How to implement a terminal/log with widgets?

[tillfalko]

One downside of turning my script into a prompt_toolkit Application is that I can no longer just write to stdout. How would I implement something like a scrolling log with line-wrapping using widgets?
I would like an area that I can print to, with simple line-wrapping, and the ability to scroll while text is being printed.

What I've tried:

Label

I first tried to use a label since I don't need the text to be user-editable. I thought I could simply append the text I wanted to print at the end of the current text, but I couldn't figure out how to update the label text and have it update visually.

TextArea or Buffer + BufferControl + Window

From what I can tell a buffer wants to be used to insert text at a cursor position which must be visible on the screen. TextArea works the same way. That means that whenever I print text, I need to store the current scroll position, move to the bottom and insert text, then restore the previous position. I could not get scrolling to work with wrap_lines = True for the life of me. #686 may be related. I had to manually wrap lines by checking the terminal width and inserting \n.

    async def write(self, text: str):
        ri = self.output.render_info
        at_bottom = True
        if ri:
            at_bottom = (ri.vertical_scroll + ri.window_height >= ri.ui_content.line_count)
        old_cursor = self.output_buffer.cursor_position

        try:
            self.output_buffer.cursor_position = len(self.output_buffer.text)
            free_space = ri.window_width - ri.cursor_position.x - 1
            to_print = ''
            while text != '':
                to_print += text[0]
                free_space = ri.window_width if text[0] == '\n' else free_space - 1
                text = text[1:]

                if free_space < 1:
                    text = '\n' + text

            self.output_buffer.insert_text(to_print) 
        finally:
            pass

        if not at_bottom:
            self.output_buffer.cursor_position = old_cursor

        self.app.invalidate()

This works, but it's fragile, ugly, and breaks when the user resizes their terminal.