import { createConnection, Connection } from "mysql";
import { conf } from "./ConfigHelper";

/**
 * Database helper
 * 
 * @author Pierre HUBERT
 */

export interface QueryInformation {
	table: string,
	fields ?: Array<String>,
	where ?: Object,
	limit ?: number,
}

export class DatabaseHelper {

	private static connection : Connection;

	/**
	 * Connect to database
	 */
	static async connect() {
		this.connection = createConnection({
			host: conf().database.host,
			user: conf().database.user,
			password: conf().database.password,
			database: conf().database.dbName
		});

		await new Promise((resolve, reject) => {
			this.connection.connect(err => {

				if(err) {
					console.error("Could not connect to database !");
					console.error(err);
					reject(err);
					return;
				}

				console.info("Connected to database.");
				resolve();
			});
		})
	}

	/**
	 * Query the database (SELECT)
	 * 
	 * @param info Information about the query
	 */
	static async Query(info: QueryInformation) : Promise<Array<any>> {
		// Prepare SQL request
		let request = "SELECT ";
		
		// Requested fields
		request += info.fields ? info.fields.join(",") : "*";
		
		request += " FROM " + info.table;
		let args = [];

		// Add where arguments
		if(info.where) {
			request += " WHERE ";

			for(const k in info.where) {
				if(!info.where.hasOwnProperty(k))
					continue;
				const v = info.where[k].toString();

				request += k;
				request += v.startsWith("%") || v.endsWith("%") ? " LIKE " : " = "
				request += "? AND "

				args.push(v);
			};

			// Remove the last (useless) AND
			request = request.substr(0, request.length - 4)
		}

		// Limit (if any)
		if(info.limit)
			request += " LIMIT " + info.limit;

		
		// Execute request
		return await new Promise((resolve, reject) => {
			this.connection.query( request, args, (err, result, fields) => {
				if(err) {
					reject(err);
					return;
				}

				resolve(result);
			});
		});
	}

	/**
	 * Query a single row on the database
	 * 
	 * @param info Information about the request
	 * @returns First matching row / null if none found
	 */
	static async QueryRow(info : QueryInformation) : Promise<any | null> {
		info.limit = 1;
		const result = await this.Query(info);

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

	/**
	 * Insert an new entry into the database
	 * 
	 * @param info Information about the entry
	 * @returns The ID of the inserted column (if any)
	 */
	static async InsertRow(table : string, values : any) : Promise<number> {
		return new Promise((resolve, reject) => {
			this.connection.query("INSERT INTO " + table + " SET ?", values, (err, results, f) => {
				if(err)
					reject(err);
				else
					resolve(results.insertId);
			});
		});
	}

	/**
	 * Delete entries from a table
	 * 
	 * @param table Target table
	 * @param where Where arguments
	 */
	static async DeleteRows(table: string, where: any) {

		let whereArgs = "";
		let args = [];

		// Process conditions
		for (const key in where) {
			if (where.hasOwnProperty(key)) {
				const value = where[key];
				whereArgs += (whereArgs == "" ? "" : " AND ") + key + " = ?";
				args.push(value);
			}
		}

		if(whereArgs == "")
			throw Error("Error : table could accidentally get purged!");

		return new Promise((resolve, reject) => {
			this.connection.query("DELETE FROM " + table + " WHERE " + whereArgs, args, (err, r, f) => {
				if(err) reject(err)
				else resolve();
			});
		})
	}
}