const mongo = require('mongodb');
const MongoClient = mongo.MongoClient;
const ObjectID = mongo.ObjectID;
const DBName = "EMI_SOCIAL";
const mongoUrl = process.env.MONGO_URL;
const postDB = require("./dbTools/post.js");
const profileDB = require("./dbTools/profile.js");


const getDB = new Promise((resolve, reject) => {
    const DB = {ObjectID: mongo.ObjectID};
    MongoClient.connect(mongoUrl, function(err, db) {
        if (err) return reject(err);
    
        DB.db = db;
        DB.ObjectID = ObjectID;
        console.log("Connected to DB!");
        DB.usersCol = db.db(DBName).collection("users");
        DB.tokensCol = db.db(DBName).collection("tokens");
    
        DB.checkSessionOnDB = async (session_id, user_sid)=>{
            const temp_id = new mongo.ObjectID(session_id);
            //We can add cache, like a temporary Redis entry, to avoid calling the DB on each call
            const doc = await DB.tokensCol.findOne({"_id":temp_id});
            if(doc && doc.uid == user_sid){
                const userMongoId = new mongo.ObjectID(user_sid);
                const userInfo = await DB.usersCol.findOne({"_id": userMongoId}, {fields: {password: 0}});
                return userInfo;
            }
            return false;
        };

        DB.getUser = (username)=>{
            return DB.usersCol.findOne({ username: username });
        }

        DB.getUserById = (userid)=>{
            const _id = new mongo.ObjectID(userid);
            return DB.usersCol.findOne({ _id });
        }

        let usernamesCache = {}
        DB.getUsernameByIdCache = async (userid)=>{
            if(usernamesCache[userid]) return usernamesCache[userid];
            const _id = new mongo.ObjectID(userid);
            let user = await DB.usersCol.findOne({ _id });
            usernamesCache[userid] = user.username;
            return usernamesCache[userid];
        }

        DB.newUser = (userInformation)=>{
            return DB.usersCol.insertOne(userInformation).catch((err)=>{
                if (err.name === 'MongoError' && err.code === 11000) {
                    // Duplicate username
                    return "User already exists";
                }
                console.log(err);
                return "System Error";
            });
        };

        DB.newSession = (user_id)=>{
            return DB.tokensCol.insertOne({uid: user_id});
        }

        DB.removeSession = (session_id)=>{
            const temp_id = new mongo.ObjectID(session_id);
            return DB.tokensCol.deleteOne({"_id":temp_id});
        }

        postDB(DB);
        profileDB(DB);
    
        resolve(DB);
    });
});

exports.getDB = getDB;