import 'package:flutter/material.dart';

/// User's theme preference, persisted in the learning snapshot.
enum AppThemeMode { system, light, dark }

/// One brightness worth of brand colours. Two const instances below hold the
/// light and dark values; [AppColors] mirrors the active one so the many
/// widgets that read `AppColors.x` directly recolour when the theme changes.
class _Palette {
  const _Palette({
    required this.paper,
    required this.surface,
    required this.surfaceMuted,
    required this.ink,
    required this.muted,
    required this.line,
    required this.green,
    required this.softGreen,
    required this.warm,
    required this.warmInk,
  });

  final Color paper;
  final Color surface;
  final Color surfaceMuted;
  final Color ink;
  final Color muted;
  final Color line;
  final Color green;
  final Color softGreen;
  final Color warm;
  final Color warmInk;
}

const _light = _Palette(
  paper: Color(0xFFF5F7F3),
  surface: Colors.white,
  surfaceMuted: Color(0xFFF1F5F0),
  ink: Color(0xFF19211B),
  muted: Color(0xFF647268),
  line: Color(0xFFD8E1D9),
  green: Color(0xFF176B46),
  softGreen: Color(0xFFE2F3E8),
  warm: Color(0xFFFFF0E3),
  warmInk: Color(0xFF9E4C18),
);

const _dark = _Palette(
  paper: Color(0xFF11150F),
  surface: Color(0xFF1B211A),
  surfaceMuted: Color(0xFF232B22),
  ink: Color(0xFFE8EEE6),
  muted: Color(0xFF9CA99D),
  line: Color(0xFF33402F),
  green: Color(0xFF2FA36B),
  softGreen: Color(0xFF17311F),
  warm: Color(0xFF352618),
  warmInk: Color(0xFFEBAA78),
);

/// Brand colours for the active brightness. Values are reassigned by
/// [AppColors.applyBrightness]; call it before building the widget tree.
abstract final class AppColors {
  static Color paper = _light.paper;
  static Color surface = _light.surface;
  static Color surfaceMuted = _light.surfaceMuted;
  static Color ink = _light.ink;
  static Color muted = _light.muted;
  static Color line = _light.line;
  static Color green = _light.green;
  static Color softGreen = _light.softGreen;
  static Color warm = _light.warm;
  static Color warmInk = _light.warmInk;

  static Brightness brightness = Brightness.light;

  static void applyBrightness(Brightness value) {
    final p = value == Brightness.dark ? _dark : _light;
    brightness = value;
    paper = p.paper;
    surface = p.surface;
    surfaceMuted = p.surfaceMuted;
    ink = p.ink;
    muted = p.muted;
    line = p.line;
    green = p.green;
    softGreen = p.softGreen;
    warm = p.warm;
    warmInk = p.warmInk;
  }
}

ThemeData buildAppTheme(Brightness brightness) {
  final p = brightness == Brightness.dark ? _dark : _light;
  final scheme =
      ColorScheme.fromSeed(
        seedColor: p.green,
        brightness: brightness,
      ).copyWith(
        surface: p.surface,
        onSurface: p.ink,
        primary: p.green,
        onPrimary: Colors.white,
        outline: p.line,
      );

  return ThemeData(
    useMaterial3: true,
    brightness: brightness,
    colorScheme: scheme,
    scaffoldBackgroundColor: p.paper,
    fontFamily: 'PingFang SC',
    appBarTheme: AppBarTheme(
      backgroundColor: p.surface,
      foregroundColor: p.ink,
      elevation: 0,
      centerTitle: false,
    ),
    textTheme: TextTheme(
      headlineMedium: TextStyle(
        color: p.ink,
        fontSize: 26,
        height: 1.25,
        fontWeight: FontWeight.w600,
        letterSpacing: -0.6,
      ),
      titleLarge: TextStyle(
        color: p.ink,
        fontSize: 18,
        fontWeight: FontWeight.w600,
      ),
      bodyLarge: TextStyle(color: p.ink, fontSize: 16, height: 1.5),
      bodyMedium: TextStyle(color: p.muted, fontSize: 14, height: 1.5),
    ),
  );
}