//! A simple connection pool

extern mod extra;

use extra::arc::MutexArc;

use super::{PostgresNotificationIterator,
            PostgresConnection,
            NormalPostgresStatement,
            PostgresDbError,
            PostgresConnectError,
            PostgresTransaction};
use super::types::ToSql;

struct InnerConnectionPool {
    url: ~str,
    pool: ~[PostgresConnection],
}

impl InnerConnectionPool {
    fn new_connection(&mut self) -> Option<PostgresConnectError> {
        match PostgresConnection::try_connect(self.url) {
            Ok(conn) => {
                self.pool.push(conn);
                None
            }
            Err(err) => Some(err)
        }
    }
}

/// A simple fixed-size Postgres connection pool.
///
/// It can be shared across tasks.
#[deriving(Clone)]
pub struct PostgresConnectionPool {
    priv pool: MutexArc<InnerConnectionPool>
}

impl PostgresConnectionPool {
    /// Attempts to create a new pool with the specified number of connections.
    ///
    /// Returns an error if the specified number of connections cannot be
    /// created.
    pub fn try_new(url: &str, pool_size: uint)
            -> Result<PostgresConnectionPool, PostgresConnectError> {
        let mut pool = InnerConnectionPool {
            url: url.to_owned(),
            pool: ~[],
        };

        while pool.pool.len() < pool_size {
            match pool.new_connection() {
                None => (),
                Some(err) => return Err(err)
            }
        }

        Ok(PostgresConnectionPool {
            pool: MutexArc::new(pool)
        })
    }

    /// A convenience function wrapping `try_new`.
    ///
    /// Fails if the pool cannot be created.
    pub fn new(url: &str, pool_size: uint) -> PostgresConnectionPool {
        match PostgresConnectionPool::try_new(url, pool_size) {
            Ok(pool) => pool,
            Err(err) => fail!("Unable to initialize pool: {}", err.to_str())
        }
    }

    /// Retrieves a connection from the pool.
    ///
    /// If all connections are in use, blocks until one becomes available.
    pub fn get_connection(&self) -> PooledPostgresConnection {
        let conn = unsafe {
            do self.pool.unsafe_access_cond |pool, cvar| {
                while pool.pool.is_empty() {
                    cvar.wait();
                }

                pool.pool.pop()
            }
        };

        PooledPostgresConnection {
            pool: self.clone(),
            conn: Some(conn)
        }
    }
}

/// A Postgres connection pulled from a connection pool.
///
/// It will be returned to the pool when it falls out of scope, even due to
/// task failure.
pub struct PooledPostgresConnection {
    priv pool: PostgresConnectionPool,
    // TODO remove the Option wrapper when drop takes self by value
    priv conn: Option<PostgresConnection>
}

impl Drop for PooledPostgresConnection {
    fn drop(&mut self) {
        unsafe {
            do self.pool.pool.unsafe_access |pool| {
                pool.pool.push(self.conn.take_unwrap());
            }
        }
    }
}

impl PooledPostgresConnection {
    /// Like `PostgresConnection::try_prepare`.
    pub fn try_prepare<'a>(&'a self, query: &str)
            -> Result<NormalPostgresStatement<'a>, PostgresDbError> {
        self.conn.get_ref().try_prepare(query)
    }

    /// Like `PostgresConnection::prepare`.
    pub fn prepare<'a>(&'a self, query: &str) -> NormalPostgresStatement<'a> {
        self.conn.get_ref().prepare(query)
    }

    /// Like `PostgresConnection::try_update`.
    pub fn try_update(&self, query: &str, params: &[&ToSql])
            -> Result<uint, PostgresDbError> {
        self.conn.get_ref().try_update(query, params)
    }

    /// Like `PostgresConnection::update`.
    pub fn update(&self, query: &str, params: &[&ToSql]) -> uint {
        self.conn.get_ref().update(query, params)
    }

    /// Like `PostgresConnection::transaction`.
    pub fn transaction<'a>(&'a self) -> PostgresTransaction<'a> {
        self.conn.get_ref().transaction()
    }

    /// Like `PostgresConnection::notifications`.
    pub fn notifications<'a>(&'a self) -> PostgresNotificationIterator<'a> {
        self.conn.get_ref().notifications()
    }
}