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

/// ─────────────────────────────────────────────────────────────────────────
/// THE LAYERS HAVE TO BE VISIBLE TO BE LAYERS
///
/// The app looked flat for a measurable reason, not an aesthetic one: white on
/// the page ground was a **1.124 : 1** step. A tonal difference does not begin
/// to read as a *different surface* until roughly 1.25, and on the budget LCD
/// this app ships to it needs the top of that band. So every screen that
/// wanted its content to separate grew a border or a shadow to do the ground's
/// job — which is how an app ends up looking like a stack of rounded
/// rectangles while its ground does nothing.
///
/// There were also five near-identical light tokens, three of them within
/// 1.03 of the canvas: indistinguishable, and therefore five names for two
/// decisions.
///
/// These pin the arithmetic. A contrast rule that lives only in a comment is a
/// rule that gets undone by the next person who nudges a hex.
/// ─────────────────────────────────────────────────────────────────────────
double _luminance(Color c) {
  double channel(double v) =>
      v <= 0.03928 ? v / 12.92 : math.pow((v + 0.055) / 1.055, 2.4).toDouble();
  return 0.2126 * channel(c.r) + 0.7152 * channel(c.g) + 0.0722 * channel(c.b);
}

double contrast(Color a, Color b) {
  final la = _luminance(a);
  final lb = _luminance(b);
  final hi = math.max(la, lb);
  final lo = math.min(la, lb);
  return (hi + 0.05) / (lo + 0.05);
}

void main() {
  group('the ladder has real rungs', () {
    test('a working surface separates from the canvas without a border', () {
      final step = contrast(MilerSurface.working, MilerSurface.canvas);
      expect(
        step,
        greaterThanOrEqualTo(1.25),
        reason:
            'white on the canvas is $step : 1 — below ~1.25 a surface does '
            'not read as a surface, and screens start drawing their own '
            'outlines to compensate',
      );
      // And not so far that the page turns into a dark frame around content.
      expect(step, lessThan(1.6));
    });

    test('the canvas is never white', () {
      expect(MilerSurface.canvas, isNot(MilerSurface.working));
      expect(MilerSurface.canvas, isNot(const Color(0xFFFFFFFF)));
    });

    test('raised and floating carry lift, working does not', () {
      // What separates an action surface from a reading surface is that it
      // appears to sit above the page — the fill is the same on purpose.
      expect(MilerSurface.raisedShadow, isNotEmpty);
      expect(MilerSurface.floatingShadow, isNotEmpty);
      expect(MilerSurface.raised, MilerSurface.working);
    });

    test('the scrim carries the modal separation', () {
      // A sheet that needs a heavy shadow to be legible is a sheet whose scrim
      // is too weak.
      expect(MilerSurface.scrim.a, greaterThan(0.3));
    });
  });

  group('text stays readable on every layer', () {
    // AA body is 4.5:1. Every operational colour is asserted on the canvas —
    // the darkest ground text sits on — so a screen cannot fail by moving
    // content from a card onto the page.
    final grounds = <String, Color>{
      'canvas': MilerSurface.canvas,
      'working': MilerSurface.working,
    };
    final inks = <String, Color>{
      'slateText': ColorConstants.slateText,
      'secondaryText': ColorConstants.secondaryText,
      'onSurfaceVariant': ColorConstants.onSurfaceVariant,
      'primary': ColorConstants.primary,
      'acceptGreen': ColorConstants.acceptGreen,
      'warning': ColorConstants.warning,
      'errorRed': ColorConstants.errorRed,
    };

    for (final g in grounds.entries) {
      for (final ink in inks.entries) {
        test('${ink.key} on ${g.key} clears AA', () {
          final r = contrast(ink.value, g.value);
          expect(
            r,
            greaterThanOrEqualTo(4.5),
            reason: '${ink.key} on ${g.key} is ${r.toStringAsFixed(2)} : 1',
          );
        });
      }
    }
  });

  group('the near-duplicate tokens are gone or justified', () {
    test('the inset tone is distinguishable from the surface it sits on', () {
      // The only nesting the system allows. If it cannot be seen against the
      // working surface it is furniture, not a layer.
      final step = contrast(MilerSurface.inset, MilerSurface.working);
      expect(step, greaterThan(1.05));
    });

    test('brand red is identity, error red is not the same colour', () {
      // Red must not mean two things. Navigation/primary and failure have to
      // be tellable apart at a glance, outdoors.
      expect(ColorConstants.primary, isNot(ColorConstants.errorRed));
      expect(
        contrast(ColorConstants.primary, ColorConstants.errorRed),
        greaterThan(1.15),
        reason: 'brand red and error red must not read as the same ink',
      );
    });
  });
}