use std::marker::PhantomData;
use futures::future::{Future, ok, err};

use error::Error;
use httprequest::HttpRequest;
use httpresponse::HttpResponse;

/// Trait defines object that could be registered as route handler
#[allow(unused_variables)]
pub trait Handler<S>: 'static {

    /// The type of value that handler will return.
    type Result: Responder;

    /// Handle request
    fn handle(&mut self, req: HttpRequest<S>) -> Self::Result;
}

/// Trait implemented by types that generate responses for clients.
///
/// Types that implement this trait can be used as the return type of a handler.
pub trait Responder {
    /// The associated item which can be returned.
    type Item: Into<Reply>;

    /// The associated error which can be returned.
    type Error: Into<Error>;

    /// Convert itself to `Reply` or `Error`.
    fn respond_to(self, req: HttpRequest) -> Result<Self::Item, Self::Error>;
}

/// Combines two different responder types into a single type
///
/// ```rust
/// # extern crate actix_web;
/// # extern crate futures;
/// # use futures::future::Future;
/// use actix_web::AsyncResponder;
/// use futures::future::result;
/// use actix_web::{Either, Error, HttpRequest, HttpResponse, httpcodes};
///
/// type RegisterResult = Either<HttpResponse, Box<Future<Item=HttpResponse, Error=Error>>>;
///
///
/// fn index(req: HttpRequest) -> RegisterResult {
///     if is_a_variant() { // <- choose variant A
///         Either::A(
///             httpcodes::HttpBadRequest.with_body("Bad data"))
///     } else {
///         Either::B(      // <- variant B
///             result(HttpResponse::Ok()
///                    .content_type("text/html")
///                    .body(format!("Hello!"))
///                    .map_err(|e| e.into())).responder())
///     }
/// }
/// # fn is_a_variant() -> bool { true }
/// # fn main() {}
/// ```
#[derive(Debug)]
pub enum Either<A, B> {
    /// First branch of the type
    A(A),
    /// Second branch of the type
    B(B),
}

impl<A, B> Responder for Either<A, B>
    where A: Responder, B: Responder
{
    type Item = Reply;
    type Error = Error;

    fn respond_to(self, req: HttpRequest) -> Result<Reply, Error> {
        match self {
            Either::A(a) => match a.respond_to(req) {
                Ok(val) => Ok(val.into()),
                Err(err) => Err(err.into()),
            },
            Either::B(b) => match b.respond_to(req) {
                Ok(val) => Ok(val.into()),
                Err(err) => Err(err.into()),
            },
        }
    }
}


#[doc(hidden)]
/// Convenience trait that convert `Future` object into `Boxed` future
pub trait AsyncResponder<I, E>: Sized {
    fn responder(self) -> Box<Future<Item=I, Error=E>>;
}

impl<F, I, E> AsyncResponder<I, E> for F
    where F: Future<Item=I, Error=E> + 'static,
          I: Responder + 'static,
          E: Into<Error> + 'static,
{
    fn responder(self) -> Box<Future<Item=I, Error=E>> {
        Box::new(self)
    }
}

/// Handler<S> for Fn()
impl<F, R, S> Handler<S> for F
    where F: Fn(HttpRequest<S>) -> R + 'static,
          R: Responder + 'static
{
    type Result = R;

    fn handle(&mut self, req: HttpRequest<S>) -> R {
        (self)(req)
    }
}

/// Represents response process.
pub struct Reply(ReplyItem);

pub(crate) enum ReplyItem {
    Message(HttpResponse),
    Future(Box<Future<Item=HttpResponse, Error=Error>>),
}

impl Reply {

    /// Create async response
    #[inline]
    pub fn async<F>(fut: F) -> Reply
        where F: Future<Item=HttpResponse, Error=Error> + 'static
    {
        Reply(ReplyItem::Future(Box::new(fut)))
    }

    /// Send response
    #[inline]
    pub fn response<R: Into<HttpResponse>>(response: R) -> Reply {
        Reply(ReplyItem::Message(response.into()))
    }

    #[inline]
    pub(crate) fn into(self) -> ReplyItem {
        self.0
    }

    #[cfg(test)]
    pub(crate) fn as_response(&self) -> Option<&HttpResponse> {
        match self.0 {
            ReplyItem::Message(ref resp) => Some(resp),
            _ => None,
        }
    }
}

impl Responder for Reply {
    type Item = Reply;
    type Error = Error;

    fn respond_to(self, _: HttpRequest) -> Result<Reply, Error> {
        Ok(self)
    }
}

impl Responder for HttpResponse {
    type Item = Reply;
    type Error = Error;

    #[inline]
    fn respond_to(self, _: HttpRequest) -> Result<Reply, Error> {
        Ok(Reply(ReplyItem::Message(self)))
    }
}

impl From<HttpResponse> for Reply {

    #[inline]
    fn from(resp: HttpResponse) -> Reply {
        Reply(ReplyItem::Message(resp))
    }
}

impl<T: Responder, E: Into<Error>> Responder for Result<T, E>
{
    type Item = <T as Responder>::Item;
    type Error = Error;

    fn respond_to(self, req: HttpRequest) -> Result<Self::Item, Self::Error> {
        match self {
            Ok(val) => match val.respond_to(req) {
                Ok(val) => Ok(val),
                Err(err) => Err(err.into()),
            },
            Err(err) => Err(err.into()),
        }
    }
}

impl<E: Into<Error>> From<Result<Reply, E>> for Reply {
    #[inline]
    fn from(res: Result<Reply, E>) -> Self {
        match res {
            Ok(val) => val,
            Err(err) => Reply(ReplyItem::Message(err.into().into())),
        }
    }
}

impl<E: Into<Error>> From<Result<HttpResponse, E>> for Reply {
    #[inline]
    fn from(res: Result<HttpResponse, E>) -> Self {
        match res {
            Ok(val) => Reply(ReplyItem::Message(val)),
            Err(err) => Reply(ReplyItem::Message(err.into().into())),
        }
    }
}

impl From<Box<Future<Item=HttpResponse, Error=Error>>> for Reply {
    #[inline]
    fn from(fut: Box<Future<Item=HttpResponse, Error=Error>>) -> Reply {
        Reply(ReplyItem::Future(fut))
    }
}

/// Convenience type alias
pub type FutureResponse<I, E=Error> = Box<Future<Item=I, Error=E>>;

impl<I, E> Responder for Box<Future<Item=I, Error=E>>
    where I: Responder + 'static,
          E: Into<Error> + 'static
{
    type Item = Reply;
    type Error = Error;

    #[inline]
    fn respond_to(self, req: HttpRequest) -> Result<Reply, Error> {
        let fut = self.map_err(|e| e.into())
            .then(move |r| {
                match r.respond_to(req) {
                    Ok(reply) => match reply.into().0 {
                        ReplyItem::Message(resp) => ok(resp),
                        _ => panic!("Nested async replies are not supported"),
                    },
                    Err(e) => err(e),
                }
            });
        Ok(Reply::async(fut))
    }
}

/// Trait defines object that could be registered as resource route
pub(crate) trait RouteHandler<S>: 'static {
    fn handle(&mut self, req: HttpRequest<S>) -> Reply;
}

/// Route handler wrapper for Handler
pub(crate)
struct WrapHandler<S, H, R>
    where H: Handler<S, Result=R>,
          R: Responder,
          S: 'static,
{
    h: H,
    s: PhantomData<S>,
}

impl<S, H, R> WrapHandler<S, H, R>
    where H: Handler<S, Result=R>,
          R: Responder,
          S: 'static,
{
    pub fn new(h: H) -> Self {
        WrapHandler{h, s: PhantomData}
    }
}

impl<S, H, R> RouteHandler<S> for WrapHandler<S, H, R>
    where H: Handler<S, Result=R>,
          R: Responder + 'static,
          S: 'static,
{
    fn handle(&mut self, req: HttpRequest<S>) -> Reply {
        let req2 = req.without_state();
        match self.h.handle(req).respond_to(req2) {
            Ok(reply) => reply.into(),
            Err(err) => Reply::response(err.into()),
        }
    }
}

/// Async route handler
pub(crate)
struct AsyncHandler<S, H, F, R, E>
    where H: Fn(HttpRequest<S>) -> F + 'static,
          F: Future<Item=R, Error=E> + 'static,
          R: Responder + 'static,
          E: Into<Error> + 'static,
          S: 'static,
{
    h: Box<H>,
    s: PhantomData<S>,
}

impl<S, H, F, R, E> AsyncHandler<S, H, F, R, E>
    where H: Fn(HttpRequest<S>) -> F + 'static,
          F: Future<Item=R, Error=E> + 'static,
          R: Responder + 'static,
          E: Into<Error> + 'static,
          S: 'static,
{
    pub fn new(h: H) -> Self {
        AsyncHandler{h: Box::new(h), s: PhantomData}
    }
}

impl<S, H, F, R, E> RouteHandler<S> for AsyncHandler<S, H, F, R, E>
    where H: Fn(HttpRequest<S>) -> F + 'static,
          F: Future<Item=R, Error=E> + 'static,
          R: Responder + 'static,
          E: Into<Error> + 'static,
          S: 'static,
{
    fn handle(&mut self, req: HttpRequest<S>) -> Reply {
        let req2 = req.without_state();
        let fut = (self.h)(req)
            .map_err(|e| e.into())
            .then(move |r| {
                match r.respond_to(req2) {
                    Ok(reply) => match reply.into().0 {
                        ReplyItem::Message(resp) => ok(resp),
                        _ => panic!("Nested async replies are not supported"),
                    },
                    Err(e) => err(e),
                }
            });
        Reply::async(fut)
    }
}