import "package:collection/collection.dart";
import "package:fast_immutable_collections/fast_immutable_collections.dart";
import "package:material_ui/material_ui.dart";
import "package:flutter_riverpod/flutter_riverpod.dart";
import "package:nexus/controllers/account_data.dart";
import "package:nexus/controllers/rooms.dart";
import "package:nexus/controllers/settings.dart";
import "package:nexus/controllers/top_level_spaces.dart";
import "package:nexus/controllers/space_edges.dart";
import "package:nexus/models/room.dart";
import "package:nexus/models/room_metadata.dart";
import "package:nexus/models/space.dart";
import "package:nexus/models/subspace.dart";

class SpacesController extends AsyncNotifier<IList<Space>> {
  @override
  Future<IList<Space>> build() async {
    final rooms = ref.watch(RoomsController.provider);
    final topLevelSpaceIds = ref.watch(TopLevelSpacesController.provider);
    final spaceEdges = ref.watch(SpaceEdgesController.provider);
    final accountData = ref.watch(AccountDataController.provider);

    final childrenById = spaceEdges.map(
      (spaceId, edges) =>
          MapEntry(spaceId, edges.map((edge) => edge.childId).toList()),
    );

    /// Everything under [spaceId], however deep, skipping any already
    /// [visited] so cycles end.
    ISet<String> collectDescendants(
      String spaceId, [
      ISet<String> visited = const .empty(),
    ]) => (childrenById[spaceId] ?? const []).fold(
      visited,
      (visited, childId) => visited.contains(childId)
          ? visited
          : collectDescendants(childId, visited.add(childId)),
    );

    Space buildSpace(String spaceId) {
      final space = rooms[spaceId];
      final directChildrenIds = childrenById[spaceId] ?? const [];

      return .new(
        id: spaceId,
        room: space,
        title: space?.metadata?.name ?? "Unnamed Space",
        children: .new(
          directChildrenIds
              .where((childId) => !childrenById.containsKey(childId))
              .map((childId) => rooms[childId])
              .nonNulls,
        ),
        subSpaces: .new(
          directChildrenIds
              .where(childrenById.containsKey)
              .map(
                (childId) => switch (rooms[childId]) {
                  final room? => Subspace(
                    room: room,
                    children: .new(
                      collectDescendants(childId)
                          .map((id) => rooms[id])
                          .nonNulls,
                    ),
                  ),
                  null => null,
                },
              )
              .nonNulls,
        ),
      );
    }

    final spaces = topLevelSpaceIds
        .where(rooms.containsKey)
        .map(buildSpace)
        .toIList();

    final usedRooms = spaces
        .expand(
          (space) => [
            ...space.children,
            ...space.subSpaces.expand((s) => s.children),
          ],
        )
        .toISet();
    final usedRoomIds = usedRooms.map((room) => room.metadata?.id).toSet();

    final directMessages = accountData.directMessages.values.flattened.toSet();

    final otherRooms = rooms.entries
        .where(
          (e) =>
              !usedRoomIds.contains(e.key) &&
              !topLevelSpaceIds.contains(e.key) &&
              !childrenById.containsKey(e.key),
        )
        .map((e) => e.value)
        .toIList();

    final homeRooms = otherRooms
        .addAll(
          await ref.watch(
                SettingsController.provider.selectAsync(
                  (data) => data.showAllInHome,
                ),
              )
              ? usedRooms
              : .empty(),
        )
        .where((r) => !directMessages.contains(r.metadata?.id))
        .toIList();

    final dmRooms = otherRooms
        .where((r) => directMessages.contains(r.metadata?.id))
        .toIList();

    final allSpaces = <Space>[
      .new(
        id: "home",
        title: "Home",
        icon: Icons.home,
        children: homeRooms,
        subSpaces: .new(),
      ),
      .new(
        id: "dms",
        title: "Direct Messages",
        icon: Icons.people,
        children: dmRooms,
        subSpaces: .new(),
      ),
      ...spaces,
    ];

    final roomOrder = await ref.watch(
      SettingsController.provider.selectAsync((data) => data.roomOrder),
    );

    // Mentioned -> Unread -> Other
    int unreadPriority(Room room) => switch (room.metadata) {
      RoomMetadata(unreadHighlights: > 0) => 0,
      RoomMetadata(unreadNotifications: > 0) ||
      RoomMetadata(unreadMessages: > 0) => 1,
      _ => 2,
    };

    return allSpaces
        .map(
          (space) => space.copyWith(
            children: space.children.sort((a, b) {
              if (roomOrder == .unreadFirst) {
                final byUnread = unreadPriority(a).compareTo(unreadPriority(b));
                if (byUnread != 0) return byUnread;
              }

              // Most recent activity first
              return (b.metadata?.sortingTimestamp ?? DateTime(0)).compareTo(
                a.metadata?.sortingTimestamp ?? DateTime(0),
              );
            }),
          ),
        )
        .toIList();
  }

  static final provider = AsyncNotifierProvider<SpacesController, IList<Space>>(
    SpacesController.new,
  );
}