feat: add NUTS3 codes

src/PostalRegistry.Api.Oslo/Infrastructure/Modules/ApiModule.cs

@@ -8,6 +8,7 @@ namespace PostalRegistry.Api.Oslo.Infrastructure.Modules
     using Microsoft.Extensions.Configuration;
     using Microsoft.Extensions.DependencyInjection;
     using Microsoft.Extensions.Logging;
+    using Nuts;
     using Projections.Legacy;
     using Projections.Syndication.Modules;
 
@@ -39,6 +40,9 @@ protected override void Load(ContainerBuilder builder)
                 .RegisterType<ProblemDetailsHelper>()
                 .AsSelf();
 
+            builder.RegisterType<Nuts3Service>()
+                .SingleInstance();
+
             builder.Populate(_services);
         }
     }

src/PostalRegistry.Api.Oslo/Nuts/Nuts3Service.cs

@@ -0,0 +1,59 @@
+namespace PostalRegistry.Api.Oslo.Nuts
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Globalization;
+    using System.IO;
+    using System.Linq;
+    using System.Text;
+    using CsvHelper;
+    using CsvHelper.Configuration;
+
+    public sealed class Nuts3Service
+    {
+        private const string Nuts3FileName = "nuts3_postal_v1.csv";
+        private readonly List<Nuts3Record> _nuts3Records = new List<Nuts3Record>();
+
+        public Nuts3Service()
+        {
+            var filePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Nuts", Nuts3FileName);
+
+            if (!File.Exists(filePath))
+            {
+                // Handle the case where the file does not exist
+                throw new FileNotFoundException("NUTS3 CSV file not found.");
+            }
+
+            var csvConfiguration = new CsvConfiguration(CultureInfo.InvariantCulture){
+                Delimiter = ";",
+                HasHeaderRecord = true,
+                Encoding = Encoding.UTF8,
+                Quote = '\''
+            };
+
+            using var reader = new StreamReader(filePath);
+            using var csvReader = new CsvReader(reader, csvConfiguration);
+            csvReader.Read(); // skip first record Header as ReadHeader doesn't work
+
+            while (csvReader.Read())
+            {
+                var nuts3Code = csvReader.GetField<string>(0);
+                var postalCode = csvReader.GetField<string>(1);
+
+                _nuts3Records.Add(new Nuts3Record(nuts3Code, postalCode));
+            }
+        }
+
+        public Nuts3Record? GetNuts3ByPostalCode(string postalCode)
+        {
+            return _nuts3Records.FirstOrDefault(x => x.PostalCode == postalCode);
+        }
+
+        public IEnumerable<Nuts3Record> GetPostalCodesByNuts3(string nuts3Code)
+        {
+            return _nuts3Records.Where(x => string.Equals(x.Nuts3Code, nuts3Code, StringComparison.OrdinalIgnoreCase));
+        }
+    }
+
+    public record Nuts3Record(string Nuts3Code, string PostalCode);
+}