//! LP-specific entry point.
//!
//! Splits LP from the QP `Q.is_zero` dispatch so that LP-only paths
//! (simplex, future IPM-first / crash / postsolve) are owned by this
//! module. `solve_qp_with(Q=0)` keeps backward compat by forwarding
//! here; the two call sites are distinguishable via `SolverResult.stats.route`.

use crate::options::SolverOptions;
use crate::problem::{LpProblem, SolveRoute, SolveStatus, SolverResult};

/// Solve an LP directly. Sets `result.stats.route = SolveRoute::LpDirect`.
///
/// Returns [`SolveStatus::NumericalError`] if `options` fails validation;
/// validation is performed by the underlying `simplex::solve_with`.
pub fn solve_lp_with(problem: &LpProblem, options: &SolverOptions) -> SolverResult {
    let mut result = crate::simplex::solve_with(problem, options);
    result.stats.route = SolveRoute::LpDirect;
    result.stats.deadline_triggered = matches!(result.status, SolveStatus::Timeout);
    result
}

/// LP entry from `solve_qp_with(Q=0)`. Sets `result.stats.route = SolveRoute::LpForwardedFromQp`.
pub(crate) fn solve_lp_forwarded_from_qp(problem: &LpProblem, options: &SolverOptions) -> SolverResult {
    let mut result = crate::simplex::solve_with(problem, options);
    result.stats.route = SolveRoute::LpForwardedFromQp;
    result.stats.deadline_triggered = matches!(result.status, SolveStatus::Timeout);
    result
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::problem::ConstraintType;
    use crate::sparse::CscMatrix;

    fn make_trivial_lp() -> LpProblem {
        // minimize x  s.t.  x <= 5,  x >= 0
        let a = CscMatrix::from_triplets(&[0], &[0], &[1.0], 1, 1).unwrap();
        LpProblem::new_general(
            vec![1.0],
            a,
            vec![5.0],
            vec![ConstraintType::Le],
            vec![(0.0, f64::INFINITY)],
            None,
        )
        .unwrap()
    }

    /// Invalid options produce NumericalError via `solve_lp_with`.
    ///
    /// Validation is performed by `simplex::solve_with` (the load-bearing sentinel
    /// lives in `simplex::entry::invalid_options_rejected_at_simplex_entry`).
    #[test]
    fn invalid_options_rejected_at_lp_entry() {
        let lp = make_trivial_lp();
        let cases: &[(&str, SolverOptions)] = &[
            ("nan primal_tol", SolverOptions { primal_tol: f64::NAN, ..Default::default() }),
            ("inf primal_tol", SolverOptions { primal_tol: f64::INFINITY, ..Default::default() }),
            ("neg timeout_secs", SolverOptions { timeout_secs: Some(-0.5), ..Default::default() }),
            ("zero threads", SolverOptions { threads: 0, ..Default::default() }),
            ("nan dual_tol", SolverOptions { dual_tol: f64::NAN, ..Default::default() }),
        ];
        for (label, opts) in cases {
            let result = solve_lp_with(&lp, opts);
            assert_eq!(
                result.status,
                SolveStatus::NumericalError,
                "solve_lp_with with {label} must return NumericalError"
            );
        }
    }
}
