import gradio as gr


def add_assignment(assignments):
    """
    add one blank assignment to the saved list
    """
    assignments = assignments or []
    return assignments + [""]


def delete_assignment(assignments, index):
    """
    delete one assignment using its position in the list
    """
    assignments = assignments or []

    if 0 <= index < len(assignments):
        assignments.pop(index)

    return assignments


def update_assignment(assignments, new_text, index):
    """
    save the updated text for one assignment
    """
    assignments = assignments or []

    if 0 <= index < len(assignments):
        assignments[index] = new_text

    return assignments


def clear_all():
    """
    delete every assignment
    """
    return []


with gr.Blocks(title="Assignment Tracker") as demo:
    gr.Markdown("# Assignment Tracker")
    gr.Markdown(
        "Click **Add assignment** whenever you need another textbox."
    )

    # Start with no assignments.
    # The assignments are saved in the user's browser.
    saved_assignments = gr.BrowserState(
        value=[],
        key="assignment_tracker_data"
    )

    with gr.Row():
        add_button = gr.Button(
            "Add assignment",
            variant="primary"
        )

        clear_button = gr.Button("Clear all")

    status = gr.Markdown()

    # This section redraws itself whenever saved_assignments changes.
    @gr.render(inputs=saved_assignments)
    def display_assignments(assignments):
        assignments = assignments or []

        if len(assignments) == 0:
            gr.Markdown(
                "You currently have no assignments. "
                "Click **Add assignment** to create one."
            )

        for index, assignment_text in enumerate(assignments):
            with gr.Row():
                assignment_box = gr.Textbox(
                    value=assignment_text,
                    label=f"Assignment {index + 1}",
                    placeholder="Enter an assignment...",
                    lines=2,
                    key=f"assignment-{index}"
                )

                delete_button = gr.Button(
                    "Delete",
                    size="sm",
                    key=f"delete-{index}"
                )

            # Save whenever the user finishes editing the textbox.
            assignment_box.change(
                fn=lambda text, current_assignments, i=index:
                    update_assignment(
                        current_assignments,
                        text,
                        i
                    ),
                inputs=[
                    assignment_box,
                    saved_assignments
                ],
                outputs=saved_assignments
            )

            # Delete this particular assignment.
            delete_button.click(
                fn=lambda current_assignments, i=index:
                    delete_assignment(
                        current_assignments,
                        i
                    ),
                inputs=saved_assignments,
                outputs=saved_assignments
            )

    add_button.click(
        fn=add_assignment,
        inputs=saved_assignments,
        outputs=saved_assignments
    )

    clear_button.click(
        fn=clear_all,
        inputs=None,
        outputs=saved_assignments
    )


if __name__ == "__main__":
    demo.launch()