"""
Risk level classification and trend calculation utilities.
"""
from typing import Literal

from config import (
    RISK_HIGH,
    RISK_MEDIUM_HIGH,
    RISK_MEDIUM,
    RISK_MEDIUM_LOW,
    TREND_SLOPE_THRESHOLD,
)


def risk_value_to_level(risk_value: float) -> str:
    """Convert risk value (0-1) to risk level string."""
    if risk_value >= RISK_HIGH:
        return "high"
    elif risk_value >= RISK_MEDIUM_HIGH:
        return "medium_high"
    elif risk_value >= RISK_MEDIUM:
        return "medium"
    elif risk_value >= RISK_MEDIUM_LOW:
        return "medium_low"
    else:
        return "low"


def calculate_trend(values: list[float]) -> Literal["up", "down", "stable"]:
    """Calculate trend direction from a series of values using linear regression slope."""
    if len(values) < 2:
        return "stable"

    n = len(values)
    x_mean = (n - 1) / 2
    y_mean = sum(values) / n

    numerator = sum((i - x_mean) * (values[i] - y_mean) for i in range(n))
    denominator = sum((i - x_mean) ** 2 for i in range(n))

    if denominator == 0:
        return "stable"

    slope = numerator / denominator

    if y_mean == 0:
        return "stable"

    relative_slope = slope / y_mean

    if relative_slope > TREND_SLOPE_THRESHOLD:
        return "up"
    elif relative_slope < -TREND_SLOPE_THRESHOLD:
        return "down"
    else:
        return "stable"