# -*- coding: utf-8 -*-
"""
Created on Thu Oct 21 21:45:24 2010

Author: josef-pktd
"""

import numpy as np
from scipy import signal

def armaloop(arcoefs, macoefs, x):
    '''get arma recursion in simple loop

    for simplicity assumes that ma polynomial is not longer than the ar-polynomial

    Parameters
    ----------
    arcoefs : array_like
        autoregressive coefficients in right hand side parameterization
    macoefs : array_like
        moving average coefficients, without leading 1

    Returns
    -------
    y : ndarray
        predicted values, initial values are the same as the observed values
    e : ndarray
        predicted residuals, zero for initial observations

    Notes
    -----
    Except for the treatment of initial observations this is the same as using
    scipy.signal.lfilter, which is much faster. Written for testing only
    '''
    arcoefs_r = np.asarray(arcoefs)
    macoefs_r = np.asarray(macoefs)
    x = np.asarray(x)
    nobs = x.shape[0]
    #assume ar longer than ma
    arlag = arcoefs_r.shape[0]
    malag = macoefs_r.shape[0]
    maxlag = max(arlag, malag)
    print(maxlag)
    y = np.zeros(x.shape, float)
    e = np.zeros(x.shape, float)
    y[:maxlag] = x[:maxlag]

    #if malag > arlaga:
    for t in range(arlag, maxlag):
        y[t] = (x[t-arlag:t] * arcoefs_r).sum(0) + (e[:t] * macoefs_r[:t]).sum(0)
        e[t] = x[t] - y[t]

    for t in range(maxlag, nobs):
        #wrong broadcasting, 1d only
        y[t] = (x[t-arlag:t] * arcoefs_r).sum(0) + (e[t-malag:t] * macoefs_r).sum(0)
        e[t] = x[t] - y[t]

    return y, e

arcoefs, macoefs = -np.array([1, -0.8, 0.2])[1:], np.array([1., 0.5, 0.1])[1:]
print(armaloop(arcoefs, macoefs, np.ones(10)))
print(armaloop([0.8], [], np.ones(10)))
print(armaloop([0.8], [], np.arange(2,10)))
y, e = armaloop([0.1], [0.8], np.arange(2,10))
print(e)
print(signal.lfilter(np.array([1, -0.1]), np.array([1., 0.8]), np.arange(2,10)))

y, e = armaloop([], [0.8], np.ones(10))
print(e)
print(signal.lfilter(np.array([1, -0.]), np.array([1., 0.8]), np.ones(10)))

ic=signal.lfiltic(np.array([1, -0.1]), np.array([1., 0.8]), np.ones([0]), np.array([1]))
print(signal.lfilter(np.array([1, -0.1]), np.array([1., 0.8]), np.ones(10), zi=ic))

zi = signal.lfilter_zi(np.array([1, -0.8, 0.2]), np.array([1., 0, 0]))
print(signal.lfilter(np.array([1, -0.1]), np.array([1., 0.8]), np.ones(10), zi=zi))
print(signal.filtfilt(np.array([1, -0.8]), np.array([1.]), np.ones(10)))

#todo write examples/test across different versions
