import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class ReadFile {
	/**
	 * Opens a file and returns a list of all the lines in the file
	 * @param filename the name of the file with, only allowing a .txt extension
	 * @return The contents of the file
	 */
	public List<String> open(String filename) throws IllegalArgumentException, FileNotFoundException {
		// Check that the filetype is correct, otherwise, throw IllegalArgumentException
		if (!filename.endsWith(".txt")) {
			throw new IllegalArgumentException("The filename is not a .txt format");
		}
		
		// Open the file that was defined
		File file = new File(filename);
		Scanner reader = new Scanner(file);
		
		// List for all the separate lines on the database
		List<String> data = new ArrayList<>();
		
		// Go through all the lines in the file and append them to the list `data`
		while (reader.hasNextLine()) {
			String currentData = reader.nextLine();
			data.add(currentData);
		}
		
		return data;
	}
}