diet-guard/app/lib/ui/theme.dart

/// The app's design tokens: one identical palette shared across every one
/// of kuhy's apps (Flutter, web, Python/Tkinter alike) — see the
/// `unified-design-system` skill (`~/.claude/skills/unified-design-system/`)
/// for the frozen token table this file implements. Built from an explicit
/// `ColorScheme`, not `ColorScheme.fromSeed`, because the shared palette is
/// hand-picked, not algorithmically derived from one seed color.
library;

import 'package:flutter/material.dart';

/// Builds the app's single dark `ThemeData` from the shared token set.
ThemeData buildAppTheme() {
  const colorScheme = ColorScheme.dark(
    surface: Color(0xFF211D1B), // ink
    surfaceContainerHighest: Color(0xFF38312E), // ink-raised-2
    surfaceContainerHigh: Color(0xFF2B2624), // ink-raised-1
    onSurface: Color(0xFFECEAE9), // text-on-dark
    onSurfaceVariant: Color(0xFFAAA09A), // muted-on-dark
    outline: Color(0xFF463E3A), // line-dark
    primary: Color(0xFFB8862E), // accent
    onPrimary: Color(
      0xFF211D1B,
    ), // on-fill — every filled surface uses dark text
    // secondary/tertiary — the shared palette has one accent, not a
    // separate secondary hue, so these mirror primary. Without an explicit
    // value here, widgets that reach for secondaryContainer (e.g.
    // SegmentedButton's selected segment) silently fall back to Flutter's
    // stock Material teal — confirmed live on-device in the todo app,
    // which shares this same theme.dart template.
    secondary: Color(0xFFB8862E), // accent
    onSecondary: Color(0xFF211D1B), // on-fill
    secondaryContainer: Color(0xFF463E3A), // line-dark
    onSecondaryContainer: Color(0xFFB8862E), // accent
    tertiary: Color(0xFFB8862E), // accent
    onTertiary: Color(0xFF211D1B), // on-fill
    tertiaryContainer: Color(0xFF463E3A), // line-dark
    onTertiaryContainer: Color(0xFFB8862E), // accent
    error: Color(0xFFE2585F), // danger
    onError: Color(0xFF211D1B), // on-fill
  );
  return ThemeData(
    useMaterial3: true,
    colorScheme: colorScheme,
    scaffoldBackgroundColor: colorScheme.surface,
    extensions: const [AppStatusColors.dark],
    textTheme: const TextTheme(
      bodyLarge: TextStyle(fontSize: AppTextSize.body),
      bodyMedium: TextStyle(fontSize: AppTextSize.body),
      titleLarge: TextStyle(fontSize: AppTextSize.title),
      titleMedium: TextStyle(fontSize: AppTextSize.subtitle),
      labelMedium: TextStyle(fontSize: AppTextSize.label),
      labelSmall: TextStyle(fontSize: AppTextSize.caption),
    ),
    // Previously unset, so every TextField fell back to M3's default
    // indigo focus color instead of the shared palette (open finding from
    // the unified-design-system component doc).
    inputDecorationTheme: InputDecorationTheme(
      filled: true,
      fillColor: colorScheme.surfaceContainerHigh,
      border: OutlineInputBorder(
        borderRadius: BorderRadius.circular(AppRadius.sm),
        borderSide: BorderSide(color: colorScheme.outline),
      ),
      enabledBorder: OutlineInputBorder(
        borderRadius: BorderRadius.circular(AppRadius.sm),
        borderSide: BorderSide(color: colorScheme.outline),
      ),
      focusedBorder: OutlineInputBorder(
        borderRadius: BorderRadius.circular(AppRadius.sm),
        borderSide: BorderSide(color: colorScheme.primary, width: 2),
      ),
      labelStyle: TextStyle(color: colorScheme.onSurfaceVariant),
    ),
    // Previously unset, so every Divider fell back to M3's default grey
    // instead of `line-dark` (same open finding as above).
    dividerTheme: DividerThemeData(
      color: colorScheme.outline,
      thickness: 1,
      space: AppSpacing.md,
    ),
  );
}

/// Semantic status colors M3's [ColorScheme] has no role for (it only has
/// `error`). Success/warning are the shared `unified-design-system` values —
/// every status indicator (calendar day, slot chip, sync state) should read
/// these instead of an ad hoc `Colors.green`/`Colors.amber`.
@immutable
class AppStatusColors extends ThemeExtension<AppStatusColors> {
  /// Creates a status-color set.
  const AppStatusColors({required this.success, required this.warning});

  /// The shared dark-theme instance — success/warning from the unified
  /// palette (danger already exists as `colorScheme.error`).
  static const dark = AppStatusColors(
    success: Color(0xFF8A9A3C),
    warning: Color(0xFFE0A63C),
  );

  /// Positive/on-track status (e.g. a fully-logged, in-budget day).
  final Color success;

  /// Caution/pending status (e.g. a partially-logged day).
  final Color warning;

  @override
  AppStatusColors copyWith({Color? success, Color? warning}) => AppStatusColors(
    success: success ?? this.success,
    warning: warning ?? this.warning,
  );

  @override
  AppStatusColors lerp(AppStatusColors? other, double t) {
    if (other is! AppStatusColors) return this;
    return AppStatusColors(
      success: Color.lerp(success, other.success, t) ?? success,
      warning: Color.lerp(warning, other.warning, t) ?? warning,
    );
  }
}

/// Shared spacing scale (4px base) — round any new value to one of these
/// instead of introducing an off-scale literal.
abstract final class AppSpacing {
  /// 4px.
  static const double xs = 4;

  /// 8px.
  static const double sm = 8;

  /// 16px.
  static const double md = 16;

  /// 24px.
  static const double lg = 24;

  /// 32px.
  static const double xl = 32;

  /// 48px.
  static const double xxl = 48;
}

/// Shared corner-radius scale. Nested radii should be `outer - gap`, not a
/// fixed constant — compute per instance per safe-design-rules rule 24.
abstract final class AppRadius {
  /// Buttons, inputs, chips.
  static const double sm = 8;

  /// Cards.
  static const double md = 12;

  /// Sheets, dialogs.
  static const double lg = 16;
}

/// Shared type scale (px). `body` is the floor for anything a user reads;
/// `label`/`caption` are for UI chrome only (timestamps, badges, tags).
abstract final class AppTextSize {
  /// 12px — chrome only.
  static const double caption = 12;

  /// 14px — chrome only.
  static const double label = 14;

  /// 16px — the floor for actual reading content.
  static const double body = 16;

  /// 20px.
  static const double subtitle = 20;

  /// 24px.
  static const double title = 24;

  /// 32px.
  static const double display = 32;
}

/// Line-length and layout caps for the desktop surface.
///
/// The Linux desktop build is this same Dart running as Flutter **web** in a
/// Chrome `--app` window, so every screen is laid out at whatever width that
/// window happens to be — commonly 1366px on the laptop. Without a cap, a
/// phone-width single-column design simply stretches: prose ran ~180 characters
/// per line (roughly 2x the readable limit) and a four-digit calorie field
/// spanned ~1334px. Neither is clipped, so nothing looks broken; it is just
/// unusable to read.
abstract final class AppWidth {
  /// 640px — the prose/paragraph cap (tokens.md rule 21, 40rem, ~65-70 chars).
  static const double prose = 640;

  /// 420px — cap for a single-purpose input (a number, a short name).
  ///
  /// Narrower than [prose] because a field wider than its longest plausible
  /// value reads as a layout error rather than an affordance.
  static const double field = 420;

  /// Viewport height below which the layout should switch to its compact form.
  ///
  /// 700px, i.e. 768 minus typical window chrome: the supported floor is a
  /// 1366x768 panel, and these are *short* landscape viewports, which
  /// phone-portrait test sizes never exercise.
  static const double shortViewport = 700;
}