const express = require('express');
const multer = require('multer');
const XLSX = require('xlsx');
const path = require('path');

const app = express();
const upload = multer({ dest: 'uploads/' });

let students = [];
let scores = {};

// Middleware to serve static files
app.use(express.static('public'));

// Endpoint to upload Excel file
app.post('/upload', upload.single('file'), (req, res) => {
    const workbook = XLSX.readFile(req.file.path);
    const sheetName = workbook.SheetNames[0];
    const sheet = workbook.Sheets[sheetName];
    students = XLSX.utils.sheet_to_json(sheet);
    
    // Initialize scores
    students.forEach(student => {
        scores[student.id] = { name: student.name, points: 0 };
    });
    
    res.json(students);
});

// Endpoint to randomly select a student
app.get('/random', (req, res) => {
    if (students.length === 0) return res.status(400).send('No students available.');

    // Calculate weights based on scores
    const weights = students.map(student => {
        return Math.max(1, 10 - scores[student.id].points); // Higher score -> lower weight
    });

    const totalWeight = weights.reduce((sum, weight) => sum + weight, 0);
    const randomNum = Math.random() * totalWeight;
    let cumulativeWeight = 0;

    for (let i = 0; i < students.length; i++) {
        cumulativeWeight += weights[i];
        if (randomNum < cumulativeWeight) {
            return res.json(students[i]);
        }
    }
});

// Endpoint to update scores
app.post('/update-score', (req, res) => {
    const { id, correctRepeat, correctAnswer } = req.body;
    
    if (!scores[id]) return res.status(400).send('Invalid student ID.');

    if (correctRepeat) {
        scores[id].points += 0.5;
    } else {
        scores[id].points -= 1;
    }

    if (correctAnswer) {
        scores[id].points += 1; // Adjust according to your scoring logic
    }

    res.json(scores[id]);
});

// Start the server
app.listen(3000, () => {
    console.log('Server is running on http://localhost:3000');
});