fluffychat/lib/pangea/common/utils/async_state.dart

import 'dart:async';
import 'dart:io';

import 'package:flutter/material.dart';

import 'package:fluffychat/pangea/common/utils/error_handler.dart';

/// A generic sealed class that represents the state of an asynchronous operation.
sealed class AsyncState<T> {
  /// Base constructor for all asynchronous state variants.
  const AsyncState();

  /// Represents an idle state before any asynchronous work has begun.
  const factory AsyncState.idle() = AsyncIdle<T>;

  /// Represents an in-progress loading state.
  const factory AsyncState.loading() = AsyncLoading<T>;

  /// Represents a completed asynchronous operation with a successful [value].
  const factory AsyncState.loaded(T value) = AsyncLoaded<T>;

  /// Represents a failed asynchronous operation with an [error].
  const factory AsyncState.error(Object error) = AsyncError<T>;
}

/// The idle state of an [AsyncState], indicating no active or completed work.
///
/// Use this as the initial state before triggering an async operation.
class AsyncIdle<T> extends AsyncState<T> {
  /// Creates an idle [AsyncState].
  const AsyncIdle();
}

/// The loading state of an [AsyncState], indicating that work is in progress.
///
/// This state is typically used to show a loading spinner or progress indicator.
class AsyncLoading<T> extends AsyncState<T> {
  /// Creates a loading [AsyncState].
  const AsyncLoading();
}

/// The success state of an [AsyncState], containing a completed [value].
///
/// This state indicates that the asynchronous work finished successfully.
class AsyncLoaded<T> extends AsyncState<T> {
  /// The result of the successful asynchronous operation.
  final T value;

  /// Creates a loaded [AsyncState] with a [value].
  const AsyncLoaded(this.value);
}

/// The error state of an [AsyncState], containing an [error].
///
/// This state indicates that the asynchronous work failed.
class AsyncError<T> extends AsyncState<T> {
  /// The error produced during the asynchronous operation.
  final Object error;

  /// Creates an error [AsyncState] with an [error].
  const AsyncError(this.error);
}

abstract class AsyncLoader<T> {
  final ValueNotifier<AsyncState<T>> state = ValueNotifier(AsyncState.idle());
  bool _disposed = false;

  bool get isIdle => state.value is AsyncIdle<T>;
  bool get isLoading => state.value is AsyncLoading<T>;
  bool get isLoaded => state.value is AsyncLoaded<T>;
  bool get isError => state.value is AsyncError<T>;

  T? get value => isLoaded ? (state.value as AsyncLoaded<T>).value : null;

  Completer<T> completer = Completer<T>();

  void dispose() {
    _disposed = true;
    state.dispose();
  }

  Future<T> fetch();

  Future<void> load() async {
    if (state.value is AsyncLoaded) {
      // If already loading or loaded, do nothing.
      return;
    }

    state.value = AsyncState.loading();

    try {
      final result = await fetch();
      if (_disposed) return;
      state.value = AsyncState.loaded(result);
      completer.complete(result);
    } catch (e, s) {
      completer.completeError(e);
      if (!_disposed) {
        state.value = AsyncState.error(e);
      }

      if (e is! HttpException) {
        ErrorHandler.logError(e: e, s: s, data: {});
      }
    }
  }

  void reset() {
    if (_disposed) return;
    state.value = AsyncState.idle();
    completer = Completer<T>();
  }
}