import gradio as gr
from pypdf import PdfReader, PdfWriter

def merge_pdfs(files):
    if not files:
        return None

    writer = PdfWriter()

    for f in files:
        reader = PdfReader(f.name)
        for page in reader.pages:
            writer.add_page(page)

    output_file = "merged.pdf"
    with open(output_file, "wb") as out_f:
        writer.write(out_f)

    return output_file


with gr.Blocks(title="PDF Notes App") as demo:
    gr.Markdown(
        """
        # 📄 PDF Notes App  
        Upload multiple PDF files and merge them into a single PDF.
        """
    )

    pdfs = gr.File(
        file_types=[".pdf"],
        file_count="multiple",
        label="Upload PDF Files"
    )

    merge_btn = gr.Button("Merge PDFs")
    output_pdf = gr.File(label="Merged PDF")

    merge_btn.click(
        fn=merge_pdfs,
        inputs=pdfs,
        outputs=output_pdf
    )

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