/*
 * MIT License
 *
 * Copyright (c) 2020-present Cloudogu GmbH and Contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package sonia.scm.repository.spi;

import org.eclipse.jgit.diff.DiffEntry;
import org.eclipse.jgit.diff.DiffFormatter;
import org.eclipse.jgit.util.QuotedString;
import sonia.scm.repository.api.DiffCommandBuilder;

import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import static java.nio.charset.StandardCharsets.UTF_8;

/**
 * @author Sebastian Sdorra
 */
public class GitDiffCommand extends AbstractGitCommand implements DiffCommand {

  GitDiffCommand(GitContext context) {
    super(context);
  }

  @Override
  public DiffCommandBuilder.OutputStreamConsumer getDiffResult(DiffCommandRequest request) throws IOException {
    @SuppressWarnings("squid:S2095") // repository will be closed with the RepositoryService
      org.eclipse.jgit.lib.Repository repository = open();

    Differ.Diff diff = Differ.diff(repository, request);

    return output -> {
      try (DiffFormatter formatter = new DiffFormatter(new DequoteOutputStream(output))) {
        formatter.setRepository(repository);

        for (DiffEntry e : diff.getEntries()) {
          if (idOrPathChanged(e)) {
            formatter.format(e);
          }
        }

        formatter.flush();
      }
    };
  }

  private boolean idOrPathChanged(DiffEntry e) {
    return !e.getOldId().equals(e.getNewId()) || !e.getNewPath().equals(e.getOldPath());
  }

  static class DequoteOutputStream extends OutputStream {

    private static final String[] DEQUOTE_STARTS = {
      "--- ",
      "+++ ",
      "diff --git "
    };

    private final OutputStream target;

    private boolean afterNL = true;
    private boolean writeToBuffer = false;
    private int numberOfPotentialBeginning = -1;
    private int potentialBeginningCharCount = 0;
    private boolean inPotentialQuotedLine = false;

    private final ByteArrayOutputStream buffer = new ByteArrayOutputStream();

    DequoteOutputStream(OutputStream target) {
      this.target = new BufferedOutputStream(target);
    }

    @Override
    public void write(int i) throws IOException {
      if (i == (int) '\n') {
        handleNewLine(i);
        return;
      }

      if (afterNL) {
        afterNL = false;
        if (foundPotentialBeginning(i)) {
          return;
        }
        numberOfPotentialBeginning = -1;
        inPotentialQuotedLine = false;
      }

      if (inPotentialQuotedLine && i == '"') {
        handleQuote();
        return;
      }

      if (numberOfPotentialBeginning > -1 && checkForFurtherBeginning(i)) {
        return;
      }

      if (writeToBuffer) {
        buffer.write(i);
      } else {
        target.write(i);
      }
    }

    private boolean checkForFurtherBeginning(int i) throws IOException {
      if (i == DEQUOTE_STARTS[numberOfPotentialBeginning].charAt(potentialBeginningCharCount)) {
        if (potentialBeginningCharCount + 1 < DEQUOTE_STARTS[numberOfPotentialBeginning].length()) {
          ++potentialBeginningCharCount;
        } else {
          inPotentialQuotedLine = true;
        }
        target.write(i);
        return true;
      } else {
        numberOfPotentialBeginning = -1;
      }
      return false;
    }

    private boolean foundPotentialBeginning(int i) throws IOException {
      for (int n = 0; n < DEQUOTE_STARTS.length; ++n) {
        if (i == DEQUOTE_STARTS[n].charAt(0)) {
          numberOfPotentialBeginning = n;
          potentialBeginningCharCount = 1;
          target.write(i);
          return true;
        }
      }
      return false;
    }

    private void handleQuote() throws IOException {
      if (writeToBuffer) {
        buffer.write('"');
        dequoteBuffer();
      } else {
        writeToBuffer = true;
        buffer.reset();
        buffer.write('"');
      }
    }

    private void handleNewLine(int i) throws IOException {
      afterNL = true;
      if (writeToBuffer) {
        dequoteBuffer();
      }
      target.write(i);
    }

    private void dequoteBuffer() throws IOException {
      byte[] bytes = buffer.toByteArray();
      String dequote = QuotedString.GIT_PATH.dequote(bytes, 0, bytes.length);
      target.write(dequote.getBytes(UTF_8));
      writeToBuffer = false;
    }

    @Override
    public void flush() throws IOException {
      target.flush();
    }
  }
}
