// handler.ts - Lambda handler with proper typing
import {
  APIGatewayProxyEventV2,
  APIGatewayProxyResultV2,
  SQSEvent,
  ScheduledEvent,
  Context,
} from "aws-lambda";

// Reusable across invocations (connection reuse)
let dbConnection: PrismaClient | null = null;

function getDb(): PrismaClient {
  if (!dbConnection) {
    dbConnection = new PrismaClient({
      datasources: {
        db: { url: process.env.DATABASE_URL },
      },
    });
  }
  return dbConnection;
}

// API Gateway handler
export async function apiHandler(
  event: APIGatewayProxyEventV2,
  context: Context
): Promise<APIGatewayProxyResultV2> {
  // Don't wait for event loop to drain (for connection reuse)
  context.callbackWaitsForEmptyEventLoop = false;

  try {
    const method = event.requestContext.http.method;
    const path = event.rawPath;

    if (method === "GET" && path === "/api/users") {
      const db = getDb();
      const users = await db.user.findMany({ take: 50 });
      return response(200, { users });
    }

    if (method === "POST" && path === "/api/users") {
      const body = JSON.parse(event.body ?? "{}");
      const db = getDb();
      const user = await db.user.create({ data: body });
      return response(201, { user });
    }

    return response(404, { error: "Not found" });
  } catch (error) {
    console.error("Handler error:", error);
    return response(500, { error: "Internal server error" });
  }
}

// SQS event handler (batch processing)
export async function sqsHandler(event: SQSEvent): Promise<{ batchItemFailures: Array<{ itemIdentifier: string }> }> {
  const failures: string[] = [];

  for (const record of event.Records) {
    try {
      const body = JSON.parse(record.body);
      await processMessage(body);
    } catch (error) {
      console.error(`Failed to process message ${record.messageId}:`, error);
      failures.push(record.messageId);
    }
  }

  // Partial batch failure reporting (only retry failed messages)
  return {
    batchItemFailures: failures.map((id) => ({ itemIdentifier: id })),
  };
}

// Scheduled event handler (cron)
export async function cronHandler(event: ScheduledEvent): Promise<void> {
  console.log("Running scheduled task at:", event.time);
  const db = getDb();

  // Clean up expired sessions
  const deleted = await db.session.deleteMany({
    where: { expiresAt: { lt: new Date() } },
  });

  console.log(`Cleaned up ${deleted.count} expired sessions`);
}

function response(statusCode: number, body: Record<string, unknown>): APIGatewayProxyResultV2 {
  return {
    statusCode,
    headers: {
      "Content-Type": "application/json",
      "Access-Control-Allow-Origin": process.env.ALLOWED_ORIGIN ?? "*",
    },
    body: JSON.stringify(body),
  };
}

# template.yaml - AWS SAM template
AWSTemplateFormatVersion: "2010-09-09"
Transform: AWS::Serverless-2016-10-31

Globals:
  Function:
    Runtime: nodejs20.x
    Timeout: 30
    MemorySize: 256
    Environment:
      Variables:
        DATABASE_URL: !Ref DatabaseUrl
        NODE_OPTIONS: "--enable-source-maps"

Resources:
  ApiFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: dist/handler.apiHandler
      Events:
        Api:
          Type: HttpApi
          Properties:
            Path: /api/{proxy+}
            Method: ANY
    Metadata:
      BuildMethod: esbuild
      BuildProperties:
        Minify: true
        Target: es2022
        Sourcemap: true
        EntryPoints:
          - src/handler.ts

  QueueProcessor:
    Type: AWS::Serverless::Function
    Properties:
      Handler: dist/handler.sqsHandler
      Events:
        Queue:
          Type: SQS
          Properties:
            Queue: !GetAtt ProcessingQueue.Arn
            BatchSize: 10
            FunctionResponseTypes:
              - ReportBatchItemFailures

  ScheduledCleanup:
    Type: AWS::Serverless::Function
    Properties:
      Handler: dist/handler.cronHandler
      Events:
        Schedule:
          Type: Schedule
          Properties:
            Schedule: rate(1 hour)

  ProcessingQueue:
    Type: AWS::SQS::Queue
    Properties:
      VisibilityTimeout: 180
      RedrivePolicy:
        deadLetterTargetArn: !GetAtt DLQ.Arn
        maxReceiveCount: 3

  DLQ:
    Type: AWS::SQS::Queue

// app/api/geo/route.ts - Edge Function
export const runtime = "edge"; // Run on Vercel Edge Network

export async function GET(request: Request) {
  // Access geo information (available at the edge)
  const country = request.headers.get("x-vercel-ip-country") ?? "US";
  const city = request.headers.get("x-vercel-ip-city") ?? "Unknown";

  // Edge-compatible KV store
  const cachedData = await kv.get(`content:${country}`);
  if (cachedData) {
    return Response.json(cachedData);
  }

  // Lightweight processing at the edge
  const content = await getLocalizedContent(country);
  await kv.set(`content:${country}`, content, { ex: 3600 });

  return Response.json(content, {
    headers: {
      "Cache-Control": "public, s-maxage=3600, stale-while-revalidate=86400",
    },
  });
}

// middleware.ts - Edge Middleware for auth, redirects, A/B testing
import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";

export const config = {
  matcher: ["/dashboard/:path*", "/api/:path*"],
};

export function middleware(request: NextRequest) {
  // Auth check at the edge (fast, runs before serverless function)
  const token = request.cookies.get("session_token");

  if (!token && request.nextUrl.pathname.startsWith("/dashboard")) {
    return NextResponse.redirect(new URL("/login", request.url));
  }

  // A/B test assignment at the edge
  const abCookie = request.cookies.get("ab-pricing");
  if (!abCookie && request.nextUrl.pathname === "/pricing") {
    const variant = Math.random() < 0.5 ? "control" : "new-layout";
    const response = NextResponse.next();
    response.cookies.set("ab-pricing", variant, { maxAge: 60 * 60 * 24 * 30 });

    // Rewrite to variant-specific page
    if (variant === "new-layout") {
      return NextResponse.rewrite(new URL("/pricing-v2", request.url));
    }
    return response;
  }

  return NextResponse.next();
}

// 1. Minimize bundle size with esbuild tree-shaking
// esbuild.config.mjs
import { build } from "esbuild";

await build({
  entryPoints: ["src/handler.ts"],
  bundle: true,
  minify: true,
  platform: "node",
  target: "node20",
  outdir: "dist",
  external: [
    // Don't bundle the AWS SDK (already available in Lambda)
    "@aws-sdk/*",
  ],
  // Tree-shake unused code
  treeShaking: true,
  // Source maps for debugging
  sourcemap: true,
});

// 2. Lazy-load heavy dependencies
let _sharp: typeof import("sharp") | null = null;

async function getSharp() {
  if (!_sharp) {
    _sharp = await import("sharp");
  }
  return _sharp;
}

// Only load sharp when actually processing images
export async function imageHandler(event: APIGatewayProxyEventV2) {
  if (event.rawPath.includes("/resize")) {
    const sharp = await getSharp();
    // Use sharp...
  }
}

// 3. Provisioned concurrency for critical paths
// In SAM template:
// Properties:
//   ProvisionedConcurrencyConfig:
//     ProvisionedConcurrentExecutions: 5

// 4. Keep-alive with scheduled warming (cheaper than provisioned concurrency)
// CloudWatch rule: rate(5 minutes) -> Lambda with warming event
export async function handler(event: unknown) {
  // Check if this is a warming invocation
  if ((event as Record<string, unknown>).source === "serverless-warming") {
    console.log("Warming invocation, returning early");
    return { statusCode: 200, body: "warm" };
  }

  // Normal handler logic...
}

// prisma/schema.prisma - Use Prisma Accelerate or Data Proxy for serverless
datasource db {
  provider = "postgresql"
  // Direct connection for migrations
  url      = env("DATABASE_URL")
  // Pooled connection for serverless runtime
  directUrl = env("DIRECT_DATABASE_URL")
}

generator client {
  provider = "prisma-client-js"
}

// For AWS Lambda: Use RDS Proxy
// DATABASE_URL = "postgresql://user:pass@my-rds-proxy.proxy-xxx.region.rds.amazonaws.com:5432/mydb"

// For Vercel/Cloudflare: Use Neon serverless driver or Prisma Accelerate
import { Pool, neonConfig } from "@neondatabase/serverless";
import { PrismaNeon } from "@prisma/adapter-neon";
import { PrismaClient } from "@prisma/client";
import ws from "ws";

// Required for Node.js environments
neonConfig.webSocketConstructor = ws;

const pool = new Pool({ connectionString: process.env.DATABASE_URL });
const adapter = new PrismaNeon(pool);
const prisma = new PrismaClient({ adapter });

// Connection reuse pattern
let client: PrismaClient | null = null;

export function getClient(): PrismaClient {
  if (!client) {
    client = new PrismaClient({
      log: process.env.NODE_ENV === "development" ? ["query"] : [],
    });
  }
  return client;
}