ommx 3.0.0-beta.2

use super::*;
use crate::{CoefficientError, VariableIDSet};

impl Function {
    /// Reduce binary powers in the function.
    ///
    /// For binary variables, x^n = x for any n >= 1, so we can reduce higher powers to linear terms.
    ///
    /// Returns `true` if any reduction was performed, `false` otherwise.
    pub fn reduce_binary_power(
        &mut self,
        binary_ids: &VariableIDSet,
    ) -> Result<bool, CoefficientError> {
        Ok(match self {
            Function::Zero => false,
            Function::Constant(_) => false,
            Function::Linear(_) => false, // Linear functions are already in reduced form.
            Function::Quadratic(q) => q.reduce_binary_power(binary_ids)?,
            Function::Polynomial(p) => p.reduce_binary_power(binary_ids)?,
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{coeff, quadratic};
    use ::approx::assert_abs_diff_eq;

    #[test]
    fn test_function_reduce_binary_power() {
        let binary_ids = crate::variable_ids!(1);

        // Test Zero function
        let mut f = Function::Zero;
        assert!(!f.reduce_binary_power(&binary_ids).unwrap());

        // Test Constant function
        let mut f = Function::Constant(coeff!(5.0));
        assert!(!f.reduce_binary_power(&binary_ids).unwrap());

        // Test Quadratic function with binary variable
        let mut f = Function::Quadratic(
            (quadratic!(1, 1) + (coeff!(2.0) * quadratic!(1, 2)).unwrap()).unwrap(),
        );
        assert!(f.reduce_binary_power(&binary_ids).unwrap());

        let expected = Function::Quadratic(
            (quadratic!(1) + (coeff!(2.0) * quadratic!(1, 2)).unwrap()).unwrap(),
        );
        assert_abs_diff_eq!(f, expected);
    }
}