"""
Data validation utilities.
Single Responsibility: Validate data quality and consistency.
"""
import pandas as pd
import numpy as np
from typing import List, Dict, Optional
from datetime import datetime


class DataValidator:
    """
    Validates hydrological and meteorological datasets.
    Checks for data quality issues, temporal consistency, and physical constraints.
    """

    def __init__(self):
        """Initialize data validator."""
        self.validation_results = {}

    def validate(
        self,
        df: pd.DataFrame,
        date_col: str = "date",
        station_col: str = "station_id",
        required_cols: Optional[List[str]] = None
    ) -> Dict[str, bool]:
        """
        Run all validation checks.

        Args:
            df: DataFrame to validate
            date_col: Name of date column
            station_col: Name of station ID column
            required_cols: List of required columns

        Returns:
            Dictionary with validation results
        """
        results = {}

        # Schema validation
        results["has_required_columns"] = self._validate_schema(df, required_cols)

        # Date validation
        if date_col in df.columns:
            results["dates_valid"] = self._validate_dates(df, date_col)
            results["no_temporal_gaps"] = self._check_temporal_continuity(
                df, date_col, station_col
            )

        # Data range validation (physical constraints)
        results["values_in_valid_range"] = self._validate_ranges(df)

        # Consistency checks
        if station_col in df.columns:
            results["no_duplicate_station_dates"] = self._check_duplicates(
                df, date_col, station_col
            )

        self.validation_results = results
        return results

    def _validate_schema(
        self,
        df: pd.DataFrame,
        required_cols: Optional[List[str]]
    ) -> bool:
        """Check if required columns exist."""
        if required_cols is None:
            return True
        return all(col in df.columns for col in required_cols)

    def _validate_dates(self, df: pd.DataFrame, date_col: str) -> bool:
        """Validate date column format and range."""
        try:
            dates = pd.to_datetime(df[date_col])
            # Check if dates are in reasonable range (1900-2030)
            min_date = pd.Timestamp("1900-01-01")
            max_date = pd.Timestamp("2030-12-31")
            return (dates >= min_date).all() and (dates <= max_date).all()
        except Exception:
            return False

    def _check_temporal_continuity(
        self,
        df: pd.DataFrame,
        date_col: str,
        station_col: str,
        max_gap_days: int = 7
    ) -> bool:
        """
        Check for large temporal gaps in time series.

        Args:
            df: DataFrame
            date_col: Date column name
            station_col: Station column name
            max_gap_days: Maximum allowed gap in days

        Returns:
            True if no large gaps exist
        """
        if station_col not in df.columns:
            return True

        df_sorted = df.sort_values([station_col, date_col])
        df_sorted[date_col] = pd.to_datetime(df_sorted[date_col])

        # Check gaps per station
        for station in df_sorted[station_col].unique():
            station_data = df_sorted[df_sorted[station_col] == station]
            dates = station_data[date_col]
            if len(dates) > 1:
                gaps = dates.diff().dt.days.dropna()
                if (gaps > max_gap_days).any():
                    return False

        return True

    def _validate_ranges(self, df: pd.DataFrame) -> bool:
        """
        Validate that values are within physically meaningful ranges.
        Hydrological constraints.
        """
        # Physical constraints for hydrological variables
        constraints = {
            # Discharge (m³/s): must be >= 0
            "QmnJ": (0, None),
            "QIXnJ": (0, None),
            "QmM": (0, None),
            "QIXM": (0, None),
            # Water level (m): must be >= 0
            "HIXnJ": (0, None),
            "HIXM": (0, None),
            # Temperature (°C): reasonable range
            "T_Q": (-40, 50),
            # Humidity (%): 0-100
            "HU_Q": (0, 100),
            # Precipitation (mm): >= 0
            "PRELIQ_Q": (0, None),
            "PRENEI_Q": (0, None),
            # Radiation (W/m²): >= 0
            "DLI_Q": (0, None),
            "SSI_Q": (0, None),
            # ETP (mm): >= 0
            "ETP_Q": (0, None),
            # Wind speed (m/s): >= 0
            "FF_Q": (0, None)
        }

        for col, (min_val, max_val) in constraints.items():
            if col in df.columns:
                values = df[col].dropna()
                if min_val is not None and (values < min_val).any():
                    return False
                if max_val is not None and (values > max_val).any():
                    return False

        return True

    def _check_duplicates(
        self,
        df: pd.DataFrame,
        date_col: str,
        station_col: str
    ) -> bool:
        """Check for duplicate station-date combinations."""
        if date_col in df.columns and station_col in df.columns:
            return not df.duplicated(subset=[date_col, station_col]).any()
        return True

    def get_validation_summary(self) -> str:
        """Get human-readable validation summary."""
        if not self.validation_results:
            return "No validation performed yet"

        passed = sum(self.validation_results.values())
        total = len(self.validation_results)

        summary = f"Validation: {passed}/{total} checks passed\n"
        for check, result in self.validation_results.items():
            status = "✓" if result else "✗"
            summary += f"  {status} {check}\n"

        return summary