use axum::{
    extract::FromRequestParts,
    http::{request::Parts, HeaderName, HeaderValue},
};
use axum_extra::typed_header::TypedHeader;

/// A typed header. When used as a bare extractor, reads from the
/// `Last-Event-Id` HTTP header.
pub struct LastEventId(pub String);

static LAST_EVENT_ID: HeaderName = HeaderName::from_static("last-event-id");

impl headers::Header for LastEventId {
    fn name() -> &'static HeaderName {
        &LAST_EVENT_ID
    }

    fn decode<'i, I>(values: &mut I) -> Result<Self, headers::Error>
    where
        I: Iterator<Item = &'i HeaderValue>,
    {
        let value = values.next().ok_or_else(headers::Error::invalid)?;
        if let Ok(value) = value.to_str() {
            Ok(Self(value.into()))
        } else {
            Err(headers::Error::invalid())
        }
    }

    fn encode<E>(&self, values: &mut E)
    where
        E: Extend<HeaderValue>,
    {
        let Self(value) = self;
        // Must panic or suppress; the trait provides no other options.
        let value = HeaderValue::from_str(value).expect("LastEventId is a valid header value");

        values.extend(std::iter::once(value));
    }
}

#[async_trait::async_trait]
impl<S> FromRequestParts<S> for LastEventId
where
    S: Send + Sync,
{
    type Rejection = <TypedHeader<Self> as FromRequestParts<S>>::Rejection;

    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        // This is purely for ergonomics: it allows `RequestedAt` to be extracted
        // without having to wrap it in `Extension<>`. Callers _can_ still do that,
        // but they aren't forced to.
        let TypedHeader(requested_at) =
            TypedHeader::<Self>::from_request_parts(parts, state).await?;

        Ok(requested_at)
    }
}

impl From<String> for LastEventId {
    fn from(header: String) -> Self {
        Self(header)
    }
}

impl std::ops::Deref for LastEventId {
    type Target = str;

    fn deref(&self) -> &Self::Target {
        let Self(header) = self;
        header
    }
}