Fix POS stuck in loading state when tapping POS tab before tab visibility / site settings are refreshed where there are multiple subscribers to the same async stream and only the first one gets the value.

Author: jaclync

WooCommerce/Classes/ViewRelated/Dashboard/Settings/POS/POSTabEligibilityChecker.swift

@@ -47,6 +47,7 @@ protocol POSEntryPointEligibilityCheckerProtocol {
 final class POSTabEligibilityChecker: POSEntryPointEligibilityCheckerProtocol {
     private var siteSettingsEligibility: POSEligibilityState?
     private var featureFlagEligibility: POSEligibilityState?
+    private var siteSettingsTask: Task<[SiteSetting], Never>?
 
     private let siteID: Int64
     private let userInterfaceIdiom: UIUserInterfaceIdiom
@@ -238,14 +239,28 @@ private extension POSTabEligibilityChecker {
     }
 
     func waitForSiteSettingsRefresh() async -> [SiteSetting] {
-        for await siteSettings in siteSettings.settingsStream {
-            guard siteSettings.siteID == siteID, siteSettings.settings.isNotEmpty, siteSettings.source != .initialLoad else {
-                continue
+        // Uses a shared task so that multiple calls can await the same result since site settings can be emitted only once.
+        if let existingTask = siteSettingsTask {
+            return await existingTask.value
+        }
+
+        let task = Task<[SiteSetting], Never> { [weak self] in
+            guard let self else { return [] }
+
+            for await siteSettings in siteSettings.settingsStream {
+                guard siteSettings.siteID == self.siteID, siteSettings.settings.isNotEmpty, siteSettings.source != .initialLoad else {
+                    continue
+                }
+                siteSettingsTask = nil
+                return siteSettings.settings
             }
-            return siteSettings.settings
+            // If we get here, the stream completed without yielding any values for our site ID which is unexpected.
+            siteSettingsTask = nil
+            return []
         }
-        // If we get here, the stream completed without yielding any values for our site ID which is unexpected.
-        return []
+
+        siteSettingsTask = task
+        return await task.value
     }
 
     func isEligibleFromCountryAndCurrencyCode(countryCode: CountryCode, currencyCode: CurrencyCode) -> POSEligibilityState {