import sys

#
# A quick method to read in all neccessary parameters.
# In the homework assignment you will have to extent it appropriately.
#
# Note that we use a simple check methods to check whether the inputs are what we
# expect, and, if numeric, in a reasonable, physically sane range.
#

def read_parameters():
    """Read cannon shot parameters from the command line."""
    if len(sys.argv) == 5:
        vlaunch    = check_float(sys.argv[1], 0.0)
        angle      = check_float(sys.argv[2], 0.0, 180)
        b2_m       = check_float(sys.argv[3], 0.0)
        dt         = check_float(sys.argv[4], 0.0)
    else:
        vlaunch    = read_float('Launch velocity in ms^-1? (recommended: 700) ', 0.0)
        angle      = read_float('Launch angle in degrees? ', 0, 180)
        b2_m       = read_float('B2/m in m^-1? (recommended: 4e-5) ', 0.0)
        dt         = read_float('Size of timestep in s? ', 0.0)
        print
    return vlaunch, angle, b2_m, dt


def check_float(value, minimum=None, maximum=None):
    """Check that a value is a float in the required range"""

    value = float(value)

    if minimum is not None and value < minimum:
        raise ValueError, 'Below minimum.'
    
    if maximum is not None and value >= maximum:
        raise ValueError, 'Above maximum.'

    return value


def read_float(question, minimum=None, maximum=None):
    """Read a float value from the command line"""

    while True:
        try:
            value = raw_input(question)
            value = check_float(value, minimum, maximum)
            break

        except ValueError, message:
            print message, '--- Try again.'

    return value


def check_enum(value, choices):
    """Read an enum string value from the command line"""

    if not value in choices:
        raise ValueError, 'Not in list %s.' % str(choices)

    return value



def read_enum(question, choices):
    """Read an enum string value from the command line"""

    while True:
        try:
            value = raw_input(question)
            value = check_enum(value, choices)
            break

        except ValueError, message:
            print message, '--- Try again.'

    return value