Send email with Next.js

// Local demonstration only. Do not expose this endpoint as a production mail service.
export async function handleDemo(request, env=process.env, send=fetch) {
 if(env.NODE_ENV!=='development')return Response.json({error:'Demo disabled in production'}, {status:404});
 const origin=request.headers.get('origin');
 let localOrigin=false;
 try {const u=new URL(origin);localOrigin=u.protocol==='http:'&&['localhost','127.0.0.1'].includes(u.hostname)&&u.host===request.headers.get('host');} catch {}
 if(!localOrigin)return Response.json({error:'Same-origin local requests only'}, {status:403});
 const payload={from:env.SENDAR_FROM||'hello@example.com',to:[env.SENDAR_TO||'reader@example.net'],subject:'Your booking is confirmed',text:'Demo booking: 12 October, 10:00 UTC. Reference DEMO-123.'};
 if(env.SENDAR_SEND!=='1')return Response.json({mode:'preview',message:'No email sent. Configure a verified sender and controlled recipient before enabling live sending.',payload});
 if(!env.SENDAR_API_KEY||!env.SENDAR_FROM||!env.SENDAR_TO)return Response.json({error:'Configure SENDAR_API_KEY, SENDAR_FROM and SENDAR_TO'}, {status:400});
 try {
  const response=await send('https://sendar.app/api/emails',{method:'POST',headers:{Authorization:`Bearer ${env.SENDAR_API_KEY}`,'Content-Type':'application/json'},body:JSON.stringify(payload),signal:AbortSignal.timeout(15000)});
  const data=await response.json();
  if(!response.ok)return Response.json({error:`Sendar returned HTTP ${response.status}. Inspect your email log before retrying.`},{status:502});
  return Response.json({mode:'live',id:data.id,status:data.status,message:'Inspect the Sendar email log and recipient inbox. Acceptance does not guarantee delivery.'});
 } catch {return Response.json({error:'Outcome uncertain. Inspect your Sendar email log before trying again.'},{status:502});}
}