feat: implement set-based invoice payment calculations and enhance email logging configuration

Fuchs.Tests/ProcessWebComServiceTests.cs

@@ -70,6 +70,7 @@ public class ProcessWebComServiceTests
     private sealed class CapturingComService : ProcessWebComService
     {
         public readonly List<(bool success, List<string> log)> Entries = new();
+        public readonly List<string> Configs = new();
 
         public CapturingComService(
             IOptions<ProcessWebComSettings> settings,
@@ -83,6 +84,7 @@ public class ProcessWebComServiceTests
             DateTime sent, bool success, IEnumerable<string> errors)
         {
             Entries.Add((success, errors.ToList()));
+            Configs.Add(config);
             return Task.CompletedTask;
         }
     }
@@ -267,6 +269,90 @@ public class ProcessWebComServiceTests
         Assert.Equal(when, pl.Single(p => p.ParameterName == "@DateSent").Value);
     }
 
+    // ── Audit-log config: fds__emaillog.config must be the JSON fds_wgd_lastEmails parses ─
+    // Regression: the service logged config = "" on every path; OPENJSON('') throws, which took
+    // the "last emails" dashboard widget down and lost who/what/attachments from the audit trail.
+    [Fact]
+    public void BuildAuditConfig_FullInput_ProducesLegacyShapeWithoutBody()
+    {
+        var files = new Dictionary<string, byte[]> { ["Rechnung R2026-0119.pdf"] = [1, 2], ["x.xml"] = [3] };
+
+        string json = ProcessWebComService.BuildAuditConfig(
+            "SanitärFuchs - Rechnung", "buchhaltung@example.de", "Buchhaltung Erne", "chef@example.de", files.Keys);
+
+        var o = JObject.Parse(json);
+        Assert.Equal("SanitärFuchs - Rechnung", (string?)o["subject"]);
+        Assert.Equal("", (string?)o["from"]);
+        Assert.Equal(new[] { "\"Buchhaltung Erne\" <buchhaltung@example.de>" }, o["to"]!.Select(t => (string?)t));
+        Assert.Equal(new[] { "chef@example.de" }, o["cc"]!.Select(t => (string?)t));
+        Assert.Empty(o["bcc"]!);
+        Assert.Equal(new[] { "Rechnung R2026-0119.pdf", "x.xml" }, o["attachments"]!.Select(t => (string?)t));
+        Assert.Null(o["body"]);                                  // never the HTML body
+        Assert.DoesNotContain("AQI=", json);                     // never attachment bytes (base64 of 1,2)
+    }
+
+    [Theory]
+    [InlineData(null,  "a@b.de", "a@b.de")]                      // no name → bare address
+    [InlineData("",    "a@b.de", "a@b.de")]
+    [InlineData("  ",  "a@b.de", "a@b.de")]
+    [InlineData("Ann", "a@b.de", "\"Ann\" <a@b.de>")]         // name → quoted display form the widget unwraps
+    [InlineData(" Ann ", "a@b.de", "\"Ann\" <a@b.de>")]
+    public void BuildAuditConfig_RecipientName_FormatsToArrayEntry(string? name, string email, string expected)
+    {
+        var o = JObject.Parse(ProcessWebComService.BuildAuditConfig("S", email, name, null, null));
+
+        Assert.Equal(new[] { expected }, o["to"]!.Select(t => (string?)t));
+        Assert.Empty(o["cc"]!);
+        Assert.Empty(o["attachments"]!);
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    public void BuildAuditConfig_NullOrEmptySubject_StillValidJson(string? subject)
+    {
+        var o = JObject.Parse(ProcessWebComService.BuildAuditConfig(subject!, "a@b.de", null, null, null));
+        Assert.Equal("", (string?)o["subject"]);
+    }
+
+    public static IEnumerable<object[]> AllAuditPaths() =>
+    [
+        [ "success",       HttpStatusCode.OK,                  true,  "kunde@example.de" ],
+        [ "api-error",     HttpStatusCode.InternalServerError, true,  "kunde@example.de" ],
+        [ "disabled",      HttpStatusCode.OK,                  false, "kunde@example.de" ],
+        [ "invalid-email", HttpStatusCode.OK,                  true,  "not-an-email"     ],
+    ];
+
+    [Theory]
+    [MemberData(nameof(AllAuditPaths))]
+    public async Task SendEmailAsync_EveryAuditPath_LogsParsableConfigWithRecipientSubjectAndAttachments(
+        string path, HttpStatusCode status, bool enabled, string email)
+    {
+        var svc = CreateCapturing(new StubHandler(status), enabled: enabled);
+        var att = new Dictionary<string, byte[]> { ["Mahnung.pdf"] = [9, 9] };
+
+        await svc.SendEmailAsync("inv_cfg_" + path, "Subj " + path, "<p>x</p>", email, "Kunde", att);
+
+        string config = Assert.Single(svc.Configs);
+        var o = JObject.Parse(config);                            // was "" → OPENJSON error in fds_wgd_lastEmails
+        Assert.Equal("Subj " + path, (string?)o["subject"]);
+        Assert.Equal(new[] { $"\"Kunde\" <{email}>" }, o["to"]!.Select(t => (string?)t));
+        Assert.Equal(new[] { "Mahnung.pdf" }, o["attachments"]!.Select(t => (string?)t));
+    }
+
+    [Fact]
+    public async Task SendEmailAsync_OverrideRecipientSet_ConfigRecordsActualRecipientAndPrefixedSubject()
+    {
+        var svc = CreateCapturing(new StubHandler(HttpStatusCode.OK), overrideRecipient: "dev-inbox@example.test");
+
+        await svc.SendEmailAsync("inv_cfg_ovr", "Subject", "<p>x</p>", "kunde@example.de", "Kunde", null, cc: "cc@example.de");
+
+        var o = JObject.Parse(Assert.Single(svc.Configs));
+        Assert.Equal(new[] { "\"Kunde\" <dev-inbox@example.test>" }, o["to"]!.Select(t => (string?)t)); // where it really went
+        Assert.Empty(o["cc"]!);                                                                          // cc is dropped by the override
+        Assert.StartsWith("[DEV → kunde@example.de] ", (string?)o["subject"]);                     // original recipient stays traceable
+    }
+
     // ── Dev/test recipient override safety net ─────────────────────────────────
     [Fact]
     public async Task SendEmailAsync_OverrideRecipientSet_RedirectsToOverrideAddress()