Rork Max のジオフェンスが20件で頭打ちになる問題を、動的再登録で解く

import CoreLocation
 
struct GeoTarget {
    let id: String
    let coordinate: CLLocationCoordinate2D
    let radius: CLLocationDistance   // 100〜150m を推奨（後述）
}
 
final class GeofenceCoordinator: NSObject, CLLocationManagerDelegate {
    private let manager = CLLocationManager()
    private var allTargets: [GeoTarget] = []
 
    // iOS の上限は20。安全マージンとして18件に抑える（理由は後述）
    private let maxActiveRegions = 18
 
    var onEnter: ((String) -> Void)?
 
    override init() {
        super.init()
        manager.delegate = self
        manager.allowsBackgroundLocationUpdates = true
    }
 
    func start(with targets: [GeoTarget]) {
        allTargets = targets
        manager.requestAlwaysAuthorization()
        // 20件の入れ替えを駆動する粗い監視
        manager.startMonitoringSignificantLocationChanges()
        if let here = manager.location {
            reregisterNearest(to: here.coordinate)
        }
    }
 
    /// 現在地に近い順で maxActiveRegions 件だけを監視し直す
    private func reregisterNearest(to center: CLLocationCoordinate2D) {
        let origin = CLLocation(latitude: center.latitude, longitude: center.longitude)
 
        let nearest = allTargets
            .sorted {
                let a = CLLocation(latitude: $0.coordinate.latitude, longitude: $0.coordinate.longitude)
                let b = CLLocation(latitude: $1.coordinate.latitude, longitude: $1.coordinate.longitude)
                return a.distance(from: origin) < b.distance(from: origin)
            }
            .prefix(maxActiveRegions)
 
        let nextIDs = Set(nearest.map(\.id))
 
        // すでに監視中で、今回の20件に含まれないものだけ解除する
        for region in manager.monitoredRegions where !nextIDs.contains(region.identifier) {
            manager.stopMonitoring(for: region)
        }
 
        // 新たに監視対象になったものだけ登録する
        let currentIDs = Set(manager.monitoredRegions.map(\.identifier))
        for target in nearest where !currentIDs.contains(target.id) {
            let region = CLCircularRegion(
                center: target.coordinate,
                radius: target.radius,
                identifier: target.id
            )
            region.notifyOnEntry = true
            region.notifyOnExit = false
            manager.startMonitoring(for: region)
        }
    }
 
    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let here = locations.last else { return }
        reregisterNearest(to: here.coordinate)
    }
 
    func locationManager(_ manager: CLLocationManager, didEnterRegion region: CLRegion) {
        onEnter?(region.identifier)
    }
}

func locationManager(_ manager: CLLocationManager,
                     didDetermineState state: CLRegionState,
                     for region: CLRegion) {
    if state == .inside {
        onEnter?(region.identifier)   // 越境なしで内側にいた場合の補完
    }
}