'internal method used for computation of total amount of an expense in the company currency and
in the expense currency, given the account_move_lines that will be created. It also do some small
transformations at these account_move_lines (for multi-currency purposes)
:param account_move_lines: list of dict
:rtype: tuple of 3 elements (a, b ,c)
a: total in company currency
b: total in hr.expense currency
c: account_move_lines potentially modified'

@api.multi
def _compute_expense_totals(self, company_currency, account_move_lines, move_date):

    self.ensure_one()
    total = 0.0
    total_currency = 0.0
    for line in account_move_lines:
        line['currency_id'] = False
        line['amount_currency'] = False
        if (self.currency_id != company_currency):
            line['currency_id'] = self.currency_id.id
            line['amount_currency'] = line['price']
            line['price'] = self.currency_id.with_context(date=(move_date or fields.Date.context_today(self))).compute(line['price'], company_currency)
        total -= line['price']
        total_currency -= (line['amount_currency'] or line['price'])
    return (total, total_currency, account_move_lines)
