#!/usr/bin/env python3

import argparse
import cv2
import moviepy.editor as mp

MIN_INTERESTING_FRAMES = 20
MOVEMENT_THRESHOLD = 1000

def main():
    # argparse
    parser = argparse.ArgumentParser()
    parser.add_argument('filename')
    args = parser.parse_args()

    # get video info
    vid = cv2.VideoCapture(args.filename)
    ret, colorFrame = vid.read()
    frame = cv2.cvtColor(colorFrame, cv2.COLOR_BGR2GRAY)
    fps = vid.get(cv2.CAP_PROP_FPS)
    fnum = int(vid.get(cv2.CAP_PROP_FRAME_COUNT))
    dur = fnum // fps
    print("video stats: \n"
          f"fps:    {fps}\n"
          f"frames: {fnum}\n"
          f"length: {int(dur//60):02}:{int(dur%60):02}\n")

    # prepare to find interesting segments
    print("finding interesting segments ...")
    i = 0
    clips = []
    startFrame = 0
    inSegment = False

    # start a segment if we aren't already in one.
    def maybeStartSegment(i):
        nonlocal inSegment, startFrame
        if inSegment == False:
            inSegment = True
            startFrame = i
            print( f"found one! frame {i:8} to ... ", end="", flush=True)

    # end a segment if we are in one, and then save the
    # start and end frames if it was a long enough segment
    def maybeEndSegment(i):
        nonlocal inSegment
        if inSegment == True:
            inSegment = False
            if i - startFrame > MIN_INTERESTING_FRAMES:
                print( f"{i:6} ! ")
                clips.append((startFrame, i))
            else:
                print( f"nvm, too short.")

    # loop through each frame
    while(True):
        i += 1;
        ret, colorFrame = vid.read()

        # if theres no more frames, break the loop &
        # maybe end the current segment
        if not ret:
            maybeEndSegment(i)
            break;

        # calculate the difference between the current & last frame
        # then run the Canny algorithm to find edges within the
        # diff. edges in the diff indicate that something is moving
        # in the frame.
        prev = frame
        frame = cv2.cvtColor(colorFrame, cv2.COLOR_BGR2GRAY)
        diff = cv2.subtract(frame, prev)
        edges = cv2.Canny(diff, 100, 200)

        # number of non zero (not true block) pixels in the edge frame.
        # large number indicates edges which indicates movment.
        nz = cv2.countNonZero(edges)

        if nz > MOVEMENT_THRESHOLD:
            maybeStartSegment(i)
        else:
            maybeEndSegment(i)

    # finished looping
    vid.release()
    print("done! time to chop up the video :) ")

    # convert the segment indicators from frame number to seconds
    def frame2second(f):
        return round(f / fps, 2)
    clipsSeconds = [ (frame2second(x),frame2second(y)) for (x,y) in clips ]
    print( clipsSeconds )

    # slice that bitch up & export it!
    movie = mp.VideoFileClip(args.filename)
    clips = [ movie.subclip(s, e) for (s,e) in clipsSeconds ]
    trimmed = mp.concatenate_videoclips(clips)
    out_filename = args.filename.replace('.mp4', '') + '_trimmed.mp4'
    trimmed.write_videofile(out_filename)

    print("enjoy!")

if __name__ == "__main__":
    main();