import 'dart:async';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/foundation.dart';
import 'handle_validator.dart';
import 'rider_profile_models.dart';

/// Service managing public rider profile persistence, unique handle reservations,
/// and privacy preferences in Cloud Firestore.
class RiderProfileService {
  final FirebaseFirestore? _firestore;

  RiderProfileService({FirebaseFirestore? firestore})
      : _firestore = firestore ?? _resolveFirestore();

  static FirebaseFirestore? _resolveFirestore() {
    try {
      if (Firebase.apps.isNotEmpty) return FirebaseFirestore.instance;
    } catch (_) {}
    return null;
  }

  bool get isAvailable => _firestore != null;

  /// Fetches a rider's profile by UID.
  Future<RiderProfile?> getProfile(String uid) async {
    final firestore = _firestore;
    if (firestore == null) return null;

    try {
      final doc = await firestore.collection('users').doc(uid).get();
      if (!doc.exists || doc.data() == null) return null;
      return RiderProfile.fromJson(doc.data()!);
    } catch (e) {
      debugPrint('[RiderProfileService] Failed to load profile for $uid: $e');
      return null;
    }
  }

  /// Realtime stream of a rider's profile by UID.
  Stream<RiderProfile?> profileStream(String uid) {
    final firestore = _firestore;
    if (firestore == null) return Stream.value(null);

    return firestore
        .collection('users')
        .doc(uid)
        .snapshots()
        .map((snapshot) {
          if (!snapshot.exists || snapshot.data() == null) return null;
          try {
            return RiderProfile.fromJson(snapshot.data()!);
          } catch (e) {
            debugPrint('[RiderProfileService] Stream parse error for $uid: $e');
            return null;
          }
        })
        .handleError((e) {
          debugPrint('[RiderProfileService] Stream error for $uid: $e');
          return null;
        });
  }

  /// Checks if a normalized handle is available for reservation.
  /// If [currentUid] is provided, returning true if the handle is already owned by [currentUid].
  Future<bool> isHandleAvailable(String handle, {String? currentUid}) async {
    final validation = HandleValidator.validate(handle);
    if (!validation.isValid) return false;

    final firestore = _firestore;
    if (firestore == null) return true;

    final normalized = validation.normalizedHandle!;
    try {
      final doc = await firestore.collection('handles').doc(normalized).get();
      if (!doc.exists) return true;

      final data = doc.data();
      final ownerUid = data?['uid'] as String?;
      return currentUid != null && ownerUid == currentUid;
    } catch (e) {
      debugPrint('[RiderProfileService] Error checking handle $normalized: $e');
      return false;
    }
  }

  /// Saves or updates a rider's profile while atomically securing the handle reservation.
  Future<RiderProfile> saveProfile({
    required String uid,
    required String handle,
    required String displayName,
    String bio = '',
    String region = '',
    String? avatarPreset,
    String? avatarUrl,
    ProfilePrivacySettings? privacySettings,
  }) async {
    final validation = HandleValidator.validate(handle);
    if (!validation.isValid) {
      throw ArgumentError(validation.error);
    }
    final normalizedHandle = validation.normalizedHandle!;

    final firestore = _firestore;
    final now = DateTime.now();

    if (firestore == null) {
      // Offline/local fallback
      return RiderProfile(
        uid: uid,
        handle: normalizedHandle,
        displayName: displayName.trim(),
        bio: bio.trim(),
        region: region.trim(),
        avatarPreset: avatarPreset,
        avatarUrl: avatarUrl,
        privacySettings: privacySettings ?? const ProfilePrivacySettings(),
        createdAt: now,
        updatedAt: now,
      );
    }

    final userRef = firestore.collection('users').doc(uid);
    final handleRef = firestore.collection('handles').doc(normalizedHandle);

    // Read current user profile to determine previous handle if changing
    final currentDoc = await userRef.get();
    final existingProfile =
        currentDoc.exists && currentDoc.data() != null
            ? RiderProfile.fromJson(currentDoc.data()!)
            : null;

    final previousHandle = existingProfile?.handle;
    final isChangingHandle =
        previousHandle != null && previousHandle != normalizedHandle;

    await firestore.runTransaction((transaction) async {
      // 1. Verify handle availability
      final handleSnapshot = await transaction.get(handleRef);
      if (handleSnapshot.exists) {
        final ownerUid = handleSnapshot.data()?['uid'] as String?;
        if (ownerUid != uid) {
          throw StateError('Handle @$normalizedHandle is already taken.');
        }
      }

      // 2. Reserve new handle
      transaction.set(handleRef, {
        'handle': normalizedHandle,
        'uid': uid,
        'createdAt': FieldValue.serverTimestamp(),
      });

      // 3. Release previous handle if changed
      if (isChangingHandle) {
        final oldHandleRef = firestore.collection('handles').doc(previousHandle);
        transaction.delete(oldHandleRef);
      }

      // 4. Save profile document
      final updatedProfile = RiderProfile(
        uid: uid,
        handle: normalizedHandle,
        displayName: displayName.trim().isEmpty ? normalizedHandle : displayName.trim(),
        bio: bio.trim(),
        region: region.trim(),
        avatarPreset: avatarPreset,
        avatarUrl: avatarUrl,
        privacySettings: privacySettings ?? existingProfile?.privacySettings ?? const ProfilePrivacySettings(),
        createdAt: existingProfile?.createdAt ?? now,
        updatedAt: now,
      );

      transaction.set(userRef, updatedProfile.toJson(), SetOptions(merge: true));
    });

    final saved = await getProfile(uid);
    return saved ??
        RiderProfile(
          uid: uid,
          handle: normalizedHandle,
          displayName: displayName.trim(),
          bio: bio.trim(),
          region: region.trim(),
          avatarPreset: avatarPreset,
          avatarUrl: avatarUrl,
          privacySettings: privacySettings ?? const ProfilePrivacySettings(),
          createdAt: existingProfile?.createdAt ?? now,
          updatedAt: now,
        );
  }

  /// Releases the rider's handle and cleans up the profile doc.
  Future<void> deleteProfile(String uid) async {
    final firestore = _firestore;
    if (firestore == null) return;

    try {
      final userRef = firestore.collection('users').doc(uid);
      final doc = await userRef.get();
      if (doc.exists && doc.data() != null) {
        final handle = doc.data()?['username'] as String?;
        if (handle != null && handle.isNotEmpty) {
          await firestore.collection('handles').doc(handle.toLowerCase()).delete();
        }
      }
      await userRef.delete();
    } catch (e) {
      debugPrint('[RiderProfileService] Failed to delete profile for $uid: $e');
      rethrow;
    }
  }
}