/*
 * Copyright 2000-2017 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intellij.codeInsight.completion;

import com.intellij.openapi.Disposable;
import com.intellij.openapi.editor.Document;
import com.intellij.openapi.editor.event.DocumentEvent;
import com.intellij.openapi.editor.event.DocumentListener;
import com.intellij.openapi.editor.impl.event.DocumentEventImpl;
import com.intellij.openapi.util.Disposer;
import com.intellij.openapi.util.Key;
import com.intellij.psi.PsiFile;
import com.intellij.psi.util.PsiModificationTracker;
import org.jetbrains.annotations.Nullable;

import java.util.LinkedList;

/**
 * @author peter
 */
class OffsetTranslator implements Disposable {
  static final Key<OffsetTranslator> RANGE_TRANSLATION = Key.create("completion.rangeTranslation");

  private final PsiFile myOriginalFile;
  private final Document myCopyDocument;
  private final LinkedList<DocumentEvent> myTranslation = new LinkedList<>();

  OffsetTranslator(final Document originalDocument, final PsiFile originalFile, Document copyDocument) {
    myOriginalFile = originalFile;
    myCopyDocument = copyDocument;
    myCopyDocument.putUserData(RANGE_TRANSLATION, this);
    Disposer.register(originalFile.getProject(), this);

    final LinkedList<DocumentEvent> sinceCommit = new LinkedList<>();
    originalDocument.addDocumentListener(new DocumentListener() {
      @Override
      public void documentChanged(DocumentEvent e) {
        if (isUpToDate()) {
          DocumentEventImpl inverse =
            new DocumentEventImpl(originalDocument, e.getOffset(), e.getNewFragment(), e.getOldFragment(), 0, false);
          sinceCommit.addLast(inverse);
        }
      }
    }, this);
    
    myCopyDocument.addDocumentListener(new DocumentListener() {
      @Override
      public void documentChanged(DocumentEvent e) {
        if (isUpToDate()) {
          myTranslation.addFirst(e);
        }
      }
    }, this);

    originalFile.getProject().getMessageBus().connect(this).subscribe(PsiModificationTracker.TOPIC, new PsiModificationTracker.Listener() {
      long lastModCount = originalFile.getViewProvider().getModificationStamp();
      @Override
      public void modificationCountChanged() {
        if (isUpToDate() && lastModCount != originalFile.getViewProvider().getModificationStamp()) {
          myTranslation.addAll(sinceCommit);
          sinceCommit.clear();
        }
      }
    });

  }

  private boolean isUpToDate() {
    return this == myCopyDocument.getUserData(RANGE_TRANSLATION) && myOriginalFile.isValid();
  }

  @Override
  public void dispose() {
    if (isUpToDate()) {
      myCopyDocument.putUserData(RANGE_TRANSLATION, null);
    }
  }

  @Nullable
  Integer translateOffset(Integer offset) {
    for (DocumentEvent event : myTranslation) {
      offset = translateOffset(offset, event);
      if (offset == null) {
        return null;
      }
    }
    return offset;
  }

  @Nullable
  private static Integer translateOffset(int offset, DocumentEvent event) {
    if (event.getOffset() < offset && offset < event.getOffset() + event.getNewLength()) {
      if (event.getOldLength() == 0) {
        return event.getOffset();
      }

      return null;
    }

    return offset <= event.getOffset() ? offset : offset - event.getNewLength() + event.getOldLength();
  }

}