disintegrate 4.0.0

Disintegrate is a Rust library to build event-sourced applications.
Documentation 
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//! Event store is responsible for storing and retrieving events.
//!
//! It is designed to be implemented by different storage backends, such as databases
//! or distributed event sourcing systems. Implementations of this trait should handle event persistence, querying,
//! and conflict resolution in a way that aligns with the specific requirements and constraints of the underlying
//! storage system.
//!
//! For more details and specific implementations, refer to the trait documentation and individual implementations
//! of the `EventStore` trait.
use crate::{
    event::{Event, EventId, PersistedEvent},
    stream_query::StreamQuery,
};

use async_trait::async_trait;
use futures::stream::BoxStream;
use std::error::Error as StdError;
/// An event store.
///
/// This trait provides methods for streaming events and appending events to the event store.
#[async_trait]
pub trait EventStore<ID, E>
where
    ID: EventId,
    E: Event + Send + Sync,
{
    type Error: Send + Sync;

    // Streams events based on the provided query.
    ///
    /// # Arguments
    ///
    /// * `query` - The stream query specifying the filtering conditions.
    ///
    /// # Returns
    ///
    /// A `Result` containing a boxed stream of `StreamItem` matching the query, or an error.
    fn stream<'a, QE>(
        &'a self,
        query: &'a StreamQuery<ID, QE>,
    ) -> BoxStream<'a, Result<StreamItem<ID, QE>, Self::Error>>
    where
        QE: TryFrom<E> + Event + 'static + Clone + Send + Sync,
        <QE as TryFrom<E>>::Error: StdError + 'static + Send + Sync;

    /// Appends a batch of events to the event store.
    ///
    /// # Arguments
    ///
    /// * `events` - A vector of events to append to the event store.
    /// * `query` - The stream query associated with the appended events.
    /// * `last_event_id` - The ID of the last event in the event stream that was queried before appending.
    ///
    /// # Returns
    ///
    /// A `Result` containing a vector of `PersistedEvent` representing the appended events, or an error.
    ///
    /// # Notes
    ///
    /// The `append` method re-executes the `query` and checks if there are new events between the `last_event_id`
    /// queried and the appended events' IDs. If new events are found, a conflict has occurred, and the conflict
    /// handling mechanism should be implemented accordingly.
    async fn append<QE>(
        &self,
        events: Vec<E>,
        query: StreamQuery<ID, QE>,
        last_event_id: ID,
    ) -> Result<Vec<PersistedEvent<ID, E>>, Self::Error>
    where
        E: Clone + 'async_trait,
        QE: Event + 'static + Clone + Send + Sync;

    /// Appends a batch of events to the event store **without** verifying if
    /// new events have been added since the last read.
    ///
    /// This method is useful when you are certain that no other process
    /// has modified the event store in a way that would make your logic stale.
    ///
    /// If you need to guarantee that no duplicate events are added,
    /// use the `append` method instead, providing a query that ensures uniqueness.
    ///
    /// # Arguments
    ///
    /// * `events` - A vector of events to append to the event store.
    ///
    ///# Returns
    ///
    /// A `Result` containing a vector of `PersistedEvent` representing the appended events, or an error.
    async fn append_without_validation(
        &self,
        events: Vec<E>,
    ) -> Result<Vec<PersistedEvent<ID, E>>, Self::Error>
    where
        E: Clone + 'async_trait;
}

/// An item in the event stream.
#[derive(Debug, Clone)]
pub enum StreamItem<ID: EventId, E: Event> {
    /// An event in the stream.
    Event(PersistedEvent<ID, E>),
    /// The end of the stream. The id is the version of the db at the time of the query.
    End(ID),
}

impl<ID: EventId, E: Event> StreamItem<ID, E> {
    pub fn id(&self) -> ID {
        match self {
            StreamItem::Event(event) => event.id,
            StreamItem::End(id) => *id,
        }
    }
}

impl<ID: EventId, E: Event> From<PersistedEvent<ID, E>> for StreamItem<ID, E> {
    fn from(event: PersistedEvent<ID, E>) -> Self {
        StreamItem::Event(event)
    }
}