#![forbid(unsafe_code)]
#![deny(
    clippy::dbg_macro,
    missing_copy_implementations,
    rustdoc::missing_crate_level_docs,
    missing_debug_implementations,
    missing_docs,
    nonstandard_style,
    unused_qualifications
)]

/*!
http reverse and forward proxy trillium handler

*/

mod body_streamer;
mod forward_proxy_connect;
pub mod upstream;

use body_streamer::stream_body;
use full_duplex_async_copy::full_duplex_copy;
use futures_lite::future::zip;
use size::{Base, Size};
use std::{borrow::Cow, fmt::Debug, future::IntoFuture};
use trillium::{
    async_trait, Conn, Handler, KnownHeaderName,
    Status::{NotFound, SwitchingProtocols},
    Upgrade,
};
use trillium_forwarding::Forwarded;
use trillium_http::{HeaderName, HeaderValue, Headers, Status, Version};
use upstream::{IntoUpstreamSelector, UpstreamSelector};

pub use forward_proxy_connect::ForwardProxyConnect;
pub use trillium_client::{Client, Connector};
pub use url::Url;

/// constructs a new [`Proxy`]. alias of [`Proxy::new`]
pub fn proxy<I>(client: impl Into<Client>, upstream: I) -> Proxy<I::UpstreamSelector>
where
    I: IntoUpstreamSelector,
{
    Proxy::new(client, upstream)
}

/**
the proxy handler
*/
#[derive(Debug)]
pub struct Proxy<U> {
    upstream: U,
    client: Client,
    pass_through_not_found: bool,
    halt: bool,
    via_pseudonym: Option<Cow<'static, str>>,
    allow_websocket_upgrade: bool,
}

impl<U: UpstreamSelector> Proxy<U> {
    /**
    construct a new proxy handler that sends all requests to the upstream
    provided

    ```
    use trillium_smol::ClientConfig;
    use trillium_proxy::Proxy;

    let proxy = Proxy::new(ClientConfig::default(), "http://docs.trillium.rs/trillium_proxy");
    ```

     */
    pub fn new<I>(client: impl Into<Client>, upstream: I) -> Self
    where
        I: IntoUpstreamSelector<UpstreamSelector = U>,
    {
        Self {
            upstream: upstream.into_upstream(),
            client: client.into(),
            pass_through_not_found: true,
            halt: true,
            via_pseudonym: None,
            allow_websocket_upgrade: false,
        }
    }

    /**
    chainable constructor to set the 404 Not Found handling
    behavior. By default, this proxy will pass through the trillium
    Conn unmodified if the proxy response is a 404 not found, allowing
    it to be chained in a tuple handler. To modify this behavior, call
    proxy_not_found, and the full 404 response will be forwarded. The
    Conn will be halted unless [`Proxy::without_halting`] was
    configured

    ```
    # use trillium_smol::ClientConfig;
    # use trillium_proxy::Proxy;
    let proxy = Proxy::new(ClientConfig::default(), "http://trillium.rs")
        .proxy_not_found();
    ```
    */
    pub fn proxy_not_found(mut self) -> Self {
        self.pass_through_not_found = false;
        self
    }

    /**
    The default behavior for this handler is to halt the conn on any
    response other than a 404. If [`Proxy::proxy_not_found`] has been
    configured, the default behavior for all response statuses is to
    halt the trillium conn. To change this behavior, call
    without_halting when constructing the proxy, and it will not halt
    the conn. This is useful when passing the proxy reply through
    [`trillium_html_rewriter`](https://docs.trillium.rs/trillium_html_rewriter).

    ```
    # use trillium_smol::ClientConfig;
    # use trillium_proxy::Proxy;
    let proxy = Proxy::new(ClientConfig::default(), "http://trillium.rs")
        .without_halting();
    ```
    */
    pub fn without_halting(mut self) -> Self {
        self.halt = false;
        self
    }

    /// populate the pseudonym for a
    /// [`Via`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Via)
    /// header. If no pseudonym is provided, no via header will be
    /// inserted.
    pub fn with_via_pseudonym(mut self, via_pseudonym: impl Into<Cow<'static, str>>) -> Self {
        self.via_pseudonym = Some(via_pseudonym.into());
        self
    }

    /// Allow websockets to be proxied
    ///
    /// This is not currently the default, but that may change at some (semver-minor) point in the
    /// future
    pub fn with_websocket_upgrades(mut self) -> Self {
        self.allow_websocket_upgrade = true;
        self
    }

    fn set_via_pseudonym(&self, headers: &mut Headers, version: Version) {
        if let Some(via) = &self.via_pseudonym {
            let via = match headers.get_values(KnownHeaderName::Via) {
                Some(old_via) => format!(
                    "{version} {via}, {}",
                    old_via
                        .iter()
                        .filter_map(HeaderValue::as_str)
                        .collect::<Vec<_>>()
                        .join(", ")
                ),

                None => format!("{version} {via}"),
            };

            headers.insert(KnownHeaderName::Via, via);
        };
    }
}

#[derive(Debug)]
struct UpstreamUpgrade(Upgrade);

#[async_trait]
impl<U: UpstreamSelector> Handler for Proxy<U> {
    async fn init(&mut self, _info: &mut trillium::Info) {
        log::info!("proxying to {:?}", self.upstream);
    }

    async fn run(&self, mut conn: Conn) -> Conn {
        let Some(request_url) = self.upstream.determine_upstream(&mut conn) else {
            return conn;
        };

        log::debug!("proxying to {}", request_url.as_str());

        let mut forwarded = Forwarded::from_headers(conn.request_headers())
            .ok()
            .flatten()
            .unwrap_or_default()
            .into_owned();

        if let Some(peer_ip) = conn.peer_ip() {
            forwarded.add_for(peer_ip.to_string());
        };

        if let Some(host) = conn.inner().host() {
            forwarded.set_host(host);
        }

        let mut request_headers = conn
            .request_headers()
            .clone()
            .without_headers([
                KnownHeaderName::Connection,
                KnownHeaderName::KeepAlive,
                KnownHeaderName::ProxyAuthenticate,
                KnownHeaderName::ProxyAuthorization,
                KnownHeaderName::Te,
                KnownHeaderName::Trailer,
                KnownHeaderName::TransferEncoding,
                KnownHeaderName::Upgrade,
                KnownHeaderName::Host,
                KnownHeaderName::XforwardedBy,
                KnownHeaderName::XforwardedFor,
                KnownHeaderName::XforwardedHost,
                KnownHeaderName::XforwardedProto,
                KnownHeaderName::XforwardedSsl,
            ])
            .with_inserted_header(KnownHeaderName::Forwarded, forwarded.to_string());

        let mut connection_is_upgrade = false;
        for header in conn
            .request_headers()
            .get_str(KnownHeaderName::Connection)
            .unwrap_or_default()
            .split(',')
            .map(|h| trillium::HeaderName::from(h.trim()))
        {
            if header == KnownHeaderName::Upgrade {
                connection_is_upgrade = true;
            }
            request_headers.remove(header);
        }

        if self.allow_websocket_upgrade
            && connection_is_upgrade
            && conn
                .request_headers()
                .eq_ignore_ascii_case(KnownHeaderName::Upgrade, "websocket")
        {
            request_headers.extend([
                (KnownHeaderName::Upgrade, "WebSocket"),
                (KnownHeaderName::Connection, "Upgrade"),
            ]);
        }

        self.set_via_pseudonym(&mut request_headers, conn.inner().http_version());
        let content_length = !matches!(
            conn.request_headers()
                .get_str(KnownHeaderName::ContentLength),
            Some("0") | None
        );

        let chunked = conn
            .request_headers()
            .eq_ignore_ascii_case(KnownHeaderName::TransferEncoding, "chunked");
        let method = conn.method();
        let conn_result = if chunked || content_length {
            let (body_fut, request_body) = stream_body(&mut conn);

            let client_fut = self
                .client
                .build_conn(method, request_url)
                .with_headers(request_headers)
                .with_body(request_body)
                .into_future();

            zip(body_fut, client_fut).await.1
        } else {
            self.client
                .build_conn(method, request_url)
                .with_headers(request_headers)
                .await
        };

        let mut client_conn = match conn_result {
            Ok(client_conn) => client_conn,
            Err(e) => {
                return conn
                    .with_status(Status::ServiceUnavailable)
                    .halt()
                    .with_state(e);
            }
        };

        let mut conn = match client_conn.status() {
            Some(SwitchingProtocols) => {
                conn.headers_mut()
                    .extend(std::mem::take(client_conn.response_headers_mut()));

                conn.with_state(UpstreamUpgrade(Upgrade::from(client_conn)))
                    .with_status(SwitchingProtocols)
            }

            Some(NotFound) if self.pass_through_not_found => {
                client_conn.recycle().await;
                return conn;
            }

            Some(status) => {
                conn.headers_mut()
                    .append_all(client_conn.response_headers().clone());
                conn.with_body(client_conn).with_status(status)
            }

            None => return conn.with_status(Status::ServiceUnavailable).halt(),
        };

        let connection = conn
            .response_headers_mut()
            .remove(KnownHeaderName::Connection);

        conn.response_headers_mut().remove_all(
            connection
                .iter()
                .flatten()
                .filter_map(|s| s.as_str())
                .flat_map(|s| s.split(','))
                .map(|t| HeaderName::from(t.trim()).into_owned()),
        );

        conn.response_headers_mut().remove_all([
            KnownHeaderName::KeepAlive,
            KnownHeaderName::ProxyAuthenticate,
            KnownHeaderName::ProxyAuthorization,
            KnownHeaderName::Te,
            KnownHeaderName::Trailer,
            KnownHeaderName::TransferEncoding,
        ]);

        self.set_via_pseudonym(conn.response_headers_mut(), Version::Http1_1);

        if self.halt {
            conn.halt()
        } else {
            conn
        }
    }

    fn has_upgrade(&self, upgrade: &Upgrade) -> bool {
        upgrade.state.contains::<UpstreamUpgrade>()
    }

    async fn upgrade(&self, mut upgrade: Upgrade) {
        let Some(UpstreamUpgrade(upstream)) = upgrade.state.take() else {
            return;
        };
        let downstream = upgrade;
        match full_duplex_copy(upstream, downstream).await {
            Err(e) => log::error!("upgrade stream error: {:?}", e),
            Ok((up, down)) => {
                log::debug!("streamed upgrade {} up and {} down", bytes(up), bytes(down))
            }
        }
    }
}

fn bytes(bytes: u64) -> String {
    Size::from_bytes(bytes)
        .format()
        .with_base(Base::Base10)
        .to_string()
}