#!/usr/bin/env python3.4
"""
Calculate titration volumes from concentrate.

Pariksheet Nanda <omsai@member.fsf.org> 2015

License: Public Domain

"""

from argparse import ArgumentParser

if __name__ == '__main__':
    parser = ArgumentParser(
        #'titer',
        description='Calculate titration volumes from concentrate.'
    )
    parser.add_argument(
        'concentrate_density',
        type=float,
        help='original solution density (in 10^4 cells / ml).'
    )
    parser.add_argument(
        '-t',
        '--diluted-density',
        type=float,
        default=10.0,
        help='required solution density (default: 10x10^4 cells/ml).'
    )
    parser.add_argument(
        '-v',
        '--media-volume',
        type=float,
        default=10.0,
        help='final volume of media only (default: 10 ml).'
    )
    args = parser.parse_args()

    if args.concentrate_density < args.diluted_density:
        raise ValueError("Stock solution density {0} cannot be less than diluted {1}.".format(args.concentrate_density, args.diluted_density))

    concentrate_sub_volume = (
        args.diluted_density * args.media_volume
        / (args.concentrate_density - args.diluted_density)
    )
    """
    We derive the above equation as follows:
    c1 * v1 = c2 * v2

    Where 1 = concentrate solution and 2 = diluted solution.
    We need to solve for v1:

    c1 * v1 = c2 * (v_media + v1)
    c1 * v1 = c2 * v_media + c2 * v1
    c1 * v1 - c2 * v1 = c2 * v_media
    v1 * (c1 - c2) = c2 * v_media
    v1 = c2 * v_media / (c1 - c2)

    """

    print('Add {0} ul of stock to {1} ml of media, to get a dilution of {2} x 10^4 cells/ml using a concentrate density of {3} x 10^4 cells/ml'.format(
        int(concentrate_sub_volume * 1000),
        args.media_volume,
        args.diluted_density,
        args.concentrate_density,
    ))