Add a delete symbol that is in the right bottom corner of the results filed it should be an overlay like the search button. If the user presses it the results field should be emptied. The assigned variables should not be deleted. Python 3.12 code: import math
import re
from typing import Any, Union, Callable

from PySide6.QtWidgets import (
    QApplication, QMainWindow, QWidget, QVBoxLayout, QHBoxLayout,
    QLineEdit, QTextEdit, QScrollBar, QPushButton, QLabel, QFrame,
    QGridLayout
)
from PySide6.QtGui import QFont
from PySide6.QtCore import Qt, QSize

def convert_angle(func: Callable[[float], float], x: float, use_degrees: bool) -> float:
    """Apply trig function with optional degree conversion."""
    return func(math.radians(x)) if use_degrees else func(x)

def kilograms_to_pounds(kg: float) -> float:
    """Convert kilograms to pounds."""
    return kg / 0.45359237

def pounds_to_kilograms(lb: float) -> float:
    """Convert pounds to kilograms."""
    return lb * 0.45359237

def celsius_to_kelvin(c: float) -> float:
    """Convert Celsius to Kelvin."""
    return c + 273.15

def kelvin_to_celsius(k: float) -> float:
    """Convert Kelvin to Celsius."""
    return k - 273.15

def celsius_to_fahrenheit(c: float) -> float:
    """Convert Celsius to Fahrenheit."""
    return c * 9 / 5 + 32

def fahrenheit_to_celsius(f: float) -> float:
    """Convert Fahrenheit to Celsius."""
    return (f - 32) * 5 / 9

def capitalize_sentence(sentence: str) -> str:
    """Capitalize first letter of each word."""
    return ' '.join(word.capitalize() for word in sentence.split())

def remove_duplicates(text: str) -> str:
    """Remove duplicate words and empty lines."""
    words = ' '.join(line.strip() for line in text.splitlines() if line.strip()).split()
    return ' '.join(dict.fromkeys(words))

def get_safe_globals(use_degrees: bool, variables: dict) -> dict:
    """Provide safe globals for expression evaluation."""
    trig_funcs = {'sin', 'cos', 'tan', 'asin', 'acos', 'atan'}
    safe_globals = {
        "sqrt": math.sqrt,
        "log": math.log10,
        "ln": math.log,
        "pi": math.pi,
        "e": math.e,
        "lb": kilograms_to_pounds,
        "kg": pounds_to_kilograms,
        "C": kelvin_to_celsius,
        "K": celsius_to_kelvin,
        "F": celsius_to_fahrenheit,
        "CF": fahrenheit_to_celsius,
        "capitalize": capitalize_sentence,
        "duplicates": remove_duplicates,
    }
    for func in trig_funcs:
        safe_globals[func] = lambda x, f=func: convert_angle(getattr(math, f), x, use_degrees)
    safe_globals.update(variables)
    return safe_globals

def preprocess_text_functions(expression: str) -> str:
    """Preprocess text functions with argument quotes."""
    def add_quotes(match):
        func, args = match.groups()
        return f'{func}("{args}")' if func in ['capitalize', 'duplicates'] else match.group(0)
    return re.sub(r'\b(capitalize|duplicates)\s*\(\s*([^)]+)\s*\)', add_quotes, expression)

def validate_inverse_trig(expression: str, safe_globals: dict) -> Union[str, None]:
    """Check inverse trig function domain validity."""
    for func, arg in re.findall(r"(\b\w+\b)\s*\(\s*([^)]+)\s*\)", expression):
        if func in ["asin", "acos"]:
            try:
                value = eval(arg, {"__builtins__": None}, safe_globals)
                if abs(value) > 1:
                    return f"Error: {func}(x) is undefined for |x| > 1"
            except Exception as e:
                return f"Error: {e}"
    return None

def safe_evaluate(expression: str, safe_globals: dict) -> Union[str, Any]:
    """Safely evaluate expression and format result with three decimal places."""
    try:
        result = eval(expression, {"__builtins__": None}, safe_globals)
        if isinstance(result, (int, float)):
            if isinstance(result, float):
                abs_result = abs(result)
                if (abs_result >= 1e9) or (abs_result != 0 and abs_result < 1e-6):
                    result = f"{result:.3e}"
                else:
                    result = f"{result:.3f}"
            else:
                if len(str(abs(result))) > 9:
                    result = f"{result:.3e}"
                else:
                    result = str(result)
            return result
        else:
            return str(result)
    except Exception as e:
        return f"Error: {e}"

def evaluate_expression(expression: str, variables: dict, use_degrees: bool = False) -> Union[float, str]:
    """Evaluate math expression considering modes."""
    assignment_match = re.match(r'^\s*([a-zA-Z_]\w*)\s*=\s*(.+)$', expression)
    expression = preprocess_text_functions(expression)
    safe_globals = get_safe_globals(use_degrees, variables)
    
    if assignment_match:
        var_name, var_expr = assignment_match.groups()
        var_value = safe_evaluate(var_expr, safe_globals)
        try:
            # Convert the evaluated value to float or int if possible
            if isinstance(var_value, str) and not var_value.startswith("Error"):
                if '.' in var_value:
                    var_value_converted = float(var_value)
                else:
                    var_value_converted = int(var_value)
                variables[var_name] = var_value_converted
                return f"{var_name} = {var_value_converted}"
            else:
                return var_value  # Return the error message
        except ValueError:
            return f"Error: Cannot assign non-numeric value to variable '{var_name}'"
    else:
        error = validate_inverse_trig(expression, safe_globals)
        if error:
            return error
        return safe_evaluate(expression, safe_globals)

class CalculatorGUI(QMainWindow):
    """PySide6-based calculator application."""

    def __init__(self):
        super().__init__()
        self.use_degrees = False
        self.variables = {}
        self.history_entries = []
        self.setup_window()
        self.create_widgets()
        self.layout_widgets()
        self.connect_signals()

    def setup_window(self) -> None:
        """Set main window properties."""
        self.setWindowTitle("Calculator")
        self.setGeometry(100, 100, 1280, 720)

    def create_widgets(self) -> None:
        """Initialize GUI components."""
        font = QFont()
        font.setPointSize(12)
        font.setFamily('Literata')

        self.entry = QLineEdit()
        self.entry.setFont(font)
        self.entry.setPlaceholderText('Enter expression')
        self.entry.setClearButtonEnabled(True)
        self.entry.returnPressed.connect(self.calculate)

        self.history_text = QTextEdit()
        self.history_text.setFont(font)
        self.history_text.setReadOnly(True)

        self.scrollbar = QScrollBar(Qt.Vertical)
        self.history_text.setVerticalScrollBar(self.scrollbar)

        self.search_button = QPushButton("🔍", self.history_text)
        self.search_button.setFixedSize(24, 24)
        self.search_button.setToolTip("Search History")
        self.search_button.setStyleSheet("""
            QPushButton {
                border: none;
                background-color: rgba(255, 255, 255, 200);
                font-size: 14px;
                border-radius: 12px;
            }
            QPushButton:hover {
                background-color: rgba(0, 120, 215, 200);
                color: white;
            }
        """)
        self.search_button.clicked.connect(self.toggle_search)

        self.search_bar = QLineEdit(self.history_text)
        self.search_bar.setPlaceholderText("Search...")
        self.search_bar.setFixedHeight(24)
        self.search_bar.setVisible(False)
        self.search_bar.setStyleSheet("""
            QLineEdit {
                border: 1px solid gray;
                border-radius: 4px;
                padding: 2px 4px;
                background-color: white;
            }
        """)
        self.search_bar.textChanged.connect(self.filter_history)
        self.search_bar.setClearButtonEnabled(True)

        self.function_buttons = {
            "Functions": ["sqrt", "sin", "cos", "tan", "asin", "acos", "atan", "log", "ln"],
            "Conversions": ["lb", "kg", "K", "C", "F", "CF"],
            "Text": ["capitalize", "duplicates"],
            "Constants": ["pi", "e"],
            "Settings": []
        }
        self.function_frame = QFrame()
        self.create_function_buttons(font)

    def create_function_buttons(self, font: QFont) -> None:
        """Create buttons for calculator functions."""
        layout = QGridLayout()
        categories = [("Functions", 3), ("Conversions", 2), ("Text", 2), ("Constants", 2), ("Settings", 1)]
        starting_col = 0

        for category, col_span in categories:
            label = QLabel(category)
            label.setFont(font)
            layout.addWidget(label, 0, starting_col, 1, col_span, Qt.AlignCenter)

            buttons = self.function_buttons.get(category, [])
            if category == "Functions":
                for i, func in enumerate(buttons):
                    button = QPushButton(func)
                    button.setFont(font)
                    button.clicked.connect(lambda _, f=func: self.insert_function(f, False))
                    layout.addWidget(button, (i // 3) + 1, starting_col + (i % 3))

            elif category == "Settings":
                self.mode_button = QPushButton("Radians")
                self.mode_button.setFont(font)
                self.mode_button.clicked.connect(self.toggle_mode)
                layout.addWidget(self.mode_button, 1, starting_col, 1, 1)

            elif category == "Conversions":
                for idx, func in enumerate(buttons):
                    display_text = {
                        "lb": "lb(kg)", "kg": "kg(lb)", "K": "K(°C)",
                        "C": "°C(K)", "F": "F(°C)", "CF": "°C(F)"
                    }.get(func, func)
                    button = QPushButton(display_text)
                    button.setFont(font)
                    button.clicked.connect(lambda _, f=func: self.insert_function(f, False))
                    row, col = 1 + idx // 2, starting_col + idx % 2
                    layout.addWidget(button, row, col)

            elif category == "Text":
                num_buttons = len(buttons)
                num_rows = math.ceil(num_buttons / col_span)

                for idx, func in enumerate(buttons):
                    button = QPushButton(func)
                    button.setFont(font)
                    layout.addWidget(button, 1 + idx // col_span, starting_col + idx % col_span)

                for extra in range(col_span * num_rows - num_buttons):
                    layout.addWidget(QLabel(""), 1 + extra // col_span, starting_col + extra % col_span)

            else:
                for idx, func in enumerate(buttons):
                    button = QPushButton(func)
                    button.setFont(font)
                    button.clicked.connect(lambda _, f=func, c=(category == "Constants"): self.insert_function(f, c))
                    row, col = 1 + idx // col_span, starting_col + idx % col_span
                    layout.addWidget(button, row, col)

                for extra in range(col_span * math.ceil(len(buttons)/col_span) - len(buttons)):
                    layout.addWidget(QLabel(""), 1 + extra // col_span, starting_col + extra % col_span)

            starting_col += col_span

        self.function_frame.setLayout(layout)

    def layout_widgets(self) -> None:
        """Arrange widgets in the main window."""
        central_widget = QWidget()
        main_layout = QVBoxLayout()

        main_layout.addWidget(self.entry)

        history_layout = QHBoxLayout()
        history_layout.addWidget(self.history_text)
        history_layout.addWidget(self.scrollbar)
        main_layout.addLayout(history_layout)

        main_layout.addWidget(self.function_frame)

        central_widget.setLayout(main_layout)
        self.setCentralWidget(central_widget)

    def connect_signals(self) -> None:
        """Connect widget signals."""
        QApplication.instance().focusChanged.connect(self.on_focus_changed)

    def toggle_mode(self) -> None:
        """Toggle between degrees and radians."""
        self.use_degrees = not self.use_degrees
        self.mode_button.setText("Degrees" if self.use_degrees else "Radians")

    def insert_function(self, function: str, is_constant: bool = False) -> None:
        """Insert function or constant in entry."""
        current_text = self.entry.text()
        cursor_position = self.entry.cursorPosition()
        if is_constant:
            new_text = f"{current_text[:cursor_position]}{function}"
            new_cursor_position = cursor_position + len(function)
        else:
            new_text = f"{current_text[:cursor_position]}{function}(" \
                       f"{') ' if function not in ['capitalize', 'duplicates'] else ''}" \
                       f"{current_text[cursor_position:]}"
            new_cursor_position = cursor_position + len(function) + 1
        self.entry.setText(new_text)
        self.entry.setCursorPosition(new_cursor_position)
        self.entry.setFocus()

    def calculate(self) -> None:
        """Evaluate entered expression."""
        expression = self.entry.text().strip()
        if expression:
            result = evaluate_expression(
                expression, self.variables, use_degrees=self.use_degrees
            )
            self.display_result(expression, result)
            self.entry.clear()

    def display_result(self, expression: str, result: Union[float, str]) -> None:
        """Show result in history."""
        mode = "D" if self.use_degrees else "R"
        if re.match(r'^\s*[a-zA-Z_]\w*\s*=\s*.+$', expression):
            history_entry = f"[{mode}] {result}"
        else:
            history_entry = f"[{mode}] {expression} = {result}"
        self.history_entries.append(history_entry)
        self.refresh_history()
        self.history_text.verticalScrollBar().setValue(
            self.history_text.verticalScrollBar().maximum()
        )

    def toggle_search(self) -> None:
        """Toggle search bar visibility."""
        is_visible = self.search_bar.isVisible()
        self.search_bar.setVisible(not is_visible)
        if not is_visible:
            self.search_bar.setFocus()
            self.search_bar.setText("")
        else:
            self.search_bar.clear()
        self.update_search_bar_position()
        self.refresh_history()

    def filter_history(self, text: str) -> None:
        """Filter history based on search input."""
        self.refresh_history(text)

    def refresh_history(self, filter_text: str = "") -> None:
        """Refresh history view with optional filtering."""
        self.history_text.clear()
        for entry in self.history_entries:
            if filter_text.lower() in entry.lower():
                self.history_text.append(entry)

    def resizeEvent(self, event) -> None:
        """Handle window resize events."""
        super().resizeEvent(event)
        self.update_search_bar_position()

    def update_search_bar_position(self) -> None:
        """Reposition search button and bar, moving search button left when search bar is open."""
        margin_right = 5
        margin_top = 5
        spacing = 5

        history_width = self.history_text.viewport().width()

        search_bar_width = int(history_width * 0.25)
        total_width = self.search_button.width() + spacing + search_bar_width

        if total_width > history_width:
            search_bar_width = history_width - self.search_button.width() - spacing - margin_right

        if self.search_bar.isVisible():
            self.search_button.move(
                history_width - total_width - margin_right,
                margin_top
            )
            self.search_bar.setFixedWidth(search_bar_width)
            self.search_bar.move(
                self.search_button.x() + self.search_button.width() + spacing,
                self.search_button.y()
            )
        else:
            self.search_button.move(
                history_width - self.search_button.width() - margin_right,
                margin_top
            )

    def on_focus_changed(self, old: QWidget, new: QWidget) -> None:
        """Auto-hide search if focus is lost."""
        if self.search_bar.isVisible() and not self.search_bar.text().strip() and new != self.search_bar:
            self.toggle_search()

    def showEvent(self, event) -> None:
        """Position search button on showing the window."""
        super().showEvent(event)
        self.update_search_bar_position()

def main() -> None:
    """Start the calculator application."""
    app = QApplication([])
    calculator = CalculatorGUI()
    calculator.show()
    app.exec()

if __name__ == "__main__":
    main()