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use crate::math::Real;

/// Rules used to combine two coefficients.
///
/// This is used to determine the effective restitution and
/// friction coefficients for a contact between two colliders.
/// Each collider has its combination rule of type
/// `CoefficientCombineRule`. And the rule
/// actually used is given by `max(first_combine_rule as usize, second_combine_rule as usize)`.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
pub enum CoefficientCombineRule {
    /// The two coefficients are averaged.
    Average = 0,
    /// The smallest coefficient is chosen.
    Min,
    /// The two coefficients are multiplied.
    Multiply,
    /// The greatest coefficient is chosen.
    Max,
}

impl CoefficientCombineRule {
    pub(crate) fn from_value(val: u8) -> Self {
        match val {
            0 => CoefficientCombineRule::Average,
            1 => CoefficientCombineRule::Min,
            2 => CoefficientCombineRule::Multiply,
            3 => CoefficientCombineRule::Max,
            _ => panic!("Invalid coefficient combine rule."),
        }
    }

    pub(crate) fn combine(coeff1: Real, coeff2: Real, rule_value1: u8, rule_value2: u8) -> Real {
        let effective_rule = rule_value1.max(rule_value2);

        match effective_rule {
            0 => (coeff1 + coeff2) / 2.0,
            1 => coeff1.min(coeff2),
            2 => coeff1 * coeff2,
            _ => coeff1.max(coeff2),
        }
    }
}