#!/usr/bin/env python

import argparse
import subprocess
import sys
import syslog
import re


def get_command_result(command):
    """Executes the command and return the resulting output.

    Args:
        command: A string contains the command to be executed.

    Returns:
        A string which contains the output of command.
    """
    command_stdout = ""

    try:
        proc_instance = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                                         shell=True, universal_newlines=True)
        command_stdout, command_stderr = proc_instance.communicate()
        if proc_instance.returncode != 0:
            syslog.syslog(syslog.LOG_ERR, "[memory_checker] Failed to execute the command '{}'. Return code: '{}'"
                          .format(command, proc_instance.returncode))
            sys.exit(1)
    except (OSError, ValueError) as err:
        syslog.syslog(syslog.LOG_ERR, "[memory_checker] Failed to execute the command '{}'. Error: '{}'"
                      .format(command, err))
        sys.exit(2)

    return command_stdout.strip()


def check_memory_usage(container_name, threshold_value):
    """Checks the memory usage of a container and writes an alerting messages into
    the syslog if the memory usage is larger than the threshold value.

    Args:
        container_name: A string represtents name of a container
        threshold_value: An integer indicates the threshold value (Bytes) of memory usage.

    Returns:
        None.
    """
    command = "docker stats --no-stream --format \{{\{{.MemUsage\}}\}} {}".format(container_name)
    command_stdout = get_command_result(command)
    mem_usage = command_stdout.split("/")[0].strip()
    match_obj = re.match(r"\d+\.?\d*", mem_usage)
    if match_obj:
        mem_usage_value = float(mem_usage[match_obj.start():match_obj.end()])
        mem_usage_unit = mem_usage[match_obj.end():]

        mem_usage_bytes = 0.0
        if mem_usage_unit == "B":
            mem_usage_bytes = mem_usage_value
        elif mem_usage_unit == "KiB":
            mem_usage_bytes = mem_usage_value * 1024
        elif mem_usage_unit == "MiB":
            mem_usage_bytes = mem_usage_value * 1024 ** 2
        elif mem_usage_unit == "GiB":
            mem_usage_bytes = mem_usage_value * 1024 ** 3

        if mem_usage_bytes > threshold_value:
            print("[{}]: Memory usage ({} Bytes) is larger than the threshold ({} Bytes)!"
                  .format(container_name, mem_usage_bytes, threshold_value))
            sys.exit(3)
    else:
        syslog.syslog(syslog.LOG_ERR, "[memory_checker] Failed to retrieve memory value from '{}'"
                      .format(mem_usage))
        sys.exit(4)


def main():
    parser = argparse.ArgumentParser(description="Check memory usage of a container \
            and an alerting message will be written into syslog if memory usage \
            is larger than the threshold value", usage="/usr/bin/memory_checker <container_name> <threshold_value_in_bytes>")
    parser.add_argument("container_name", help="container name")
    # TODO: Currently the threshold value is hard coded as a command line argument and will
    # remove this in the new version since we want to read this value from 'CONFIG_DB'.
    parser.add_argument("threshold_value", type=int, help="threshold value in bytes")
    args = parser.parse_args()

    check_memory_usage(args.container_name, args.threshold_value)


if __name__ == "__main__":
    main()