/*
 * Copyright (c) 2011, the Dart project authors.
 * 
 * Licensed under the Eclipse Public License v1.0 (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.eclipse.org/legal/epl-v10.html
 * 
 * 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.google.dart.tools.ui.internal.text.functions;

import com.ibm.icu.text.BreakIterator;

import org.eclipse.swt.graphics.GC;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;

/*
 * Not a real reader. Could change if requested
 */
public class LineBreakingReader {

  private BufferedReader fReader;
  private GC fGC;
  private int fMaxWidth;

  private String fLine;
  private int fOffset;

  private BreakIterator fLineBreakIterator;
  private boolean fBreakWords;

  /**
   * Creates a reader that breaks an input text to fit in a given width.
   * 
   * @param reader Reader of the input text
   * @param gc The graphic context that defines the currently used font sizes
   * @param maxLineWidth The max width (pixels) where the text has to fit in
   */
  public LineBreakingReader(Reader reader, GC gc, int maxLineWidth) {
    fReader = new BufferedReader(reader);
    fGC = gc;
    fMaxWidth = maxLineWidth;
    fOffset = 0;
    fLine = null;
    fLineBreakIterator = BreakIterator.getLineInstance();
    fBreakWords = true;
  }

  public boolean isFormattedLine() {
    return fLine != null;
  }

  /**
   * Reads the next line. The lengths of the line will not exceed the given maximum width.
   * 
   * @return the next line
   * @throws IOException
   */
  public String readLine() throws IOException {
    if (fLine == null) {
      String line = fReader.readLine();
      if (line == null) {
        return null;
      }

      int lineLen = fGC.textExtent(line).x;
      if (lineLen < fMaxWidth) {
        return line;
      }
      fLine = line;
      fLineBreakIterator.setText(line);
      fOffset = 0;
    }
    int breakOffset = findNextBreakOffset(fOffset);
    String res;
    if (breakOffset != BreakIterator.DONE) {
      res = fLine.substring(fOffset, breakOffset);
      fOffset = findWordBegin(breakOffset);
      if (fOffset == fLine.length()) {
        fLine = null;
      }
    } else {
      res = fLine.substring(fOffset);
      fLine = null;
    }
    return res;
  }

  private int findNextBreakOffset(int currOffset) {
    int currWidth = 0;
    int nextOffset = fLineBreakIterator.following(currOffset);
    while (nextOffset != BreakIterator.DONE) {
      String word = fLine.substring(currOffset, nextOffset);
      int wordWidth = fGC.textExtent(word).x;
      int nextWidth = wordWidth + currWidth;
      if (nextWidth > fMaxWidth) {
        if (currWidth > 0) {
          return currOffset;
        }

        if (!fBreakWords) {
          return nextOffset;
        }

        // need to fit into fMaxWidth
        int length = word.length();
        while (length >= 0) {
          length--;
          word = word.substring(0, length);
          wordWidth = fGC.textExtent(word).x;
          if (wordWidth + currWidth < fMaxWidth) {
            return currOffset + length;
          }
        }
        return nextOffset;
      }
      currWidth = nextWidth;
      currOffset = nextOffset;
      nextOffset = fLineBreakIterator.next();
    }
    return nextOffset;
  }

  private int findWordBegin(int idx) {
    while (idx < fLine.length() && Character.isWhitespace(fLine.charAt(idx))) {
      idx++;
    }
    return idx;
  }
}