package com.fosspowered.peist.service;

import com.fosspowered.peist.model.dao.Paste;
import com.fosspowered.peist.model.exceptions.PeistAccessDeniedException;
import com.fosspowered.peist.model.exceptions.PeistInternalException;
import com.fosspowered.peist.model.exceptions.PeistInvalidRequestException;
import com.fosspowered.peist.model.exceptions.PeistNotFoundException;
import com.fosspowered.peist.model.json.PasteRequest;
import com.fosspowered.peist.model.json.PasteResponse;
import com.fosspowered.peist.repository.PasteRepository;
import java.nio.charset.StandardCharsets;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.sql.Date;
import java.util.ArrayList;
import java.util.Base64;
import java.util.Calendar;
import java.util.List;
import java.util.Optional;
import java.util.UUID;
import java.util.stream.Collectors;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;
import lombok.extern.log4j.Log4j2;
import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

@Service
@Log4j2
public class PasteService {
  private final PasteRepository pasteRepository;

  private final String systemKey;

  PasteService(PasteRepository pasteRepository, @Value("${system-key}") String systemKey) {
    this.pasteRepository = pasteRepository;
    this.systemKey = systemKey;
  }

  public PasteResponse addPaste(PasteRequest request) {
    Paste paste = buildPasteData(request);
    this.pasteRepository.save(paste);
    return buildPasteResponse(paste);
  }

  private String convertToCipher(Date creationDate, String key, String text) {
    SecretKeySpec keySpec = buildSpec(creationDate, key);
    try {
      Cipher cipher = Cipher.getInstance("AES");
      cipher.init(Cipher.ENCRYPT_MODE, keySpec);
      byte[] cipherBytes = cipher.doFinal(text.getBytes(StandardCharsets.UTF_8));
      return Base64.getEncoder().encodeToString(cipherBytes);
    } catch (InvalidKeyException
        | IllegalBlockSizeException
        | BadPaddingException
        | NoSuchAlgorithmException
        | NoSuchPaddingException e) {
      throw new RuntimeException(e);
    }
  }

  private String convertFromCipher(Date creationDate, String key, String cipherText) {
    SecretKeySpec keySpec = buildSpec(creationDate, key);

    try {
      Cipher cipher = Cipher.getInstance("AES");
      cipher.init(Cipher.DECRYPT_MODE, keySpec);
      return new String(cipher.doFinal(Base64.getDecoder().decode(cipherText)));
    } catch (BadPaddingException e) {
      throw new PeistAccessDeniedException("Access denied for paste.");
    } catch (NoSuchAlgorithmException
        | InvalidKeyException
        | NoSuchPaddingException
        | IllegalBlockSizeException e) {
      log.error("Error while processing", e);
      throw new PeistInternalException("Error while processing");
    }
  }

  private SecretKeySpec buildSpec(Date creationDate, String key) {
    String keyStr =
        String.format(
            "%s%s%s", systemKey, StringUtils.isNotBlank(key) ? key : "", creationDate.getTime());
    try {
      MessageDigest sha = MessageDigest.getInstance("SHA-256");
      return new SecretKeySpec(sha.digest(keyStr.getBytes(StandardCharsets.UTF_8)), "AES");
    } catch (NoSuchAlgorithmException e) {
      throw new RuntimeException(e);
    }
  }

  public PasteResponse fetchPaste(String urlId) {
    return fetchPaste(urlId, null);
  }

  public PasteResponse fetchPaste(String urlId, String key) {
    Paste paste = fetchPasteFromDB(urlId);
    String text = convertFromCipher(paste.getCreationDate(), key, paste.getPasteData());
    paste.setPasteData(text);
    return buildPasteResponse(paste);
  }

  private Paste fetchPasteFromDB(String urlId) {
    if (StringUtils.isBlank(urlId)) {
      throw new PeistInvalidRequestException("Invalid request as urlId is invalid: " + urlId);
    }
    Optional<Paste> paste = this.pasteRepository.findByUrlId(urlId);
    if (paste.isPresent()) {
      return paste.get();
    } else {
      throw new PeistNotFoundException("Paste not found for urlId: " + urlId);
    }
  }

  public List<PasteResponse> fetchRecentPastes() {
    List<Paste> pasteList = new ArrayList<>(this.pasteRepository.findAll());
    return pasteList.stream().map(this::buildPasteResponse).collect(Collectors.toList());
  }

  private PasteResponse buildPasteResponse(Paste paste) {

    return PasteResponse.builder()
        .urlId(paste.getUrlId())
        .creationDate(paste.getCreationDate())
        .author(paste.getAuthor())
        .language(paste.getLanguage())
        .title(paste.getTitle())
        .expiryDate(paste.getExpiryDate())
        .isVisible(paste.getIsVisible())
        .pasteData(paste.getPasteData())
        .build();
  }

  private Paste buildPasteData(PasteRequest pasteRequest) {
    Calendar now = Calendar.getInstance();
    Date creationDate = new Date(now.getTime().getTime());
    now.add(Calendar.SECOND, pasteRequest.getTtl());
    Date expiryDate = new Date(now.getTime().getTime());

    String secretKey = pasteRequest.getSecretKey();
    boolean isVisible = StringUtils.isNotBlank(pasteRequest.getSecretKey());
    String text = convertToCipher(creationDate, secretKey, pasteRequest.getPasteData());

    Paste paste = new Paste();
    paste.setUrlId(UUID.randomUUID().toString());
    paste.setCreationDate(creationDate);
    paste.setTitle(pasteRequest.getTitle());
    paste.setAuthor(pasteRequest.getAuthor());
    paste.setLanguage(pasteRequest.getLanguage());
    paste.setExpiryDate(expiryDate);
    paste.setIsVisible(isVisible);
    paste.setPasteData(text);
    return paste;
  }
}
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