PC-1344: load json file at runtime

HerPublicWebsite.BusinessLogic/Services/EligiblePostcode/EligiblePostcodeService.cs

@@ -1,5 +1,6 @@
 using HerPublicWebsite.BusinessLogic.Extensions;
 using Microsoft.Extensions.Logging;
+using Newtonsoft.Json;
 
 namespace HerPublicWebsite.BusinessLogic.Services.EligiblePostcode;
 
@@ -10,11 +11,32 @@ public interface IEligiblePostcodeService
 
 public class EligiblePostcodeService : IEligiblePostcodeService
 {
+    // build structure means json file is in different location when running locally
+    private const string PostcodeJsonPath = "Services/EligiblePostcode/EligiblePostcodeData.json";
+
+    private const string LocalPostcodeJsonPath =
+        "../HerPublicWebsite.BusinessLogic/Services/EligiblePostcode/EligiblePostcodeData.json";
+
+    private readonly List<string> eligiblePostcodes;
     private readonly ILogger<EligiblePostcodeService> logger;
-    
+
     public EligiblePostcodeService(ILogger<EligiblePostcodeService> logger)
     {
         this.logger = logger;
+        string jsonContents;
+
+        if (File.Exists(LocalPostcodeJsonPath))
+        {
+            using var reader = new StreamReader(LocalPostcodeJsonPath);
+            jsonContents = reader.ReadToEnd();
+        }
+        else
+        {
+            using var reader = new StreamReader(PostcodeJsonPath);
+            jsonContents = reader.ReadToEnd();
+        }
+
+        eligiblePostcodes = JsonConvert.DeserializeObject<List<string>>(jsonContents);
     }
 
     // Check whether a postcode is in the list of eligible postcodes found on this page
@@ -30,7 +52,7 @@ public bool IsEligiblePostcode(string postcode)
             logger.LogError("IsEligiblePostcode was called with a string that is not a valid postcode: {}", postcode);
             return false;
         }
-        
-        return EligiblePostcodeData.EligiblePostcodes.Contains(normalisedPostcode);
+
+        return eligiblePostcodes.Contains(normalisedPostcode);
     }
-}
+}