initial commit

lib/InvoiceNo.php

@@ -0,0 +1,29 @@
+<?php
+function nextInvoiceNo(PDO $pdo, int $year): string {
+  $pdo->beginTransaction();
+  try {
+    // row lock (InnoDB)
+    $stmt = $pdo->prepare("SELECT last_number FROM invoice_counters WHERE year = :y FOR UPDATE");
+    $stmt->execute([':y' => $year]);
+    $row = $stmt->fetch(PDO::FETCH_ASSOC);
+
+    if (!$row) {
+      $last = 0;
+      $pdo->prepare("INSERT INTO invoice_counters (year, last_number) VALUES (:y, 0)")
+          ->execute([':y' => $year]);
+    } else {
+      $last = (int)$row['last_number'];
+    }
+
+    $next = $last + 1;
+    $pdo->prepare("UPDATE invoice_counters SET last_number = :n WHERE year = :y")
+        ->execute([':n' => $next, ':y' => $year]);
+
+    $pdo->commit();
+
+    return sprintf("RE-%d-%04d", $year, $next);
+  } catch (Throwable $e) {
+    $pdo->rollBack();
+    throw $e;
+  }
+}