From f235ad08019f725070583609bfd45f53f3aa322e Mon Sep 17 00:00:00 2001
From: patrick-zippenfenig <patrick@zippenfenig.de>
Date: Sun, 7 Aug 2022 12:42:11 +0200
Subject: [PATCH] automatic resolution switching

---
 .../SwiftTimeZoneLookup.swift                 | 48 ++++++++++++++-----
 .../SwiftTimeZoneLookupTests.swift            |  6 ++-
 2 files changed, 42 insertions(+), 12 deletions(-)

diff --git a/Sources/SwiftTimeZoneLookup/SwiftTimeZoneLookup.swift b/Sources/SwiftTimeZoneLookup/SwiftTimeZoneLookup.swift
index 6ef1e05..2183ed2 100644
--- a/Sources/SwiftTimeZoneLookup/SwiftTimeZoneLookup.swift
+++ b/Sources/SwiftTimeZoneLookup/SwiftTimeZoneLookup.swift
@@ -8,34 +8,60 @@ public enum SwiftTimeZoneLookupError: Error {
 
 public struct SwiftTimeZoneLookupResult {
     /// Timezone identifier like `Europe/Berlin`
-    let timezone: String
+    public let timezone: String
     
     /// Country name like `Germany`
-    let countryName: String?
+    public let countryName: String?
     
     /// 2 character country code like `DE` for Germany
-    let countryAlpha2: String?
+    public let countryAlpha2: String?
 }
 
 public final class SwiftTimeZoneLookup {
-    private let database: OpaquePointer
+    /// 0.00017 degrees (~20m) resolution
+    private let database21: OpaquePointer
+    
+    /// 0.0055 degrees (~0.5km) resolution
+    private let database16: OpaquePointer
     
     /// Throws if the timezone database could not be opened
     public init() throws {
         guard let timezone21 = Bundle.module.url(forResource: "timezone21", withExtension: "bin") else {
             throw SwiftTimeZoneLookupError.couldNotFindTimezone21bin
         }
-        guard let database = timezone21.withUnsafeFileSystemRepresentation({ timezone21 in
-            ZDOpenDatabase(timezone21)
-        }) else {
+        guard let timezone16 = Bundle.module.url(forResource: "timezone16", withExtension: "bin") else {
+            throw SwiftTimeZoneLookupError.couldNotFindTimezone21bin
+        }
+        
+        guard let database21 = timezone21.withUnsafeFileSystemRepresentation(ZDOpenDatabase) else {
             throw SwiftTimeZoneLookupError.couldNotOpenDatabase
         }
-        self.database = database
+        guard let database16 = timezone16.withUnsafeFileSystemRepresentation(ZDOpenDatabase) else {
+            throw SwiftTimeZoneLookupError.couldNotOpenDatabase
+        }
+        
+        self.database21 = database21
+        self.database16 = database16
+    }
+    
+    /// Try with lower resolution first and use high resolution database if too close to the border
+    private func highResLookup(latitude: Float, longitude: Float) -> UnsafeMutablePointer<ZoneDetectResult>? {
+        var safezone: Float = .nan
+        guard let result = ZDLookup(database16, latitude, longitude, &safezone) else {
+            return nil
+        }
+        if safezone >= 0.0055*2 {
+            return result
+        }
+        guard let result21 = ZDLookup(database21, latitude, longitude, &safezone) else {
+            return nil
+        }
+        return result21
     }
     
     /// Resolve timezone by coordinate and return timezone, country name and alpha2
     public func lookup(latitude: Float, longitude: Float) -> SwiftTimeZoneLookupResult? {
-        guard let result = ZDLookup(database, latitude, longitude, nil) else {
+        guard let result = highResLookup(latitude: latitude, longitude: longitude) else {
             return nil
         }
         defer { ZDFreeResults(result) }
@@ -72,7 +98,7 @@ public final class SwiftTimeZoneLookup {
     
     /// Resolve the timz
     public func simple(latitude: Float, longitude: Float) -> String? {
-        guard let result = ZDLookup(database, latitude, longitude, nil) else {
+        guard let result = highResLookup(latitude: latitude, longitude: longitude) else {
             return nil
         }
         defer { ZDFreeResults(result) }
@@ -100,6 +126,6 @@ public final class SwiftTimeZoneLookup {
     }
     
     deinit {
-        ZDCloseDatabase(database)
+        ZDCloseDatabase(database21)
     }
 }
diff --git a/Tests/SwiftTimeZoneLookupTests/SwiftTimeZoneLookupTests.swift b/Tests/SwiftTimeZoneLookupTests/SwiftTimeZoneLookupTests.swift
index 01b8e6f..6e71fcf 100644
--- a/Tests/SwiftTimeZoneLookupTests/SwiftTimeZoneLookupTests.swift
+++ b/Tests/SwiftTimeZoneLookupTests/SwiftTimeZoneLookupTests.swift
@@ -1,5 +1,5 @@
 import XCTest
-@testable import SwiftTimeZoneLookup
+import SwiftTimeZoneLookup
 
 final class SwiftTimeZoneLookupTests: XCTestCase {
     func testLookup() throws {
@@ -13,5 +13,9 @@ final class SwiftTimeZoneLookupTests: XCTestCase {
         
         XCTAssertEqual(database.lookup(latitude: 42.5, longitude: -8.6)?.countryName, "Spain")
         XCTAssertEqual(database.lookup(latitude: 42.5, longitude: -8.6)?.countryAlpha2, "ES")
+        
+        // on the border to the netherlands. Requires high resolution lookup
+        XCTAssertEqual(database.simple(latitude: 53.242293, longitude: 7.209253), "Europe/Berlin")
+        XCTAssertEqual(database.simple(latitude: 53.239692, longitude: 7.207879), "Europe/Amsterdam")
     }
 }