readcon_db/

export_h5md.rs

//! Cooked H5MD arrays collected from CON/RCSO. The HDF5 file is written
//! by the Python binding (h5py). This module owns layout so tests can
//! check `[T][N][3]` without h5py.

use crate::corpus::ConCorpus;
use crate::error::Result;
use crate::select::Select;

/// Time-dependent cooked trajectory for one `traj_id`.
#[derive(Clone, Debug)]
pub struct H5mdArrays {
    pub n_frames: usize,
    pub natoms: usize,
    /// `[T][N][3]` row-major f64.
    pub positions: Vec<f64>,
    /// `[T][3][3]` H5MD box/edges (lattice vectors, or boxl+angles).
    pub edges: Vec<f64>,
    /// Integer Z, length `N`.
    pub species_z: Vec<i32>,
    /// `[T][N][3]` if any frame has forces; frames without forces are zeros.
    pub forces: Option<Vec<f64>>,
    /// `[T][N][3]` if any frame has velocities; frames without are zeros.
    pub velocities: Option<Vec<f64>>,
    pub velocity_unit: String,
    /// H5MD `box` boundary strings, from CON `pbc` (periodic when absent).
    pub boundary: [String; 3],
    /// `[T]` times in [`H5MD_TIME_ATTR`] (CON time or `i * timestep`, else frame index).
    pub times: Vec<f64>,
    pub time_unit: String,
    pub length_unit: String,
    pub force_unit: String,
}

/// MDA/H5MD engine units (one dest system, same split as metatomic model vs engine).
pub const H5MD_LENGTH_CORE: &str = "angstrom";
pub const H5MD_LENGTH_ATTR: &str = "Angstrom";
pub const H5MD_TIME_CORE: &str = "ps";
pub const H5MD_TIME_ATTR: &str = "ps";
/// Historical clock unit for v1, v2, and v3.0 when `units.time` is absent.
///
/// Spec v3.1 does not default a missing clock unit. CON-header.3 defaults
/// only angstrom and amu. CON-units.4 forbids a silent `time: fs`. A v3.1
/// clock without `units.time` is an error.
pub const CON_TIME_DEFAULT: &str = "fs";

/// Options for [`ConCorpus::collect_h5md_with`].
///
/// `velocity_time_unit` overrides D10. Use it for a file that breaks the
/// rule: natural-unit numbers under a v3.1 `fs` label, or true fs numbers
/// on a v1, v2, or v3.0 frame. The same string is the clock unit when a
/// v3.1 frame has `time` or `timestep` and no `units.time`. A present
/// `units.time` still scales the clock.
#[derive(Clone, Debug, Default)]
pub struct H5mdCollectOpts {
    pub velocity_time_unit: Option<String>,
}
pub const H5MD_FORCE_ATTR: &str = "kJ mol-1 Angstrom-1";
pub const H5MD_VELOCITY_ATTR: &str = "Angstrom ps-1";
/// 1 kJ mol^{-1} Å^{-1} in N. CODATA 2018 N_A.
const KJ_MOL_ANGSTROM_SI: f64 = (1000.0 / 6.022_140_76e23) / 1e-10;

fn boundary_from_pbc(pbc: Option<[bool; 3]>) -> [String; 3] {
    let p = pbc.unwrap_or([true, true, true]);
    std::array::from_fn(|i| {
        if p[i] {
            "periodic".into()
        } else {
            "none".into()
        }
    })
}

fn boxl_to_edges33(boxl: &[f64; 3]) -> [f64; 9] {
    [boxl[0], 0.0, 0.0, 0.0, boxl[1], 0.0, 0.0, 0.0, boxl[2]]
}

fn uc(from: &str, to: &str) -> Result<f64> {
    readcon_core::units::unit_conversion_factor(from, to)
        .map_err(|e| crate::error::Error::Message(e.to_string()))
}

fn header_unit(h: &readcon_core::types::FrameHeader, dim: &str, default: &str) -> String {
    h.unit_for(dim)
        .map(str::to_string)
        .unwrap_or_else(|| default.to_string())
}

/// `value_h5 = factor * value_con` for force (energy/length → kJ mol^{-1} Å^{-1}).
fn force_scale_to_engine(energy_u: &str, length_u: &str) -> Result<f64> {
    let e_j = uc(energy_u, "J")?;
    let l_m = uc(length_u, "m")?;
    Ok((e_j / l_m) / KJ_MOL_ANGSTROM_SI)
}

fn time_scale_to_ps(from: &str) -> Result<f64> {
    match uc(from, H5MD_TIME_CORE) {
        Ok(f) => Ok(f),
        Err(_) if from.eq_ignore_ascii_case("ns") || from.eq_ignore_ascii_case("nanosecond") => {
            Ok(1e3)
        }
        Err(e) => Err(e),
    }
}

fn declared_time_unit(h: &readcon_core::types::FrameHeader) -> Option<String> {
    h.unit_for("time")
        .map(str::trim)
        .filter(|u| !u.is_empty())
        .map(str::to_string)
}

fn positive_timestep(h: &readcon_core::types::FrameHeader) -> Option<f64> {
    h.timestep().filter(|x| x.is_finite() && *x > 0.0)
}

fn frame_time_ps(
    h: &readcon_core::types::FrameHeader,
    frame_idx: u32,
    override_unit: Option<&str>,
) -> Result<f64> {
    let clock = h.time().is_some() || positive_timestep(h).is_some();
    if !clock {
        return Ok(f64::from(frame_idx));
    }
    let from = if let Some(unit) = declared_time_unit(h) {
        unit
    } else if crate::units_canon::velocity_time_is_declared(h) {
        match override_unit.map(str::trim).filter(|u| !u.is_empty()) {
            Some(unit) => unit.to_string(),
            None => {
                return Err(crate::error::Error::Message(
                    "v3.1 frame has a clock but no units.time (D10)".into(),
                ));
            }
        }
    } else {
        CON_TIME_DEFAULT.to_string()
    };
    let scale = time_scale_to_ps(&from)?;
    if let Some(t) = h.time() {
        return Ok(t * scale);
    }
    if let Some(dt) = positive_timestep(h) {
        return Ok(f64::from(frame_idx) * dt * scale);
    }
    Ok(f64::from(frame_idx))
}

pub(crate) fn edges33_from_header(h: &readcon_core::types::FrameHeader) -> [f64; 9] {
    if let Some(arr) = h.metadata.get("lattice_vectors").and_then(|v| v.as_array()) {
        if arr.len() == 3 {
            let mut out = [0.0f64; 9];
            let mut ok = true;
            for (i, row) in arr.iter().enumerate() {
                let Some(r) = row.as_array() else {
                    ok = false;
                    break;
                };
                if r.len() != 3 {
                    ok = false;
                    break;
                }
                for (j, c) in r.iter().enumerate() {
                    let Some(x) = c.as_f64() else {
                        ok = false;
                        break;
                    };
                    out[i * 3 + j] = x;
                }
            }
            if ok {
                return out;
            }
        }
    }
    boxl_angles_to_edges33(&h.boxl, &h.angles)
}

fn boxl_angles_to_edges33(boxl: &[f64; 3], angles: &[f64; 3]) -> [f64; 9] {
    let ortho = angles.iter().all(|&a| a == 0.0 || (a - 90.0).abs() < 1e-9);
    if ortho {
        return boxl_to_edges33(boxl);
    }
    let deg = |a: f64| a * std::f64::consts::PI / 180.0;
    let (lx, ly, lz) = (boxl[0], boxl[1], boxl[2]);
    let (alpha, beta, gamma) = (deg(angles[0]), deg(angles[1]), deg(angles[2]));
    let ax = lx;
    let bx = ly * gamma.cos();
    let by = ly * gamma.sin();
    let cx = lz * beta.cos();
    let cy = lz * (alpha.cos() - beta.cos() * gamma.cos()) / gamma.sin();
    let cz = (lz * lz - cx * cx - cy * cy).max(0.0).sqrt();
    [ax, 0.0, 0.0, bx, by, 0.0, cx, cy, cz]
}

fn velocity_time_unit_for(
    header: &readcon_core::types::FrameHeader,
    has_velocities: bool,
    override_unit: Option<&str>,
) -> Result<String> {
    if let Some(unit) = override_unit {
        let _ = time_scale_to_ps(unit)?;
        return Ok(unit.to_string());
    }
    if crate::units_canon::velocity_time_is_declared(header) {
        match header.unit_for("time") {
            Some(unit) if !unit.trim().is_empty() => Ok(unit.to_string()),
            _ if has_velocities => Err(crate::error::Error::Message(
                "v3.1 frame has velocities but no units.time (D10)".into(),
            )),
            // No velocity section. This string is not the clock unit.
            _ => Ok(CON_TIME_DEFAULT.to_string()),
        }
    } else {
        Ok(crate::units_canon::NATURAL_TIME_UNIT.to_string())
    }
}

impl ConCorpus {
    /// Collect one trajectory as H5MD-shaped arrays (fixed `N`).
    /// Times are dest `ps`: CON `header.time()`, or `i * timestep`, else
    /// the frame index. A v3.1 clock with no `units.time` is an error
    /// unless [`H5mdCollectOpts::velocity_time_unit`] is set. v1, v2, and
    /// v3.0 clocks with no `units.time` use `fs`. Velocities use D10
    /// (see [`H5mdCollectOpts`]).
    pub fn collect_h5md(&self, traj_id: u64) -> Result<H5mdArrays> {
        self.collect_h5md_with(traj_id, &H5mdCollectOpts::default())
    }

    /// [`collect_h5md`] with an explicit velocity time override.
    pub fn collect_h5md_with(&self, traj_id: u64, opts: &H5mdCollectOpts) -> Result<H5mdArrays> {
        let keys = self.select(&Select::new().trajectory(traj_id))?;
        if keys.is_empty() {
            return Err(crate::error::Error::Message("no frames for traj".into()));
        }
        let first = self.get_frame(keys[0])?;
        let natoms = first.atom_data.len();
        let species_z: Vec<i32> = first
            .atom_data
            .iter()
            .map(|a| readcon_core::helpers::symbol_to_atomic_number(a.symbol.as_ref()) as i32)
            .collect();
        let n_frames = keys.len();
        let boundary = boundary_from_pbc(first.header.pbc());
        let mut positions = Vec::with_capacity(n_frames * natoms * 3);
        let mut edges = Vec::with_capacity(n_frames * 9);
        let mut times = Vec::with_capacity(n_frames);
        let mut force_rows: Vec<Option<Vec<[f64; 3]>>> = Vec::with_capacity(n_frames);
        let mut vel_rows: Vec<Option<Vec<[f64; 3]>>> = Vec::with_capacity(n_frames);
        for (i, k) in keys.iter().enumerate() {
            let fr = if i == 0 {
                first.clone()
            } else {
                self.get_frame(*k)?
            };
            let length_u = header_unit(&fr.header, "length", H5MD_LENGTH_CORE);
            let energy_u = header_unit(&fr.header, "energy", "eV");
            let len_scale = uc(&length_u, H5MD_LENGTH_CORE)?;
            times.push(frame_time_ps(
                &fr.header,
                k.frame_idx,
                opts.velocity_time_unit.as_deref(),
            )?);
            let e33 = edges33_from_header(&fr.header);
            for x in e33 {
                edges.push(x * len_scale);
            }
            if fr.atom_data.len() != natoms {
                return Err(crate::error::Error::Message(
                    "H5MD export needs fixed natoms in the trajectory".into(),
                ));
            }
            if boundary_from_pbc(fr.header.pbc()) != boundary {
                return Err(crate::error::Error::Message(
                    "H5MD export needs fixed box/boundary in the trajectory".into(),
                ));
            }
            let z_here: Vec<i32> = fr
                .atom_data
                .iter()
                .map(|a| readcon_core::helpers::symbol_to_atomic_number(a.symbol.as_ref()) as i32)
                .collect();
            if z_here != species_z {
                return Err(crate::error::Error::Message(
                    "H5MD export needs fixed species Z in the trajectory".into(),
                ));
            }
            let (pos_src, vel_src, frc_src) = if let Some(c) = self.get_cooked_soa(*k)? {
                (c.positions, c.velocities, c.forces)
            } else {
                let pos: Vec<[f64; 3]> = fr.atom_data.iter().map(|a| [a.x, a.y, a.z]).collect();
                let vel = if fr.atom_data.iter().any(|a| a.velocity().is_some()) {
                    Some(
                        fr.atom_data
                            .iter()
                            .map(|a| a.velocity().unwrap_or([0.0; 3]))
                            .collect(),
                    )
                } else {
                    None
                };
                let frc = if fr.atom_data.iter().any(|a| a.force().is_some()) {
                    Some(
                        fr.atom_data
                            .iter()
                            .map(|a| a.force().unwrap_or([0.0; 3]))
                            .collect(),
                    )
                } else {
                    None
                };
                (pos, vel, frc)
            };
            let vel_time = velocity_time_unit_for(
                &fr.header,
                vel_src.is_some(),
                opts.velocity_time_unit.as_deref(),
            )?;
            let vel_scale = len_scale / time_scale_to_ps(&vel_time)?;
            for p in &pos_src {
                positions.extend_from_slice(&[
                    p[0] * len_scale,
                    p[1] * len_scale,
                    p[2] * len_scale,
                ]);
            }
            vel_rows.push(match vel_src {
                Some(rows) => Some(
                    rows.into_iter()
                        .map(|r| [r[0] * vel_scale, r[1] * vel_scale, r[2] * vel_scale])
                        .collect(),
                ),
                None => None,
            });
            force_rows.push(match frc_src {
                Some(rows) => {
                    let fscale = force_scale_to_engine(&energy_u, &length_u)?;
                    Some(
                        rows.into_iter()
                            .map(|r| [r[0] * fscale, r[1] * fscale, r[2] * fscale])
                            .collect(),
                    )
                }
                None => None,
            });
        }
        let forces = if force_rows.iter().any(|f| f.is_some()) {
            let mut fbuf = vec![0.0f64; n_frames * natoms * 3];
            for (ti, fo) in force_rows.iter().enumerate() {
                if let Some(rows) = fo {
                    let off = ti * natoms * 3;
                    for (i, row) in rows.iter().enumerate() {
                        fbuf[off + i * 3] = row[0];
                        fbuf[off + i * 3 + 1] = row[1];
                        fbuf[off + i * 3 + 2] = row[2];
                    }
                }
            }
            Some(fbuf)
        } else {
            None
        };
        let velocities = if vel_rows.iter().any(|v| v.is_some()) {
            let mut vbuf = vec![0.0f64; n_frames * natoms * 3];
            for (ti, vo) in vel_rows.iter().enumerate() {
                if let Some(rows) = vo {
                    let off = ti * natoms * 3;
                    for (i, row) in rows.iter().enumerate() {
                        vbuf[off + i * 3] = row[0];
                        vbuf[off + i * 3 + 1] = row[1];
                        vbuf[off + i * 3 + 2] = row[2];
                    }
                }
            }
            Some(vbuf)
        } else {
            None
        };
        Ok(H5mdArrays {
            n_frames,
            natoms,
            positions,
            edges,
            species_z,
            forces,
            velocities,
            velocity_unit: H5MD_VELOCITY_ATTR.into(),
            boundary,
            times,
            time_unit: H5MD_TIME_ATTR.into(),
            length_unit: H5MD_LENGTH_ATTR.into(),
            force_unit: H5MD_FORCE_ATTR.into(),
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::path::PathBuf;

    fn fixture(name: &str) -> PathBuf {
        PathBuf::from(env!("CARGO_MANIFEST_DIR"))
            .join("resources/test")
            .join(name)
    }

    #[test]
    fn collect_h5md_tn3_from_con() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let n = db
            .append_trajectory_path(1, fixture("tiny_multi_cuh2.con"))
            .unwrap();
        assert!(n >= 2);
        let a = db.collect_h5md(1).unwrap();
        assert_eq!(a.n_frames, n as usize);
        assert!(a.natoms >= 1);
        assert_eq!(a.positions.len(), a.n_frames * a.natoms * 3);
        assert_eq!(a.edges.len(), a.n_frames * 9);
        assert_eq!(a.species_z.len(), a.natoms);
        assert!(a.species_z.iter().all(|&z| z > 0));
        assert_eq!(a.boundary.len(), 3);
        assert_eq!(
            a.boundary,
            [
                "periodic".to_string(),
                "periodic".to_string(),
                "periodic".to_string()
            ]
        );
        assert_eq!(a.times.len(), a.n_frames);
        for (i, t) in a.times.iter().enumerate() {
            assert!(
                (*t - i as f64).abs() < 1e-12,
                "frame-index dest ps: times[{i}]={t}"
            );
        }
        assert!((a.positions[0] - 0.6394).abs() < 1e-4);
        let i_h1 = a.natoms * 3 + 2 * 3;
        assert!(
            (a.positions[i_h1] - 8.8549).abs() < 1e-4,
            "tn3 frame1 H dest Å x={}",
            a.positions[i_h1]
        );
    }

    #[test]
    fn export_extxyz_writes_pbc_and_triclinic_lattice() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0].header.angles = [60.0, 90.0, 70.0];
        frames[0]
            .header
            .metadata
            .insert("pbc".into(), serde_json::json!([false, true, false]));
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let keys = db
            .select(&crate::select::Select::new().trajectory(1))
            .unwrap();
        let xyz = dir.path().join("t.xyz");
        db.export_extxyz(&keys, &xyz, "energy").unwrap();
        let out = std::fs::read_to_string(&xyz).unwrap();
        assert!(out.contains("pbc=\"F T F\""), "{out}");
        assert!(!out.contains("pbc=\"T T T\""));
        let e = crate::export_h5md::edges33_from_header(&frames[0].header);
        assert!(e[3].abs() > 1e-9, "triclinic b_x");
        assert!(out.contains(&format!("{:.10}", e[3])), "{out}");
    }

    #[test]
    fn collect_h5md_rejects_changing_natoms() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.con"))
            .unwrap();
        db.extend_trajectory_path(1, fixture("sulfolene.con"))
            .unwrap();
        let err = db.collect_h5md(1).unwrap_err();
        assert!(err.to_string().contains("fixed natoms"), "{err}");
    }

    #[test]
    fn collect_h5md_rejects_changing_pbc() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_multi_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        assert!(frames.len() >= 2);
        frames[0]
            .header
            .metadata
            .insert("pbc".into(), serde_json::json!([true, true, true]));
        frames[1]
            .header
            .metadata
            .insert("pbc".into(), serde_json::json!([false, false, false]));
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let err = db.collect_h5md(1).unwrap_err();
        assert!(err.to_string().contains("fixed box/boundary"), "{err}");
    }

    #[test]
    fn collect_h5md_open_readonly() {
        let dir = tempfile::tempdir().unwrap();
        {
            let db = ConCorpus::open(dir.path()).unwrap();
            db.append_trajectory_path(1, fixture("tiny_multi_cuh2.con"))
                .unwrap();
            db.close();
        }
        let ro = ConCorpus::open_readonly(dir.path()).unwrap();
        let a = ro.collect_h5md(1).unwrap();
        assert!(a.n_frames >= 2);
        assert_eq!(a.positions.len(), a.n_frames * a.natoms * 3);
        assert!((a.positions[0] - 0.6394).abs() < 1e-4);
        let i_h1 = a.natoms * 3 + 2 * 3;
        assert!(
            (a.positions[i_h1] - 8.8549).abs() < 1e-4,
            "readonly frame1 H dest Å x={}",
            a.positions[i_h1]
        );
    }

    #[test]
    fn collect_h5md_two_frame_distinct_boxl() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        let mut f1 = frames[0].clone();
        f1.header.boxl = [20.0, 21.702, 100.0];
        frames.push(f1);
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!(a.n_frames >= 2);
        assert!((a.edges[0] - 15.3456).abs() < 1e-4, "e0={}", a.edges[0]);
        assert!((a.edges[9] - 20.0).abs() < 1e-9, "e9={}", a.edges[9]);
    }

    #[test]
    fn collect_h5md_mixed_pbc_f_t_f() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0]
            .header
            .metadata
            .insert("pbc".into(), serde_json::json!([false, true, false]));
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert_eq!(
            a.boundary,
            [
                "none".to_string(),
                "periodic".to_string(),
                "none".to_string()
            ]
        );
    }

    #[test]
    fn collect_h5md_boundary_none_from_pbc_false() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0]
            .header
            .metadata
            .insert("pbc".into(), serde_json::json!([false, false, false]));
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert_eq!(
            a.boundary,
            ["none".to_string(), "none".to_string(), "none".to_string()]
        );
    }

    #[test]
    fn collect_h5md_pads_mixed_forces() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.con"))
            .unwrap();
        db.extend_trajectory_path(1, fixture("tiny_cuh2_forces.con"))
            .unwrap();
        let a = db.collect_h5md(1).unwrap();
        let f = a.forces.expect("second frame carries forces");
        assert_eq!(f.len(), a.n_frames * a.natoms * 3);
        assert!(a.n_frames >= 2);
        assert!(f[..a.natoms * 3].iter().all(|&x| x == 0.0));
        assert!(f[a.natoms * 3..].iter().any(|&x| x != 0.0));
    }

    #[test]
    fn collect_h5md_con_fallback_matches_rcso() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_multi_cuh2.con"))
            .unwrap();
        let key = crate::keys::FrameKey {
            traj_id: 1,
            frame_idx: 0,
        };
        assert!(!db.has_valid_cooked_soa(key).unwrap());
        let from_con = db.collect_h5md(1).unwrap();
        db.recook_all().unwrap();
        assert!(db.has_valid_cooked_soa(key).unwrap());
        let from_rcso = db.collect_h5md(1).unwrap();
        assert_eq!(from_con.n_frames, from_rcso.n_frames);
        assert_eq!(from_con.positions, from_rcso.positions);
        assert_eq!(from_con.edges, from_rcso.edges);
        assert_eq!(from_con.species_z, from_rcso.species_z);
        let blob = db.get_cooked_soa_bytes(key).unwrap().expect("stored RCSO");
        let decoded = crate::cooked_soa::CookedSoa::decode(&blob).unwrap();
        assert_eq!(decoded.positions.len(), from_rcso.natoms);
        assert!((decoded.positions[0][0] - 0.6394).abs() < 1e-4);
        assert!((from_rcso.positions[0] - 0.6394).abs() < 1e-4);
        assert_eq!(decoded.positions[0][0], from_con.positions[0]);
        // tiny_multi_cuh2.con frame 1 first H: dest Å x = 8.8549
        let i_h1 = from_rcso.natoms * 3 + 2 * 3;
        assert!(
            (from_rcso.positions[i_h1] - 8.8549).abs() < 1e-4,
            "frame1 H x={}",
            from_rcso.positions[i_h1]
        );
        assert!((from_con.positions[i_h1] - 8.8549).abs() < 1e-4);
    }

    #[test]
    fn collect_h5md_uses_con_time_and_fs_unit() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0].header.set_time(12.5);
        frames[0].header.metadata.insert(
            "units".into(),
            serde_json::json!({"length":"angstrom","energy":"eV","mass":"amu","time":"fs"}),
        );
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!(
            (a.times[0] - 0.0125).abs() < 1e-12,
            "12.5 fs -> ps, got {}",
            a.times[0]
        );
        assert_eq!(a.time_unit, "ps");
    }

    #[test]
    fn collect_h5md_scales_nm_length_to_angstrom() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        let box0 = frames[0].header.boxl[0];
        frames[0].header.metadata.insert(
            "units".into(),
            serde_json::json!({"length":"nm","energy":"eV","mass":"amu","time":"fs"}),
        );
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        let scale = uc("nm", "angstrom").unwrap();
        assert!((scale - 10.0).abs() < 1e-12);
        assert!((a.edges[0] - box0 * scale).abs() < 1e-9);
        assert!(
            (a.positions[0] - 0.6394 * scale).abs() < 1e-4,
            "dest Å x0 from nm-labelled CON, got {}",
            a.positions[0]
        );
        assert_eq!(a.length_unit, "Angstrom");
    }

    #[test]
    fn collect_h5md_ns_time_to_ps() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0].header.set_time(2.0);
        frames[0].header.metadata.insert(
            "units".into(),
            serde_json::json!({"length":"angstrom","energy":"eV","mass":"amu","time":"ns"}),
        );
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!(
            (a.times[0] - 2000.0).abs() < 1e-9,
            "2 ns -> ps, got {}",
            a.times[0]
        );
        assert_eq!(a.time_unit, "ps");
    }

    #[test]
    fn collect_h5md_converts_force_via_core_units() {
        let factor = force_scale_to_engine("eV", "angstrom").unwrap();
        assert!((factor - 96.485_332).abs() < 1e-3, "got {factor}");
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2_forces.con"))
            .unwrap();
        let a = db.collect_h5md(1).unwrap();
        let f = a.forces.expect("forces");
        let cooked = crate::cooked_soa::CookedSoa::decode(
            &db.pack_frame(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap(),
        )
        .unwrap();
        let native = cooked.forces.expect("native");
        assert!((f[0] - native[0][0] * factor).abs() < 1e-8);
        assert_eq!(a.force_unit, "kJ mol-1 Angstrom-1");
        assert_eq!(a.length_unit, "Angstrom");
    }

    #[test]
    fn collect_h5md_triclinic_edges_from_angles() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0].header.angles = [60.0, 90.0, 70.0];
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert_eq!(a.edges.len(), 9);
        assert!(a.edges[3].abs() > 1e-9, "b_x from gamma != 90");
        let ortho = boxl_to_edges33(&frames[0].header.boxl);
        assert_ne!(a.edges, ortho.to_vec());
    }

    #[test]
    fn collect_h5md_undeclared_time_is_con_fs() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0].header.set_time(12.5);
        frames[0].header.metadata.remove("units");
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!(
            (a.times[0] - 0.0125).abs() < 1e-12,
            "v2 12.5 with no units.time is fs -> 0.0125 ps, got {}",
            a.times[0]
        );
    }

    #[test]
    fn collect_h5md_uses_i_times_timestep() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_multi_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        assert!(frames.len() >= 2);
        for fr in &mut frames {
            fr.header.metadata.remove("time");
            fr.header.set_timestep(10.0);
            fr.header.metadata.remove("units");
        }
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!(a.times.len() >= 2);
        assert!((a.times[0] - 0.0).abs() < 1e-12, "got {}", a.times[0]);
        assert!(
            (a.times[1] - 0.01).abs() < 1e-12,
            "i=1 * 10 fs -> 0.01 ps, got {}",
            a.times[1]
        );
        assert!((a.positions[0] - 0.6394).abs() < 1e-4);
        let i_h1 = a.natoms * 3 + 2 * 3;
        assert!(
            (a.positions[i_h1] - 8.8549).abs() < 1e-4,
            "frame1 H dest Å x={}",
            a.positions[i_h1]
        );
    }

    #[test]
    fn collect_h5md_set_units_converts_then_export_matches() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        let box0 = frames[0].header.boxl[0];
        frames[0].header.metadata.insert(
            "units".into(),
            serde_json::json!({"length":"angstrom","energy":"eV"}),
        );
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let before = db.collect_h5md(1).unwrap();
        db.set_trajectory_units(1, serde_json::json!({"length":"nm","energy":"eV"}))
            .unwrap();
        let after = db.collect_h5md(1).unwrap();
        assert!((before.edges[0] - box0).abs() < 1e-9);
        assert!((after.edges[0] - box0).abs() < 1e-9);
        let u = db
            .frame_units(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap()
            .unwrap();
        assert_eq!(u["length"], "nm");
        assert_eq!(before.times.len(), after.times.len());
        for (bt, at) in before.times.iter().zip(&after.times) {
            assert!(
                (bt - at).abs() < 1e-12,
                "dest time after set_units {bt} vs {at}"
            );
        }
    }

    #[test]
    fn collect_h5md_rejects_changing_species_z() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_multi_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        assert!(frames.len() >= 2);
        assert!(!frames[1].atom_data.is_empty());
        frames[1].atom_data[0].symbol = std::sync::Arc::from("Au");
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let err = db.collect_h5md(1).unwrap_err();
        assert!(err.to_string().contains("fixed species Z"), "{err}");
    }

    #[test]
    fn collect_h5md_after_cook_set_units_keeps_dest_vel() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.convel"))
            .unwrap();
        db.cook_frame(crate::keys::FrameKey {
            traj_id: 1,
            frame_idx: 0,
        })
        .unwrap();
        let before = db.collect_h5md(1).unwrap();
        db.set_trajectory_units(1, serde_json::json!({"length": "nm", "energy": "eV"}))
            .unwrap();
        assert!(!db
            .has_valid_cooked_soa(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap());
        let native_xyz = db
            .get_positions(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap();
        assert!(
            (native_xyz[0][0] - 0.06394).abs() < 1e-5,
            "native nm x0={}",
            native_xyz[0][0]
        );
        let after = db.collect_h5md(1).unwrap();
        let bv = before.velocities.expect("vel");
        let av = after.velocities.expect("vel");
        assert_eq!(bv.len(), av.len());
        let native = db
            .get_velocities(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap()
            .expect("native vel");
        let u = db
            .frame_units(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap();
        for (i, (b, a)) in bv.iter().zip(av.iter()).enumerate() {
            assert!(
                (b - a).abs() < 1e-9,
                "dest vel[{i}]: before={b} after={a} native0={} units={u:?}",
                native[0][0]
            );
        }
        db.set_trajectory_units(
            1,
            serde_json::json!({"length": "nm", "energy": "eV", "time": "ps"}),
        )
        .unwrap();
        let after_t = db.collect_h5md(1).unwrap();
        let avt = after_t.velocities.expect("vel after time relabel");
        for (i, (b, a)) in bv.iter().zip(avt.iter()).enumerate() {
            assert!(
                (b - a).abs() < 1e-9,
                "dest vel after set_units time[{i}]: {b} vs {a}"
            );
        }
        assert_eq!(before.times.len(), after_t.times.len());
        for (bt, at) in before.times.iter().zip(&after_t.times) {
            assert!((bt - at).abs() < 1e-12, "dest time {bt} vs {at}");
        }
    }

    #[test]
    fn collect_h5md_after_cook_and_set_units() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2_forces.con"))
            .unwrap();
        db.cook_frame(crate::keys::FrameKey {
            traj_id: 1,
            frame_idx: 0,
        })
        .unwrap();
        assert!(db
            .has_valid_cooked_soa(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap());
        let before = db.collect_h5md(1).unwrap();
        db.set_trajectory_units(1, serde_json::json!({"length": "nm", "energy": "eV"}))
            .unwrap();
        let after = db.collect_h5md(1).unwrap();
        assert!((before.edges[0] - after.edges[0]).abs() < 1e-9);
        assert_eq!(before.positions.len(), after.positions.len());
        for (i, (b, a)) in before
            .positions
            .iter()
            .zip(after.positions.iter())
            .enumerate()
        {
            assert!(
                (b - a).abs() < 1e-9,
                "dest Å positions after cook+set_units[{i}]: {b} vs {a}"
            );
        }
        let bf = before.forces.expect("dest forces");
        let af = after.forces.expect("dest forces after set_units");
        assert_eq!(bf.len(), af.len());
        let factor = force_scale_to_engine("eV", "angstrom").unwrap();
        assert!(
            (bf[0] - 0.123456 * factor).abs() < 1e-6,
            "dest force0={}",
            bf[0]
        );
        for (i, (b, a)) in bf.iter().zip(af.iter()).enumerate() {
            assert!(
                (b - a).abs() < 1e-8,
                "dest force after cook+set_units[{i}]: {b} vs {a}"
            );
        }
        db.set_trajectory_units(1, serde_json::json!({"length": "nm", "energy": "hartree"}))
            .unwrap();
        let after_e = db.collect_h5md(1).unwrap();
        let after_energy = after_e.forces.expect("dest forces after set_units energy");
        assert_eq!(bf.len(), after_energy.len());
        for (i, (b, a)) in bf.iter().zip(after_energy.iter()).enumerate() {
            assert!(
                (b - a).abs() < 1e-8,
                "dest force after set_units energy[{i}]: {b} vs {a}"
            );
        }
        assert_eq!(
            db.frame_units(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap()
            .unwrap()["length"],
            "nm"
        );
        assert_eq!(
            db.frame_units(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap()
            .unwrap()["energy"],
            "hartree"
        );
    }

    #[test]
    fn collect_h5md_species_z_cu_h() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.con"))
            .unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!(a.species_z.iter().any(|&z| z == 29), "{:?}", a.species_z);
        assert!(a.species_z.iter().any(|&z| z == 1), "{:?}", a.species_z);
    }

    #[test]
    fn collect_h5md_lattice_vectors_win() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let text = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let mut frames = Vec::new();
        for item in readcon_core::iterators::ConFrameIterator::new(&text) {
            frames.push(item.unwrap());
        }
        frames[0].header.metadata.insert(
            "lattice_vectors".into(),
            serde_json::json!([[2.0, 0.0, 0.0], [0.5, 2.0, 0.0], [0.0, 0.0, 3.0]]),
        );
        db.append_trajectory_frames(1, &frames, "t").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!((a.edges[0] - 2.0).abs() < 1e-12);
        assert!((a.edges[3] - 0.5).abs() < 1e-12);
        assert!((a.edges[8] - 3.0).abs() < 1e-12);
    }

    #[test]
    fn collect_h5md_writes_velocities() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.convel"))
            .unwrap();
        let a = db.collect_h5md(1).unwrap();
        let v = a.velocities.expect("velocities");
        assert_eq!(v.len(), a.n_frames * a.natoms * 3);
        assert!(v.iter().any(|&x| x != 0.0));
        assert_eq!(a.velocity_unit, "Angstrom ps-1");
        let scale = natural_velocity_scale();
        assert!(
            (v[0] - 0.001234 * scale).abs() < 1e-9,
            "v2 convel is the natural unit (D10), got {}",
            v[0]
        );
    }

    #[test]
    fn collect_h5md_pads_mixed_velocities() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.con"))
            .unwrap();
        db.extend_trajectory_path(1, fixture("tiny_cuh2.convel"))
            .unwrap();
        let a = db.collect_h5md(1).unwrap();
        let v = a.velocities.expect("velocities");
        assert!(a.n_frames >= 2);
        assert!(v[..a.natoms * 3].iter().all(|&x| x == 0.0));
        assert!(v[a.natoms * 3..].iter().any(|&x| x != 0.0));
    }

    #[test]
    fn extend_trajectory_path_units_stamps() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.con"))
            .unwrap();
        db.extend_trajectory_path_units(
            1,
            fixture("tiny_cuh2_forces.con"),
            Some(serde_json::json!({"length":"A","energy":"ev"})),
        )
        .unwrap();
        let u = db
            .frame_units(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 1,
            })
            .unwrap()
            .unwrap();
        assert_eq!(u["length"], "angstrom");
        assert_eq!(u["energy"], "eV");
    }

    fn natural_velocity_scale() -> f64 {
        let t_ps = time_scale_to_ps(crate::units_canon::NATURAL_TIME_UNIT).unwrap();
        1.0 / t_ps
    }

    fn with_line2(src: &str, line2: &str) -> String {
        let mut lines: Vec<String> = src.lines().map(str::to_string).collect();
        lines[1] = line2.to_string();
        let mut out = lines.join("\n");
        out.push('\n');
        out
    }

    #[test]
    fn collect_h5md_v30_ignores_fs_label() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.convel")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"sections":["velocities"],"units":{"length":"angstrom","energy":"eV","mass":"amu","time":"fs"}}"#,
        );
        db.append_trajectory_str(1, &text, "v30").unwrap();
        let a = db.collect_h5md(1).unwrap();
        let v = a.velocities.expect("vel");
        let scale = natural_velocity_scale();
        assert!(
            (v[0] - 0.001234 * scale).abs() < 1e-9,
            "v3.0 fs label is not the velocity unit, got {}",
            v[0]
        );
    }

    #[test]
    fn collect_h5md_v31_uses_units_time_fs() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.convel")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"con_spec_minor":1,"sections":["velocities"],"units":{"length":"angstrom","energy":"eV","mass":"amu","time":"fs"}}"#,
        );
        db.append_trajectory_str(1, &text, "v31").unwrap();
        let a = db.collect_h5md(1).unwrap();
        let v = a.velocities.expect("vel");
        assert!(
            (v[0] - 1.234).abs() < 1e-9,
            "v3.1 units.time fs -> A/ps, got {}",
            v[0]
        );
    }

    #[test]
    fn collect_h5md_v31_velocities_without_time_fail() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.convel")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"con_spec_minor":1,"sections":["velocities"],"units":{"length":"angstrom","energy":"eV","mass":"amu"}}"#,
        );
        // readcon-core 0.17 rejects this header at parse time, before export.
        let err = db
            .append_trajectory_str(1, &text, "v31-notime")
            .unwrap_err();
        assert!(err.to_string().contains("requires units.time"), "{err}");
    }

    #[test]
    fn collect_h5md_v30_clock_without_time_is_fs() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"time":12.5,"units":{"length":"angstrom","energy":"eV"}}"#,
        );
        db.append_trajectory_str(1, &text, "v30-clock").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!(
            (a.times[0] - 0.0125).abs() < 1e-12,
            "v3.0 clock with no units.time is fs, got {}",
            a.times[0]
        );
    }

    #[test]
    fn collect_h5md_v31_clock_without_time_fails() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"con_spec_minor":1,"time":12.5,"units":{"length":"angstrom","energy":"eV"}}"#,
        );
        db.append_trajectory_str(1, &text, "v31-clock").unwrap();
        let err = db.collect_h5md(1).unwrap_err();
        let msg = err.to_string();
        assert!(msg.contains("no units.time"), "{err}");
        assert!(msg.contains("clock"), "{err}");
    }

    #[test]
    fn collect_h5md_v31_timestep_without_time_fails() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"con_spec_minor":1,"timestep":10.0,"units":{"length":"angstrom","energy":"eV"}}"#,
        );
        db.append_trajectory_str(1, &text, "v31-dt").unwrap();
        let err = db.collect_h5md(1).unwrap_err();
        let msg = err.to_string();
        assert!(msg.contains("no units.time"), "{err}");
        assert!(msg.contains("clock"), "{err}");
    }

    #[test]
    fn collect_h5md_v31_clock_override_is_fs() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"con_spec_minor":1,"time":12.5,"units":{"length":"angstrom","energy":"eV"}}"#,
        );
        db.append_trajectory_str(1, &text, "v31-clock-fs").unwrap();
        let opts = H5mdCollectOpts {
            velocity_time_unit: Some("fs".into()),
        };
        let a = db.collect_h5md_with(1, &opts).unwrap();
        assert!(
            (a.times[0] - 0.0125).abs() < 1e-12,
            "override fs on a v3.1 clock, got {}",
            a.times[0]
        );
    }

    #[test]
    fn collect_h5md_v31_present_time_ignores_clock_override() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"con_spec_minor":1,"time":2.0,"units":{"length":"angstrom","energy":"eV","time":"ns"}}"#,
        );
        db.append_trajectory_str(1, &text, "v31-ns").unwrap();
        let opts = H5mdCollectOpts {
            velocity_time_unit: Some("fs".into()),
        };
        let a = db.collect_h5md_with(1, &opts).unwrap();
        assert!(
            (a.times[0] - 2000.0).abs() < 1e-9,
            "present units.time ns still scales the clock, got {}",
            a.times[0]
        );
    }

    #[test]
    fn collect_h5md_v31_without_clock_is_frame_index() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        let src = std::fs::read_to_string(fixture("tiny_cuh2.con")).unwrap();
        let text = with_line2(
            &src,
            r#"{"con_spec_version":3,"con_spec_minor":1,"units":{"length":"angstrom","energy":"eV"}}"#,
        );
        db.append_trajectory_str(1, &text, "v31-noclock").unwrap();
        let a = db.collect_h5md(1).unwrap();
        assert!((a.times[0] - 0.0).abs() < 1e-12, "got {}", a.times[0]);
    }

    #[test]
    fn collect_h5md_velocity_time_override_fs_on_v2() {
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("tiny_cuh2.convel"))
            .unwrap();
        let opts = H5mdCollectOpts {
            velocity_time_unit: Some("fs".into()),
        };
        let a = db.collect_h5md_with(1, &opts).unwrap();
        let v = a.velocities.expect("vel");
        assert!(
            (v[0] - 1.234).abs() < 1e-9,
            "override fs on a v2 file, got {}",
            v[0]
        );
    }

    /// eonclient 3.6.0 (conda-forge, c4efc62) `setThermalVelocity` on a
    /// two-atom ljcluster frame, then `matter2convel`. Printed KE is
    /// `getKineticEnergy` before the 6-decimal write.
    #[test]
    fn eon36_convel_h5md_ke_matches_printed() {
        let printed = 1.5004770201120763e-2;
        let dir = tempfile::tempdir().unwrap();
        let db = ConCorpus::open(dir.path()).unwrap();
        db.append_trajectory_path(1, fixture("eon36_lj_dimer.convel"))
            .unwrap();
        let fr = db
            .get_frame(crate::keys::FrameKey {
                traj_id: 1,
                frame_idx: 0,
            })
            .unwrap();
        assert_eq!(fr.header.spec_version, 3);
        assert!(crate::units_canon::con_spec_minor(&fr.header).is_none());
        assert_eq!(fr.header.unit_for("time"), Some("fs"));
        let mut masses = Vec::new();
        for (n, m) in fr
            .header
            .natms_per_type
            .iter()
            .zip(&fr.header.masses_per_type)
        {
            for _ in 0..*n {
                masses.push(*m);
            }
        }
        let native: Vec<[f64; 3]> = fr
            .atom_data
            .iter()
            .map(|a| a.velocity().expect("vel"))
            .collect();
        assert_eq!(masses.len(), native.len());
        let half_ulp = 5e-7;
        let mut bound = 0.0;
        for (m, v) in masses.iter().zip(&native) {
            for c in v {
                bound += m * c.abs() * half_ulp + 0.5 * m * half_ulp * half_ulp;
            }
        }
        let a = db.collect_h5md(1).unwrap();
        let dest = a.velocities.expect("h5md vel");
        let t_ps = time_scale_to_ps(crate::units_canon::NATURAL_TIME_UNIT).unwrap();
        let mut ke = 0.0;
        for (i, m) in masses.iter().enumerate() {
            let vx = dest[i * 3] * t_ps;
            let vy = dest[i * 3 + 1] * t_ps;
            let vz = dest[i * 3 + 2] * t_ps;
            ke += 0.5 * m * (vx * vx + vy * vy + vz * vz);
        }
        assert!(
            (ke - printed).abs() <= bound,
            "H5MD KE {ke} vs eOn {printed}, 6-decimal bound {bound}"
        );
        assert_eq!(a.velocity_unit, "Angstrom ps-1");
    }
}