# Quantities with units

# This file's encoding must be UTF-8Y with BOM so Python will auto-detect UTF-8

import re

import format

import strings

import util

class MissingUnitsException(Exception):

    def __init__(self, quantity):

        Exception.__init__(self, 'Quantity has no units: '

            +strings.ustr(quantity))

def std_units(units):

    if units == None: return units

    else: return strings.remove_suffix('.', units) # for abbr ending in '.'

    # TODO: deal with '"° and abbrs

class Quantity:

    def __init__(self, value='', units=None):

        self.value = value

        self.units = std_units(util.none_if(units, u''))

def quantity2str(quantity):

    str_ = quantity.value

    if quantity.units != None: str_ += ' '+quantity.units

    return str_

Quantity.__str__ = quantity2str

Quantity.__repr__ = quantity2str

def str2quantity(str_):

    value = str_

    units = None

    if not str_.isdigit(): # optimization to avoid regexp for simple cases

        match = re.match(ur'(?i)^\s*(.*?\d\.?)\s*([a-z%\'"°][\w.*/^-]*?)?\s*$',

            str_)

        if match: value, units = match.groups() # has units

    return Quantity(value, units)

def set_default_units(quantity, units):

    if quantity.units == None: quantity.units = units

conversions = {

    ('%', None): 1./100

}

def convert(quantity, units):

    units = std_units(units)

    if quantity.units == units: return quantity # units already correct

    try: conversion = conversions[(quantity.units, units)]

    except KeyError:

        if units == None: return Quantity(quantity.value, units) # remove units

        elif quantity.units == None: raise MissingUnitsException(quantity)

            # can't convert quantity with unknown units

        else: raise NotImplementedError('Unit conversion not implemented yet')

    else:

        return Quantity(str(format.str2float(quantity.value)*conversion), units)