import 'package:flutter/foundation.dart';

import 'package:miler/data/miler_api.dart';

/// Resolves a BOOKING id into the BOOKING ASSIGNMENT id that the accept/reject
/// endpoints key on.
///
/// Why this exists: `POST /miler/assignments/{id}/accept` looks the row up by
/// `bookingassignmentid`, but everything the app renders comes from
/// `GET /miler/bookings`, whose rows only carry `bookingid`. Those two ids come
/// from different sequences and do not match, so sending a booking id makes the
/// backend answer 404 "assignment not found" — the rider taps Accept, sees
/// success, and the booking is never actually accepted server-side.
///
/// `GET /miler/assignments` is the only place the pairing is exposed, so we
/// fetch it and keep a short-lived bookingid -> bookingassignmentid map.
class AssignmentLookup {
  AssignmentLookup._();

  /// bookingid (as string) -> bookingassignmentid
  static final Map<String, int> _cache = <String, int>{};

  /// bookingid (as string) -> the hub's solved stop number.
  ///
  /// ── Why the sequence lives here and not on the booking ──
  ///
  /// `step` is written onto **`bookingassignments`**, not onto the booking: the
  /// hub's batch-assign endpoint sends each affected rider's whole active set to
  /// the route optimizer and writes the returned road-network order back onto
  /// the assignment rows. So `GET /miler/bookings` — the app's one read of the
  /// day — cannot carry it, and this endpoint is the only place it exists.
  ///
  /// It was being thrown away. This class fetched the assignment rows for their
  /// ids and dropped everything else, so `Trip.sortStops` — which documents
  /// `step` as authoritative and says the app must never second-guess the
  /// admin's order — never saw one and fell back to booked time on every run.
  /// The rider was choosing his own order while the hub believed it had solved
  /// one for him.
  ///
  /// `step: 0` means *not sequenced*, never *first*, and is not stored.
  static final Map<String, int> _steps = <String, int>{};

  static DateTime? _fetchedAt;

  /// Assignments change whenever the hub assigns work, so the map goes stale
  /// quickly. Short enough to pick up new work, long enough that a burst of
  /// accepts doesn't refetch per tap.
  static const Duration _ttl = Duration(seconds: 30);

  /// Assignment states that are still actionable by the rider. A booking can
  /// legitimately have several assignment rows over its life (assign → reject →
  /// reassign), so when more than one exists we want the live one, not the
  /// rejected corpse.
  static const Set<String> _actionable = {'Assigned', 'Accepted'};

  static bool get _isStale {
    final at = _fetchedAt;
    return at == null || DateTime.now().difference(at) > _ttl;
  }

  static void invalidate() {
    _cache.clear();
    _steps.clear();
    _fetchedAt = null;
  }

  /// The hub's stop order, by booking id, refreshed on the same TTL as the ids.
  ///
  /// Best-effort by contract: sequencing is a separate service and the flow doc
  /// is explicit that it being down must leave bookings *assigned but
  /// unordered* rather than undo anything. An empty map therefore means "no
  /// solved order available", which the sort reads as "fall back to booked
  /// time" — not as "every stop is step 0".
  static Future<Map<String, int>> steps() async {
    if (_isStale) await _refresh();
    return Map<String, int>.unmodifiable(_steps);
  }

  /// The assignment id for [bookingId], or null when the backend has no
  /// assignment row for it (or the call fails).
  ///
  /// Refetches once on a cache miss before giving up: a booking the hub just
  /// assigned will not be in a cache populated moments earlier, and that is
  /// exactly the case the rider hits when accepting fresh work.
  static Future<int?> idForBooking(dynamic bookingId) async {
    final String key = bookingId?.toString().trim() ?? '';
    if (key.isEmpty) return null;

    if (_isStale) {
      await _refresh();
    }
    final cached = _cache[key];
    if (cached != null) return cached;

    // Miss against a warm cache — the assignment may have been created since.
    await _refresh();
    return _cache[key];
  }

  static Future<void> _refresh() async {
    try {
      // Through [MilerApi], not a hand-rolled `http.get`. It was the latter,
      // which meant this one call carried its own header building, its own
      // envelope unwrapping and its own idea of what a 2xx is — and, because it
      // bypassed `MilerApi.client`, it was the only request in the app that a
      // test could not stub, so the suite made real network calls to the
      // production API while checking a repository.
      final res = await MilerApi.assignments();
      if (!res.ok) {
        debugPrint('[ASSIGNMENTS] fetch failed: HTTP ${res.status}');
        return;
      }

      final List<dynamic> data = res.list;
      if (data.isEmpty && res.data is! List) {
        debugPrint('[ASSIGNMENTS] no assignment rows in the response');
        return;
      }

      final next = buildIndex(data);
      _cache
        ..clear()
        ..addAll(next);
      final nextSteps = buildStepIndex(data);
      _steps
        ..clear()
        ..addAll(nextSteps);
      _fetchedAt = DateTime.now();
      debugPrint(
        '[ASSIGNMENTS] cached ${_cache.length} booking->assignment ids, '
        '${_steps.length} sequenced',
      );
    } catch (e) {
      debugPrint('[ASSIGNMENTS] fetch error: $e');
    }
  }

  /// Collapses the assignment rows into one bookingid -> bookingassignmentid
  /// entry per booking.
  ///
  /// The backend orders by `assignedat DESC`, so the first row seen for a
  /// booking is its newest. Keep that one, but let an actionable row override a
  /// newer terminal one — a booking that was assigned, rejected, then
  /// reassigned must resolve to the live assignment, not the rejected corpse.
  @visibleForTesting
  static Map<String, int> buildIndex(List<dynamic> rows) {
    final index = <String, int>{};
    final tookActionable = <String>{};

    for (final row in rows.whereType<Map>()) {
      final bookingKey = row['bookingid']?.toString().trim() ?? '';
      final assignmentId = _asInt(row['bookingassignmentid']);
      if (bookingKey.isEmpty || assignmentId == null) continue;

      final status = (row['assignmentstatus'] ?? '').toString().trim();
      final isActionable = _actionable.contains(status);

      if (!index.containsKey(bookingKey)) {
        index[bookingKey] = assignmentId;
        if (isActionable) tookActionable.add(bookingKey);
      } else if (isActionable && !tookActionable.contains(bookingKey)) {
        index[bookingKey] = assignmentId;
        tookActionable.add(bookingKey);
      }
    }

    return index;
  }

  /// Collapses the assignment rows into one bookingid -> step entry.
  ///
  /// Same newest-first, actionable-wins rule as [buildIndex] — a booking that
  /// was assigned, rejected and reassigned must take the live assignment's
  /// sequence, not the rejected corpse's — so the two indexes cannot describe
  /// different assignment rows for the same booking.
  @visibleForTesting
  static Map<String, int> buildStepIndex(List<dynamic> rows) {
    final index = <String, int>{};
    final tookActionable = <String>{};

    for (final row in rows.whereType<Map>()) {
      final bookingKey = row['bookingid']?.toString().trim() ?? '';
      if (bookingKey.isEmpty) continue;

      final step = _asInt(row['step']) ?? 0;
      final status = (row['assignmentstatus'] ?? '').toString().trim();
      final isActionable = _actionable.contains(status);

      final seen =
          index.containsKey(bookingKey) || tookActionable.contains(bookingKey);
      if (seen && !(isActionable && !tookActionable.contains(bookingKey))) {
        continue;
      }
      if (isActionable) tookActionable.add(bookingKey);

      // 0 is "not sequenced". Storing it would make an unsequenced stop look
      // like it had been solved into position zero.
      if (step > 0) {
        index[bookingKey] = step;
      } else {
        index.remove(bookingKey);
      }
    }

    return index;
  }

  static int? _asInt(dynamic v) {
    if (v is int) return v;
    if (v is num) return v.toInt();
    return int.tryParse(v?.toString() ?? '');
  }
}