use std::collections::HashMap;
use std::marker::PhantomData;
use std::rc::Rc;
use std::sync::Arc;

use cookie::{Cookie, CookieJar, Key};
use futures::Future;
use futures::future::{FutureResult, err as FutErr, ok as FutOk};
use http::header::{self, HeaderValue};
use serde::{Deserialize, Serialize};
use serde_json;
use serde_json::error::Error as JsonError;
use time::Duration;

use error::{Error, ResponseError, Result};
use httprequest::HttpRequest;
use httpresponse::HttpResponse;
use middleware::{Middleware, Response, Started};

/// The helper trait to obtain your session data from a request.
///
/// ```rust
/// use actix_web::*;
/// use actix_web::middleware::RequestSession;
///
/// fn index(mut req: HttpRequest) -> Result<&'static str> {
///     // access session data
///     if let Some(count) = req.session().get::<i32>("counter")? {
///         req.session().set("counter", count+1)?;
///     } else {
///         req.session().set("counter", 1)?;
///     }
///
///     Ok("Welcome!")
/// }
/// # fn main() {}
/// ```
pub trait RequestSession {
    fn session(&mut self) -> Session;
}

impl<S> RequestSession for HttpRequest<S> {
    fn session(&mut self) -> Session {
        if let Some(s_impl) = self.extensions().get_mut::<Arc<SessionImplBox>>() {
            if let Some(s) = Arc::get_mut(s_impl) {
                return Session(s.0.as_mut());
            }
        }
        Session(unsafe { &mut DUMMY })
    }
}

/// The high-level interface you use to modify session data.
///
/// Session object could be obtained with
/// [`RequestSession::session`](trait.RequestSession.html#tymethod.session)
/// method. `RequestSession` trait is implemented for `HttpRequest`.
///
/// ```rust
/// use actix_web::*;
/// use actix_web::middleware::RequestSession;
///
/// fn index(mut req: HttpRequest) -> Result<&'static str> {
///     // access session data
///     if let Some(count) = req.session().get::<i32>("counter")? {
///         req.session().set("counter", count+1)?;
///     } else {
///         req.session().set("counter", 1)?;
///     }
///
///     Ok("Welcome!")
/// }
/// # fn main() {}
/// ```
pub struct Session<'a>(&'a mut SessionImpl);

impl<'a> Session<'a> {
    /// Get a `value` from the session.
    pub fn get<T: Deserialize<'a>>(&'a self, key: &str) -> Result<Option<T>> {
        if let Some(s) = self.0.get(key) {
            Ok(Some(serde_json::from_str(s)?))
        } else {
            Ok(None)
        }
    }

    /// Set a `value` from the session.
    pub fn set<T: Serialize>(&mut self, key: &str, value: T) -> Result<()> {
        self.0.set(key, serde_json::to_string(&value)?);
        Ok(())
    }

    /// Remove value from the session.
    pub fn remove(&'a mut self, key: &str) {
        self.0.remove(key)
    }

    /// Clear the session.
    pub fn clear(&'a mut self) {
        self.0.clear()
    }
}

struct SessionImplBox(Box<SessionImpl>);

#[doc(hidden)]
unsafe impl Send for SessionImplBox {}
#[doc(hidden)]
unsafe impl Sync for SessionImplBox {}

/// Session storage middleware
///
/// ```rust
/// # extern crate actix;
/// # extern crate actix_web;
/// use actix_web::App;
/// use actix_web::middleware::{SessionStorage, CookieSessionBackend};
///
/// fn main() {
///    let app = App::new().middleware(
///        SessionStorage::new(                      // <- create session middleware
///            CookieSessionBackend::signed(&[0; 32]) // <- create cookie session backend
///               .secure(false))
///    );
/// }
/// ```
pub struct SessionStorage<T, S>(T, PhantomData<S>);

impl<S, T: SessionBackend<S>> SessionStorage<T, S> {
    /// Create session storage
    pub fn new(backend: T) -> SessionStorage<T, S> {
        SessionStorage(backend, PhantomData)
    }
}

impl<S: 'static, T: SessionBackend<S>> Middleware<S> for SessionStorage<T, S> {
    fn start(&self, req: &mut HttpRequest<S>) -> Result<Started> {
        let mut req = req.clone();

        let fut = self.0
            .from_request(&mut req)
            .then(move |res| match res {
                Ok(sess) => {
                    req.extensions()
                        .insert(Arc::new(SessionImplBox(Box::new(sess))));
                    FutOk(None)
                }
                Err(err) => FutErr(err),
            });
        Ok(Started::Future(Box::new(fut)))
    }

    fn response(
        &self, req: &mut HttpRequest<S>, resp: HttpResponse
    ) -> Result<Response> {
        if let Some(s_box) = req.extensions().remove::<Arc<SessionImplBox>>() {
            s_box.0.write(resp)
        } else {
            Ok(Response::Done(resp))
        }
    }
}

/// A simple key-value storage interface that is internally used by `Session`.
#[doc(hidden)]
pub trait SessionImpl: 'static {
    fn get(&self, key: &str) -> Option<&str>;

    fn set(&mut self, key: &str, value: String);

    fn remove(&mut self, key: &str);

    fn clear(&mut self);

    /// Write session to storage backend.
    fn write(&self, resp: HttpResponse) -> Result<Response>;
}

/// Session's storage backend trait definition.
#[doc(hidden)]
pub trait SessionBackend<S>: Sized + 'static {
    type Session: SessionImpl;
    type ReadFuture: Future<Item = Self::Session, Error = Error>;

    /// Parse the session from request and load data from a storage backend.
    fn from_request(&self, request: &mut HttpRequest<S>) -> Self::ReadFuture;
}

/// Dummy session impl, does not do anything
struct DummySessionImpl;

static mut DUMMY: DummySessionImpl = DummySessionImpl;

impl SessionImpl for DummySessionImpl {
    fn get(&self, _: &str) -> Option<&str> {
        None
    }
    fn set(&mut self, _: &str, _: String) {}
    fn remove(&mut self, _: &str) {}
    fn clear(&mut self) {}
    fn write(&self, resp: HttpResponse) -> Result<Response> {
        Ok(Response::Done(resp))
    }
}

/// Session that uses signed cookies as session storage
pub struct CookieSession {
    changed: bool,
    state: HashMap<String, String>,
    inner: Rc<CookieSessionInner>,
}

/// Errors that can occur during handling cookie session
#[derive(Fail, Debug)]
pub enum CookieSessionError {
    /// Size of the serialized session is greater than 4000 bytes.
    #[fail(display = "Size of the serialized session is greater than 4000 bytes.")]
    Overflow,
    /// Fail to serialize session.
    #[fail(display = "Fail to serialize session")]
    Serialize(JsonError),
}

impl ResponseError for CookieSessionError {}

impl SessionImpl for CookieSession {
    fn get(&self, key: &str) -> Option<&str> {
        if let Some(s) = self.state.get(key) {
            Some(s)
        } else {
            None
        }
    }

    fn set(&mut self, key: &str, value: String) {
        self.changed = true;
        self.state.insert(key.to_owned(), value);
    }

    fn remove(&mut self, key: &str) {
        self.changed = true;
        self.state.remove(key);
    }

    fn clear(&mut self) {
        self.changed = true;
        self.state.clear()
    }

    fn write(&self, mut resp: HttpResponse) -> Result<Response> {
        if self.changed {
            let _ = self.inner.set_cookie(&mut resp, &self.state);
        }
        Ok(Response::Done(resp))
    }
}

enum CookieSecurity {
    Signed,
    Private,
}

struct CookieSessionInner {
    key: Key,
    security: CookieSecurity,
    name: String,
    path: String,
    domain: Option<String>,
    secure: bool,
    max_age: Option<Duration>,
}

impl CookieSessionInner {
    fn new(key: &[u8], security: CookieSecurity) -> CookieSessionInner {
        CookieSessionInner {
            security,
            key: Key::from_master(key),
            name: "actix-session".to_owned(),
            path: "/".to_owned(),
            domain: None,
            secure: true,
            max_age: None,
        }
    }

    fn set_cookie(
        &self, resp: &mut HttpResponse, state: &HashMap<String, String>
    ) -> Result<()> {
        let value =
            serde_json::to_string(&state).map_err(CookieSessionError::Serialize)?;
        if value.len() > 4064 {
            return Err(CookieSessionError::Overflow.into());
        }

        let mut cookie = Cookie::new(self.name.clone(), value);
        cookie.set_path(self.path.clone());
        cookie.set_secure(self.secure);
        cookie.set_http_only(true);

        if let Some(ref domain) = self.domain {
            cookie.set_domain(domain.clone());
        }

        if let Some(max_age) = self.max_age {
            cookie.set_max_age(max_age);
        }

        let mut jar = CookieJar::new();

        match self.security {
            CookieSecurity::Signed => jar.signed(&self.key).add(cookie),
            CookieSecurity::Private => jar.private(&self.key).add(cookie),
        }

        for cookie in jar.delta() {
            let val = HeaderValue::from_str(&cookie.to_string())?;
            resp.headers_mut().append(header::SET_COOKIE, val);
        }

        Ok(())
    }

    fn load<S>(&self, req: &mut HttpRequest<S>) -> HashMap<String, String> {
        if let Ok(cookies) = req.cookies() {
            for cookie in cookies {
                if cookie.name() == self.name {
                    let mut jar = CookieJar::new();
                    jar.add_original(cookie.clone());

                    let cookie_opt = match self.security {
                        CookieSecurity::Signed => jar.signed(&self.key).get(&self.name),
                        CookieSecurity::Private => {
                            jar.private(&self.key).get(&self.name)
                        }
                    };
                    if let Some(cookie) = cookie_opt {
                        if let Ok(val) = serde_json::from_str(cookie.value()) {
                            return val;
                        }
                    }
                }
            }
        }
        HashMap::new()
    }
}

/// Use cookies for session storage.
///
/// `CookieSessionBackend` creates sessions which are limited to storing
/// fewer than 4000 bytes of data (as the payload must fit into a single
/// cookie). An Internal Server Error is generated if the session contains more
/// than 4000 bytes.
///
/// A cookie may have a security policy of *signed* or *private*. Each has a
/// respective `CookieSessionBackend` constructor.
///
/// A *signed* cookie is stored on the client as plaintext alongside
/// a signature such that the cookie may be viewed but not modified by the
/// client.
///
/// A *private* cookie is stored on the client as encrypted text
/// such that it may neither be viewed nor modified by the client.
///
/// The constructors take a key as an argument.
/// This is the private key for cookie session - when this value is changed,
/// all session data is lost. The constructors will panic if the key is less
/// than 32 bytes in length.
///
///
/// # Example
///
/// ```rust
/// # extern crate actix_web;
/// use actix_web::middleware::CookieSessionBackend;
///
/// # fn main() {
/// let backend: CookieSessionBackend = CookieSessionBackend::signed(&[0; 32])
///     .domain("www.rust-lang.org")
///     .name("actix_session")
///     .path("/")
///     .secure(true);
/// # }
/// ```
pub struct CookieSessionBackend(Rc<CookieSessionInner>);

impl CookieSessionBackend {
    /// Construct new *signed* `CookieSessionBackend` instance.
    ///
    /// Panics if key length is less than 32 bytes.
    pub fn signed(key: &[u8]) -> CookieSessionBackend {
        CookieSessionBackend(Rc::new(CookieSessionInner::new(
            key,
            CookieSecurity::Signed,
        )))
    }

    /// Construct new *private* `CookieSessionBackend` instance.
    ///
    /// Panics if key length is less than 32 bytes.
    pub fn private(key: &[u8]) -> CookieSessionBackend {
        CookieSessionBackend(Rc::new(CookieSessionInner::new(
            key,
            CookieSecurity::Private,
        )))
    }

    /// Sets the `path` field in the session cookie being built.
    pub fn path<S: Into<String>>(mut self, value: S) -> CookieSessionBackend {
        Rc::get_mut(&mut self.0).unwrap().path = value.into();
        self
    }

    /// Sets the `name` field in the session cookie being built.
    pub fn name<S: Into<String>>(mut self, value: S) -> CookieSessionBackend {
        Rc::get_mut(&mut self.0).unwrap().name = value.into();
        self
    }

    /// Sets the `domain` field in the session cookie being built.
    pub fn domain<S: Into<String>>(mut self, value: S) -> CookieSessionBackend {
        Rc::get_mut(&mut self.0).unwrap().domain = Some(value.into());
        self
    }

    /// Sets the `secure` field in the session cookie being built.
    ///
    /// If the `secure` field is set, a cookie will only be transmitted when the
    /// connection is secure - i.e. `https`
    pub fn secure(mut self, value: bool) -> CookieSessionBackend {
        Rc::get_mut(&mut self.0).unwrap().secure = value;
        self
    }

    /// Sets the `max-age` field in the session cookie being built.
    pub fn max_age(mut self, value: Duration) -> CookieSessionBackend {
        Rc::get_mut(&mut self.0).unwrap().max_age = Some(value);
        self
    }
}

impl<S> SessionBackend<S> for CookieSessionBackend {
    type Session = CookieSession;
    type ReadFuture = FutureResult<CookieSession, Error>;

    fn from_request(&self, req: &mut HttpRequest<S>) -> Self::ReadFuture {
        let state = self.0.load(req);
        FutOk(CookieSession {
            changed: false,
            inner: Rc::clone(&self.0),
            state,
        })
    }
}