#!/usr/bin/env python
# coding: utf8

NOMINALS = [
    1000000.0,
    750000.0,
    470000.0,
    220000.0,
    75000.0,
    47000.0,
    22000.0,
    10000.0,
    6800.0,
    2200.0,
    1000.0,
    750.0,
    470.0,
    220.0,
    100.0,
    47.0,
    22.0,
    10.0
]


def format_value(value, suffix=''):
    order_suffix = ''
    divider = 1.0

    orders = [
        [1000000000.0, 'G'],
        [1000000.0, 'M'],
        [1000.0, 'k'],
        [1.0, ''],
        [0.001, 'm'],
        [0.000001, u'\u00b5'],
        [0.000000001, u'n'],
        [0.000000000001, u'p'],
    ]

    for suggested_divider, suggested_order_suffix in orders:
        if value >= suggested_divider:
            divider = suggested_divider
            order_suffix = suggested_order_suffix
            break

    mag_value = value / divider
    mag_value = int(mag_value * 1000)
    mod = mag_value % 1000
    if mod == 0:
        return "%i%s%s" % (mag_value / 1000.0, order_suffix, suffix)
    elif mod % 100 == 0:
        return "%.1f%s%s" % (mag_value / 1000.0, order_suffix, suffix)
    elif mod % 10 == 0:
        return "%.2f%s%s" % (mag_value / 1000.0, order_suffix, suffix)
    return "%.3f%s%s" % (mag_value / 1000.0, order_suffix, suffix)

def choose_resistors(v_in, v_out, limits='both'):
    if v_in <= v_out:
        raise Exception("Vin should be greater than Vout")
    v_in = float(v_in)
    v_out = float(v_out)
    best_r1 = None
    best_r2 = None
    best_v_out = None

    for r1 in NOMINALS:
        for r2 in NOMINALS:
            tmp_v_out = float(v_in * r2) / (r1 + r2)
            choose_this_pair = best_v_out is None

            if limits == 'both':
                choose_this_pair = choose_this_pair or abs(tmp_v_out - v_out) < abs(best_v_out - v_out)
            elif limits == 'upper':
                choose_this_pair = choose_this_pair or v_out <= tmp_v_out < best_v_out or best_v_out < v_out
            elif limits == 'lower':
                choose_this_pair = choose_this_pair or best_v_out < tmp_v_out <= v_out or best_v_out > v_out

            if choose_this_pair:
                best_r1 = r1
                best_r2 = r2
                best_v_out = tmp_v_out

    print u"R1 %s\nR2 %s\nVout %s\nDissipation %s\nFactor %f" % (
        format_value(best_r1, u'Ω'),
        format_value(best_r2, u'Ω'),
        format_value(best_v_out, 'V'),
        format_value(v_in * v_in / best_r1, 'W'),
        best_r2 / (best_r1 + best_r2)
    )


def main():
    print "\nPower supply UVLO divider"
    choose_resistors(30, 1.3, 'upper')

    print "\nPower supply feedback divider"
    choose_resistors(5, 1.225, 'lower')

    print "\nUnidirectional sensor"
    choose_resistors(5.1, 3.3, 'lower')

if __name__ == '__main__':
    main()