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use crate::{Handler, Result};

/// Maps the input before the handler calls.
#[derive(Debug, Clone)]
pub struct Before<H, F> {
    h: H,
    f: F,
}

impl<H, F> Before<H, F> {
    /// Creates a [`Before`] handler.
    #[inline]
    pub fn new(h: H, f: F) -> Self {
        Self { h, f }
    }
}

#[crate::async_trait]
impl<H, F, I, O> Handler<I> for Before<H, F>
where
    I: Send + 'static,
    F: Handler<I, Output = Result<I>>,
    H: Handler<I, Output = Result<O>>,
{
    type Output = H::Output;

    async fn call(&self, i: I) -> Self::Output {
        self.h.call(self.f.call(i).await?).await
    }
}