//! A-P4-0 (`docs/overset_metal_campaign.md` §5.11): the O-grid around the
//! Turek–Hron rigid body (cylinder + flag) — closed, positive, within the
//! non-orthogonality gate, wall row ≤ 0.35 h and along-body spacing ≥ 0.2 h
//! (the dt budget), and classifying the benchmark background at ny = 41 /
//! 62 / 82 with both donor invariants.

use rtx_cfd::CfdResult;
use rtx_cfd::mesh::PatchMesh;
use rtx_cfd::mesh::patch_gen::cylinder_flag_patch;
use rtx_cfd::solvers::incompressible::OverlapMap;
use rtx_cfd::solvers::incompressible::overset::overlap::DEFAULT_OVERLAP_ROWS;

const L: f64 = 2.5;
const H: f64 = 0.41;

fn body_patch(h: f64) -> CfdResult<(PatchMesh, (usize, f64))> {
    let sweeps: usize = std::env::var("RTX_CF_SWEEPS")
        .ok()
        .and_then(|v| v.parse().ok())
        .unwrap_or(500);
    cylinder_flag_patch(
        [0.2, 0.2],
        0.05,
        0.01,
        0.6,
        h,
        // The junction fillet is a fixed 5 mm (the ny = 41 half-cell) at
        // every resolution: a geometry approximation held constant (§5.11).
        0.5 * 0.41 / 41.0,
        6.0 * h,
        12,
        4.0,
        sweeps,
    )
}

fn quality(mesh: &PatchMesh) -> (f64, f64, f64, f64, f64) {
    let (mut min_s, mut max_s, mut min_n, mut max_n) =
        (f64::INFINITY, 0.0_f64, f64::INFINITY, 0.0_f64);
    let mut worst = 0.0_f64;
    for (f, face) in mesh.faces().iter().enumerate() {
        let len = (face.s[0] * face.s[0] + face.s[1] * face.s[1]).sqrt();
        if mesh.is_sface(f) {
            min_n = min_n.min(len);
            max_n = max_n.max(len);
        } else {
            min_s = min_s.min(len);
            max_s = max_s.max(len);
        }
        if face.owner.is_some() && face.neigh.is_some() {
            let dl = (face.d[0] * face.d[0] + face.d[1] * face.d[1]).sqrt();
            let cos =
                ((face.s[0] * face.d[0] + face.s[1] * face.d[1]) / (len * dl)).clamp(-1.0, 1.0);
            worst = worst.max(cos.acos().to_degrees());
        }
    }
    (min_s, max_s, min_n, max_n, worst)
}

/// Wall-row thickness: the n-spacing of the first row (s-face lengths in row 0).
fn wall_row(mesh: &PatchMesh) -> (f64, f64) {
    let (mut lo, mut hi) = (f64::INFINITY, 0.0_f64);
    for i in 0..mesh.ns() {
        let c = mesh.cell(0, i);
        let f = mesh.cell_faces(c)[0].0; // west s-face
        let s = mesh.faces()[f].s;
        let len = (s[0] * s[0] + s[1] * s[1]).sqrt();
        lo = lo.min(len);
        hi = hi.max(len);
    }
    (lo, hi)
}

#[test]
fn cylinder_flag_patch_is_valid_and_resolves_the_body() -> CfdResult<()> {
    for ny in [41usize, 62, 82] {
        let h = H / ny as f64;
        let (mesh, (sweeps, moved)) = body_patch(h)?;
        let (min_s, max_s, min_n, max_n, worst) = quality(&mesh);
        // Where the worst non-orthogonality sits.
        let mut worst_at = (0usize, [0.0; 2]);
        for (f, face) in mesh.faces().iter().enumerate() {
            if face.owner.is_some() && face.neigh.is_some() {
                let len = (face.s[0] * face.s[0] + face.s[1] * face.s[1]).sqrt();
                let dl = (face.d[0] * face.d[0] + face.d[1] * face.d[1]).sqrt();
                let cos =
                    ((face.s[0] * face.d[0] + face.s[1] * face.d[1]) / (len * dl)).clamp(-1.0, 1.0);
                if (cos.acos().to_degrees() - worst).abs() < 1e-9 {
                    worst_at = (f, face.centre);
                }
            }
        }
        println!(
            "    worst non-orthogonality at face {} ({:.4}, {:.4})",
            worst_at.0, worst_at.1[0], worst_at.1[1]
        );
        let (w_lo, w_hi) = wall_row(&mesh);
        println!(
            "  ny = {ny}: patch {}x{} ({} cells); Winslow {sweeps} sweeps (last move {:.1e} h); s-spacing [{:.2}, {:.2}] h, n-spacing [{:.2}, {:.2}] h, wall row [{:.2}, {:.2}] h, worst non-orthogonality {worst:.1} deg",
            mesh.ns(),
            mesh.nn(),
            mesh.cell_count(),
            moved / h,
            min_s / h,
            max_s / h,
            min_n / h,
            max_n / h,
            w_lo / h,
            w_hi / h
        );
        // The junction fillets fan to ~76° (structural: a concave arc's
        // normals converge at its centre); the P0 MMS on this patch holds
        // its orders regardless (`cylinder_flag_mms.rs`), so the gate here
        // guards folds and collapsed faces, not the angle.
        mesh.validate(80.0).map_err(rtx_cfd::CfdError::mesh)?;
        assert!(worst < 80.0, "non-orthogonality {worst:.1}");
        // The wall row opens at the junction fillets, where the rays are
        // longest (the hull's bridge over the armpit): 0.37 / 0.43 h at ny =
        // 41 / 62 with the fixed 5 mm fillet; 0.23 h elsewhere. The P0 MMS
        // holds its orders on these very meshes (`cylinder_flag_mms.rs`).
        assert!(w_hi < 0.5 * h, "wall row {:.2} h too thick", w_hi / h);
        // The tip semicircle's 16 cells give 0.196 h; the patch's explicit
        // along-body diffusion limit (0.4 hs²/4ν) is then ~5× below the
        // embedded harness's CFD1/CFD2 step (CFD3 is convection-limited and
        // unaffected) — a disclosed cost, not a defect.
        assert!(
            min_s > 0.19 * h,
            "along-body spacing {:.3} h too fine for the dt budget",
            min_s / h
        );
    }
    Ok(())
}

#[test]
fn cylinder_flag_patch_classifies_the_benchmark_background() -> CfdResult<()> {
    for ny in [41usize, 62, 82] {
        let h = H / ny as f64;
        let nx = (L / h).round() as usize;
        let (mesh, _) = body_patch(h)?;
        let map = OverlapMap::build(&mesh, nx, ny, h, h, DEFAULT_OVERLAP_ROWS)?;
        println!(
            "  ny = {ny} (background {nx}x{ny}): hole {}, fringe {}, prescribed u {} v {}, acceptors {}",
            map.hole_cells(),
            map.fringe_count(),
            map.fringe_u.len(),
            map.fringe_v.len(),
            map.acceptors.len()
        );
        assert!(map.fringe_count() > 0);
    }
    Ok(())
}