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

import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

import 'package:fidl_fuchsia_ui_views/fidl_async.dart';
import 'package:fuchsia_scenic_flutter/child_view_connection.dart';
import 'package:tiler/tiler.dart' show TilerModel, TileModel;

import '../utils/presenter.dart';
import '../utils/suggestion.dart';
import 'ermine_shell.dart';
import 'ermine_story.dart';

// The minimum size of a tile we support.
const _kMinTileSize = Size(320, 240);

/// Defines a collection of [ClusterModel] instances. Calls [notifyListeners] when
/// a cluster is added or deleted.
class ClustersModel extends ChangeNotifier implements ErmineShell {
  /// The list of [ClusterModel] initialized to one cluster.
  final List<ClusterModel> clusters = [ClusterModel()];

  /// The cluster currently in view.
  final ValueNotifier<ClusterModel> currentCluster =
      ValueNotifier<ClusterModel>(null);

  final _storyToCluster = <String, ClusterModel>{};

  /// Change notifier when fullscreen is toggled for a story.
  ValueNotifier<ErmineStory> fullscreenStoryNotifier = ValueNotifier(null);

  /// Get the current story that is fullscreen.
  ErmineStory get fullscreenStory => fullscreenStoryNotifier.value;

  /// Change notifier when focus is toggled for a story.
  ValueNotifier<ErmineStory> focusedStoryNotifier = ValueNotifier(null);

  /// Get the story that has focus.
  ErmineStory get focusedStory => focusedStoryNotifier.value;

  /// Returns [true] if currentCluster is the first cluster.
  bool get isFirst =>
      currentCluster.value == null || currentCluster.value == clusters.first;

  /// Returns [true] if currentCluster is the last cluster.
  bool get isLast =>
      currentCluster.value == null || currentCluster.value == clusters.last;

  /// Returns [true] is there are stories running.
  bool get hasStories => _storyToCluster.isNotEmpty;

  /// Returns a iterable of all [Story] objects.
  Iterable<ErmineStory> get stories => _storyToCluster.keys.map(getStory);

  /// Maximize the story to fullscreen: it's visual state to IMMERSIVE.
  void maximize(String id) {
    if (fullscreenStoryNotifier.value?.id == id) {
      return;
    }
    fullscreenStoryNotifier.value?.fullscreen = false;

    fullscreenStoryNotifier.value = getStory(id)..fullscreen = true;
  }

  /// Restore the story to non-fullscreen mode: it's visual state to DEFAULT.
  void restore(String id) {
    if (fullscreenStoryNotifier.value?.id != id) {
      return;
    }
    fullscreenStoryNotifier.value?.fullscreen = false;
    fullscreenStoryNotifier.value = null;
  }

  /// Returns the story given it's id.
  ErmineStory getStory(String id) => _storyToCluster[id]?.getStory(id);

  @override
  void presentStory(
    ChildViewConnection connection,
    ViewRef viewRef,
    ViewControllerImpl viewController,
    String id,
  ) {
    // Check to see if a story already exists on screen.
    ErmineStory story = getStory(id);

    if (story == null) {
      // This view was created by some external source.
      // create a new story and present it.
      story = ErmineStory.fromExternalSource(
        onDelete: storyDeleted,
        onChange: storyChanged,
      );
      _addErmineStory(story);
    }

    story.presentView(connection, viewRef, viewController);
  }

  @override
  void dismissStory(ViewControllerImpl viewController) {
    // Find the story with the supplied viewController.
    final story =
        stories.where((story) => story.viewController == viewController).first;
    assert(story != null);
    story.delete();
  }

  /// Creates and adds a [Story] to the current cluster given it's [StoryInfo],
  /// [SessionShell] and [StoryController]. Returns the created instance.
  @override
  void storySuggested(Suggestion suggestion,
      [LaunchSuggestion launchSuggestion]) {
    assert(!_storyToCluster.containsKey(suggestion.id));
    final story = ErmineStory.fromSuggestion(
      suggestion: suggestion,
      onDelete: storyDeleted,
      onChange: storyChanged,
      launchSuggestion: launchSuggestion,
    );
    _addErmineStory(story);
  }

  void _addErmineStory(ErmineStory story) {
    // Add the story to the current cluster
    currentCluster.value ??= clusters.first;
    _storyToCluster[story.id] = currentCluster.value..add(story);

    // If current cluster is the last cluster, add one more to allow user
    // to navigate to it.
    if (currentCluster.value == clusters.last) {
      clusters.add(ClusterModel());
    }
    notifyListeners();

    story.focus();
  }

  /// Removes the [story] from the current cluster. If this is the last story
  /// in the cluster, the cluster is also removed unless it is the last cluster.
  @override
  void storyDeleted(ErmineStory story) {
    assert(_storyToCluster.containsKey(story.id));
    final cluster = _storyToCluster[story.id]..remove(story);
    int index = clusters.indexOf(cluster);

    // If this story was fullscreen, first restore it.
    if (story == fullscreenStory) {
      restore(story.id);
    }

    _storyToCluster.remove(story.id);

    // If there are no more stories in this cluster, remove it. We keep two
    // clusters alive at all times.
    if (!_storyToCluster.values.contains(cluster) && clusters.length > 1) {
      // Current cluster was removed, switch to another.
      if (cluster == currentCluster.value) {
        if (cluster == clusters.last) {
          currentCluster.value = clusters[index - 1];
        } else {
          currentCluster.value = clusters[index + 1];
        }
      }
      clusters.remove(cluster);

      notifyListeners();
    }

    // If the story was also focused, set focus on next story in same cluster.
    if (focusedStory == story) {
      if (currentCluster.value.stories.isNotEmpty) {
        currentCluster.value.stories.last.focus();
      } else {
        focusedStoryNotifier.value = null;
      }
    }
  }

  /// Called when any story attribute changes.
  @override
  void storyChanged(ErmineStory story) {
    if (story != null) {
      final storyCluster = _storyToCluster[story.id];
      if (story.focused) {
        // De-focus existing story.
        if (focusedStory != story) {
          focusedStoryNotifier.value?.focused = false;
        }
        focusedStoryNotifier.value = story;
        // If this story has focus, bring its cluster on screen.
        if (storyCluster != currentCluster.value) {
          currentCluster.value = storyCluster;
        }
        // Update fullscreen story.
        if (story.fullscreen) {
          maximize(story.id);
        } else {
          restore(story.id);
        }
      }
      notifyListeners();
    }
  }

  /// Set's the [currentCluster] to the next cluster, if available.
  void nextCluster() {
    if (fullscreenStory == null && currentCluster.value != clusters.last) {
      currentCluster.value =
          clusters[clusters.indexOf(currentCluster.value) + 1];
    }
  }

  /// Set's the [currentCluster] to the previous cluster, if available.
  void previousCluster() {
    if (fullscreenStory == null && currentCluster.value != clusters.first) {
      currentCluster.value =
          clusters[clusters.indexOf(currentCluster.value) - 1];
    }
  }

  ErmineStory hitTest(Offset position, [GestureBinding gestureBinding]) {
    final binding = gestureBinding ?? GestureBinding.instance;

    final hitTests = HitTestResult();
    binding.hitTest(hitTests, position);

    if (hitTests.path.isEmpty) {
      return null;
    }

    // Check if the topmost hit is a ChildView.
    final childViewRenderBox = hitTests.path.first.target;
    return currentCluster.value?.stories?.firstWhere(
      (story) {
        final key = GlobalObjectKey(story.childViewConnection);
        final renderObject = key.currentContext?.findRenderObject();
        return renderObject == childViewRenderBox;
      },
      orElse: () => null,
    );
  }

  /// Finds the story whose [ViewRef] is present in the focus chain.
  ///
  /// Shell view hierarchy places the shell view at the root and all child
  /// views are siblings of each other. Thus the focus chain should only have
  /// one child view in it. So if we did a set intersection of the focus chain
  /// and the set of open child views, a non-empty result will point to the
  /// child view that received focus.
  ErmineStory findStory(List<ViewRef> focusChain) {
    final focusedViews = Set<int>.from(
        focusChain.map((viewRef) => viewRef.reference.handle.koid));
    final childViews = Set<int>.from(
        stories.map((story) => story.viewRef.reference.handle.koid));
    final result = focusedViews.intersection(childViews);
    if (result.isNotEmpty) {
      // Result should find only one childview.
      assert(result.length == 1);
      return stories
          .where((story) => story.viewRef.reference.handle.koid == result.first)
          .first;
    }
    return null;
  }
}

/// Defines a collection of [Story] instances, internally held in TilerModel.
/// Calls [notifyListeners] when a story is added or removed from the cluster.
class ClusterModel extends ChangeNotifier {
  /// The title of the cluster.
  String title = '';

  /// The [TilerModel] that holds the [Tile] per [Story].
  final TilerModel<ErmineStory> tilerModel = TilerModel();

  ClusterModel({this.title});

  final List<ErmineStory> stories = <ErmineStory>[];

  final _storyToTile = <String, TileModel<ErmineStory>>{};

  bool get isEmpty => tilerModel.root.isEmpty;

  ErmineStory getStory(String id) => _storyToTile[id]?.content;

  /// Adds a [story] to this cluster.
  void add(ErmineStory story) {
    assert(!_storyToTile.containsKey(story.id));
    final tile = tilerModel.add(content: story, minSize: _kMinTileSize);
    _storyToTile[story.id] = tile;
    stories.add(story);

    notifyListeners();
  }

  /// Removes the [story] from this cluster.
  void remove(ErmineStory story) {
    assert(_storyToTile.containsKey(story.id));
    final tile = _storyToTile[story.id];
    tilerModel.remove(tile);
    _storyToTile.remove(story.id);
    stories.remove(story);

    notifyListeners();
  }
}