#!/usr/bin/python
# -*- coding: utf-8 -*-
"""Take a vertical or horizontal slice through a video.

I had done this previously with some slow and kludgy shell scripts.
This way is faster, although presumably it won’t scale to producing
images much larger than your RAM.  It processes about 128 frames per
second at the 640×480 size I’m using.

At some point this should start using the untested argument parser in
its entrails.

"""
from __future__ import print_function

import argparse
import os
import sys

import numpy
import PIL.Image


def parse_args():
    formatter = argparse.RawDescriptionHelpFormatter
    p = argparse.ArgumentParser(description=__doc__, formatter_class=formatter)
    
    p.add_argument('-o', '--output', nargs=1,
                   help='name of output file to write or overwrite')
    p.add_argument('-d', '--decimation', type=int, default=2,
                   help='only uses one of every DECIMATION frames'
                   +' (default %(default)s)')
    p.add_argument('-h', '--horizontal', action='store_true',
                   help='take a horizontal slice of vertical pixel rows'
                   +' rather than vice versa')
    p.add_argument('-s', '--offset', type=int, default=0,
                   help='signed number of pixels to offset the slice from'
                   +' the center of each frame (default %(default)s)')
    p.add_argument('files', nargs='+',
                   help='filenames of video frames in the desired order')

    return p.parse_args()


if __name__ == '__main__':
    decimation = 2
    files = sys.argv[1:][::decimation]
    horizontal = False
    offset = +20
    outbuf = None
    for i, f in enumerate(files):
        img = PIL.Image.open(f)
        # XXX is asarray better?
        pixels = numpy.array(img)  # shape is 480×640×3 in my case
        if outbuf is None:
            if horizontal:
                out_shape = (pixels.shape[0], len(files), pixels.shape[2])
            else:
                out_shape = (len(files), pixels.shape[1], pixels.shape[2])

            outbuf = numpy.zeros(dtype=pixels.dtype, shape=out_shape)
        if horizontal:
            col = int(pixels.shape[1] // 2) + offset
            outbuf[:, i, :] = pixels[:, col, :]
        else:
            row = int(pixels.shape[0] // 2) + offset
            outbuf[i, :, :] = pixels[row, :, :]

        if not i % 64:
            print("\r%s (%d/%d)%s" % (f, i, len(files), ' ' * 40), end='')
            sys.stdout.flush()

    outimg = PIL.Image.fromarray(outbuf)
    outimg.save('../slices.png')