import 'dart:math';

import 'package:flutter_test/flutter_test.dart';
import 'package:halkyon_ui/halkyon_ui.dart';
import 'package:material_ui/material_ui.dart';

/// WCAG's contrast ratio of two colours, from 1 (none) to 21.
double _contrast(Color a, Color b) {
  final (lighter, darker) = (
    max(a.computeLuminance(), b.computeLuminance()),
    min(a.computeLuminance(), b.computeLuminance()),
  );
  return (lighter + 0.05) / (darker + 0.05);
}

/// An app's own colours, beside the shared ones.
final class const _AppColors(final Color special)
    extends ThemeExtension<_AppColors> {
  @override
  _AppColors copyWith({Color? special}) => _AppColors(special ?? this.special);

  @override
  _AppColors lerp(_AppColors? other, double t) =>
      other == null ? this : _AppColors(Color.lerp(special, other.special, t)!);
}

void main() {
  group('the picker palette', () {
    test('has the 20 colours content can be given', () {
      expect(PaletteColor.values, hasLength(20));
    });

    for (final color in PaletteColor.values) {
      test(
        '${color.name}: its text colour is readable on its fill (WCAG AA)',
        () {
          expect(
            _contrast(color.foreground, color.background),
            greaterThanOrEqualTo(4.5),
          );
        },
      );
    }

    test(
      'finds a colour by its stored name, and nothing for an unknown one',
      () {
        expect(PaletteColor.byName('cobalt'), PaletteColor.cobalt);
        expect(PaletteColor.byName('ultraviolet'), isNull);
        expect(PaletteColor.byName(null), isNull);
      },
    );
  });

  group('the theme', () {
    for (final brightness in Brightness.values) {
      test('$brightness: Material 3, with the status colours', () {
        final theme = appTheme(brightness);

        expect(theme.useMaterial3, isTrue);
        expect(theme.colorScheme.brightness, brightness);
        expect(theme.extras, isA<ThemeExtras>());
      });
    }

    test("takes an app's own extensions beside the shared ones", () {
      const colors = _AppColors(Color(0xFF123456));

      final theme = appTheme(Brightness.light, extensions: [colors]);

      expect(theme.extension<_AppColors>(), colors);
      expect(theme.extras, ThemeExtras.light);
    });

    test('light: cobalt is the primary colour, copper the accent', () {
      final scheme = appTheme(Brightness.light).colorScheme;

      expect(scheme.primary, Brand.primary);
      expect(scheme.tertiary, Brand.accent);
    });

    test("dark: the primary colour's text stays readable", () {
      final scheme = appTheme(Brightness.dark).colorScheme;

      expect(
        _contrast(scheme.onPrimary, scheme.primary),
        greaterThanOrEqualTo(4.5),
      );
      expect(
        _contrast(scheme.onSurface, scheme.surface),
        greaterThanOrEqualTo(4.5),
      );
    });

    test("the navigation bar is Material 3 Expressive's shorter one", () {
      expect(appTheme(Brightness.light).navigationBarTheme.height, 64);
    });
  });
}