import ast
import math

VERSION = "0.0.0"
sContinue = True

state = []


def show_help():
    print("vector [5,6,7...] - set the current dataset to the given vector")
    print("stdev - get the standard deviation of the current dataset")
    print("pstdev - get the population standard deviation of the current dataset")
    print("variance - get the variance of the current dataset")
    print("pvariance - get the population variance of the current dataset")
    print("mean - get the mean of the current dataset")
    print("median - get the median of the current dataset")
    print("mode - get the mode of the current dataset")
    print("var - get the variance of the current dataset")
    print("print - prints the current dataset")
    print("clear - clears the current dataset")
    print("clr - clears the screen")


def get_mean():
    """
    Get the mean value of the state vector.

    :return: The average value of the state vector.
    """
    global state
    mean = sum(state) / len(state)
    return mean


def get_median():
    """
    This function calculates the median of the state vector.
    The implementation uses the algorithm based on sorting.

    :return: The median value of the sorted `state` list.
    """
    global state
    state.sort()
    n = len(state)
    median = 0
    if n % 2 == 0:
        median = (state[n // 2 - 1] + state[n // 2]) / 2
    else:
        median = state[n // 2]
    return median


def get_mode():
    """
    :return: The most frequent element in the global variable 'state'.
    """
    global state
    from collections import Counter
    mode = Counter(state).most_common(1)[0][0]
    return mode


def get_variance():
    global state
    n = len(state)

    mean = get_mean()

    variance = sum((x - mean) ** 2 for x in state) / (n - 1)
    return variance


def get_population_variance():
    global state
    n = len(state)

    mean = get_mean()

    variance = sum((x - mean) ** 2 for x in state) / n
    return variance


def get_standard_deviation():
    variance = get_variance()
    std_dev = math.sqrt(variance)
    return std_dev


def get_population_standard_deviation():
    pvariance = get_population_variance()
    std_dev = math.sqrt(pvariance)
    return std_dev


def start_shell():
    global state
    state = []
    print(f'Welcome to math-shell v{VERSION}')
    handle_input()


def handle_input():
    global state
    value = []
    print('>>>', end=' ')
    i = input()
    should_split = i.__contains__(' ')
    if should_split:
        command, value = i.split(sep=' ', maxsplit=1)
        value = ast.literal_eval(value)
    else:
        command = i

    match command.lower():
        case 'vector':
            state = value
            print(f"Set state to: {value}")
        case 'mean':
            print(get_mean())
        case 'median':
            print(get_median())
        case 'mode':
            print(get_mode())
        case 'stdev':
            print(get_standard_deviation())
        case 'pstdev':
            print(get_population_standard_deviation())
        case 'variance':
            print(get_variance())
        case 'pvariance':
            print(get_population_variance())
        case 'print':
            if state is not None:
                print(f"{state}")
            else:
                print("No state")
        case 'exit':
            return False
        case other:
            show_help()
    return True


if __name__ == '__main__':
    start_shell()
    while sContinue:
        sContinue = handle_input()