Use zod to parse/validate environment variables

env.server.ts

import { z } from 'zod';
import { getParams } from './params';

const envSchema = z.object({
  NODE_ENV: z.string(),
  DATABASE_URL: z.string().url(),
  SESSION_SECRET: z.string(),
  AUTH_SECRET: z.string(),
  ENABLE_REGISTRATION: z.boolean().default(false),
  SMTP_HOST: z.string(),
  SMTP_PORT: z.number(),
  SMTP_USERNAME: z.string(),
  SMTP_PASSWORD: z.string(),  
});

export type EnvVars = z.infer<typeof envSchema>;

declare global {
  var __env__: EnvVars;
}

let env: EnvVars;

if (process.env.NODE_ENV === 'production') {
  env = initEnvVars();
} else {
  if (!global.__env__) {
    global.__env__ = initEnvVars();
  }
  env = global.__env__;
}

function initEnvVars(): EnvVars {
  // use params helper to validate and PARSE the env vars
  // @ts-ignore-expect-error
  const [errors, data] = getParams(
    process.env as Record<string, string>,
    envSchema,
  );
  if (errors) {
    throw new Error(JSON.stringify(errors));
  }
  return data;
}

export function getEnvVars(): EnvVars {
  return env;
}