From 2d902360b82a8eaef8fa4b582619edb42ff83737 Mon Sep 17 00:00:00 2001
From: Jacob Bandes-Storch <jacob@bandes-stor.ch>
Date: Sat, 31 Oct 2020 14:32:21 -0600
Subject: [PATCH] Replace isCurrent calculation with "next expected entry date"

---
 Shared/APODClient.swift          | 14 ++++++++++++--
 Shared/Foundation+SpacePOD.swift | 11 +++++++++++
 Shared/YearMonthDay.swift        | 19 ++++++++-----------
 3 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/Shared/APODClient.swift b/Shared/APODClient.swift
index 1a77816..81c1697 100644
--- a/Shared/APODClient.swift
+++ b/Shared/APODClient.swift
@@ -113,6 +113,11 @@ public class APODEntry: Codable {
 
 
   public static let placeholder: APODEntry = APODEntry(rawEntry: RawAPODEntry(date: YearMonthDay.today, hdurl: nil, url: nil, title: "Example", copyright: "Example copyright", explanation: nil, mediaType: "blah"), asset: .unknown(URL(fileURLWithPath: "/dev/null")), localDataURL: URL(fileURLWithPath: "/dev/null"), localImageURL: URL(fileURLWithPath: "/dev/null"))
+
+  /// The earliest expected date that the next entry will be available from the server.
+  static func nextExpectedEntryDate(after entry: APODEntry) -> Date? {
+    return entry.date.nextDate(in: .losAngeles)
+  }
 }
 
 struct RawAPODEntry: Codable {
@@ -214,10 +219,15 @@ public class APODClient {
   public func loadLatestImage() -> AnyPublisher<APODEntry, Error> {
     // Return the latest cached entry if it's not stale.
     if let lastCached = _cache.last?.value {
-      // TODO: maybe improve this by predicting the next expected entry date (midnight Pacific)?
+      // Would we expect to find a new entry if we queried the server now?
+      let newEntryExpected = APODEntry.nextExpectedEntryDate(after: lastCached)
+        .map { $0.timeIntervalSinceNow > 0 } ?? true
+
+      // Has it been an hour since we last queried the server?
       let lastCacheDate = UserDefaults.spaceAppGroup.lastAPODCacheDate
       let cacheIsStale = lastCacheDate.map { -$0.timeIntervalSinceNow > 60*60 } ?? true
-      if !lastCached.date.isCurrent && cacheIsStale {
+
+      if newEntryExpected && cacheIsStale {
         DBG("Cache is stale: \(lastCacheDate?.description ?? "never cached")")
       } else {
         DBG("Loaded \(lastCached.date) from cache")
diff --git a/Shared/Foundation+SpacePOD.swift b/Shared/Foundation+SpacePOD.swift
index b7693ad..e7bfe25 100644
--- a/Shared/Foundation+SpacePOD.swift
+++ b/Shared/Foundation+SpacePOD.swift
@@ -1,6 +1,17 @@
 import Foundation
 import Combine
 
+extension Calendar {
+  public static let losAngeles = configure(Calendar(identifier: .gregorian)) {
+    $0.locale = Locale(identifier: "en_US")
+    $0.timeZone = .losAngeles
+  }
+}
+
+extension TimeZone {
+  public static let losAngeles = TimeZone(identifier: "America/Los_Angeles")!
+}
+
 public extension DateComponents {
   init(YMDString string: String) throws {
     let components = string.split(separator: "-")
diff --git a/Shared/YearMonthDay.swift b/Shared/YearMonthDay.swift
index 9a29e68..ce236c8 100644
--- a/Shared/YearMonthDay.swift
+++ b/Shared/YearMonthDay.swift
@@ -1,7 +1,5 @@
 import Foundation
 
-let TIME_ZONE_LA = TimeZone(identifier: "America/Los_Angeles")!
-
 public struct YearMonthDay {
   public let year: Int
   public let month: Int
@@ -31,21 +29,20 @@ public struct YearMonthDay {
   }
 
   public func asDate() -> Date? {
-    guard let date = Calendar.current.date(from: DateComponents(timeZone: TIME_ZONE_LA, year: year, month: month, day: day))
+    guard let date = Calendar.current.date(from: DateComponents(timeZone: .losAngeles, year: year, month: month, day: day))
     else {
       return nil
     }
     return date
   }
 
-  var isCurrent: Bool {
-    guard let date = asDate() else {
-      return false
-    }
-    var calendar = Calendar.current
-    calendar.locale = Locale(identifier: "en_US")
-    calendar.timeZone = TIME_ZONE_LA
-    return calendar.isDateInToday(date) || calendar.isDateInTomorrow(date)
+  public func nextDate(in calendar: Calendar) -> Date? {
+    guard
+      let thisDate = calendar.date(from: DateComponents(year: year, month: month, day: day)),
+      let nextDate = calendar.date(byAdding: .day, value: 1, to: thisDate)
+    else { return nil }
+
+    return calendar.startOfDay(for: nextDate)
   }
 }