#!/usr/bin/env python3

import threading
import queue
import sys
import time
import socket
import random
import yaml
import paramiko


CONFIG = {"username": "tbastian", "workload": 0.5}


class Task:
    """ A task to be performed, consisting in a shell command, with some file
    redirected to its standard input and some file its standard output is redirected
    to. """

    class Failure(Exception):
        """ Raised if a Task failed to complete """

        def __init__(self, msg=None):
            self.msg = msg

    def __init__(self, command, in_file, out_file, human_label):
        self.command = command
        self.in_file = in_file
        self.out_file = out_file
        self.human_label = human_label

    def run(self, client):
        """ Run the task on a given client """
        try:
            stdin, stdout, stderr = client.exec_command(self.command)

            if self.in_file:
                with open(self.in_file, "rb") as in_handle:
                    buf = in_handle.read(1024)
                    while buf:
                        stdin.write(buf)
                        buf = in_handle.read(1024)
            stdin.close()

            if self.out_file:
                with open(self.out_file, "wb") as out_handle:
                    buf = stdout.read(1024)
                    while buf:
                        out_handle.write(buf)
                        buf = stdout.read(1024)

        except paramiko.ssh_exception.SSHException:
            raise Task.Failure("SSH Exception")
        except FileNotFoundError as exn:
            raise Task.Failure("{}".format(exn))


class WorkingThread(threading.Thread):
    """ A thread actually getting work done on a given machine """

    def __init__(self, host, addr, workqueue, failures):
        self.host = host
        self.addr = addr
        self.client = None
        self.workqueue = workqueue
        self.failures = failures
        super().__init__()

    def run(self):
        self.client = paramiko.client.SSHClient()
        self.client.load_system_host_keys()
        for n_try in range(3):
            try:
                self.client.connect(self.addr, username=CONFIG["username"])
                break
            except Exception as exn:
                delay = 3 + random.random() * 4
                print(
                    (
                        "[{}] Failed to connect. Retry in {:.02f} seconds."
                        + "Exception:\n{}"
                    ).format(self.host, delay, exn),
                    file=sys.stderr,
                )
                time.sleep(delay)
        else:
            print(
                "[{}] Failed to connect, stopping thread.".format(self.host),
                file=sys.stderr,
            )
            return

        try:
            while True:
                task = self.workqueue.get_nowait()  # Raises `Empty` when done
                try:
                    task.run(self.client)
                except Task.Failure as exn:
                    print(
                        "[{}] ERROR: task failed: {} - {}".format(
                            self.host, task.human_label, exn.msg
                        ),
                        file=sys.stderr,
                    )
                    self.failures.append((task, exn.msg))
        except queue.Empty:
            pass


class HostsFile:
    """ Interface to an hosts file """

    def __init__(self, path):
        self.path = path
        self.hosts = {}
        self._parse()

    def _parse(self):
        with open(self.path, "r") as handle:
            parsed = yaml.safe_load(handle)

        REQUIRED_FIELDS = ["host", "cores"]
        for entry in parsed:
            for field in REQUIRED_FIELDS:
                if field not in entry:
                    if "host" in entry:
                        raise Exception(
                            "Host {} has no {}".format(entry["host"], field)
                        )
                    raise Exception("Host has no {}".format(field))
            self.hosts[entry["host"]] = {
                "cores": entry["cores"],
                "addr": socket.gethostbyname(entry["host"]),
            }


class TasksFile:
    """ Interface to a tasks file """

    def __init__(self, path):
        self.path = path
        self.queue = queue.Queue()
        self._parse()
        self.initial_task_count = self.queue.qsize()

    def count_completed(self):
        return self.initial_task_count - self.queue.qsize()

    def percent_completed(self):
        return (self.count_completed() / self.initial_task_count) * 100

    def _parse(self):
        with open(self.path, "r") as handle:
            parsed = yaml.safe_load(handle)

        for cmd_entry in parsed:
            self._parse_cmd(cmd_entry)

    def _parse_cmd(self, cmd):
        REQUIRED_FIELDS = ["command", "data"]
        for field in REQUIRED_FIELDS:
            if field not in cmd:
                if "command" in cmd:
                    raise Exception(
                        "Command {} has no {}".format(cmd["command"], field)
                    )
                raise Exception("Command has no {}".format(field))

        for data_entry in cmd["data"]:
            task = Task(
                cmd["command"],
                data_entry.get("in"),
                data_entry.get("out"),
                data_entry.get("label", data_entry.get("in")),
            )
            self.queue.put(task)


class Orchestrator:
    """ Combines it all and actually runs stuff """

    def __init__(self):
        self.hosts = HostsFile("hosts.yml")
        self.tasks = TasksFile("tasks.yml")
        self.failures = []
        self.threads = []

        self._spawn_host_threads()

    def _spawn_host_threads(self):
        for host in self.hosts.hosts:
            host_details = self.hosts.hosts[host]
            for core_id in range(int(host_details["cores"] * CONFIG["workload"])):
                if len(self.threads) >= self.tasks.initial_task_count:
                    return
                self.threads.append(
                    WorkingThread(
                        host, host_details["addr"], self.tasks.queue, self.failures
                    )
                )

    def start(self):
        for thread in self.threads:
            thread.start()

        for thread in self.threads:
            while thread.is_alive():
                thread.join(timeout=1.0)

                print(
                    "\r[{:05.1f}% - {}/{}]".format(
                        self.tasks.percent_completed(),
                        self.tasks.count_completed(),
                        self.tasks.initial_task_count,
                    ),
                    end="",
                )


if __name__ == "__main__":
    orchestrator = Orchestrator()
    orchestrator.start()
    print("")

    if orchestrator.failures:
        nb_failures = len(orchestrator.failures)
        print(
            "{} FAILURES ({:05.1f}%)".format(
                nb_failures, 100 * nb_failures / orchestrator.tasks.initial_task_count
            ),
            file=sys.stderr,
        )
        for task, msg in orchestrator.failures:
            print("* {}: {}".format(task.human_label, msg), file=sys.stderr)