Add invoice model and validation rules

src/ImportAssist.Cli/ImportAssist.Cli.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\ImportAssist.Core\ImportAssist.Core.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

src/ImportAssist.Cli/Program.cs

@@ -0,0 +1,24 @@
+using ImportAssist.Core;
+
+InvoiceRow[] rows =
+[
+    new("INV-001", "C-100", "125.50", "EUR"),
+    new("INV-002", "",      "89.00",  "EUR"),
+    new("INV-003", "C-300", "abc",    "EUR"),
+    new("INV-004", "C-400", "-10.00", "EUR"),
+    new("",        "",      "0",      "EUR")
+];
+
+foreach (var row in rows)
+{
+    var errors = InvoiceValidator.Validate(row);
+
+    var invoiceId = string.IsNullOrWhiteSpace(row.InvoiceId)
+        ? "(ohne Rechnungsnummer)"
+        : row.InvoiceId;
+
+    Console.WriteLine(
+        errors.Count == 0
+            ? $"{invoiceId}: Gültig"
+            : $"{invoiceId}: {string.Join("; ", errors)}");
+}

src/ImportAssist.Core/ImportAssist.Core.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

src/ImportAssist.Core/InvoiceRow.cs

@@ -0,0 +1,7 @@
+namespace ImportAssist.Core;
+
+public sealed record InvoiceRow(
+    string InvoiceId,
+    string CustomerId,
+    string Amount,
+    string Currency);

src/ImportAssist.Core/InvoiceValidator.cs

@@ -0,0 +1,40 @@
+using System.Globalization;
+
+namespace ImportAssist.Core;
+
+public static class InvoiceValidator
+{
+    public static IReadOnlyList<string> Validate(InvoiceRow row)
+    {
+        var errors = new List<string>();
+
+        if (string.IsNullOrWhiteSpace(row.InvoiceId))
+        {
+            errors.Add("Rechnungsnummer fehlt.");
+        }
+
+        if (string.IsNullOrWhiteSpace(row.CustomerId))
+        {
+            errors.Add("Kundennummer fehlt.");
+        }
+
+        var allowedStyles =
+            NumberStyles.AllowLeadingSign |
+            NumberStyles.AllowDecimalPoint;
+
+        if (!decimal.TryParse(
+                row.Amount,
+                allowedStyles,
+                CultureInfo.InvariantCulture,
+                out var amount))
+        {
+            errors.Add("Betrag ist keine gültige Zahl.");
+        }
+        else if (amount <= 0)
+        {
+            errors.Add("Betrag muss größer als null sein.");
+        }
+
+        return errors;
+    }
+}