import 'dart:convert';

import 'package:shared_preferences/shared_preferences.dart';

/// Defines the contract for persisting trip payloads locally.
abstract class TripLocalDataSource {
	/// Returns all saved trip JSON payloads, newest first.
	Future<List<Map<String, dynamic>>> loadTrips();

	/// Returns a single trip payload by uuid if present.
  /// TODO - should directly return Trip?
	Future<Map<String, dynamic>?> getTrip(String uuid);

	/// Upserts the provided trip payload (also used for editing existing trips).
	Future<void> upsertTrip(Map<String, dynamic> tripJson);

	/// Removes the trip with the matching uuid.
	Future<void> deleteTrip(String uuid);
}

class TripLocalDataSourceImpl implements TripLocalDataSource {
	TripLocalDataSourceImpl({Future<SharedPreferences>? preferences})
			: _prefsFuture = preferences ?? SharedPreferences.getInstance();

	static const String _storageKey = 'savedTrips';
	final Future<SharedPreferences> _prefsFuture;

	@override
	Future<List<Map<String, dynamic>>> loadTrips() async {
		final prefs = await _prefsFuture;
		final stored = prefs.getStringList(_storageKey);
		if (stored == null) return [];
		return stored.map(_decodeTrip).toList();
	}

	@override
	Future<Map<String, dynamic>?> getTrip(String uuid) async {
		final trips = await loadTrips();
		for (final trip in trips) {
			if (trip['uuid'] == uuid) {
				return Map<String, dynamic>.from(trip);
			}
		}
		return null;
	}

	@override
	Future<void> upsertTrip(Map<String, dynamic> tripJson) async {
		final uuid = tripJson['uuid'];
		if (uuid is! String || uuid.isEmpty) {
			throw ArgumentError('Trip JSON must contain a uuid string');
		}

		final trips = await loadTrips();
		trips.removeWhere((trip) => trip['uuid'] == uuid);
		trips.insert(0, Map<String, dynamic>.from(tripJson));
		await _persistTrips(trips);
	}

	@override
	Future<void> deleteTrip(String uuid) async {
		final trips = await loadTrips();
		final updated = trips.where((trip) => trip['uuid'] != uuid).toList();
		if (updated.length == trips.length) {
			return;
		}
		await _persistTrips(updated);
	}

	Future<void> _persistTrips(List<Map<String, dynamic>> trips) async {
		final prefs = await _prefsFuture;
		final payload = trips.map(jsonEncode).toList();
		await prefs.setStringList(_storageKey, payload);
	}

	Map<String, dynamic> _decodeTrip(String raw) {
		final decoded = jsonDecode(raw);
		if (decoded is! Map<String, dynamic>) {
			throw const FormatException('Saved trip entry is not a JSON object');
		}
		return Map<String, dynamic>.from(decoded);
	}
}