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A packaging of the IntelliJ Community Edition platform-impl library. This is release number 1 of trunk branch 142.
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/*
 * Copyright 2000-2013 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.openapi.vfs.encoding;

import com.intellij.AppTopics;
import com.intellij.openapi.Disposable;
import com.intellij.openapi.application.ApplicationManager;
import com.intellij.openapi.editor.Document;
import com.intellij.openapi.editor.Editor;
import com.intellij.openapi.fileEditor.FileDocumentManager;
import com.intellij.openapi.fileEditor.FileDocumentManagerAdapter;
import com.intellij.openapi.fileEditor.impl.LoadTextUtil;
import com.intellij.openapi.fileTypes.FileType;
import com.intellij.openapi.fileTypes.FileTypes;
import com.intellij.openapi.fileTypes.StdFileTypes;
import com.intellij.openapi.project.Project;
import com.intellij.openapi.project.ProjectLocator;
import com.intellij.openapi.ui.Messages;
import com.intellij.openapi.util.Disposer;
import com.intellij.openapi.util.Pair;
import com.intellij.openapi.util.ThrowableComputable;
import com.intellij.openapi.util.text.StringUtil;
import com.intellij.openapi.vfs.*;
import com.intellij.refactoring.util.CommonRefactoringUtil;
import com.intellij.util.ArrayUtil;
import com.intellij.util.messages.MessageBusConnection;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.io.IOException;
import java.nio.charset.Charset;
import java.util.Arrays;

public class EncodingUtil {
  enum Magic8 {
    ABSOLUTELY,
    WELL_IF_YOU_INSIST,
    NO_WAY
  }

  // check if file can be loaded in the encoding correctly:
  // returns true if bytes on disk, converted to text with the charset, converted back to bytes matched
  static Magic8 isSafeToReloadIn(@NotNull VirtualFile virtualFile, @NotNull String text, @NotNull byte[] bytes, @NotNull Charset charset) {
    // file has BOM but the charset hasn't
    byte[] bom = virtualFile.getBOM();
    if (bom != null && !CharsetToolkit.canHaveBom(charset, bom)) return Magic8.NO_WAY;

    // the charset has mandatory BOM (e.g. UTF-xx) but the file hasn't or has wrong
    byte[] mandatoryBom = CharsetToolkit.getMandatoryBom(charset);
    if (mandatoryBom != null && !ArrayUtil.startsWith(bytes, mandatoryBom)) return Magic8.NO_WAY;

    String loaded = LoadTextUtil.getTextByBinaryPresentation(bytes, charset).toString();

    String separator = FileDocumentManager.getInstance().getLineSeparator(virtualFile, null);
    String toSave = StringUtil.convertLineSeparators(loaded, separator);

    String failReason = LoadTextUtil.wasCharsetDetectedFromBytes(virtualFile);
    if (failReason != null && CharsetToolkit.UTF8_CHARSET.equals(virtualFile.getCharset()) && !CharsetToolkit.UTF8_CHARSET.equals(charset)) {
      return Magic8.NO_WAY; // can't reload utf8-autodetected file in another charset
    }

    byte[] bytesToSave;
    try {
      bytesToSave = toSave.getBytes(charset);
    }
    catch (UnsupportedOperationException e) {
      return Magic8.NO_WAY;
    }
    if (bom != null && !ArrayUtil.startsWith(bytesToSave, bom)) {
      bytesToSave = ArrayUtil.mergeArrays(bom, bytesToSave); // for 2-byte encodings String.getBytes(Charset) adds BOM automatically
    }

    return !Arrays.equals(bytesToSave, bytes) ? Magic8.NO_WAY : loaded.equals(text) ? Magic8.ABSOLUTELY : Magic8.WELL_IF_YOU_INSIST;
  }

  static Magic8 isSafeToConvertTo(@NotNull VirtualFile virtualFile, @NotNull String text, @NotNull byte[] bytesOnDisk, @NotNull Charset charset) {
    try {
      String lineSeparator = FileDocumentManager.getInstance().getLineSeparator(virtualFile, null);
      String textToSave = lineSeparator.equals("\n") ? text : StringUtil.convertLineSeparators(text, lineSeparator);

      Pair chosen = LoadTextUtil.chooseMostlyHarmlessCharset(virtualFile.getCharset(), charset, textToSave);

      byte[] saved = chosen.second;

      CharSequence textLoadedBack = LoadTextUtil.getTextByBinaryPresentation(saved, charset);

      return !text.equals(textLoadedBack.toString()) ? Magic8.NO_WAY : Arrays.equals(saved, bytesOnDisk) ? Magic8.ABSOLUTELY : Magic8.WELL_IF_YOU_INSIST;
    }
    catch (UnsupportedOperationException e) { // unsupported encoding
      return Magic8.NO_WAY;
    }
  }

  public static void saveIn(@NotNull final Document document, final Editor editor, @NotNull final VirtualFile virtualFile, @NotNull final Charset charset) {
    FileDocumentManager documentManager = FileDocumentManager.getInstance();
    documentManager.saveDocument(document);
    final Project project = ProjectLocator.getInstance().guessProjectForFile(virtualFile);
    boolean writable = project == null ? virtualFile.isWritable() : ReadonlyStatusHandler.ensureFilesWritable(project, virtualFile);
    if (!writable) {
      CommonRefactoringUtil.showErrorHint(project, editor, "Cannot save the file " + virtualFile.getPresentableUrl(), "Unable to Save", null);
      return;
    }

    // first, save the file in the new charset and then mark the file as having the correct encoding
    try {
      ApplicationManager.getApplication().runWriteAction(new ThrowableComputable() {
        @Override
        public Object compute() throws IOException {
          virtualFile.setCharset(charset);
          LoadTextUtil.write(project, virtualFile, virtualFile, document.getText(), document.getModificationStamp());
          return null;
        }
      });
    }
    catch (IOException io) {
      Messages.showErrorDialog(project, io.getMessage(), "Error Writing File");
    }

    EncodingProjectManagerImpl.suppressReloadDuring(new Runnable() {
      @Override
      public void run() {
        EncodingManager.getInstance().setEncoding(virtualFile, charset);
      }
    });
  }

  static void reloadIn(@NotNull final VirtualFile virtualFile, @NotNull final Charset charset) {
    final FileDocumentManager documentManager = FileDocumentManager.getInstance();
    //Project project = ProjectLocator.getInstance().guessProjectForFile(myFile);
    //if (documentManager.isFileModified(myFile)) {
    //  int result = Messages.showDialog(project, "File is modified. Reload file anyway?", "File is Modified", new String[]{"Reload", "Cancel"}, 0, AllIcons.General.WarningDialog);
    //  if (result != 0) return;
    //}

    if (documentManager.getCachedDocument(virtualFile) == null) {
      // no need to reload document
      EncodingManager.getInstance().setEncoding(virtualFile, charset);
      return;
    }

    final Disposable disposable = Disposer.newDisposable();
    MessageBusConnection connection = ApplicationManager.getApplication().getMessageBus().connect(disposable);
    connection.subscribe(AppTopics.FILE_DOCUMENT_SYNC, new FileDocumentManagerAdapter() {
      @Override
      public void beforeFileContentReload(VirtualFile file, @NotNull Document document) {
        if (!file.equals(virtualFile)) return;
        Disposer.dispose(disposable); // disconnect

        EncodingManager.getInstance().setEncoding(file, charset);

        LoadTextUtil.setCharsetWasDetectedFromBytes(file, null);
      }
    });

    // if file was modified, the user will be asked here
    try {
      EncodingProjectManagerImpl.suppressReloadDuring(new Runnable() {
        @Override
        public void run() {
          ((VirtualFileListener)documentManager).contentsChanged(
            new VirtualFileEvent(null, virtualFile, virtualFile.getName(), virtualFile.getParent()));
        }
      });
    }
    finally {
      Disposer.dispose(disposable);
    }
  }

  // returns (hardcoded charset from the file type, explanation) or (null, null) if file type does not restrict encoding
  @NotNull
  static Pair checkHardcodedCharsetFileType(@NotNull VirtualFile virtualFile) {
    FileType fileType = virtualFile.getFileType();
    if (fileType.isBinary()) return Pair.create(null, "binary file");
    // in lesser IDEs all special file types are plain text so check for that first
    if (fileType == FileTypes.PLAIN_TEXT) return Pair.create(null, null);
    if (fileType == StdFileTypes.GUI_DESIGNER_FORM) return Pair.create(CharsetToolkit.UTF8_CHARSET, "IDEA GUI Designer form");
    if (fileType == StdFileTypes.IDEA_MODULE) return Pair.create(CharsetToolkit.UTF8_CHARSET, "IDEA module file");
    if (fileType == StdFileTypes.IDEA_PROJECT) return Pair.create(CharsetToolkit.UTF8_CHARSET, "IDEA project file");
    if (fileType == StdFileTypes.IDEA_WORKSPACE) return Pair.create(CharsetToolkit.UTF8_CHARSET, "IDEA workspace file");

    if (fileType == StdFileTypes.PROPERTIES) return Pair.create(virtualFile.getCharset(), ".properties file");

    if (fileType == StdFileTypes.XML || fileType == StdFileTypes.JSPX) {
      return Pair.create(virtualFile.getCharset(), "XML file");
    }
    return Pair.create(null, null);
  }

  @NotNull
  // returns existing charset (null means N/A), failReason: null means enabled, notnull means disabled and contains error message
  public static Pair checkCanReload(@NotNull VirtualFile virtualFile) {
    if (virtualFile.isDirectory()) {
      return Pair.create(null, "file is a directory");
    }
    FileDocumentManager documentManager = FileDocumentManager.getInstance();
    Document document = documentManager.getDocument(virtualFile);
    if (document == null) return Pair.create(null, "binary file");
    Charset charsetFromContent = ((EncodingManagerImpl)EncodingManager.getInstance()).computeCharsetFromContent(virtualFile);
    Charset existing = charsetFromContent;
    String failReason = LoadTextUtil.wasCharsetDetectedFromBytes(virtualFile);
    if (failReason != null) {
      // no point changing encoding if it was auto-detected
      existing = virtualFile.getCharset();
    }
    else if (charsetFromContent != null) {
      failReason = "hard coded in text";
    }
    else {
      Pair fileTypeCheck = checkHardcodedCharsetFileType(virtualFile);
      if (fileTypeCheck.second != null) {
        failReason = fileTypeCheck.second;
        existing = fileTypeCheck.first;
      }
    }
    if (failReason != null) {
      return Pair.create(existing, failReason);
    }
    return Pair.create(virtualFile.getCharset(), null);
  }

  @Nullable("null means enabled, notnull means disabled and contains error message")
  public static String checkCanConvert(@NotNull VirtualFile virtualFile) {
    if (virtualFile.isDirectory()) {
      return "file is a directory";
    }
    String failReason = null;

    Charset charsetFromContent = ((EncodingManagerImpl)EncodingManager.getInstance()).computeCharsetFromContent(virtualFile);
    if (charsetFromContent != null) {
      failReason = "Encoding is hard-coded in the text";
    }
    else {
      Pair check = checkHardcodedCharsetFileType(virtualFile);
      if (check.second != null) {
        failReason = check.second;
      }
    }

    if (failReason != null) {
      return failReason;
    }
    return null;
  }

  // null means enabled, (current charset, error description) otherwise
  @Nullable
  public static Pair checkSomeActionEnabled(@NotNull VirtualFile selectedFile) {
    String saveError = checkCanConvert(selectedFile);
    if (saveError == null) return null;
    Pair reloadError = checkCanReload(selectedFile);
    if (reloadError.second == null) return null;
    return Pair.create(reloadError.first, saveError);
  }

}