simple-middleware 0.3.0

use std::sync::Arc;

use futures::future::BoxFuture;
use tokio::sync::{Mutex, RwLock};

type Middleware<V, R> = Box<dyn FnMut(V, Next<V, R>) -> BoxFuture<'static, R> + Send>;
type MiddlewareMutex<V, R> = Mutex<Middleware<V, R>>;
type ListOfMiddlewares<V, R> = Vec<MiddlewareMutex<V, R>>;
type SharableListOfMiddlewares<V, R> = Arc<RwLock<ListOfMiddlewares<V, R>>>;

pub struct Manager<V, R> {
    list: SharableListOfMiddlewares<V, R>,
}

impl<V: 'static, R: 'static> Manager<V, R> {
    /// Create new instance
    pub fn new() -> Self {
        Self {
            list: Arc::default(),
        }
    }

    pub async fn last<F>(last: impl FnMut(V, Next<V, R>) -> F + Send + 'static) -> Self
    where
        F: Future<Output = R> + Send + 'static,
    {
        let s = Self::new();
        s.next(last).await;

        s
    }

    /// Start processing the value
    pub async fn send(&self, value: V) -> R {
        let total = self.list.read().await.len();

        let qq = Arc::clone(&self.list);
        let next = Next {
            list: Arc::clone(&qq),
            next: total - 1,
        };

        let lock = self.list.read().await;
        let mut callback = lock.last().unwrap().lock().await;
        (callback)(value, next).await
    }

    pub async fn next<F>(&self, mut m: impl FnMut(V, Next<V, R>) -> F + Send + 'static) -> &Self
    where
        F: Future<Output = R> + Send + 'static,
    {
        let list = Arc::clone(&self.list);
        let mut lock = list.write().await;
        lock.push(Mutex::new(Box::new(move |v, next| {
            let cb = (m)(v, next);
            Box::pin(async move { cb.await })
        })));

        self
    }
}

impl<V: 'static, R: 'static> Default for Manager<V, R> {
    fn default() -> Self {
        Self::new()
    }
}

pub struct Next<V, R> {
    list: SharableListOfMiddlewares<V, R>,
    next: usize,
}

impl<V, R> Next<V, R> {
    pub async fn call(mut self, value: V) -> R {
        let list = Arc::clone(&self.list);
        let lock = list.read().await;
        if (self.next as isize) - 1 < 0 {
            panic!("There must be a default")
        }

        self.next -= 1;
        if let Some(next) = lock.get(self.next) {
            let mut callback = next.lock().await;
            return callback(value, self).await;
        }
        panic!("There must be a default")
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[tokio::test]
    pub async fn test_last() {
        let result_str = "This is the end of the row";
        let manager = Manager::last(move |_v, _n| async move { result_str.to_string() }).await;

        assert_eq!(&manager.send(()).await, result_str);
    }

    #[tokio::test]
    pub async fn test_calling() {
        let manager = Manager {
            list: Arc::default(),
        };

        manager
            .next(|value, _next| async move { value })
            .await
            .next(|value, next| async move { next.call(value * 2).await })
            .await
            .next(|value, next| async move { next.call(value + 2).await })
            .await;

        let result: i32 = manager.send(10).await;

        assert_eq!(result, 24);
    }
}