"Back" now works for search results (#3)

- Made the application only retrieve the list of continents once per visit
- Update the verbiage for phase 3 completion

src/JobsJobsJobs/Client/AppState.cs

@@ -1,5 +1,8 @@
 using JobsJobsJobs.Shared;
 using System;
+using System.Collections.Generic;
+using System.Net.Http;
+using System.Threading.Tasks;
 
 namespace JobsJobsJobs.Client
 {
@@ -45,6 +48,33 @@ namespace JobsJobsJobs.Client
             }
         }
 
+        private IEnumerable<Continent>? _continents = null;
+
+        /// <summary>
+        /// Get a list of continents (only retrieves once per application load)
+        /// </summary>
+        /// <param name="http">The HTTP client to use to obtain continents the first time</param>
+        /// <returns>The list of continents</returns>
+        /// <exception cref="ApplicationException">If the continents cannot be loaded</exception>
+        public async Task<IEnumerable<Continent>> GetContinents(HttpClient http)
+        {
+            if (_continents == null)
+            {
+                ServerApi.SetJwt(http, this);
+                var continentResult = await ServerApi.RetrieveMany<Continent>(http, "continent/all");
+
+                if (continentResult.IsOk)
+                {
+                    _continents = continentResult.Ok;
+                }
+                else
+                {
+                    throw new ApplicationException($"Could not load continents - {continentResult.Error}");
+                }
+            }
+            return _continents;
+        }
+
         public AppState() { }
 
         private void NotifyChanged() => OnChange.Invoke();