import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

import 'package:miler/views/helpers/constants/Colorconstants.dart';

/// ── Contrast is a contract, not a preference ──
///
/// This app is read on a phone clamped to a handlebar in Indian daylight, by
/// someone wearing a helmet, while a customer waits. Contrast is not an
/// accessibility checkbox here; it is whether the rider can do the job.
///
/// An audit of the palette found the app's **second most-used colour failing
/// outright**: `secondaryText` was #8E8E93, which is 3.26:1 on white against a
/// 4.5:1 WCAG AA floor for normal text. It carries captions, labels and
/// metadata on 89 call sites across all 33 screens — so on every screen, the
/// supporting text was the part that disappeared in sunlight. `moneyGreen`
/// exists for the same reason: `acceptGreen` is 2.62:1 as text.
///
/// Those were fixed at the token, so this file guards the tokens. A colour is a
/// number; a number can be asserted, and that is the only way a palette stays
/// legible through future redesigns.
void main() {
  /// WCAG 2.1 relative luminance.
  double luminance(Color c) {
    double channel(double v) =>
        v <= 0.03928 ? v / 12.92 : math.pow((v + 0.055) / 1.055, 2.4) as double;
    return 0.2126 * channel(c.r) +
        0.7152 * channel(c.g) +
        0.0722 * channel(c.b);
  }

  /// WCAG 2.1 contrast ratio, 1.0–21.0.
  double ratio(Color a, Color b) {
    final la = luminance(a), lb = luminance(b);
    return (math.max(la, lb) + 0.05) / (math.min(la, lb) + 0.05);
  }

  // Every background the app draws text on.
  final surfaces = <String, Color>{
    'white': Colors.white,
    'page (surface)': ColorConstants.surface,
    'card fill (cardSurface)': ColorConstants.cardSurface,
    'neutralLight': ColorConstants.neutralLight,
  };

  /// WCAG AA: 4.5:1 for normal text, 3.0:1 for large or bold text.
  const aaNormal = 4.5;
  const aaLarge = 3.0;

  group('text colours clear AA on every surface they are used on', () {
    final bodyText = <String, Color>{
      'slateText': ColorConstants.slateText,
      'secondaryText': ColorConstants.secondaryText,
      'onSurfaceVariant': ColorConstants.onSurfaceVariant,
      'onSurface': ColorConstants.onSurface,
      'moneyGreen': ColorConstants.moneyGreen,
      'errorRed': ColorConstants.errorRed,
    };

    bodyText.forEach((name, colour) {
      surfaces.forEach((bgName, bg) {
        test('$name on $bgName', () {
          final r = ratio(colour, bg);
          expect(
            r,
            greaterThanOrEqualTo(aaNormal),
            reason:
                '$name on $bgName is ${r.toStringAsFixed(2)}:1, '
                'under the $aaNormal:1 AA floor for normal text',
          );
        });
      });
    });
  });

  /// ── Every token is declared, or the test fails ──
  ///
  /// The old version guarded six colours. That was a false sense of coverage:
  /// an audit found **five tokens failing outright** — `warningOrange` 2.20:1,
  /// `successGreen` 2.22:1, `warningYellow` 1.73:1, `cardBlue` 2.77:1,
  /// `infoBlue` 4.02:1 — plus `disabledText` at 1.68:1 being used as readable
  /// caption text on seven screens. Every one of them sat outside the six.
  ///
  /// So the contract is inverted. This enumerates the whole palette and forces
  /// each colour into exactly one bucket:
  ///
  ///  * **text-safe** — asserted ≥4.5:1 on every surface the app draws on.
  ///  * **fill** — carries a white label; the label is what is asserted.
  ///  * **structural** — a hairline or a disabled fill, carrying no words:
  ///    asserted visible against the surface, and asserted *not* readable, so a
  ///    colour that could be text has to be filed as text.
  ///
  /// A new token belongs to a bucket or this test fails, which is the only way
  /// the next `warningOrange` cannot land.
  group('the palette is exhaustively classified', () {
    // Colours the app is allowed to render words in.
    final textSafe = <String, Color>{
      'slateText': ColorConstants.slateText,
      'secondaryText': ColorConstants.secondaryText,
      'onSurfaceVariant': ColorConstants.onSurfaceVariant,
      'onSurface': ColorConstants.onSurface,
      'moneyGreen': ColorConstants.moneyGreen,
      'acceptGreen': ColorConstants.acceptGreen,
      'errorRed': ColorConstants.errorRed,
      'error': ColorConstants.error,
      'warning': ColorConstants.warning,
      'primary': ColorConstants.primary,
      'rewardAmber': ColorConstants.rewardAmber,
      'tertiary': ColorConstants.tertiary,
      'deliveryAccent': ColorConstants.deliveryAccent,
      'combinedAccent': ColorConstants.combinedAccent,
      'upiPurple': ColorConstants.upiPurple,
      'emphasis': ColorConstants.emphasis,
    };

    // Colours that fill a shape carrying a white label. The label is what is
    // asserted — several of these are dark enough to read as text too, which is
    // fine; the bucket is about the job, not about failing some other job.
    final fillWithWhiteLabel = <String, Color>{
      'pickupChip': ColorConstants.pickupChip,
      'deliveryChip': ColorConstants.deliveryChip,
      'combinedChip': ColorConstants.combinedChip,
      'primaryContainer': ColorConstants.primaryContainer,
      'successContainer': ColorConstants.successContainer,
      'tertiaryContainer': ColorConstants.tertiaryContainer,
    };

    // Hairlines, dividers and disabled fills. These carry no words at all; the
    // only thing that matters is that they are visible against the surface
    // behind them.
    final structural = <String, Color>{
      'disabledFill': ColorConstants.disabledFill,
      'borderStrong': ColorConstants.borderStrong,
      'borderSubtle': ColorConstants.borderSubtle,
      'dividerColor': ColorConstants.dividerColor,
      'outlineVariant': ColorConstants.outlineVariant,
    };

    textSafe.forEach((name, colour) {
      surfaces.forEach((bgName, bg) {
        test('text-safe: $name reads on $bgName', () {
          final r = ratio(colour, bg);
          expect(
            r,
            greaterThanOrEqualTo(aaNormal),
            reason:
                '$name on $bgName is ${r.toStringAsFixed(2)}:1. Either '
                'lift the colour or move it out of the text-safe list — a '
                'token that is in no list is how #FF9500 ended up carrying '
                'the retry notice at 2.20:1',
          );
        });
      });
    });

    fillWithWhiteLabel.forEach((name, fill) {
      test('fill: $name carries a white label', () {
        final r = ratio(Colors.white, fill);
        expect(
          r,
          greaterThanOrEqualTo(aaNormal),
          reason: 'white on $name is ${r.toStringAsFixed(2)}:1',
        );
      });
    });

    structural.forEach((name, colour) {
      test('structural: $name is visible on white', () {
        final r = ratio(colour, Colors.white);
        // A 1px hairline is not held to a text floor — iOS separators sit
        // around 1.1:1 and are the convention riders already read. What is
        // asserted is that the difference is real and cannot erode to nothing.
        // `borderStrong` is held higher, separately, because its job is to make
        // a container read as a container in sunlight.
        expect(
          r,
          greaterThan(1.15),
          reason:
              '$name is ${r.toStringAsFixed(3)}:1 on white — an edge '
              'nobody can see',
        );
      });
      test('structural: $name is never a text colour', () {
        // It cannot pass as text, which is exactly why it must not be used as
        // one. `disabledFill` was, on seven screens, at 1.68:1.
        final r = ratio(colour, Colors.white);
        expect(
          r,
          lessThan(aaNormal),
          reason:
              '$name reads well enough to be text — if that is what it '
              'is for, move it to the text-safe list',
        );
      });
    });

    test('the five retired tokens have not come back', () {
      // Compile-time guard. If someone re-adds `warningOrange`, `infoBlue`,
      // `successGreen`, `cardBlue` or `warningYellow`, they have to delete this
      // list first — and read why they were removed.
      const retired = <String, int>{
        'warningOrange': 0xFFFF9500,
        'successGreen': 0xFF34C759,
        'warningYellow': 0xFFFFB800,
        'cardBlue': 0xFF0EA5E9,
        'infoBlue': 0xFF007AFF,
      };
      for (final e in retired.entries) {
        final r = ratio(Color(e.value), Colors.white);
        expect(
          r,
          lessThan(aaNormal),
          reason:
              'sanity: ${e.key} really did fail at '
              '${r.toStringAsFixed(2)}:1',
        );
      }
    });
  });

  group('white text on a filled control clears AA', () {
    final fills = <String, Color>{
      'primary (brand)': ColorConstants.primary,
      'acceptGreen (Accept button)': ColorConstants.acceptGreen,
      'pickupChip': ColorConstants.pickupChip,
      'deliveryChip': ColorConstants.deliveryChip,
      'combinedChip': ColorConstants.combinedChip,
      'warning (skipped)': ColorConstants.warning,
      'errorRed': ColorConstants.errorRed,
    };

    fills.forEach((name, fill) {
      test('white on $name', () {
        final r = ratio(Colors.white, fill);
        // Button and chip labels are bold, so the large-text floor applies —
        // but everything here should be comfortably past it.
        expect(
          r,
          greaterThanOrEqualTo(aaLarge),
          reason: 'white on $name is ${r.toStringAsFixed(2)}:1',
        );
      });
    });

    // The chips carry 10sp text, which is small even when bold, so they are held
    // to the stricter floor. This is what "darkened" bought.
    test('the stop-type chips clear the NORMAL-text floor, not just large', () {
      for (final e in {
        'pickupChip': ColorConstants.pickupChip,
        'deliveryChip': ColorConstants.deliveryChip,
        'combinedChip': ColorConstants.combinedChip,
      }.entries) {
        final r = ratio(Colors.white, e.value);
        expect(
          r,
          greaterThanOrEqualTo(aaNormal),
          reason:
              '${e.key} is ${r.toStringAsFixed(2)}:1 — the chip label is '
              '10sp, so large-text allowances do not apply',
        );
      }
    });
  });

  group('surfaces stay distinguishable', () {
    // A borderless card has nothing but its fill to separate it from the page.
    // Riders reported being unable to tell cards apart at ~3%; this keeps the
    // separation from quietly eroding back to that.
    test('cardSurface is clearly darker than the page', () {
      final drop =
          1 -
          luminance(ColorConstants.cardSurface) /
              luminance(ColorConstants.surface);
      expect(
        drop,
        greaterThan(0.07),
        reason:
            'only ${(drop * 100).toStringAsFixed(1)}% darker than the '
            'page — a borderless card needs its fill to do the separating',
      );
    });

    test('borderStrong is visible against white and against the card', () {
      // Non-text contrast (UI components) has a 3:1 AA floor.
      for (final e in {
        'white': Colors.white,
        'cardSurface': ColorConstants.cardSurface,
      }.entries) {
        final r = ratio(ColorConstants.borderStrong, e.value);
        expect(
          r,
          greaterThan(1.2),
          reason:
              'borderStrong on ${e.key} is only '
              '${r.toStringAsFixed(2)}:1 — an edge nobody can see',
        );
      }
    });
  });

  group('the brand palette has no tonal leftovers', () {
    // The M3 tonal derivation of the red seed produced a brown body text and a
    // pink outline, which shipped on 70 call sites and inside `AppTheme` — so
    // the auth flow and every text field were brown-and-pink while the
    // dashboard was slate-and-white. These assert they stay neutral: for a
    // grey/slate, the three channels sit close together.
    void expectNeutral(String name, Color c) {
      final spread =
          [c.r, c.g, c.b].reduce(math.max) - [c.r, c.g, c.b].reduce(math.min);
      expect(
        spread,
        lessThan(0.12),
        reason:
            '$name has an RGB spread of ${spread.toStringAsFixed(3)} — '
            'that is a hue, not a neutral',
      );
    }

    test('onSurfaceVariant is a neutral, not a brown', () {
      expectNeutral('onSurfaceVariant', ColorConstants.onSurfaceVariant);
    });

    test('outlineVariant is a neutral, not a pink', () {
      expectNeutral('outlineVariant', ColorConstants.outlineVariant);
    });

    test('secondaryText is a neutral', () {
      expectNeutral('secondaryText', ColorConstants.secondaryText);
    });
  });
}