import java.io.*;
import java.nio.file.*;
import java.nio.charset.StandardCharsets;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.*;

/**
 * 文件管理类，负责题目的保存和历史题目的管理
 */
public class FileManager {
    private static final String BASE_DIR = "math_papers";
    private DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd-HH-mm-ss");
    
    /**
     * 保存题目到文件
     * @param user 用户信息
     * @param problems 题目列表
     * @param difficulty 难度级别（当前选择）
     * @return 保存的文件路径
     */
    public String savePaperToFile(User user, List<MathProblem> problems, String difficulty) throws IOException {
        // 创建用户文件夹
        String userDir = BASE_DIR + File.separator + user.getUsername();
        Files.createDirectories(Paths.get(userDir));
        
        // 生成文件名
        String timestamp = LocalDateTime.now().format(formatter);
        String fileName = timestamp + ".txt";
        String filePath = userDir + File.separator + fileName;
        
        // 写入题目到文件
        try (PrintWriter writer = new PrintWriter(new FileWriter(filePath, StandardCharsets.UTF_8))) {
            writer.println("数学题目卷子");
            writer.println("用户: " + user.getUsername());
            writer.println("类型: " + difficulty);
            writer.println("生成时间: " + timestamp.replace("-", "/").replace("-", ":"));
            writer.println("题目数量: " + problems.size());
            writer.println("=" + "=".repeat(50));
            writer.println();
            
            for (int i = 0; i < problems.size(); i++) {
                writer.println((i + 1) + ". " + problems.get(i).toString());
                writer.println(); // 每题之间空一行
            }
        }
        
        return filePath;
    }
    
    /**
     * 获取用户历史题目，用于重复检测
     * @param username 用户名
     * @return 历史题目集合
     */
    public Set<String> getUserHistoryProblems(String username) {
        Set<String> historyProblems = new HashSet<>();
        String userDir = BASE_DIR + File.separator + username;
        
        try {
            Path userPath = Paths.get(userDir);
            if (!Files.exists(userPath)) {
                return historyProblems;
            }
            
            // 遍历用户文件夹中的所有txt文件
            Files.walk(userPath)
                .filter(path -> path.toString().endsWith(".txt"))
                .forEach(path -> {
                    try {
                        List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);
                        for (String line : lines) {
                            // 提取题目表达式（格式：数字. 表达式 = ?）
                            if (line.matches("^\\d+\\. .+ = \\?$")) {
                                String expression = line.substring(line.indexOf(". ") + 2, line.lastIndexOf(" = ?"));
                                historyProblems.add(expression);
                            }
                        }
                    } catch (IOException e) {
                        System.err.println("读取文件失败: " + path);
                    }
                });
        } catch (IOException e) {
            System.err.println("访问用户目录失败: " + userDir);
        }
        
        return historyProblems;
    }
    
    /**
     * 检查题目是否重复
     * @param username 用户名
     * @param problem 要检查的题目
     * @return 是否重复
     */
    public boolean isDuplicateProblem(String username, MathProblem problem) {
        Set<String> historyProblems = getUserHistoryProblems(username);
        return historyProblems.contains(problem.getExpression());
    }
    
    /**
     * 生成不重复的题目列表
     * @param user 用户信息
     * @param generator 题目生成器
     * @param count 题目数量
     * @param difficulty 难度级别
     * @return 不重复的题目列表
     */
    public List<MathProblem> generateUniqueProblems(User user, MathProblemGenerator generator, 
                                                   int count, String difficulty) {
        List<MathProblem> problems = new ArrayList<>();
        Set<String> historyProblems = getUserHistoryProblems(user.getUsername());
        Set<String> currentProblems = new HashSet<>();
        
        int attempts = 0;
        int maxAttempts = count * 10; // 最多尝试次数，避免无限循环
        
        while (problems.size() < count && attempts < maxAttempts) {
            MathProblem problem = generator.generateProblem(difficulty);
            String expression = problem.getExpression();
            
            // 检查是否与历史题目或当前题目重复
            if (!historyProblems.contains(expression) && !currentProblems.contains(expression)) {
                problems.add(problem);
                currentProblems.add(expression);
            }
            
            attempts++;
        }
        
        if (problems.size() < count) {
            System.out.println("警告: 只生成了 " + problems.size() + " 道题目，可能存在重复限制。");
        }
        
        return problems;
    }
}