Shuffle/app/lib/core/theme/app_theme.dart

import 'package:flutter/material.dart';
import 'package:shuffle/core/theme/app_spacing.dart';

/// Material 3 theme base of the design system (see docs/design-system.md).
///
/// Colors come from [ColorScheme.fromSeed]; the contrast of all core pairs is
/// verified in `test/core/theme/app_theme_test.dart` (WCAG AA, >= 4.5:1 for
/// text, >= 3:1 for the focus indicator and input borders).
abstract final class AppTheme {
  static const Color seed = Color(0xFF4F46E5);

  static ThemeData light() => _build(Brightness.light);

  static ThemeData dark() => _build(Brightness.dark);

  static ColorScheme _scheme(Brightness brightness) {
    final base = ColorScheme.fromSeed(seedColor: seed, brightness: brightness);
    // Tone 50/60 outlines keep >= 3:1 against the surface (WCAG 1.4.11);
    // the M3 default outline is slightly weaker in light mode.
    return base.copyWith(
      outline: brightness == Brightness.light
          ? const Color(0xFF6B6A7A)
          : const Color(0xFF9A99AB),
    );
  }

  static ThemeData _build(Brightness brightness) {
    final scheme = _scheme(brightness);
    final textTheme = Typography.material2021(colorScheme: scheme).black
        .apply(bodyColor: scheme.onSurface, displayColor: scheme.onSurface);
    final themedText = brightness == Brightness.dark
        ? Typography.material2021(colorScheme: scheme).white.apply(
            bodyColor: scheme.onSurface,
            displayColor: scheme.onSurface,
          )
        : textTheme;

    const minSize = Size(AppSpacing.minTouchTarget, AppSpacing.minTouchTarget);
    final shape = RoundedRectangleBorder(borderRadius: AppRadius.mdAll);
    // Visible keyboard focus ring (web/desktop), contrast >= 3:1.
    final focusSide = WidgetStateProperty.resolveWith<BorderSide?>(
      (states) => states.contains(WidgetState.focused)
          ? BorderSide(color: scheme.primary, width: 3)
          : null,
    );
    // The primary ring is invisible on the primary fill of a FilledButton;
    // onSurface contrasts with both the fill and the surrounding surface.
    final filledFocusSide = WidgetStateProperty.resolveWith<BorderSide?>(
      (states) => states.contains(WidgetState.focused)
          ? BorderSide(color: scheme.onSurface, width: 3)
          : null,
    );

    OutlineInputBorder border(Color color, double width) => OutlineInputBorder(
      borderRadius: AppRadius.mdAll,
      borderSide: BorderSide(color: color, width: width),
    );

    return ThemeData(
      useMaterial3: true,
      colorScheme: scheme,
      textTheme: themedText,
      visualDensity: VisualDensity.standard,
      materialTapTargetSize: MaterialTapTargetSize.padded,
      scaffoldBackgroundColor: scheme.surface,
      focusColor: scheme.primary.withValues(alpha: 0.16),
      dividerTheme: DividerThemeData(color: scheme.outlineVariant),
      appBarTheme: AppBarTheme(
        backgroundColor: scheme.surface,
        foregroundColor: scheme.onSurface,
        centerTitle: false,
        titleTextStyle: themedText.titleLarge,
      ),
      cardTheme: CardThemeData(
        elevation: 0,
        color: scheme.surfaceContainerLow,
        shape: RoundedRectangleBorder(
          borderRadius: AppRadius.lgAll,
          side: BorderSide(color: scheme.outlineVariant),
        ),
      ),
      filledButtonTheme: FilledButtonThemeData(
        style: FilledButton.styleFrom(
          minimumSize: minSize,
          shape: shape,
          padding: const EdgeInsets.symmetric(horizontal: AppSpacing.xl),
        ).copyWith(side: filledFocusSide),
      ),
      elevatedButtonTheme: ElevatedButtonThemeData(
        style: ElevatedButton.styleFrom(
          minimumSize: minSize,
          shape: shape,
        ).copyWith(side: focusSide),
      ),
      outlinedButtonTheme: OutlinedButtonThemeData(
        style:
            OutlinedButton.styleFrom(
              minimumSize: minSize,
              shape: shape,
              side: BorderSide(color: scheme.outline),
              padding: const EdgeInsets.symmetric(horizontal: AppSpacing.xl),
            ).copyWith(
              side: WidgetStateProperty.resolveWith<BorderSide?>(
                (states) => states.contains(WidgetState.focused)
                    ? BorderSide(color: scheme.primary, width: 3)
                    : BorderSide(color: scheme.outline),
              ),
            ),
      ),
      textButtonTheme: TextButtonThemeData(
        style: TextButton.styleFrom(
          minimumSize: minSize,
          shape: shape,
          padding: const EdgeInsets.symmetric(horizontal: AppSpacing.lg),
        ).copyWith(side: focusSide),
      ),
      iconButtonTheme: IconButtonThemeData(
        style: IconButton.styleFrom(minimumSize: minSize),
      ),
      checkboxTheme: CheckboxThemeData(
        materialTapTargetSize: MaterialTapTargetSize.padded,
        side: BorderSide(color: scheme.outline, width: 2),
      ),
      inputDecorationTheme: InputDecorationTheme(
        filled: true,
        fillColor: scheme.surfaceContainerHighest,
        contentPadding: const EdgeInsets.symmetric(
          horizontal: AppSpacing.lg,
          vertical: AppSpacing.md,
        ),
        border: border(scheme.outline, 1),
        enabledBorder: border(scheme.outline, 1),
        focusedBorder: border(scheme.primary, 3),
        errorBorder: border(scheme.error, 2),
        focusedErrorBorder: border(scheme.error, 3),
        errorStyle: themedText.bodySmall?.copyWith(color: scheme.error),
        helperStyle: themedText.bodySmall?.copyWith(
          color: scheme.onSurfaceVariant,
        ),
      ),
      snackBarTheme: SnackBarThemeData(
        behavior: SnackBarBehavior.floating,
        backgroundColor: scheme.inverseSurface,
        contentTextStyle: themedText.bodyMedium?.copyWith(
          color: scheme.onInverseSurface,
        ),
        actionTextColor: scheme.inversePrimary,
        shape: RoundedRectangleBorder(borderRadius: AppRadius.smAll),
        showCloseIcon: true,
        closeIconColor: scheme.onInverseSurface,
      ),
    );
  }
}