A use case is either a module that exports a unary exec/1 function, or any unary function (an fn closure or a &Module.function/1 capture). Interact.UseCase wraps either form in a struct and provides a pipeline for controlling execution.

Pipeline

import Interact.UseCase

create(MyApp.MyUseCase)   # fully-qualified module, or a unary function
|> async()                # fire and forget; default is synchronous (optional)
|> timeout(ms)            # kill the task after ms milliseconds (optional)
|> callback(functions)    # called with the result struct after completion (optional)
|> reply(pids)            # processes to receive the result struct (optional)
|> input(data)            # input passed to exec/1
|> run()                  # execute the use case

run/2 is a shorthand for input/2 |> run/1. Every pipeline function accepts a module or function directly and calls create/1 automatically, so the pipeline can start at any step — create/1 is never required.

The struct is single-use: once run/1 is called the use case is considered started, and any further pipeline call — including run/1 itself — raises ArgumentError.

Result struct

The %Interact.UseCase{} returned by run/1 always reflects the full execution:

• output — return value of exec/1, or nil on error
• error — exception struct if exec/1 raised, nil on success
• stacktrace — stacktrace when error is an exception, nil otherwise
• started_at, finished_at — DateTime UTC timestamps
• timedout_at — DateTime UTC timestamp set when the deadline was exceeded, nil otherwise

Callbacks and replies fire even on failure, so result handling is uniform regardless of outcome.