import streamlit as st
import pandas as pd
import io

@st.cache_data(show_spinner=False)
def get_sheet_names(file) -> list[str]:
    """Return the sheet names of an Excel file."""
    excel_file = pd.ExcelFile(file)
    return excel_file.sheet_names

@st.cache_data(show_spinner=False)
def load_df(file, sheet_name):
    """Read a sheet from an Excel file into a DataFrame and cache the result."""
    return pd.read_excel(file, sheet_name=sheet_name)

buffer = io.BytesIO()

def main():
    # Create columns
    main_col1, main_col2 = st.columns([3, 7])

    # File uploader
    with main_col1:
        uploaded_file = st.file_uploader("Choose an Excel file", type=['xlsx', 'xls'])
        if uploaded_file is not None:
            # ✅ Only caching serializable sheet names
            sheet_names = get_sheet_names(uploaded_file)
            selected_sheet = st.selectbox("Select a sheet", options=sheet_names, index=0)

            # ✅ Cache the DataFrame (serializable)
            df = load_df(uploaded_file, selected_sheet)
            
            st.write(df)

    # Display the uploaded file's contents in the second column
    with main_col2:
        if uploaded_file is not None:
            # Configure multiselects based on uploaded DataFrame columns
            columns = list(df.columns)
            selected_gstin = st.multiselect("GST Identification Number (GSTIN)", columns, default=columns)
            

if __name__ == "__main__":
    st.set_page_config(layout="wide")
    main()