(_, top.cause.trace))
          continue popping
        case FCOStackFrameThenLeftTypeId:
          c = top.cause.right
          stack = new Stack(new FCOStackFrameThenRight(top.cause, result), stack)
          continue recursion
        case FCOStackFrameThenRightTypeId: {
          const l = top.leftResult

          if (O.isSome(l) && O.isSome(result)) {
            result = O.some(combineSeq(l.value, result.value))
          }

          if (O.isNone(l) && O.isSome(result)) {
            result = O.some(result.value)
          }

          if (O.isSome(l) && O.isNone(result)) {
            result = O.some(l.value)
          }

          result = O.none

          continue popping
        }
        case FCOStackFrameBothLeftTypeId:
          c = top.cause.right
          stack = new Stack(new FCOStackFrameBothRight(top.cause, result), stack)
          continue recursion
        case FCOStackFrameBothRightTypeId: {
          const l = top.leftResult

          if (O.isSome(l) && O.isSome(result)) {
            result = O.some(combinePar(l.value, result.value))
          }

          if (O.isNone(l) && O.isSome(result)) {
            result = O.some(result.value)
          }

          if (O.isSome(l) && O.isNone(result)) {
            result = O.some(l.value)
          }

          result = O.none

          continue popping
        }
      }
    }
  }

  throw new Error("Bug")
}