"""Some simple financial calculations

patterned after spreadsheet computations.

There is some complexity in each function
so that the functions behave like ufuncs with
broadcasting and being able to be called with scalars
or arrays (or other sequences).

Functions support the :class:`decimal.Decimal` type unless
otherwise stated.
"""
import warnings
from decimal import Decimal
import functools

import numpy as np
from numpy.core import overrides


_depmsg = ("numpy.{name} is deprecated and will be removed from NumPy 1.20. "
           "Use numpy_financial.{name} instead "
           "(https://pypi.org/project/numpy-financial/).")

array_function_dispatch = functools.partial(
    overrides.array_function_dispatch, module='numpy')


__all__ = ['fv', 'pmt', 'nper', 'ipmt', 'ppmt', 'pv', 'rate',
           'irr', 'npv', 'mirr']

_when_to_num = {'end':0, 'begin':1,
                'e':0, 'b':1,
                0:0, 1:1,
                'beginning':1,
                'start':1,
                'finish':0}

def _convert_when(when):
    #Test to see if when has already been converted to ndarray
    #This will happen if one function calls another, for example ppmt
    if isinstance(when, np.ndarray):
        return when
    try:
        return _when_to_num[when]
    except (KeyError, TypeError):
        return [_when_to_num[x] for x in when]


def _fv_dispatcher(rate, nper, pmt, pv, when=None):
    warnings.warn(_depmsg.format(name='fv'),
                  DeprecationWarning, stacklevel=3)
    return (rate, nper, pmt, pv)


@array_function_dispatch(_fv_dispatcher)
def fv(rate, nper, pmt, pv, when='end'):
    """
    Compute the future value.

    .. deprecated:: 1.18

       `fv` is deprecated; for details, see NEP 32 [1]_.
       Use the corresponding function in the numpy-financial library,
       https://pypi.org/project/numpy-financial.

    Given:
     * a present value, `pv`
     * an interest `rate` compounded once per period, of which
       there are
     * `nper` total
     * a (fixed) payment, `pmt`, paid either
     * at the beginning (`when` = {'begin', 1}) or the end
       (`when` = {'end', 0}) of each period

    Return:
       the value at the end of the `nper` periods

    Parameters
    ----------
    rate : scalar or array_like of shape(M, )
        Rate of interest as decimal (not per cent) per period
    nper : scalar or array_like of shape(M, )
        Number of compounding periods
    pmt : scalar or array_like of shape(M, )
        Payment
    pv : scalar or array_like of shape(M, )
        Present value
    when : {{'begin', 1}, {'end', 0}}, {string, int}, optional
        When payments are due ('begin' (1) or 'end' (0)).
        Defaults to {'end', 0}.

    Returns
    -------
    out : ndarray
        Future values.  If all input is scalar, returns a scalar float.  If
        any input is array_like, returns future values for each input element.
        If multiple inputs are array_like, they all must have the same shape.

    Notes
    -----
    The future value is computed by solving the equation::

     fv +
     pv*(1+rate)**nper +
     pmt*(1 + rate*when)/rate*((1 + rate)**nper - 1) == 0

    or, when ``rate == 0``::

     fv + pv + pmt * nper == 0

    References
    ----------
    .. [1] NumPy Enhancement Proposal (NEP) 32,
       https://numpy.org/neps/nep-0032-remove-financial-functions.html
    .. [2] Wheeler, D. A., E. Rathke, and R. Weir (Eds.) (2009, May).
       Open Document Format for Office Applications (OpenDocument)v1.2,
       Part 2: Recalculated Formula (OpenFormula) Format - Annotated Version,
       Pre-Draft 12. Organization for the Advancement of Structured Information
       Standards (OASIS). Billerica, MA, USA. [ODT Document].
       Available:
       http://www.oasis-open.org/committees/documents.php?wg_abbrev=office-formula
       OpenDocument-formula-20090508.odt


    Examples
    --------
    What is the future value after 10 years of saving $100 now, with
    an additional monthly savings of $100.  Assume the interest rate is
    5% (annually) compounded monthly?

    >>> np.fv(0.05/12, 10*12, -100, -100)
    15692.928894335748

    By convention, the negative sign represents cash flow out (i.e. money not
    available today).  Thus, saving $100 a month at 5% annual interest leads
    to $15,692.93 available to spend in 10 years.

    If any input is array_like, returns an array of equal shape.  Let's
    compare different interest rates from the example above.

    >>> a = np.array((0.05, 0.06, 0.07))/12
    >>> np.fv(a, 10*12, -100, -100)
    array([ 15692.92889434,  16569.87435405,  17509.44688102]) # may vary

    """
    when = _convert_when(when)
    (rate, nper, pmt, pv, when) = map(np.asarray, [rate, nper, pmt, pv, when])
    temp = (1+rate)**nper
    fact = np.where(rate == 0, nper,
                    (1 + rate*when)*(temp - 1)/rate)
    return -(pv*temp + pmt*fact)


def _pmt_dispatcher(rate, nper, pv, fv=None, when=None):
    warnings.warn(_depmsg.format(name='pmt'),
                  DeprecationWarning, stacklevel=3)
    return (rate, nper, pv, fv)


@array_function_dispatch(_pmt_dispatcher)
def pmt(rate, nper, pv, fv=0, when='end'):
    """
    Compute the payment against loan principal plus interest.

    .. deprecated:: 1.18

       `pmt` is deprecated; for details, see NEP 32 [1]_.
       Use the corresponding function in the numpy-financial library,
       https://pypi.org/project/numpy-financial.

    Given:
     * a present value, `pv` (e.g., an amount borrowed)
     * a future value, `fv` (e.g., 0)
     * an interest `rate` compounded once per period, of which
       there are
     * `nper` total
     * and (optional) specification of whether payment is made
       at the beginning (`when` = {'begin', 1}) or the end
       (`when` = {'end', 0}) of each period

    Return:
       the (fixed) periodic payment.

    Parameters
    ----------
    rate : array_like
        Rate of interest (per period)
    nper : array_like
        Number of compounding periods
    pv : array_like
        Present value
    fv : array_like,  optional
        Future value (default = 0)
    when : {{'begin', 1}, {'end', 0}}, {string, int}
        When payments are due ('begin' (1) or 'end' (0))

    Returns
    -------
    out : ndarray
        Payment against loan plus interest.  If all input is scalar, returns a
        scalar float.  If any input is array_like, returns payment for each
        input element. If multiple inputs are array_like, they all must have
        the same shape.

    Notes
    -----
    The payment is computed by solving the equation::

     fv +
     pv*(1 + rate)**nper +
     pmt*(1 + rate*when)/rate*((1 + rate)**nper - 1) == 0

    or, when ``rate == 0``::

      fv + pv + pmt * nper == 0

    for ``pmt``.

    Note that computing a monthly mortgage payment is only
    one use for this function.  For example, pmt returns the
    periodic deposit one must make to achieve a specified
    future balance given an initial deposit, a fixed,
    periodically compounded interest rate, and the total
    number of periods.

    References
    ----------
    .. [1] NumPy Enhancement Proposal (NEP) 32,
       https://numpy.org/neps/nep-0032-remove-financial-functions.html
    .. [2] Wheeler, D. A., E. Rathke, and R. Weir (Eds.) (2009, May).
       Open Document Format for Office Applications (OpenDocument)v1.2,
       Part 2: Recalculated Formula (OpenFormula) Format - Annotated Version,
       Pre-Draft 12. Organization for the Advancement of Structured Information
       Standards (OASIS). Billerica, MA, USA. [ODT Document].
       Available:
       http://www.oasis-open.org/committees/documents.php
       ?wg_abbrev=office-formulaOpenDocument-formula-20090508.odt

    Examples
    --------
    What is the monthly payment needed to pay off a $200,000 loan in 15
    years at an annual interest rate of 7.5%?

    >>> np.pmt(0.075/12, 12*15, 200000)
    -1854.0247200054619

    In order to pay-off (i.e., have a future-value of 0) the $200,000 obtained
    today, a monthly payment of $1,854.02 would be required.  Note that this
    example illustrates usage of `fv` having a default value of 0.

    """
    when = _convert_when(when)
    (rate, nper, pv, fv, when) = map(np.array, [rate, nper, pv, fv, when])
    temp = (1 + rate)**nper
    mask = (rate == 0)
    masked_rate = np.where(mask, 1, rate)
    fact = np.where(mask != 0, nper,
                    (1 + masked_rate*when)*(temp - 1)/masked_rate)
    return -(fv + pv*temp) / fact


def _nper_dispatcher(rate, pmt, pv, fv=None, when=None):
    warnings.warn(_depmsg.format(name='nper'),
                  DeprecationWarning, stacklevel=3)
    return (rate, pmt, pv, fv)


@array_function_dispatch(_nper_dispatcher)
def nper(rate, pmt, pv, fv=0, when='end'):
    """
    Compute the number of periodic payments.

    .. deprecated:: 1.18

       `nper` is deprecated; for details, see NEP 32 [1]_.
       Use the corresponding function in the numpy-financial library,
       https://pypi.org/project/numpy-financial.

    :class:`decimal.Decimal` type is not supported.

    Parameters
    ----------
    rate : array_like
        Rate of interest (per period)
    pmt : array_like
        Payment
    pv : array_like
        Present value
    fv : array_like, optional
        Future value
    when : {{'begin', 1}, {'end', 0}}, {string, int}, optional
        When payments are due ('begin' (1) or 'end' (0))

    Notes
    -----
    The number of periods ``nper`` is computed by solving the equation::

     fv + pv*(1+rate)**nper + pmt*(1+rate*when)/rate*((1+rate)**nper-1) = 0

    but if ``rate = 0`` then::

     fv + pv + pmt*nper = 0

    References
    ----------
    .. [1] NumPy Enhancement Proposal (NEP) 32,
       https://numpy.org/neps/nep-0032-remove-financial-functions.html

    Examples
    --------
    If you only had $150/month to pay towards the loan, how long would it take
    to pay-off a loan of $8,000 at 7% annual interest?

    >>> print(np.round(np.nper(0.07/12, -150, 8000), 5))
    64.07335

    So, over 64 months would be required to pay off the loan.

    The same analysis could be done with several different interest rates
    and/or payments and/or total amounts to produce an entire table.

    >>> np.nper(*(np.ogrid[0.07/12: 0.08/12: 0.01/12,
    ...                    -150   : -99     : 50    ,
    ...                    8000   : 9001    : 1000]))
    array([[[ 64.07334877,  74.06368256],
            [108.07548412, 127.99022654]],
           [[ 66.12443902,  76.87897353],
            [114.70165583, 137.90124779]]])

    """
    when = _convert_when(when)
    (rate, pmt, pv, fv, when) = map(np.asarray, [rate, pmt, pv, fv, when])

    use_zero_rate = False
    with np.errstate(divide="raise"):
        try:
            z = pmt*(1+rate*when)/rate
        except FloatingPointError:
            use_zero_rate = True

    if use_zero_rate:
        return (-fv + pv) / pmt
    else:
        A = -(fv + pv)/(pmt+0)