import java.io.*;
import java.text.SimpleDateFormat;
import java.util.*;

/**
 * 文件工具类：生成文件名、保存题目、读取已有题目
 */
public class FileUtils {

    // 生成文件名
    public static String generateFileName() {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss");
        return sdf.format(new Date()) + ".txt";
    }

    // 保存题目到用户文件夹
    public static void saveQuestionsToFile(String userId, String fileName, List<MathQuestion> questions) {
        File userFolder = new File(userId);
        if (!userFolder.exists()) {
            userFolder.mkdirs();
        }

        File file = new File(userFolder, fileName);
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(file))) {
            for (MathQuestion question : questions) {
                writer.write("题号 " + question.getQuestionNumber() + ": " + question.getQuestionText());
                writer.newLine();
                writer.newLine();
            }
            writer.flush();
        } catch (IOException e) {
            throw new RuntimeException("写文件失败: " + file.getAbsolutePath(), e);
        }
    }

    // 读取用户文件夹下所有 txt 文件中已存在的题目
    public static Set<String> loadExistingQuestions(String userId) {
        Set<String> existingQuestions = new HashSet<>();
        File userFolder = new File(userId);
        if (!userFolder.exists() || !userFolder.isDirectory()) return existingQuestions;

        File[] files = userFolder.listFiles((dir, name) -> name != null && name.endsWith(".txt"));
        if (files == null) return existingQuestions;

        for (File f : files) {
            try (BufferedReader reader = new BufferedReader(new FileReader(f))) {
                String line;
                while ((line = reader.readLine()) != null) {
                    line = line.trim();
                    if (line.isEmpty()) continue;
                    if (line.startsWith("题号")) {
                        int idx = line.indexOf(":");
                        if (idx != -1 && idx + 1 < line.length()) {
                            existingQuestions.add(line.substring(idx + 1).trim());
                        }
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return existingQuestions;
    }
}