## Copyright (C) 1995-2018 Andreas Weingessel
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <https://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn  {} {@var{y} =} stft (@var{x})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc}, @var{num_coef})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc}, @var{num_coef}, @var{win_type})
## @deftypefnx {} {[@var{y}, @var{c}] =} stft (@dots{})
## Compute the short-time Fourier transform of the vector @var{x} with
## @var{num_coef} coefficients by applying a window of @var{win_size} data
## points and an increment of @var{inc} points.
##
## Before computing the Fourier transform, one of the following windows
## is applied:
##
## @table @asis
## @item @qcode{"hanning"}
## win_type = 1
##
## @item @qcode{"hamming"}
## win_type = 2
##
## @item @qcode{"rectangle"}
## win_type = 3
## @end table
##
## The window names can be passed as strings or by the @var{win_type} number.
##
## The following defaults are used for unspecified arguments:
## @var{win_size} = 80, @var{inc} = 24, @var{num_coef} = 64, and
## @var{win_type} = 1.
##
## @code{@var{y} = stft (@var{x}, @dots{})} returns the absolute values of the
## Fourier coefficients according to the @var{num_coef} positive frequencies.
##
## @code{[@var{y}, @var{c}] = stft (@code{x}, @dots{})} returns the entire
## STFT-matrix @var{y} and a 3-element vector @var{c} containing the window
## size, increment, and window type, which is needed by the @code{synthesis}
## function.
## @seealso{synthesis}
## @end deftypefn

## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at>
## Description: Short-Time Fourier Transform

function [y, c] = stft (x, win_size = 80, inc = 24, num_coef = 64, win_type = 1)

  if (nargin < 1 || nargin > 5)
    print_usage ();
  endif

  if (ischar (win_type))
    switch (tolower (win_type))
      case "hanning"    win_type = 1;
      case "hamming"    win_type = 2;
      case "rectangle"  win_type = 3;
      otherwise
        error ("stft: unknown window type '%s'", win_type);
    endswitch
  endif

  ## Check whether X is a vector.
  if (! isvector (x))
    error ("stft: X must be a vector");
  endif
  x = x(:);

  ncoef = 2 * num_coef;
  if (win_size > ncoef)
    win_size = ncoef;
    printf ("stft: window size adjusted to %f\n", win_size);
  endif
  num_win = fix ((rows (x) - win_size) / inc);

  ## compute the window coefficients
  switch (win_type)
    case 1  win_coef = hanning (win_size);
    case 2  win_coef = hamming (win_size);
    case 3  win_coef = ones (win_size, 1);
  endswitch

  ## Create a matrix Z whose columns contain the windowed time-slices.
  z = zeros (ncoef, num_win + 1);
  start = 1;
  for i = 0:num_win
    z(1:win_size, i+1) = x(start:start+win_size-1) .* win_coef;
    start += inc;
  endfor

  y = fft (z);

  if (nargout == 1)
    y = abs (y(1:num_coef, :));
  else
    c = [win_size, inc, win_type];
  endif

endfunction
