import os
import psycopg2
import psycopg2.extras
import time

from subprocess import call, STDOUT
from tempfile import TemporaryFile


def available_ram():
    'determine amount of RAM in the system (in megabytes)'

    system = os.popen("uname").readlines()[0].split()[0]

    if system == 'FreeBSD':
        mem = int(os.popen("sysctl hw.physmem").readlines()[0].split()[1])
        mem /= 1024
        mem /= 1024
    elif system == 'Linux':
        mem = int(os.popen("free -m").readlines()[1].split()[1])
    else:
        mem = 0

    return mem


def run_cmd(args, env=None, cwd=None):
    'run command (a subprocess.call wrapper)'

    with TemporaryFile() as strout:

        start = time.time()
        retcode = call(args, env=env, cwd=cwd, stdout=strout, stderr=STDOUT)

        strout.seek(0)
        return (retcode, strout.read(), (time.time() - start))


def connect(dbname, conn, cursor, nretries=60, delay=1.0):
    '''Try opening a connection and a cursor. If it does not succeed (e.g.
    when the database is performing recovery after a crash, retry multiple
    times (as specified by nretries and delay in seconds).
    '''

    # if we already have connection and a cursor, return it
    if conn and cursor:
        return (conn, cursor)

    # we'll try repeatedly, with delays between the attempts
    i = 0
    while i < nretries:

        i += 1

        try:
            conn = psycopg2.connect('host=localhost dbname=%s' % (dbname,))
            # TODO do we actually need autocommit?
            conn.autocommit = True
            cursor = conn.cursor(cursor_factory=psycopg2.extras.RealDictCursor)

            return (conn, cursor)
        except Exception as e:
            # connection failure - sleep for a while, then try again
            time.sleep(delay)

    return (None, None)


def disconnect(conn, cursor):
    '''Make sure we're disconnected (but prevent exceptions)'''

    try:
        cursor.close()
    except Exception as e:
        pass

    try:
        conn.close()
    except Exception as e:
        pass