tasq/lib/providers/tasks_provider.dart

import 'dart:async';
import 'dart:io';
import 'package:flutter/foundation.dart';
import 'dart:convert';

import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:supabase_flutter/supabase_flutter.dart';
import '../models/task.dart';
import '../models/task_activity_log.dart';
import 'package:flutter/material.dart';
import 'package:flutter_dotenv/flutter_dotenv.dart';
import '../models/task_assignment.dart';
import 'profile_provider.dart';
import 'supabase_provider.dart';
import 'tickets_provider.dart';
import 'user_offices_provider.dart';
import '../utils/app_time.dart';

// Helper to insert activity log rows while sanitizing nulls and
// avoiding exceptions from malformed payloads. Accepts either a Map
// or a List<Map>.
Future<void> _insertActivityRows(dynamic client, dynamic rows) async {
  try {
    if (rows == null) return;
    if (rows is List) {
      final sanitized = rows
          .map((r) {
            if (r is Map) {
              final m = Map<String, dynamic>.from(r);
              m.removeWhere((k, v) => v == null);
              return m;
            }
            return null;
          })
          .whereType<Map<String, dynamic>>()
          .toList();
      if (sanitized.isEmpty) return;
      await client.from('task_activity_logs').insert(sanitized);
    } else if (rows is Map) {
      final m = Map<String, dynamic>.from(rows);
      m.removeWhere((k, v) => v == null);
      await client.from('task_activity_logs').insert(m);
    }
  } catch (e) {
    // Log for debugging but don't rethrow to avoid breaking caller flows
    try {
      debugPrint('[insertActivityRows] insert failed: $e');
    } catch (_) {}
  }
}

/// Task query parameters for server-side pagination and filtering.
class TaskQuery {
  /// Creates task query parameters.
  const TaskQuery({
    this.offset = 0,
    this.limit = 50,
    this.searchQuery = '',
    this.officeId,
    this.status,
    this.assigneeId,
    this.dateRange,
  });

  /// Offset for pagination.
  final int offset;

  /// Number of items per page (default: 50).
  final int limit;

  /// Full text search query.
  final String searchQuery;

  /// Filter by office ID.
  final String? officeId;

  /// Filter by status.
  final String? status;

  /// Filter by assignee ID.
  final String? assigneeId;

  /// Filter by date range.
  /// Filter by date range.
  final DateTimeRange? dateRange;

  TaskQuery copyWith({
    int? offset,
    int? limit,
    String? searchQuery,
    String? officeId,
    String? status,
    String? assigneeId,
    DateTimeRange? dateRange,
  }) {
    return TaskQuery(
      offset: offset ?? this.offset,
      limit: limit ?? this.limit,
      searchQuery: searchQuery ?? this.searchQuery,
      officeId: officeId ?? this.officeId,
      status: status ?? this.status,
      assigneeId: assigneeId ?? this.assigneeId,
      dateRange: dateRange ?? this.dateRange,
    );
  }
}

final tasksProvider = StreamProvider<List<Task>>((ref) {
  final client = ref.watch(supabaseClientProvider);
  final profileAsync = ref.watch(currentProfileProvider);
  final ticketsAsync = ref.watch(ticketsProvider);
  final assignmentsAsync = ref.watch(userOfficesProvider);
  final query = ref.watch(tasksQueryProvider);

  final profile = profileAsync.valueOrNull;
  if (profile == null) {
    return Stream.value(const <Task>[]);
  }

  final isGlobal =
      profile.role == 'admin' ||
      profile.role == 'dispatcher' ||
      profile.role == 'it_staff';

  // For RBAC early-exit: if the user has no accessible tickets/offices,
  // avoid subscribing to the full tasks stream.
  List<String> earlyAllowedTicketIds =
      ticketsAsync.valueOrNull?.map((ticket) => ticket.id).toList() ??
      <String>[];
  List<String> earlyOfficeIds =
      assignmentsAsync.valueOrNull
          ?.where((assignment) => assignment.userId == profile.id)
          .map((assignment) => assignment.officeId)
          .toSet()
          .toList() ??
      <String>[];
  if (!isGlobal && earlyAllowedTicketIds.isEmpty && earlyOfficeIds.isEmpty) {
    return Stream.value(const <Task>[]);
  }

  // NOTE: Supabase stream builder does not support `.range(...)` —
  // apply pagination and remaining filters client-side after mapping.
  final baseStream = client
      .from('tasks')
      .stream(primaryKey: ['id'])
      .map((rows) => rows.map(Task.fromMap).toList());

  return baseStream.map((allTasks) {
    debugPrint('[tasksProvider] stream event: ${allTasks.length} rows');
    // RBAC (server-side filtering isn't possible via `.range` on stream builder,
    // so enforce allowed IDs here).
    var list = allTasks;
    if (!isGlobal) {
      final allowedTicketIds =
          ticketsAsync.valueOrNull?.map((ticket) => ticket.id).toList() ??
          <String>[];
      final officeIds =
          assignmentsAsync.valueOrNull
              ?.where((assignment) => assignment.userId == profile.id)
              .map((assignment) => assignment.officeId)
              .toSet()
              .toList() ??
          <String>[];
      if (allowedTicketIds.isEmpty && officeIds.isEmpty) return <Task>[];
      final allowedTickets = allowedTicketIds.toSet();
      final allowedOffices = officeIds.toSet();
      list = list
          .where(
            (t) =>
                (t.ticketId != null && allowedTickets.contains(t.ticketId)) ||
                (t.officeId != null && allowedOffices.contains(t.officeId)),
          )
          .toList();
    }

    // Query filters (apply client-side)
    if (query.officeId != null) {
      list = list.where((t) => t.officeId == query.officeId).toList();
    }
    if (query.status != null) {
      list = list.where((t) => t.status == query.status).toList();
    }
    if (query.searchQuery.isNotEmpty) {
      final q = query.searchQuery.toLowerCase();
      list = list
          .where(
            (t) =>
                t.title.toLowerCase().contains(q) ||
                t.description.toLowerCase().contains(q) ||
                (t.taskNumber?.toLowerCase().contains(q) ?? false),
          )
          .toList();
    }

    // Sort by status groups then within-group ordering:
    // 1. queued – order by priority (desc), then queue_order (asc), then created_at
    // 2. in_progress – preserve recent order (created_at asc)
    // 3. completed – order by numeric task_number when available (asc)
    // 4. other statuses – fallback to queue_order then created_at
    int statusRank(String s) {
      switch (s) {
        case 'queued':
          return 0;
        case 'in_progress':
          return 1;
        case 'completed':
          return 2;
        default:
          return 3;
      }
    }

    int? parseTaskNumber(Task t) {
      final tn = t.taskNumber;
      if (tn == null) return null;
      final m = RegExp(r'\d+').firstMatch(tn);
      if (m == null) return null;
      return int.tryParse(m.group(0)!);
    }

    list.sort((a, b) {
      final ra = statusRank(a.status);
      final rb = statusRank(b.status);
      final rcmp = ra.compareTo(rb);
      if (rcmp != 0) return rcmp;

      // Same status: apply within-group ordering
      if (ra == 0) {
        // queued: higher priority first, then queue_order asc, then created_at
        final pcmp = b.priority.compareTo(a.priority);
        if (pcmp != 0) return pcmp;
        final aOrder = a.queueOrder ?? 0x7fffffff;
        final bOrder = b.queueOrder ?? 0x7fffffff;
        final qcmp = aOrder.compareTo(bOrder);
        if (qcmp != 0) return qcmp;
        return a.createdAt.compareTo(b.createdAt);
      }

      if (ra == 1) {
        // in_progress: keep older first
        return a.createdAt.compareTo(b.createdAt);
      }

      if (ra == 2) {
        // completed: prefer numeric task_number DESC when present
        final an = parseTaskNumber(a);
        final bn = parseTaskNumber(b);
        if (an != null && bn != null) return bn.compareTo(an);
        if (an != null) return -1;
        if (bn != null) return 1;
        return b.createdAt.compareTo(a.createdAt);
      }

      // fallback: queue_order then created_at
      final aOrder = a.queueOrder ?? 0x7fffffff;
      final bOrder = b.queueOrder ?? 0x7fffffff;
      final cmp = aOrder.compareTo(bOrder);
      if (cmp != 0) return cmp;
      return a.createdAt.compareTo(b.createdAt);
    });

    // Return the full filtered & sorted list to allow the UI layer to
    // perform pagination (desktop PaginatedDataTable expects the full
    // row count so it can render pagination controls reliably). The
    // Supabase stream currently delivers all rows and the provider
    // applies filtering/sorting; leaving pagination to the UI avoids
    // off-by-one issues where a full page of results would hide the
    // presence of a next page.
    return list;
  });
});

/// Provider for task query parameters.
final tasksQueryProvider = StateProvider<TaskQuery>((ref) => const TaskQuery());

final taskAssignmentsProvider = StreamProvider<List<TaskAssignment>>((ref) {
  final client = ref.watch(supabaseClientProvider);
  return client
      .from('task_assignments')
      .stream(primaryKey: ['task_id', 'user_id'])
      .map((rows) => rows.map(TaskAssignment.fromMap).toList());
});

/// Stream of activity logs for a single task.
final taskActivityLogsProvider =
    StreamProvider.family<List<TaskActivityLog>, String>((ref, taskId) {
      final client = ref.watch(supabaseClientProvider);
      return client
          .from('task_activity_logs')
          .stream(primaryKey: ['id'])
          .eq('task_id', taskId)
          .order('created_at', ascending: false)
          .map((rows) => rows.map((r) => TaskActivityLog.fromMap(r)).toList());
    });

final taskAssignmentsControllerProvider = Provider<TaskAssignmentsController>((
  ref,
) {
  final client = ref.watch(supabaseClientProvider);
  return TaskAssignmentsController(client);
});

final tasksControllerProvider = Provider<TasksController>((ref) {
  final client = ref.watch(supabaseClientProvider);
  return TasksController(client);
});

class TasksController {
  TasksController(this._client);

  // Supabase storage bucket for task action images. Ensure this bucket exists
  // with public read access.
  static const String _actionImageBucket = 'task_action_taken_images';

  // _client is declared dynamic allowing test doubles that mimic only the
  // subset of methods used by this class. In production it will be a
  // SupabaseClient instance.
  final dynamic _client;

  Future<void> createTask({
    required String title,
    required String description,
    String? officeId,
    String? ticketId,
    // optional request metadata when creating a task
    String? requestType,
    String? requestTypeOther,
    String? requestCategory,
  }) async {
    final actorId = _client.auth.currentUser?.id;
    final payload = <String, dynamic>{
      'title': title,
      'description': description,
    };
    if (officeId != null) {
      payload['office_id'] = officeId;
    }
    if (ticketId != null) {
      payload['ticket_id'] = ticketId;
    }
    if (requestType != null) {
      payload['request_type'] = requestType;
    }
    if (requestTypeOther != null) {
      payload['request_type_other'] = requestTypeOther;
    }
    if (requestCategory != null) {
      payload['request_category'] = requestCategory;
    }

    // Prefer server RPC that atomically generates `task_number` and inserts
    // the task; fallback to client-side insert with retry on duplicate-key.
    String? taskId;
    String? assignedNumber;

    try {
      final rpcParams = {
        'p_title': title,
        'p_description': description,
        'p_office_id': officeId,
        'p_ticket_id': ticketId,
        'p_request_type': requestType,
        'p_request_type_other': requestTypeOther,
        'p_request_category': requestCategory,
        'p_creator_id': actorId,
      };
      // Retry RPC on duplicate-key (23505) errors which may occur
      // transiently due to concurrent inserts; prefer RPC always.
      const int rpcMaxAttempts = 3;
      Map<String, dynamic>? rpcRow;
      for (var attempt = 0; attempt < rpcMaxAttempts; attempt++) {
        try {
          final rpcRes = await _client
              .rpc('insert_task_with_number', rpcParams)
              .single();
          if (rpcRes is Map) {
            rpcRow = Map<String, dynamic>.from(rpcRes);
          } else if (rpcRes is List &&
              rpcRes.isNotEmpty &&
              rpcRes.first is Map) {
            rpcRow = Map<String, dynamic>.from(rpcRes.first as Map);
          }
          break;
        } catch (err) {
          final msg = err.toString();
          final isDuplicateKey =
              msg.contains('duplicate key value') || msg.contains('23505');
          if (!isDuplicateKey || attempt == rpcMaxAttempts - 1) {
            rethrow;
          }
          await Future.delayed(Duration(milliseconds: 150 * (attempt + 1)));
          // retry
        }
      }
      if (rpcRow != null) {
        taskId = rpcRow['id'] as String?;
        assignedNumber = rpcRow['task_number'] as String?;
      }
      // ignore: avoid_print
      print('createTask via RPC assigned number=$assignedNumber id=$taskId');
    } catch (e) {
      // RPC not available or failed; fallback to client insert with retry
      const int maxAttempts = 3;
      Map<String, dynamic>? insertData;
      for (var attempt = 0; attempt < maxAttempts; attempt++) {
        try {
          insertData = await _client
              .from('tasks')
              .insert(payload)
              .select('id, task_number')
              .single();
          break;
        } catch (err) {
          final msg = err.toString();
          final isDuplicateKey =
              msg.contains('duplicate key value') || msg.contains('23505');
          if (!isDuplicateKey || attempt == maxAttempts - 1) {
            rethrow;
          }
          await Future.delayed(Duration(milliseconds: 150 * (attempt + 1)));
        }
      }
      taskId = insertData == null ? null : insertData['id'] as String?;
      assignedNumber = insertData == null
          ? null
          : insertData['task_number'] as String?;
      // ignore: avoid_print
      print('createTask fallback assigned number=$assignedNumber id=$taskId');
    }

    if (taskId == null) return;

    try {
      await _insertActivityRows(_client, {
        'task_id': taskId,
        'actor_id': actorId,
        'action_type': 'created',
      });
    } catch (_) {
      // non-fatal
    }

    // Auto-assignment should run once on creation (best-effort).
    try {
      await _autoAssignTask(taskId: taskId, officeId: officeId ?? '');
    } catch (e, st) {
      // keep creation successful but surface the error in logs for debugging
      // ignore: avoid_print
      print('autoAssignTask failed for task=$taskId: $e\n$st');
    }

    unawaited(_notifyCreated(taskId: taskId, actorId: actorId));
  }

  /// Uploads an image for a task's action field and returns the public URL.
  ///
  /// [bytes] should contain the file data and [extension] the file extension
  /// (e.g. 'png' or 'jpg'). The image will be stored under a path that
  /// includes the task ID and a timestamp to avoid collisions. Returns `null`
  /// if the upload fails.
  Future<String?> uploadActionImage({
    required String taskId,
    required Uint8List bytes,
    required String extension,
  }) async {
    final path =
        'tasks/$taskId/${DateTime.now().millisecondsSinceEpoch}.$extension';
    try {
      // debug: show upload path
      // ignore: avoid_print
      print('uploadActionImage uploading to path: $path');
      // perform the upload and capture whatever the SDK returns (it varies by platform)
      final dynamic res;
      if (kIsWeb) {
        // on web, upload binary data
        res = await _client.storage
            .from(_actionImageBucket)
            .uploadBinary(path, bytes);
      } else {
        // write bytes to a simple temp file (no nested folders)
        final tmpDir = Directory.systemTemp;
        final localFile = File(
          '${tmpDir.path}/${DateTime.now().millisecondsSinceEpoch}.$extension',
        );
        try {
          await localFile.create();
          await localFile.writeAsBytes(bytes);
        } catch (e) {
          // ignore: avoid_print
          print('uploadActionImage failed writing temp file: $e');
          return null;
        }
        res = await _client.storage
            .from(_actionImageBucket)
            .upload(path, localFile);
        try {
          await localFile.delete();
        } catch (_) {}
      }

      // debug: inspect the response object/type
      // ignore: avoid_print
      print('uploadActionImage response type=${res.runtimeType} value=$res');

      // Some SDK methods return a simple String (path) on success, others
      // return a StorageResponse with an error field. Avoid calling .error on a
      // String to prevent NoSuchMethodError as seen in logs earlier.
      if (res is String) {
        // treat as success
      } else if (res is Map && res['error'] != null) {
        // older versions might return a plain map
        // ignore: avoid_print
        print('uploadActionImage upload error: ${res['error']}');
        return null;
      } else if (res != null && res.error != null) {
        // StorageResponse case
        // ignore: avoid_print
        print('uploadActionImage upload error: ${res.error}');
        return null;
      }
    } catch (e) {
      // ignore: avoid_print
      print('uploadActionImage failed upload: $e');
      return null;
    }
    try {
      final urlRes = await _client.storage
          .from(_actionImageBucket)
          .getPublicUrl(path);
      // debug: log full response
      // ignore: avoid_print
      print('uploadActionImage getPublicUrl response: $urlRes');

      String? url;
      if (urlRes is String) {
        url = urlRes;
      } else if (urlRes is Map && urlRes['data'] is String) {
        url = urlRes['data'] as String;
      } else if (urlRes != null) {
        try {
          url = urlRes.data as String?;
        } catch (_) {
          url = null;
        }
      }

      if (url != null && url.isNotEmpty) {
        // trim whitespace/newline which may be added by SDK or logging
        return url.trim();
      }
      // fallback: construct URL manually using env variable
      final supabaseUrl = dotenv.env['SUPABASE_URL'] ?? '';
      if (supabaseUrl.isEmpty) return null;
      return '$supabaseUrl/storage/v1/object/public/$_actionImageBucket/$path'
          .trim();
    } catch (e) {
      // ignore: avoid_print
      print('uploadActionImage getPublicUrl error: $e');
      return null;
    }
  }

  Future<void> _notifyCreated({
    required String taskId,
    required String? actorId,
  }) async {
    try {
      final recipients = await _fetchRoleUserIds(
        roles: const ['dispatcher', 'it_staff'],
        excludeUserId: actorId,
      );
      if (recipients.isEmpty) return;
      final rows = recipients
          .map(
            (userId) => {
              'user_id': userId,
              'actor_id': actorId,
              'task_id': taskId,
              'type': 'created',
            },
          )
          .toList();
      await _client.from('notifications').insert(rows);
    } catch (_) {
      return;
    }
  }

  Future<List<String>> _fetchRoleUserIds({
    required List<String> roles,
    required String? excludeUserId,
  }) async {
    try {
      final data = await _client
          .from('profiles')
          .select('id, role')
          .inFilter('role', roles);
      final rows = data;
      final ids = rows
          .map((row) => row['id'] as String?)
          .whereType<String>()
          .where((id) => id.isNotEmpty && id != excludeUserId)
          .toList();
      return ids;
    } catch (_) {
      return [];
    }
  }

  /// Update only the status of a task.
  ///
  /// Before marking a task as **completed** we enforce that the
  /// request type/category metadata have been provided. This protects the
  /// business rule that details must be specified before closing.
  Future<void> updateTaskStatus({
    required String taskId,
    required String status,
  }) async {
    if (status == 'completed') {
      // fetch current metadata to validate several required fields
      try {
        final row = await _client
            .from('tasks')
            // include all columns that must be non-null/empty before completing
            .select(
              // signatories are not needed for validation; action_taken is still
              // required so we include it alongside the type/category fields.
              'request_type, request_category, action_taken',
            )
            .eq('id', taskId)
            .maybeSingle();
        if (row is! Map<String, dynamic>) {
          throw Exception('Task not found');
        }

        final rt = row['request_type'];
        final rc = row['request_category'];
        final action = row['action_taken'];

        final missing = <String>[];
        if (rt == null || (rt is String && rt.trim().isEmpty)) {
          missing.add('request type');
        }
        if (rc == null || (rc is String && rc.trim().isEmpty)) {
          missing.add('request category');
        }
        // signatories are no longer required for completion; they can be
        // filled in later.  we still require action taken to document what
        // was done.

        // if you want to enforce action taken you can uncomment this block,
        // but current business rule only mandates request metadata. we keep
        // action taken non-null for clarity.
        if (action == null || (action is String && action.trim().isEmpty)) {
          missing.add('action taken');
        }

        if (missing.isNotEmpty) {
          throw Exception(
            'The following fields must be set before completing a task: ${missing.join(', ')}.',
          );
        }
      } catch (e) {
        // rethrow so callers can handle (UI will display message)
        rethrow;
      }
    }

    await _client.from('tasks').update({'status': status}).eq('id', taskId);

    // Log important status transitions
    try {
      final actorId = _client.auth.currentUser?.id;
      if (status == 'in_progress') {
        await _insertActivityRows(_client, {
          'task_id': taskId,
          'actor_id': actorId,
          'action_type': 'started',
        });
      } else if (status == 'completed') {
        await _insertActivityRows(_client, {
          'task_id': taskId,
          'actor_id': actorId,
          'action_type': 'completed',
        });
      }
    } catch (_) {
      // ignore logging failures
    }
  }

  /// Update arbitrary fields on a task row.
  ///
  /// Primarily used to set request metadata after creation or during
  /// status transitions.
  Future<void> updateTask({
    required String taskId,
    String? requestType,
    String? requestTypeOther,
    String? requestCategory,
    String? status,
    String? requestedBy,
    String? notedBy,
    String? receivedBy,
    String? actionTaken,
  }) async {
    final payload = <String, dynamic>{};
    if (requestType != null) {
      payload['request_type'] = requestType;
    }
    if (requestTypeOther != null) {
      payload['request_type_other'] = requestTypeOther;
    }
    if (requestCategory != null) {
      payload['request_category'] = requestCategory;
    }
    if (requestedBy != null) {
      payload['requested_by'] = requestedBy;
    }
    if (notedBy != null) {
      payload['noted_by'] = notedBy;
    }
    // `performed_by` is derived from task assignments; we don't persist it here.
    if (receivedBy != null) {
      payload['received_by'] = receivedBy;
    }
    if (actionTaken != null) {
      try {
        payload['action_taken'] = jsonDecode(actionTaken);
      } catch (_) {
        // fallback: store raw string
        payload['action_taken'] = actionTaken;
      }
    }
    if (status != null) {
      payload['status'] = status;
    }
    if (payload.isEmpty) {
      return;
    }
    await _client.from('tasks').update(payload).eq('id', taskId);
  }

  /// Update editable task fields such as title, description, office or linked ticket.
  Future<void> updateTaskFields({
    required String taskId,
    String? title,
    String? description,
    String? officeId,
    String? ticketId,
  }) async {
    final payload = <String, dynamic>{};
    if (title != null) payload['title'] = title;
    if (description != null) payload['description'] = description;
    if (officeId != null) payload['office_id'] = officeId;
    if (ticketId != null) payload['ticket_id'] = ticketId;
    if (payload.isEmpty) return;

    await _client.from('tasks').update(payload).eq('id', taskId);

    // record an activity log for edit operations (best-effort)
    try {
      final actorId = _client.auth.currentUser?.id;
      await _insertActivityRows(_client, {
        'task_id': taskId,
        'actor_id': actorId,
        'action_type': 'updated',
        'meta': payload,
      });
    } catch (_) {}
  }

  // Auto-assignment logic executed once on creation.
  Future<void> _autoAssignTask({
    required String taskId,
    required String officeId,
  }) async {
    if (officeId.isEmpty) return;

    final now = AppTime.now();
    final startOfDay = DateTime(now.year, now.month, now.day);
    final nextDay = startOfDay.add(const Duration(days: 1));

    try {
      // 1) Find teams covering the office
      final teamsRows =
          (await _client.from('teams').select()) as List<dynamic>? ?? [];
      final teamIds = teamsRows
          .where((r) => (r['office_ids'] as List?)?.contains(officeId) == true)
          .map((r) => r['id'] as String)
          .toSet()
          .toList();
      if (teamIds.isEmpty) return;

      // 2) Get members of those teams
      final memberRows =
          (await _client
                  .from('team_members')
                  .select('user_id')
                  .inFilter('team_id', teamIds))
              as List<dynamic>? ??
          [];
      final candidateIds = memberRows
          .map((r) => r['user_id'] as String)
          .toSet()
          .toList();
      if (candidateIds.isEmpty) return;

      // 3) Filter by "On Duty" (have a check-in record for today)
      final dsRows =
          (await _client
                  .from('duty_schedules')
                  .select('user_id, check_in_at')
                  .inFilter('user_id', candidateIds))
              as List<dynamic>? ??
          [];

      final Map<String, DateTime> onDuty = {};
      for (final r in dsRows) {
        final userId = r['user_id'] as String?;
        final checkIn = r['check_in_at'] as String?;
        if (userId == null || checkIn == null) continue;
        final dt = DateTime.tryParse(checkIn);
        if (dt == null) continue;
        if (dt.isAfter(startOfDay.subtract(const Duration(seconds: 1))) &&
            dt.isBefore(nextDay.add(const Duration(seconds: 1)))) {
          onDuty[userId] = dt;
        }
      }
      if (onDuty.isEmpty) {
        // record a failed auto-assign attempt for observability
        try {
          await _insertActivityRows(_client, {
            'task_id': taskId,
            'actor_id': null,
            'action_type': 'auto_assign_failed',
            'meta': {'reason': 'no_on_duty_candidates'},
          });
        } catch (_) {}
        return;
      }

      // 4) For each on-duty user compute completed_tasks_count for today
      final List<_Candidate> candidates = [];
      for (final userId in onDuty.keys) {
        // get task ids assigned to user
        final taRows =
            (await _client
                    .from('task_assignments')
                    .select('task_id')
                    .eq('user_id', userId))
                as List<dynamic>? ??
            [];
        final assignedTaskIds = taRows
            .map((r) => r['task_id'] as String)
            .toList();
        int completedCount = 0;
        if (assignedTaskIds.isNotEmpty) {
          final tasksRows =
              (await _client
                      .from('tasks')
                      .select('id')
                      .inFilter('id', assignedTaskIds)
                      .gte('completed_at', startOfDay.toIso8601String())
                      .lt('completed_at', nextDay.toIso8601String()))
                  as List<dynamic>? ??
              [];
          completedCount = tasksRows.length;
        }
        candidates.add(
          _Candidate(
            userId: userId,
            checkInAt: onDuty[userId]!,
            completedToday: completedCount,
          ),
        );
      }

      if (candidates.isEmpty) {
        try {
          await _insertActivityRows(_client, {
            'task_id': taskId,
            'actor_id': null,
            'action_type': 'auto_assign_failed',
            'meta': {'reason': 'no_eligible_candidates'},
          });
        } catch (_) {}
        return;
      }

      // 5) Sort: latest check-in first (desc), then lowest completed_today
      candidates.sort((a, b) {
        final c = b.checkInAt.compareTo(a.checkInAt);
        if (c != 0) return c;
        return a.completedToday.compareTo(b.completedToday);
      });

      final chosen = candidates.first;

      // 6) Insert assignment + activity log + notification
      await _client.from('task_assignments').insert({
        'task_id': taskId,
        'user_id': chosen.userId,
      });

      try {
        await _insertActivityRows(_client, {
          'task_id': taskId,
          'actor_id': null,
          'action_type': 'assigned',
          'meta': {'auto': true, 'user_id': chosen.userId},
        });
      } catch (_) {}

      try {
        await _client.from('notifications').insert({
          'user_id': chosen.userId,
          'actor_id': null,
          'task_id': taskId,
          'type': 'assignment',
        });
      } catch (_) {}
    } catch (e, st) {
      // Log error for visibility and record a failed auto-assign activity
      // ignore: avoid_print
      print('autoAssignTask error for task=$taskId: $e\n$st');
      try {
        await _insertActivityRows(_client, {
          'task_id': taskId,
          'actor_id': null,
          'action_type': 'auto_assign_failed',
          'meta': {'reason': 'exception', 'error': e.toString()},
        });
      } catch (_) {}
      return;
    }
  }
}

/// Public DTO used by unit tests to validate selection logic.
class AutoAssignCandidate {
  AutoAssignCandidate({
    required this.userId,
    required this.checkInAt,
    required this.completedToday,
  });

  final String userId;
  final DateTime checkInAt;
  final int completedToday;
}

/// Choose the best candidate according to auto-assignment rules:
/// - latest check-in first (late-comer priority)
/// - tie-breaker: lowest completedTasks (today)
/// Returns the chosen userId or null when candidates is empty.
String? chooseAutoAssignCandidate(List<AutoAssignCandidate> candidates) {
  if (candidates.isEmpty) return null;
  final list = List<AutoAssignCandidate>.from(candidates);
  list.sort((a, b) {
    final c = b.checkInAt.compareTo(a.checkInAt);
    if (c != 0) return c;
    return a.completedToday.compareTo(b.completedToday);
  });
  return list.first.userId;
}

class _Candidate {
  _Candidate({
    required this.userId,
    required this.checkInAt,
    required this.completedToday,
  });
  final String userId;
  final DateTime checkInAt;
  final int completedToday;
}

class TaskAssignmentsController {
  TaskAssignmentsController(this._client);

  final SupabaseClient _client;

  Future<void> replaceAssignments({
    required String taskId,
    required String? ticketId,
    required List<String> newUserIds,
    required List<String> currentUserIds,
  }) async {
    final nextIds = newUserIds.toSet();
    final currentIds = currentUserIds.toSet();
    final toAdd = nextIds.difference(currentIds).toList();
    final toRemove = currentIds.difference(nextIds).toList();

    if (toAdd.isNotEmpty) {
      final rows = toAdd
          .map((userId) => {'task_id': taskId, 'user_id': userId})
          .toList();
      await _client.from('task_assignments').insert(rows);

      // Insert activity log(s) for assignment(s).
      try {
        final actorId = _client.auth.currentUser?.id;
        final logRows = toAdd
            .map(
              (userId) => {
                'task_id': taskId,
                'actor_id': actorId,
                'action_type': 'assigned',
                'meta': {'user_id': userId},
              },
            )
            .toList();
        await _insertActivityRows(_client, logRows);
      } catch (_) {
        // non-fatal
      }

      await _notifyAssigned(taskId: taskId, ticketId: ticketId, userIds: toAdd);
    }
    if (toRemove.isNotEmpty) {
      await _client
          .from('task_assignments')
          .delete()
          .eq('task_id', taskId)
          .inFilter('user_id', toRemove);

      // Record a reassignment event (who removed -> who added)
      try {
        final actorId = _client.auth.currentUser?.id;
        await _insertActivityRows(_client, {
          'task_id': taskId,
          'actor_id': actorId,
          'action_type': 'reassigned',
          'meta': {'from': toRemove, 'to': toAdd},
        });
      } catch (_) {
        // non-fatal
      }
    }
  }

  Future<void> _notifyAssigned({
    required String taskId,
    required String? ticketId,
    required List<String> userIds,
  }) async {
    if (userIds.isEmpty) return;
    try {
      final actorId = _client.auth.currentUser?.id;
      final rows = userIds
          .map(
            (userId) => {
              'user_id': userId,
              'actor_id': actorId,
              'task_id': taskId,
              'ticket_id': ticketId,
              'type': 'assignment',
            },
          )
          .toList();
      await _client.from('notifications').insert(rows);
    } catch (_) {
      return;
    }
  }

  Future<void> removeAssignment({
    required String taskId,
    required String userId,
  }) async {
    await _client
        .from('task_assignments')
        .delete()
        .eq('task_id', taskId)
        .eq('user_id', userId);
  }
}