"""ELO Rating System for ServeSync"""

K_FACTOR = 32  # Standard K-factor


def expected_score(rating_a: float, rating_b: float) -> float:
    """Calculate expected score for player A vs player B"""
    return 1 / (1 + 10 ** ((rating_b - rating_a) / 400))


def calculate_elo_change(winner_rating: float, loser_rating: float) -> tuple[float, float]:
    """
    Calculate ELO changes after a match.
    Returns (winner_change, loser_change)
    """
    expected_winner = expected_score(winner_rating, loser_rating)
    expected_loser = expected_score(loser_rating, winner_rating)

    winner_change = K_FACTOR * (1 - expected_winner)
    loser_change = K_FACTOR * (0 - expected_loser)

    return round(winner_change, 2), round(loser_change, 2)


def calculate_team_elo(player1_rating: float, player2_rating: float = None) -> float:
    """Calculate team ELO (average for doubles)"""
    if player2_rating is None:
        return player1_rating
    return (player1_rating + player2_rating) / 2


def get_tier_from_elo(elo: float) -> str:
    """Get membership tier based on ELO rating"""
    if elo < 1000:
        return "bronze"
    elif elo < 1200:
        return "silver"
    elif elo < 1500:
        return "gold"
    elif elo < 1800:
        return "platinum"
    else:
        return "elite"


def is_valid_match(player_elo: float, match_min_elo: float, match_max_elo: float) -> bool:
    """Check if player is within ELO range for skill-based match"""
    return match_min_elo <= player_elo <= match_max_elo


def get_elo_range(player_elo: float, tolerance: float = 200) -> tuple[float, float]:
    """Get valid ELO range for matching"""
    return (max(0, player_elo - tolerance), player_elo + tolerance)