import time
import sys
import datetime
import threading


class SimulationThread(threading.Thread):
    """
    Singleton class for the simulation thread.

    Usage is the call the classmethod initialize first
    """

    instance = None

    @classmethod
    def initialize(cls, periods, start_time=None, run_time=None, time_factor=1.0, verbose=False):
        """
        Initializes the singleton Thread with the given values.  The given arguments are passed directly to the instance constructor.  See the `__init__` method for argument details.
        """
        cls.instance = SimulationThread(periods, start_time, run_time, time_factor, verbose)

    @classmethod
    def get_instance(cls):
        """
        Returns the simulation thread object, or None if initialize() has not been called.
        """
        return cls.instance

    def __init__(self, periods, start_time, run_time, time_factor, verbose):
        """
        Creates a simulation with the provided data and settings.

        Args:
            periods (list): A list of dictionaries that represent the traffic light periods (peak/off-peak etc) as specified in the problem description.  See the provided `periods.json` file for the intended format, as this variable is intended to be a json.load() version of this data.
            start_time (datetime.time): The time at which the simulation should start.
            run_time (int): The amount of (real) time the simulation should run for before terminating.  If None, run indefinitely or until signal_stop() is called.
            time_factor (float): The time "accelleration" factor at which the simulation should run.  A value of 1.0 indicates indentity with real time, and higher values run faster (e.g. 4.0 = four simulated seconds for each real second).
            verbose (bool): If True, outputs progress information to stdout (for testing purposes only).
        """
        # Parent constructor call (required). Uses parameter daemon=True to ensure thread shutdown when parent program finishes executing
        # See https://docs.python.org/3/library/threading.html
        super().__init__(daemon=True)

        self.mutex = threading.Lock()

        self.periods = periods
        self.start_simulation_time = start_time
        self.run_real_time = run_time
        self.time_factor = time_factor
        self.verbose = verbose

        # NOT a status variable, instead indicates whether signal_stop() has been called
        self.running = True

        self.current_period_index = 0
        self.current_state_index = 0

        self.next_changeover_real_time = None

        self.start_simulation_datetime = None
        self.current_simulation_datetime = None

        # For convenience, convert all ISO format times to datetime.time objects
        for period in self.periods:
            period["timestart"] = datetime.time.fromisoformat(period["timestart"])

        # Essential - periods are assumed to be in chronological order
        self.periods.sort(key=lambda x: x["timestart"])

    def signal_stop(self):
        """
        Signals the thread to stop, regardless of run time
        """
        self.mutex.acquire()
        self.running = False
        self.mutex.release()

    def force_to_time(self, new_time):
        """
        Resets the simulation time to the provided time.  This is for testing purposes; the current state is IGNORED and the sequence immediately resets to the beginning.
        """
        new_simulation_datetime = datetime.datetime.fromisoformat("1900-01-01 " + new_time.isoformat())
        self.mutex.acquire()
        print()
        self.current_period_index = self._get_period_index(self.periods, new_simulation_datetime.time())
        self.current_state_index = 0
        self.next_changeover_real_time = time.time() + (self.periods[self.current_period_index]["states"][self.current_state_index]["duration"] / self.time_factor)
        self.mutex.release()

    def get_snapshot(self):
        """
        Returns a dictionary of the current simulated state
        """
        self.mutex.acquire()
        return_data = {
            "current_period_name": self.periods[self.current_period_index]["name"],
            "current_period_verbose_name": self.periods[self.current_period_index]["verbose-name"],
            "current_period_index": self.current_period_index,
            "current_state_index": self.current_state_index,
            "current_state_data": self.periods[self.current_period_index]["states"][self.current_state_index],
            "next_changeover_real_time": self.next_changeover_real_time,
            "simulation_time": self.current_simulation_datetime.time(),
            "time_remaining": (self.next_changeover_real_time - time.time()) * self.time_factor,
        }
        self.mutex.release()
        return return_data

    def _get_period_index(self, test_time: datetime.time):
        """
        Returns the index of the period corresponding to the given time
        """
        for i, period in enumerate(self.periods):
            if i == len(self.periods) - 1:
                return i
            if test_time >= period["timestart"] and \
                    test_time < self.periods[i + 1]["timestart"]:
                return i

        # Should NOT be reached since last state assumed to last until midnight
        raise

    def run(self):
        """
        Main thread loop.  Note that this method should NOT be called directly: as a subclass of threading.Thread, the inherited start() method should be used instead.

        The loop executes until one of the following conditions is met:
        - The given run_time is exceeded (in real seconds), or
        - signal_stop() has been called
        - The executing program finishes (daemon=True)
        """
        start_real_time = time.time()

        if self.start_simulation_time is None:
            self.start_simulation_datetime = datetime.datetime.now()
        else:
            self.start_simulation_datetime = datetime.datetime.fromisoformat(
                "1900-01-01 " + self.start_simulation_time.isoformat())

        self.current_period_index = self._get_period_index(self.start_simulation_datetime.time())
        self.current_state_index = 0

        self.next_changeover_real_time = start_real_time + (self.periods[self.current_period_index]["states"][self.current_state_index]["duration"] / self.time_factor)

        if self.verbose:
            print("Starting with simulation time {}".format(self.start_simulation_datetime.time()))
            print("Initial state data: {}".format(self.periods[self.current_period_index]["states"][self.current_state_index]))
            if self.run_real_time is None:
                print("No simulation time limit.")
            else:
                print("Simulation duration (in real second(s)): {}".format(self.run_real_time))
            print("Time compression factor: {}".format(self.time_factor))

        while (self.run_real_time is None) or (self.run_real_time is not None and time.time() < start_real_time + self.run_real_time):
            self.mutex.acquire()

            if not self.running:
                self.mutex.release()
                break

            now = time.time()
            self.current_simulation_datetime = self.start_simulation_datetime + datetime.timedelta(seconds=int((now - start_real_time) * self.time_factor))
            timed_period_index = self._get_period_index(self.current_simulation_datetime.time())

            if now >= self.next_changeover_real_time:
                timed_period_index = self._get_period_index(self.current_simulation_datetime.time())
                if timed_period_index != self.current_period_index and self.current_state_index == len(self.periods[self.current_period_index]["states"])-1:
                    if self.verbose:
                        print()
                        print("{} : Changing PERIOD from {} to {}".format(self.current_simulation_datetime.time(), self.periods[self.current_period_index]["name"], self.periods[timed_period_index]["name"]))
                        print("  Old state data: {}".format(self.periods[self.current_period_index]["states"][self.current_state_index]))

                    # Safe to change period
                    self.current_period_index = timed_period_index
                    self.current_state_index = 0

                    if self.verbose:
                        print("  New state data: {}".format(self.periods[self.current_period_index]["states"][self.current_state_index]))
                        print("  Next changeover in {} second(s)".format(self.periods[self.current_period_index]["states"][self.current_state_index]["duration"]))
                else:
                    # Current sequence still completing, not safe to change to next period
                    next_cycle_index = (self.current_state_index + 1) % len(self.periods[self.current_period_index]["states"])

                    if self.verbose:
                        print()
                        print("{} : {} : Changing state from {} to {}".format(self.current_simulation_datetime.time(), self.periods[self.current_period_index]["name"], self.current_state_index, next_cycle_index))
                        if self.current_period_index != timed_period_index:
                            print("  [period change pending]")
                        print("  Old state data: {}".format(self.periods[self.current_period_index]["states"][self.current_state_index]))
                        print("  New state data: {}".format(self.periods[self.current_period_index]["states"][next_cycle_index]))
                        print("  Next changeover in {} second(s)".format(self.periods[self.current_period_index]["states"][next_cycle_index]["duration"]))

                    self.current_state_index = next_cycle_index

                # Ensure this calculation is done based on the PREVIOUS scheduled time to avoid "timing drift"
                self.next_changeover_real_time = self.next_changeover_real_time + (self.periods[self.current_period_index]["states"][self.current_state_index]["duration"] / self.time_factor)
            else:
                if self.verbose:
                    print(".", end="")
                    sys.stdout.flush()

            self.mutex.release()
            time.sleep(1.0 / self.time_factor)