hartree-cli 0.1.2

//! Parsing and validation for the `--ts-*` transition-state CLI flags.
//!
//! Pure and side-effect-free so it is unit-testable without touching argv or the
//! solver: [`apply_ts_option`] mutates a borrowed [`TsOptions`] (built via
//! `TsOptions::default()`, the documented way to construct the `#[non_exhaustive]`
//! struct) from one flag/value pair, and [`parse_ts_algo`] decodes `--ts-algo`.
//! Error strings mirror the existing CLI style ("--flag must be ...").

use hartree::CoordScanSpec;
use hartree::core::units::ANGSTROM_TO_BOHR;
use hartree::opt::internals::Internal;
use hartree::opt::ts::{Coordinates, IrcMethod, TsAlgorithm, TsOptions, VerifyHessian};

/// The value-taking `--ts-*` flags, so the argv loop in `main.rs` can recognise
/// them in one membership test before routing through [`apply_ts_option`].
/// `--ts-irc` is a bare boolean and is handled directly in `main.rs`.
pub const TS_VALUE_FLAGS: &[&str] = &[
    "--ts-max-iter",
    "--ts-follow",
    "--ts-recalc-hessian",
    "--ts-stall-refresh",
    "--ts-trust",
    "--ts-fd-step",
    "--ts-neg-tol",
    "--ts-algo",
    "--ts-dimer-delta",
    "--ts-irc-method",
    "--ts-irc-step",
    "--ts-irc-max-steps",
    "--ts-irc-gtol",
    "--ts-verify-hessian",
    "--ts-coordinates",
];

/// Parse the `--ts-algo` value. Accepts "prfo" and "dimer" (case-insensitive).
pub fn parse_ts_algo(s: &str) -> Result<TsAlgorithm, String> {
    match s.to_ascii_lowercase().as_str() {
        "prfo" => Ok(TsAlgorithm::Prfo),
        "dimer" => Ok(TsAlgorithm::Dimer),
        _ => Err(format!("--ts-algo must be one of prfo, dimer (got {s:?})")),
    }
}

/// Parse the `--ts-irc-method` value. Accepts "dvv", "gs2", and "eulerpc"
/// (case-insensitive).
pub fn parse_irc_method(s: &str) -> Result<IrcMethod, String> {
    match s.to_ascii_lowercase().as_str() {
        "dvv" => Ok(IrcMethod::Dvv),
        "gs2" => Ok(IrcMethod::GonzalezSchlegel),
        "eulerpc" => Ok(IrcMethod::EulerPc),
        _ => Err(format!(
            "--ts-irc-method must be one of dvv, gs2, eulerpc (got {s:?})"
        )),
    }
}

/// Parse the `--ts-coordinates` value. Accepts "mass-weighted" (aliases
/// "cartesian"/"mw") and "internal" (alias "internals"), case-insensitive.
pub fn parse_coordinates(s: &str) -> Result<Coordinates, String> {
    match s.to_ascii_lowercase().as_str() {
        "mass-weighted" | "massweighted" | "mw" | "cartesian" | "cart" => {
            Ok(Coordinates::MassWeighted)
        }
        "internal" | "internals" => Ok(Coordinates::Internal),
        _ => Err(format!(
            "--ts-coordinates must be one of mass-weighted, internal (got {s:?})"
        )),
    }
}

/// Parse the `--ts-scan-coord` value into a [`CoordScanSpec`].
///
/// Syntax: `idx,idx[,idx[,idx]]:start:end:steps` — comma-separated atom indices
/// (0-based, into the input geometry) selecting the coordinate to drive, then the value
/// range and grid-point count, colon-separated:
/// - 2 indices `i,j` → bond `i–j` (range in Angstrom),
/// - 3 indices `i,k,j` → valence angle with centre `k` in the middle (range in degrees),
/// - 4 indices `i,j,k,l` → dihedral about the central `j–k` bond (range in degrees).
///
/// `steps` is the number of grid points (≥ 3). Bond ranges are converted to Bohr and
/// angle/dihedral ranges to radians, the units the scan driver works in.
pub fn parse_scan_coord(s: &str) -> Result<CoordScanSpec, String> {
    let bad = || {
        format!(
            "--ts-scan-coord must be \"i,j[,k[,l]]:start:end:steps\" \
             (2-4 atom indices, then range and step count); got {s:?}"
        )
    };
    let fields: Vec<&str> = s.split(':').collect();
    if fields.len() != 4 {
        return Err(bad());
    }
    let indices: Vec<usize> = fields[0]
        .split(',')
        .map(|t| t.trim().parse::<usize>().map_err(|_| bad()))
        .collect::<Result<_, _>>()?;
    let start: f64 = fields[1].trim().parse().map_err(|_| bad())?;
    let end: f64 = fields[2].trim().parse().map_err(|_| bad())?;
    let steps: usize = fields[3].trim().parse().map_err(|_| bad())?;
    if !start.is_finite() || !end.is_finite() {
        return Err("--ts-scan-coord range bounds must be finite".to_string());
    }
    if steps < 3 {
        return Err("--ts-scan-coord needs at least 3 grid points".to_string());
    }

    // Distinct atom indices, and a non-empty range.
    if (start - end).abs() < 1e-12 {
        return Err("--ts-scan-coord start and end must differ".to_string());
    }

    let (coordinate, to_internal): (Internal, fn(f64) -> f64) = match *indices.as_slice() {
        [i, j] => (Internal::Bond(i, j), |v| v * ANGSTROM_TO_BOHR),
        [i, k, j] => (Internal::Angle(i, k, j), f64::to_radians),
        [i, j, k, l] => (Internal::Dihedral(i, j, k, l), f64::to_radians),
        _ => {
            return Err(format!(
                "--ts-scan-coord takes 2-4 atom indices (bond, angle, or dihedral); got {} in {s:?}",
                indices.len()
            ));
        }
    };
    if has_duplicate(&indices) {
        return Err(format!(
            "--ts-scan-coord atom indices must be distinct; got {indices:?}"
        ));
    }

    Ok(CoordScanSpec::new(
        coordinate,
        to_internal(start),
        to_internal(end),
        steps,
    ))
}

fn has_duplicate(indices: &[usize]) -> bool {
    for a in 0..indices.len() {
        for b in (a + 1)..indices.len() {
            if indices[a] == indices[b] {
                return true;
            }
        }
    }
    false
}

/// Parse the `--ts-verify-hessian` value. Accepts "strict", "maintained", and "auto"
/// (case-insensitive).
pub fn parse_verify_hessian(s: &str) -> Result<VerifyHessian, String> {
    match s.to_ascii_lowercase().as_str() {
        "strict" => Ok(VerifyHessian::Strict),
        "maintained" => Ok(VerifyHessian::Maintained),
        "auto" => Ok(VerifyHessian::Auto),
        _ => Err(format!(
            "--ts-verify-hessian must be one of strict, maintained, auto (got {s:?})"
        )),
    }
}

/// Apply one value-taking `--ts-*` flag to `opts`, validating the value. Returns
/// an error string (mirroring the existing CLI error style) on bad input.
pub fn apply_ts_option(opts: &mut TsOptions, flag: &str, value: &str) -> Result<(), String> {
    match flag {
        "--ts-max-iter" => opts.max_iter = parse_usize(flag, value)?, // >= 1
        "--ts-follow" => opts.follow_mode = parse_usize_zero_ok(flag, value)?, // >= 0
        "--ts-recalc-hessian" => opts.recalc_hessian = parse_usize_zero_ok(flag, value)?, // 0 = Bofill only
        "--ts-stall-refresh" => opts.stall_refresh = parse_usize_zero_ok(flag, value)?,   // 0 = off
        "--ts-trust" => opts.trust_radius = parse_pos_f64(flag, value, "bohr")?,          // > 0
        "--ts-fd-step" => opts.fd_step = parse_pos_f64(flag, value, "bohr")?,             // > 0
        "--ts-neg-tol" => opts.negative_mode_tol = parse_pos_f64(flag, value, "a.u.")?,   // > 0
        "--ts-algo" => opts.algorithm = parse_ts_algo(value)?,
        "--ts-dimer-delta" => opts.dimer_delta = parse_pos_f64(flag, value, "bohr")?, // > 0
        "--ts-irc-method" => opts.irc_method = parse_irc_method(value)?,
        "--ts-irc-step" => opts.irc_step = parse_pos_f64(flag, value, "√amu·bohr")?, // > 0
        "--ts-irc-max-steps" => opts.irc_max_steps = parse_usize(flag, value)?,      // >= 1
        "--ts-irc-gtol" => opts.irc_gtol = parse_pos_f64(flag, value, "a.u.")?,      // > 0
        "--ts-verify-hessian" => opts.verify_hessian = parse_verify_hessian(value)?,
        "--ts-coordinates" => opts.coordinates = parse_coordinates(value)?,
        other => return Err(format!("internal error: unhandled ts flag {other}")),
    }
    Ok(())
}

/// Parse a `usize` that must be at least 1 (e.g. an iteration count).
fn parse_usize(flag: &str, value: &str) -> Result<usize, String> {
    let n: usize = value
        .parse()
        .map_err(|_| format!("{flag} must be a positive integer"))?;
    if n == 0 {
        return Err(format!("{flag} must be a positive integer (>= 1)"));
    }
    Ok(n)
}

/// Parse a `usize` that may be 0 (e.g. a mode index / recompute cadence).
fn parse_usize_zero_ok(flag: &str, value: &str) -> Result<usize, String> {
    value
        .parse()
        .map_err(|_| format!("{flag} must be a non-negative integer"))
}

/// Parse a strictly positive, finite `f64`. `unit` names the value's units for
/// the error message (e.g. "bohr", "a.u.").
fn parse_pos_f64(flag: &str, value: &str, unit: &str) -> Result<f64, String> {
    let x: f64 = value
        .parse()
        .map_err(|_| format!("{flag} must be a positive number ({unit})"))?;
    if !x.is_finite() || x <= 0.0 {
        return Err(format!("{flag} must be a positive number ({unit})"));
    }
    Ok(x)
}

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

    #[test]
    fn parse_ts_algo_accepts_known_values() {
        assert_eq!(parse_ts_algo("prfo").unwrap(), TsAlgorithm::Prfo);
        assert_eq!(parse_ts_algo("dimer").unwrap(), TsAlgorithm::Dimer);
        // Case-insensitive.
        assert_eq!(parse_ts_algo("PRFO").unwrap(), TsAlgorithm::Prfo);
        assert_eq!(parse_ts_algo("Dimer").unwrap(), TsAlgorithm::Dimer);
    }

    #[test]
    fn parse_ts_algo_rejects_unknown_values() {
        assert!(parse_ts_algo("neb").is_err());
        assert!(parse_ts_algo("bogus").is_err());
        assert!(parse_ts_algo("").is_err());
    }

    #[test]
    fn parse_irc_method_accepts_known_values() {
        assert_eq!(parse_irc_method("dvv").unwrap(), IrcMethod::Dvv);
        assert_eq!(
            parse_irc_method("gs2").unwrap(),
            IrcMethod::GonzalezSchlegel
        );
        assert_eq!(parse_irc_method("eulerpc").unwrap(), IrcMethod::EulerPc);
        // Case-insensitive.
        assert_eq!(parse_irc_method("DVV").unwrap(), IrcMethod::Dvv);
        assert_eq!(parse_irc_method("EulerPC").unwrap(), IrcMethod::EulerPc);
    }

    #[test]
    fn parse_irc_method_rejects_unknown_values() {
        assert!(parse_irc_method("gonzalez").is_err());
        assert!(parse_irc_method("bogus").is_err());
        assert!(parse_irc_method("").is_err());
    }

    #[test]
    fn apply_sets_each_field_from_valid_value() {
        let mut o = TsOptions::default();
        apply_ts_option(&mut o, "--ts-max-iter", "42").unwrap();
        assert_eq!(o.max_iter, 42);

        apply_ts_option(&mut o, "--ts-follow", "2").unwrap();
        assert_eq!(o.follow_mode, 2);

        apply_ts_option(&mut o, "--ts-recalc-hessian", "5").unwrap();
        assert_eq!(o.recalc_hessian, 5);

        apply_ts_option(&mut o, "--ts-stall-refresh", "5").unwrap();
        assert_eq!(o.stall_refresh, 5);
        // 0 disables the aid (the default behaviour).
        apply_ts_option(&mut o, "--ts-stall-refresh", "0").unwrap();
        assert_eq!(o.stall_refresh, 0);

        apply_ts_option(&mut o, "--ts-trust", "0.15").unwrap();
        assert_eq!(o.trust_radius, 0.15);

        apply_ts_option(&mut o, "--ts-fd-step", "1e-3").unwrap();
        assert_eq!(o.fd_step, 1e-3);

        apply_ts_option(&mut o, "--ts-neg-tol", "2e-4").unwrap();
        assert_eq!(o.negative_mode_tol, 2e-4);

        apply_ts_option(&mut o, "--ts-algo", "dimer").unwrap();
        assert_eq!(o.algorithm, TsAlgorithm::Dimer);

        apply_ts_option(&mut o, "--ts-dimer-delta", "5e-3").unwrap();
        assert_eq!(o.dimer_delta, 5e-3);

        apply_ts_option(&mut o, "--ts-irc-method", "gs2").unwrap();
        assert_eq!(o.irc_method, IrcMethod::GonzalezSchlegel);

        apply_ts_option(&mut o, "--ts-irc-step", "0.05").unwrap();
        assert_eq!(o.irc_step, 0.05);

        apply_ts_option(&mut o, "--ts-irc-max-steps", "250").unwrap();
        assert_eq!(o.irc_max_steps, 250);

        apply_ts_option(&mut o, "--ts-irc-gtol", "2e-3").unwrap();
        assert_eq!(o.irc_gtol, 2e-3);

        apply_ts_option(&mut o, "--ts-verify-hessian", "auto").unwrap();
        assert_eq!(o.verify_hessian, VerifyHessian::Auto);
    }

    #[test]
    fn parse_verify_hessian_accepts_known_values() {
        assert_eq!(
            parse_verify_hessian("strict").unwrap(),
            VerifyHessian::Strict
        );
        assert_eq!(
            parse_verify_hessian("maintained").unwrap(),
            VerifyHessian::Maintained
        );
        assert_eq!(parse_verify_hessian("auto").unwrap(), VerifyHessian::Auto);
        // Case-insensitive.
        assert_eq!(parse_verify_hessian("Auto").unwrap(), VerifyHessian::Auto);
        assert!(parse_verify_hessian("bogus").is_err());
        assert!(parse_verify_hessian("").is_err());
    }

    #[test]
    fn parse_coordinates_accepts_known_values_and_aliases() {
        assert_eq!(
            parse_coordinates("mass-weighted").unwrap(),
            Coordinates::MassWeighted
        );
        assert_eq!(parse_coordinates("mw").unwrap(), Coordinates::MassWeighted);
        assert_eq!(
            parse_coordinates("cartesian").unwrap(),
            Coordinates::MassWeighted
        );
        assert_eq!(
            parse_coordinates("internal").unwrap(),
            Coordinates::Internal
        );
        assert_eq!(
            parse_coordinates("Internals").unwrap(),
            Coordinates::Internal
        );
        assert!(parse_coordinates("bogus").is_err());
        assert!(parse_coordinates("").is_err());

        let mut o = TsOptions::default();
        apply_ts_option(&mut o, "--ts-coordinates", "internal").unwrap();
        assert_eq!(o.coordinates, Coordinates::Internal);
        assert!(apply_ts_option(&mut o, "--ts-coordinates", "bogus").is_err());
    }

    #[test]
    fn parse_scan_coord_accepts_bond_angle_dihedral() {
        use std::f64::consts::PI;

        // Bond: 2 indices, range converted Angstrom → Bohr.
        let bond = parse_scan_coord("0,1:1.0:2.0:11").unwrap();
        assert_eq!(bond.coordinate, Internal::Bond(0, 1));
        assert!((bond.start - 1.0 * ANGSTROM_TO_BOHR).abs() < 1e-12);
        assert!((bond.end - 2.0 * ANGSTROM_TO_BOHR).abs() < 1e-12);
        assert_eq!(bond.n_points, 11);

        // Angle: 3 indices, centre in the middle, range degrees → radians.
        let angle = parse_scan_coord("0,1,2:90:180:7").unwrap();
        assert_eq!(angle.coordinate, Internal::Angle(0, 1, 2));
        assert!((angle.start - PI / 2.0).abs() < 1e-12);
        assert!((angle.end - PI).abs() < 1e-12);
        assert_eq!(angle.n_points, 7);

        // Dihedral: 4 indices, range degrees → radians.
        let dih = parse_scan_coord("0,1,2,3:-180:180:13").unwrap();
        assert_eq!(dih.coordinate, Internal::Dihedral(0, 1, 2, 3));
        assert!((dih.start + PI).abs() < 1e-12);
        assert!((dih.end - PI).abs() < 1e-12);
    }

    #[test]
    fn parse_scan_coord_rejects_bad_specs() {
        // Wrong field count.
        assert!(parse_scan_coord("0,1:1.0:2.0").is_err());
        // Too few / too many atom indices.
        assert!(parse_scan_coord("0:1.0:2.0:11").is_err());
        assert!(parse_scan_coord("0,1,2,3,4:1.0:2.0:11").is_err());
        // Non-numeric index / range / steps.
        assert!(parse_scan_coord("a,1:1.0:2.0:11").is_err());
        assert!(parse_scan_coord("0,1:x:2.0:11").is_err());
        assert!(parse_scan_coord("0,1:1.0:2.0:two").is_err());
        // Fewer than 3 grid points.
        assert!(parse_scan_coord("0,1:1.0:2.0:2").is_err());
        // Degenerate range and repeated indices.
        assert!(parse_scan_coord("0,1:1.5:1.5:11").is_err());
        assert!(parse_scan_coord("0,0:1.0:2.0:11").is_err());
    }

    #[test]
    fn apply_accepts_zero_for_zero_ok_fields() {
        let mut o = TsOptions::default();
        apply_ts_option(&mut o, "--ts-follow", "0").unwrap();
        assert_eq!(o.follow_mode, 0);
        apply_ts_option(&mut o, "--ts-recalc-hessian", "0").unwrap();
        assert_eq!(o.recalc_hessian, 0);
    }

    #[test]
    fn apply_rejects_bad_values() {
        let mut o = TsOptions::default();
        assert!(apply_ts_option(&mut o, "--ts-trust", "0").is_err());
        assert!(apply_ts_option(&mut o, "--ts-trust", "-1").is_err());
        assert!(apply_ts_option(&mut o, "--ts-fd-step", "nan").is_err());
        assert!(apply_ts_option(&mut o, "--ts-fd-step", "-1").is_err());
        assert!(apply_ts_option(&mut o, "--ts-max-iter", "0").is_err());
        assert!(apply_ts_option(&mut o, "--ts-neg-tol", "0").is_err());
        assert!(apply_ts_option(&mut o, "--ts-algo", "bogus").is_err());
        assert!(apply_ts_option(&mut o, "--ts-irc-method", "bogus").is_err());
        assert!(apply_ts_option(&mut o, "--ts-irc-step", "0").is_err());
        assert!(apply_ts_option(&mut o, "--ts-irc-step", "-1").is_err());
        assert!(apply_ts_option(&mut o, "--ts-irc-max-steps", "0").is_err());
        assert!(apply_ts_option(&mut o, "--ts-dimer-delta", "0").is_err());
        assert!(apply_ts_option(&mut o, "--ts-dimer-delta", "-1").is_err());
        assert!(apply_ts_option(&mut o, "--ts-dimer-delta", "nan").is_err());
        assert!(apply_ts_option(&mut o, "--ts-irc-gtol", "0").is_err());
        assert!(apply_ts_option(&mut o, "--ts-irc-gtol", "-1").is_err());
        // A non-numeric integer is rejected too.
        assert!(apply_ts_option(&mut o, "--ts-max-iter", "abc").is_err());
        assert!(apply_ts_option(&mut o, "--ts-follow", "-1").is_err());
    }

    #[test]
    fn rejected_values_do_not_mutate_defaults() {
        // A failed parse must leave the option untouched (validation happens
        // before assignment).
        let mut o = TsOptions::default();
        let before = o.trust_radius;
        let _ = apply_ts_option(&mut o, "--ts-trust", "-1");
        assert_eq!(o.trust_radius, before);
    }

    #[test]
    fn value_flag_table_is_exhaustive() {
        // Every value flag routes through `apply_ts_option` without hitting the
        // "internal error" arm.
        let mut o = TsOptions::default();
        for &flag in TS_VALUE_FLAGS {
            // Flags taking an enum keyword need a valid keyword; the rest accept "1".
            let value = match flag {
                "--ts-algo" => "prfo",
                "--ts-irc-method" => "dvv",
                "--ts-verify-hessian" => "strict",
                "--ts-coordinates" => "internal",
                _ => "1",
            };
            apply_ts_option(&mut o, flag, value)
                .unwrap_or_else(|e| panic!("flag {flag} should parse value {value:?}: {e}"));
        }
    }
}