ADD empty rows in table until getting footer

Question

I am new to reportLab package and I want create an Invoice , So I want header on the first Page , than table that can be one more than one page but if for example comes into 2 pages and half ( half of page 3) it shouldn't not end in half of page I should add empty rows to the footer which has a static height, the idea I have is to calculat remaing space at the last page from bottom - footer height , all this free space i will add into empty rows in my table I have coded this:

 import random
 from reportlab.lib import colors
 from reportlab.lib.pagesizes import letter
 from reportlab.platypus import SimpleDocTemplate, Table, TableStyle, Spacer, Paragraph
 from reportlab.lib.styles import getSampleStyleSheet


  class InvoiceGenerator:
    def __init__(self, pdf_filename):
            self.pdf_filename = pdf_filename
            self.story = []
    def generate_invoice(self):
        doc = SimpleDocTemplate(self.pdf_filename, pagesize=letter)

        # Add elements to the story
        self.add_header(doc)
        self.add_table(doc)
        self.add_footer(doc)

        # Build the PDF
        doc.build(self.story)
        print(f"Document Height: {doc.height}")

    def add_header(self,doc):
     
        # Calculate the remaining space on the last page after adding the table

        # Calculate the height of the footer
        header_text = "Hello"
        header_paragraph = Paragraph(header_text, self.get_style('header'))
      
        
    def add_table(self, doc):
        # Example table data with random values
        table_data = [["Designation", "Quantities", "Unit Price", "Total Price"]]
        for _ in range(180):  # You can adjust the number of rows as needed
            designation = random.choice(['Product A', 'Product B', 'Product C'])
            quantities = random.randint(1, 10)
            unit_price = random.randint(1, 10)
            total_price = quantities * unit_price
            table_data.append([designation, quantities, unit_price, total_price])

        # Create the table
        table = Table(table_data)
        table.setStyle(TableStyle([
            ('BOX', (0, 0), (-1, -1), 1, colors.black),
        ]))

        # Add the table to the story
        self.story.append(table)

    def add_footer(self, doc):
        # Calculate the remaining space on the last page after adding the table
        remaining_space = doc.bottomMargin

        # Calculate the height of the footer
        footer_text = "Hello"
        footer_paragraph = Paragraph(footer_text, self.get_style('footer'))
        footer_height = footer_paragraph.wrap(doc.width, remaining_space)[1]

        # Calculate the number of blank rows based on the remaining space minus the height of the footer
        num_blank_rows = int((remaining_space - footer_height) / 12)  # Adjust the spacing as needed

        # Add blank rows to fill the remaining space on the last page
        for _ in range(num_blank_rows):
            self.story.append(Spacer(1, 12))  # Adjust the spacing as needed

        # Add the footer
        self.story.append(footer_paragraph)

    def get_style(self, style_type):
        styles = getSampleStyleSheet()
        if style_type == 'header':
            return styles['Heading1']
        if style_type == 'footer':
            return styles['Heading2']
        else:
            return None




  # Example usage
pdf_filename = "invoice_example.pdf"
invoice_generator = InvoiceGenerator(pdf_filename)
invoice_generator.generate_invoice()

result i get

but table must has empty rows until end of page