import numpy as np


def make_pulse(stim):
    """
    Generate a pulse train for current / voltage command. Returns a tuple.
    
    
    Parameters
    ----------
    stim : dict
        Holds parameters that determine stimulus shape:
        
        * delay : time before first pulse
        * Sfreq : frequency of pulses
        * dur : duration of one pulse or main pulse
        * predur : duration of prepulse (default should be 0 for no prepulse)
        * amp : pulse amplitude
        * preamp : amplitude of prepulse
        * PT : delay between end of train and test pulse (0 for no test)
        * NP : number of pulses
        * hold : holding level (optional)
        * dt : timestep

    Returns
    -------
    w : stimulus waveform
    maxt : duration of waveform
    tstims : index of each pulse in the train
    """
    defaults = {
        "delay": 10,
        "Sfreq": 50,
        "dur": 100,
        "predur": 0.0,
        "post": 50.0,
        "amp": None,
        "preamp": 0.0,
        "PT": 0,
        "NP": 1,
        "hold": 0.0,
        "dt": None,
    }
    for k in stim:
        if k not in defaults:
            raise Exception("Stim parameter '%s' not accepted." % k)
    defaults.update(stim)
    stim = defaults
    for k, v in stim.items():
        if v is None:
            raise Exception("Must specify stim parameter '%s'." % k)

    dt = stim["dt"]
    delay = int(np.floor(stim["delay"] / dt))
    ipi = int(np.floor((1000.0 / stim["Sfreq"]) / dt))
    pdur = int(np.floor(stim["dur"] / dt))
    posttest = int(np.floor(stim["PT"] / dt))
    ndur = 5
    if stim["predur"] > 0.0:
        predur = int(np.floor(stim["predur"] / dt))
    else:
        predur = 0.0
    if stim["PT"] == 0:
        ndur = 1

    maxt = dt * (delay + predur + (ipi * (stim["NP"] + 3)) + posttest + pdur * ndur)
    hold = stim.get("hold", None)

    w = np.zeros(int(np.floor(maxt / dt)))
    if hold is not None:
        w += hold

    #   make pulse
    tstims = [0] * int(stim["NP"])
    for j in range(0, int(stim["NP"])):
        prestart = delay
        start = int(prestart + predur + j * ipi)
        if predur > 0.0:
            w[prestart : prestart + predur] = stim["preamp"]
        w[start : start + pdur] = stim["amp"]
        tstims[j] = start
    if stim["PT"] > 0.0:
        for i in range(start + posttest, start + posttest + pdur):
            w[i] = stim["amp"]
    w = np.append(w, 0.0)
    maxt = maxt + dt
    return (w, maxt, tstims)