feat(POS-010): completed feature

project/src/modules/pos/api/pos.routes.ts

@@ -640,4 +640,48 @@ export async function registerPosRoutes(app: FastifyInstance, deps: PosRouteDeps
     return reply.send(result.rows[0]);
   });
 
+
+  // ── POS-010: Discount validation ──────────────────────────────────────────
+
+  app.post('/pos/discounts/validate', {
+    schema: {
+      tags: ['POS Terminal'],
+      summary: 'Validate discount before applying',
+      body: {
+        type: 'object',
+        required: ['unitPriceCents', 'discountCents'],
+        properties: {
+          unitPriceCents: { type: 'integer', minimum: 0 },
+          discountCents: { type: 'integer', minimum: 0 },
+          discountPercent: { type: 'number', minimum: 0, maximum: 100 },
+          role: { type: 'string', enum: ['admin', 'pos_manager', 'pos_cashier'] },
+        },
+      },
+      response: { 401: errorSchema, 403: errorSchema },
+    } as FastifySchema,
+  }, async (request, reply) => {
+    const user = await authenticate(request);
+    requireAnyRole(user, ['admin', 'pos_manager', 'pos_cashier'] as ReadonlyArray<Role>);
+    const body = (request.body ?? {}) as { unitPriceCents?: number; discountCents?: number; discountPercent?: number; role?: string };
+    const unitPriceCents = body.unitPriceCents ?? 0;
+    const discountCents = body.discountCents ?? 0;
+    const discountPercent = body.discountPercent ?? (unitPriceCents > 0 ? (discountCents / unitPriceCents) * 100 : 0);
+
+    // Cashiers capped at 50% per item
+    const maxPercent = user.role === 'pos_manager' || user.role === 'admin' ? 100 : 50;
+    if (discountPercent > maxPercent) {
+      throw new AppError(403, 'DISCOUNT_EXCEEDED', `Discount ${discountPercent.toFixed(0)}% exceeds max ${maxPercent}% for role`);
+    }
+    if (discountCents > unitPriceCents) {
+      throw new AppError(400, 'INVALID_DISCOUNT', 'Discount cannot exceed unit price');
+    }
+    return reply.send({
+      valid: true,
+      maxPercent,
+      appliedPercent: discountPercent,
+      appliedCents: discountCents,
+      finalPriceCents: unitPriceCents - discountCents,
+    });
+  });
+
 }