rskit-chain 0.1.0-alpha.2

Sequential chain execution pattern for rskit
Documentation 
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use rskit_errors::AppResult;
use std::future::Future;
use std::pin::Pin;
use std::sync::Arc;
use tokio_util::sync::CancellationToken;

/// Boxed future returned by chain steps.
pub type StepFuture<T> = Pin<Box<dyn Future<Output = AppResult<T>> + Send + 'static>>;

type StepProgressFn = Arc<dyn Fn(u8, Option<String>) + Send + Sync>;
type ExecuteFn<I, O> = dyn Fn(I, StepContext) -> StepFuture<O> + Send + Sync;
type CleanupFn = dyn Fn() -> StepFuture<()> + Send + Sync;

/// Per-step execution context.
#[derive(Clone)]
pub struct StepContext {
    cancel: CancellationToken,
    progress: Option<StepProgressFn>,
}

impl StepContext {
    pub(crate) fn new(cancel: CancellationToken, progress: Option<StepProgressFn>) -> Self {
        Self { cancel, progress }
    }

    /// Return the cancellation token shared by the chain execution.
    #[must_use]
    pub fn cancellation_token(&self) -> &CancellationToken {
        &self.cancel
    }

    /// Whether cancellation has been requested.
    #[must_use]
    pub fn is_cancelled(&self) -> bool {
        self.cancel.is_cancelled()
    }

    /// Report step-local progress.
    pub fn progress(&self, percent: u8, message: Option<String>) {
        if let Some(progress) = &self.progress {
            progress(percent.min(100), message);
        }
    }
}

/// A typed operation in a sequential chain.
pub struct Step<I, O> {
    id: String,
    name: String,
    execute: Arc<ExecuteFn<I, O>>,
    cleanup: Option<Arc<CleanupFn>>,
}

impl<I, O> Step<I, O>
where
    I: Send + 'static,
    O: Send + 'static,
{
    /// Create a typed chain step.
    #[must_use]
    pub fn new<F, Fut>(id: impl Into<String>, name: impl Into<String>, execute: F) -> Self
    where
        F: Fn(I, StepContext) -> Fut + Send + Sync + 'static,
        Fut: Future<Output = AppResult<O>> + Send + 'static,
    {
        Self {
            id: id.into(),
            name: name.into(),
            execute: Arc::new(move |input, context| Box::pin(execute(input, context))),
            cleanup: None,
        }
    }

    /// Create a typed chain step using `id` as the display name.
    #[must_use]
    pub fn from_fn<F, Fut>(id: impl Into<String>, execute: F) -> Self
    where
        F: Fn(I, StepContext) -> Fut + Send + Sync + 'static,
        Fut: Future<Output = AppResult<O>> + Send + 'static,
    {
        let id = id.into();
        Self::new(id.clone(), id, execute)
    }

    /// Register cleanup to run only if a later step fails or cancellation interrupts the chain.
    #[must_use]
    pub fn with_cleanup<F, Fut>(mut self, cleanup: F) -> Self
    where
        F: Fn() -> Fut + Send + Sync + 'static,
        Fut: Future<Output = AppResult<()>> + Send + 'static,
    {
        self.cleanup = Some(Arc::new(move || Box::pin(cleanup())));
        self
    }

    /// Unique step identifier.
    #[must_use]
    pub fn id(&self) -> &str {
        &self.id
    }

    /// Human-readable step name.
    #[must_use]
    pub fn name(&self) -> &str {
        &self.name
    }

    pub(crate) fn execute(&self, input: I, context: StepContext) -> StepFuture<O> {
        (self.execute)(input, context)
    }

    pub(crate) fn cleanup(&self) -> Option<Arc<CleanupFn>> {
        self.cleanup.clone()
    }
}