import 'dart:convert';

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

import 'models.dart';

/// One signed-in session: the two tokens, when the access token dies, and who
/// the customer is.
@immutable
class Session {
  const Session({
    required this.accessToken,
    required this.refreshToken,
    required this.expiresAt,
    this.customer,
  });

  final String accessToken;
  final String refreshToken;

  /// Absolute expiry, computed from the `expiresIn` the server sent.
  final DateTime expiresAt;

  final Customer? customer;

  /// Treated as expired a minute early, so a call started just before the
  /// boundary does not land just after it.
  bool get isExpired =>
      DateTime.now().isAfter(expiresAt.subtract(const Duration(minutes: 1)));

  Session copyWith({
    String? accessToken,
    String? refreshToken,
    DateTime? expiresAt,
    Customer? customer,
  }) => Session(
    accessToken: accessToken ?? this.accessToken,
    refreshToken: refreshToken ?? this.refreshToken,
    expiresAt: expiresAt ?? this.expiresAt,
    customer: customer ?? this.customer,
  );

  Map<String, dynamic> toJson() => {
    'accessToken': accessToken,
    'refreshToken': refreshToken,
    'expiresAt': expiresAt.millisecondsSinceEpoch,
    if (customer != null) 'customer': customer!.toJson(),
  };

  static Session? fromJson(Map<String, dynamic> json) {
    final access = json['accessToken'] as String?;
    final refresh = json['refreshToken'] as String?;
    final expires = json['expiresAt'];
    if (access == null || access.isEmpty) return null;
    if (refresh == null || refresh.isEmpty) return null;
    return Session(
      accessToken: access,
      refreshToken: refresh,
      expiresAt: expires is int
          ? DateTime.fromMillisecondsSinceEpoch(expires)
          : DateTime.now(),
      customer: json['customer'] is Map<String, dynamic>
          ? Customer.fromJson(json['customer'] as Map<String, dynamic>)
          : null,
    );
  }
}

/// Where the session lives between launches.
///
/// The refresh token is valid for 60 days and **rotates on every use** — a
/// replayed one revokes the whole chain server-side. So the two rules this
/// class exists to enforce are: persist the newest token the moment it arrives,
/// and never hand out a half-written session.
abstract class SessionStore {
  Future<Session?> read();
  Future<void> write(Session session);
  Future<void> clear();
}

/// Keychain on iOS, EncryptedSharedPreferences on Android.
class SecureSessionStore implements SessionStore {
  SecureSessionStore({FlutterSecureStorage? storage})
    // Keychain on iOS by default; Android needs asking, or it falls back to a
    // plaintext preferences file — which is the one place a 60-day refresh
    // token must never sit.
    : _storage =
          storage ??
          const FlutterSecureStorage(
            aOptions: AndroidOptions(encryptedSharedPreferences: true),
          );

  final FlutterSecureStorage _storage;

  static const String _key = 'dm_cx_session_v1';

  @override
  Future<Session?> read() async {
    try {
      final raw = await _storage.read(key: _key);
      if (raw == null || raw.isEmpty) return null;
      final decoded = jsonDecode(raw);
      if (decoded is! Map<String, dynamic>) return null;
      return Session.fromJson(decoded);
    } catch (e) {
      // A session we cannot read is a session we do not have. Signing the
      // customer out is recoverable; crashing at launch is not.
      debugPrint('[SESSION] unreadable, treating as signed out: $e');
      return null;
    }
  }

  @override
  Future<void> write(Session session) async {
    try {
      await _storage.write(key: _key, value: jsonEncode(session.toJson()));
    } catch (e) {
      // Losing persistence costs the customer a re-login next launch. It must
      // not cost them the sign-in they just completed.
      debugPrint('[SESSION] could not persist: $e');
    }
  }

  @override
  Future<void> clear() async {
    try {
      await _storage.delete(key: _key);
    } catch (e) {
      debugPrint('[SESSION] could not clear: $e');
    }
  }
}

/// In-memory store. Tests only — a session that does not survive the process
/// is not a session.
class MemorySessionStore implements SessionStore {
  Session? _session;

  @override
  Future<Session?> read() async => _session;

  @override
  Future<void> write(Session session) async => _session = session;

  @override
  Future<void> clear() async => _session = null;
}