# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.


"""This file provides util functions used by RPM infrastructure."""


import csv
import os
import logging

import rpm_infrastructure_exception
from config import rpm_config


MAPPING_FILE = os.path.join(
        os.path.dirname(__file__),
        rpm_config.get('CiscoPOE', 'servo_interface_mapping_file'))


def load_servo_interface_mapping(mapping_file=MAPPING_FILE):
    """
    Load servo-switch-interface mapping from a CSV file.

    In the file, the first column represents servo hostnames,
    the second column represents switch hostnames, the third column
    represents interface names. Columns are saparated by comma.

    chromeos1-rack3-host12-servo,chromeos1-poe-switch1,fa31
    chromeos1-rack4-host2-servo,chromeos1-poe-switch1,fa32
    ,chromeos1-poe-switch1,fa33
    ...

    A row without a servo hostname indicates that no servo
    has been connected to the corresponding interface.
    This method ignores such rows.

    @param mapping_file: A csv file that stores the mapping.
                         If None, the setting in rpm_config.ini will be used.

    @return a dictionary that maps servo host name to a
              tuple of switch hostname and interface.
              e.g. {
              'chromeos1-rack3-host12-servo': ('chromeos1-poe-switch1', 'fa31')
               ...}

    @raises: rpm_infrastructure_exception.RPMInfrastructureException
             when arg mapping_file is None.
    """
    if not mapping_file:
        raise rpm_infrastructure_exception.RPMInfrastructureException(
                'mapping_file is None.')
    servo_interface = {}
    with open(mapping_file) as csvfile:
        reader = csv.reader(csvfile, delimiter=',')
        for row in reader:
            servo_hostname = row[0].strip()
            switch_hostname = row[1].strip()
            interface = row[2].strip()
            if servo_hostname:
                servo_interface[servo_hostname] = (switch_hostname, interface)
    return servo_interface


def reload_servo_interface_mapping_if_necessary(
        check_point, mapping_file=MAPPING_FILE):
    """Reload the servo-interface mapping file if it is modified.

    This method checks if the last-modified time of |mapping_file| is
    later than |check_point|, if so, it reloads the file.

    @param check_point: A float number representing a time, used to determine
                        whether we need to reload the mapping file.
    @param mapping_file: A csv file that stores the mapping, if none,
                         the setting in rpm_config.ini will be used.

    @return: If the file is reloaded, returns a tuple
             (last_modified_time, servo_interface) where
             the first element is the last_modified_time of the
             mapping file, the second element is a dictionary that
             maps servo hostname to (switch hostname, interface).
             If the file is not reloaded, return None.

    @raises: rpm_infrastructure_exception.RPMInfrastructureException
             when arg mapping_file is None.
    """
    if not mapping_file:
        raise rpm_infrastructure_exception.RPMInfrastructureException(
                'mapping_file is None.')
    last_modified = os.path.getmtime(mapping_file)
    if check_point < last_modified:
        servo_interface = load_servo_interface_mapping(mapping_file)
        logging.info('Servo-interface mapping file %s is reloaded.',
                     mapping_file)
        return (last_modified, servo_interface)
    return None