#!/usr/bin/env python3
import argparse
from pathlib import Path

import cv2 as cv
import numpy as np


def odd_kernel(value: str) -> int:
    kernel = int(value)
    if kernel < 1 or kernel % 2 == 0:
        raise argparse.ArgumentTypeError("blur kernel must be a positive odd integer")
    return kernel


parser = argparse.ArgumentParser(description="Detect image edges with OpenCV Canny.")
parser.add_argument("input_image", type=Path)
parser.add_argument("output_image", type=Path)
parser.add_argument("--low", type=float, default=80.0)
parser.add_argument("--high", type=float, default=160.0)
parser.add_argument("--blur", type=odd_kernel, default=5)
parser.add_argument("--aperture", type=odd_kernel, default=3)
parser.add_argument("--l2-gradient", action="store_true")
args = parser.parse_args()

if args.aperture not in {3, 5, 7}:
    raise SystemExit("aperture must be 3, 5, or 7")
if args.low >= args.high:
    raise SystemExit("--low must be lower than --high")

gray = cv.imread(str(args.input_image), cv.IMREAD_GRAYSCALE)
if gray is None:
    raise SystemExit(f"could not read image: {args.input_image}")

source = cv.GaussianBlur(gray, (args.blur, args.blur), 0)
edges = cv.Canny(
    source,
    args.low,
    args.high,
    apertureSize=args.aperture,
    L2gradient=args.l2_gradient,
)

args.output_image.parent.mkdir(parents=True, exist_ok=True)
if not cv.imwrite(str(args.output_image), edges):
    raise SystemExit(f"could not write image: {args.output_image}")

edge_pixels = int(np.count_nonzero(edges))
total_pixels = edges.size
edge_percent = edge_pixels / total_pixels * 100

print(f"input: {args.input_image}")
print(f"image size: {gray.shape[1]}x{gray.shape[0]}")
print(f"thresholds: {args.low:.0f}/{args.high:.0f}")
print(f"blur kernel: {args.blur}x{args.blur}")
print(f"aperture: {args.aperture}")
print(f"edge pixels: {edge_pixels} ({edge_percent:.2f}%)")
print(f"output: {args.output_image}")