"""
Environment variable validation for thrillwiki project.

This module validates environment variables on Django startup to catch
configuration errors early. It checks:
- Required variables are set
- Values have correct types
- Values are within valid ranges
- URLs are properly formatted
- Cross-variable dependencies are satisfied

Why python-decouple?
- Already used across the project for consistency
- Provides type casting and default values
- Supports .env files and environment variables
"""

import logging
import re
import warnings
from typing import Any, Callable, Optional
from urllib.parse import urlparse

from decouple import config, UndefinedValueError

logger = logging.getLogger("thrillwiki")

# =============================================================================
# Validation Rules
# =============================================================================

# Required environment variables with their validation rules
REQUIRED_VARIABLES = {
    "SECRET_KEY": {
        "type": str,
        "min_length": 50,
        "description": "Django secret key for cryptographic signing",
    },
    "DATABASE_URL": {
        "type": str,
        "validator": "url",
        "description": "Database connection URL",
    },
}

# Optional variables that should be validated if present
OPTIONAL_VARIABLES = {
    "DEBUG": {
        "type": bool,
        "default": True,
        "description": "Debug mode flag",
    },
    "ALLOWED_HOSTS": {
        "type": str,
        "description": "Comma-separated list of allowed hosts",
    },
    "REDIS_URL": {
        "type": str,
        "validator": "url",
        "description": "Redis connection URL",
    },
    "EMAIL_PORT": {
        "type": int,
        "min_value": 1,
        "max_value": 65535,
        "description": "SMTP server port",
    },
    "CACHE_MIDDLEWARE_SECONDS": {
        "type": int,
        "min_value": 0,
        "max_value": 86400,
        "description": "Cache timeout in seconds",
    },
    "API_RATE_LIMIT_PER_MINUTE": {
        "type": int,
        "min_value": 1,
        "max_value": 10000,
        "description": "API rate limit per minute",
    },
    "API_RATE_LIMIT_PER_HOUR": {
        "type": int,
        "min_value": 1,
        "max_value": 100000,
        "description": "API rate limit per hour",
    },
    "SECURE_HSTS_SECONDS": {
        "type": int,
        "min_value": 0,
        "max_value": 31536000 * 2,  # Max 2 years
        "description": "HSTS max-age in seconds",
    },
    "SESSION_COOKIE_AGE": {
        "type": int,
        "min_value": 60,
        "max_value": 86400 * 365,  # Max 1 year
        "description": "Session cookie age in seconds",
    },
    "JWT_ACCESS_TOKEN_LIFETIME_MINUTES": {
        "type": int,
        "min_value": 1,
        "max_value": 1440,  # Max 24 hours
        "description": "JWT access token lifetime in minutes",
    },
    "JWT_REFRESH_TOKEN_LIFETIME_DAYS": {
        "type": int,
        "min_value": 1,
        "max_value": 365,
        "description": "JWT refresh token lifetime in days",
    },
    "SENTRY_TRACES_SAMPLE_RATE": {
        "type": float,
        "min_value": 0.0,
        "max_value": 1.0,
        "description": "Sentry trace sampling rate",
    },
}

# Cross-variable validation rules
CROSS_VARIABLE_RULES = [
    {
        "name": "production_security",
        "condition": lambda: config("DEBUG", default=True, cast=bool) is False,
        "requirements": [
            ("SECRET_KEY", lambda v: len(v) >= 50, "must be at least 50 characters"),
            ("ALLOWED_HOSTS", lambda v: v and v.strip(), "must be set in production"),
        ],
        "description": "Production security requirements",
    },
    {
        "name": "ssl_configuration",
        "condition": lambda: config("SECURE_SSL_REDIRECT", default=False, cast=bool),
        "requirements": [
            ("SESSION_COOKIE_SECURE", lambda v: v, "should be True with SSL redirect"),
            ("CSRF_COOKIE_SECURE", lambda v: v, "should be True with SSL redirect"),
        ],
        "description": "SSL configuration consistency",
    },
]


# =============================================================================
# Validation Functions
# =============================================================================


def validate_url(value: str) -> bool:
    """Validate that a value is a valid URL."""
    try:
        result = urlparse(value)
        return all([result.scheme, result.netloc])
    except Exception:
        return False


def validate_email(value: str) -> bool:
    """Validate that a value is a valid email address."""
    email_pattern = r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$"
    return bool(re.match(email_pattern, value))


def validate_type(value: Any, expected_type: type) -> bool:
    """Validate that a value is of the expected type."""
    if expected_type == bool:
        # Special handling for boolean strings
        return isinstance(value, bool) or str(value).lower() in (
            "true", "false", "1", "0", "yes", "no"
        )
    return isinstance(value, expected_type)


def validate_range(
    value: Any,
    min_value: Optional[Any] = None,
    max_value: Optional[Any] = None
) -> bool:
    """Validate that a value is within a specified range."""
    if min_value is not None and value < min_value:
        return False
    if max_value is not None and value > max_value:
        return False
    return True


def validate_length(value: str, min_length: int = 0, max_length: int = None) -> bool:
    """Validate that a string value meets length requirements."""
    if len(value) < min_length:
        return False
    if max_length is not None and len(value) > max_length:
        return False
    return True


VALIDATORS = {
    "url": validate_url,
    "email": validate_email,
}


# =============================================================================
# Main Validation Functions
# =============================================================================


def validate_variable(name: str, rules: dict) -> list[str]:
    """
    Validate a single environment variable against its rules.

    Args:
        name: Environment variable name
        rules: Validation rules dictionary

    Returns:
        List of error messages (empty if valid)
    """
    errors = []

    try:
        # Get the value with appropriate type casting
        var_type = rules.get("type", str)
        default = rules.get("default", None)

        if var_type == bool:
            value = config(name, default=default, cast=bool)
        elif var_type == int:
            value = config(name, default=default, cast=int)
        elif var_type == float:
            value = config(name, default=default, cast=float)
        else:
            value = config(name, default=default)

    except UndefinedValueError:
        errors.append(f"{name}: Required variable is not set")
        return errors
    except ValueError as e:
        errors.append(f"{name}: Invalid value - {e}")
        return errors

    # Type validation
    if not validate_type(value, rules.get("type", str)):
        errors.append(
            f"{name}: Expected type {rules['type'].__name__}, "
            f"got {type(value).__name__}"
        )

    # Length validation (for strings)
    if isinstance(value, str):
        min_length = rules.get("min_length", 0)
        max_length = rules.get("max_length")
        if not validate_length(value, min_length, max_length):
            errors.append(
                f"{name}: Length must be between {min_length} and "
                f"{max_length or 'unlimited'}"
            )

    # Range validation (for numbers)
    if isinstance(value, (int, float)):
        min_value = rules.get("min_value")
        max_value = rules.get("max_value")
        if not validate_range(value, min_value, max_value):
            errors.append(
                f"{name}: Value must be between {min_value} and {max_value}"
            )

    # Custom validator
    validator_name = rules.get("validator")
    if validator_name and validator_name in VALIDATORS:
        if not VALIDATORS[validator_name](value):
            errors.append(f"{name}: Failed {validator_name} validation")

    return errors


def validate_cross_rules() -> list[str]:
    """
    Validate cross-variable dependencies.

    Returns:
        List of error/warning messages
    """
    errors = []

    for rule in CROSS_VARIABLE_RULES:
        try:
            # Check if the condition applies
            if not rule["condition"]():
                continue

            # Check each requirement
            for var_name, check_fn, message in rule["requirements"]:
                try:
                    value = config(var_name, default=None)
                    if value is not None and not check_fn(value):
                        errors.append(
                            f"{rule['name']}: {var_name} {message}"
                        )
                except Exception:
                    errors.append(
                        f"{rule['name']}: Could not validate {var_name}"
                    )

        except Exception as e:
            errors.append(f"Cross-validation error for {rule['name']}: {e}")

    return errors


def validate_all_settings(raise_on_error: bool = False) -> dict:
    """
    Validate all environment variables.

    Args:
        raise_on_error: If True, raise ValueError on first error

    Returns:
        Dictionary with 'errors' and 'warnings' lists
    """
    result = {
        "errors": [],
        "warnings": [],
        "valid": True,
    }

    # Validate required variables
    for name, rules in REQUIRED_VARIABLES.items():
        errors = validate_variable(name, rules)
        result["errors"].extend(errors)

    # Validate optional variables (if set)
    for name, rules in OPTIONAL_VARIABLES.items():
        try:
            # Only validate if the variable is set
            config(name)
            errors = validate_variable(name, rules)
            result["warnings"].extend(errors)  # Warnings for optional vars
        except UndefinedValueError:
            pass  # Optional variable not set, that's fine

    # Validate cross-variable rules
    cross_errors = validate_cross_rules()
    result["warnings"].extend(cross_errors)

    # Set validity
    result["valid"] = len(result["errors"]) == 0

    # Handle errors
    if result["errors"]:
        for error in result["errors"]:
            logger.error(f"Configuration error: {error}")

        if raise_on_error:
            raise ValueError(
                f"Configuration validation failed: {result['errors']}"
            )

    # Log warnings
    for warning in result["warnings"]:
        logger.warning(f"Configuration warning: {warning}")

    return result


def run_startup_validation() -> None:
    """
    Run configuration validation on application startup.

    This function should be called during Django initialization
    to catch configuration errors early.
    """
    debug_mode = config("DEBUG", default=True, cast=bool)

    result = validate_all_settings(raise_on_error=not debug_mode)

    if result["valid"]:
        logger.info("Configuration validation passed")
    else:
        if debug_mode:
            for error in result["errors"]:
                warnings.warn(f"Configuration error: {error}")
        else:
            raise ValueError(
                "Configuration validation failed. Check logs for details."
            )


# =============================================================================
# Django Management Command Support
# =============================================================================


def get_validation_report() -> str:
    """
    Generate a detailed validation report.

    Returns:
        Formatted string report
    """
    result = validate_all_settings(raise_on_error=False)

    lines = ["=" * 60]
    lines.append("Configuration Validation Report")
    lines.append("=" * 60)
    lines.append("")

    if result["valid"]:
        lines.append("Status: PASSED")
    else:
        lines.append("Status: FAILED")

    lines.append("")
    lines.append(f"Errors: {len(result['errors'])}")
    lines.append(f"Warnings: {len(result['warnings'])}")
    lines.append("")

    if result["errors"]:
        lines.append("-" * 40)
        lines.append("Errors:")
        for error in result["errors"]:
            lines.append(f"  - {error}")
        lines.append("")

    if result["warnings"]:
        lines.append("-" * 40)
        lines.append("Warnings:")
        for warning in result["warnings"]:
            lines.append(f"  - {warning}")
        lines.append("")

    lines.append("=" * 60)

    return "\n".join(lines)