// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/// Provides utilities for testing engine code.
library matchers;

import 'dart:html' as html;
import 'dart:math' as math;

import 'package:html/parser.dart' as html_package;
import 'package:html/dom.dart' as html_package;

import 'package:meta/meta.dart';
import 'package:test/test.dart';

import 'package:flutter_web_ui/ui.dart';
import 'package:flutter_web_ui/src/engine.dart';

/// Enumerates all persisted surfaces in the tree rooted at [root].
///
/// If [root] is `null` returns all surfaces from the last rendered scene.
///
/// Surfaces are returned in a depth-first order.
Iterable<PersistedSurface> enumerateSurfaces([PersistedSurface root]) {
  root ??= SceneBuilder.debugLastFrameScene;
  final List<PersistedSurface> surfaces = <PersistedSurface>[root];

  root.visitChildren((PersistedSurface surface) {
    surfaces.addAll(enumerateSurfaces(surface));
  });

  return surfaces;
}

/// Enumerates all pictures nested under [root].
///
/// If [root] is `null` returns all pictures from the last rendered scene.
Iterable<PersistedPicture> enumeratePictures([PersistedSurface root]) {
  root ??= SceneBuilder.debugLastFrameScene;
  return enumerateSurfaces(root).whereType<PersistedPicture>();
}

/// Enumerates all offset surfaces nested under [root].
///
/// If [root] is `null` returns all pictures from the last rendered scene.
Iterable<PersistedOffset> enumerateOffsets([PersistedSurface root]) {
  root ??= SceneBuilder.debugLastFrameScene;
  return enumerateSurfaces(root).whereType<PersistedOffset>();
}

/// Computes the distance between two values.
///
/// The distance should be a metric in a metric space (see
/// https://en.wikipedia.org/wiki/Metric_space). Specifically, if `f` is a
/// distance function then the following conditions should hold:
///
/// - f(a, b) >= 0
/// - f(a, b) == 0 if and only if a == b
/// - f(a, b) == f(b, a)
/// - f(a, c) <= f(a, b) + f(b, c), known as triangle inequality
///
/// This makes it useful for comparing numbers, [Color]s, [Offset]s and other
/// sets of value for which a metric space is defined.
typedef DistanceFunction<T> = num Function(T a, T b);

/// The type of a union of instances of [DistanceFunction<T>] for various types
/// T.
///
/// This type is used to describe a collection of [DistanceFunction<T>]
/// functions which have (potentially) unrelated argument types. Since the
/// argument types of the functions may be unrelated, the only thing that the
/// type system can statically assume about them is that they accept null (since
/// all types in Dart are nullable).
///
/// Calling an instance of this type must either be done dynamically, or by
/// first casting it to a [DistanceFunction<T>] for some concrete T.
typedef AnyDistanceFunction = num Function(Null a, Null b);

const Map<Type, AnyDistanceFunction> _kStandardDistanceFunctions =
    <Type, AnyDistanceFunction>{
  Color: _maxComponentColorDistance,
  Offset: _offsetDistance,
  int: _intDistance,
  double: _doubleDistance,
  Rect: _rectDistance,
  Size: _sizeDistance,
};

int _intDistance(int a, int b) => (b - a).abs();
double _doubleDistance(double a, double b) => (b - a).abs();
double _offsetDistance(Offset a, Offset b) => (b - a).distance;

double _maxComponentColorDistance(Color a, Color b) {
  int delta = math.max<int>((a.red - b.red).abs(), (a.green - b.green).abs());
  delta = math.max<int>(delta, (a.blue - b.blue).abs());
  delta = math.max<int>(delta, (a.alpha - b.alpha).abs());
  return delta.toDouble();
}

double _rectDistance(Rect a, Rect b) {
  double delta =
      math.max<double>((a.left - b.left).abs(), (a.top - b.top).abs());
  delta = math.max<double>(delta, (a.right - b.right).abs());
  delta = math.max<double>(delta, (a.bottom - b.bottom).abs());
  return delta;
}

double _sizeDistance(Size a, Size b) {
  final Offset delta = b - a;
  return delta.distance;
}

/// Asserts that two values are within a certain distance from each other.
///
/// The distance is computed by a [DistanceFunction].
///
/// If `distanceFunction` is null, a standard distance function is used for the
/// `runtimeType` of the `from` argument. Standard functions are defined for
/// the following types:
///
///  * [Color], whose distance is the maximum component-wise delta.
///  * [Offset], whose distance is the Euclidean distance computed using the
///    method [Offset.distance].
///  * [Rect], whose distance is the maximum component-wise delta.
///  * [Size], whose distance is the [Offset.distance] of the offset computed as
///    the difference between two sizes.
///  * [int], whose distance is the absolute difference between two integers.
///  * [double], whose distance is the absolute difference between two doubles.
///
/// See also:
///
///  * [moreOrLessEquals], which is similar to this function, but specializes in
///    [double]s and has an optional `epsilon` parameter.
///  * [closeTo], which specializes in numbers only.
Matcher within<T>({
  @required num distance,
  @required T from,
  DistanceFunction<T> distanceFunction,
}) {
  distanceFunction ??= _kStandardDistanceFunctions[from.runtimeType];

  if (distanceFunction == null) {
    throw ArgumentError(
        'The specified distanceFunction was null, and a standard distance '
        'function was not found for type ${from.runtimeType} of the provided '
        '`from` argument.');
  }

  return _IsWithinDistance<T>(distanceFunction, from, distance);
}

class _IsWithinDistance<T> extends Matcher {
  const _IsWithinDistance(this.distanceFunction, this.value, this.epsilon);

  final DistanceFunction<T> distanceFunction;
  final T value;
  final num epsilon;

  @override
  bool matches(Object object, Map<dynamic, dynamic> matchState) {
    if (object is! T) {
      return false;
    }
    if (object == value) {
      return true;
    }
    final T test = object;
    final num distance = distanceFunction(test, value);
    if (distance < 0) {
      throw ArgumentError(
          'Invalid distance function was used to compare a ${value.runtimeType} '
          'to a ${object.runtimeType}. The function must return a non-negative '
          'double value, but it returned $distance.');
    }
    matchState['distance'] = distance;
    return distance <= epsilon;
  }

  @override
  Description describe(Description description) =>
      description.add('$value (±$epsilon)');

  @override
  Description describeMismatch(
    Object object,
    Description mismatchDescription,
    Map<dynamic, dynamic> matchState,
    bool verbose,
  ) {
    mismatchDescription
        .add('was ${matchState['distance']} away from the desired value.');
    return mismatchDescription;
  }
}

/// Controls how test HTML is canonicalized by [canonicalizeHtml] function.
///
/// In all cases whitespace between elements is stripped.
enum HtmlComparisonMode {
  /// Retains all attributes.
  ///
  /// Useful when very precise HTML comparison is needed that includes both
  /// layout and non-layout style attributes. This mode is rarely needed. Most
  /// tests should use [layoutOnly] or [nonLayoutOnly].
  everything,

  /// Retains only layout style attributes, such as "width".
  ///
  /// Useful when testing layout because it filters out all the noise that does
  /// not affect layout.
  layoutOnly,

  /// Retains only non-layout style attributes, such as "color".
  ///
  /// Useful when testing styling because it filters out all the noise from the
  /// layout attributes.
  nonLayoutOnly,

  /// Do not consider attributes when comparing HTML.
  noAttributes,
}

/// Rewrites [htmlContent] by removing irrelevant style attributes.
///
/// If [throwOnUnusedAttributes] is `true`, throws instead of rewriting. Set
/// [throwOnUnusedAttributes] to `true` to check that expected HTML strings do
/// not contain irrelevant attributes. It is ok for actual HTML to contain all
/// kinds of attributes. They only need to be filtered out before testing.
String canonicalizeHtml(String htmlContent,
    {HtmlComparisonMode mode = HtmlComparisonMode.nonLayoutOnly,
    bool throwOnUnusedAttributes = false}) {
  if (htmlContent == null || htmlContent.trim().isEmpty) {
    return '';
  }

  String _unusedAttribute(String name) {
    if (throwOnUnusedAttributes) {
      fail('Provided HTML contains style attribute "$name" which '
          'is not used for comparison in the test. The HTML was:\n\n$htmlContent');
    }

    return null;
  }

  html_package.Element _cleanup(html_package.Element original) {
    String replacementTag = original.localName;
    switch (replacementTag) {
      case 'flt-scene':
        replacementTag = 's';
        break;
      case 'flt-transform':
        replacementTag = 't';
        break;
      case 'flt-opacity':
        replacementTag = 'o';
        break;
      case 'flt-clip':
        final String clipType = original.attributes['clip-type'];
        switch (clipType) {
          case 'rect':
            replacementTag = 'clip';
            break;
          case 'rrect':
            replacementTag = 'rclip';
            break;
          case 'physical-shape':
            replacementTag = 'pshape';
            break;
          default:
            throw Exception('Unknown clip type: $clipType');
        }
        break;
      case 'flt-clip-interior':
        replacementTag = 'clip-i';
        break;
      case 'flt-picture':
        replacementTag = 'pic';
        break;
      case 'flt-canvas':
        replacementTag = 'c';
        break;
      case 'flt-dom-canvas':
        replacementTag = 'd';
        break;
      case 'flt-semantics':
        replacementTag = 'sem';
        break;
      case 'flt-semantics-container':
        replacementTag = 'sem-c';
        break;
      case 'flt-semantics-value':
        replacementTag = 'sem-v';
        break;
      case 'flt-semantics-img':
        replacementTag = 'sem-img';
        break;
      case 'flt-semantics-text-field':
        replacementTag = 'sem-tf';
        break;
    }

    final html_package.Element replacement =
        html_package.Element.tag(replacementTag);

    if (mode != HtmlComparisonMode.noAttributes) {
      original.attributes.forEach((dynamic name, String value) {
        if (name == 'style') {
          return;
        }
        if (name.startsWith('aria-')) {
          replacement.attributes[name] = value;
        }
      });

      if (original.attributes.containsKey('style')) {
        final String styleValue = original.attributes['style'];

        int attrCount = 0;
        final String processedAttributes = styleValue
            .split(';')
            .map((String attr) {
              attr = attr.trim();
              if (attr.isEmpty) {
                return null;
              }

              if (mode != HtmlComparisonMode.everything) {
                final bool forLayout = mode == HtmlComparisonMode.layoutOnly;
                final List<String> parts = attr.split(':');
                if (parts.length == 2) {
                  final String name = parts.first;
                  // Whether the attribute is one that's set to the same value and
                  // never changes. Such attributes are usually not interesting to
                  // test.
                  final bool isStaticAttribute = const <String>[
                    'top',
                    'left',
                    'position',
                  ].contains(name);

                  if (isStaticAttribute) {
                    return _unusedAttribute(name);
                  }

                  // Whether the attribute is set by the layout system.
                  final bool isLayoutAttribute = const <String>[
                    'top',
                    'left',
                    'bottom',
                    'right',
                    'position',
                    'width',
                    'height',
                    'font-size',
                    'transform',
                    'transform-origin',
                    'white-space',
                  ].contains(name);

                  if (forLayout && !isLayoutAttribute ||
                      !forLayout && isLayoutAttribute) {
                    return _unusedAttribute(name);
                  }
                }
              }

              attrCount++;
              return attr.trim();
            })
            .where((String attr) => attr != null && attr.isNotEmpty)
            .join('; ');

        if (attrCount > 0) {
          replacement.attributes['style'] = processedAttributes;
        }
      }
    } else if (throwOnUnusedAttributes && original.attributes.isNotEmpty) {
      fail('Provided HTML contains attributes. However, the comparison mode '
          'is $mode. The HTML was:\n\n$htmlContent');
    }

    for (html_package.Node child in original.nodes) {
      if (child is html_package.Text && child.text.trim().isEmpty) {
        continue;
      }

      if (child is html_package.Element) {
        replacement.append(_cleanup(child));
      } else {
        replacement.append(child.clone(true));
      }
    }

    return replacement;
  }

  final html_package.DocumentFragment originalDom =
      html_package.parseFragment(htmlContent);

  final html_package.DocumentFragment cleanDom =
      html_package.DocumentFragment();
  for (html_package.Element child in originalDom.children) {
    cleanDom.append(_cleanup(child));
  }

  return cleanDom.outerHtml;
}

/// Tests that [element] has the HTML structure described by [expectedHtml].
void expectHtml(html.Element element, String expectedHtml,
    {HtmlComparisonMode mode = HtmlComparisonMode.nonLayoutOnly}) {
  expectedHtml =
      canonicalizeHtml(expectedHtml, mode: mode, throwOnUnusedAttributes: true);
  final String actualHtml = canonicalizeHtml(element.outerHtml, mode: mode);
  expect(actualHtml, expectedHtml);
}

/// Tests that [currentHtml] matches [expectedHtml].
///
/// The comparison does not consider every minutia of the DOM. By default it
/// tests the element tree structure and non-layout style attributes, and
/// ignores everything else. If you are testing layout specifically, pass the
/// [HtmlComparisonMode.layoutOnly] as the [mode] argument.
///
/// To keep test HTML strings manageable, you may use short HTML tag names
/// instead of the full names:
///
/// * <flt-scene> is interchangeable with <s>
/// * <flt-transform> is interchangeable with <t>
/// * <flt-opacity> is interchangeable with <o>
/// * <flt-clip clip-type="rect"> is interchangeable with <clip>
/// * <flt-clip clip-type="rrect"> is interchangeable with <rclip>
/// * <flt-clip clip-type="physical-shape"> is interchangeable with <pshape>
/// * <flt-picture> is interchangeable with <pic>
/// * <flt-canvas> is interchangeable with <c>
///
/// To simplify test HTML strings further the elements corresponding to the
/// root view [RenderView], such as <flt-scene> (i.e. <s>), are also stripped
/// out before comparison.
///
/// Example:
///
/// If you call [WidgetTester.pumpWidget] that results in HTML
/// `<s><t><pic><c><p>Hello</p></c></pic></t></s>`, you don't have to specify
/// `<s><t>` tags and simply expect `<pic><c><p>Hello</p></c></pic>`.
void expectPageHtml(String expectedHtml,
    {HtmlComparisonMode mode = HtmlComparisonMode.nonLayoutOnly}) {
  expectedHtml = canonicalizeHtml(expectedHtml, mode: mode);
  final String actualHtml = canonicalizeHtml(currentHtml, mode: mode);
  expect(actualHtml, expectedHtml);
}

/// Currently rendered HTML DOM as an HTML string.
String get currentHtml {
  return domRenderer.sceneElement?.outerHtml ?? '';
}

class SceneTester {
  SceneTester(this.scene);

  final Scene scene;

  void expectSceneHtml(String expectedHtml) {
    expectHtml(scene.webOnlyRootElement, expectedHtml,
        mode: HtmlComparisonMode.noAttributes);
  }
}