"""
Data loading and preprocessing module.
"""

from sqlalchemy import create_engine, text
import pandas as pd
from datetime import datetime
import logging
import os
from .config import DB_CONFIG, TABLE_NAME

logger = logging.getLogger(__name__)

class DataLoader:
    def __init__(self):
        self.engine = None
        self.df = None
        self.chunk_size = 10000  # Load 10,000 rows at a time

    def connect(self):
        """Establish database connection."""
        try:
            logger.info("Attempting to connect to database...")
            DATABASE_URL = f"postgresql://{DB_CONFIG['user']}:{DB_CONFIG['password']}@{DB_CONFIG['host']}:{DB_CONFIG['port']}/{DB_CONFIG['name']}"
            self.engine = create_engine(DATABASE_URL)
            with self.engine.connect() as conn:
                # First check if table exists
                check_table = text(f"SELECT EXISTS (SELECT FROM information_schema.tables WHERE table_name = '{TABLE_NAME}')")
                table_exists = conn.execute(check_table).scalar()
                
                if not table_exists:
                    logger.error(f"Table {TABLE_NAME} does not exist in the database")
                    return False
                
                # Get row count
                count_query = text(f"SELECT COUNT(*) FROM {TABLE_NAME}")
                row_count = conn.execute(count_query).scalar()
                logger.info(f"Table {TABLE_NAME} exists with {row_count} rows")
                
                # Get version
                result = conn.execute(text("SELECT version();"))
                logger.info("Connected successfully to database!")
                return True
        except Exception as e:
            logger.error(f"Error connecting to database: {str(e)}")
            return False

    def load_from_csv(self, file_path):
        """Load data from a CSV file."""
        try:
            logger.info(f"Loading data from CSV file: {file_path}")
            if not os.path.exists(file_path):
                logger.error(f"CSV file not found: {file_path}")
                return None

            # Load data in chunks
            chunks = []
            for chunk in pd.read_csv(file_path, chunksize=self.chunk_size):
                # Preprocess chunk
                chunk['trx_start_date'] = pd.to_datetime(chunk['trx_start_date'])
                chunk['trx_end_date'] = pd.to_datetime(chunk['trx_end_date'])
                
                # Rename columns if needed
                if 'd1' in chunk.columns:
                    chunk = chunk.rename(columns={
                        'd1': 'trx_type',
                        'd2': 'trx_subtype',
                        'd3': 'initiated_by',
                        'd4': 'customer_id'
                    })
                
                chunk = chunk.dropna()
                chunks.append(chunk)
            
            # Combine all chunks
            self.df = pd.concat(chunks, ignore_index=True)
            logger.info(f"Successfully loaded {len(self.df)} rows from CSV")
            
            # Basic data validation
            logger.info("Performing data validation...")
            logger.info(f"Columns in dataset: {self.df.columns.tolist()}")
            logger.info(f"Data types:\n{self.df.dtypes}")
            logger.info(f"Missing values:\n{self.df.isnull().sum()}")
            
            return self.df
        except Exception as e:
            logger.error(f"Error loading data from CSV: {str(e)}")
            return None

    def load_from_db(self):
        """Load and preprocess transaction data from database in chunks."""
        if not self.engine:
            logger.info("No database connection. Attempting to connect...")
            if not self.connect():
                logger.error("Failed to establish database connection")
                return None

        try:
            logger.info(f"Loading data from table: {TABLE_NAME}")
            
            # First get total count
            with self.engine.connect() as conn:
                count_query = text(f"SELECT COUNT(*) FROM {TABLE_NAME}")
                total_rows = conn.execute(count_query).scalar()
                logger.info(f"Total rows to process: {total_rows}")
            
            # Load data in chunks
            chunks = []
            offset = 0
            
            while True:
                logger.info(f"Loading chunk starting at offset {offset}")
                query = f"SELECT * FROM {TABLE_NAME} LIMIT {self.chunk_size} OFFSET {offset}"
                chunk = pd.read_sql(query, self.engine)
                
                if chunk.empty:
                    break
                    
                # Preprocess chunk
                chunk['trx_start_date'] = pd.to_datetime(chunk['trx_start_date'])
                chunk['trx_end_date'] = pd.to_datetime(chunk['trx_end_date'])
                
                # Rename columns
                chunk = chunk.rename(columns={
                    'd1': 'trx_type',
                    'd2': 'trx_subtype',
                    'd3': 'initiated_by',
                    'd4': 'customer_id'
                })
                
                chunk = chunk.dropna()
                chunks.append(chunk)
                offset += self.chunk_size
                
                if offset >= total_rows:
                    break
            
            # Combine all chunks
            self.df = pd.concat(chunks, ignore_index=True)
            logger.info(f"Successfully loaded {len(self.df)} rows of data")
            
            # Basic data validation
            logger.info("Performing data validation...")
            logger.info(f"Columns in dataset: {self.df.columns.tolist()}")
            logger.info(f"Data types:\n{self.df.dtypes}")
            logger.info(f"Missing values:\n{self.df.isnull().sum()}")
            
            return self.df
        except Exception as e:
            logger.error(f"Error loading data: {str(e)}")
            return None

    def load_data(self, source='db', file_path=None):
        """Load data from either database or CSV file."""
        if source == 'db':
            return self.load_from_db()
        elif source == 'csv':
            if not file_path:
                logger.error("File path must be provided when loading from CSV")
                return None
            return self.load_from_csv(file_path)
        else:
            logger.error(f"Invalid source: {source}. Must be 'db' or 'csv'")
            return None

    def get_data(self):
        """Get the loaded DataFrame."""
        if self.df is None:
            logger.warning("No data loaded. Call load_data() first.")
        return self.df