import 'dart:convert';

/// Represents a transport segment (vol/train/bus) tied to a trip.
///
/// Includes identifiers (PNR/train number), schedule times, status, carrier
/// and station/airport codes for display and potential real-time tracking.
class TransportSegment {
  /// Unique identifier for this segment entry.
  final String id;

  /// Segment type: `flight`, `train`, `bus` (extendable).
  final String type;

  /// Carrier code (e.g., AF, SN, TGV, OUIGO).
  final String carrier;

  /// Public number (e.g., AF763, TGV 8401).
  final String number;

  /// Booking reference / PNR if available.
  final String? pnr;

  /// Departure code (IATA/CRS) or station name.
  final String departureCode;

  /// Arrival code (IATA/CRS) or station name.
  final String arrivalCode;

  /// Planned departure time (UTC).
  final DateTime departureUtc;

  /// Planned arrival time (UTC).
  final DateTime arrivalUtc;

  /// Current status string (scheduled/delayed/cancelled/boarding/in_air etc.).
  final String status;

  /// Gate/platform when known.
  final String? gate;

  /// Seat assignment if provided.
  final String? seat;

  /// Created-at timestamp for ordering.
  final DateTime createdAt;

  /// Creates a transport segment entry.
  const TransportSegment({
    required this.id,
    required this.type,
    required this.carrier,
    required this.number,
    required this.departureCode,
    required this.arrivalCode,
    required this.departureUtc,
    required this.arrivalUtc,
    required this.status,
    required this.createdAt,
    this.pnr,
    this.gate,
    this.seat,
  });

  /// Helper to instantiate a new scheduled segment with defaults.
  factory TransportSegment.newSegment({
    required String id,
    required String type,
    required String carrier,
    required String number,
    required String departureCode,
    required String arrivalCode,
    required DateTime departureUtc,
    required DateTime arrivalUtc,
    String? pnr,
    String? gate,
    String? seat,
  }) {
    return TransportSegment(
      id: id,
      type: type,
      carrier: carrier,
      number: number,
      pnr: pnr,
      departureCode: departureCode,
      arrivalCode: arrivalCode,
      departureUtc: departureUtc,
      arrivalUtc: arrivalUtc,
      gate: gate,
      seat: seat,
      status: 'scheduled',
      createdAt: DateTime.now().toUtc(),
    );
  }

  /// Returns a copy with updated fields.
  TransportSegment copyWith({
    String? id,
    String? type,
    String? carrier,
    String? number,
    String? pnr,
    String? departureCode,
    String? arrivalCode,
    DateTime? departureUtc,
    DateTime? arrivalUtc,
    String? status,
    String? gate,
    String? seat,
    DateTime? createdAt,
  }) {
    return TransportSegment(
      id: id ?? this.id,
      type: type ?? this.type,
      carrier: carrier ?? this.carrier,
      number: number ?? this.number,
      pnr: pnr ?? this.pnr,
      departureCode: departureCode ?? this.departureCode,
      arrivalCode: arrivalCode ?? this.arrivalCode,
      departureUtc: departureUtc ?? this.departureUtc,
      arrivalUtc: arrivalUtc ?? this.arrivalUtc,
      status: status ?? this.status,
      gate: gate ?? this.gate,
      seat: seat ?? this.seat,
      createdAt: createdAt ?? this.createdAt,
    );
  }

  /// Serializes the segment to JSON for persistence.
  Map<String, dynamic> toJson() {
    return {
      'id': id,
      'type': type,
      'carrier': carrier,
      'number': number,
      'pnr': pnr,
      'departureCode': departureCode,
      'arrivalCode': arrivalCode,
      'departureUtc': departureUtc.toIso8601String(),
      'arrivalUtc': arrivalUtc.toIso8601String(),
      'status': status,
      'gate': gate,
      'seat': seat,
      'createdAt': createdAt.toIso8601String(),
    };
  }

  /// Deserializes a segment from JSON.
  factory TransportSegment.fromJson(Map<String, dynamic> json) {
    return TransportSegment(
      id: json['id'] as String,
      type: json['type'] as String,
      carrier: json['carrier'] as String,
      number: json['number'] as String,
      pnr: json['pnr'] as String?,
      departureCode: json['departureCode'] as String,
      arrivalCode: json['arrivalCode'] as String,
      departureUtc: DateTime.parse(json['departureUtc'] as String),
      arrivalUtc: DateTime.parse(json['arrivalUtc'] as String),
      status: json['status'] as String,
      gate: json['gate'] as String?,
      seat: json['seat'] as String?,
      createdAt: DateTime.parse(json['createdAt'] as String),
    );
  }

  /// Encodes a list of segments to JSON string.
  static String encodeList(List<TransportSegment> segments) {
    return json.encode(segments.map((s) => s.toJson()).toList());
  }

  /// Decodes a list of segments from JSON string.
  static List<TransportSegment> decodeList(String raw) {
    final decoded = json.decode(raw) as List<dynamic>;
    return decoded
        .cast<Map<String, dynamic>>()
        .map(TransportSegment.fromJson)
        .toList();
  }
}