import { flag } from 'flags/next'; // Framework adapters: flags/next, flags/sveltekit

// Define a boolean flag
export const showNewCheckout = flag({
  key: 'show-new-checkout',
  description: 'Enable the redesigned checkout flow',
  decide: () => false, // default value
});

// Define a multi-variant flag
export const theme = flag({
  key: 'theme',
  options: [
    { value: 'light', label: 'Light Theme' },
    { value: 'dark', label: 'Dark Theme' },
    { value: 'auto', label: 'Auto' },
  ],
  decide: () => 'auto',
});

// Read flag values (Server Components, Route Handlers, Server Actions)
const isEnabled = await showNewCheckout();
const currentTheme = await theme();

import { flag, dedupe } from 'flags/next';
import { vercelAdapter } from '@flags-sdk/vercel';

type Entities = {
  user?: { id: string; email: string; plan: string };
  team?: { id: string; name: string };
};

// Dedupe ensures identify runs once per request
const identify = dedupe(async (): Promise<Entities> => {
  const session = await getSession();
  return {
    user: session?.user ? {
      id: session.user.id,
      email: session.user.email,
      plan: session.user.plan,
    } : undefined,
  };
});

export const premiumFeature = flag<boolean, Entities>({
  key: 'premium-feature',
  adapter: vercelAdapter(), // reads FLAGS env var automatically
  identify,
});

// app/.well-known/vercel/flags/route.ts
import { createFlagsDiscoveryEndpoint, getProviderData } from 'flags/next';
import * as flags from '../../../../flags';

export const GET = createFlagsDiscoveryEndpoint(() => getProviderData(flags));

// pages/api/vercel/flags.ts
import { verifyAccess, version } from 'flags';
import { getProviderData } from 'flags/next';
import * as flags from '../../../flags';

export default async function handler(req, res) {
  const access = await verifyAccess(req.headers['authorization']);
  if (!access) return res.status(401).json(null);
  res.setHeader('x-flags-sdk-version', version);
  return res.json(getProviderData(flags));
}

// next.config.js (rewrite)
module.exports = {
  async rewrites() {
    return [{ source: '/.well-known/vercel/flags', destination: '/api/vercel/flags' }];
  },
};

export const layoutVariant = flag({
  key: 'layout-variant',
  options: [{ value: 'a' }, { value: 'b' }],
  decide: () => 'a',
});

export const precompute = [layoutVariant];

export function createExampleAdapter() {
  return function exampleAdapter<ValueType, EntitiesType>(): Adapter<ValueType, EntitiesType> {
    return {
      origin(key) { return `https://example.com/flags/${key}`; },
      async decide({ key }): Promise<ValueType> { return false as ValueType; },
    };
  };
}