/* Copyright rememberjava.com. Licensed under GPL 3. See http://rememberjava.com/license */
package com.rememberjava.ui;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Random;
import java.util.stream.Collectors;

import javax.swing.JComponent;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.SwingUtilities;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Element;
import javax.swing.text.JTextComponent;
import javax.swing.text.Utilities;

/**
 * Example use of a left margin line number for a JEditorPane in a JScrollPane.
 * Uses a separate component for the RowHeaderView of the JScrollPane. Pads the
 * line numbers up to 999, highlights the currently active line, handles wrapped
 * lines and resizing of the editor.
 */
public class RowHeaderViewLineNumbers extends JFrame {

  private static final long serialVersionUID = 1L;

  public final int MARGIN_WIDTH_PX = 28;

  public static void main(String[] args) throws IOException {
    new RowHeaderViewLineNumbers();
  }

  public RowHeaderViewLineNumbers() throws IOException {
    JEditorPane editor = new JTextPane();
    LineNumbersView lineNumbers = new LineNumbersView(editor);

    JScrollPane scroll = new JScrollPane(editor);
    scroll.setRowHeaderView(lineNumbers);
    getContentPane().add(scroll);

    setSize(500, 500);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

    editor.setText(getRandomText());
  }

  /**
   * Returns the first 100 words of the default dictionary (on Ubuntu / Debian)
   * and injects random line breaks.
   */
  private String getRandomText() throws IOException {
    Random rnd = new Random();
    return Files.readAllLines(Paths.get("/usr/share/dict/words")).stream().limit(100)
        .map(word -> (rnd.nextInt(15) == 0 ? "\n" : "") + word).collect(Collectors.joining(" "));
  }

  /**
   * Left hand side RowHeaderView for a JEditorPane in a JScrollPane. Highlights
   * the currently selected line. Handles line wrapping, frame resizing.
   */
  class LineNumbersView extends JComponent implements DocumentListener, CaretListener, ComponentListener {

    private static final long serialVersionUID = 1L;

    private JTextComponent editor;

    private Font font;

    public LineNumbersView(JTextComponent editor) {
      this.editor = editor;

      editor.getDocument().addDocumentListener(this);
      editor.addComponentListener(this);
      editor.addCaretListener(this);
    }

    @Override
    public void paintComponent(Graphics g) {
      super.paintComponent(g);

      Rectangle clip = g.getClipBounds();
      int startOffset = editor.viewToModel(new Point(0, clip.y));
      int endOffset = editor.viewToModel(new Point(0, clip.y + clip.height));

      while (startOffset <= endOffset) {
        try {
          String lineNumber = getLineNumber(startOffset);
          if (lineNumber != null) {
            int x = getInsets().left + 2;
            int y = getOffsetY(startOffset);

            font = font != null ? font : new Font(Font.MONOSPACED, Font.BOLD, editor.getFont().getSize());
            g.setFont(font);

            g.setColor(isCurrentLine(startOffset) ? Color.RED : Color.BLACK);

            g.drawString(lineNumber, x, y);
          }

          startOffset = Utilities.getRowEnd(editor, startOffset) + 1;
        } catch (BadLocationException e) {
          e.printStackTrace();
          // ignore and continue
        }
      }
    }

    /**
     * Returns the line number of the element based on the given (start) offset
     * in the editor model. Returns null if no line number should or could be
     * provided (e.g. for wrapped lines).
     */
    private String getLineNumber(int offset) {
      Element root = editor.getDocument().getDefaultRootElement();
      int index = root.getElementIndex(offset);
      Element line = root.getElement(index);

      return line.getStartOffset() == offset ? String.format("%3d", index + 1) : null;
    }

    /**
     * Returns the y axis position for the line number belonging to the element
     * at the given (start) offset in the model.
     */
    private int getOffsetY(int offset) throws BadLocationException {
      FontMetrics fontMetrics = editor.getFontMetrics(editor.getFont());
      int descent = fontMetrics.getDescent();

      Rectangle r = editor.modelToView(offset);
      int y = r.y + r.height - descent;

      return y;
    }

    /**
     * Returns true if the given start offset in the model is the selected (by
     * cursor position) element.
     */
    private boolean isCurrentLine(int offset) {
      int caretPosition = editor.getCaretPosition();
      Element root = editor.getDocument().getDefaultRootElement();
      return root.getElementIndex(offset) == root.getElementIndex(caretPosition);
    }

    /**
     * Schedules a refresh of the line number margin on a separate thread.
     */
    private void documentChanged() {
      SwingUtilities.invokeLater(() -> {
        repaint();
      });
    }

    /**
     * Updates the size of the line number margin based on the editor height.
     */
    private void updateSize() {
      Dimension size = new Dimension(MARGIN_WIDTH_PX, editor.getHeight());
      setPreferredSize(size);
      setSize(size);
    }

    @Override
    public void insertUpdate(DocumentEvent e) {
      documentChanged();
    }

    @Override
    public void removeUpdate(DocumentEvent e) {
      documentChanged();
    }

    @Override
    public void changedUpdate(DocumentEvent e) {
      documentChanged();
    }

    @Override
    public void caretUpdate(CaretEvent e) {
      documentChanged();
    }

    @Override
    public void componentResized(ComponentEvent e) {
      updateSize();
      documentChanged();
    }

    @Override
    public void componentMoved(ComponentEvent e) {
    }

    @Override
    public void componentShown(ComponentEvent e) {
      updateSize();
      documentChanged();
    }

    @Override
    public void componentHidden(ComponentEvent e) {
    }
  }
}