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//! This module provides implementations of [Handler]

use crate::{Handler, Reporting};
use coap_message::{MinimalWritableMessage, MutableWritableMessage, ReadableMessage};
use coap_numbers::code;

/// An easy way to have resources that may or may not be there in a tree, considering that Handler
/// is not object safe and thus, `if let Some(x) { all = all.at(...) }` won't work.
///
/// This returns 4.04 Not Found if the inner handler is absent, and otherwise forwards request and
/// response building.
impl<H> Handler for Option<H>
where
    H: Handler,
{
    type RequestData = Option<H::RequestData>;
    // FIXME: One of those should become a wrapper, so we don't need to unwrap() in the error
    // handler. (The way it's written right now it'd be in the ExtractRequestError, but wrapping
    // the error to go NOT_FOUND there might be more intuitive).
    type ExtractRequestError = H::ExtractRequestError;
    type BuildResponseError<M: MinimalWritableMessage> = H::BuildResponseError<M>;

    fn extract_request_data<M: ReadableMessage>(
        &mut self,
        request: &M,
    ) -> Result<Self::RequestData, Self::ExtractRequestError> {
        match self {
            None => Ok(None),
            Some(h) => Ok(Some(h.extract_request_data(request)?)),
        }
    }

    fn estimate_length(&mut self, request: &Self::RequestData) -> usize {
        match (self, request) {
            (Some(h), Some(r)) => h.estimate_length(r),
            _ => 1,
        }
    }

    fn build_response<M: MutableWritableMessage>(
        &mut self,
        response: &mut M,
        request: Self::RequestData,
    ) -> Result<(), H::BuildResponseError<M>> {
        // Not using the match-2-tuple pattern of above b/c of
        // "error[E0009]: cannot bind by-move and by-ref in the same pattern"
        if let Some(h) = self {
            if let Some(r) = request {
                return h.build_response(response, r);
            }
        }

        use coap_message::Code;
        response.set_code(M::Code::new(code::NOT_FOUND).unwrap());

        Ok(())
    }
}

impl<H> Reporting for Option<H>
where
    H: Reporting,
{
    type Record<'res> = H::Record<'res>
    where
        Self: 'res;
    type Reporter<'res> = OptionReporter<'res, H>
    where
        Self: 'res;

    fn report(&self) -> Self::Reporter<'_> {
        // This could be as simple as
        //
        // self.into_iter().map(|h| H::report(h)).into_iter().flatten()
        //
        // with TAIT; haven't managed without without introducing this helper:
        OptionReporter::<H>(self.as_ref().map(|h| h.report()))
    }
}

/// Helper type for the [Reporting] implementation on Option
pub struct OptionReporter<'res, H: Reporting + 'res>(Option<H::Reporter<'res>>);

impl<'res, H: Reporting + 'res> Iterator for OptionReporter<'res, H> {
    type Item = H::Record<'res>;
    fn next(&mut self) -> Option<H::Record<'res>> {
        self.0.as_mut().and_then(|s| s.next())
    }
}