import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../data/models/knowledge_item.dart';
import '../data/repositories/knowledge_repository.dart';
import 'api_client_provider.dart';

export '../data/models/knowledge_item.dart';

/// Immutable state for the Knowledge screen's two-tier paginated feed.
class KnowledgeState {
  final List<int> ids;
  final Map<int, KnowledgeItem> items;
  final int totalIds;
  final bool isLoadingIds;
  final bool isLoadingBatch;
  final bool hasMore;
  final String? noteType; // null = All
  final List<String> activeTags;
  final String? searchQuery;
  final Map<String, int> counts;
  final List<String> availableTags;
  final String? error;

  const KnowledgeState({
    this.ids = const [],
    this.items = const {},
    this.totalIds = 0,
    this.isLoadingIds = false,
    this.isLoadingBatch = false,
    this.hasMore = false,
    this.noteType,
    this.activeTags = const [],
    this.searchQuery,
    this.counts = const {},
    this.availableTags = const [],
    this.error,
  });

  /// Items in server-defined ID order, only those already hydrated.
  List<KnowledgeItem> get orderedItems =>
      ids.where(items.containsKey).map((id) => items[id]!).toList();

  /// IDs that have been fetched but not yet hydrated.
  List<int> get unhydratedIds =>
      ids.where((id) => !items.containsKey(id)).toList();

  KnowledgeState copyWith({
    List<int>? ids,
    Map<int, KnowledgeItem>? items,
    int? totalIds,
    bool? isLoadingIds,
    bool? isLoadingBatch,
    bool? hasMore,
    Object? noteType = _keep,
    List<String>? activeTags,
    Object? searchQuery = _keep,
    Map<String, int>? counts,
    List<String>? availableTags,
    Object? error = _keep,
  }) =>
      KnowledgeState(
        ids: ids ?? this.ids,
        items: items ?? this.items,
        totalIds: totalIds ?? this.totalIds,
        isLoadingIds: isLoadingIds ?? this.isLoadingIds,
        isLoadingBatch: isLoadingBatch ?? this.isLoadingBatch,
        hasMore: hasMore ?? this.hasMore,
        noteType:
            identical(noteType, _keep) ? this.noteType : noteType as String?,
        activeTags: activeTags ?? this.activeTags,
        searchQuery: identical(searchQuery, _keep)
            ? this.searchQuery
            : searchQuery as String?,
        counts: counts ?? this.counts,
        availableTags: availableTags ?? this.availableTags,
        error: identical(error, _keep) ? this.error : error as String?,
      );

  static const _keep = Object();
}

class KnowledgeNotifier extends Notifier<KnowledgeState> {
  @override
  KnowledgeState build() => const KnowledgeState();

  KnowledgeRepository get _repo => ref.read(knowledgeRepositoryProvider);

  // ── Filter setters — each resets and re-fetches ──────────────────────────

  Future<void> setTypeFilter(String? noteType) async {
    state = KnowledgeState(noteType: noteType, activeTags: state.activeTags);
    await _fetchFromScratch();
  }

  Future<void> toggleTag(String tag) async {
    final tags = state.activeTags.contains(tag)
        ? state.activeTags.where((t) => t != tag).toList()
        : [...state.activeTags, tag];
    state = KnowledgeState(
      noteType: state.noteType,
      activeTags: tags,
      searchQuery: state.searchQuery,
    );
    await _fetchFromScratch();
  }

  Future<void> setSearch(String? q) async {
    final query = (q?.trim().isEmpty ?? true) ? null : q?.trim();
    state = KnowledgeState(
      noteType: state.noteType,
      activeTags: state.activeTags,
      searchQuery: query,
    );
    await _fetchFromScratch();
  }

  Future<void> refresh() async {
    // Keep current items visible during re-fetch (no flicker).
    try {
      if (state.noteType == 'task') {
        final tasks = await ref.read(tasksApiProvider).getAll();
        final items = {
          for (final t in tasks) t.id: KnowledgeItem.fromTask(t),
        };
        state = state.copyWith(
          ids: tasks.map((t) => t.id).toList(),
          items: items,
          totalIds: tasks.length,
          hasMore: false,
        );
        await _loadCounts();
        return;
      }

      final (ids, total) = await _repo.fetchIds(
        noteType: state.noteType,
        tags: state.activeTags,
        q: state.searchQuery,
        limit: 50,
        offset: 0,
      );
      // Hydrate the new IDs
      final batch = await _repo.fetchBatch(ids);
      final freshItems = {for (final item in batch) item.id: item};
      state = state.copyWith(
        ids: ids,
        items: freshItems,
        totalIds: total,
        hasMore: ids.length < total,
      );
      await Future.wait([_loadCounts(), _loadTags()]);
    } catch (_) {
      // Silent — stale data is better than an error on refresh
    }
  }

  // ── Scroll-triggered loaders ─────────────────────────────────────────────

  /// Hydrate the next 12 un-hydrated IDs. Call when approaching scroll end.
  Future<void> hydrateNext() async {
    if (state.isLoadingBatch) return;
    final toFetch = state.unhydratedIds.take(12).toList();
    if (toFetch.isEmpty) {
      // All fetched IDs are hydrated — try loading more IDs.
      if (state.hasMore && !state.isLoadingIds) await _loadMoreIds();
      return;
    }
    state = state.copyWith(isLoadingBatch: true);
    try {
      final fetched = await _repo.fetchBatch(toFetch);
      final updated = Map<int, KnowledgeItem>.from(state.items);
      for (final item in fetched) {
        updated[item.id] = item;
      }
      state = state.copyWith(items: updated, isLoadingBatch: false);
    } catch (_) {
      state = state.copyWith(isLoadingBatch: false);
    }
  }

  // ── Private helpers ──────────────────────────────────────────────────────

  Future<void> _fetchFromScratch() async {
    state = state.copyWith(isLoadingIds: true, error: null);
    try {
      if (state.noteType == 'task') {
        // Tasks live under /api/tasks — fetch all and convert directly.
        final tasks = await ref.read(tasksApiProvider).getAll();
        final items = {
          for (final t in tasks) t.id: KnowledgeItem.fromTask(t),
        };
        state = state.copyWith(
          ids: tasks.map((t) => t.id).toList(),
          items: items,
          totalIds: tasks.length,
          isLoadingIds: false,
          hasMore: false,
        );
        await _loadCounts();
        return;
      }

      final (ids, total) = await _repo.fetchIds(
        noteType: state.noteType,
        tags: state.activeTags,
        q: state.searchQuery,
        limit: 50,
        offset: 0,
      );
      state = state.copyWith(
        ids: ids,
        items: {},
        totalIds: total,
        isLoadingIds: false,
        hasMore: ids.length < total,
      );
      // Load counts and tags in parallel with the first batch hydration.
      await Future.wait([
        hydrateNext(),
        _loadCounts(),
        _loadTags(),
      ]);
    } catch (e) {
      state = state.copyWith(
        isLoadingIds: false,
        error: e.toString(),
      );
    }
  }

  Future<void> _loadMoreIds() async {
    if (!state.hasMore || state.isLoadingIds) return;
    state = state.copyWith(isLoadingIds: true);
    try {
      final (newIds, total) = await _repo.fetchIds(
        noteType: state.noteType,
        tags: state.activeTags,
        q: state.searchQuery,
        limit: 50,
        offset: state.ids.length,
      );
      final combined = [...state.ids, ...newIds];
      state = state.copyWith(
        ids: combined,
        totalIds: total,
        isLoadingIds: false,
        hasMore: combined.length < total,
      );
      // Hydrate the newly fetched IDs immediately — the user is
      // already at the scroll bottom so _onScroll won't re-fire.
      await hydrateNext();
    } catch (_) {
      state = state.copyWith(isLoadingIds: false);
    }
  }

  Future<void> _loadCounts() async {
    try {
      final counts = await _repo.fetchCounts(tags: state.activeTags);
      state = state.copyWith(counts: counts);
    } catch (_) {}
  }

  Future<void> _loadTags() async {
    try {
      final tags = await _repo.fetchTags(noteType: state.noteType);
      state = state.copyWith(availableTags: tags);
    } catch (_) {}
  }
}

final knowledgeProvider =
    NotifierProvider<KnowledgeNotifier, KnowledgeState>(KnowledgeNotifier.new);