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use diesel::sqlite::SqliteConnection;
use dotenv::dotenv;
use r2d2;
use r2d2_diesel::ConnectionManager;
use rocket::http::Status;
use rocket::request::{self, FromRequest};
use rocket::{Outcome, Request, State};
use std::env;
use std::ops::Deref;

/// An alias to the type for a pool of Diesel `SQLite` connections.
pub type Pool = r2d2::Pool<ConnectionManager<SqliteConnection>>;

/// Initializes a database pool.
pub fn init_pool() -> Pool {
    dotenv().ok();
    let database_url = env::var("DATABASE_URL").expect("DATABASE_URL must be set");
    let manager = ConnectionManager::<SqliteConnection>::new(database_url);
    r2d2::Pool::new(manager).expect("db pool")
}

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

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

    #[inline(always)]
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

/// 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 Conn {
    type Error = ();

    fn from_request(request: &'a Request<'r>) -> request::Outcome<Conn, ()> {
        let pool = match request.guard::<State<Pool>>() {
            Outcome::Success(pool) => pool,
            Outcome::Failure(e) => return Outcome::Failure(e),
            Outcome::Forward(_) => return Outcome::Forward(()),
        };

        match pool.get() {
            Ok(conn) => Outcome::Success(Conn(conn)),
            Err(_) => Outcome::Failure((Status::ServiceUnavailable, ())),
        }
    }
}