# -*- coding: utf-8 -*-
#
# PgManager - manage database connections
#
# Requires: Python 2.6, psycopg2
#
# Copyright (c) 2010, 2011  Radek Brich <radek.brich@devl.cz>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

"""Postgres database connection manager

PgManager wraps psycopg2 connect function, adding following features:

 * Manage database connection parameters - link connection parameters
   to an unique identifier, retrieve connection object by this identifier

 * Connection pooling - connections with same identifier are pooled and reused

 * Easy query using the with statement - retrieve cursor directly by connection
   identifier, don't worry about connections

 * Dict rows - cursor has additional methods like fetchall_dict(), which
   returns dict row instead of ordinary list-like row

Example:

import pgmanager

pgm = pgmanager.get_instance()
pgm.create_conn(hostaddr='127.0.0.1', dbname='postgres')

with pgm.cursor() as curs:
    curs.execute('SELECT now() AS now')
    row = curs.fetchone_dict()
    print row.now

First, we have obtained PgManager instance. This is like calling
PgManager(), although in our example the instance is global. That means
getting the instance in another module brings us all the defined connections
etc.

On second line we created connection named 'default' (this name can be left out).
The with statement obtains connection (actually connects to database when needed),
then returns cursor for this connection. On exit, the connection is returned
to the pool or closed (depending on number of connections on pool and setting
of keep_open parameter).

The row returned by fetchone_dict() is special dict object, which can be accessed
using item or attribute access, that is row['now'] or row.now.
"""

from contextlib import contextmanager
import logging
import threading
import select

import psycopg2
import psycopg2.extensions

from psycopg2 import DatabaseError, IntegrityError


class PgManagerError(Exception):

    pass


class ConnectionInfo:

    def __init__(self, dsn, isolation_level=None, init_statement=None, keep_open=1):
        self.dsn = dsn
        self.isolation_level = isolation_level
        self.init_statement = init_statement
        self.keep_open = keep_open


class RowDict(dict):

    def __getattr__(self, key):
        return self[key]


class Cursor(psycopg2.extensions.cursor):

    def execute(self, query, args=None):
        try:
            return super(Cursor, self).execute(query, args)
        finally:
            log.debug(self.query.decode('utf8'))

    def callproc(self, procname, args=None):
        try:
            return super(Cursor, self).callproc(procname, args)
        finally:
            log.debug(self.query.decode('utf8'))

    def row_dict(self, row, lstrip=None):
        adjustname = lambda a: a
        if lstrip:
            adjustname = lambda a: a.lstrip(lstrip)
        return RowDict(zip([adjustname(desc[0]) for desc in self.description], row))

    def fetchone_dict(self, lstrip=None):
        row = super(Cursor, self).fetchone()
        if not row:
            return row
        return self.row_dict(row, lstrip)

    def fetchall_dict(self, lstrip=None):
        rows = super(Cursor, self).fetchall()
        return [self.row_dict(row, lstrip) for row in rows]


class Connection(psycopg2.extensions.connection):

    def cursor(self, name=None):
        if name is None:
            return super(Connection, self).cursor(cursor_factory=Cursor)
        else:
            return super(Connection, self).cursor(name, cursor_factory=Cursor)


class PgManager:

    def __init__(self):
        self.conn_known = {}  # available connections
        self.conn_pool = {}
        self.lock = threading.Lock()

    def __del__(self):
        for conn in tuple(self.conn_known.keys()):
            self.destroy_conn(conn)

    def create_conn(self, name='default', isolation_level=None, dsn=None, **kw):
        '''Create named connection.'''
        if name in self.conn_known:
            raise PgManagerError('Connection name "%s" already registered.' % name)

        if dsn is None:
            dsn = ' '.join([x[0]+'='+str(x[1]) for x in kw.items()])

        isolation_level = self._normalize_isolation_level(isolation_level)
        ci = ConnectionInfo(dsn, isolation_level)

        self.conn_known[name] = ci
        self.conn_pool[name] = []

    def close_conn(self, name='default'):
        '''Close all connections of given name.
        
        Connection credentials are still saved.
        
        '''
        while len(self.conn_pool[name]):
            conn = self.conn_pool[name].pop()
            conn.close()

    def destroy_conn(self, name='default'):
        '''Destroy connection.
        
        Counterpart of create_conn.
        
        '''
        if not name in self.conn_known:
            raise PgManagerError('Connection name "%s" not registered.' % name)

        self.close_conn(name)

        del self.conn_known[name]
        del self.conn_pool[name]

    def get_conn(self, name='default'):
        '''Get connection of name 'name' from pool.'''
        self.lock.acquire()
        try:
            if not name in self.conn_known:
                raise PgManagerError("Connection name '%s' not registered." % name)

            conn = None
            while len(self.conn_pool[name]) and conn is None:
                conn = self.conn_pool[name].pop()
                if conn.closed:
                    conn = None

            if conn is None:
                ci = self.conn_known[name]
                conn = psycopg2.connect(ci.dsn, connection_factory=Connection)
                if not ci.isolation_level is None:
                    conn.set_isolation_level(ci.isolation_level)
                if ci.init_statement:
                    curs = conn.cursor()
                    curs.execute(ci.init_statement)
                    curs.close()
        finally:
            self.lock.release()
        return conn

    def put_conn(self, conn, name='default'):
        '''Put connection back to pool.
        
        Name must be same as used for get_conn,
        otherwise things become broken.
        
        '''
        self.lock.acquire()
        try:
            if not name in self.conn_known:
                raise PgManagerError("Connection name '%s' not registered." % name)

            if len(self.conn_pool[name]) >= self.conn_known[name].keep_open:
                conn.close()
                return

            if conn.get_transaction_status() == psycopg2.extensions.TRANSACTION_STATUS_UNKNOWN:
                conn.close()
                return

            # connection returned to the pool must not be in transaction
            if conn.get_transaction_status() != psycopg2.extensions.TRANSACTION_STATUS_IDLE:
                conn.rollback()

            self.conn_pool[name].append(conn)
        finally:
            self.lock.release()

    @contextmanager
    def cursor(self, name='default'):
        '''Cursor context.
        
        Uses any connection of name 'name' from pool
        and returns cursor for that connection.
        
        '''
        conn = self.get_conn(name)

        try:
            curs = conn.cursor()
            yield curs
        finally:
            curs.close()
            self.put_conn(conn, name)

    def wait_for_notify(self, name='default', timeout=5):
        '''Wait for asynchronous notifies, return the last one.
        
        Returns None on timeout.
        
        '''
        conn = self.get_conn(name)
        
        try:
            # any residual notify?
            # then return it, that should not break anything
            if conn.notifies:
                return conn.notifies.pop()

            if select.select([conn], [], [], timeout) == ([], [], []):
                # timeout
                return None
            else:
                conn.poll()

                # return just the last notify (we do not care for older ones)
                if conn.notifies:
                    return conn.notifies.pop()
                return None
        finally:
            # clean notifies
            while conn.notifies:
                conn.notifies.pop()
            self.put_conn(conn, name)

    def _normalize_isolation_level(self, level):
        if type(level) == str:
            if level.lower() == 'autocommit':
                return psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
            if level.lower() == 'read_committed':
                return psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
            if level.lower() == 'serializable':
                return psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE
            raise PgManagerError('Unknown isolation level name: "%s"', level)
        return level


try:
    NullHandler = logging.NullHandler
except AttributeError:
    class NullHandler(logging.Handler):
        def emit(self, record):
            pass


log = logging.getLogger("pgmanager")
log.addHandler(NullHandler())


instance = None


def get_instance():
    global instance
    if instance is None:
        instance = PgManager()
    return instance