From 27ea5e560cc5f52e82447d86a140f1a28081a12e Mon Sep 17 00:00:00 2001
From: Bob Mottram <bob@libreserver.org>
Date: Wed, 18 May 2022 17:06:26 +0100
Subject: [PATCH] Test all themes for color contrast

---
 tests.py                 | 41 +++++++++++++++++++++++++++++++++
 webapp_theme_designer.py | 49 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)

diff --git a/tests.py b/tests.py
index 7f6ba9a22..1dad076c2 100644
--- a/tests.py
+++ b/tests.py
@@ -148,6 +148,7 @@ from content import remove_long_words
 from content import replace_content_duplicates
 from content import remove_text_formatting
 from content import remove_html_tag
+from theme import get_themes_list
 from theme import update_default_themes_list
 from theme import set_css_param
 from theme import scan_themes_for_scripts
@@ -182,6 +183,7 @@ from blocking import load_cw_lists
 from blocking import add_cw_from_lists
 from happening import dav_month_via_server
 from happening import dav_day_via_server
+from webapp_theme_designer import color_contrast
 
 
 TEST_SERVER_GROUP_RUNNING = False
@@ -7092,6 +7094,44 @@ def _test_diff_content() -> None:
     assert html_str == expected
 
 
+def _test_color_contrast_value(base_dir: str) -> None:
+    print('test_color_contrast_value')
+    minimum_color_contrast = 4.5
+    background = 'black'
+    foreground = 'white'
+    contrast = color_contrast(background, foreground)
+    assert contrast
+    assert contrast > 20
+    assert contrast < 22
+    foreground = 'grey'
+    contrast = color_contrast(background, foreground)
+    assert contrast
+    assert contrast > 5
+    assert contrast < 6
+    themes = get_themes_list(base_dir)
+    for theme_name in themes:
+        theme_filename = base_dir + '/theme/' + theme_name + '/theme.json'
+        if not os.path.isfile(theme_filename):
+            continue
+        theme_json = load_json(theme_filename)
+        if not theme_json:
+            continue
+        if not theme_json.get('main-fg-color'):
+            continue
+        if not theme_json.get('main-bg-color'):
+            continue
+        foreground = theme_json['main-fg-color']
+        background = theme_json['main-bg-color']
+        contrast = color_contrast(background, foreground)
+        if contrast is None:
+            continue
+        if contrast < minimum_color_contrast:
+            print('Theme ' + theme_name + ' has not enough color contrast ' +
+                  str(contrast) + ' < ' + str(minimum_color_contrast))
+        assert contrast >= minimum_color_contrast
+    print('Color contrast is ok for all themes')
+
+
 def run_all_tests():
     base_dir = os.getcwd()
     print('Running tests...')
@@ -7109,6 +7149,7 @@ def run_all_tests():
     _test_checkbox_names()
     _test_thread_functions()
     _test_functions()
+    _test_color_contrast_value(base_dir)
     _test_diff_content()
     _test_bold_reading()
     _test_published_to_local_timezone()
diff --git a/webapp_theme_designer.py b/webapp_theme_designer.py
index 7fb18299e..b88752b20 100644
--- a/webapp_theme_designer.py
+++ b/webapp_theme_designer.py
@@ -331,3 +331,52 @@ def html_theme_designer(css_cache: {}, base_dir: str,
     theme_form += '</div>\n'
     theme_form += html_footer()
     return theme_form
+
+
+def _relative_luminance(color: str) -> float:
+    """ Returns the relative luminance for the given color
+    """
+    color = color.lstrip('#')
+    rgb = list(int(color[i:i+2], 16) for i in (0, 2, 4))
+    srgb = (
+        rgb[0] / 255.0,
+        rgb[1] / 255.0,
+        rgb[2] / 255.0
+    )
+    if srgb[0] <= 0.03928:
+        rgb[0] = srgb[0] / 12.92
+    else:
+        rgb[0] = pow(((srgb[0] + 0.055) / 1.055), 2.4)
+    if srgb[1] <= 0.03928:
+        rgb[1] = srgb[1] / 12.92
+    else:
+        rgb[1] = pow(((srgb[1] + 0.055) / 1.055), 2.4)
+    if srgb[2] <= 0.03928:
+        rgb[2] = srgb[2] / 12.92
+    else:
+        rgb[2] = pow(((srgb[2] + 0.055) / 1.055), 2.4)
+
+    return \
+        0.2126 * rgb[0] + 0.7152 * rgb[1] + 0.0722 * rgb[2]
+
+
+def color_contrast(background: str, foreground: str) -> float:
+    """returns the color contrast
+    """
+    if not background.startswith('#'):
+        if color_to_hex.get(background):
+            background = color_to_hex[background]
+        else:
+            return None
+    if not foreground.startswith('#'):
+        if color_to_hex.get(foreground):
+            foreground = color_to_hex[foreground]
+        else:
+            return None
+    background_luminance = _relative_luminance(background)
+    foreground_luminance = _relative_luminance(foreground)
+    if background_luminance > foreground_luminance:
+        return (0.05 + background_luminance) / (0.05 + foreground_luminance)
+    else:
+        return (0.05 + foreground_luminance) / (0.05 + background_luminance)
+    return None