// A self-contained, plug-and-play button. Drop this single file into any
// Flutter project — no packages, no DI, no widget wrapping.
//
//   1. Use it anywhere:
//        AppButton(text: "Continue", onPressed: _submit)
//        AppButton(text: "Cancel", type: AppButtonType.secondary)
//        AppButton(text: "Saving", isLoading: true, size: AppButtonSize.md)
//
//   2. Restyle once at startup — or never, the defaults stand on their own:
//        AppButton.configure(light: AppButtonColors.light.copyWith(accent: myBlue));
//
//   3. Press feedback runs on a spring, not a curve. Scale and fill are
//      driven by one animation so they land together.

import "package:flutter/material.dart";
import "package:flutter/physics.dart";

// ---------------------------------------------------------------------------
// Public enums
// ---------------------------------------------------------------------------

/// Visual weight of a button — sets fill, border, and press feedback.
enum AppButtonType {
  /// Accent-filled solid. The one call to action on a screen.
  primary,

  /// Outlined and transparent. Secondary actions beside a primary.
  secondary,

  /// Bare text. Low-emphasis actions — dismiss, learn more, skip.
  tertiary,
}

/// Size step — sets padding and text style.
enum AppButtonSize {
  /// Compact, for dense rows and inline actions.
  sm,

  /// The everyday size.
  md,

  /// Full-height, for primary actions at the bottom of a screen.
  lg,
}

/// Interaction state a color token is resolved against.
enum AppButtonState {
  /// Enabled and untouched.
  defaultState,

  /// Non-interactive — disabled, or busy with [AppButton.isLoading].
  disabled,
}

// ---------------------------------------------------------------------------
// Theme
// ---------------------------------------------------------------------------

/// Color tokens for a button palette.
///
/// Use [light] and [dark] presets, or build your own and pass them to
/// [AppButton.configure].
@immutable
class AppButtonColors {
  /// Creates a button color palette.
  const AppButtonColors({
    required this.foreground,
    required this.muted,
    required this.surface,
    required this.accent,
    required this.accentForeground,
    required this.accentStrong,
    required this.border,
    required this.disabled,
  });

  /// Label on secondary and tertiary buttons.
  final Color foreground;

  /// Label on a disabled button of any type.
  final Color muted;

  /// Pressed fill for the flat types, which have no resting background.
  final Color surface;

  /// Primary fill.
  final Color accent;

  /// Label on a primary button.
  final Color accentForeground;

  /// Pressed primary fill.
  final Color accentStrong;

  /// Outline on a secondary button.
  final Color border;

  /// Fill on a disabled primary or secondary button.
  final Color disabled;

  /// Default palette for light mode.
  static const AppButtonColors light = AppButtonColors(
    foreground: Color(0xFF1C2229),
    muted: Color(0xFF6C7278),
    surface: Color(0xFFEAEFF5),
    accent: Color(0xFF8000FF),
    accentForeground: Color(0xFFFFFFFF),
    accentStrong: Color(0xFF5C00B8),
    border: Color(0xFFD8DFE6),
    disabled: Color(0xFFB3B8BE),
  );

  /// Default palette for dark mode.
  static const AppButtonColors dark = AppButtonColors(
    foreground: Color(0xFFDADEE3),
    muted: Color(0xFF8B9095),
    surface: Color(0xFF1D2227),
    accent: Color(0xFFD7F881),
    accentForeground: Color(0xFF0E1216),
    accentStrong: Color(0xFFE8FFA8),
    border: Color(0xFF353B42),
    disabled: Color(0xFF484E54),
  );

  /// Resting fill for [type] in [state], or null when the type has none.
  Color? backgroundFor(AppButtonType type, AppButtonState state) {
    if (state == AppButtonState.disabled) {
      return switch (type) {
        AppButtonType.primary || AppButtonType.secondary => disabled,
        AppButtonType.tertiary => null,
      };
    }
    return switch (type) {
      AppButtonType.primary => accent,
      AppButtonType.secondary || AppButtonType.tertiary => null,
    };
  }

  /// Label color for [type] in [state].
  Color foregroundFor(AppButtonType type, AppButtonState state) {
    if (state == AppButtonState.disabled) return muted;
    return switch (type) {
      AppButtonType.primary => accentForeground,
      AppButtonType.secondary || AppButtonType.tertiary => foreground,
    };
  }

  /// Outline for [type] in [state], or null when the type has none.
  Color? borderFor(AppButtonType type, AppButtonState state) {
    return switch (type) {
      AppButtonType.primary || AppButtonType.tertiary => null,
      AppButtonType.secondary =>
        state == AppButtonState.disabled ? disabled : border,
    };
  }

  /// Returns a copy with the given fields replaced.
  AppButtonColors copyWith({
    Color? foreground,
    Color? muted,
    Color? surface,
    Color? accent,
    Color? accentForeground,
    Color? accentStrong,
    Color? border,
    Color? disabled,
  }) {
    return AppButtonColors(
      foreground: foreground ?? this.foreground,
      muted: muted ?? this.muted,
      surface: surface ?? this.surface,
      accent: accent ?? this.accent,
      accentForeground: accentForeground ?? this.accentForeground,
      accentStrong: accentStrong ?? this.accentStrong,
      border: border ?? this.border,
      disabled: disabled ?? this.disabled,
    );
  }
}

/// Typography and metrics per [AppButtonSize].
@immutable
class AppButtonSizing {
  /// Creates sizing settings.
  const AppButtonSizing({
    this.fontFamily,
    this.sm = const TextStyle(
      fontSize: 12,
      height: 16 / 12,
      fontWeight: FontWeight.w500,
    ),
    this.md = const TextStyle(
      fontSize: 14,
      height: 20 / 14,
      fontWeight: FontWeight.w500,
    ),
    this.lg = const TextStyle(
      fontSize: 14,
      height: 20 / 14,
      fontWeight: FontWeight.w500,
    ),
    this.smPadding = const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
    this.mdPadding = const EdgeInsets.symmetric(horizontal: 24, vertical: 12),
    this.lgPadding = const EdgeInsets.symmetric(horizontal: 24, vertical: 16),
    this.borderRadius = 24,
    this.gap = 8,
  });

  static const Object _unset = Object();

  /// Applied to every style unless a style names its own family.
  ///
  /// Defaults to the ambient font so a fresh project needs no asset setup.
  final String? fontFamily;

  /// Label style for [AppButtonSize.sm].
  final TextStyle sm;

  /// Label style for [AppButtonSize.md].
  final TextStyle md;

  /// Label style for [AppButtonSize.lg].
  final TextStyle lg;

  /// Padding for [AppButtonSize.sm].
  final EdgeInsets smPadding;

  /// Padding for [AppButtonSize.md].
  final EdgeInsets mdPadding;

  /// Padding for [AppButtonSize.lg].
  final EdgeInsets lgPadding;

  /// Corner radius of the button shape.
  final double borderRadius;

  /// Space between icon and label.
  final double gap;

  /// Resolves the label style for [size] with [color] and [fontFamily].
  TextStyle textFor(AppButtonSize size, Color color) {
    final TextStyle style = switch (size) {
      AppButtonSize.sm => sm,
      AppButtonSize.md => md,
      AppButtonSize.lg => lg,
    };
    return style.copyWith(
      color: color,
      fontFamily: style.fontFamily ?? fontFamily,
    );
  }

  /// Returns the padding for [size].
  EdgeInsets paddingFor(AppButtonSize size) => switch (size) {
    AppButtonSize.sm => smPadding,
    AppButtonSize.md => mdPadding,
    AppButtonSize.lg => lgPadding,
  };

  /// Returns a copy with the given fields replaced.
  ///
  /// Pass `fontFamily: null` explicitly to clear a previously set family.
  AppButtonSizing copyWith({
    Object? fontFamily = _unset,
    TextStyle? sm,
    TextStyle? md,
    TextStyle? lg,
    EdgeInsets? smPadding,
    EdgeInsets? mdPadding,
    EdgeInsets? lgPadding,
    double? borderRadius,
    double? gap,
  }) {
    return AppButtonSizing(
      fontFamily: fontFamily == _unset
          ? this.fontFamily
          : fontFamily as String?,
      sm: sm ?? this.sm,
      md: md ?? this.md,
      lg: lg ?? this.lg,
      smPadding: smPadding ?? this.smPadding,
      mdPadding: mdPadding ?? this.mdPadding,
      lgPadding: lgPadding ?? this.lgPadding,
      borderRadius: borderRadius ?? this.borderRadius,
      gap: gap ?? this.gap,
    );
  }
}

/// Global button configuration — colors, sizing, and press feel.
@immutable
class AppButtonTheme {
  /// Creates a button theme.
  const AppButtonTheme({
    this.light = AppButtonColors.light,
    this.dark = AppButtonColors.dark,
    this.sizing = const AppButtonSizing(),
    this.pressScale = 0.03,
    this.brightnessResolver,
  }) : assert(
         pressScale >= 0 && pressScale < 1,
         "pressScale must be in [0, 1)",
       );

  static const Object _unset = Object();

  /// Palette used when [brightnessOf] resolves to [Brightness.light].
  final AppButtonColors light;

  /// Palette used when [brightnessOf] resolves to [Brightness.dark].
  final AppButtonColors dark;

  /// Typography and metrics per size.
  final AppButtonSizing sizing;

  /// How far the button shrinks at full press — 0.03 is a 3% dip.
  final double pressScale;

  /// Escape hatch for apps that drive brightness off something other than the
  /// ambient [Theme].
  final Brightness Function(BuildContext context)? brightnessResolver;

  /// Resolves the current brightness for [context].
  Brightness brightnessOf(BuildContext context) =>
      brightnessResolver?.call(context) ?? Theme.of(context).brightness;

  /// Returns the color palette for [context]'s current brightness.
  AppButtonColors colorsOf(BuildContext context) =>
      brightnessOf(context) == Brightness.dark ? dark : light;

  /// Returns a copy with the given fields replaced.
  ///
  /// Pass `brightnessResolver: null` explicitly to clear a custom resolver.
  AppButtonTheme copyWith({
    AppButtonColors? light,
    AppButtonColors? dark,
    AppButtonSizing? sizing,
    double? pressScale,
    Object? brightnessResolver = _unset,
  }) {
    return AppButtonTheme(
      light: light ?? this.light,
      dark: dark ?? this.dark,
      sizing: sizing ?? this.sizing,
      pressScale: pressScale ?? this.pressScale,
      brightnessResolver: brightnessResolver == _unset
          ? this.brightnessResolver
          : brightnessResolver as Brightness Function(BuildContext context)?,
    );
  }
}

// ---------------------------------------------------------------------------
// Springs
// ---------------------------------------------------------------------------

/// A press is a physical event, so it settles on a spring rather than over a
/// fixed duration. Approximates iOS's smooth interactive spring.
abstract final class _AppButtonSprings {
  /// Near-critical (zeta ~0.9) — quick, barely a wobble. A button that
  /// visibly bounced under a fingertip would read as loose, not lively.
  static const SpringDescription press = SpringDescription(
    mass: 1,
    stiffness: 480,
    damping: 39,
  );
}

// ---------------------------------------------------------------------------
// Button
// ---------------------------------------------------------------------------

/// A spring-animated button with three weights and three sizes.
///
/// Requires [text], [leadingIcon], or [trailingIcon]. Pass [onPressed] to
/// enable it; a null callback, [isDisabled], or [isLoading] all render the
/// disabled treatment and swallow taps.
class AppButton extends StatefulWidget {
  /// Creates a button.
  const AppButton({
    super.key,
    this.text,
    this.onPressed,
    this.isLoading = false,
    this.isDisabled = false,
    this.backgroundColor,
    this.foregroundColor,
    this.disabledBackgroundColor,
    this.borderColor,
    this.borderRadius,
    this.padding,
    this.width,
    this.height,
    this.leadingIcon,
    this.trailingIcon,
    this.textStyle,
    this.semanticLabel,
    this.type = AppButtonType.primary,
    this.size = AppButtonSize.lg,
  }) : assert(
         text != null || leadingIcon != null || trailingIcon != null,
         "AppButton requires text or an icon.",
       );

  static AppButtonTheme _theme = const AppButtonTheme();

  /// The active button theme.
  static AppButtonTheme get theme => _theme;

  /// Restyles every [AppButton] in the app. Safe to call more than once;
  /// buttons already on screen pick the change up on their next build.
  static void configure({
    AppButtonColors? light,
    AppButtonColors? dark,
    AppButtonSizing? sizing,
    double? pressScale,
    Object? brightnessResolver = AppButtonTheme._unset,
  }) {
    _theme = _theme.copyWith(
      light: light,
      dark: dark,
      sizing: sizing,
      pressScale: pressScale,
      brightnessResolver: brightnessResolver,
    );
  }

  /// Resets the theme to defaults. For use in tests only.
  @visibleForTesting
  static void debugReset() => _theme = const AppButtonTheme();

  /// Label text. Optional when an icon is supplied.
  final String? text;

  /// Tap handler. A null callback disables the button.
  final VoidCallback? onPressed;

  /// Swaps the content for a spinner and blocks taps.
  final bool isLoading;

  /// Renders the disabled treatment and blocks taps.
  final bool isDisabled;

  /// Overrides the resolved fill.
  final Color? backgroundColor;

  /// Overrides the resolved label and icon color.
  final Color? foregroundColor;

  /// Overrides the resolved disabled fill.
  final Color? disabledBackgroundColor;

  /// Overrides the resolved outline.
  final Color? borderColor;

  /// Overrides [AppButtonSizing.borderRadius].
  final double? borderRadius;

  /// Overrides the padding for [size].
  final EdgeInsets? padding;

  /// Fixed width. Null hugs the content.
  final double? width;

  /// Fixed height. Null hugs the content.
  final double? height;

  /// Icon before the label.
  final Widget? leadingIcon;

  /// Icon after the label. Replaced by the spinner on a loading tertiary.
  final Widget? trailingIcon;

  /// Overrides the resolved label style. Color is still applied on top.
  final TextStyle? textStyle;

  /// Screen-reader label. Defaults to [text]; supply one for icon-only buttons.
  final String? semanticLabel;

  /// Visual weight.
  final AppButtonType type;

  /// Size step.
  final AppButtonSize size;

  @override
  State<AppButton> createState() => _AppButtonState();
}

class _AppButtonState extends State<AppButton>
    with SingleTickerProviderStateMixin {
  /// 0 = at rest, 1 = fully pressed. One value drives scale and fill so they
  /// arrive together instead of drifting apart on separate curves.
  late final AnimationController _press = AnimationController.unbounded(
    vsync: this,
  )..value = 0;

  bool _isPressed = false;

  bool get _isDisabled =>
      widget.isDisabled || widget.onPressed == null || widget.isLoading;

  @override
  void didUpdateWidget(AppButton oldWidget) {
    super.didUpdateWidget(oldWidget);
    // Disabled mid-press: release rather than stay stranded in the pressed
    // look, since the gesture callbacks that would have released it are gone.
    if (_isDisabled) _setPressed(false);
  }

  @override
  void dispose() {
    _press.dispose();
    super.dispose();
  }

  void _setPressed(bool value) {
    if (_isPressed == value) return;
    _isPressed = value;
    _press.animateWith(
      SpringSimulation(
        _AppButtonSprings.press,
        _press.value,
        value ? 1 : 0,
        0,
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    final AppButtonTheme theme = AppButton._theme;
    final AppButtonColors colors = theme.colorsOf(context);
    final AppButtonSizing sizing = theme.sizing;

    final bool isDisabled = _isDisabled;
    final AppButtonState state = isDisabled
        ? AppButtonState.disabled
        : AppButtonState.defaultState;

    final Color fgColor =
        widget.foregroundColor ?? colors.foregroundFor(widget.type, state);
    final double borderRadius = widget.borderRadius ?? sizing.borderRadius;
    final EdgeInsets padding = widget.padding ?? sizing.paddingFor(widget.size);
    final TextStyle textStyle = widget.textStyle == null
        ? sizing.textFor(widget.size, fgColor)
        : widget.textStyle!.copyWith(color: fgColor);
    final Color? borderColor =
        widget.borderColor ?? colors.borderFor(widget.type, state);

    // Solid accent fill for an unstyled, enabled primary — same idea as
    // stormej.me `bg-primary` (no gradient, no glow).
    final bool usesAccent =
        widget.type == AppButtonType.primary &&
        widget.backgroundColor == null &&
        !isDisabled;

    final Color? restingBg = isDisabled
        ? (widget.disabledBackgroundColor ??
              colors.backgroundFor(widget.type, AppButtonState.disabled))
        : (widget.backgroundColor ??
              (usesAccent
                  ? colors.accent
                  : colors.backgroundFor(widget.type, state)));

    // Press: primary darkens toward accentStrong; flat types pick up surface.
    final Color? pressedBg = switch (widget.type) {
      AppButtonType.primary => usesAccent ? colors.accentStrong : restingBg,
      AppButtonType.secondary || AppButtonType.tertiary => colors.surface,
    };

    final Widget content = Align(
      widthFactor: widget.width == null ? 1 : null,
      heightFactor: widget.height == null ? 1 : null,
      child: _buildContent(fgColor, textStyle, sizing.gap),
    );

    return Semantics(
      button: true,
      enabled: !isDisabled,
      label: widget.semanticLabel ?? widget.text,
      child: GestureDetector(
        onTap: isDisabled ? null : widget.onPressed,
        onTapDown: isDisabled ? null : (_) => _setPressed(true),
        onTapUp: isDisabled ? null : (_) => _setPressed(false),
        onTapCancel: isDisabled ? null : () => _setPressed(false),
        child: AnimatedBuilder(
          animation: _press,
          builder: (BuildContext context, Widget? child) {
            final double t = _press.value;
            // Scale rides any overshoot the spring produces. Colors clamp:
            // a stop extrapolated past its endpoint is a different color,
            // not a livelier one.
            final double ct = t.clamp(0.0, 1.0);

            return Transform.scale(
              scale: 1 - theme.pressScale * t,
              child: Container(
                width: widget.width,
                height: widget.height,
                padding: padding,
                decoration: ShapeDecoration(
                  color: Color.lerp(restingBg, pressedBg, ct),
                  shape: RoundedSuperellipseBorder(
                    borderRadius: BorderRadius.circular(borderRadius),
                    side: borderColor == null
                        ? BorderSide.none
                        : BorderSide(color: borderColor),
                  ),
                ),
                child: child,
              ),
            );
          },
          child: content,
        ),
      ),
    );
  }

  Widget _buildContent(Color fgColor, TextStyle textStyle, double gap) {
    // Every type but tertiary swaps its whole content for the spinner —
    // tertiary is bare text, so a swap would collapse the button's width.
    if (widget.isLoading && widget.type != AppButtonType.tertiary) {
      return _AppButtonSpinner(color: fgColor, size: 18);
    }

    final bool hasText = widget.text != null && widget.text!.isNotEmpty;
    final List<Widget> children = <Widget>[];

    void add(Widget child) {
      if (children.isNotEmpty) children.add(SizedBox(width: gap));
      children.add(child);
    }

    if (widget.leadingIcon != null) {
      add(_themedIcon(widget.leadingIcon!, fgColor));
    }
    if (hasText) {
      add(Text(widget.text!, style: textStyle));
    }
    if (widget.isLoading && widget.type == AppButtonType.tertiary) {
      add(_AppButtonSpinner(color: fgColor, size: 16));
    } else if (widget.trailingIcon != null) {
      add(_themedIcon(widget.trailingIcon!, fgColor));
    }

    return Row(
      mainAxisSize: MainAxisSize.min,
      mainAxisAlignment: MainAxisAlignment.center,
      children: children,
    );
  }

  Widget _themedIcon(Widget icon, Color color) =>
      IconTheme(data: IconThemeData(color: color), child: icon);
}

class _AppButtonSpinner extends StatelessWidget {
  const _AppButtonSpinner({required this.color, required this.size});

  final Color color;
  final double size;

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      width: size,
      height: size,
      child: CircularProgressIndicator(
        strokeWidth: 2,
        valueColor: AlwaysStoppedAnimation<Color>(color),
      ),
    );
  }
}