src/streamlit_app.py

import streamlit as st
import requests
import math

# --- Logic Functions ---

def calculate_distance(postal1, postal2, onemap_token=None):
    """
    Calculates the Euclidean distance in km between two postal codes using OneMap API.
    
    Returns:
        tuple: (distance_km, error_message)
            - distance_km (float): Distance in km, or None if error.
            - error_message (str): None if success, else specific error description.
    """
    def get_coordinates(postal):
        try:
            # Basic format validation (Singapore postal codes are 6 digits)
            if not str(postal).isdigit() or len(str(postal)) != 6:
                 return None, f"Invalid Postal Format: {postal}"

            url = f"https://www.onemap.gov.sg/api/common/elastic/search?searchVal={postal}&returnGeom=Y&getAddrDetails=N&pageNum=1"
            headers = {}
            if onemap_token:
                headers["Authorization"] = onemap_token
            
            response = requests.get(url, headers=headers, timeout=5)
            
            if response.status_code != 200:
                return None, f"OneMap API Error: Status {response.status_code}"
                
            data = response.json()
            
            if data['found'] > 0:
                result = data['results'][0]
                return (float(result['X']), float(result['Y'])), None
            return None, f"Invalid Postal Code: {postal}"
        except requests.exceptions.RequestException as e:
            return None, f"OneMap API Connection Error: {str(e)}"
        except Exception as e:
            return None, f"Unexpected Error: {str(e)}"

    coord1, err1 = get_coordinates(postal1)
    if err1:
        return None, err1

    coord2, err2 = get_coordinates(postal2)
    if err2:
        return None, err2

    # Calculate Euclidean distance on SVY21 plane (coordinates are in meters)
    distance_meters = math.sqrt((coord1[0] - coord2[0])**2 + (coord1[1] - coord2[1])**2)
    return distance_meters / 1000.0, None

def get_distance_category(distance_km):
    if distance_km < 1.0:
        return 1 # < 1km
    elif distance_km < 2.0:
        return 2 # 1-2km
    else:
        return 3 # > 2km

def get_registration_phase(citizenship, user_postal, school_postal, 
                           has_sibling, is_alumni, is_staff, is_mk, 
                           is_volunteer, is_church_clan, is_community_leader, 
                           is_pr=False, onemap_token=None):
    """
    Determines the earliest eligible P1 registration phase and priority code.
    
    Args:
        citizenship (str): "SCPR" or "International".
        user_postal (str): 6-digit postal code of user.
        school_postal (str): 6-digit postal code of school.
        ... boolean args ...
        is_pr (bool): True if Permanent Resident, False if Singapore Citizen. Only relevant if citizenship="SCPR".
        
    Returns:
        str: The priority code (e.g. "P1", "P2A-1") OR "ERROR: <Reason>"
    """
    
    # --- Logic ---
    if citizenship == "International":
        return "P3"

    # Phase 1: Guaranteed (Conceptually P1 does not balloting by distance usually, but let's assign P1)
    if has_sibling:
        return "P1"        

    # Calculate Distance - Catching specific errors from the helper
    dist, error_msg = calculate_distance(user_postal, school_postal, onemap_token)
    
    if error_msg:
        return f"ERROR: {error_msg}"

    # Helper for priority suffix
    def get_suffix(d_km, is_pr_status):
        cat = get_distance_category(d_km)
        # SC: 1, 2, 3
        # PR: 4, 5, 6
        if is_pr_status:
            return f"-{cat + 3}"
        else:
            return f"-{cat}"

    suffix = get_suffix(dist, is_pr)

    # Phase 2A
    if is_alumni or is_staff or is_mk:
        return f"P2A{suffix}"

    # Phase 2B
    # Check Community Leader specific 2km rule
    valid_community_leader = is_community_leader and (dist < 2.0)
    
    if is_volunteer or is_church_clan or valid_community_leader:
        return f"P2B{suffix}"

    # Phase 2C
    return f"P2C{suffix}"


# --- Streamlit App ---

def main():
    st.set_page_config(page_title="P1 Registration Eligibility Checker", page_icon="cP", layout="wide")
    
    st.title("P1 Registration Eligibility Checker")
    st.markdown("""
    Check which phase your child is eligible for in the Primary 1 (P1) Registration Exercise.
    *Based on 2025 rules for 2026 intake.*
    """)
    st.divider()

    # 1. Citizenship
    st.subheader("1. Citizenship")
    citizenship_radio = st.radio(
        "What is the child's citizenship status?",
        ["Singapore Citizen", "Permanent Resident", "International Student"],
        horizontal=True
    )
    
    is_pr = False
    citizenship_code = "SCPR"
    
    if citizenship_radio == "International Student":
        citizenship_code = "International"
        st.warning("International Students must register in **Phase 3**.")
        st.info("Important: You must submit an 'Indication of Interest' form online (typically in May/June) before you can register in Phase 3 (typically in October).")
        return # Stop execution for International students as other questions are irrelevant
    elif citizenship_radio == "Permanent Resident":
        is_pr = True
        citizenship_code = "SCPR"
    else:
        # Singapore Citizen
        is_pr = False
        citizenship_code = "SCPR"

    st.divider()
    
    # 2. Postal Codes
    st.subheader("2. Location (Postal Codes)")
    st.info("Distance is calculated using the OneMap API.")
    
    col_postal1, col_postal2 = st.columns(2)
    with col_postal1:
        user_postal = st.text_input("Home Postal Code", max_chars=6, help="Enter your 6-digit home postal code.")
    with col_postal2:
        school_postal = st.text_input("School Postal Code", max_chars=6, help="Enter the 6-digit postal code of the school.")
        
    with st.expander("Advanced: OneMap API Token (Optional)"):
        onemap_token = st.text_input("API Token", type="password", help="If public API limits are hit, enter a valid OneMap token here.")
        if not onemap_token:
            onemap_token = None

    st.divider()
    
    # 3. School Connections
    st.subheader("3. Eligibility Criteria")
    st.write("Tick all that apply to see your eligible phase.")

    col1, col2 = st.columns(2)

    with col1:
        st.markdown("**Phase 1**")
        has_sibling = st.checkbox(
            "Child has a sibling currently studying in the school of choice",
            help="For a child who has a sibling currently studying in the primary school."
        )
        
        st.markdown("**Phase 2A**")
        is_alumni = st.checkbox(
            "Parent/Sibling is an alumni",
            help="For a child whose parent or sibling is a former student of the primary school, including those who have joined the alumni association."
        )
        is_staff = st.checkbox(
            "Parent is a staff member or SAC/SMC member",
            help="For a child whose parent is a member of the School Advisory or Management Committee, or a staff member of the primary school."
        )
        is_mk = st.checkbox(
            "Child attends MOE Kindergarten at the school",
            help="For a child from the MOE Kindergarten under the purview of and located within the primary school."
        )

    with col2:
        st.markdown("**Phase 2B**")
        is_volunteer = st.checkbox(
            "Parent is a school volunteer",
            help="For a child whose parent has joined the primary school as a parent volunteer not later than 1 July of the year before P1 registration and has given at least 40 hours of voluntary service to the school by 30 June of the registration year."
        )
        is_church_clan = st.checkbox(
            "Parent is a member of endorsed church/clan",
            help="For a child whose parent is a member endorsed by the church or clan directly connected with the primary school."
        )
        is_community_leader = st.checkbox(
            "Parent is an active community leader",
            help="For a child whose parent is endorsed as an active community leader. *Note: Must be within 2km of the school to qualify for Phase 2B.*"
        )

    st.divider()
    
    # Calculate Button
    if st.button("Check Eligibility", type="primary", use_container_width=True):
        if not user_postal or len(user_postal) != 6 or not user_postal.isdigit():
            st.error("Please enter a valid 6-digit Home Postal Code.")
        elif not school_postal or len(school_postal) != 6 or not school_postal.isdigit():
            st.error("Please enter a valid 6-digit School Postal Code.")
        else:
            with st.spinner("Calculating distance and eligibility..."):
                result = get_registration_phase(
                    citizenship=citizenship_code,
                    user_postal=user_postal,
                    school_postal=school_postal,
                    has_sibling=has_sibling,
                    is_alumni=is_alumni,
                    is_staff=is_staff,
                    is_mk=is_mk,
                    is_volunteer=is_volunteer,
                    is_church_clan=is_church_clan,
                    is_community_leader=is_community_leader,
                    is_pr=is_pr,
                    onemap_token=onemap_token
                )
                
                if result.startswith("ERROR:"):
                    st.error(result)
                else:
                    st.success(f"**Your eligible Phase & Priority Code: {result}**")
                    
                    # Explain code
                    phase = result.split("-")[0]
                    priority = result.split("-")[1] if "-" in result else ""
                    
                    explanation = ""
                    if phase == "P1":
                        explanation = "Phase 1: Guaranteed admission."
                    elif "P2A" in phase:
                        explanation = "Phase 2A: For alumni, staff, and MOE Kindergarten children."
                    elif "P2B" in phase:
                        explanation = "Phase 2B: For volunteers, church/clan members, and community leaders."
                    elif "P2C" in phase:
                        explanation = "Phase 2C: Open to all eligible children."
                        
                    if priority:
                        cat_map = {
                            "1": "Singapore Citizen < 1km",
                            "2": "Singapore Citizen 1-2km",
                            "3": "Singapore Citizen > 2km",
                            "4": "Permanent Resident < 1km",
                            "5": "Permanent Resident 1-2km",
                            "6": "Permanent Resident > 2km"
                        }
                        explanation += f"\n\n**Priority Category**: {cat_map.get(priority, 'Unknown')}"
                        
                    st.info(explanation)

    st.caption("Note: This tool is for reference only. Official eligibility is determined by MOE. Distance is calculated via OneMap API (Euclidean/Straight-line).")

if __name__ == "__main__":
    main()