// Copyright (c) 2009 The Chromium Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

package org.chromium.debug.ui.editors;

import java.util.regex.Pattern;

import org.chromium.debug.core.ChromiumDebugPlugin;

import org.eclipse.jface.text.BadLocationException;

import org.eclipse.jface.text.IDocument;

import org.eclipse.jface.text.IRegion;

import org.eclipse.jface.text.Region;

/**

 * A utility for handling JavaScript-related data.

 */

public class JavascriptUtil {

  private static final String OPEN_BRACKET = "["; //$NON-NLS-1$

  private static final String CLOSE_BRACKET = "]"; //$NON-NLS-1$

  private static final String ID_CHARS_REGEX = "\\p{L}_$\\d"; //$NON-NLS-1$

  private static final String QUALIFIED_ID_CHARS_REGEX = ID_CHARS_REGEX + "\\.\\[\\]"; //$NON-NLS-1$

  /**

   * Contains chars acceptable as part of expression to inspect to the right of

   * the cursor.

   */

  public static final Pattern ID_PATTERN =

      Pattern.compile(OPEN_BRACKET + ID_CHARS_REGEX + CLOSE_BRACKET);

  /**

   * Contains chars acceptable as part of expression to inspect to the left of

   * the cursor.

   */

  public static final Pattern QUALIFIED_ID_PATTERN =

      Pattern.compile(OPEN_BRACKET + QUALIFIED_ID_CHARS_REGEX + CLOSE_BRACKET);

  public static boolean isJsIdentifierCharacter(char ch, boolean qualified) {

    return qualified

        ? QUALIFIED_ID_PATTERN.matcher(String.valueOf(ch)).find()

        : ID_PATTERN.matcher(String.valueOf(ch)).find();

  }

  /**

   * Returns a JavaScript qualified identifier surrounding the character at

   * {@code offset} position in the given {@code document}.

   *

   * @param document to extract an identifier from

   * @param offset of the pivot character (before, in, or after the identifier)

   * @return JavaScript identifier, or {@code null} if none found

   */

  public static String extractSurroundingJsIdentifier(IDocument document, int offset) {

    IRegion region = getSurroundingIdentifierRegion(document, offset, true);

    try {

      return region == null

          ? null

          : document.get(region.getOffset(), region.getLength());

    } catch (BadLocationException e) {

      ChromiumDebugPlugin.log(e);

      return null;

    }

  }

  /**

   * Returns a region enclosing a JavaScript identifier found in {@code doc} at

   * the {@code offset} position. If {@code qualified == true}, all leading

   * qualifying names will be included into the region, otherwise the member

   * operator (".") will be considered as an identifier terminator.

   *

   * @param doc the document to extract an identifier region from

   * @param offset of the pivot character (before, in, or after the identifier)

   * @param qualified whether to read qualified identifiers rather than simple

   *        ones

   * @return an IRegion corresponding to the JavaScript identifier overlapping

   *         offset, or null if none

   */

  public static IRegion getSurroundingIdentifierRegion(

      IDocument doc, int offset, boolean qualified) {

    if (doc == null) {

      return null;

    }

    try {

      int squareBrackets = 0;

      char ch = doc.getChar(offset);

      if (!isJsIdentifierCharacter(ch, qualified) && offset > 0) {

        --offset; // cursor is AFTER the identifier

      }

      int start = offset;

      int end = offset;

      int goodStart = offset;

      while (start >= 0) {

        ch = doc.getChar(start);

        if (!isJsIdentifierCharacter(ch, qualified)) {

          break;

        }

        if (ch == '[') {

          squareBrackets--;

        } else if (ch == ']') {

          squareBrackets++;

        }

        if (squareBrackets < 0) {

          break;

        }

        goodStart = start;

        --start;

      }

      start = goodStart;

      int length = doc.getLength();

      while (end < length) {

        try {

          ch = doc.getChar(end);

          if (!isJsIdentifierCharacter(ch, false)) {

            // stop at the current name qualifier

            // rather than scan through the entire qualified id

            break;

          }

          ++end;

        } catch (BadLocationException e) {

          ChromiumDebugPlugin.log(e);

        }

      }

      if (start >= end) {

        return null;

      } else {

        return new Region(start, end - start);

      }

    } catch (BadLocationException e) {

      ChromiumDebugPlugin.log(e);

      return null;

    }

  }

  private JavascriptUtil() {

    // not instantiable

  }

}