// Format of the required matrix.json file:
// {
//   "user_id": "@statusbot:tomsmeding.com",
//   "password": "PASSWORD OF THE USER",
//   "room_id": "!ROOMID:tomsmeding.com"
// }

// Furthermore, accounts.json is required in the standard format ([[user, pass]])

// API:
// POST /statusbot
// { "sender": "who are you", "text": "content of the status message" }

// State in this file (gstate): the above matrix.json plus:
// {
//   config: the above matrix.json,
//   home_server: "tomsmeding.com",  // nominal server in the user id
//   matrix_server: "matrix.tomsmeding.com",  // actual matrix server address, without port
//   access_token: "some access token",
//   req_counter: 1  // counter for transaction requests to the matrix server
// }

// Saves persist state under key "access_tokens":
// {
//   "@statusbot:tomsmeding.com|!ROOMID:tomsmeding.com": ["access token", req_counter: int]
// }

const cmn = require("../$common.js");
const fs = require("fs");
const https = require("https");
const URL = require("url");
const bodyParser = require("body-parser");

let moddir = null;

const persist = require("node-persist").create({
  dir: cmn.persistdir + "/statusbot",
  continuous: false,
  interval: false
});
persist.initSync();

let persistTokens = persist.getItemSync("access_tokens");
if (!persistTokens) {
  persistTokens = {};
  persist.setItemSync("access_tokens", persistTokens);
}

let gstate = null;

// cb: (status: int, body: string) => ()
function fetch(method, headers, hostname, path, data, cb) {
  const req = https.request({method, headers, hostname, path}, res => {
    let body = "";
    res.on("data", data => { body += data; });
    res.on("end", () => cb(res.statusCode, body));
  });
  req.on("error", () => cb(null, null))
  req.write(data);
  req.end();
}

// ms: int (milliseconds)
// f: ((...Args) => ()) => ()
// cb: (true, ...Args) => () | (false) => ()
// Callback is invoked with 'false' if the timeout expired, or with 'true' if 'f' finished before the timeout.
function ptimeout(ms, f, cb) {
  let cbinvoked = false;

  const tmout = setTimeout(() => {
    if (cbinvoked) return;
    cbinvoked = true;
    cb(false);
  }, ms);

  f((...args) => {
    if (cbinvoked) return;
    cbinvoked = true;
    clearTimeout(tmout);
    cb(true, ...args);
  });
}

class PRatelimit {
  constructor(mindelayms) {
    this._mindelayms = mindelayms;
    this._queue = [];  // [(() => ()) => ()]
    this._ready = true;  // true: should run job immediately; false: should enqueue
  }

  // f: (() => ()) => ()
  submit(f) {
    if (this._ready) {
      this._ready = false;
      f(() => this.startWaiting());
    } else {
      this._queue.push(f);
    }
  }

  startWaiting() {
    setTimeout(() => {
      if (this._queue.length > 0) {
        const f = this._queue.shift();
        f(() => this.startWaiting());
      } else {
        this._ready = true;
      }
    }, this._mindelayms);
  }
}

// f: ((true, ...Args) => () | (false) => ()) => ()
// cb: (true, ...Args) => () | (false) => ()
// The callback to f should be invoked with 'true' plus further arguments if it
// succeeded, and 'false' if it did not.
// Based on this info, if f failed, f is retried a few times. Once ntimes has
// been exhausted or a call succeeds, cb is invoked with respectively either
// (false) or (true, ...args).
function pretry(interval, multiplier, ntimes, f, cb) {
  let tm = interval;
  let ncalled = 0;

  function schedule() {
    setTimeout(() => {
      f((success, ...args) => {
        if (success) {
          cb(true, ...args);
          return;
        }

        ncalled++;
        tm *= multiplier;
        if (ncalled >= ntimes) cb(false);
        else schedule();
      });
    }, tm);
  }

  schedule();
}

// cb: (state) => ()
function augmentConfig(config, cb) {
  const m = config.user_id.match(/^@[^:]+:(.*)$/);
  if (!m) {
    throw new Error("statusbot: Cannot parse matrix ID (must be in @user:domain format)");
  }
  const home_server = m[1];

  const pkey = `${config.user_id}|${config.room_id}`
  let access_token = undefined;
  let req_counter = undefined;
  if (pkey in persistTokens) {
    [access_token, req_counter] = persistTokens[pkey];
  }

  // wait a bit with requesting this in case the homeserver in question is the same server as us
  pretry(500, 1.4, 10,
    cb => {
      console.log("statusbot: Attempting to get matrix server info");
      fetch("GET", {}, home_server, "/.well-known/matrix/server", "", (status, body) => {
        if (status != 200) {
          cb(false);  // attempt failed (perhaps a later attempt will succeed)
          return;
        }
        let mserver;
        try {
          mserver = JSON.parse(body)["m.server"];
        } catch (e) {
          cb(false);  // invalid JSON response, try again later
          return;
        }
        const m = mserver.match(/^([^:]*)(:443)?$/);
        if (!m) {
          throw new Error(`statusbot: Matrix server port not 443 (sorry): <${mserver}>`);
        }
        const matrix_server = m[1];
        // attempt succeeded!
        cb(true, {config, home_server, matrix_server, access_token, req_counter});
      });
    },
    (success, state) => {
      if (success) {
        console.log("statusbot: Successfully got matrix server info.");
        cb(state);
      } else throw new Error(`statusbot: Failed getting https://${home_server}/.well-known/matrix/server`);
    }
  );
}

function updatePersist() {
  persistTokens[`${gstate.config.user_id}|${gstate.config.room_id}`] = [gstate.access_token, gstate.req_counter];
  persist.setItemSync("access_tokens", persistTokens);
}

// Sets access token in state.
// cb: (success: bool, body: string) => ()
function matrixLogin(cb) {
  const data = JSON.stringify({
    type: "m.login.password",
    identifier: {type: "m.id.user", user: gstate.config.user_id},
    password: gstate.config.password,
  });
  fetch("POST", {}, gstate.matrix_server, "/_matrix/client/v3/login", data, (status, body) => {
    if (status != 200) { cb(false, body); return; }
    try {
      const response = JSON.parse(body);
      gstate.access_token = response.access_token;
      gstate.req_counter = 1;
      updatePersist();
      cb(true, body);
    } catch (e) {
      cb(false, body);
    }
  });
}

// cb: (status: int, body: string) => ()
// Status 401: access token invalid
// Status 200: success
// Anything else: ? (see body?)
function matrixSendMsg(text, cb) {
  if (gstate.access_token == undefined) { cb(401); return; }

  const headers = {Authorization: `Bearer ${gstate.access_token}`};
  const url = `/_matrix/client/v3/rooms/${gstate.config.room_id}/send/m.room.message/${gstate.req_counter}`;
  gstate.req_counter++;
  updatePersist();  // req_counter changed

  const data = JSON.stringify({
    msgtype: "m.text",
    body: text,
  });

  fetch("PUT", headers, gstate.matrix_server, url, data, (status, body) => {
    cb(status, body);
  });
}

// cb: () => ()
function logFailure(message, cb) {
  fs.appendFile(moddir + "/faillog.txt", `[${new Date().toISOString()}] ${message}\n`, err => {
    if (err) console.error(err);
    cb();
  });
}

// Tries to send a message, trying login if the access token is invalid.
// cb: (success: bool) => ()
function matrixSendMsgLogin(text, cb) {
  matrixSendMsg(text, (status, body) => {
    switch (status) {
      case 200:
        cb(true);
        break;

      case 401:
        matrixLogin((success, body) => {
          if (!success) {
            logFailure(`Failed to log in: ${body}`, () => cb(false));
            return;
          }

          matrixSendMsg(text, (status, body) => {
            switch (status) {
              case 200: cb(true); return;
              case 401: logFailure(`401 even after login: ${body}`, () => cb(false)); break;
              default: logFailure(`Failed to send message: ${body}`, () => cb(false)); break;
            }
          });
        });
        break;

      default:
        logFailure(`Failed to send message: ${body}`, () => cb(false));
        break;
    }
  })
}

module.exports = function(app, io, _moddir) {
  moddir = _moddir;

  let config, accounts;
  try {
    config = require("./matrix.json");
    accounts = require("./accounts.json");
  } catch (e) {
    console.error(e);
    return false;
  }

  const ratelimit = new PRatelimit(1000);

  augmentConfig(config, state => {
    gstate = state;

    app.post("/statusbot", bodyParser.json(), cmn.authgen(accounts), (req, res) => {
      if (typeof req.body.sender != "string" || typeof req.body.text != "string") {
        return res.sendStatus(400);
      }
      ratelimit.submit(rlcb => {
        ptimeout(5000,
          cb => matrixSendMsgLogin(`[${req.body.sender}] ${req.body.text}`, cb),
          (finished, success) => {
            if (!finished) {
              res.sendStatus(504);  // gateway timeout
              logFailure(`Timed out on message: [${req.body.sender}] ${req.body.text}`, () => {});
            } else if (!success) res.sendStatus(503);  // service unavailable
            else res.sendStatus(200);
            rlcb();
          }
        );
      });
    });
  });
};