wip trying to implement "person as a function" in workflow

[zach-klippenstein]

Inspired by the end of @swankjesse's talk Coroutines Party Tricks. Very rough sketch, missing the auto-loading screen feature, mostly just because I ran out of time. See the kdoc on BackStackWorkflow for more.

enum class MyOutputs {
  Back,
  Done,
}

data class RetryScreen(
  val message: String,
  val onRetryClicked: () -> Unit,
  val onCancelClicked: () -> Unit,
) : Screen

data object LoadingScreen : Screen

class MyWorkflow(
  private val child1: Workflow<Unit, String, Screen>,
  private val child2: Workflow<Unit, String, Screen>,
  private val child3: Workflow<String, Nothing, Screen>,
  private val networkCall: suspend (String) -> String
) : BackStackWorkflow<String, MyOutputs>() {

  override suspend fun BackStackScope.runBackStack(
    props: StateFlow<String>,
    emitOutput: (MyOutputs) -> Unit
  ) {
    // Step 1
    showWorkflow(child1) { output ->
      when (output) {
        "back" -> emitOutput(MyOutputs.Back)
        "next" -> {
          // Step 2
          val childResult = showWorkflow(child2) { output ->
              // Removes child2 from the stack, cancels the output handler from step 1, and just
              // leaves child1 rendering.
            if (output == "back") goBack()
            output
          }

          // Step 3 – make a network call, showing a retry screen if it fails. If the user cancels
          // instead of retrying, we go back to showing child1.
          val networkResult = networkCallWithRetry(childResult)

          // Step 4: Show a workflow for 3 seconds then finish.
          launch {
            delay(3.seconds)
            emitOutput(MyOutputs.Done)
          }
          showWorkflow(child3, flowOf(networkResult))
        }

        else -> error("Unexpected output: $output")
      }
    }
  }

  override fun createIdleScreen(): Screen = LoadingScreen

  private suspend fun BackStackParentScope.networkCallWithRetry(
    request: String
  ): String {
    // TODO: Show a loading screen automatically.
    var networkResult = networkCall(request)
    while (networkResult == "failure") {
      showScreen {
        RetryScreen(
          message = networkResult,
          onRetryClicked = { continueWith(Unit) },
          // Go back to showing child1.
          onCancelClicked = { goBack() }
        )
      }
      networkResult = networkCall(request)
    }
    return networkResult
  }
}

[swankjesse]

This is exciting!

In case you missed it, the toy version of this from the talk is here:
https://github.com/swankjesse/coroutines-party-tricks/blob/main/code/lib/src/main/kotlin/com/publicobject/tricks/navigation/RealDisplay.kt

[swankjesse]

So cool