Add PDF invoice generation: implement backend API, introduce PdfService, update frontend repository and UI with download logic, and mark roadmap task complete.

backend/services/billing/billing-service/build.gradle.kts

@@ -21,6 +21,7 @@ dependencies {
   implementation(libs.spring.boot.starter.validation)
   implementation(libs.spring.boot.starter.actuator)
   implementation(libs.jackson.module.kotlin)
+  implementation(libs.openpdf)
   implementation(libs.spring.cloud.starter.consul.discovery)
   implementation(libs.micrometer.tracing.bridge.brave)
   implementation(libs.zipkin.reporter.brave)

backend/services/billing/billing-service/src/main/kotlin/at/mocode/billing/api/rest/BillingController.kt

@@ -5,11 +5,14 @@ package at.mocode.billing.api.rest
 import at.mocode.billing.domain.model.Buchung
 import at.mocode.billing.domain.model.BuchungsTyp
 import at.mocode.billing.domain.model.TeilnehmerKonto
+import at.mocode.billing.service.PdfService
 import at.mocode.billing.service.TeilnehmerKontoService
 import at.mocode.core.domain.serialization.InstantSerializer
 import jakarta.validation.Valid
 import jakarta.validation.constraints.NotBlank
 import jakarta.validation.constraints.NotNull
+import org.springframework.http.HttpHeaders
+import org.springframework.http.MediaType
 import org.springframework.http.ResponseEntity
 import org.springframework.web.bind.annotation.*
 import kotlin.time.Instant
@@ -20,7 +23,8 @@ import kotlinx.serialization.Serializable
 @RestController
 @RequestMapping("/api/billing")
 class BillingController(
-    private val kontoService: TeilnehmerKontoService
+    private val kontoService: TeilnehmerKontoService,
+    private val pdfService: PdfService
 ) {
 
     data class KontoDto(
@@ -106,6 +110,19 @@ class BillingController(
         return ResponseEntity.ok(konto.toDto())
     }
 
+    @GetMapping("/konten/{kontoId}/rechnung", produces = [MediaType.APPLICATION_PDF_VALUE])
+    fun downloadRechnung(@PathVariable kontoId: String): ResponseEntity<ByteArray> {
+        val uuid = try { Uuid.parse(kontoId) } catch (_: Exception) { return ResponseEntity.badRequest().build() }
+        val konto = kontoService.getKontoById(uuid) ?: return ResponseEntity.notFound().build()
+
+        val pdf = pdfService.generateRechnung(konto)
+
+        return ResponseEntity.ok()
+            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"rechnung_${konto.personName.replace(" ", "_")}.pdf\"")
+            .contentType(MediaType.APPLICATION_PDF)
+            .body(pdf)
+    }
+
     private fun TeilnehmerKonto.toDto() = KontoDto(
         kontoId = kontoId.toString(),
         veranstaltungId = veranstaltungId.toString(),

backend/services/billing/billing-service/src/main/kotlin/at/mocode/billing/service/PdfService.kt

@@ -0,0 +1,92 @@
+@file:OptIn(ExperimentalUuidApi::class)
+
+package at.mocode.billing.service
+
+import at.mocode.billing.domain.model.TeilnehmerKonto
+import at.mocode.billing.domain.repository.BuchungRepository
+import com.lowagie.text.*
+import com.lowagie.text.pdf.PdfPCell
+import com.lowagie.text.pdf.PdfPTable
+import com.lowagie.text.pdf.PdfWriter
+import org.springframework.stereotype.Service
+import java.awt.Color
+import java.io.ByteArrayOutputStream
+import java.text.NumberFormat
+import java.util.*
+import kotlin.uuid.ExperimentalUuidApi
+
+@Service
+class PdfService(
+    private val buchungRepository: BuchungRepository
+) {
+
+    fun generateRechnung(konto: TeilnehmerKonto): ByteArray {
+        val out = ByteArrayOutputStream()
+        val document = Document(PageSize.A4)
+        PdfWriter.getInstance(document, out)
+
+        document.open()
+
+        // Header
+        val titleFont = FontFactory.getFont(FontFactory.HELVETICA_BOLD, 18f)
+        val header = Paragraph("Rechnung / Kontoauszug", titleFont)
+        header.alignment = Element.ALIGN_CENTER
+        header.spacingAfter = 20f
+        document.add(header)
+
+        // Teilnehmer Info
+        val infoFont = FontFactory.getFont(FontFactory.HELVETICA, 12f)
+        document.add(Paragraph("Teilnehmer: ${konto.personName}", infoFont))
+        document.add(Paragraph("Datum: ${java.time.LocalDate.now()}", infoFont))
+        document.add(Paragraph("Konto-ID: ${konto.kontoId}", infoFont))
+        document.add(Paragraph("Veranstaltung: ${konto.veranstaltungId}", infoFont))
+        document.add(Paragraph(" ", infoFont))
+
+        // Tabelle
+        val table = PdfPTable(4)
+        table.widthPercentage = 100f
+        table.setWidths(floatArrayOf(2f, 4f, 2f, 2f))
+
+        val headFont = FontFactory.getFont(FontFactory.HELVETICA_BOLD, 11f)
+
+        fun addCell(text: String, font: Font = headFont, bgColor: Color? = Color.LIGHT_GRAY) {
+            val cell = PdfPCell(Phrase(text, font))
+            if (bgColor != null) cell.backgroundColor = bgColor
+            cell.setPadding(5f)
+            table.addCell(cell)
+        }
+
+        addCell("Datum")
+        addCell("Zweck")
+        addCell("Typ")
+        addCell("Betrag")
+
+        val buchungen = buchungRepository.findByKonto(konto.kontoId)
+        val currencyFormat = NumberFormat.getCurrencyInstance(Locale.GERMANY)
+        val bodyFont = FontFactory.getFont(FontFactory.HELVETICA, 10f)
+
+        buchungen.forEach { b ->
+            addCell(b.gebuchtAm.toString().substring(0, 10), bodyFont, null)
+            addCell(b.verwendungszweck, bodyFont, null)
+            addCell(b.typ.name, bodyFont, null)
+            val betragStr = currencyFormat.format(b.betragCent / 100.0)
+            addCell(betragStr, bodyFont, null)
+        }
+
+        document.add(table)
+
+        // Saldo
+        val saldoFont = FontFactory.getFont(FontFactory.HELVETICA_BOLD, 14f)
+        val saldoPara = Paragraph(" ", saldoFont)
+        saldoPara.spacingBefore = 20f
+        document.add(saldoPara)
+
+        val saldoText = "Gesamtsaldo: ${currencyFormat.format(konto.saldoCent / 100.0)}"
+        val finalSaldo = Paragraph(saldoText, saldoFont)
+        finalSaldo.alignment = Element.ALIGN_RIGHT
+        document.add(finalSaldo)
+
+        document.close()
+        return out.toByteArray()
+    }
+}