// SPDX-FileCopyrightText: 2026 FocusFlow contributors
// SPDX-License-Identifier: AGPL-3.0-only

/// Coordinates Today Screen Controller state for the FocusFlow Flutter UI.
library;

import 'package:flutter/foundation.dart';
import 'package:scheduler_core/scheduler_core.dart';

import '../models/today_screen_models.dart';

/// Reads Today state from the scheduler application layer.
typedef TodayStateReader = Future<ApplicationResult<TodayState>> Function();

/// Base state for the compact Today screen.
sealed class TodayScreenState {
  /// Creates a Today screen state.
  const TodayScreenState();
}

/// Indicates that the Today screen is loading.
class TodayScreenLoading extends TodayScreenState {
  /// Creates a loading Today screen state.
  const TodayScreenLoading();
}

/// Indicates that the Today screen has renderable timeline data.
class TodayScreenReady extends TodayScreenState {
  /// Creates a ready state with mapped screen [data].
  const TodayScreenReady(this.data);

  /// Presentation model for the Today screen.
  final TodayScreenData data;
}

/// Indicates that the Today screen loaded successfully with no cards.
class TodayScreenEmpty extends TodayScreenState {
  /// Creates an empty Today screen state.
  const TodayScreenEmpty();
}

/// Indicates that the Today screen failed to load.
class TodayScreenFailure extends TodayScreenState {
  /// Creates a failure state with a displayable [message].
  const TodayScreenFailure(this.message);

  /// User-facing failure message or code.
  final String message;
}

/// Loads Today screen data and tracks selected timeline cards.
class TodayScreenController extends ChangeNotifier {
  /// Creates a Today screen controller from a read callback.
  TodayScreenController({required this.read});

  /// Callback used to read Today state.
  final TodayStateReader read;

  /// Private state stored as `_state` for this implementation.
  /// The field is intentionally scoped to this library so only the owning type can change the related scheduler or UI behavior.
  TodayScreenState _state = const TodayScreenLoading();

  /// Private state stored as `_selectedCard` for this implementation.
  /// The field is intentionally scoped to this library so only the owning type can change the related scheduler or UI behavior.
  TimelineCardModel? _selectedCard;

  /// Current Today screen loading/data/failure state.
  TodayScreenState get state => _state;

  /// Currently selected timeline card, if a modal should be visible.
  TimelineCardModel? get selectedCard => _selectedCard;

  /// Loads Today state and maps it into presentation data.
  Future<void> load() async {
    _state = const TodayScreenLoading();
    notifyListeners();
    try {
      final result = await read();
      final failure = result.failure;
      if (failure != null) {
        _state = TodayScreenFailure(failure.detailCode ?? failure.code.name);
        notifyListeners();
        return;
      }

      final data = TodayScreenData.fromTodayState(result.requireValue);
      _syncSelectedCard(data);
      _state = data.cards.isEmpty
          ? const TodayScreenEmpty()
          : TodayScreenReady(data);
      notifyListeners();
    } on Object catch (error) {
      _state = TodayScreenFailure(error.toString());
      notifyListeners();
    }
  }

  /// Selects [card] when the card allows selection.
  void selectCard(TimelineCardModel card) {
    if (!card.isSelectable) {
      return;
    }
    _selectedCard = card;
    notifyListeners();
  }

  /// Clears the selected timeline card.
  void clearSelection() {
    if (_selectedCard == null) {
      return;
    }
    _selectedCard = null;
    notifyListeners();
  }

  /// Runs the `_syncSelectedCard` helper used inside this library.
  /// The helper centralizes a small piece of transformation or validation so higher-level scheduler flow remains easier to read.
  void _syncSelectedCard(TodayScreenData data) {
    final selected = _selectedCard;
    if (selected == null) {
      return;
    }
    for (final card in data.cards) {
      if (card.id == selected.id) {
        _selectedCard = card;
        return;
      }
    }
    _selectedCard = null;
  }
}