import streamlit as st
import os
from pathlib import Path

# Use relative path for better portability
DATA_DIR = Path("data")  # Create a 'data' directory in the same folder as the script

def get_subjects():
    """Returns a list of subject directories."""
    DATA_DIR.mkdir(exist_ok=True)  # Create data directory if it doesn't exist
    return sorted([
        name.name
        for name in DATA_DIR.iterdir()
        if name.is_dir()
    ])

def get_units(subject):
    """Returns a list of unit directories within a subject."""
    subject_path = DATA_DIR / subject
    return sorted([
        name.name
        for name in subject_path.iterdir()
        if name.is_dir()
    ]) if subject_path.exists() else []

def get_notes(subject, unit):
    """Returns a list of note files within a unit."""
    unit_path = DATA_DIR / subject / unit
    return sorted([
        name.name
        for name in unit_path.iterdir()
        if name.suffix == '.md'
    ]) if unit_path.exists() else []

def load_note(subject, unit, note):
    """Loads the content of a note file."""
    note_path = DATA_DIR / subject / unit / note
    try:
        return note_path.read_text(encoding="utf-8")
    except Exception as e:
        st.error(f"Error loading note: {e}")
        return None

st.set_page_config(
    page_title="Notes App",
    page_icon="📝",
    layout="wide",
    initial_sidebar_state="expanded",
)

# Custom CSS with simplified styling
st.markdown("""
    <style>
    .main > div {
        padding: 2rem;
        max-width: 100%;
    }
    .stMarkdown {
        font-size: 1rem;
    }
    </style>
    """, unsafe_allow_html=True)

st.title("📝 Notes App")

# Initialize session state
for key in ['selected_subject', 'selected_unit', 'selected_note']:
    if key not in st.session_state:
        st.session_state[key] = None

# Sidebar navigation
with st.sidebar:
    st.header("Navigation")
    
    # Subject selection
    subjects = get_subjects()
    if subjects:
        selected_subject = st.selectbox(
            "Select Subject",
            subjects,
            key="subject_selectbox",
            index=subjects.index(st.session_state['selected_subject']) if st.session_state['selected_subject'] in subjects else 0
        )
        st.session_state['selected_subject'] = selected_subject
        
        # Unit selection
        units = get_units(selected_subject)
        if units:
            selected_unit = st.selectbox(
                "Select Unit",
                units,
                key="unit_selectbox",
                index=units.index(st.session_state['selected_unit']) if st.session_state['selected_unit'] in units else 0
            )
            st.session_state['selected_unit'] = selected_unit
            
            # Note selection
            notes = get_notes(selected_subject, selected_unit)
            if notes:
                selected_note = st.selectbox(
                    "Select Note",
                    notes,
                    key="note_selectbox",
                    index=notes.index(st.session_state['selected_note']) if st.session_state['selected_note'] in notes else 0
                )
                st.session_state['selected_note'] = selected_note
            else:
                st.info("No notes found in this unit.")
                st.session_state['selected_note'] = None
        else:
            st.info("No units found in this subject.")
            st.session_state['selected_unit'] = None
    else:
        st.info("No subjects found. Add some notes to get started!")

# Main content area
if all([st.session_state['selected_subject'], 
        st.session_state['selected_unit'], 
        st.session_state['selected_note']]):
    
    st.header(f"{st.session_state['selected_subject']} / {st.session_state['selected_unit']} / {Path(st.session_state['selected_note']).stem}")
    
    note_content = load_note(
        st.session_state['selected_subject'],
        st.session_state['selected_unit'],
        st.session_state['selected_note']
    )
    
    if note_content:
        st.markdown(note_content)
else:
    st.info("Select a subject, unit, and note from the sidebar to view content.")