use diesel::pg::PgConnection;
use r2d2;
use r2d2_diesel::ConnectionManager;
use dotenv::dotenv;
use std::env;

// An alias to the type for a pool of Diesel PostgreSql connections.
type Pool = r2d2::Pool<ConnectionManager<PgConnection>>;

/// Initializes a database pool.
pub fn init_db_pool() -> Pool {
    dotenv().ok();

    let config = r2d2::Config::default();
    let dburl = env::var("DATABASE_URL")
        .expect("DATABASE_URL environment variable must be set");

    let manager = ConnectionManager::<PgConnection>::new(dburl);
    r2d2::Pool::new(config, manager).expect("db pool")
}

use std::ops::Deref;
use rocket::http::Status;
use rocket::request::{self, FromRequest};
use rocket::{Request, State, Outcome};

// Connection request guard type: a wrapper around an r2d2 pooled connection.
pub struct DbConn(pub r2d2::PooledConnection<ConnectionManager<PgConnection>>);

/// Attempts to retrieve a single connection from the managed database pool. If
/// no pool is currently managed, fails with an `InternalServerError` status. If
/// no connections are available, fails with a `ServiceUnavailable` status.
impl<'a, 'r> FromRequest<'a, 'r> for DbConn {
    type Error = ();

    fn from_request(request: &'a Request<'r>) -> request::Outcome<DbConn, ()> {
        let pool = request.guard::<State<Pool>>()?;
        match pool.get() {
            Ok(conn) => Outcome::Success(DbConn(conn)),
            Err(_) => Outcome::Failure((Status::ServiceUnavailable, ()))
        }
    }
}

// For the convenience of using an &DbConn as an &SqliteConnection.
impl Deref for DbConn {
    type Target = PgConnection;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

macro_rules! implement_responder_for {
    // Implement a responder for the given template type
    //
    // Seems I can't add the lifetime after the matcher,
    // like this: `$template_type<'a>`
    // So it will have to be passed in to the argument at
    // the macro incovation instead.
    ($template_type:ty) => (
        impl<'a> ::rocket::response::Responder<'a> for $template_type {
            fn respond_to(self, _: &::rocket::Request) -> Result<::rocket::Response<'static>, ::rocket::http::Status> {
                ::rocket::Response::build()
                    .header(::rocket::http::ContentType::HTML)
                    .sized_body(::std::io::Cursor::new(format!("{}", &self)))
                    .ok()
            }
        }
    )
}