"use strict";

const fs = require("fs");
const util = require("util");
const crypto = require("crypto");
const argon2 = require("argon2");
const {sj, parseCookies, res204, err400, err401, err500} = require("./utils");

const rf = util.promisify(fs.readFile);
const wf = util.promisify(fs.writeFile);
const randHex = len => crypto.randomBytes(len).toString("hex");

module.exports = config => {
const {
  TOKEN_RENEW_AGE, TOKEN_MAX_AGE, TOKEN_LENGTH, SESSION_ID_LENGTH,
  USERNAME_MAX_LENGTH, PASSWORD_MIN_LENGTH, PASSWORD_MAX_LENGTH,
  RATE_LIMIT_MAX_LEVEL, RATE_LIMIT_MAX_WAITING,
  fingerprintIP} = config.auth;
const {DOMAIN, SECURE} = config;
const exports = {};

// Run once immediately, then every interval until not called
function debounce(fn, interval=100) {
  let timer, doubled;
  const timeoutFn = () => {
    timer = undefined;
    if (doubled) {
      timer = setTimeout(timeoutFn, interval);
      doubled = false;
      return fn();
    }
  };

  return () => {
    if (doubled) return;
    if (timer) return doubled = true;
    timer = setTimeout(timeoutFn, interval);
    return fn();
  };
};

function loadJSONSync(path) {
  const obj = {};
  try {
    Object.assign(obj, JSON.parse(fs.readFileSync(path)));
  } catch(e) {
    console.log(Date.now()+` Error loading ${path}, creating fallback empty set`);
    fs.rename(path, path+".bad."+Date.now(), err => {});
  }
  return obj;
}

const checkTokenAge = tokenData =>
  (Date.now()-tokenData.timestamp > TOKEN_MAX_AGE*1000) ||
  (tokenData.renewed && Date.now()-tokenData.renewed > 1000);
const setTokenCookie = (res, token, keepSession) =>
  res.setHeader("Set-Cookie", `token=${token}; `+
    (token? keepSession? "Max-Age="+TOKEN_MAX_AGE+"; " : "" : "Max-Age=0; ")+
    `HttpOnly; SameSite=Strict; Domain=${DOMAIN}`+(SECURE?"; Secure":""));
  //res.setHeader("Cache-Control", 'no-cache="Set-Cookie"'); // Done globally in app.js
  // TODO Centralize cache options?

const userIDsFile = "private/userIDs.json";
const userNames = loadJSONSync(userIDsFile), userIDs = {};
for (const [uid, username] of Object.entries(userNames)) userIDs[username.toLowerCase()] = uid;
const writeUIDs = debounce(() => wf(userIDsFile, JSON.stringify(userNames)));
const getUID = exports.getUID = username =>
  userIDs.hasOwnProperty(username.toLowerCase()) && userIDs[username.toLowerCase()];
const getUsername = exports.getUsername = uid =>
  userNames.hasOwnProperty(uid) && userNames[uid];
const createUID = username => { let uid;
  do { uid = randHex(5); } while (getUsername(uid));
  userIDs[username.toLowerCase()] = uid;
  writeUIDs();
  return uid;
}
const changeUsername = (uid, newName) => {
  if (userIDs[newName.toLowerCase()] !== uid) return false;
  const oldName = userNames[uid].toLowerCase();
  userNames[uid] = newName;
  delete userIDs[oldName];
  userIDs[newName.toLowerCase()] = uid;
  writeUIDs();
  return true;
};

const tokensFile = "private/tokens.json";
const tokens = loadJSONSync(tokensFile), userSessions = {},
  sessionIDs = new Set(), renewedTokens = {};
const getUserSessions = uid => userSessions[uid] ||= new Set();
for (const [token, tokenData] of Object.entries(tokens)) {
  if (checkTokenAge(tokenData)) delete tokens[token];
  else {
    getUserSessions(tokenData.uid).add(token);
    sessionIDs.add(tokenData.sessionID);
  }
}
const newSessionID = () => { let id;
  do { id = randHex(SESSION_ID_LENGTH); } while (sessionIDs.has(id));
  return id;
};

const writeTokens = debounce(() => wf(tokensFile, JSON.stringify(tokens)));
const deleteToken = (token, sessionEnd) => {
  const tokenData = tokens[token];
  if (sessionEnd) sessionIDs.delete(tokenData.sessionID);
  userSessions[tokenData?.uid]?.delete(token);
  delete tokens[token];
  writeTokens();
};
const getToken = token => {
  if (token.length !== TOKEN_LENGTH*2) {
    console.log(Date.now()+" [WARN] Incorrect token format");
    return false;
  }

  if (renewedTokens[token]) {
    // Possible hijacking, nip both ends
    deleteToken(renewedTokens[token], true);
    return false;
  }

  const tokenData = tokens.hasOwnProperty(token) && tokens[token];
  if (tokenData) {
    if (checkTokenAge(tokenData)) {
      deleteToken(token, true);
      return false;
    }
    tokenData.lastUsed = Date.now();
    writeTokens();
  }
  return tokenData;
};
const createToken = (uid, meta) => { let token;
  do { token = randHex(TOKEN_LENGTH); } while (getToken(token));
  const now = Date.now();
  tokens[token] = Object.assign(meta, {uid, timestamp:now, lastUsed:now});
  getUserSessions(uid).add(token);
  writeTokens();
  return token;
};
const renewToken = (res, token, fingerprint, gracePeriod=500) => {
  const tokenData = tokens[token];
  if (tokenData.renewed) return;
  tokenData.renewed = Date.now();
  const newToken = createToken(tokenData.uid,
    Object.assign(fingerprint, {
      sessionID: tokenData.sessionID,
      keepSession: tokenData.keepSession,
      sessionStart: tokenData.sessionStart,
    }));

  setTokenCookie(res, newToken, tokenData.keepSession);

  setTimeout(() => {
    deleteToken(token);
    renewedTokens[token] = newToken;
  }, gracePeriod); // Let parallel requests finish
  setTimeout(() => delete renewedTokens[token], TOKEN_RENEW_AGE*1000);
};

const collectFingerprint = req => ({
  userAgent: req.headers["user-agent"],
  ip: fingerprintIP(req),
  // TODO GeoIP? Maintain set?
  // TODO Sec-CH-UA
});

const checkReferer = req => {
  if (req.headers["referer"] && !req.headers["referer"].includes(DOMAIN))
    console.log(Date.now()+" [WARN] Unexpected HTTP Referer: "+req.headers["referer"]); };

async function login(req, res, match, data) {
  const currentToken = parseCookies(req)?.token;
  if (currentToken || !data.username || !data.password) return err400(res);
  const error = {success:false, msg:"Bad username or password"};
  const sendError = res => { rateLimitIP(req, 2, 9); sj(res, error); };

  const uid = getUID(data.username);
  if (!uid) return sendError(res); // User doesn't exist

  let user;
  try { user = JSON.parse(await rf(`private/${uid}.json`));
  } catch (e) { return err500(res); } // Can't load user data

  checkReferer(req);

  const pass = user.password;
  if (pass.startsWith("$change")) {
    if (pass.split("$")[2] && pass.split("$")[2] !== data.password) return sendError(res);
    console.log(Date.now()+" Logging in "+uid+", must change password");
    return sj(res, {success:true, changePassword:true});

  } else if (pass.startsWith("$argon2")) {
    if (data.password.length > PASSWORD_MAX_LENGTH) return sendError(res); // Avoid DDOS
    if (!await argon2.verify(pass, data.password)) return sendError(res);
    if (user.mustChangePassword) {
      console.log(Date.now()+" Logging in "+uid+", must change password");
      return sj(res, {success:true, changePassword:true});
    }

    console.log(Date.now()+" Logging in "+uid);
    setTokenCookie(res, createToken(uid,
      Object.assign(collectFingerprint(req), {
        sessionID: newSessionID(),
        keepSession: data.keepSession,
        sessionStart: Date.now(),
      })), data.keepSession);
    return sj(res, {success:true});

  } else return err500(res);
}

function logout(req, res) {
  const token = parseCookies(req)?.token;
  const tokenData = getToken(token);
  if (tokenData) {
    console.log(Date.now()+" Logging out "+tokenData.uid);
    deleteToken(token, true);
  } else {
    console.log(Date.now()+" [WARN] Logging out bad token");
    rateLimitIP(req, -2, 4);
  }
  setTokenCookie(res, "");
  res204(res);
}

function changePassword(req, res, match, data) {
  const token = parseCookies(req)?.token;

  const fn = async () => {
    if (!data.password || !data.newPassword
        || (!token && !data.username)) return err400(res);
    const error = token?
      {success:false, msg:"Bad password"}:
      {success:false, msg:"Bad username or password"};
    const sendError = res => { rateLimitIP(req, token?3:2, 9); sj(res, error); };

    const uid = token? req.uid : getUID(data.username);
    if (!uid) return token? err401(res) : sendError(req);

    let user;
    try { user = JSON.parse(await rf(`private/${uid}.json`));
    } catch (e) { return err500(res); }

    checkReferer(req);

    const pass = user.password;
    if (pass.startsWith("$change")) {
      if (pass.split("$")[2] && pass.split("$")[2] !== data.password) return sendError(req);

    } else if (pass.startsWith("$argon2")) {
      if (data.password.length > PASSWORD_MAX_LENGTH) return sendError(req); // Avoid DDOS
      if (!await argon2.verify(pass, data.password)) return sendError(req);
      if (!token && !user.mustChangePassword) return err401(res); // Must log in; OTP etc.

    } else return err500(res);

    if (data.newPassword.length < PASSWORD_MIN_LENGTH)
      return sj(res, {success:false, msg:`New password is too short (must be >=${PASSWORD_MIN_LENGTH} chars)`})
    if (data.newPassword.length > PASSWORD_MAX_LENGTH)
      return sj(res, {success:false, msg:`New password is too long (must be <=${PASSWORD_MAX_LENGTH} chars)`})

    console.log(Date.now()+" Changing password for "+uid);
    user.password = await argon2.hash(data.newPassword, {type: argon2.argon2id});
    await wf(`private/${uid}.json`, JSON.stringify(user));

    if (!res.getHeader("Set-Cookie")) { // Might have been renewed by authed()
      if (token) renewToken(res, token, fingerprint, 0);
      else setTokenCookie(res, createToken(uid,
        Object.assign(collectFingerprint(req), {
          sessionID: newSessionID(),
          sessionStart: Date.now(),
          keepSession: data.keepSession,
        })), data.keepSession);
    }

    sj(res, {success:true});
  };

  if (token) return authed(fn)(req, res);
  else return fn();
}

async function changeUsernameReq(req, res, match, data) {
  if (!data.newUsername || !data.password) return err400(res);
  if (data.newUsername.length > USERNAME_MAX_LENGTH)
    return sj(res, {success:false, msg:`New username is too long (must be <=${USERNAME_MAX_LENGTH} chars)`})

  const error = {success:false, msg:"Bad password"};
  const sendError = res => { rateLimitIP(req, 3, 9); sj(res, error); };

  let user;
  try { user = JSON.parse(await rf(`private/${req.uid}.json`));
  } catch (e) { return err500(res); }

  const pass = user.password;
  if (pass.startsWith("$change")) {
    if (pass.split("$")[2] && pass.split("$")[2] !== data.password) return sendError(req);

  } else if (pass.startsWith("$argon2")) {
    if (data.password.length > PASSWORD_MAX_LENGTH) return sendError(req); // Avoid DDOS
    if (!await argon2.verify(pass, data.password)) return sendError(req);

  } else return err500(res);

  console.log(Date.now()+` Changing username for ${req.uid} to ${data.newUsername}`);

  rateLimitIP(req, -2, 7); // To limit name probing

  if (changeUsername(req.uid, data.newUsername)) return sj(res, {success:true});
  else return sj(res, {success:false, msg:"Username already taken"})
}

function sessionList(req, res) {
  console.log(Date.now()+" Getting session list for "+req.uid);
  sj(res, {
    active: Array.from(getUserSessions(req.uid))
      .map(t => tokens[t]).filter(s => !checkTokenAge(s) && !s.renewed)
      .map(s => ({
        id: s.sessionID,
        currentSession: s.sessionID === req.sessionID,
        sessionStart: s.sessionStart,
        userAgent: s.userAgent,
        lastUsed: s.lastUsed,
        ip: s.ip,
        // TODO other fingerprint info users should see to validate sessions
      })),
    recent: [], // TODO
  });
}

function deauthSession(req, res, match, data) {
  if (!data.id || data.id.length !== SESSION_ID_LENGTH) return err400(res);
  console.log(Date.now()+" Deauthing session "+req.uid+":"+data.id);
  const token = Array.from(getUserSessions(req.uid)).find(t => tokens[t].hash.startsWith(data.id));
  if (!token) { console.log(Date.now()+" [WARN] Session doesn't exist"); return err400(res); }
  deleteToken(token, true);

  if (req.sessionID === data.id) setTokenCookie(res, "");
  return res204(res);
}

function deauthAll(req, res) {
  const uid = req.uid;
  console.log(Date.now()+" Ending all sessions for "+uid);
  const sessions = Array.from(getUserSessions(req.uid));
  for (const token of sessions) deleteToken(token, true);
  setTokenCookie(res, "");
  return res204(res);
}

const rateLimitIPs = {};
const rateLimitTime = level => 100 * Math.pow(2, level);
function rateLimitIP(req, level, stickiness) { // TODO verify
  const ip = fingerprintIP(req);
  const rl = rateLimitIPs[ip] ||= {level, startingLevel:level, waiting:0};
  const delta = level > rl.level? level - rl.level : 1;
  rl.level += delta;

  if (rl.level >= 0)
    console.log(Date.now()+` [WARN] Rate limiting ${ip} (${level}:${rl.level})`);

  setTimeout(() => {
    if (rl.level >= 0) console.log(Date.now()+` Rate limiting decreased for ${ip}`);
    rl.level -= delta;
    if (rl.level === rl.startingLevel) delete rateLimitIPs[ip];
  }, rateLimitTime(rl.level + stickiness));
}
const rateLimit = fn => (req, res, ...rest) => {
  const rl = rateLimitIPs[fingerprintIP(req)];
  if (!rl || rl.level < 0) return fn(req, res, ...rest);
  if (rl.level > RATE_LIMIT_MAX_LEVEL ||
      rl.waiting > RATE_LIMIT_MAX_WAITING) {
    console.log(Date.now()+" [WARN] Aborting request (rate limiting maxed out)");
    return req.destroy();
  }

  console.log(Date.now()+` [WARN] Rate limiting request for ${rateLimitTime(rl.level)}ms`);

  rl.waiting++;
  setTimeout(() => {
    rl.waiting--;
    fn(req, res, ...rest);
  }, rateLimitTime(rl.level));
}

function authed(fn) { return rateLimit((req, res, ...rest) => {
  const token = parseCookies(req)?.token;
  if (!token) return err401(res);

  const tokenData = getToken(token);
  const uid = tokenData?.uid;
  if (!tokenData) {
    console.log(Date.now()+" [WARN] Bad token");
    rateLimitIP(req, -2, 4);
    setTokenCookie(res, "");
    return err401(res);
  }

  checkReferer(req);

  const fingerprint = collectFingerprint(req);
  if (Date.now()-tokenData.timestamp < TOKEN_RENEW_AGE*1000 &&
      fingerprint.ip !== tokenData.ip && fingerprint.userAgent !== tokenData.userAgent) {
    console.log(Date.now()+" [WARN] Fingerprint check failed");
    deleteToken(token, true);
    rateLimitIP(req, 0, 4);
    setTokenCookie(res, "");
    return err401(res);
  }
  // TODO other verification from fingerprint
  // - if user-agent changes too much (could be browser update if small)
  // - if IP alternates between 2+ places too fast

  if (Date.now()-tokenData.timestamp > TOKEN_RENEW_AGE*1000 && !tokenData.renewed) {
    console.log(Date.now()+" Renewing token for "+uid);
    renewToken(res, token, fingerprint);
  }

  req.uid = uid;
  req.sessionID = tokenData.sessionID;
  return fn(req, res, ...rest);
}); } exports.authed = authed;

exports.attach = (app) => { // TODO make endpoints RESTier?
  app.jpost("/login", rateLimit(login)); // {username, password[, keepSession]} -> {success[, msg][, mustChangePassword]}
  app.post("/logout", rateLimit(logout));
  app.jpost("/change-password", rateLimit(changePassword)); // {password, newPassword[, username[, keepSession]]} -> {success[, msg]}
  app.jpost("/change-username", authed(changeUsernameReq)); // {newUsername, password} -> {success[, msg]}
  app.get("/session-list", authed(sessionList)); // -> {active:[{id:<sessionID>, ...}, ...], recent:[...]}
  app.jpost("/deauth-session", authed(deauthSession)); // {id:<sessionID>}
  app.post("/deauth-all", authed(deauthAll));
};

// TODO
// - create user
// - delete user
// - OTP (MITM/XSS/shoulder surfing; ensure codes only work once)
// - PIN (client-side, and easy session verification)
// - normalize error response times?
// - rate limit username/uid signin attempts?
// - log failed attempts, then notify user
// - https://github.com/zxcvbn-ts/zxcvbn
// - non-login-event user notification system (warnings, must change password...)
// - encrypt `private/` on disk using TPM?

return exports; };