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use std::boxed::Box;
use std::sync::Arc;
use std::future::Future;
use std::io;
pub type MiddlewareReturnValue<T> = Box<dyn Future<Output=Result<T, io::Error>> + Send>;
pub type Middleware<T, M> = fn(T, next: M) -> MiddlewareReturnValue<T>;
pub type Runnable<T> = Box<dyn Fn(T, &Option<Box<MiddlewareChain<T>>>) -> MiddlewareReturnValue<T> + Send + Sync>;
pub struct MiddlewareChain<T: 'static> {
pub runnable: Arc<Runnable<T>>,
is_assigned: bool,
chained: Option<Box<MiddlewareChain<T>>>
}
impl<T: 'static> MiddlewareChain<T> {
pub fn new() -> Self {
MiddlewareChain {
runnable: Arc::new(Box::new(|_: T, _: &Option<Box<MiddlewareChain<T>>>| panic!("Use of unassigned middleware chain, be sure to run `assign` first."))),
is_assigned: false,
chained: None
}
}
pub fn assign(&mut self, chain: Runnable<T>) {
self.runnable = Arc::new(chain);
self.is_assigned = true;
}
pub fn run(&self, context: T) -> MiddlewareReturnValue<T> {
if self.is_assigned {
(self.runnable)(context, &self.chained)
} else if let Some(ref chain) = self.chained {
chain.run(context)
} else {
(self.runnable)(context, &self.chained)
}
}
pub fn chain(&mut self, chain: MiddlewareChain<T>) {
match self.chained {
Some(ref mut existing_chain) => existing_chain.chain(chain),
None => self.chained = Some(Box::new(chain))
};
}
pub fn is_assigned(&self) -> bool {
if self.is_assigned {
true
} else {
match self.chained {
Some(ref chained) => chained.is_assigned(),
None => false
}
}
}
}
impl<T: 'static> Default for MiddlewareChain<T> {
fn default() -> Self {
Self::new()
}
}
impl<T: 'static> Clone for MiddlewareChain<T> {
fn clone(&self) -> Self {
MiddlewareChain {
runnable: self.runnable.clone(),
is_assigned: self.is_assigned,
chained: self.chained.clone()
}
}
}
#[macro_export]
macro_rules! middleware {
[ @tailtype $ctx:ty => $head:expr ] => { $ctx };
[ @tailtype $ctx:ty => $head:expr, $($tail_t:ty => $tail_e:expr),+ ] => { middleware![@tailtype $( $tail_t => $tail_e ),*] };
[ @internal $ctx:ty => $head:expr, $ender:expr ] => (
|context: $ctx| {
Box::new(
$head(
context.into(), |ctx| {
$ender(ctx.into())
})
.map(|ctx| ctx.into()))
}
);
[ @internal $ctx:ty => $head:expr, $($tail_t:ty => $tail_e:expr),+ , $ender:expr ] => (
|context: $ctx| {
Box::new(
$head(
context.into(), |ctx: $ctx| {
middleware![@internal $( $tail_t => $tail_e ),*, $ender](ctx.into())
})
.map(|ctx| ctx.into()))
}
);
[ $ctx:ty => $head:expr ] => {{
use std::boxed::Box;
use futures::future::Future;
let mut chain: MiddlewareChain<$ctx> = MiddlewareChain::new();
fn dummy(context: $ctx, next: impl Fn($ctx) -> MiddlewareReturnValue<$ctx> + Send) -> MiddlewareReturnValue<$ctx> {
next(context)
}
chain.assign(Box::new(|context, chain| {
middleware![@internal $ctx => $head,
$ctx => dummy,
|ctx| {
match chain {
Some(val) => val.run(ctx),
None => panic!("End of chain")
}
}](context)
}));
chain
}};
[ $ctx:ty => $head:expr, $($tail_t:ty => $tail_e:expr),+ ] => {{
use std::boxed::Box;
use futures::future::Future;
let mut chain = MiddlewareChain::new();
fn dummy(context: $ctx, next: impl Fn($ctx) -> MiddlewareReturnValue<$ctx> + Send) -> MiddlewareReturnValue<$ctx> {
next(context)
}
chain.assign(Box::new(|context, chain| {
middleware![@internal $ctx => $head, $( $tail_t => $tail_e ),* ,
$ctx => dummy,
|ctx| {
match chain {
Some(val) => val.run(ctx),
None => panic!("End of chain")
}
}](context)
}));
chain
}};
}