import type { Cookies } from '@sveltejs/kit';
import { dev } from '$app/environment';
import * as fs from 'node:fs';
import * as path from 'node:path';

const TOKEN_URL = 'https://api.beatleader.com/oauth2/token';

const ACCESS_COOKIE = 'bl_access_token';
const REFRESH_COOKIE = 'bl_refresh_token';
const EXPIRES_COOKIE = 'bl_expires_at';
const SESSION_COOKIE = 'bl_session_cookie';
const STATE_COOKIE = 'bl_oauth_state';
const REDIRECT_COOKIE = 'bl_redirect_to';

// Persistent storage locations
const DATA_DIR = '.data';
const CREDS_FILE = 'beatleader_oauth.json';
const TOKENS_FILE = 'beatleader_tokens.json';

function cookieOptions() {
  return {
    path: '/',
    httpOnly: true as const,
    sameSite: 'lax' as const,
    secure: dev ? false : true
  };
}

export function createOAuthState(): string {
  // Use crypto.randomUUID for sufficiently random state
  return crypto.randomUUID();
}

export function setStateCookie(cookies: Cookies, state: string): void {
  cookies.set(STATE_COOKIE, state, { ...cookieOptions(), maxAge: 600 }); // 10 min
}

export function consumeAndValidateState(cookies: Cookies, received: string | null): boolean {
  const stored = cookies.get(STATE_COOKIE);
  cookies.delete(STATE_COOKIE, cookieOptions());
  return Boolean(stored && received && stored === received);
}

export function setRedirectCookie(cookies: Cookies, redirectTo: string | null | undefined): void {
  if (!redirectTo) return;
  try {
    const url = new URL(redirectTo, 'http://dummy');
    const value = url.pathname + (url.search || '') + (url.hash || '');
    cookies.set(REDIRECT_COOKIE, value, { ...cookieOptions(), maxAge: 600 });
  } catch {
    // ignore invalid redirect
  }
}

export function consumeRedirectCookie(cookies: Cookies): string | null {
  const value = cookies.get(REDIRECT_COOKIE) ?? null;
  cookies.delete(REDIRECT_COOKIE, cookieOptions());
  return value;
}

export function setTokens(
  cookies: Cookies,
  tokenData: { access_token: string; refresh_token?: string; expires_in?: number }
): void {
  const expiresAt = Date.now() + ((tokenData.expires_in ?? 3600) * 1000);
  cookies.set(ACCESS_COOKIE, tokenData.access_token, { ...cookieOptions(), maxAge: tokenData.expires_in ?? 3600 });
  if (tokenData.refresh_token) {
    // 30 days by default for refresh; adjust as needed
    cookies.set(REFRESH_COOKIE, tokenData.refresh_token, { ...cookieOptions(), maxAge: 30 * 24 * 3600 });
  }
  cookies.set(EXPIRES_COOKIE, String(expiresAt), { ...cookieOptions(), maxAge: 30 * 24 * 3600 });

  // Persist token data to disk for reuse across restarts (single-user assumption)
  try {
    writeJsonPersistent(TOKENS_FILE, {
      access_token: tokenData.access_token,
      refresh_token: tokenData.refresh_token ?? null,
      expires_at: expiresAt
    });
  } catch {
    // ignore persistence errors
  }
}

export function clearTokens(cookies: Cookies): void {
  cookies.delete(ACCESS_COOKIE, cookieOptions());
  cookies.delete(REFRESH_COOKIE, cookieOptions());
  cookies.delete(EXPIRES_COOKIE, cookieOptions());
  try {
    deletePersistent(TOKENS_FILE);
  } catch {
    // ignore
  }
}

/**
 * Persist BeatLeader website session cookies captured from upstream Set-Cookie headers.
 * Only cookie name=value pairs are stored (attributes are discarded). Stored both in httpOnly cookie and on disk.
 */
export function setBeatLeaderSessionFromSetCookieHeaders(cookies: Cookies, setCookieHeaders: string[] | undefined | null): void {
  if (!setCookieHeaders || setCookieHeaders.length === 0) return;
  const nameValuePairs: string[] = [];
  for (const raw of setCookieHeaders) {
    const firstSemi = raw.indexOf(';');
    const pair = firstSemi === -1 ? raw.trim() : raw.slice(0, firstSemi).trim();
    if (!pair) continue;
    // Filter out obviously invalid pairs
    if (!pair.includes('=')) continue;
    const [name, value] = pair.split('=');
    if (!name || value === undefined) continue;
    nameValuePairs.push(`${name}=${value}`);
  }
  if (nameValuePairs.length === 0) return;
  try {
    cookies.set(SESSION_COOKIE, JSON.stringify(nameValuePairs), { ...cookieOptions(), maxAge: 30 * 24 * 3600 });
  } catch {}
  try {
    writeJsonPersistent('beatleader_session.json', { cookies: nameValuePairs });
  } catch {}
}

/**
 * Returns a Cookie header string ("a=b; c=d") suitable for upstream requests, if a BL session is stored.
 */
export function getBeatLeaderSessionCookieHeader(cookies: Cookies): string | null {
  try {
    const raw = cookies.get(SESSION_COOKIE);
    if (raw) {
      const arr = JSON.parse(raw) as string[];
      if (Array.isArray(arr) && arr.length > 0) return arr.join('; ');
    }
  } catch {}
  try {
    const persisted = readJsonPersistent<{ cookies?: string[] }>('beatleader_session.json');
    if (persisted?.cookies && persisted.cookies.length > 0) return persisted.cookies.join('; ');
  } catch {}
  return null;
}

export function clearBeatLeaderSession(cookies: Cookies): void {
  cookies.delete(SESSION_COOKIE, cookieOptions());
  try {
    deletePersistent('beatleader_session.json');
  } catch {}
}

export function getAccessTokenFromCookies(cookies: Cookies): { token: string | null; expiresAt: number | null } {
  const token = cookies.get(ACCESS_COOKIE) ?? null;
  const expiresRaw = cookies.get(EXPIRES_COOKIE);
  const expiresAt = expiresRaw ? Number(expiresRaw) : null;
  return { token, expiresAt };
}

export async function refreshAccessToken(cookies: Cookies): Promise<string | null> {
  const refreshToken = cookies.get(REFRESH_COOKIE);
  let tokenToUse: string | undefined = refreshToken ?? undefined;
  if (!tokenToUse) {
    // Try persistent token store
    const persisted = readJsonPersistent<{ refresh_token?: string | null }>(TOKENS_FILE);
    tokenToUse = (persisted?.refresh_token ?? undefined) as string | undefined;
  }
  if (!tokenToUse) return null;

  const creds = readJsonPersistent<{ client_id?: string; client_secret?: string }>(CREDS_FILE);
  const clientId = creds?.client_id;
  const clientSecret = creds?.client_secret;
  if (!clientId || !clientSecret) return null;

  const res = await fetch(TOKEN_URL, {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'refresh_token',
      client_id: clientId,
      client_secret: clientSecret,
      refresh_token: tokenToUse
    })
  });

  if (!res.ok) {
    clearTokens(cookies);
    return null;
  }

  const tokenData = await res.json();
  setTokens(cookies, tokenData);
  return tokenData.access_token as string;
}

export async function getValidAccessToken(cookies: Cookies): Promise<string | null> {
  const { token, expiresAt } = getAccessTokenFromCookies(cookies);
  if (token && expiresAt && Date.now() < expiresAt - 10_000) {
    return token; // still valid (with 10s skew)
  }
  // Try refresh
  const refreshed = await refreshAccessToken(cookies);
  if (refreshed) return refreshed;

  // As last resort, if we have a persisted access token that may still be valid, use it
  const persisted = readJsonPersistent<{ access_token?: string | null; expires_at?: number | null }>(TOKENS_FILE);
  if (persisted?.access_token && persisted?.expires_at && Date.now() < (persisted.expires_at - 10_000)) {
    cookies.set(ACCESS_COOKIE, persisted.access_token, { ...cookieOptions(), maxAge: Math.floor((persisted.expires_at - Date.now()) / 1000) });
    cookies.set(EXPIRES_COOKIE, String(persisted.expires_at), { ...cookieOptions(), maxAge: 30 * 24 * 3600 });
    return persisted.access_token;
  }
  return null;
}

export function buildAuthorizeUrl(origin: string, scopes: string[]): URL {
  const creds = readJsonPersistent<{ client_id?: string; client_secret?: string }>(CREDS_FILE);
  const clientId = creds?.client_id;
  if (!clientId) throw new Error('BeatLeader OAuth is not configured. Visit /tools/beatleader-oauth to set it up.');
  const redirectUri = `${origin}/auth/beatleader/callback`;
  const url = new URL('https://api.beatleader.com/oauth2/authorize');
  url.searchParams.set('client_id', clientId);
  // BeatLeader expects scopes without the "scp:" prefix in the authorization request
  const requestedScopes = scopes.map(s => s.replace(/^scp:/, '')).join(' ');
  url.searchParams.set('scope', requestedScopes);
  url.searchParams.set('response_type', 'code');
  url.searchParams.set('redirect_uri', redirectUri);
  return url;
}

export async function exchangeCodeForTokens(origin: string, code: string): Promise<{ access_token: string; refresh_token?: string; expires_in?: number } | null> {
  const creds = readJsonPersistent<{ client_id?: string; client_secret?: string }>(CREDS_FILE);
  const clientId = creds?.client_id;
  const clientSecret = creds?.client_secret;
  if (!clientId || !clientSecret) return null;
  const redirectUri = `${origin}/auth/beatleader/callback`;

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

  if (!res.ok) return null;
  return (await res.json()) as any;
}

// Persistent storage helpers (single-user local setup)
function ensureDataDir(): void {
  try {
    if (!fs.existsSync(DATA_DIR)) fs.mkdirSync(DATA_DIR, { recursive: true });
  } catch {
    // ignore
  }
}

function resolvePath(name: string): string {
  return path.join(process.cwd(), DATA_DIR, name);
}

function writeJsonPersistent<T extends object>(name: string, data: T): void {
  ensureDataDir();
  fs.writeFileSync(resolvePath(name), JSON.stringify(data, null, 2), 'utf-8');
}

function readJsonPersistent<T>(name: string): T | null {
  try {
    const p = resolvePath(name);
    if (!fs.existsSync(p)) return null;
    const raw = fs.readFileSync(p, 'utf-8');
    return JSON.parse(raw) as T;
  } catch {
    return null;
  }
}

function deletePersistent(name: string): void {
  try {
    const p = resolvePath(name);
    if (fs.existsSync(p)) fs.unlinkSync(p);
  } catch {
    // ignore
  }
}

export function storeOAuthCredentials(input: { client_id: string; client_secret: string; scopes?: string[]; redirect_urls?: string[] }): void {
  writeJsonPersistent(CREDS_FILE, input);
}

export function readOAuthCredentials(): { client_id: string; client_secret: string; scopes?: string[]; redirect_urls?: string[] } | null {
  return readJsonPersistent(CREDS_FILE);
}