import decimal
import itertools
import operator

import babel.numbers

from .. import rate as oxrrate

class Formatter:
    def __init__(self, rate, signed_currencies=(), base_fmt='#,##0.###'):
        self.rate = rate
        self.base_fmt = base_fmt
        self.base_fmt_noprec = base_fmt.rsplit('.', 1)[0]
        self.signed_currencies = set(code for code in signed_currencies
                                     if self.can_sign_currency(code))

    def can_sign_currency(self, code):
        return len(babel.numbers.get_currency_symbol(code)) == 1

    def format_currency(self, amount, code, currency_digits=True):
        if currency_digits:
            fmt = self.base_fmt
        else:
            fmt = '{}.{}'.format(self.base_fmt_noprec, '#' * -amount.as_tuple().exponent)
        if code in self.signed_currencies:
            fmt = '¤' + fmt
        else:
            fmt = fmt + ' ¤¤'
        return babel.numbers.format_currency(amount, code, fmt, currency_digits=currency_digits)

    def format_rate(self, rate):
        return "{:g}".format(rate)

    def format_rate_pair(self, from_curr, to_curr):
        from_amt = 1
        to_amt = self.rate.convert(from_amt, from_curr, to_curr)
        return "{} {} = {} {}".format(
            self.format_rate(from_amt), from_curr,
            self.format_rate(to_amt), to_curr,
        )

    def format_rate_pair_bidir(self, from_curr, to_curr, sep='\n'):
        return "{}{}{}".format(
            self.format_rate_pair(from_curr, to_curr),
            sep,
            self.format_rate_pair(to_curr, from_curr),
        )

    def format_conversion(self, from_amt, from_curr, to_curr):
        to_amt = self.rate.convert(from_amt, from_curr, to_curr)
        return "{} = {}".format(
            self.format_currency(from_amt, from_curr),
            self.format_currency(to_amt, to_curr),
        )


class LedgerFormatter(Formatter):
    RATE_PREC = 5

    def normalize_rate(self, rate, prec=None):
        # Return prec nonzero digits of precision, if available.
        if prec is None:
            prec = self.RATE_PREC
        _, digits, exponent = rate.normalize().as_tuple()
        prec -= min(0, exponent + len(digits))
        quant_to = '1.{}'.format('0' * prec)
        try:
            qrate = rate.quantize(decimal.Decimal(quant_to))
        except decimal.InvalidOperation:
            # The original rate doesn't have that much precision, so use it raw.
            qrate = rate
        return qrate.normalize()

    def format_rate(self, rate, prec=None):
        return str(self.normalize_rate(rate, prec))

    def format_ledger_rate(self, rate, curr, prec=None):
        nrate = self.normalize_rate(rate, prec)
        rate_s = self.format_currency(nrate, curr, currency_digits=False)
        return "{{={0}}} @ {0}".format(rate_s)

    def format_rate_pair(self, from_curr, to_curr):
        from_amt = 1
        to_amt = self.rate.convert(from_amt, from_curr, to_curr)
        return "{} {} {}".format(
            from_amt, from_curr, self.format_ledger_rate(to_amt, to_curr))

    def format_conversion(self, from_amt, from_curr, to_curr):
        to_rate = self.rate.convert(1, from_curr, to_curr)
        to_amt = self.rate.convert(from_amt, from_curr, to_curr)
        return "{} {}\n{}".format(
            self.format_currency(from_amt, from_curr),
            self.format_ledger_rate(to_rate, to_curr),
            self.format_currency(to_amt, to_curr),
        )


def run(config, stdout, stderr):
    loaders = config.get_loaders()
    with loaders.historical(config.args.date, config.args.base) as rate_json:
        rate = oxrrate.Rate.from_json_file(rate_json)
    if loaders.should_cache():
        config.cache.save_rate(rate)
    if config.args.ledger:
        formatter = LedgerFormatter(rate, config.args.signed_currencies)
    else:
        formatter = Formatter(rate)
    if not config.args.from_currency:
        for from_curr in sorted(rate.rates):
            print(formatter.format_rate_pair_bidir(from_curr, config.args.to_currency),
                  file=stdout)
    elif config.args.amount is None:
        print(formatter.format_rate_pair_bidir(config.args.from_currency, config.args.to_currency),
              file=stdout)
    else:
        print(formatter.format_conversion(config.args.amount,
                                          config.args.from_currency,
                                          config.args.to_currency),
              file=stdout)