#![feature(try_blocks, yeet_expr)]

use std::convert::Infallible;
use std::net::SocketAddr;

use http::request::Parts;
use http_body_util::{BodyExt as _, Full};
use hyper::body::Bytes;
use hyper::server::conn::http1;
use hyper::service::service_fn;
use hyper_util::rt::TokioIo;
use puppy::auth::{SigError, Signer};
use puppy::{auth::verify_signature, config::Config};
use puppy::fetch::signatures::Signature;
use serde_json::{from_slice, json, Value};
use tokio::net::TcpListener;

#[tokio::main]
async fn main() {
    let config = Config {
        ap_domain: "test.piss-on.me".to_string(),
        wf_domain: "test.piss-on.me".to_string(),
        port: 1312,
    };
    start(&config).await.unwrap();
}

pub async fn start(cfg: &Config) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
    let addr = SocketAddr::from(([127, 0, 0, 1], cfg.port));
    let listener = TcpListener::bind(addr).await?;

    // We start a loop to continuously accept incoming connections
    loop {
        let (stream, _) = listener.accept().await?;

        // Use an adapter to access something implementing `tokio::io` traits as if they implement
        // `hyper::rt` IO traits.
        let io = TokioIo::new(stream);

        let cfg = cfg.clone();
        // Spawn a tokio task to serve multiple connections concurrently
        tokio::task::spawn(async move {
            // Finally, we bind the incoming connection to our `hello` service
            if let Err(err) = http1::Builder::new()
                // `service_fn` converts our function in a `Service`
                .serve_connection(io, service_fn(|req| handle(req, cfg.clone())))
                .await
            {
                eprintln!("Error serving connection: {:?}", err);
            }
        });
    }
}

type Request = hyper::Request<hyper::body::Incoming>;
type Response<T = Full<Bytes>> = hyper::Response<T>;

/// The request handler.
async fn handle(req: Request, cfg: Config) -> Result<Response, Infallible> {
    // We need to fetch the entire body of the request for signature validation, because that involves making
    // a digest of the request body in some cases.
    let request = {
        let (req, body) = req.into_parts();
        let Ok(body) = body.collect().await.map(|b| b.to_bytes()) else {
            return Ok(error::invalid_body("Could not get request body"));
        };
        http::Request::from_parts(req, body)
    };
    // Simplified representation of a request, so we can pattern match on it more easily in the dispatchers.
    let req = make_req(&request);
    eprintln!("{request:?}: open");
    // We'll use the path to pick where specifically to send the request.
    // Check request signature at the door. Even if it isn't needed for a particular endpoint, failing fast
    // with a clear error message will save anyone trying to get *their* signatures implementation a major
    // headache.
    let res = match verify_signature(&request, &cfg).await {
        // If the request was signed and the signature was accepted, they can access the protected endpoints.
        Ok(Some(sig)) => dispatch_signed(req, sig, cfg).await,
        // Unsigned requests can see a smaller subset of endpoints, most notably the verification actor.
        Ok(None) => dispatch_public(req, cfg).await,
        // If a signature was provided *but it turned out to be unverifiable*, show them the error message.
        Err(err) => error::bad_signature(match err {
            SigError::VerificationFailed { error } => format!("Verification failed: {error}"),
            SigError::ParseSignature { error } => format!("Failed to parse signature: {error}"),
            SigError::FailedToFetchKey { keyid } => format!("Failed to fetch {keyid}"),
        }),
    };
    eprintln!(
        "{} {}: done (status: {})",
        request.method(),
        request.uri(),
        res.status()
    );
    Ok(res)
}

// A parsed HTTP request for easy handling.
struct Req<'a> {
    method: &'a Method,
    body: Bytes,
    // URI bits
    params: Vec<(&'a str, &'a str)>,
    path: Vec<&'a str>,
}

impl Req<'_> {
    fn path(&self) -> &[&str] {
        &self.path
    }
}

fn make_req<'x>(r: &'x http::Request<Bytes>) -> Req<'x> {
    let path: Vec<&str> = r
        .uri()
        .path()
        .split('/')
        .filter(|s| !s.is_empty())
        .collect();
    let params: Vec<(&str, &str)> = r
        .uri()
        .query()
        .into_iter()
        .flat_map(|s| s.split('&'))
        .filter_map(|s| s.split_once('='))
        .collect();
    Req {
        method: r.method(),
        body: r.body().clone(),
        params,
        path,
    }
}

use hyper::Method;

const POST: &Method = &Method::POST;
const GET: &Method = &Method::GET;

/// Handle a signed and verified request.
///
/// This function is where all requests to a protected endpoint have to go through. If the request
/// was signed but does not target a protected endpoint, this function will fall back to the
/// [`dispatch_public`] handler.
async fn dispatch_signed(req: Req<'_>, sig: Signer, cfg: Config) -> Response {
    eprintln!("Dispatching signed request");
    match (req.method, req.path()) {
        // Viewing ActivityPub objects requires a signed request, i.e. "authorized fetch".
        // The one exception for this is `/s/request-verifier`, which is where the request
        // verification actor lives.
        (GET, ["o", ulid]) => api::ap::serve_object(ulid),
        // POSTs to an actor's inbox need to be signed to prevent impersonation.
        (POST, ["o", ulid, "inbox"]) => with_json(&req.body, |json| {
            // We only handle the intermediate parsing of the json, full resolution of the
            // activity object will happen inside the inbox handler itself.
            api::ap::inbox(ulid, sig, json, cfg)
        }),
        // Try the resources for which no signature is required as well.
        _ => dispatch_public(req, cfg).await,
    }
}

/// Dispatch `req` to an unprotected endpoint. If the requested path does not exist, the
/// function will return a 404 response.
async fn dispatch_public(req: Req<'_>, cfg: Config) -> Response {
    eprintln!("Dispatching public request");
    match (req.method, req.path()) {
        (GET, ["proxy"]) => api::ap::proxy(&req.params).await,
        (GET, [".well-known", "webfinger"]) => api::wf::resolve(&req.params, cfg),
        (GET, ["s", "request-verifier"]) => api::ap::serve_verifier_actor(cfg),
        (m, p) => {
            eprintln!("404: {m} {p:?}");
            error::not_found()
        }
    }
}

fn with_json(body: &[u8], f: impl FnOnce(Value) -> Response) -> Response {
    let Ok(json) = from_slice(body) else {
        return error::invalid_body("Could not decode as JSON");
    };
    f(json)
}

/// A quick, simple way to construct a response.
fn respond<const N: usize>(
    status: u16,
    body: Option<impl Into<Bytes>>,
    headers: [(&str, &str); N],
) -> Response {
    let mut resp = Response::<()>::builder().status(status);
    for (name, data) in headers {
        resp = resp.header(name, data);
    }
    resp.body(match body {
        Some(bytes) => Full::new(bytes.into()),
        None => Full::new(Bytes::default()),
    })
    .unwrap()
}

mod api;

mod error {
    //! Pre-baked error responses.

    use http_body_util::Full;
    use super::Response;

    /// 404 response.
    pub fn not_found() -> Response {
        let body = Full::new("Not found".into());
        Response::<()>::builder()
            .status(404)
            .header("content-type", "text/plain")
            .body(body)
            .unwrap()
    }

    /// 403 response indicating a bad request signature.
    pub fn bad_signature(err: String) -> Response {
        let body = Full::new(err.into());
        Response::<()>::builder()
            .status(403)
            .header("content-type", "text/plain")
            .body(body)
            .unwrap()
    }

    pub fn invalid_body(err: impl ToString) -> Response {
        let body = Full::new(err.to_string().into());
        Response::<()>::builder()
            .status(400)
            .header("content-type", "text/plain")
            .body(body)
            .unwrap()
    }
}