import crypto from 'crypto';
import { getDb } from './db.js';
import { createRemoteJWKSet, jwtVerify } from 'jose';
import { assertSafeUrl } from './ssrf.js';

const SESSION_COOKIE = 'enkelbudget_session';
const TRANSACTION_COOKIE = 'enkelbudget_auth_tx';
const discoveryCache = new Map();
const jwksCache = new Map();

function getJwks(jwksUri) {
  if (!jwksCache.has(jwksUri)) {
    jwksCache.set(jwksUri, createRemoteJWKSet(new URL(jwksUri)));
  }
  return jwksCache.get(jwksUri);
}

function base64url(input) {
  return Buffer.from(input)
    .toString('base64')
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/g, '');
}

function sha256base64url(input) {
  return crypto.createHash('sha256').update(input).digest('base64url');
}

function parseList(value) {
  return String(value || '')
    .split(',')
    .map(item => item.trim())
    .filter(Boolean);
}

function parseCookies(header) {
  const cookies = {};
  for (const part of String(header || '').split(';')) {
    const index = part.indexOf('=');
    if (index < 0) continue;
    const name = part.slice(0, index).trim();
    const value = part.slice(index + 1).trim();
    cookies[name] = decodeURIComponent(value);
  }
  return cookies;
}

function signValue(value, secret) {
  return crypto.createHmac('sha256', secret).update(value).digest('base64url');
}

function encodeSignedValue(value, secret) {
  return `${value}.${signValue(value, secret)}`;
}

function decodeSignedValue(raw, secret) {
  if (!raw) return null;
  const index = raw.lastIndexOf('.');
  if (index < 0) return null;
  const value = raw.slice(0, index);
  const signature = raw.slice(index + 1);
  const expected = signValue(value, secret);
  const signatureBuffer = Buffer.from(signature);
  const expectedBuffer = Buffer.from(expected);
  if (signatureBuffer.length !== expectedBuffer.length) return null;
  if (!crypto.timingSafeEqual(signatureBuffer, expectedBuffer)) return null;
  return value;
}

function serializeCookie(name, value, options = {}) {
  const parts = [`${name}=${encodeURIComponent(value)}`];
  if (options.maxAge !== undefined) parts.push(`Max-Age=${options.maxAge}`);
  if (options.httpOnly !== false) parts.push('HttpOnly');
  parts.push(`Path=${options.path || '/'}`);
  parts.push(`SameSite=${options.sameSite || 'Lax'}`);
  if (options.secure) parts.push('Secure');
  return parts.join('; ');
}

function normalizeIssuer(value) {
  return String(value || '').trim().replace(/\/+$/, '');
}

function normalizeAbsoluteUrl(value) {
  const raw = String(value || '').trim();
  if (!raw) return '';
  if (raw.startsWith('ttps://')) return `h${raw}`;
  if (raw.startsWith('tps://')) return `ht${raw}`;
  return raw;
}

function getEnvAuthDefaults() {
  const issuer = normalizeIssuer(process.env.OIDC_ISSUER);
  const discoveryUrl = String(process.env.OIDC_DISCOVERY_URL || '').trim()
    || (issuer ? `${issuer}/.well-known/openid-configuration` : '');
  const clientId = String(process.env.OIDC_CLIENT_ID || '').trim();
  const clientSecret = String(process.env.OIDC_CLIENT_SECRET || '').trim();
  const appBaseUrl = normalizeIssuer(process.env.APP_BASE_URL);
  const redirectUri = normalizeAbsoluteUrl(process.env.OIDC_REDIRECT_URI)
    || (appBaseUrl ? `${appBaseUrl}/auth/callback` : '');
  const sessionSecret = String(process.env.AUTH_SESSION_SECRET || process.env.SESSION_SECRET || clientSecret).trim();

  return {
    enabled: Boolean(issuer && clientId && clientSecret && redirectUri && sessionSecret),
    issuer,
    discovery_url: discoveryUrl,
    client_id: clientId,
    client_secret: clientSecret,
    redirect_uri: redirectUri,
    scope: String(process.env.OIDC_SCOPE || 'openid profile email groups').trim(),
    session_secret: sessionSecret,
    session_ttl_hours: Math.max(1, parseInt(process.env.AUTH_SESSION_TTL_HOURS || '12', 10) || 12),
    allowed_groups: String(process.env.OIDC_ALLOWED_GROUPS || '').trim(),
    allowed_emails: String(process.env.OIDC_ALLOWED_EMAILS || '').trim(),
    allowed_domains: String(process.env.OIDC_ALLOWED_DOMAINS || '').trim(),
  };
}

function normalizeStoredSettings(input = {}, fallback = {}) {
  const issuer = normalizeIssuer(input.issuer ?? fallback.issuer);
  const discoveryUrl = String((input.discovery_url ?? fallback.discovery_url) || '').trim()
    || (issuer ? `${issuer}/.well-known/openid-configuration` : '');
  const clientId = String((input.client_id ?? fallback.client_id) || '').trim();
  const clientSecret = String((input.client_secret ?? fallback.client_secret) || '').trim();
  const redirectUri = normalizeAbsoluteUrl((input.redirect_uri ?? fallback.redirect_uri) || '');
  const scope = String((input.scope ?? fallback.scope) || 'openid profile email groups').trim() || 'openid profile email groups';
  const sessionSecret = String((input.session_secret ?? fallback.session_secret) || '').trim() || clientSecret;
  const allowedGroups = String((input.allowed_groups ?? fallback.allowed_groups) || '').trim();
  const allowedEmails = String((input.allowed_emails ?? fallback.allowed_emails) || '').trim();
  const allowedDomains = String((input.allowed_domains ?? fallback.allowed_domains) || '').trim();
  const sessionTtlHours = Math.max(1, parseInt(input.session_ttl_hours ?? fallback.session_ttl_hours ?? 12, 10) || 12);
  const explicitEnabled = input.enabled !== undefined ? Boolean(input.enabled) : Boolean(fallback.enabled);

  return {
    enabled: explicitEnabled && Boolean(issuer && clientId && clientSecret && redirectUri && sessionSecret),
    issuer,
    discovery_url: discoveryUrl,
    client_id: clientId,
    client_secret: clientSecret,
    redirect_uri: redirectUri,
    scope,
    session_secret: sessionSecret,
    session_ttl_hours: sessionTtlHours,
    allowed_groups: allowedGroups,
    allowed_emails: allowedEmails,
    allowed_domains: allowedDomains,
  };
}

export async function getAuthSettings() {
  const db = await getDb();
  db.data.auth ||= { settings: {}, sessions: [], pending: [] };
  db.data.auth.settings ||= {};
  db.data.auth.sessions ||= [];
  db.data.auth.pending ||= [];

  const fallback = getEnvAuthDefaults();
  const settings = normalizeStoredSettings(db.data.auth.settings, fallback);
  db.data.auth.settings = {
    ...db.data.auth.settings,
    enabled: settings.enabled,
    issuer: settings.issuer,
    discovery_url: settings.discovery_url,
    client_id: settings.client_id,
    client_secret: settings.client_secret,
    redirect_uri: settings.redirect_uri,
    scope: settings.scope,
    session_secret: settings.session_secret,
    allowed_groups: settings.allowed_groups,
    allowed_emails: settings.allowed_emails,
    allowed_domains: settings.allowed_domains,
    session_ttl_hours: settings.session_ttl_hours,
  };

  return settings;
}

export async function getPublicAuthSettings() {
  const settings = await getAuthSettings();
  return {
    enabled: settings.enabled,
    issuer: settings.issuer,
    discovery_url: settings.discovery_url,
    client_id: settings.client_id,
    redirect_uri: settings.redirect_uri,
    scope: settings.scope,
    session_ttl_hours: settings.session_ttl_hours,
    allowed_groups: settings.allowed_groups,
    allowed_emails: settings.allowed_emails,
    allowed_domains: settings.allowed_domains,
    has_client_secret: Boolean(settings.client_secret),
    has_session_secret: Boolean(settings.session_secret),
    is_valid: Boolean(settings.issuer && settings.client_id && settings.client_secret && settings.redirect_uri && settings.session_secret),
  };
}

export async function updateAuthSettings(input) {
  const db = await getDb();
  db.data.auth ||= { settings: {}, sessions: [], pending: [] };
  db.data.auth.settings ||= {};
  db.data.auth.sessions ||= [];
  db.data.auth.pending ||= [];

  const current = normalizeStoredSettings(db.data.auth.settings, getEnvAuthDefaults());
  const next = normalizeStoredSettings({
    ...current,
    enabled: input.enabled,
    issuer: input.issuer,
    discovery_url: input.discovery_url,
    client_id: input.client_id,
    client_secret: typeof input.client_secret === 'string' && input.client_secret.trim() ? input.client_secret.trim() : current.client_secret,
    redirect_uri: input.redirect_uri,
    scope: input.scope,
    session_secret: typeof input.session_secret === 'string' && input.session_secret.trim() ? input.session_secret.trim() : current.session_secret,
    allowed_groups: input.allowed_groups,
    allowed_emails: input.allowed_emails,
    allowed_domains: input.allowed_domains,
    session_ttl_hours: input.session_ttl_hours,
  });

  if (input.clear_client_secret) next.client_secret = '';
  if (input.clear_session_secret) next.session_secret = '';
  next.enabled = Boolean(input.enabled) && Boolean(next.issuer && next.client_id && next.client_secret && next.redirect_uri && next.session_secret);

  db.data.auth.settings = { ...next };
  await db.write();
  return getPublicAuthSettings();
}

async function getEffectiveAuthConfig() {
  const settings = await getAuthSettings();
  return {
    enabled: settings.enabled,
    issuer: settings.issuer,
    discoveryUrl: settings.discovery_url,
    clientId: settings.client_id,
    clientSecret: settings.client_secret,
    redirectUri: settings.redirect_uri,
    scope: settings.scope,
    sessionSecret: settings.session_secret,
    sessionTtlHours: settings.session_ttl_hours,
    allowedGroups: parseList(settings.allowed_groups),
    allowedEmails: parseList(settings.allowed_emails).map(item => item.toLowerCase()),
    allowedDomains: parseList(settings.allowed_domains).map(item => item.toLowerCase()),
  };
}

async function getDiscovery(config) {
  const cacheKey = config.discoveryUrl;
  const cached = discoveryCache.get(cacheKey);
  if (cached && Date.now() - cached.fetchedAt < 60 * 60 * 1000) {
    return cached.value;
  }

  await assertSafeUrl(config.discoveryUrl);
  const response = await fetch(config.discoveryUrl);
  if (!response.ok) {
    throw new Error(`Kunde inte läsa OIDC discovery (${response.status})`);
  }

  const data = await response.json();
  discoveryCache.set(cacheKey, { value: data, fetchedAt: Date.now() });
  return data;
}

function normalizeGroups(value) {
  if (Array.isArray(value)) return value.map(item => String(item));
  if (typeof value === 'string') return value.split(',').map(item => item.trim()).filter(Boolean);
  return [];
}

function buildUserProfile(idTokenClaims, userInfo) {
  const source = { ...idTokenClaims, ...userInfo };
  return {
    sub: source.sub,
    name: source.name || source.preferred_username || source.email || source.sub,
    email: source.email || null,
    preferred_username: source.preferred_username || null,
    groups: normalizeGroups(source.groups),
  };
}

function ensureAuthorizedUser(config, user) {
  if (config.allowedEmails.length && !config.allowedEmails.includes(String(user.email || '').toLowerCase())) {
    throw new Error('Det här kontot är inte tillåtet för Enkelbudget.');
  }

  if (config.allowedDomains.length) {
    const domain = String(user.email || '').split('@')[1]?.toLowerCase() || '';
    if (!config.allowedDomains.includes(domain)) {
      throw new Error('E-postdomänen är inte tillåten för Enkelbudget.');
    }
  }

  if (config.allowedGroups.length) {
    const groups = (user.groups || []).map(group => group.toLowerCase());
    const hasMatch = config.allowedGroups.some(group => groups.includes(group.toLowerCase()));
    if (!hasMatch) {
      throw new Error('Kontot saknar rätt Pocket ID-grupp för att logga in.');
    }
  }
}

async function cleanupAuthState(db) {
  const now = Date.now();
  const sessions = db.data.auth.sessions || [];
  db.data.auth.sessions = sessions.filter(session => !session.expires_at || new Date(session.expires_at).getTime() > now);

  const pending = db.data.auth.pending || [];
  db.data.auth.pending = pending.filter(transaction => now - new Date(transaction.created_at).getTime() < 15 * 60 * 1000);
}

async function saveDb(db) {
  await cleanupAuthState(db);
  await db.write();
}

function getSafeReturnTo(value) {
  if (!value || typeof value !== 'string') return '/';
  if (!value.startsWith('/')) return '/';
  if (value.startsWith('//')) return '/';
  if (value.startsWith('/api/')) return '/';
  if (value.startsWith('/auth/')) return '/';
  if (value.startsWith('/login')) return '/';
  if (value.includes('returnTo=')) return '/';
  return value;
}

async function createPendingTransaction(returnTo) {
  const config = await getEffectiveAuthConfig();
  const discovery = await getDiscovery(config);
  const db = await getDb();
  db.data.auth ||= { settings: {}, sessions: [], pending: [] };
  db.data.auth.settings ||= {};
  db.data.auth.sessions ||= [];
  db.data.auth.pending ||= [];

  const state = crypto.randomUUID();
  const nonce = crypto.randomUUID();
  const codeVerifier = base64url(crypto.randomBytes(48));
  const transactionId = crypto.randomUUID();

  db.data.auth.pending.push({
    id: transactionId,
    state,
    nonce,
    code_verifier: codeVerifier,
    return_to: getSafeReturnTo(returnTo),
    created_at: new Date().toISOString(),
  });
  await saveDb(db);

  const params = new URLSearchParams({
    client_id: config.clientId,
    redirect_uri: config.redirectUri,
    response_type: 'code',
    scope: config.scope,
    state,
    nonce,
    code_challenge: sha256base64url(codeVerifier),
    code_challenge_method: 'S256',
  });

  return {
    config,
    transactionId,
    authUrl: `${discovery.authorization_endpoint}?${params.toString()}`,
  };
}

async function exchangeCodeForSession(code, transaction) {
  const config = await getEffectiveAuthConfig();
  const discovery = await getDiscovery(config);

  const tokenResponse = await fetch(discovery.token_endpoint, {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'authorization_code',
      code,
      redirect_uri: config.redirectUri,
      client_id: config.clientId,
      client_secret: config.clientSecret,
      code_verifier: transaction.code_verifier,
    }),
  });

  if (!tokenResponse.ok) {
    const details = await tokenResponse.text();
    throw new Error(`Pocket ID nekade tokenutbytet (${tokenResponse.status}). ${details}`.trim());
  }

  const tokenData = await tokenResponse.json();

  if (!tokenData.id_token) {
    throw new Error('Pocket ID returnerade inget id_token.');
  }
  if (!discovery.jwks_uri) {
    throw new Error('OIDC discovery saknar jwks_uri – kan inte verifiera id_token.');
  }

  // Verifierar signatur, iss, aud och exp kryptografiskt mot providerns JWKS.
  let idTokenClaims;
  try {
    const jwks = getJwks(discovery.jwks_uri);
    const verified = await jwtVerify(tokenData.id_token, jwks, {
      issuer: normalizeIssuer(discovery.issuer || config.issuer),
      audience: config.clientId,
    });
    idTokenClaims = verified.payload;
  } catch (error) {
    throw new Error(`Kunde inte verifiera id_token från Pocket ID: ${error.message}`);
  }

  if (idTokenClaims.nonce && idTokenClaims.nonce !== transaction.nonce) {
    throw new Error('Pocket ID returnerade ett id_token med fel nonce.');
  }

  let userInfo = {};
  if (discovery.userinfo_endpoint && tokenData.access_token) {
    const userInfoResponse = await fetch(discovery.userinfo_endpoint, {
      headers: { Authorization: `Bearer ${tokenData.access_token}` },
    });

    if (!userInfoResponse.ok) {
      const details = await userInfoResponse.text();
      throw new Error(`Kunde inte läsa användarprofil från Pocket ID (${userInfoResponse.status}). ${details}`.trim());
    }

    userInfo = await userInfoResponse.json();

    // Skydd mot att userinfo tillhör en annan användare än id_token.
    if (userInfo.sub && idTokenClaims.sub && userInfo.sub !== idTokenClaims.sub) {
      throw new Error('userinfo-svaret matchar inte id_token (sub skiljer sig).');
    }
  }

  const user = buildUserProfile(idTokenClaims, userInfo);
  ensureAuthorizedUser(config, user);

  const sessionId = crypto.randomUUID();
  const expiresAt = new Date(Date.now() + config.sessionTtlHours * 60 * 60 * 1000).toISOString();

  const db = await getDb();
  db.data.auth ||= { settings: {}, sessions: [], pending: [] };
  db.data.auth.sessions.push({
    id: sessionId,
    user,
    created_at: new Date().toISOString(),
    expires_at: expiresAt,
  });
  db.data.auth.pending = (db.data.auth.pending || []).filter(item => item.id !== transaction.id);
  await saveDb(db);

  return {
    config,
    id: sessionId,
    user,
    expires_at: expiresAt,
    return_to: getSafeReturnTo(transaction.return_to),
  };
}

export async function getAuthSession(req) {
  const config = await getEffectiveAuthConfig();
  if (!config.enabled) {
    return { enabled: false, authenticated: false, user: null };
  }

  const cookies = parseCookies(req.headers.cookie);
  const signedValue = decodeSignedValue(cookies[SESSION_COOKIE], config.sessionSecret);
  if (!signedValue) {
    return { enabled: true, authenticated: false, user: null };
  }

  const db = await getDb();
  db.data.auth ||= { settings: {}, sessions: [], pending: [] };
  db.data.auth.settings ||= {};
  db.data.auth.sessions ||= [];
  db.data.auth.pending ||= [];
  await cleanupAuthState(db);
  const session = db.data.auth.sessions.find(item => item.id === signedValue);
  if (!session) {
    return { enabled: true, authenticated: false, user: null };
  }

  return {
    enabled: true,
    authenticated: true,
    user: session.user,
    expires_at: session.expires_at,
  };
}

export async function handleOidcLogin(req, res) {
  const { config, transactionId, authUrl } = await createPendingTransaction(req.query.returnTo);
  if (!config.enabled) {
    res.redirect('/');
    return;
  }

  res.setHeader('Set-Cookie', serializeCookie(
    TRANSACTION_COOKIE,
    encodeSignedValue(transactionId, config.sessionSecret),
    { maxAge: 15 * 60, secure: req.secure || req.headers['x-forwarded-proto'] === 'https' }
  ));
  res.redirect(authUrl);
}

export async function handleOidcCallback(req, res) {
  const config = await getEffectiveAuthConfig();
  if (!config.enabled) {
    res.redirect('/');
    return;
  }

  const cookies = parseCookies(req.headers.cookie);
  const transactionId = decodeSignedValue(cookies[TRANSACTION_COOKIE], config.sessionSecret);
  const db = await getDb();
  db.data.auth ||= { settings: {}, sessions: [], pending: [] };
  db.data.auth.settings ||= {};
  db.data.auth.sessions ||= [];
  db.data.auth.pending ||= [];
  const transaction = (db.data.auth.pending || []).find(item => item.id === transactionId);

  if (!transaction || transaction.state !== req.query.state) {
    res.status(400).send('Ogiltig eller utgången Pocket ID-inloggning.');
    return;
  }

  if (!req.query.code) {
    res.status(400).send('Pocket ID returnerade ingen auth code.');
    return;
  }

  try {
    const session = await exchangeCodeForSession(String(req.query.code), transaction);
    res.setHeader('Set-Cookie', [
      serializeCookie(
        SESSION_COOKIE,
        encodeSignedValue(session.id, session.config.sessionSecret),
        {
          maxAge: session.config.sessionTtlHours * 60 * 60,
          secure: req.secure || req.headers['x-forwarded-proto'] === 'https',
        }
      ),
      serializeCookie(
        TRANSACTION_COOKIE,
        '',
        {
          maxAge: 0,
          secure: req.secure || req.headers['x-forwarded-proto'] === 'https',
        }
      ),
    ]);
    res.redirect(session.return_to || '/');
  } catch (error) {
    db.data.auth.pending = (db.data.auth.pending || []).filter(item => item.id !== transaction.id);
    await saveDb(db);
    res.status(500).send(`Pocket ID-inloggningen misslyckades: ${error.message}`);
  }
}

export async function handleOidcLogout(req, res) {
  const config = await getEffectiveAuthConfig();
  if (config.enabled) {
    const cookies = parseCookies(req.headers.cookie);
    const sessionId = decodeSignedValue(cookies[SESSION_COOKIE], config.sessionSecret);
    if (sessionId) {
      const db = await getDb();
      db.data.auth ||= { settings: {}, sessions: [], pending: [] };
      db.data.auth.settings ||= {};
      db.data.auth.sessions ||= [];
      db.data.auth.pending ||= [];
      db.data.auth.sessions = (db.data.auth.sessions || []).filter(item => item.id !== sessionId);
      await saveDb(db);
    }
  }

  res.setHeader('Set-Cookie', serializeCookie(
    SESSION_COOKIE,
    '',
    { maxAge: 0, secure: req.secure || req.headers['x-forwarded-proto'] === 'https' }
  ));
  res.json({ ok: true });
}

export async function renderLoginPage(req, res) {
  const config = await getEffectiveAuthConfig();
  if (!config.enabled) {
    res.redirect('/');
    return;
  }

  const returnTo = encodeURIComponent(getSafeReturnTo(String(req.query.returnTo || '/')));
  res.type('html').send(`<!doctype html>
<html lang="sv">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>Logga in - Enkelbudget</title>
    <style>
      :root { color-scheme: light; }
      body { margin: 0; font-family: system-ui, sans-serif; background: linear-gradient(160deg, #eff6ff, #ffffff 45%, #ecfeff); color: #0f172a; }
      main { min-height: 100vh; display: grid; place-items: center; padding: 24px; }
      .card { width: min(460px, 100%); background: rgba(255,255,255,.94); border: 1px solid #dbeafe; border-radius: 24px; box-shadow: 0 24px 80px rgba(15, 23, 42, .12); padding: 28px; }
      .eyebrow { font-size: 12px; font-weight: 700; letter-spacing: .16em; text-transform: uppercase; color: #2563eb; }
      h1 { margin: 10px 0 12px; font-size: 30px; line-height: 1.1; }
      p { margin: 0 0 22px; color: #475569; line-height: 1.55; }
      .actions { display: flex; justify-content: center; margin-top: 8px; }
      a { display: inline-flex; align-items: center; justify-content: center; min-width: 240px; max-width: 100%; border-radius: 14px; background: #2563eb; color: white; text-decoration: none; font-weight: 700; padding: 14px 22px; box-shadow: 0 10px 24px rgba(37, 99, 235, .18); }
      .hint { margin-top: 14px; font-size: 13px; color: #64748b; text-align: center; }
    </style>
  </head>
  <body>
    <main>
      <section class="card">
        <div class="eyebrow">Pocket ID</div>
        <h1>Logga in i Enkelbudget</h1>
        <p>Appen är skyddad med OIDC/SSO via Pocket ID. Fortsätt med ditt godkända konto för att komma åt budget, lån, transaktioner och inställningar.</p>
        <div class="actions">
          <a href="/auth/login?returnTo=${returnTo}">Fortsätt med Pocket ID</a>
        </div>
        <div class="hint">Om du inte ska vara här: stäng fliken eller kontrollera grupp- och klientinställningarna i Pocket ID.</div>
      </section>
    </main>
  </body>
</html>`);
}

export async function requireApiAuth(req, res, next) {
  try {
    const session = await getAuthSession(req);
    req.auth = session;

    if (!session.enabled || session.authenticated) {
      next();
      return;
    }

    res.status(401).json({
      error: 'Autentisering krävs',
      login_url: `/login?returnTo=${encodeURIComponent(req.originalUrl === '/api/auth/session' ? '/' : req.originalUrl.replace(/^\/api/, '') || '/')}`,
    });
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
}