const initSqlJs = require('sql.js');
const fs = require('fs');
const { resourceUsage } = require('process');

let db = null;
const DB_PATH = './ka.db';

// Helper functions

function getNextKANumber() {
    const result = db.exec('SELECT ka_number FROM articles ORDER BY id DESC LIMIT 1')

    if (result.length > 0 && result[0].values.length > 0) {
        const lastKANumber = result[0].values[0][0];
        const number = parseInt(lastKANumber.replace('KA', '')) + 1;
        return `KA${String(number).padStart(3, '0')}`;
    }

    return 'KA001';
}

async function initDb() {
    const SQL = await initSqlJs();

    console.log('Initializing Database...');

    // Loading Database if it already exists
    if (fs.existsSync(DB_PATH)) {
        const buffer = fs.readFileSync(DB_PATH);
        db = new SQL.Database(buffer);
        console.log('Database Loaded')
    } else {
        
        // Creating a new one if it does not
        console.log('Database not found. Creating new instance...')
        db = new SQL.Database();

        // Creating Knowledge Article table
        db.run(`
            CREATE TABLE articles (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                ka_number TEXT UNIQUE,
                title TEXT,
                content TEXT,
                created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
                updated_at DATETIME
            )
        `);

        db.run("CREATE INDEX idx_ka_number ON articles(ka_number)");

        // Saving the created db to file
        const data = db.export();
        fs.writeFileSync(DB_PATH, Buffer.from(data));
        console.log(`Database created at ${DB_PATH}`);
    }

    return db;
}

// Get all articles from the DB
function getAllArticles() {
    const result = db.exec("SELECT * FROM articles ORDER BY created_at DESC");

    if (result.length === 0) {
        return [];
    }

    const columns = result[0].columns;
    const rows = result[0].values;

    const articles = rows.map(row => {
        const article = {};

        columns.forEach((col, index) => {
            article[col] = row[index];
        });
        
        return article;
    })

    return articles;
}

// Get a specific article from the DB
function getArticle(ka_num) {
    const stmt = db.prepare('SELECT * FROM articles where ka_number = ?');
    stmt.bind([ka_num]);

    if (stmt.step()) {
        const article = stmt.getAsObject();
        stmt.free();
        return article;
    }

    stmt.free();
    return null;
}

// Create a new article
function createArticle(title, content) {
    const ka_num = getNextKANumber();

    db.run(
        "INSERT INTO articles (ka_number, title, content) VALUES (?, ?, ?)",
        [ka_num, title, content]
    );

    // Saving updated DB to file
    const data = db.export();
    fs.writeFileSync(DB_PATH, Buffer.from(data));

    return getArticle(ka_num);
}

function updateArticle(ka_num, title, content) {
    db.run(
        "UPDATE articles SET title = ?, content = ?, updated_at = CURRENT_TIMESTAMP WHERE ka_number = ?",
        [title, content, ka_num]
    );

    // Saving updated DB to file
    const data = db.export();
    fs.writeFileSync(DB_PATH, Buffer.from(data));

    return getArticle(ka_num);
}

// Delete the article from the DB
function deleteArticle(ka_num) {
    db.run(
        "DELETE FROM articles WHERE ka_number = ?",
        [ka_num]
    );

    // Saving updated DB to file
    const data = db.export();
    fs.writeFileSync(DB_PATH, Buffer.from(data));
}

// Simple search to look for matching terms or KA number
function searchArticles(query) {
    const searchTerm = `%${query}%`;
    const stmt = db.prepare(
        "SELECT * FROM articles WHERE title LIKE ? OR content LIKE ? or ka_number LIKE ? ORDER BY created_at DESC"
    );
    stmt.bind([searchTerm, searchTerm, searchTerm]);

    const results = [];
    while (stmt.step()) {
        results.push(stmt.getAsObject());
    }
    stmt.free();

    return results;
}

module.exports = { initDb, getAllArticles, getArticle, createArticle, updateArticle, deleteArticle, searchArticles };