"""
Data loading module with optimized pandas operations.
Uses vectorized operations instead of .apply() for performance.
"""

import pandas as pd
import numpy as np
from pathlib import Path
from functools import lru_cache
import re
from typing import Optional

from .config import settings
from .schemas import (
    COLUMN_MAPPINGS,
    NUMERIC_COLUMNS,
    SCHOOL_TYPE_MAP,
    NULL_VALUES,
    LA_CODE_TO_NAME,
)


def extract_year_from_folder(folder_name: str) -> Optional[int]:
    """Extract the end year from folder name like '2023-2024' -> 2024."""
    match = re.search(r'(\d{4})-(\d{4})', folder_name)
    if match:
        return int(match.group(2))
    return None


def parse_numeric_vectorized(series: pd.Series) -> pd.Series:
    """
    Vectorized numeric parsing - much faster than .apply().
    Handles SUPP, NE, NA, NP, %, etc.
    """
    # Convert to string first
    str_series = series.astype(str)
    
    # Replace null values with NaN
    for null_val in NULL_VALUES:
        str_series = str_series.replace(null_val, np.nan)
    
    # Remove % signs
    str_series = str_series.str.rstrip('%')
    
    # Convert to numeric
    return pd.to_numeric(str_series, errors='coerce')


def create_address_vectorized(df: pd.DataFrame) -> pd.Series:
    """
    Vectorized address creation - much faster than .apply().
    """
    parts = []
    
    if 'address1' in df.columns:
        parts.append(df['address1'].fillna('').astype(str))
    if 'town' in df.columns:
        parts.append(df['town'].fillna('').astype(str))
    if 'postcode' in df.columns:
        parts.append(df['postcode'].fillna('').astype(str))
    
    if not parts:
        return pd.Series([''] * len(df), index=df.index)
    
    # Combine parts with comma separator, filtering empty strings
    result = pd.Series([''] * len(df), index=df.index)
    for i, row_idx in enumerate(df.index):
        row_parts = [p.iloc[i] if hasattr(p, 'iloc') else p[i] for p in parts]
        row_parts = [p for p in row_parts if p and p.strip()]
        result.iloc[i] = ', '.join(row_parts)
    
    return result


def create_address_fast(df: pd.DataFrame) -> pd.Series:
    """
    Fast vectorized address creation using string concatenation.
    """
    addr1 = df.get('address1', pd.Series([''] * len(df))).fillna('').astype(str)
    town = df.get('town', pd.Series([''] * len(df))).fillna('').astype(str)
    postcode = df.get('postcode', pd.Series([''] * len(df))).fillna('').astype(str)
    
    # Build address with proper separators
    result = addr1.str.strip()
    
    # Add town if not empty
    town_mask = town.str.strip() != ''
    result = result.where(~town_mask, result + ', ' + town.str.strip())
    
    # Add postcode if not empty  
    postcode_mask = postcode.str.strip() != ''
    result = result.where(~postcode_mask, result + ', ' + postcode.str.strip())
    
    # Clean up leading commas
    result = result.str.lstrip(', ')
    
    return result


def load_year_data(year_folder: Path, year: int) -> Optional[pd.DataFrame]:
    """Load and process data for a single year."""
    ks2_file = year_folder / "england_ks2final.csv"
    if not ks2_file.exists():
        return None
    
    try:
        print(f"Loading data from {ks2_file}")
        df = pd.read_csv(ks2_file, low_memory=False)
        
        # Handle column types
        if 'LEA' in df.columns and df['LEA'].dtype == 'object':
            df['LEA'] = pd.to_numeric(df['LEA'], errors='coerce')
        if 'URN' in df.columns and df['URN'].dtype == 'object':
            df['URN'] = pd.to_numeric(df['URN'], errors='coerce')
        
        # Filter to schools only (RECTYPE == 1 means school level data)
        if 'RECTYPE' in df.columns:
            df = df[df['RECTYPE'] == 1].copy()
        
        # Add year and local authority name
        df['year'] = year
        
        # Try different column names for LA name
        la_name_cols = ['LANAME', 'LA (name)', 'LA_NAME', 'LA NAME']
        la_col_found = None
        for col in la_name_cols:
            if col in df.columns:
                la_col_found = col
                break
        
        if la_col_found:
            df['local_authority'] = df[la_col_found]
        elif 'LEA' in df.columns:
            # Map LEA codes to names using our mapping
            df['local_authority'] = df['LEA'].map(LA_CODE_TO_NAME).fillna(df['LEA'].astype(str))
        
        # Rename columns using mapping
        rename_dict = {k: v for k, v in COLUMN_MAPPINGS.items() if k in df.columns}
        df = df.rename(columns=rename_dict)
        
        # Create address field (vectorized)
        df['address'] = create_address_fast(df)
        
        # Map school type codes to names (vectorized)
        if 'school_type_code' in df.columns:
            df['school_type'] = df['school_type_code'].map(SCHOOL_TYPE_MAP).fillna('Other')
        
        # Parse numeric columns (vectorized - much faster than .apply())
        for col in NUMERIC_COLUMNS:
            if col in df.columns:
                df[col] = parse_numeric_vectorized(df[col])
        
        print(f"  Loaded {len(df)} schools for year {year}")
        return df
        
    except Exception as e:
        print(f"Error loading {ks2_file}: {e}")
        return None


@lru_cache(maxsize=1)
def load_school_data() -> pd.DataFrame:
    """
    Load and combine all school data from CSV files in year folders.
    Uses lru_cache for singleton-like behavior.
    """
    all_data = []
    
    data_dir = settings.data_dir
    if data_dir.exists():
        for year_folder in data_dir.iterdir():
            if year_folder.is_dir() and re.match(r'\d{4}-\d{4}', year_folder.name):
                year = extract_year_from_folder(year_folder.name)
                if year is None:
                    continue
                
                df = load_year_data(year_folder, year)
                if df is not None:
                    all_data.append(df)
    
    if all_data:
        result = pd.concat(all_data, ignore_index=True)
        print(f"\nTotal records loaded: {len(result)}")
        print(f"Unique schools: {result['urn'].nunique()}")
        print(f"Years: {sorted(result['year'].unique())}")
        return result
    else:
        print("No data files found. Creating empty DataFrame.")
        return pd.DataFrame()


def clear_cache():
    """Clear the data cache to force reload."""
    load_school_data.cache_clear()