#!/usr/bin/env python3
"""Render regression checks. Requires Firefox and Pillow; the page itself needs neither."""
import subprocess
import tempfile
import unittest
from pathlib import Path
from PIL import Image, ImageChops, ImageStat

HERE = Path(__file__).resolve().parent


class IceRenderTest(unittest.TestCase):
    def test_loop_mouse_and_visible_plasma(self):
        subprocess.run(['python3', str(HERE / 'build_plasma.py')], check=True)
        with tempfile.TemporaryDirectory() as directory:
            root = Path(directory)
            profile = root / 'profile'
            profile.mkdir()

            def render(name, parameters):
                output = root / (name + '.png')
                url = (HERE / 'ice_plasma.html').as_uri() + '#shot&' + parameters
                subprocess.run(['firefox', '--headless', '--new-instance', '--profile', str(profile),
                                '--window-size=320,240', '--screenshot=' + str(output), url],
                               check=True, timeout=120, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
                # Exclude the on-screen instructions.
                with Image.open(output) as image:
                    return image.convert('RGB').crop((0, 0, 320, 180))

            start = render('start', 't=0&mx=0.5&my=0.5')
            loop = render('loop', 't=30&mx=0.5&my=0.5')
            moved = render('moved', 't=0&mx=0.9&my=0.5')
            halfway = render('halfway', 't=15&mx=0.5&my=0.5')
            difference = lambda a, b: sum(ImageStat.Stat(ImageChops.difference(a, b)).mean) / 3
            self.assertLess(difference(start, loop), 1.0)
            self.assertGreater(difference(start, moved), 3.0)
            self.assertGreater(difference(start, halfway), 3.0)
            self.assertGreater(ImageStat.Stat(start).stddev[2], 10.0)
            luminance = start.convert('L').histogram()
            pixels = sum(luminance)
            self.assertLess(sum(luminance[:20]) / pixels, 0.10)  # No vast black voids.
            self.assertGreater(sum(luminance[:35]) / pixels, 0.08)  # The depth stays dark.


if __name__ == '__main__':
    unittest.main()