/****************************************************************/
/************* INITIALISATION ***********************************/
/****************************************************************/
let express = require('express');
let path = require('path');
let bodyParser = require('body-parser');
let mysql = require('mysql');

let app = express();

// Define the static folder
app.use(express.static(path.join(__dirname, 'public')));

// Neded for parsing json data
app.use(bodyParser.json());

// Inform that server is alive
console.log("Server running on 8080.");

// Listen to a port
app.listen(8080);

/****************************************************************/
/************* DATABASE QUERY ***********************************/
/****************************************************************/
// define an object with connection parameters
const CONNECTION_PARAMETERS = {
    host: "localhost",
    port: 55555,
    user: "root",
    password: "sa",
    database: "firstdb"
};
/**
 * Runs a query.
 * @param {object} conParam - The object with connection parameters.
 * @param {string} sql - The sql query.
 * @returns {[object]} An array with results.
 * @throws {error} An error resulting from interaction with database.
 */
function performDatabaseQuery(conParam, sql) {
    return new Promise(function (resolve, reject) {
        // create a connection to db
        let con = mysql.createConnection(CONNECTION_PARAMETERS);
        // open the connection
        con.connect(function (err) {
            // if connection error occurs, the client must be informed
            if (err) {
                reject(new Error("Eroare la conectarea la baza de date." + err.message));
            } else {
                // run query
                con.query(sql, function (err, result) {

                    if (err) {
                        // if query error occurs, the client must be informed
                        reject(new Error("Eroare la inserarea datelor." + err.message));
                    } else {
                        // if we are here => Hooray, no errors!
                        resolve(result);
                    }
                });
            }
        });
    });
}

/****************************************************************/
/************* DEFINE ROUTES ************************************/
/****************************************************************/
// post on /student
app.post('/student', async function (req, res) {
    try {
        // get data from client request
        let student = {
            name: req.body.name,
            grade: req.body.grade
        };
        // data must be validated on the server
        testValidity(student);
        // prepare the insert query
        let sql = "INSERT INTO students (name, grade) VALUES ('" + student.name + "','" + student.grade + "');";
        // run query
        await performDatabaseQuery(CONNECTION_PARAMETERS, sql);
        // inform the client about successful operation
        res.status(200).send();
    } catch (err) {
        // inform the client about errors
        res.status(500).send("Eroare server." + err.message);
        throw err;
    }
});
// get on /student
app.get('/student', async function (req, res) {
    try {
        // prepare the select query
        let sql = "SELECT * FROM students;";
        // run query
        let result = await performDatabaseQuery(CONNECTION_PARAMETERS, sql);
        // inform the client about successful operation
        res.status(200).send(result);
    } catch (err) {
        // inform the client about errors
        res.status(500).send("Eroare server." + err.message);
        throw err;
    }
});
// delete on /student
app.delete('/student', async function (req, res) {
    try {
        // get data from client request
        let id = req.body.id;
        // prepare the delete query
        let sql = "DELETE FROM students WHERE id = " + id + ";";
        console.log(sql);
        // run query
        await performDatabaseQuery(CONNECTION_PARAMETERS, sql);
        // inform the client about successful operation
        res.status(200).send();
    } catch (err) {
        // inform the client about errors
        res.status(500).send("Eroare server." + err.message);
        throw err;
    }
});
app.put('/student', async function (req, res) {
    try {
        // get data from client request
        let student = {
            name: req.body.name,
            grade: req.body.grade,
            id:req.body.id
        };
        // data must be validated on the server
        testValidity(student);
        // prepare the insert query
        let sql = "UPDATE students SET name='"+ student.name+ "',grade='"+student.grade+"' WHERE id='"+student.id+"';";
        // run query
        await performDatabaseQuery(CONNECTION_PARAMETERS, sql);
        // inform the client about successful operation
        res.status(200).send();
    } catch (err) {
        // inform the client about errors
        res.status(500).send("Eroare server." + err.message);
        throw err;
    }
});
/****************************************************************/
/************* VALIDATION FUNCTIONS *****************************/
/****************************************************************/
// private constants for validation
const NAME_MIN_LENGTH = 3;
const NAME_MAX_LENGTH = 100;
const GRADE_MIN_VALUE = 1;
const GRADE_MAX_VALUE = 10;
/**
 * Test the validity of a student (name and grade).
 * @param {object} student - The student to be validated.
 * @throws {error} An error resulting from validation.
 */
function testValidity(student) {
    let errorMessages = "";
    if (typeof student.name === "undefined" || student.name === null || student.name.length < NAME_MIN_LENGTH || student.name.length > NAME_MAX_LENGTH) {
        errorMessages += "Name should have at least three characters and should not exceed fifty characters.";
    }
    if (typeof student.grade === "undefined" || student.grade === null || isNaN(student.grade) || student.age < GRADE_MIN_VALUE || student.grade > GRADE_MAX_VALUE) {
        errorMessages += "Grade should be a number between 1 and 10.";
    }
    if (errorMessages) {
        throw new Error(errorMessages);
    }
}