code_editor.py

from PyQt5.QtWidgets import QPlainTextEdit, QWidget, QTextEdit
from PyQt5.QtCore import Qt, QRect, QSize
from PyQt5.QtGui import QPainter, QColor, QFont, QTextCursor, QSyntaxHighlighter, QTextCharFormat, QTextFormat

class LineNumberArea(QWidget):
    def __init__(self, editor):
        super().__init__(editor)
        self.editor = editor

    def sizeHint(self):
        return QSize(self.editor.line_number_area_width(), 0)

    def paintEvent(self, event):
        self.editor.line_number_area_paint_event(event)

class CodeEditor(QPlainTextEdit):
    def __init__(self, *args):
        super(CodeEditor, self).__init__(*args)

        self.line_number_area = LineNumberArea(self)

        self.blockCountChanged.connect(self.update_line_number_area_width)
        self.updateRequest.connect(self.update_line_number_area)
        self.cursorPositionChanged.connect(self.highlight_current_line)

        self.update_line_number_area_width(0)
        self.highlight_current_line()

        self.setLineWrapMode(QPlainTextEdit.NoWrap)
        self.setTabStopDistance(self.fontMetrics().horizontalAdvance(' ') * 4)

        self.setReadOnly(False)

    def line_number_area_width(self):
        digits = 1
        max_num = max(1, self.blockCount())
        while max_num >= 10:
            max_num //= 10
            digits += 1
        space = 3 + self.fontMetrics().horizontalAdvance('9') * digits
        return space

    def update_line_number_area_width(self, _):
        self.setViewportMargins(self.line_number_area_width(), 0, 0, 0)

    def update_line_number_area(self, rect, dy):
        if dy:
            self.line_number_area.scroll(0, dy)
        else:
            self.line_number_area.update(0, rect.y(), self.line_number_area.width(), rect.height())

        if rect.contains(self.viewport().rect()):
            self.update_line_number_area_width(0)

    def resizeEvent(self, event):
        super(CodeEditor, self).resizeEvent(event)
        cr = self.contentsRect()
        self.line_number_area.setGeometry(QRect(cr.left(), cr.top(), self.line_number_area_width(), cr.height()))

    def line_number_area_paint_event(self, event):
        painter = QPainter(self.line_number_area)
        painter.fillRect(event.rect(), Qt.lightGray)

        block = self.firstVisibleBlock()
        block_number = block.blockNumber()
        top = int(self.blockBoundingGeometry(block).translated(self.contentOffset()).top())
        bottom = top + int(self.blockBoundingRect(block).height())

        while block.isValid() and top <= event.rect().bottom():
            if block.isVisible() and bottom >= event.rect().top():
                number = str(block_number + 1)
                painter.setPen(Qt.black)
                painter.drawText(0, top, self.line_number_area.width(), self.fontMetrics().height(), Qt.AlignRight, number)

            block = block.next()
            top = bottom
            bottom = top + int(self.blockBoundingRect(block).height())
            block_number += 1

    def highlight_current_line(self):
        extra_selections = []

        if not self.isReadOnly():
            selection = QTextEdit.ExtraSelection()
            line_color = QColor(Qt.yellow).lighter(160)
            selection.format.setBackground(line_color)
            selection.format.setProperty(QTextFormat.FullWidthSelection, True)
            selection.cursor = self.textCursor()
            selection.cursor.clearSelection()
            extra_selections.append(selection)

        self.setExtraSelections(extra_selections)

    def keyPressEvent(self, event):
        if event.key() in [Qt.Key_Return, Qt.Key_Enter]:
            self.handle_return()
        elif event.key() == Qt.Key_Tab:
            self.handle_tab()
        elif event.key() == Qt.Key_Backspace:
            self.handle_backspace()
        else:
            super(CodeEditor, self).keyPressEvent(event)

    def handle_return(self):
        cursor = self.textCursor()
        current_line = cursor.block().text()
        indentation = self._get_indentation(current_line)
        
        # Check if the current line ends with a colon
        if current_line.strip().endswith(':'):
            indentation += '    '  # Add an extra level of indentation
        
        cursor.insertText('\n' + indentation)

    def handle_tab(self):
        cursor = self.textCursor()
        cursor.insertText('    ')  # Insert 4 spaces for a tab

    def handle_backspace(self):
        cursor = self.textCursor()
        current_line = cursor.block().text()
        if current_line.endswith('    '):  # If line ends with 4 spaces
            for _ in range(4):  # Remove all 4 spaces at once
                cursor.deletePreviousChar()
        else:
            cursor.deletePreviousChar()  # Normal backspace behavior

    def _get_indentation(self, line):
        return line[:len(line) - len(line.lstrip())]