Map Error

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/**
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 * Represents a value that may be returned directly or through a Promise.
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 *
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 * Flow helpers accept `Awaitable` callbacks so synchronous and asynchronous logic can share the
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 * same behavior authoring APIs.
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 *
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 * @typeParam T - Value produced either immediately or asynchronously.
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 */
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export type Awaitable<T> = T | Promise<T>;
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/**
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 * Successful `Result` variant.
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 *
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 * `Ok` carries the typed success value through Flow pipelines. Use `ok` to create branded values
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 * that can be detected by `isResult`.
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 *
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 * @typeParam T - Success value type.
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 */
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export type Ok<T> = {
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  ok: true;
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  value: T;
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};
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/**
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 * Failed `Result` variant.
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 *
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 * `Err` carries expected domain errors. Runtime failures such as cancellation and thrown
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 * exceptions are modeled separately by the runtime helpers.
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 *
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 * @typeParam E - Expected error value type.
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 */
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export type Err<E> = {
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  ok: false;
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  error: E;
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};
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/**
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 * Explicit success-or-failure outcome used throughout Flow.
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 *
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 * Flow behaviors return `Result` values instead of throwing for expected application failures.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 */
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export type Result<T, E> = Ok<T> | Err<E>;
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/**
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 * Structural result shape accepted by `from`.
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 *
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 * Use this when adapting unbranded result-like values into branded Flow results.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 */
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export type ResultLike<T, E> = Ok<T> | Err<E>;
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const resultBrand = Symbol("archyn.result");
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/**
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 * Creates a branded successful result.
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 *
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 * Branded results are recognized by `isResult`, which allows `task` callbacks to distinguish
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 * explicit `Result` returns from plain successful values.
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 *
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 * @typeParam T - Success value type.
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 * @param value - Value to carry in the success variant.
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 * @returns A branded `Ok` result.
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 *
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 * @example
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 * ```ts
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 * const result = ok({ id: "user_1" });
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 * ```
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 */
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export function ok<T>(value: T): Ok<T> {
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  return brandResult({ ok: true, value });
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}
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/**
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 * Creates a branded failed result.
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 *
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 * Use `err` for expected domain failures that should stay typed and recoverable by Flow helpers.
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 *
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 * @typeParam E - Expected error value type.
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 * @param error - Error value to carry in the failure variant.
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 * @returns A branded `Err` result.
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 *
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 * @example
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 * ```ts
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 * const result = err({ kind: "not-found" });
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 * ```
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 */
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export function err<E>(error: E): Err<E> {
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  return brandResult({ ok: false, error });
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}
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/**
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 * Converts a structural result-like value into a branded Flow result.
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 *
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 * This is useful when adapting results from another library or from plain object literals.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 * @param result - Structural success or failure object.
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 * @returns A branded Flow `Result`.
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 */
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export function from<T, E>(result: ResultLike<T, E>): Result<T, E> {
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  return result.ok ? ok(result.value) : err(result.error);
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}
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/**
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 * Narrows a result to the successful variant.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 * @param result - Result to inspect.
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 * @returns `true` when the result is `Ok`.
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 */
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export function isOk<T, E>(result: Result<T, E>): result is Ok<T> {
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  return result.ok;
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}
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/**
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 * Narrows a result to the failed variant.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 * @param result - Result to inspect.
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 * @returns `true` when the result is `Err`.
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 */
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export function isErr<T, E>(result: Result<T, E>): result is Err<E> {
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  return !result.ok;
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}
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/**
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 * Exhaustively handles both result variants and returns one value.
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 *
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 * `match` keeps success and error handling explicit without manual branching at the call site.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 * @typeParam R - Handler return type.
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 * @param result - Result to handle.
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 * @param handlers - Callbacks for the success and failure variants.
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 * @returns The value returned by the matching handler.
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 *
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 * @example
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 * ```ts
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 * const label = match(result, {
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 *   ok: (user) => user.name,
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 *   err: (error) => error.kind,
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 * });
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 * ```
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 */
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export function match<T, E, R>(
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  result: Result<T, E>,
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  handlers: {
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    ok: (value: T) => R;
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    err: (error: E) => R;
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  },
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): R {
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  return result.ok ? handlers.ok(result.value) : handlers.err(result.error);
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}
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/**
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 * Returns the success value or throws the error value.
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 *
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 * Prefer typed recovery helpers for expected failures. `unwrap` is best reserved for tests,
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 * boundaries that intentionally throw, or places where a failure is impossible by construction.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 * @param result - Result to unwrap.
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 * @returns The success value.
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 * @throws The `Err.error` value when the result failed.
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 */
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export function unwrap<T, E>(result: Result<T, E>): T {
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  if (result.ok) {
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    return result.value;
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  }
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  throw result.error;
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}
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/**
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 * Returns the success value or a fallback.
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 *
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 * Use this when a failure can be safely collapsed into a default value.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 * @param result - Result to read.
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 * @param fallback - Value returned when the result failed.
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 * @returns The success value or fallback.
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 *
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 * @example
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 * ```ts
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 * const count = unwrapOr(result, 0);
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 * ```
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 */
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export function unwrapOr<T, E>(result: Result<T, E>, fallback: T): T {
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  return result.ok ? result.value : fallback;
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}
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/**
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 * Namespace-style collection of core result helpers.
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 *
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 * This object is convenient when passing the result toolkit as a single value. The individual
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 * named functions remain the preferred imports for tree-shakeable application code.
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 */
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export const Result = {
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  ok,
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  err,
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  from,
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  isOk,
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  isErr,
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  match,
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  unwrap,
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  unwrapOr,
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};
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/**
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 * Detects branded Flow results created by `ok`, `err`, or `from`.
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 *
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 * `task` uses this guard to preserve explicit results while wrapping plain callback returns in
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 * `ok`.
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 *
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 * @typeParam T - Success value type.
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 * @typeParam E - Expected error value type.
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 * @param value - Plain value or potential result.
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 * @returns `true` when the value is a branded Flow `Result`.
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 */
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export function isResult<T, E>(value: T | Result<T, E>): value is Result<T, E> {
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  return typeof value === "object" && value !== null && resultBrand in value;
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}
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function brandResult<R extends Ok<unknown> | Err<unknown>>(result: R): R {
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  Object.defineProperty(result, resultBrand, {
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    value: true,
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  });
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  return result;
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}

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import { type Awaitable, type Err, type Result, err } from "./result";
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/**
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 * Runtime error returned when execution is cancelled through an `AbortSignal`.
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 *
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 * Cancellation is cooperative. Flow helpers check the signal before and after async work and pass
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 * linked signals to child behaviors where appropriate.
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 */
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export type Cancelled = {
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  kind: "cancelled";
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  reason?: unknown;
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};
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/**
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 * Runtime error returned when user code throws.
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 *
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 * Thrown exceptions are kept separate from expected domain errors so recovery helpers do not hide
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 * programming or platform failures.
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 */
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export type Thrown = {
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  kind: "thrown";
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  error: unknown;
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};
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/**
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 * Runtime-level failure union added around every behavior's domain error type.
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 *
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 * Domain errors describe expected application failures. `RuntimeError` describes cancellation or
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 * unexpected thrown exceptions observed by the Flow runtime.
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 */
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export type RuntimeError = Cancelled | Thrown;
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/**
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 * Execution context passed to every behavior.
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 *
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 * The context always includes an `AbortSignal` and may include application-specific fields.
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 *
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 * @typeParam C - Custom context object type.
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 */
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export type RuntimeContext<C extends object = {}> = C & {
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  signal: AbortSignal;
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};
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/**
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 * Executable Flow workflow unit.
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 *
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 * A behavior receives typed input, reads runtime context, and resolves to a `Result` containing
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 * either typed output, typed domain error, or a runtime error.
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 *
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 * @typeParam I - Input type.
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 * @typeParam O - Output type.
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 * @typeParam E - Expected domain error type.
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 * @typeParam C - Custom context type.
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 */
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export type Behavior<I, O, E = unknown, C extends object = {}> = (
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  input: I,
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  context: RuntimeContext<C>,
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) => Promise<Result<O, E | RuntimeError>>;
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/**
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 * Extracts the input type from a behavior.
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 *
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 * @typeParam T - Behavior type to inspect.
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 */
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export type BehaviorInput<T> =
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  T extends Behavior<infer I, infer _O, infer _E, infer _C> ? I : never;
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/**
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 * Extracts the output type from a behavior.
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 *
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 * @typeParam T - Behavior type to inspect.
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 */
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export type BehaviorOutput<T> =
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  T extends Behavior<infer _I, infer O, infer _E, infer _C> ? O : never;
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/**
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 * Extracts the expected domain error type from a behavior.
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 *
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 * @typeParam T - Behavior type to inspect.
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 */
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export type BehaviorError<T> =
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  T extends Behavior<infer _I, infer _O, infer E, infer _C> ? E : never;
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/**
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 * Extracts the custom context type from a behavior.
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 *
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 * @typeParam T - Behavior type to inspect.
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 */
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export type BehaviorContext<T> =
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  T extends Behavior<infer _I, infer _O, infer _E, infer C> ? C : never;
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/**
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 * Executes a behavior with runtime error protection.
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 *
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 * The runner checks cancellation before and after behavior execution and converts thrown
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 * exceptions into `Thrown` results.
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 *
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 * @typeParam I - Input type.
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 * @typeParam O - Output type.
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 * @typeParam E - Expected domain error type.
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 * @typeParam C - Custom context type.
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 * @param behavior - Behavior to execute.
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 * @param input - Input passed to the behavior.
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 * @param context - Runtime context containing an `AbortSignal`.
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 * @returns The behavior result, cancellation result, or thrown runtime result.
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 */
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export async function runBehavior<I, O, E, C extends object>(
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  behavior: Behavior<I, O, E, C>,
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  input: I,
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  context: RuntimeContext<C>,
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): Promise<Result<O, E | RuntimeError>> {
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  if (context.signal.aborted) {
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    return resultFromSignal(context.signal);
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  }
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  try {
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    const result = await behavior(input, context);
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    if (context.signal.aborted) {
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      return resultFromSignal(context.signal);
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    }
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    return result;
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  } catch (error) {
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    if (context.signal.aborted) {
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      return resultFromSignal(context.signal);
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    }
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    return thrown(error);
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  }
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}
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/**
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 * Defines a behavior from a callback that returns a `Result`.
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 *
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 * Use `define` for low-level helpers that already operate in the result channel. Most application
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 * code should use `task`, which also accepts plain successful values.
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 *
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 * @typeParam I - Input type.
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 * @typeParam O - Output type.
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 * @typeParam E - Expected domain error type.
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 * @typeParam C - Custom context type.
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 * @param run - Callback invoked for each behavior execution.
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 * @returns A behavior protected by cancellation and thrown-exception handling.
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 */
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export function define<I, O, E = unknown, C extends object = {}>(
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  run: (input: I, context: RuntimeContext<C>) => Awaitable<Result<O, E>>,
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): Behavior<I, O, E, C> {
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  return async (input, context) => {
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    if (context.signal.aborted) {
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      return resultFromSignal(context.signal);
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    }
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    try {
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      const result = await run(input, context);
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      if (context.signal.aborted) {
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        return resultFromSignal(context.signal);
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      }
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      return result;
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    } catch (error) {
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      if (context.signal.aborted) {
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        return cancelled(context.signal.reason);
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      }
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      return thrown(error);
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    }
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  };
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}
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/**
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 * Runs a behavior with an optional application context.
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 *
175
 * If no signal is provided, Flow creates a fresh non-aborted signal. Expected failures remain in
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 * the returned `Result`; thrown exceptions are converted to `Thrown`.
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 *
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 * @typeParam I - Input type.
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 * @typeParam O - Output type.
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 * @typeParam E - Expected domain error type.
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 * @typeParam C - Custom context type.
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 * @param behavior - Behavior to execute.
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 * @param input - Input passed to the behavior.
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 * @param context - Optional custom context and optional `AbortSignal`.
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 * @returns A result containing behavior output, domain error, or runtime error.
186
 *
187
 * @example
188
 * ```ts
189
 * const result = await run(loadUser, "user_1");
190
 * ```
191
 */
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export async function run<I, O, E, C extends object = {}>(
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  behavior: Behavior<I, O, E, C>,
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  input: I,
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  context: C & { signal?: AbortSignal } = {} as C & { signal?: AbortSignal },
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): Promise<Result<O, E | RuntimeError>> {
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  const { signal = new AbortController().signal, ...rest } = context;
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  return runBehavior(behavior, input, {
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    ...(rest as C),
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    signal,
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  });
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}
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/**
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 * Creates a cancellation result.
207
 *
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 * @param reason - Optional cancellation reason from an `AbortSignal`.
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 * @returns A failed result containing `Cancelled`.
210
 */
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export function cancelled(reason?: unknown): Err<Cancelled> {
212
  if (reason === undefined) {
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    return err({ kind: "cancelled" });
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  }
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  return err({ kind: "cancelled", reason });
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}
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/**
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 * Narrows an error value to `Cancelled`.
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 *
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 * @param error - Error value to inspect.
223
 * @returns `true` when the value is a cancellation runtime error.
224
 */
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export function isCancelled(error: unknown): error is Cancelled {
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  return (
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    typeof error === "object" && error !== null && "kind" in error && error.kind === "cancelled"
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  );
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}
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/**
232
 * Creates a thrown-exception runtime result.
233
 *
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 * @param error - Exception or thrown value.
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 * @returns A failed result containing `Thrown`.
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 */
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export function thrown(error: unknown): Err<Thrown> {
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  return err({ kind: "thrown", error });
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}
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/**
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 * Narrows an error value to `Thrown`.
243
 *
244
 * @param error - Error value to inspect.
245
 * @returns `true` when the value is a thrown runtime error.
246
 */
247
export function isThrown(error: unknown): error is Thrown {
248
  return typeof error === "object" && error !== null && "kind" in error && error.kind === "thrown";
249
}
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251
/**
252
 * Narrows an error value to a Flow runtime error.
253
 *
254
 * Recovery helpers use this guard so they only handle expected domain errors.
255
 *
256
 * @param error - Error value to inspect.
257
 * @returns `true` for `Cancelled` or `Thrown`.
258
 */
259
export function isRuntimeError(error: unknown): error is RuntimeError {
260
  return isCancelled(error) || isThrown(error);
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}
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/**
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 * Converts an aborted signal into a cancellation result.
265
 *
266
 * @param signal - Aborted signal whose reason should be preserved.
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 * @returns A failed result containing `Cancelled`.
268
 */
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export function resultFromSignal(signal: AbortSignal): Err<Cancelled> {
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  return cancelled(signal.reason);
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}
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273
/**
274
 * Replaces the signal on a runtime context.
275
 *
276
 * This advanced helper is used by timeout and parallel helpers when they create child abort
277
 * controllers.
278
 *
279
 * @typeParam C - Custom context type.
280
 * @param context - Existing runtime context.
281
 * @param signal - Replacement signal.
282
 * @returns A context with the same custom fields and the replacement signal.
283
 */
284
export function contextWithSignal<C extends object>(
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  context: RuntimeContext<C>,
286
  signal: AbortSignal,
287
): RuntimeContext<C> {
288
  return { ...context, signal };
289
}
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291
/**
292
 * Aborts a controller only when it has not already been aborted.
293
 *
294
 * @param controller - Controller to abort.
295
 * @param reason - Optional abort reason.
296
 */
297
export function abortController(controller: AbortController, reason?: unknown): void {
298
  if (!controller.signal.aborted) {
299
    controller.abort(reason);
300
  }
301
}
302

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/**
304
 * Links a parent signal to a child controller.
305
 *
306
 * The returned cleanup function removes the listener when the child work has settled.
307
 *
308
 * @param parent - Parent signal to observe.
309
 * @param controller - Child controller to abort when the parent aborts.
310
 * @returns Cleanup function that unlinks the abort listener.
311
 */
312
export function linkAbortSignal(parent: AbortSignal, controller: AbortController): () => void {
313
  if (parent.aborted) {
314
    abortController(controller, parent.reason);
315
    return () => {};
316
  }
317

318
  const onAbort = () => abortController(controller, parent.reason);
319
  parent.addEventListener("abort", onAbort, { once: true });
320

321
  return () => parent.removeEventListener("abort", onAbort);
322
}
323

324
/**
325
 * Creates a child controller linked to a parent signal.
326
 *
327
 * This advanced helper powers timeout, race, and parallel execution helpers.
328
 *
329
 * @param parent - Parent signal to link from.
330
 * @returns The child controller and an unlink cleanup function.
331
 */
332
export function createLinkedController(parent: AbortSignal): {
333
  controller: AbortController;
334
  unlink: () => void;
335
} {
336
  const controller = new AbortController();
337
  const unlink = linkAbortSignal(parent, controller);
338

339
  return { controller, unlink };
340
}