import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * 文件服务的文本文件实现。
 * 负责将题目数据以文本格式读写到本地文件系统。
 */
public class FileService implements IFileService {

  private static final DateTimeFormatter FILE_NAME_FORMATTER =
          DateTimeFormatter.ofPattern("yyyy-MM-dd-HH-mm-ss");

  @Override
  public void saveProblems(User user, List<Equation> problems) throws IOException {
    Path userDirectory = Paths.get(user.getStoragePath());
    // 确保用户的专属目录存在
    if (!Files.exists(userDirectory)) {
      Files.createDirectories(userDirectory);
    }

    String timestamp = LocalDateTime.now().format(FILE_NAME_FORMATTER);
    String fileName = timestamp + ".txt";
    Path filePath = userDirectory.resolve(fileName);

    try (BufferedWriter writer = new BufferedWriter(new FileWriter(filePath.toFile()))) {
      for (int i = 0; i < problems.size(); i++) {
        String problemLine = (i + 1) + ". " + problems.get(i).toString();
        writer.write(problemLine);
        writer.newLine();
        // 满足题目之间空一行的格式要求
        if (i < problems.size() - 1) {
          writer.newLine();
        }
      }
    }
  }

  @Override
  public Set<String> loadAllProblemHistory(User user) throws IOException {
    Set<String> historySet = new HashSet<>();
    Path userDirectoryPath = Paths.get(user.getStoragePath());
    File userDirectory = userDirectoryPath.toFile();

    if (!userDirectory.exists() || !userDirectory.isDirectory()) {
      return historySet; // 如果目录不存在，直接返回空集合
    }

    File[] files = userDirectory.listFiles((dir, name) -> name.toLowerCase().endsWith(".txt"));
    if (files == null) {
      return historySet;
    }

    for (File file : files) {
      try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
        String line;
        while ((line = reader.readLine()) != null) {
          if (!line.trim().isEmpty()) {
            String cleanedLine = line.replaceFirst("^\\d+\\.\\s*", "");
            historySet.add(cleanedLine);
          }
        }
      }
    }

    return historySet;
  }

}