import utils

class tax_brackets:
    """A class to represent tax brackets and some operations on them."""

    def __init__(self, brackets):
        self.brackets = brackets

    def compute_taxes_for_income(self, income):
        """Compute the tax bill for income given our brackets."""
        taxes_due = 0
        while income > 1:
            (threshold, rate) = self.get_bracket_for_income(income)
            taxes_due += (income - threshold) * rate
            income = threshold
        assert taxes_due >= 0, "Somehow computed negative tax bill?!"
        return taxes_due

    def get_bracket_for_income(self, income):
        """Return the bracket that the last dollar of income was in."""
        assert income > 0, "Income should be >0 to be taxed"
        rate = 0.0
        threshold = 0
        for bracket in self.brackets:
            # Bracket is a tuple of (monetary_threshold,
            # tax_rate).  So bracket[0] is a dollar amount and
            # bracket[1] is a tax rate.  e.g. ( 250000, 0.20 )
            # indicates that every dollar you earn over 250K is
            # taxed at 20%.
            if (income > bracket[0] and rate < bracket[1]):
                threshold = bracket[0]
                rate = bracket[1]
        return (threshold, rate)

    def get_bracket_above_income(self, income):
        """Return the next bracket above the one activated by income."""
        assert income > 0, "Income should be >0 to be taxed"
        rate = 1.0
        threshold = None

        # Walk the income tax brackets and look for the one just above
        # the one this year's income is activating.
        for bracket in self.brackets:
            if (bracket[0] > income and bracket[1] < rate):
                threshold = bracket[0]
                rate = bracket[1]

        # Note: this can return (None, 1.0) iff the income is already
        # in the top tax bracket.
        return (threshold, rate)

    def get_bracket_below_income(self, income):
        """Return the next bracket below the one activated by income."""
        assert income > 0, "Income should be >0 to be taxed"
        bracket = self.get_bracket_for_income(income)
        income = bracket[0]
        return self.get_bracket_for_income(income)

    def get_effective_tax_rate_for_income(self, income):
        """Compute and return the effective tax rate for an income."""
        if income <= 0: return 0
        tax_bill = self.compute_taxes_for_income(income)
        return float(tax_bill) / income

    def adjust_with_multiplier(self, multiplier):
        """Every year the IRS adjusts the income tax brackets for inflation."""
        for bracket in self.brackets:
            if bracket[0] != 1:
                bracket[0] *= multiplier

    def dump(self):
        """Print out the tax brackets we're using in here."""
        for x in self.brackets:
            print "{:<20} -> {:<3}".format(utils.format_money(x[0]),
                                           utils.format_rate(x[1]))