import { createHash } from 'node:crypto';

import { auth0Config } from '../apps/api/src/auth0.js';

import { oauthStore, randomOAuthValue, type OAuthStore } from '../apps/api/src/oauth-store.js';

import { DEFAULT_MCP_AUTH_SCOPES } from '../apps/api/src/access-control.js';

import { assertProductionConfiguration } from '../apps/api/src/production-config.js';

assertProductionConfiguration('auth');

const allowedScopes = new Set<string>(DEFAULT_MCP_AUTH_SCOPES);

function oauthError(error: string, description: string, status = 400): Response {

  return Response.json({ error, error_description: description }, { status });

}

export async function authorize(request: Request, store: OAuthStore): Promise<Response> {

  const url = new URL(request.url);

  const clientId = url.searchParams.get('client_id');

  const redirectUri = url.searchParams.get('redirect_uri');

  const responseType = url.searchParams.get('response_type');

  const codeChallenge = url.searchParams.get('code_challenge');

  const challengeMethod = url.searchParams.get('code_challenge_method');

  if (!clientId || !redirectUri)

    return oauthError('invalid_request', 'Missing client or redirect URI');

  const client = await store.getClient(clientId);

  if (!client || !client.redirectUris.includes(redirectUri))

    return oauthError('invalid_request', 'Unknown client or redirect URI');

  if (responseType !== 'code') return oauthError('unsupported_response_type', 'Use code');

  if (!codeChallenge || challengeMethod !== 'S256')

    return oauthError('invalid_request', 'PKCE with S256 is required');

  const requestedScopes = (url.searchParams.get('scope') ?? DEFAULT_MCP_AUTH_SCOPES.join(' '))

    .split(/\s+/)

    .filter(Boolean);

  if (!requestedScopes.length || requestedScopes.some((scope) => !allowedScopes.has(scope)))

    return oauthError('invalid_scope', 'One or more requested OpenClasp scopes are unsupported');

  const transactionId = randomOAuthValue('oc_tx_');

  const auth0Verifier = randomOAuthValue('');

  const auth0Challenge = createHash('sha256').update(auth0Verifier).digest('base64url');

  await store.createTransaction({

    transactionId,

    clientId,

    redirectUri,

    ...(url.searchParams.has('state') ? { downstreamState: url.searchParams.get('state')! } : {}),

    scope: requestedScopes.join(' '),

    codeChallenge,

    auth0Verifier,

  });

  const config = auth0Config();

  const auth0Url = new URL(`${config.issuer}authorize`);

  auth0Url.search = new URLSearchParams({

    client_id: config.dashboardClientId,

    redirect_uri: `${config.publicOrigin}/sso-callback`,

    response_type: 'code',

    scope: 'openid profile email',

    audience: config.audience,

    state: transactionId,

    code_challenge: auth0Challenge,

    code_challenge_method: 'S256',

  }).toString();

  return Response.redirect(auth0Url, 302);

}

export async function GET(request: Request): Promise<Response> {

  try {

    return await authorize(request, oauthStore());

  } catch {

    return oauthError('temporarily_unavailable', 'OAuth service unavailable', 503);

  }

}