feat: init payments + split payment in project workspace

- initProjectPayments: crea Acconto 50%/Saldo 50% se il progetto non ha pagamenti
- splitPayment: divide un pagamento in due rate con importi custom
- SplitPaymentForm: form client interattivo con anteprima live della rata 2
- PaymentsTab: stato vuoto con CTA + pulsante Dividi per ogni riga
- projectId prop opzionale per attivare le feature solo nel contesto progetto

src/app/admin/projects/[id]/page.tsx

@@ -86,6 +86,7 @@ export default async function ProjectDetailPage({
             payments={payments}
             acceptedTotal={project.accepted_total ?? "0"}
             clientId={id}
+            projectId={id}
           />
         </TabsContent>
 

src/app/admin/projects/project-actions.ts

@@ -4,7 +4,7 @@ import { revalidatePath } from "next/cache";
 import { getServerSession } from "next-auth";
 import { authOptions } from "@/lib/auth";
 import { db } from "@/db";
-import { projects, clients } from "@/db/schema";
+import { projects, clients, payments } from "@/db/schema";
 import { eq } from "drizzle-orm";
 import { nanoid } from "nanoid";
 
@@ -53,3 +53,58 @@ export async function updateProjectAcceptedTotal(projectId: string, acceptedTota
   await db.update(projects).set({ accepted_total: acceptedTotal }).where(eq(projects.id, projectId));
   revalidatePath(`/admin/projects/${projectId}`);
 }
+
+// Creates Acconto 50% + Saldo 50% stubs for a project that has no payments yet.
+export async function initProjectPayments(projectId: string): Promise<void> {
+  await requireAdmin();
+  const rows = await db
+    .select({ accepted_total: projects.accepted_total })
+    .from(projects)
+    .where(eq(projects.id, projectId))
+    .limit(1);
+  if (!rows[0]) throw new Error("Progetto non trovato");
+  const total = parseFloat(rows[0].accepted_total ?? "0");
+  const half = (total / 2).toFixed(2);
+  await db.insert(payments).values([
+    { project_id: projectId, label: "Acconto 50%", amount: half, status: "da_saldare" },
+    { project_id: projectId, label: "Saldo 50%", amount: half, status: "da_saldare" },
+  ]);
+  revalidatePath(`/admin/projects/${projectId}`);
+}
+
+// Splits one payment into two with custom amounts. The original row keeps
+// its label (+ " – Rata 1"), a new row is created with the remainder.
+export async function splitPayment(
+  paymentId: string,
+  projectId: string,
+  firstAmountStr: string
+): Promise<void> {
+  await requireAdmin();
+  const first = parseFloat(firstAmountStr);
+  if (isNaN(first) || first <= 0) throw new Error("Importo non valido");
+
+  const rows = await db.select().from(payments).where(eq(payments.id, paymentId)).limit(1);
+  if (!rows[0]) throw new Error("Pagamento non trovato");
+
+  const original = rows[0];
+  const total = parseFloat(original.amount);
+  const second = parseFloat((total - first).toFixed(2));
+  if (second <= 0) throw new Error("Il primo importo deve essere inferiore al totale");
+
+  // Strip any existing " – Rata N" suffix so re-splits stay clean.
+  const baseLabel = original.label.replace(/ – Rata \d+$/, "");
+
+  await db
+    .update(payments)
+    .set({ amount: first.toFixed(2), label: `${baseLabel} – Rata 1` })
+    .where(eq(payments.id, paymentId));
+
+  await db.insert(payments).values({
+    project_id: projectId,
+    label: `${baseLabel} – Rata 2`,
+    amount: second.toFixed(2),
+    status: original.status,
+  });
+
+  revalidatePath(`/admin/projects/${projectId}`);
+}

src/components/admin/SplitPaymentForm.tsx

@@ -0,0 +1,91 @@
+"use client";
+
+import { useState, useTransition } from "react";
+import { useRouter } from "next/navigation";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { splitPayment } from "@/app/admin/projects/project-actions";
+
+interface Props {
+  paymentId: string;
+  projectId: string;
+  currentAmount: number;
+}
+
+export function SplitPaymentForm({ paymentId, projectId, currentAmount }: Props) {
+  const [open, setOpen] = useState(false);
+  const [firstAmount, setFirstAmount] = useState("");
+  const [isPending, startTransition] = useTransition();
+  const router = useRouter();
+
+  const first = parseFloat(firstAmount) || 0;
+  const second = parseFloat((currentAmount - first).toFixed(2));
+  const isValid = first > 0 && first < currentAmount;
+
+  function handleOpen() {
+    setFirstAmount((currentAmount / 2).toFixed(2));
+    setOpen(true);
+  }
+
+  function handleSubmit(e: React.FormEvent) {
+    e.preventDefault();
+    if (!isValid) return;
+    startTransition(async () => {
+      await splitPayment(paymentId, projectId, first.toFixed(2));
+      setOpen(false);
+      setFirstAmount("");
+      router.refresh();
+    });
+  }
+
+  if (!open) {
+    return (
+      <Button type="button" size="sm" variant="ghost" className="text-xs h-7 px-2" onClick={handleOpen}>
+        Dividi
+      </Button>
+    );
+  }
+
+  return (
+    <form onSubmit={handleSubmit} className="mt-3 pt-3 border-t border-gray-100">
+      <p className="text-xs text-gray-500 mb-2">Imposta il primo importo — il resto diventa la seconda rata:</p>
+      <div className="flex items-start gap-2">
+        <div className="flex-1 space-y-1">
+          <Input
+            type="number"
+            step="0.01"
+            min="0.01"
+            max={(currentAmount - 0.01).toFixed(2)}
+            value={firstAmount}
+            onChange={(e) => setFirstAmount(e.target.value)}
+            className="h-8 text-sm"
+            required
+          />
+          {isValid && (
+            <p className="text-xs text-[#71717a]">
+              Rata 1: € {first.toLocaleString("it-IT", { minimumFractionDigits: 2 })} &nbsp;|&nbsp;
+              Rata 2: € {second.toLocaleString("it-IT", { minimumFractionDigits: 2 })}
+            </p>
+          )}
+          {firstAmount && !isValid && (
+            <p className="text-xs text-red-500">
+              Inserisci un importo tra 0,01 e {(currentAmount - 0.01).toLocaleString("it-IT", { minimumFractionDigits: 2 })}
+            </p>
+          )}
+        </div>
+        <Button type="submit" size="sm" className="h-8" disabled={!isValid || isPending}>
+          {isPending ? "…" : "Conferma"}
+        </Button>
+        <Button
+          type="button"
+          size="sm"
+          variant="ghost"
+          className="h-8"
+          onClick={() => { setOpen(false); setFirstAmount(""); }}
+        >
+          Annulla
+        </Button>
+      </div>
+    </form>
+  );
+}

src/components/admin/tabs/PaymentsTab.tsx

@@ -2,15 +2,18 @@ import {
   updatePaymentStatus,
   updateAcceptedTotal,
 } from "@/app/admin/clients/[id]/actions";
+import { initProjectPayments } from "@/app/admin/projects/project-actions";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
+import { SplitPaymentForm } from "@/components/admin/SplitPaymentForm";
 import type { Payment } from "@/db/schema";
 
 type Props = {
   payments: Payment[];
   acceptedTotal: string;
   clientId: string;
+  projectId?: string; // set only from project detail page — enables init & split
 };
 
 const statusLabels: Record<string, string> = {
@@ -19,7 +22,7 @@ const statusLabels: Record<string, string> = {
   saldato: "Saldato",
 };
 
-export async function PaymentsTab({ payments, acceptedTotal, clientId }: Props) {
+export async function PaymentsTab({ payments, acceptedTotal, clientId, projectId }: Props) {
   return (
     <div className="space-y-6 max-w-md">
       {/* Accepted total */}
@@ -53,20 +56,50 @@ export async function PaymentsTab({ payments, acceptedTotal, clientId }: Props)
         </p>
       </div>
 
+      {/* Empty state — project has no payments yet */}
+      {projectId && payments.length === 0 && (
+        <div className="bg-white border border-dashed border-gray-300 rounded-lg p-6 text-center">
+          <p className="text-sm text-[#71717a] mb-4">
+            Nessun pagamento configurato. Crea le rate standard Acconto e Saldo.
+          </p>
+          <form
+            action={async () => {
+              "use server";
+              await initProjectPayments(projectId);
+            }}
+          >
+            <Button type="submit" size="sm">
+              Crea Acconto &amp; Saldo
+            </Button>
+          </form>
+        </div>
+      )}
+
       {/* Payment rows */}
-      {payments.map((p) => (
+      {payments.map((p) => {
+        const amount = parseFloat(p.amount);
+        return (
           <div
             key={p.id}
             className="bg-white border border-gray-200 rounded-lg p-4"
           >
             <div className="flex items-center justify-between mb-2">
               <h3 className="font-medium text-gray-900">{p.label}</h3>
+              <div className="flex items-center gap-2">
                 <span className="text-sm text-gray-600">
                   €{" "}
-              {parseFloat(p.amount).toLocaleString("it-IT", {
+                  {amount.toLocaleString("it-IT", {
                     minimumFractionDigits: 2,
                   })}
                 </span>
+                {projectId && amount > 0 && (
+                  <SplitPaymentForm
+                    paymentId={p.id}
+                    projectId={projectId}
+                    currentAmount={amount}
+                  />
+                )}
+              </div>
             </div>
             <form
               action={async (fd: FormData) => {
@@ -91,7 +124,8 @@ export async function PaymentsTab({ payments, acceptedTotal, clientId }: Props)
               </Button>
             </form>
           </div>
-      ))}
+        );
+      })}
     </div>
   );
 }