oxideav-cli-convert 0.0.5

//! IM-style arg parser.
//!
//! `convert INPUT [-op VALUE]... OUTPUT` — first positional arg is
//! the input, last positional arg is the output, everything in
//! between is `-flag` pairs.  Most single-word ops take exactly one
//! following value; a few (`-strip`) are valueless.  Any unrecognised
//! flag errors out with a clear message — we never silently drop.

use crate::op::{
    AlphaOp, CameraSpec, ConvertPlan, Dither, GltfFormatChoice, LightSpec, Mesh3DOptions,
    Mesh3DRenderMode, Op, PageAtom, PageSelector, PrintfTemplate, ProjectionMode, ResizeMode,
    StlFormatChoice,
};
use oxideav_core::Error;

/// Every flag the parser below recognises, stored without the leading
/// dash(es). Single-dash IM-style ops AND the double-dash GNU-style
/// modes (`--probe`, `--json`, `--watch`) both land in here; the
/// caller reattaches whichever lead the user typed when rendering a
/// suggestion. Kept as a flat sorted slice rather than a `HashSet`
/// because the list is small (~55 entries), the lookup is a single
/// scan inside the Levenshtein helper, and a sorted slice is trivial
/// to keep aligned with the `match` arms below.
///
/// MUST stay in sync with the `match flag.as_str()` arms in [`parse`].
/// A flag missing from this table downgrades the suggestion quality
/// (the user mistypes a real flag and gets no hint) but doesn't break
/// parsing, so the worst case is a quiet UX regression — easy to spot
/// in review.
const KNOWN_FLAG_NAMES: &[&str] = &[
    "aa",
    "alpha",
    "auto-gamma",
    "background",
    "bg",
    "blur",
    "brightness-contrast",
    "camera",
    "colorize",
    "colors",
    "colorspace",
    "contrast",
    "crop",
    "define",
    "density",
    "dither",
    "edge",
    "equalize",
    "extent",
    "flip",
    "flop",
    "format",
    "fov",
    "fuzz",
    "gamma",
    "gltf-format",
    "json",
    "level",
    "light",
    "modulate",
    "monochrome",
    "negate",
    "normalize",
    "ping",
    "posterize",
    "probe",
    "projection",
    "quality",
    "render",
    "resize",
    "roll",
    "rotate",
    "sepia",
    "sharpen",
    "solarize",
    "stl-format",
    "strip",
    "thumbnail",
    "threshold",
    "trim",
    "unsharp",
    "vignette",
    "watch",
];

/// Parse the slice that comes after `oxideav convert`.
///
/// Returns a `ConvertPlan` on success or an `Error::Invalid` /
/// `Error::Unsupported` tagged with the specific `-flag` so callers
/// can print the offending argument.
pub fn parse(args: &[String]) -> Result<ConvertPlan, Error> {
    if args.is_empty() {
        return Err(Error::invalid(
            "convert: no input file given (usage: convert [-op VALUE]... INPUT [-op VALUE]... OUTPUT)",
        ));
    }

    // ImageMagick allows ops to appear before AND after the input
    // (e.g. `convert -density 300 in.pdf -resize 800x600 out.png`).
    // Walk every arg in order: anything starting with `-` is a flag
    // (which may consume the following arg as its value); everything
    // else is a positional. After parsing, the FIRST positional is the
    // input and the LAST is the output. Multi-input is a documented
    // round-2 follow-up; we error if more than two positionals are
    // present.
    let mut ops: Vec<Op> = Vec::new();
    let mut positionals: Vec<String> = Vec::new();
    let mut pending_dither = Dither::None;
    let mut ping = false;
    let mut probe = false;
    let mut probe_json = false;
    let mut probe_watch = false;
    let mut mesh3d_options = Mesh3DOptions::default();
    // Track the most recent `-background` colour in source order so
    // `-extent` (which paints padding pixels with the active background)
    // captures the correct value at parse time. Defaults to IM's opaque
    // white when the user didn't set `-background` before `-extent`.
    let mut current_bg: [u8; 4] = [255, 255, 255, 255];
    // Track the most recent `-fuzz N[%]` value in source order so a
    // following `-trim` reads this tolerance. IM treats `-fuzz` as a
    // state setting that survives until the next `-fuzz`; pinning the
    // value onto each emitted `Op::Trim` at parse time preserves the
    // source-order semantics for the plan walker and side-channel
    // (a later `-fuzz` does NOT retroactively rewrite an earlier
    // `-trim`'s tolerance).
    let mut current_fuzz: u8 = 0;

    let mut i = 0;
    while i < args.len() {
        let flag = &args[i];
        let val = |k: usize| -> Result<&str, Error> {
            args.get(k)
                .map(|s| s.as_str())
                .ok_or_else(|| Error::invalid(format!("convert: {flag}: missing value")))
        };

        // Non-flag → positional.
        if !flag.starts_with('-') {
            positionals.push(flag.clone());
            i += 1;
            continue;
        }

        match flag.as_str() {
            "-resize" => {
                let v = val(i + 1)?;
                let (mode, core) = ResizeMode::split_suffix(v);
                let (w, h) = parse_resize_geometry(core, mode)
                    .map_err(|e| Error::invalid(format!("convert: -resize: {e}")))?;
                ops.push(Op::Resize {
                    width: w,
                    height: h,
                    mode,
                });
                i += 2;
            }
            // `-thumbnail` is IM's "make a small representative image"
            // convenience flag. Same geometry grammar as `-resize`;
            // semantics differ in that IM also strips metadata and
            // (for JPEG inputs) honours EXIF orientation. We unroll it
            // into [`Op::Thumbnail`] which the runners expand to
            // `Resize { mode } + Strip` (auto-orient is documented as
            // a follow-up — needs an EXIF reader on the source side).
            "-thumbnail" => {
                let v = val(i + 1)?;
                let (mode, core) = ResizeMode::split_suffix(v);
                let (w, h) = parse_resize_geometry(core, mode)
                    .map_err(|e| Error::invalid(format!("convert: -thumbnail: {e}")))?;
                ops.push(Op::Thumbnail {
                    width: w,
                    height: h,
                    mode,
                });
                i += 2;
            }
            // `-define KEY[=VALUE]` — opaque codec-specific tunable.
            // Forwarded literally to the sink encoder; the encoder
            // ignores keys it doesn't recognise. IM's grammar uses `:`
            // inside the key as a namespace separator (e.g.
            // `jpeg:dct-method=float`); we don't parse that — the key
            // is preserved verbatim.
            "-define" => {
                let v = val(i + 1)?;
                let (key, value) = match v.split_once('=') {
                    Some((k, val)) => (k.to_string(), Some(val.to_string())),
                    None => (v.to_string(), None),
                };
                if key.is_empty() {
                    return Err(Error::invalid(format!(
                        "convert: -define: '{v}' has an empty KEY (expected KEY[=VALUE])"
                    )));
                }
                ops.push(Op::Define { key, value });
                i += 2;
            }
            "-blur" => {
                let v = val(i + 1)?;
                let (radius, sigma) =
                    parse_blur(v).map_err(|e| Error::invalid(format!("convert: -blur: {e}")))?;
                ops.push(Op::Blur { radius, sigma });
                i += 2;
            }
            "-edge" => {
                let v = val(i + 1)?;
                let r: u32 = v.parse().map_err(|_| {
                    Error::invalid(format!(
                        "convert: -edge: '{v}' is not a non-negative integer"
                    ))
                })?;
                ops.push(Op::Edge { radius: r });
                i += 2;
            }
            "-colors" => {
                let v = val(i + 1)?;
                let n: u32 = v.parse().map_err(|_| {
                    Error::invalid(format!(
                        "convert: -colors: '{v}' is not a non-negative integer"
                    ))
                })?;
                if !(2..=256).contains(&n) {
                    return Err(Error::invalid(format!(
                        "convert: -colors {n} out of range (2..=256)"
                    )));
                }
                ops.push(Op::Colors {
                    count: n,
                    dither: pending_dither,
                });
                i += 2;
            }
            "-dither" => {
                let v = val(i + 1)?;
                pending_dither = Dither::parse(v).map_err(Error::invalid)?;
                i += 2;
            }
            // `-monochrome` (no value) — IM's "make me a 1-bit dithered
            // black-and-white image" convenience flag. Equivalent to the
            // chain `-colorspace gray -colors 2 -dither floyd_steinberg`,
            // so we lower it to those three primitive ops here rather
            // than carving out a dedicated runner path. The order
            // matters: grayscale-first means the palette-builder sees
            // luminance values rather than colour, so the 2-entry
            // palette lands on black + white instead of two arbitrary
            // colour samples. Floyd-Steinberg is IM's documented
            // default for the 1-bit reduction (newer IM exposes
            // `-define dither:` to override; we don't yet plumb that).
            // A user who wants the un-dithered "Atkinson cut" behaviour
            // can still write the chain by hand with `-dither none`.
            "-monochrome" => {
                ops.push(Op::Colorspace("gray".to_string()));
                ops.push(Op::Colors {
                    count: 2,
                    dither: Dither::FloydSteinberg,
                });
                i += 1;
            }
            "-format" => {
                let v = val(i + 1)?;
                ops.push(Op::Format(v.to_string()));
                i += 2;
            }
            "-quality" => {
                let v = val(i + 1)?;
                let q: u32 = v.parse().map_err(|_| {
                    Error::invalid(format!(
                        "convert: -quality: '{v}' is not a non-negative integer"
                    ))
                })?;
                // IM-conventional cap: every lossy codec convert
                // forwards `-quality` to (JPEG, WebP, AVIF, …) expects
                // `0..=100`. Without this guard `-quality 9999` and
                // `-quality 150` silently propagate and the encoder
                // drops the key — looking to the user like the flag
                // was honoured. Reject up-front with a clear range so
                // the typo (`-quality 1000` instead of `-quality 100`)
                // surfaces at parse time. The 0/100 endpoints stay
                // accepted: 0 is "smallest acceptable" on JPEG and
                // 100 is "highest". Out-of-band values were never
                // useful — codecs ignore them.
                if q > 100 {
                    return Err(Error::invalid(format!(
                        "convert: -quality: {q} out of range (must be in 0..=100; common values: 75 default, 85 web, 95 archival)"
                    )));
                }
                ops.push(Op::Quality(q));
                i += 2;
            }
            "-strip" => {
                ops.push(Op::Strip);
                i += 1;
            }
            "-ping" => {
                ping = true;
                i += 1;
            }
            // `--probe` is GNU-style double-dash because it's a
            // session-scope mode switch (no value, no per-input
            // semantics) — same shape as `--help` / `--version` would
            // have if the convert verb owned them. Single-dash `-probe`
            // is reserved as a future IM-style probe-OP that might
            // legitimately want an argument.
            "--probe" => {
                probe = true;
                i += 1;
            }
            // `--json` selects a machine-readable output flavour for
            // the probe summary. It's only meaningful paired with
            // `--probe`; the validation runs after the loop so we can
            // emit a clear "needs --probe" error rather than a generic
            // "unknown flag" one.
            "--json" => {
                probe_json = true;
                i += 1;
            }
            // `--watch` re-runs the probe whenever the input file's
            // mtime changes. Like `--json`, it's only meaningful paired
            // with `--probe` (there's no other long-running mode for it
            // to attach to); the post-loop validation surfaces a clear
            // "needs --probe" error rather than a generic "unknown
            // flag" one.
            "--watch" => {
                probe_watch = true;
                i += 1;
            }
            "-density" => {
                let v = val(i + 1)?;
                let n: u32 = v.parse().map_err(|_| {
                    Error::invalid(format!(
                        "convert: -density: '{v}' is not a non-negative integer"
                    ))
                })?;
                if n == 0 {
                    return Err(Error::invalid("convert: -density must be > 0"));
                }
                ops.push(Op::Density(n));
                i += 2;
            }
            "-background" => {
                let v = val(i + 1)?;
                let rgba = parse_color(v).map_err(Error::invalid)?;
                // Bake the current background into the parse state so a
                // subsequent `-extent` reads this value rather than the
                // initial IM-default white.
                current_bg = rgba;
                ops.push(Op::Background(rgba));
                i += 2;
            }
            "-alpha" => {
                let v = val(i + 1)?;
                let a = AlphaOp::parse(v).map_err(Error::invalid)?;
                ops.push(Op::Alpha(a));
                i += 2;
            }
            "-rotate" => {
                let v = val(i + 1)?;
                let n: i32 = v.parse().map_err(|_| {
                    Error::invalid(format!("convert: -rotate: '{v}' is not an integer"))
                })?;
                // Round-1 supports only quarter-turn rotations.
                // Other angles need a real resampler (bilinear / lanczos
                // sample at non-integer coordinates), which we'll wire
                // through oxideav-image-filter once it lands.
                if !matches!(n, 90 | 180 | 270 | -90 | -180 | -270) {
                    return Err(Error::invalid(format!(
                        "convert: -rotate: only multiples of 90 supported (got {n})"
                    )));
                }
                ops.push(Op::Rotate { degrees: n });
                i += 2;
            }
            "-flip" => {
                ops.push(Op::Flip);
                i += 1;
            }
            "-flop" => {
                ops.push(Op::Flop);
                i += 1;
            }
            "-negate" => {
                ops.push(Op::Negate);
                i += 1;
            }
            "-crop" => {
                let v = val(i + 1)?;
                let (w, h, x, y) =
                    parse_crop(v).map_err(|e| Error::invalid(format!("convert: -crop: {e}")))?;
                ops.push(Op::Crop { x, y, w, h });
                i += 2;
            }
            "-extent" => {
                // IM-style canvas re-window: `WxH`, `WxH+X+Y`, `WxH-X-Y`,
                // or any mix of signs on the two offsets. The background
                // colour painted under padding pixels is the one set by
                // the most recent `-background` op in source order — we
                // bake it into the op here so the plan walker / inline
                // pixel-xform path don't need to track parser state.
                let v = val(i + 1)?;
                let (w, h, x, y) = parse_extent(v)
                    .map_err(|e| Error::invalid(format!("convert: -extent: {e}")))?;
                ops.push(Op::Extent {
                    width: w,
                    height: h,
                    x,
                    y,
                    bg: current_bg,
                });
                i += 2;
            }
            // `-fuzz N[%]` updates the in-band fuzz state. IM's grammar
            // accepts either a raw byte value (`0..=255`) or a percent
            // (`N%`, `0..=100`) — share the `-threshold` / `-solarize`
            // parser. The flag itself produces no `Op`; it only mutates
            // `current_fuzz`, which a following `-trim` reads.
            "-fuzz" => {
                let v = val(i + 1)?;
                current_fuzz = parse_threshold_pct(v)
                    .map_err(|e| Error::invalid(format!("convert: -fuzz: {e}")))?;
                i += 2;
            }
            // `-trim` (valueless) — auto-crop the bounding box of pixels
            // differing from the corner-pixel reference background by
            // more than the active `-fuzz` tolerance. The tolerance is
            // captured at parse time so source-order semantics survive
            // through the plan walker and the inline side-channel.
            "-trim" => {
                ops.push(Op::Trim { fuzz: current_fuzz });
                i += 1;
            }
            // `-roll ±X±Y` — IM-style circular pixel shift. Both X and
            // Y offsets must be present and signed; columns wrap around
            // the right edge when `dx > 0`, rows wrap around the bottom
            // edge when `dy > 0`. Width / height stay unchanged. Shares
            // the signed-offset parser used by `-extent`'s `±X±Y` tail.
            "-roll" => {
                let v = val(i + 1)?;
                let (dx, dy) =
                    parse_roll(v).map_err(|e| Error::invalid(format!("convert: -roll: {e}")))?;
                ops.push(Op::Roll { dx, dy });
                i += 2;
            }
            // ---- Round-next: IM-style image-filter flags wired
            // through to the matching `oxideav-image-filter` factory. ----
            "-sharpen" => {
                let v = val(i + 1)?;
                let (radius, sigma) =
                    parse_blur(v).map_err(|e| Error::invalid(format!("convert: -sharpen: {e}")))?;
                ops.push(Op::Sharpen { radius, sigma });
                i += 2;
            }
            "-unsharp" => {
                let v = val(i + 1)?;
                let (radius, sigma, amount, threshold) = parse_unsharp(v)
                    .map_err(|e| Error::invalid(format!("convert: -unsharp: {e}")))?;
                ops.push(Op::Unsharp {
                    radius,
                    sigma,
                    amount,
                    threshold,
                });
                i += 2;
            }
            "-gamma" => {
                let v = val(i + 1)?;
                let g: f32 = v.parse().map_err(|_| {
                    Error::invalid(format!("convert: -gamma: '{v}' is not a finite float"))
                })?;
                if !g.is_finite() || g <= 0.0 {
                    return Err(Error::invalid(format!(
                        "convert: -gamma: value must be > 0 (got {g})"
                    )));
                }
                ops.push(Op::Gamma { value: g });
                i += 2;
            }
            "-brightness-contrast" => {
                let v = val(i + 1)?;
                let (b, c) = parse_brightness_contrast(v)
                    .map_err(|e| Error::invalid(format!("convert: -brightness-contrast: {e}")))?;
                ops.push(Op::BrightnessContrast {
                    brightness: b,
                    contrast: c,
                });
                i += 2;
            }
            "-contrast" => {
                // IM's `-contrast` takes no arg and applies a single
                // small contrast bump. Repeated `-contrast` accumulates.
                ops.push(Op::Contrast { delta: 1 });
                i += 1;
            }
            "-sepia" => {
                let v = val(i + 1)?;
                let t = parse_percent_or_unit(v)
                    .map_err(|e| Error::invalid(format!("convert: -sepia: {e}")))?;
                ops.push(Op::Sepia { threshold: t });
                i += 2;
            }
            "-modulate" => {
                let v = val(i + 1)?;
                let (b, s, h) = parse_modulate(v)
                    .map_err(|e| Error::invalid(format!("convert: -modulate: {e}")))?;
                ops.push(Op::Modulate {
                    brightness: b,
                    saturation: s,
                    hue: h,
                });
                i += 2;
            }
            "-level" => {
                let v = val(i + 1)?;
                let (b, g, w) =
                    parse_level(v).map_err(|e| Error::invalid(format!("convert: -level: {e}")))?;
                ops.push(Op::Level {
                    black: b,
                    gamma: g,
                    white: w,
                });
                i += 2;
            }
            "-normalize" => {
                ops.push(Op::Normalize);
                i += 1;
            }
            "-threshold" => {
                let v = val(i + 1)?;
                let n = parse_threshold_pct(v)
                    .map_err(|e| Error::invalid(format!("convert: -threshold: {e}")))?;
                ops.push(Op::Threshold { value: n });
                i += 2;
            }
            "-posterize" => {
                let v = val(i + 1)?;
                let n: u32 = v.parse().map_err(|_| {
                    Error::invalid(format!(
                        "convert: -posterize: '{v}' is not a non-negative integer"
                    ))
                })?;
                if n < 2 {
                    return Err(Error::invalid(format!(
                        "convert: -posterize: levels must be >= 2 (got {n})"
                    )));
                }
                ops.push(Op::Posterize { levels: n });
                i += 2;
            }
            "-solarize" => {
                let v = val(i + 1)?;
                let n = parse_threshold_pct(v)
                    .map_err(|e| Error::invalid(format!("convert: -solarize: {e}")))?;
                ops.push(Op::Solarize { value: n });
                i += 2;
            }
            "-vignette" => {
                let v = val(i + 1)?;
                let (radius, sigma, x, y) = parse_vignette(v)
                    .map_err(|e| Error::invalid(format!("convert: -vignette: {e}")))?;
                ops.push(Op::Vignette {
                    radius,
                    sigma,
                    x,
                    y,
                });
                i += 2;
            }
            "-colorize" => {
                let v = val(i + 1)?;
                let (color, amount) = parse_colorize(v)
                    .map_err(|e| Error::invalid(format!("convert: -colorize: {e}")))?;
                ops.push(Op::Colorize { color, amount });
                i += 2;
            }
            "-equalize" => {
                ops.push(Op::Equalize);
                i += 1;
            }
            "-auto-gamma" => {
                ops.push(Op::AutoGamma);
                i += 1;
            }
            "-colorspace" => {
                let v = val(i + 1)?;
                let cs = v.trim().to_string();
                // Round-1 only routes `gray`/`grey` to the grayscale
                // factory; other colourspaces become a recorded no-op
                // (the input keeps its native colourspace).
                let lower = cs.to_ascii_lowercase();
                if !matches!(lower.as_str(), "gray" | "grey" | "rgb" | "srgb") {
                    return Err(Error::unsupported(format!(
                        "convert: -colorspace '{cs}' is not yet wired (round-1 supports gray/grey/rgb/srgb)"
                    )));
                }
                ops.push(Op::Colorspace(cs));
                i += 2;
            }
            // ---- Per-format encoder option flags for the 3D
            //      side-channel. Stored on `ConvertPlan::mesh3d_options`,
            //      not as `Op` entries, since they're plan-level
            //      switches that only the mesh3d_runner consumes
            //      (raster ops have no analogous notion). The flags
            //      are accepted on every input shape (PDF / raster /
            //      etc.) and silently ignored when the side-channel
            //      doesn't fire — matches IM's tolerant-of-irrelevant-
            //      flags posture.
            "-stl-format" => {
                let v = val(i + 1)?;
                let choice = StlFormatChoice::parse(v).map_err(Error::invalid)?;
                mesh3d_options.stl_format = Some(choice);
                i += 2;
            }
            "-gltf-format" => {
                let v = val(i + 1)?;
                let choice = GltfFormatChoice::parse(v).map_err(Error::invalid)?;
                mesh3d_options.gltf_format = Some(choice);
                i += 2;
            }
            // `-render flat|wireframe` selects the 3D→raster surface
            // model. Stored on `Mesh3DOptions` (sister to `-stl-format`
            // and `-gltf-format`) so it never leaks into the regular
            // pipeline path. Silently ignored when the input/output
            // pair doesn't trigger the 3D→raster side-channel.
            "-render" => {
                let v = val(i + 1)?;
                let mode = Mesh3DRenderMode::parse(v).map_err(Error::invalid)?;
                mesh3d_options.render_mode = Some(mode);
                i += 2;
            }
            // `-light AZIMUTH,ELEVATION,INTENSITY` — directional light
            // override for the 3D→raster renderer's Gouraud / Phong
            // shading paths. Stored on `Mesh3DOptions::light`; silently
            // ignored when the input/output pair doesn't trigger 3D
            // rendering.
            "-light" => {
                let v = val(i + 1)?;
                let spec = LightSpec::parse(v).map_err(Error::invalid)?;
                mesh3d_options.light = Some(spec);
                i += 2;
            }
            // `-camera ELEVATION,AZIMUTH,DISTANCE` — camera override for
            // the 3D→raster renderer (replaces the auto-framed default).
            "-camera" => {
                let v = val(i + 1)?;
                let spec = CameraSpec::parse(v).map_err(Error::invalid)?;
                mesh3d_options.camera = Some(spec);
                i += 2;
            }
            // `-projection perspective|orthographic` — projection mode
            // for the 3D→raster renderer. Default is perspective.
            "-projection" => {
                let v = val(i + 1)?;
                let mode = ProjectionMode::parse(v).map_err(Error::invalid)?;
                mesh3d_options.projection = Some(mode);
                i += 2;
            }
            // `-fov DEGREES` — vertical field of view for the 3D→raster
            // renderer's perspective projection. Default is 60°. Ignored
            // for orthographic projection.
            "-fov" => {
                let v = val(i + 1)?;
                let fov: f32 = v
                    .parse()
                    .map_err(|_| Error::invalid(format!("convert: -fov: '{v}' is not a number")))?;
                if !fov.is_finite() || fov <= 0.0 || fov >= 180.0 {
                    return Err(Error::invalid(format!(
                        "convert: -fov: {fov} must be in (0, 180) degrees"
                    )));
                }
                mesh3d_options.fov_deg = Some(fov);
                i += 2;
            }
            // `-bg COLOR` — background fill for the 3D render canvas.
            // Default is transparent black. Distinct from `-background`
            // which is the IM canvas-fill for alpha-remove + PDF.
            "-bg" => {
                let v = val(i + 1)?;
                let colour = parse_color(v).map_err(Error::invalid)?;
                mesh3d_options.bg = Some(colour);
                i += 2;
            }
            // `-aa N` — supersampling factor for the 3D→raster
            // renderer (rasterise at N × output, box-filter back to
            // 1 × output). `1` means no supersampling. `>= 2` trades
            // memory + CPU for smoother triangle edges. Stored on
            // `Mesh3DOptions::aa`; silently ignored when the
            // input/output pair doesn't trigger 3D rendering. We
            // cap at 8 to keep memory bounded — at 8× a 1024²
            // render needs ~80 MB just for the framebuffer + z-buffer
            // and that already costs more than most users want.
            "-aa" => {
                let v = val(i + 1)?;
                let factor: u32 = v.parse().map_err(|_| {
                    Error::invalid(format!("convert: -aa: '{v}' is not a positive integer"))
                })?;
                if !(1..=8).contains(&factor) {
                    return Err(Error::invalid(format!(
                        "convert: -aa: factor {factor} out of range (must be in 1..=8)"
                    )));
                }
                mesh3d_options.aa = Some(factor);
                i += 2;
            }
            other => {
                // Reach here only on `-`-prefixed args (non-`-` was
                // pushed to `positionals` above). Add a "did you mean?"
                // hint when the bogus token is a close edit of a known
                // flag — same Levenshtein-cutoff helper the mesh3d-runner
                // uses for extension typos. We strip the leading dashes
                // before comparing so `-quailty` matches `-quality` at a
                // 2-edit distance (transposition) instead of being
                // scored 3 because of the dash overhead, and we
                // reattach the same dash flavour (single or double) the
                // user typed when rendering the suggestion. Unknown
                // tokens that aren't close to any flag (e.g. `-fnord`)
                // produce the bare error, exactly as before.
                let (lead, bare) = if let Some(rest) = other.strip_prefix("--") {
                    ("--", rest)
                } else {
                    ("-", other.strip_prefix('-').unwrap_or(other))
                };
                let hint = crate::suggest::closest_match(bare, KNOWN_FLAG_NAMES)
                    .map(|s| format!(" (did you mean '{lead}{s}'?)"))
                    .unwrap_or_default();
                return Err(Error::invalid(format!(
                    "convert: unknown flag '{other}'{hint}"
                )));
            }
        }
    }

    if positionals.is_empty() {
        return Err(Error::invalid(
            "convert: no input file given (usage: convert [-op VALUE]... INPUT [-op VALUE]... OUTPUT)",
        ));
    }
    // `--probe` is mutually exclusive with an output positional —
    // probing means "describe, don't write", and the user passing both
    // is almost always a mistake (typo'd a flag, copy-pasted from a
    // real conversion). Surface it as a clear actionable error rather
    // than silently writing or silently dropping the output arg.
    if probe && positionals.len() >= 2 {
        return Err(Error::invalid(format!(
            "convert: --probe cannot be combined with an output file ('{}'); use either --probe OR an output file, not both",
            positionals[1]
        )));
    }
    if positionals.len() < 2 && !ping && !probe {
        return Err(Error::invalid(
            "convert: no output file given (usage: convert [-op VALUE]... INPUT [-op VALUE]... OUTPUT)",
        ));
    }
    if positionals.len() > 2 {
        return Err(Error::unsupported(format!(
            "convert: {} positional arguments given but multi-input is not yet supported (round-2 follow-up); pass exactly INPUT OUTPUT",
            positionals.len()
        )));
    }
    // `--json` is only meaningful as a formatting modifier on
    // `--probe`. Without `--probe` there's no probe summary to
    // serialise, so we'd otherwise silently swallow the flag.
    if probe_json && !probe {
        return Err(Error::invalid(
            "convert: --json requires --probe (today --json only formats the probe summary)",
        ));
    }
    // `--watch` re-runs the probe on mtime change; only meaningful
    // paired with `--probe`. Without `--probe` there's no long-running
    // mode for it to attach to.
    if probe_watch && !probe {
        return Err(Error::invalid(
            "convert: --watch requires --probe (today --watch only re-runs the probe on input mtime change)",
        ));
    }

    let (raw_input, input_pages) = split_input_selector(&positionals[0])?;
    let input = translate_input_shorthand(raw_input);
    let output = positionals.get(1).cloned().unwrap_or_default();
    let output_template = if output.is_empty() {
        None
    } else {
        parse_printf_template(&output)?
    };

    Ok(ConvertPlan {
        input,
        input_pages,
        ops,
        output,
        output_template,
        ping,
        probe,
        probe_json,
        probe_watch,
        mesh3d_options,
    })
}

/// Strip an ImageMagick-style `[N]` / `[N-M]` / `[A,B,…]` page-selector
/// suffix from the input path. Examples:
///
/// * `input.pdf[0]` → `("input.pdf", Some(Single(0)))`
/// * `input.pdf[2-5]` → `("input.pdf", Some(Range(2, 5)))`
/// * `input.pdf[-1]` → `("input.pdf", Some(Single(-1)))` (resolves to last page)
/// * `input.pdf[5--1]` → `("input.pdf", Some(Range(5, -1)))` (page 5 to last)
/// * `input.pdf[0,2,4]` → `("input.pdf", Some(List([Single(0), Single(2), Single(4)])))`
/// * `input.pdf[0-2,5,-1]` → `("input.pdf", Some(List([Range(0,2), Single(5), Single(-1)])))`
///
/// Inputs with no `[…]` suffix return `(input, None)`.
///
/// Returns an `Err` for malformed selectors (`[abc]`, `[1-2-3]`, `[]`,
/// `[,]`, `[0,,1]`, unbalanced brackets, etc.) so the user gets a
/// clear message.
pub(crate) fn split_input_selector(s: &str) -> Result<(&str, Option<PageSelector>), Error> {
    if !s.ends_with(']') {
        return Ok((s, None));
    }
    let open = match s.rfind('[') {
        Some(i) => i,
        None => {
            return Err(Error::invalid(format!(
                "convert: input '{s}' has a closing `]` with no matching `[`"
            )));
        }
    };
    let body = &s[open + 1..s.len() - 1];
    if body.is_empty() {
        return Err(Error::invalid(format!(
            "convert: input '{s}' has an empty `[]` page selector"
        )));
    }
    let sel = parse_page_selector_body(s, body)?;
    Ok((&s[..open], Some(sel)))
}

/// Parse the inside of a `[…]` page-selector. Splits on `,`, then each
/// piece on a single `-` (taking care to keep a LEADING `-` as the
/// sign of a negative endpoint, not a range separator). One atom →
/// `Single`/`Range` variant; multiple atoms → `List`.
fn parse_page_selector_body(input: &str, body: &str) -> Result<PageSelector, Error> {
    // Comma-separated list of atoms. IM accepts `[0,2,4]` for "pages
    // 0, 2, and 4"; we extend to ranges-within-lists (`[0-2,5,-1]`).
    let pieces: Vec<&str> = body.split(',').collect();
    let mut atoms: Vec<PageAtom> = Vec::with_capacity(pieces.len());
    for piece in &pieces {
        let trimmed = piece.trim();
        if trimmed.is_empty() {
            return Err(Error::invalid(format!(
                "convert: input '{input}': page selector '{body}' has an empty atom (between commas)"
            )));
        }
        atoms.push(parse_page_atom(input, trimmed)?);
    }
    Ok(if atoms.len() == 1 {
        // Preserve the single-atom variants — most callers only care
        // about the one-atom case and matching `Single(2)` is far
        // friendlier than walking a one-element `List([Single(2)])`.
        match atoms.into_iter().next().unwrap() {
            PageAtom::Single(n) => PageSelector::Single(n),
            PageAtom::Range(a, b) => PageSelector::Range(a, b),
        }
    } else {
        PageSelector::List(atoms)
    })
}

/// Parse one atom of a page selector. Accepts `N`, `-N`, `N-M`,
/// `-N-M`, `N--M`, `-N--M`. Returns `Single(n)` for plain indices
/// (possibly negative) and `Range(a, b)` for two-endpoint specs.
///
/// The trick: `-` is both the unary sign for negative indices AND the
/// range separator. We split off a leading `-` first (so `-1` doesn't
/// look like a range with an empty start), then look for the next `-`
/// as the range delimiter, treating a leading `-` on the second
/// endpoint the same way.
fn parse_page_atom(input: &str, atom: &str) -> Result<PageAtom, Error> {
    // Peel off a leading `-` as the sign of the first endpoint (if any).
    let (first_sign, rest) = if let Some(rest) = atom.strip_prefix('-') {
        ("-", rest)
    } else {
        ("", atom)
    };
    if rest.is_empty() {
        return Err(Error::invalid(format!(
            "convert: input '{input}': page selector atom '{atom}' is just a sign with no digits"
        )));
    }
    // Now look for a `-` separator (range). Anything past the first
    // digit-run that's `-` opens the second endpoint.
    match rest.find('-') {
        None => {
            // Single atom — `first_sign + rest` is a plain integer.
            let n: isize = format!("{first_sign}{rest}").parse().map_err(|_| {
                Error::invalid(format!(
                    "convert: input '{input}': page selector atom '{atom}' is not an integer page index"
                ))
            })?;
            Ok(PageAtom::Single(n))
        }
        Some(sep) => {
            // Range. Left endpoint is `first_sign + rest[..sep]`.
            let left = format!("{first_sign}{}", &rest[..sep]);
            let right_raw = &rest[sep + 1..];
            if left.is_empty() || left == "-" {
                return Err(Error::invalid(format!(
                    "convert: input '{input}': page selector atom '{atom}' has no left endpoint"
                )));
            }
            if right_raw.is_empty() {
                return Err(Error::invalid(format!(
                    "convert: input '{input}': page selector atom '{atom}' has no right endpoint"
                )));
            }
            // The right side may itself start with `-` to mark a
            // negative endpoint (e.g. `5--1` = page 5 to last). After
            // splitting on the FIRST `-`, anything beyond that
            // shouldn't carry yet ANOTHER unparseable `-`.
            let a: isize = left.parse().map_err(|_| {
                Error::invalid(format!(
                    "convert: input '{input}': page selector atom '{atom}': left endpoint '{left}' is not an integer"
                ))
            })?;
            let b: isize = right_raw.parse().map_err(|_| {
                Error::invalid(format!(
                    "convert: input '{input}': page selector atom '{atom}': right endpoint '{right_raw}' is not an integer (expected `N-M`, `-N-M`, or `N--M`)"
                ))
            })?;
            Ok(PageAtom::Range(a, b))
        }
    }
}

/// Scan an output filename for a single `%[0-9]*d` token.
///
/// Returns `Ok(Some(template))` when exactly one such token is found;
/// `Ok(None)` when there is no `%` at all (the literal-filename case);
/// `Err` when there are multiple `%d` tokens or any unsupported format
/// specifier (`%s`, `%x`, `%%`, …). The two-pass design keeps the
/// invariant that `output_template == None` iff the filename is a plain
/// path that should be written to verbatim.
pub(crate) fn parse_printf_template(s: &str) -> Result<Option<PrintfTemplate>, Error> {
    let bytes = s.as_bytes();
    let mut i = 0usize;
    let mut found: Option<(usize, u8, usize)> = None; // (start, width, end)
    while i < bytes.len() {
        if bytes[i] != b'%' {
            i += 1;
            continue;
        }
        let start = i;
        i += 1;
        let mut width: u8 = 0;
        while i < bytes.len() && bytes[i].is_ascii_digit() {
            // Cap width to a sensible limit to avoid pathological inputs.
            let d = (bytes[i] - b'0') as u32;
            let next = (width as u32) * 10 + d;
            if next > 20 {
                return Err(Error::invalid(format!(
                    "convert: output template '{s}' has an unreasonable width specifier"
                )));
            }
            width = next as u8;
            i += 1;
        }
        if i >= bytes.len() {
            return Err(Error::invalid(format!(
                "convert: output template '{s}' has a `%` with no format specifier"
            )));
        }
        match bytes[i] {
            b'd' => {
                if found.is_some() {
                    return Err(Error::invalid(format!(
                        "convert: output template '{s}' has more than one `%d` token (expected exactly one)"
                    )));
                }
                found = Some((start, width, i + 1));
                i += 1;
            }
            other => {
                return Err(Error::invalid(format!(
                    "convert: output template '{s}' uses unsupported format specifier '%{}' (only `%d`, `%03d`, etc. are accepted)",
                    other as char
                )));
            }
        }
    }
    Ok(found.map(|(start, width, end)| PrintfTemplate {
        prefix: s[..start].to_string(),
        width,
        suffix: s[end..].to_string(),
    }))
}

/// CSS L3 named colours + `#hex` 3/4/6/8 form. Same grammar as
/// `oxideav-generator`'s `xc:` parser. Kept local to convert so we
/// don't have to pull `oxideav-generator` in when the `generator`
/// feature is off.
fn parse_color(s: &str) -> Result<[u8; 4], String> {
    let s = s.trim();
    if let Some(hex) = s.strip_prefix('#') {
        return parse_hex_color(hex);
    }
    match s.to_ascii_lowercase().as_str() {
        "transparent" | "none" => Ok([0, 0, 0, 0]),
        "black" => Ok([0, 0, 0, 255]),
        "white" => Ok([255, 255, 255, 255]),
        "red" => Ok([255, 0, 0, 255]),
        "green" => Ok([0, 128, 0, 255]),
        "lime" => Ok([0, 255, 0, 255]),
        "blue" => Ok([0, 0, 255, 255]),
        "yellow" => Ok([255, 255, 0, 255]),
        "cyan" | "aqua" => Ok([0, 255, 255, 255]),
        "magenta" | "fuchsia" => Ok([255, 0, 255, 255]),
        "gray" | "grey" => Ok([128, 128, 128, 255]),
        "silver" => Ok([192, 192, 192, 255]),
        "maroon" => Ok([128, 0, 0, 255]),
        "olive" => Ok([128, 128, 0, 255]),
        "purple" => Ok([128, 0, 128, 255]),
        "teal" => Ok([0, 128, 128, 255]),
        "navy" => Ok([0, 0, 128, 255]),
        "orange" => Ok([255, 165, 0, 255]),
        other => Err(format!(
            "convert: unknown colour '{other}' (try a `#hex` value or one of: black/white/red/green/blue/yellow/cyan/magenta/gray/transparent/…)"
        )),
    }
}

fn parse_hex_color(hex: &str) -> Result<[u8; 4], String> {
    fn hex_digit(c: u8) -> Result<u8, String> {
        match c {
            b'0'..=b'9' => Ok(c - b'0'),
            b'a'..=b'f' => Ok(c - b'a' + 10),
            b'A'..=b'F' => Ok(c - b'A' + 10),
            _ => Err(format!("'{}' is not a hex digit", c as char)),
        }
    }
    let h = hex.as_bytes();
    let pair = |a: u8, b: u8| -> Result<u8, String> { Ok(hex_digit(a)? * 16 + hex_digit(b)?) };
    let dup = |a: u8| -> Result<u8, String> {
        let d = hex_digit(a)?;
        Ok(d * 16 + d)
    };
    match h.len() {
        3 => Ok([dup(h[0])?, dup(h[1])?, dup(h[2])?, 255]),
        4 => Ok([dup(h[0])?, dup(h[1])?, dup(h[2])?, dup(h[3])?]),
        6 => Ok([pair(h[0], h[1])?, pair(h[2], h[3])?, pair(h[4], h[5])?, 255]),
        8 => Ok([
            pair(h[0], h[1])?,
            pair(h[2], h[3])?,
            pair(h[4], h[5])?,
            pair(h[6], h[7])?,
        ]),
        _ => Err(format!(
            "'#{hex}' is not a valid hex colour (expected 3/4/6/8 hex digits)"
        )),
    }
}

/// Apply the `oxideav-generator` shorthand translator when it's
/// linked in; otherwise return the input verbatim. Keeping the call
/// behind a feature gate means the convert verb still works (with a
/// clear error from the source registry) when the generator crate is
/// excluded.
#[cfg(feature = "generator")]
fn translate_input_shorthand(input: &str) -> String {
    oxideav_generator::shorthand::translate(input)
}

#[cfg(not(feature = "generator"))]
fn translate_input_shorthand(input: &str) -> String {
    input.to_string()
}

/// Parse the geometry-without-suffix portion of a `-resize` /
/// `-thumbnail` arg, branching on the scaling mode the suffix already
/// selected.
///
/// Most modes parse exactly like `WxH` (two positive integers). A few
/// modes have looser grammar:
///
/// - [`ResizeMode::Percent`] — `N`, `Nx`, `xN`, `NxN`. A bare `N`
///   applies to both axes; missing axes default to the other one
///   (`200x` → `200x200`; `x200` → `200x200`). Components must be
///   integer percentages > 0.
/// - [`ResizeMode::Area`] — same `WxH` shape; the runtime treats
///   `W*H` as the target pixel area.
/// - Everything else — strict `WxH`, both > 0.
fn parse_resize_geometry(s: &str, mode: ResizeMode) -> Result<(u32, u32), String> {
    if matches!(mode, ResizeMode::Percent) {
        // `N` / `Nx` / `xN` / `NxN`. Single-number form replicates.
        let s = s.trim();
        let (w_str, h_str) = match s.split_once(['x', 'X']) {
            None => (s, s), // bare N → both axes
            Some((w, h)) => {
                let w = if w.is_empty() { h } else { w };
                let h = if h.is_empty() { w } else { h };
                (w, h)
            }
        };
        let w: u32 = w_str
            .parse()
            .map_err(|_| format!("'{w_str}' is not a non-negative integer percent"))?;
        let h: u32 = h_str
            .parse()
            .map_err(|_| format!("'{h_str}' is not a non-negative integer percent"))?;
        if w == 0 || h == 0 {
            return Err("percent values must both be > 0".into());
        }
        return Ok((w, h));
    }
    parse_wxh(s)
}

/// Parse `WxH` — width × height. Accepts either lowercase `x` or
/// uppercase `X`. Both parts must be non-negative integers.
fn parse_wxh(s: &str) -> Result<(u32, u32), String> {
    let (w, h) = s
        .split_once(['x', 'X'])
        .ok_or_else(|| format!("'{s}' is not in WxH form"))?;
    let w: u32 = w
        .parse()
        .map_err(|_| format!("'{w}' is not a non-negative integer"))?;
    let h: u32 = h
        .parse()
        .map_err(|_| format!("'{h}' is not a non-negative integer"))?;
    if w == 0 || h == 0 {
        return Err("width and height must both be positive".into());
    }
    Ok((w, h))
}

/// Parse `-crop WxH+X+Y` (and the simpler `WxH+X+Y` permutations IM
/// also accepts). All four numbers are required; IM-style geometry
/// modifiers (`%`, `!`, `^`, `<`, `>`, `@`, `-X-Y` negative offsets)
/// are NOT yet supported in round-1 — they'd need centering / aspect
/// math we don't have. Bbox bounds checking against the actual image
/// dims happens at apply time, not here.
fn parse_crop(s: &str) -> Result<(u32, u32, u32, u32), String> {
    // Reject IM modifiers up front with a clear message, otherwise
    // they'd be silently swallowed by parse() of `0` etc.
    for mark in ['%', '!', '^', '<', '>', '@'] {
        if s.contains(mark) {
            return Err(format!(
                "'{s}' uses IM modifier '{mark}' (round-1 supports plain WxH+X+Y only)"
            ));
        }
    }
    // IM also accepts `-X` for negative offsets; round-1 sticks to
    // `+X+Y` only.
    let mut parts = s.split('+');
    let wh = parts
        .next()
        .ok_or_else(|| format!("'{s}' is missing the WxH component"))?;
    let x_str = parts
        .next()
        .ok_or_else(|| format!("'{s}' is missing the +X offset (expected WxH+X+Y)"))?;
    let y_str = parts
        .next()
        .ok_or_else(|| format!("'{s}' is missing the +Y offset (expected WxH+X+Y)"))?;
    if parts.next().is_some() {
        return Err(format!("'{s}' has more than two `+` separators"));
    }
    let (w, h) = parse_wxh(wh)?;
    let x: u32 = x_str
        .parse()
        .map_err(|_| format!("'{x_str}' is not a non-negative integer X offset"))?;
    let y: u32 = y_str
        .parse()
        .map_err(|_| format!("'{y_str}' is not a non-negative integer Y offset"))?;
    Ok((w, h, x, y))
}

/// Parse `-extent WxH[±X±Y]` — IM's canvas re-window.
///
/// Accepts `WxH` (offset defaults to `(0, 0)`), `WxH+X+Y`, `WxH-X-Y`,
/// `WxH+X-Y`, or `WxH-X+Y`. Width / height must both be positive (a
/// zero-area canvas has nothing to paint); offsets are signed so the
/// IM convention of negative translation (moving the source toward the
/// upper-left so its right or bottom edge can fit inside the window)
/// rides through unchanged.
///
/// We deliberately reject the geometry modifiers (`%`, `!`, `^`, `<`,
/// `>`, `@`) the same way `parse_crop` does — `-extent` in IM accepts
/// some of those but their semantics are source-size-dependent and
/// would need a runtime resolution pass that hasn't landed yet.
fn parse_extent(s: &str) -> Result<(u32, u32, i32, i32), String> {
    for mark in ['%', '!', '^', '<', '>', '@'] {
        if s.contains(mark) {
            return Err(format!(
                "'{s}' uses IM modifier '{mark}' (-extent currently supports plain WxH[±X±Y] only)"
            ));
        }
    }
    // Find the boundary between `WxH` and the first signed offset (if
    // any). The first `+` or `-` AFTER the initial character marks
    // where the offset section starts; we keep position 0 untouched so
    // a leading `-` on `WxH` (illegal — `W` must be positive) is
    // surfaced by `parse_wxh`'s unsigned parse rather than mis-split as
    // an offset.
    let head_end = s
        .char_indices()
        .skip(1)
        .find(|(_, c)| *c == '+' || *c == '-')
        .map(|(i, _)| i)
        .unwrap_or(s.len());
    let head = &s[..head_end];
    let tail = &s[head_end..];
    let (w, h) = parse_wxh(head)?;
    let (x, y) = parse_extent_offsets(tail)?;
    Ok((w, h, x, y))
}

/// Parse the `±X±Y` tail of an `-extent` geometry string. Returns
/// `(0, 0)` for an empty tail. Both signs are required when any
/// offset is given — `WxH+X` (single offset) is rejected so the user
/// gets a clearer message than "parse failed on empty Y".
fn parse_extent_offsets(s: &str) -> Result<(i32, i32), String> {
    if s.is_empty() {
        return Ok((0, 0));
    }
    // Walk char-by-char to find the start of the Y offset — the
    // SECOND sign character in the tail. Splitting on `+`/`-` directly
    // would mishandle the mix-of-signs cases (`+X-Y`, `-X+Y`).
    let bytes = s.as_bytes();
    if bytes[0] != b'+' && bytes[0] != b'-' {
        return Err(format!(
            "'{s}' offset section must start with `+` or `-` (expected WxH+X+Y, WxH-X-Y, or mixed)"
        ));
    }
    let mut split = None;
    for (i, b) in bytes.iter().enumerate().skip(1) {
        if *b == b'+' || *b == b'-' {
            split = Some(i);
            break;
        }
    }
    let split = split
        .ok_or_else(|| format!("'{s}' has a single offset; expected both X and Y (WxH±X±Y)"))?;
    let x_str = &s[..split];
    let y_str = &s[split..];
    // Reject IM's `WxH+X+Y+Z` accidental extra-offset case.
    if y_str[1..].contains('+') || y_str[1..].contains('-') {
        return Err(format!("'{s}' has more than two signed offsets"));
    }
    let x: i32 = x_str
        .parse()
        .map_err(|_| format!("'{x_str}' is not a signed integer X offset"))?;
    let y: i32 = y_str
        .parse()
        .map_err(|_| format!("'{y_str}' is not a signed integer Y offset"))?;
    Ok((x, y))
}

/// Parse the value after `-roll`. IM's canonical grammar is
/// `±X±Y` — both offsets present, each prefixed by an explicit sign.
/// Reuses [`parse_extent_offsets`] for the actual signed-int split so
/// the two flags stay grammar-identical; rejects the empty / single-
/// offset cases with the same shape of error the user sees on
/// `-extent`. Negative offsets are accepted as-is — the inline /
/// pipeline shift routines wrap them mod width / height.
fn parse_roll(s: &str) -> Result<(i32, i32), String> {
    if s.is_empty() {
        return Err("empty offset (expected ±X±Y, e.g. +5+10)".to_string());
    }
    parse_extent_offsets(s)
}

/// Parse `-blur RxS` or `-blur R`. When sigma is omitted we follow
/// IM's convention of `sigma = radius / 2.0`. Unlike IM we don't
/// accept floats for radius — `Blur::new` takes `u32`.
fn parse_blur(s: &str) -> Result<(u32, f32), String> {
    let (radius_str, sigma_str) = match s.split_once(['x', 'X']) {
        Some((r, s)) => (r, Some(s)),
        None => (s, None),
    };
    let radius: u32 = radius_str
        .parse()
        .map_err(|_| format!("'{radius_str}' is not a non-negative integer"))?;
    let sigma: f32 = match sigma_str {
        Some(s) => s
            .parse()
            .map_err(|_| format!("'{s}' is not a non-negative float"))?,
        None => (radius as f32) / 2.0,
    };
    Ok((radius, sigma))
}

/// Parse `-unsharp RxS+amount+threshold` (any subset accepted in
/// source order: `R`, `RxS`, `RxS+A`, `RxS+A+T`).
///
/// Defaults match `oxideav_image_filter::Unsharp`'s conventions:
/// sigma = radius/2, amount = 1.0, threshold = 0 (out of 255).
fn parse_unsharp(s: &str) -> Result<(u32, f32, f32, u8), String> {
    // `+` separates the three optional tail components. Keep the
    // first chunk (radius / sigma) intact.
    let mut parts = s.splitn(3, '+');
    let head = parts.next().unwrap_or(s);
    let amount_str = parts.next();
    let threshold_str = parts.next();
    let (radius, sigma) = parse_blur(head)?;
    let amount: f32 = match amount_str {
        Some(a) => a
            .parse()
            .map_err(|_| format!("'{a}' is not a finite float"))?,
        None => 1.0,
    };
    let threshold: u8 = match threshold_str {
        // IM lets the threshold be either an integer 0..=255 or a
        // percentage. Accept both shapes; cap to u8.
        Some(t) => parse_threshold_pct(t)?,
        None => 0,
    };
    Ok((radius, sigma, amount, threshold))
}

/// Parse `-brightness-contrast B[xC]` / `B[,C]` / `B`. IM uses both
/// `x` and `,` as separators in different docs; accept either.
/// Range is `[-100..=100]` per IM.
fn parse_brightness_contrast(s: &str) -> Result<(f32, f32), String> {
    let (bs, cs) = match s.split_once(['x', 'X', ',']) {
        Some((a, b)) => (a, Some(b)),
        None => (s, None),
    };
    let b: f32 = bs
        .parse()
        .map_err(|_| format!("'{bs}' is not a finite float"))?;
    let c: f32 = match cs {
        Some(s) if !s.is_empty() => s
            .parse()
            .map_err(|_| format!("'{s}' is not a finite float"))?,
        _ => 0.0,
    };
    if !(-100.0..=100.0).contains(&b) {
        return Err(format!("brightness {b} out of range (-100..=100)"));
    }
    if !(-100.0..=100.0).contains(&c) {
        return Err(format!("contrast {c} out of range (-100..=100)"));
    }
    Ok((b, c))
}

/// Parse a value that's either a percentage (`50%`) or a unit-range
/// scalar (`0.5`). Used by `-sepia`. Returns the scalar in 0..=1.
fn parse_percent_or_unit(s: &str) -> Result<f32, String> {
    let s = s.trim();
    if let Some(p) = s.strip_suffix('%') {
        let v: f32 = p
            .parse()
            .map_err(|_| format!("'{p}' is not a finite float"))?;
        if !(0.0..=100.0).contains(&v) {
            return Err(format!("'{s}' is out of range (0%..=100%)"));
        }
        return Ok(v / 100.0);
    }
    let v: f32 = s
        .parse()
        .map_err(|_| format!("'{s}' is not a finite float"))?;
    if !(0.0..=1.0).contains(&v) {
        return Err(format!("'{s}' is out of range (0.0..=1.0)"));
    }
    Ok(v)
}

/// Parse `-modulate B[,S[,H]]`. Each element is percent-of-base
/// (100 = identity). Missing tail elements default to 100 / 100 / 100.
fn parse_modulate(s: &str) -> Result<(f32, f32, f32), String> {
    let mut parts = s.split(',').map(|p| p.trim());
    let b = parts
        .next()
        .ok_or_else(|| format!("'{s}' is missing the brightness value"))?;
    let s_field = parts.next();
    let h_field = parts.next();
    if parts.next().is_some() {
        return Err(format!(
            "'{s}' has more than 3 components (expected B[,S[,H]])"
        ));
    }
    let bv: f32 = b
        .parse()
        .map_err(|_| format!("'{b}' is not a finite float"))?;
    let sv: f32 = match s_field {
        Some(t) if !t.is_empty() => t
            .parse()
            .map_err(|_| format!("'{t}' is not a finite float"))?,
        _ => 100.0,
    };
    let hv: f32 = match h_field {
        Some(t) if !t.is_empty() => t
            .parse()
            .map_err(|_| format!("'{t}' is not a finite float"))?,
        _ => 100.0,
    };
    Ok((bv, sv, hv))
}

/// Parse `-level B[/G[/W]]` or `-level B,G,W`. IM accepts both
/// separators. Black/white are 0..=255 (or `N%` for a percentage).
/// Gamma is `> 0`.
fn parse_level(s: &str) -> Result<(u8, f32, u8), String> {
    let parts: Vec<&str> = s.split(['/', ',']).map(|p| p.trim()).collect();
    if parts.is_empty() || parts.len() > 3 {
        return Err(format!("'{s}' is not in B[/G[/W]] form (1..=3 components)"));
    }
    let black = parse_byte_or_percent(parts[0])?;
    let gamma: f32 = if parts.len() >= 2 && !parts[1].is_empty() {
        let g: f32 = parts[1]
            .parse()
            .map_err(|_| format!("'{}' is not a finite float", parts[1]))?;
        if !g.is_finite() || g <= 0.0 {
            return Err(format!("gamma {g} must be > 0"));
        }
        g
    } else {
        1.0
    };
    let white = if parts.len() == 3 && !parts[2].is_empty() {
        parse_byte_or_percent(parts[2])?
    } else {
        255
    };
    if black > white {
        return Err(format!(
            "black point ({black}) must be <= white point ({white})"
        ));
    }
    Ok((black, gamma, white))
}

/// Parse `0..=255` or `N%` → byte. Used by `-level`.
fn parse_byte_or_percent(s: &str) -> Result<u8, String> {
    if let Some(p) = s.strip_suffix('%') {
        let v: f32 = p
            .parse()
            .map_err(|_| format!("'{p}' is not a finite float"))?;
        if !(0.0..=100.0).contains(&v) {
            return Err(format!("'{s}' is out of range (0%..=100%)"));
        }
        return Ok((v * 2.55).round().clamp(0.0, 255.0) as u8);
    }
    let n: u32 = s
        .parse()
        .map_err(|_| format!("'{s}' is not a non-negative integer"))?;
    if n > 255 {
        return Err(format!("'{s}' is out of range (0..=255)"));
    }
    Ok(n as u8)
}

/// Parse `-threshold N%` / `-threshold N` / `-solarize N%` —
/// returns the resulting 0..=255 byte value.
fn parse_threshold_pct(s: &str) -> Result<u8, String> {
    parse_byte_or_percent(s.trim())
}

/// Parse `-vignette R[+S][+X[+Y]]`.
///
/// Mirrors IM's `-vignette geometry`-style argument. `R+S` are the
/// Gaussian radius and sigma in pixels; `S` defaults to `R / 2.0` when
/// omitted (matching IM and our `-blur RxS` convention). `+X+Y` are the
/// **normalised** image-relative centre offsets in `[0.0, 1.0]`
/// (default `0.5 / 0.5` = image centre). IM's `-vignette R+S+X+Y` uses
/// pixel offsets for `X+Y`, but the image-filter `Vignette` factory is
/// resolution-independent and takes them normalised; document the
/// difference here. To target the centre — by far the common case —
/// pass just `R` (e.g. `-vignette 50`).
fn parse_vignette(s: &str) -> Result<(f32, f32, f32, f32), String> {
    let mut parts = s.split('+');
    let r_str = parts
        .next()
        .ok_or_else(|| format!("'{s}' is missing the radius component"))?;
    let radius: f32 = r_str
        .parse()
        .map_err(|_| format!("'{r_str}' is not a finite float radius"))?;
    if !radius.is_finite() || radius < 0.0 {
        return Err(format!("radius {radius} must be >= 0"));
    }
    let s_part = parts.next();
    let sigma: f32 = match s_part {
        Some(t) if !t.is_empty() => t
            .parse()
            .map_err(|_| format!("'{t}' is not a finite float sigma"))?,
        _ => radius / 2.0,
    };
    if !sigma.is_finite() || sigma < 0.0 {
        return Err(format!("sigma {sigma} must be >= 0"));
    }
    let x: f32 = match parts.next() {
        Some(t) if !t.is_empty() => t
            .parse()
            .map_err(|_| format!("'{t}' is not a finite float x"))?,
        _ => 0.5,
    };
    let y: f32 = match parts.next() {
        Some(t) if !t.is_empty() => t
            .parse()
            .map_err(|_| format!("'{t}' is not a finite float y"))?,
        _ => 0.5,
    };
    if parts.next().is_some() {
        return Err(format!("'{s}' has more than 4 components"));
    }
    if !x.is_finite() || !y.is_finite() {
        return Err(format!("x/y must be finite (got x={x}, y={y})"));
    }
    Ok((radius, sigma, x, y))
}

/// Parse `-colorize C[xC[xC]]/A%`.
///
/// The colour part `C[xC[xC]]` accepts the same grammar as
/// [`parse_color`] — CSS L3 named colours and `#hex` 3/4/6/8 forms —
/// PLUS the IM-style `R[xG[xB]]` per-channel byte triplet. When only
/// `/A%` is given (no colour part), the target defaults to white. The
/// `A%` portion is a percentage in `[0%..=100%]`; we accept either
/// `N%` or a unit scalar `0.0..=1.0`.
fn parse_colorize(s: &str) -> Result<([u8; 4], f32), String> {
    let s = s.trim();
    let (color_part, amount_part) = match s.split_once('/') {
        Some((c, a)) => (c, a),
        // No `/A%` — interpret the whole string as the amount, with a
        // white default colour. IM's rare "single-arg" form.
        None => ("", s),
    };
    let color = if color_part.is_empty() {
        [255, 255, 255, 255]
    } else if color_part.contains('x') || color_part.contains('X') {
        // R[xG[xB]] per-channel byte triplet.
        let mut parts = color_part.split(['x', 'X']);
        let r_str = parts
            .next()
            .ok_or_else(|| format!("'{color_part}' is missing the R component"))?;
        let r: u32 = r_str
            .parse()
            .map_err(|_| format!("'{r_str}' is not a non-negative integer"))?;
        if r > 255 {
            return Err(format!("R component {r} out of range (0..=255)"));
        }
        let g: u32 = match parts.next() {
            Some(t) if !t.is_empty() => t
                .parse()
                .map_err(|_| format!("'{t}' is not a non-negative integer"))?,
            _ => r,
        };
        if g > 255 {
            return Err(format!("G component {g} out of range (0..=255)"));
        }
        let b: u32 = match parts.next() {
            Some(t) if !t.is_empty() => t
                .parse()
                .map_err(|_| format!("'{t}' is not a non-negative integer"))?,
            _ => g,
        };
        if b > 255 {
            return Err(format!("B component {b} out of range (0..=255)"));
        }
        if parts.next().is_some() {
            return Err(format!(
                "'{color_part}' has more than 3 components (expected R[xG[xB]])"
            ));
        }
        [r as u8, g as u8, b as u8, 255]
    } else {
        // CSS named / `#hex`.
        parse_color(color_part)?
    };
    let amount = parse_percent_or_unit(amount_part)?;
    Ok((color, amount))
}

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

    fn to_vec(s: &[&str]) -> Vec<String> {
        s.iter().map(|x| x.to_string()).collect()
    }

    #[test]
    fn minimal_input_output() {
        let p = parse(&to_vec(&["in.png", "out.jpg"])).unwrap();
        assert_eq!(p.input, "in.png");
        assert_eq!(p.output, "out.jpg");
        assert!(p.ops.is_empty());
    }

    #[test]
    fn resize_bilinear_basic() {
        let p = parse(&to_vec(&["a.png", "-resize", "800x600", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 800,
                height: 600,
                mode: ResizeMode::Default,
            }]
        );
    }

    #[test]
    fn resize_bang_flag() {
        let p = parse(&to_vec(&["a.png", "-resize", "64x32!", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 64,
                height: 32,
                mode: ResizeMode::Force,
            }]
        );
    }

    #[test]
    fn resize_fill_caret_suffix() {
        let p = parse(&to_vec(&["a.png", "-resize", "200x100^", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 200,
                height: 100,
                mode: ResizeMode::Fill,
            }]
        );
    }

    #[test]
    fn resize_shrink_only_suffix() {
        let p = parse(&to_vec(&["a.png", "-resize", "100x100>", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 100,
                height: 100,
                mode: ResizeMode::Shrink,
            }]
        );
    }

    #[test]
    fn resize_grow_only_suffix() {
        let p = parse(&to_vec(&["a.png", "-resize", "1024x1024<", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 1024,
                height: 1024,
                mode: ResizeMode::Grow,
            }]
        );
    }

    #[test]
    fn resize_percent_two_axis() {
        let p = parse(&to_vec(&["a.png", "-resize", "50x200%", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 50,
                height: 200,
                mode: ResizeMode::Percent,
            }]
        );
    }

    #[test]
    fn resize_percent_single_value_replicates() {
        // IM lets a bare `N%` mean "N percent on both axes"; we follow.
        let p = parse(&to_vec(&["a.png", "-resize", "75%", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 75,
                height: 75,
                mode: ResizeMode::Percent,
            }]
        );
    }

    #[test]
    fn resize_area_at_suffix() {
        let p = parse(&to_vec(&["a.png", "-resize", "640x480@", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Resize {
                width: 640,
                height: 480,
                mode: ResizeMode::Area,
            }]
        );
    }

    #[test]
    fn thumbnail_with_geometry_modifier() {
        let p = parse(&to_vec(&["a.png", "-thumbnail", "128x128^", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Thumbnail {
                width: 128,
                height: 128,
                mode: ResizeMode::Fill,
            }]
        );
    }

    #[test]
    fn thumbnail_default_mode() {
        let p = parse(&to_vec(&["a.png", "-thumbnail", "100x100", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Thumbnail {
                width: 100,
                height: 100,
                mode: ResizeMode::Default,
            }]
        );
    }

    #[test]
    fn define_with_value_round_trips_namespaced_key() {
        let p = parse(&to_vec(&[
            "a.png",
            "-define",
            "jpeg:dct-method=float",
            "b.jpg",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Define {
                key: "jpeg:dct-method".into(),
                value: Some("float".into()),
            }]
        );
    }

    #[test]
    fn define_bare_key_no_value() {
        // `-define KEY` (no `=VALUE`) sets the flag-style key to JSON true.
        let p = parse(&to_vec(&[
            "a.png",
            "-define",
            "png:strip-comments",
            "b.png",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Define {
                key: "png:strip-comments".into(),
                value: None,
            }]
        );
    }

    #[test]
    fn define_empty_key_rejected() {
        let err = parse(&to_vec(&["a.png", "-define", "=value", "b.png"])).unwrap_err();
        assert!(
            format!("{err:?}").contains("empty KEY"),
            "unexpected error: {err:?}"
        );
    }

    #[test]
    fn blur_sigma_defaults_to_half_radius() {
        let p = parse(&to_vec(&["a.png", "-blur", "4", "b.jpg"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Blur {
                radius: 4,
                sigma: 2.0
            }]
        );
    }

    #[test]
    fn blur_explicit_sigma() {
        let p = parse(&to_vec(&["a.png", "-blur", "3x1.5", "b.jpg"])).unwrap();
        match p.ops.as_slice() {
            [Op::Blur { radius: 3, sigma }] => assert!((sigma - 1.5).abs() < 1e-6),
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn colors_picks_up_prior_dither() {
        let p = parse(&to_vec(&[
            "a.png",
            "-dither",
            "floyd_steinberg",
            "-colors",
            "64",
            "b.gif",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Colors {
                count: 64,
                dither: Dither::FloydSteinberg
            }]
        );
    }

    // ---- -monochrome ----

    /// `-monochrome` expands to the canonical IM chain `-colorspace
    /// gray -colors 2 -dither floyd_steinberg` so existing IM scripts
    /// (`convert in.png -monochrome out.png`) lower to the same op
    /// records the parser would have produced for the explicit form.
    /// We pin both the count and the ORDER (grayscale must come first
    /// so the 2-entry palette lands on black + white rather than two
    /// arbitrary colour samples).
    #[test]
    fn monochrome_expands_to_gray_2_colors_floyd_steinberg() {
        let p = parse(&to_vec(&["a.png", "-monochrome", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![
                Op::Colorspace("gray".to_string()),
                Op::Colors {
                    count: 2,
                    dither: Dither::FloydSteinberg
                },
            ]
        );
    }

    /// `-monochrome` takes no value — the next positional after it
    /// must be the output filename. Verifies the valueless-flag wiring
    /// (no consumption of the input file as a "value").
    #[test]
    fn monochrome_is_valueless() {
        let p = parse(&to_vec(&["a.png", "-monochrome", "b.png"])).unwrap();
        assert_eq!(p.input, "a.png");
        assert_eq!(p.output, "b.png");
    }

    /// Source-order semantics: a `-dither none` placed BEFORE
    /// `-monochrome` does NOT bleed into the expansion — the flag
    /// always emits its own `FloydSteinberg` choice. This pins the
    /// "monochrome is a self-contained shorthand" contract; users who
    /// want `-dither none` semantics write the chain by hand.
    #[test]
    fn monochrome_ignores_prior_pending_dither() {
        let p = parse(&to_vec(&[
            "a.png",
            "-dither",
            "none",
            "-monochrome",
            "b.png",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![
                Op::Colorspace("gray".to_string()),
                Op::Colors {
                    count: 2,
                    dither: Dither::FloydSteinberg
                },
            ]
        );
    }

    /// `-monochrome` is composable with other ops in source order:
    /// upstream ops keep their record, the two expanded entries appear
    /// at the position where `-monochrome` was given, and downstream
    /// ops follow. Catches a regression where someone might be tempted
    /// to push the expanded ops at the front of the vec.
    #[test]
    fn monochrome_keeps_source_order_with_neighbours() {
        let p = parse(&to_vec(&[
            "a.png",
            "-resize",
            "100x100",
            "-monochrome",
            "-strip",
            "b.png",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![
                Op::Resize {
                    width: 100,
                    height: 100,
                    mode: ResizeMode::Default,
                },
                Op::Colorspace("gray".to_string()),
                Op::Colors {
                    count: 2,
                    dither: Dither::FloydSteinberg
                },
                Op::Strip,
            ]
        );
    }

    #[test]
    fn rotate_90_parses() {
        let p = parse(&to_vec(&["a.png", "-rotate", "90", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Rotate { degrees: 90 }]);
    }

    #[test]
    fn rotate_negative_270_parses() {
        let p = parse(&to_vec(&["a.png", "-rotate", "-270", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Rotate { degrees: -270 }]);
    }

    #[test]
    fn rotate_45_rejected() {
        let err = parse(&to_vec(&["a.png", "-rotate", "45", "b.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("only multiples of 90 supported"),
            "unexpected message: {msg}"
        );
        assert!(msg.contains("got 45"));
    }

    #[test]
    fn rotate_non_integer_rejected() {
        let err = parse(&to_vec(&["a.png", "-rotate", "abc", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("not an integer"));
    }

    #[test]
    fn flip_and_flop_are_valueless() {
        let p = parse(&to_vec(&["a.png", "-flip", "-flop", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Flip, Op::Flop]);
    }

    #[test]
    fn negate_is_valueless() {
        let p = parse(&to_vec(&["a.png", "-negate", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Negate]);
    }

    #[test]
    fn crop_basic() {
        let p = parse(&to_vec(&["a.png", "-crop", "10x20+3+4", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Crop {
                x: 3,
                y: 4,
                w: 10,
                h: 20
            }]
        );
    }

    #[test]
    fn crop_zero_offset() {
        let p = parse(&to_vec(&["a.png", "-crop", "32x32+0+0", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Crop {
                x: 0,
                y: 0,
                w: 32,
                h: 32
            }]
        );
    }

    #[test]
    fn crop_missing_offset_rejected() {
        let err = parse(&to_vec(&["a.png", "-crop", "32x32", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("missing the +X offset"));
    }

    #[test]
    fn crop_im_modifier_rejected() {
        let err = parse(&to_vec(&["a.png", "-crop", "50%+0+0", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("IM modifier"));
    }

    // ---- -extent ----
    //
    // Default canvas (no offset section) → `(0, 0)` offsets and the
    // IM-default opaque white background (alpha 255) because no
    // `-background` was set.
    #[test]
    fn extent_default_offset_and_background() {
        let p = parse(&to_vec(&["a.png", "-extent", "100x80", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Extent {
                width: 100,
                height: 80,
                x: 0,
                y: 0,
                bg: [255, 255, 255, 255],
            }]
        );
    }

    // `WxH+X+Y` lands as positive signed offsets — basic case.
    #[test]
    fn extent_positive_offsets() {
        let p = parse(&to_vec(&["a.png", "-extent", "120x90+10+5", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Extent {
                width: 120,
                height: 90,
                x: 10,
                y: 5,
                bg: _,
            }] => {}
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    // `WxH-X-Y` lands as negative signed offsets — exercises the
    // IM convention of translating the source toward the upper-left.
    #[test]
    fn extent_negative_offsets() {
        let p = parse(&to_vec(&["a.png", "-extent", "200x150-25-30", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Extent {
                width: 200,
                height: 150,
                x: -25,
                y: -30,
                bg: _,
            }] => {}
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    // Mixed signs `WxH+X-Y` / `WxH-X+Y` ride through unchanged — IM
    // accepts every combination.
    #[test]
    fn extent_mixed_signs() {
        let p = parse(&to_vec(&["a.png", "-extent", "64x64+10-5", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Extent {
                width: 64,
                height: 64,
                x: 10,
                y: -5,
                bg: _,
            }] => {}
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    // A `-background` op preceding `-extent` is captured into the
    // resulting `Op::Extent.bg` so the plan walker stays stateless.
    #[test]
    fn extent_picks_up_prior_background() {
        let p = parse(&to_vec(&[
            "a.png",
            "-background",
            "red",
            "-extent",
            "50x50",
            "b.png",
        ]))
        .unwrap();
        // Two ops emitted: the explicit Background, then Extent
        // carrying the captured colour.
        assert_eq!(p.ops.len(), 2);
        assert!(matches!(p.ops[0], Op::Background([255, 0, 0, 255])));
        match &p.ops[1] {
            Op::Extent { bg, .. } => assert_eq!(*bg, [255, 0, 0, 255]),
            other => panic!("expected Extent, got {other:?}"),
        }
    }

    // A `-background` AFTER the `-extent` must NOT retroactively
    // change the captured padding colour — source order matters.
    #[test]
    fn extent_ignores_subsequent_background() {
        let p = parse(&to_vec(&[
            "a.png",
            "-extent",
            "50x50",
            "-background",
            "red",
            "b.png",
        ]))
        .unwrap();
        // First Op is Extent with the IM-default white.
        match &p.ops[0] {
            Op::Extent { bg, .. } => assert_eq!(*bg, [255, 255, 255, 255]),
            other => panic!("expected Extent, got {other:?}"),
        }
    }

    // A second `-extent` after a different `-background` picks up
    // the new colour while the earlier Extent retains the original.
    #[test]
    fn extent_two_calls_capture_independent_backgrounds() {
        let p = parse(&to_vec(&[
            "a.png",
            "-background",
            "red",
            "-extent",
            "50x50",
            "-background",
            "blue",
            "-extent",
            "60x60",
            "b.png",
        ]))
        .unwrap();
        let extents: Vec<&Op> = p
            .ops
            .iter()
            .filter(|o| matches!(o, Op::Extent { .. }))
            .collect();
        assert_eq!(extents.len(), 2);
        match extents[0] {
            Op::Extent { width: 50, bg, .. } => assert_eq!(*bg, [255, 0, 0, 255]),
            other => panic!("unexpected first extent: {other:?}"),
        }
        match extents[1] {
            Op::Extent { width: 60, bg, .. } => assert_eq!(*bg, [0, 0, 255, 255]),
            other => panic!("unexpected second extent: {other:?}"),
        }
    }

    // Single-offset `WxH+X` is rejected with a clear message rather
    // than silently treating it as `WxH+X+0`.
    #[test]
    fn extent_single_offset_rejected() {
        let err = parse(&to_vec(&["a.png", "-extent", "64x64+10", "b.png"])).unwrap_err();
        assert!(
            format!("{err:?}").contains("single offset"),
            "unexpected error: {err:?}"
        );
    }

    // Geometry modifiers (`%`, `!`, `^`, `<`, `>`, `@`) are rejected
    // identically to `-crop`.
    #[test]
    fn extent_im_modifier_rejected() {
        let err = parse(&to_vec(&["a.png", "-extent", "50%+0+0", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("IM modifier"));
    }

    #[test]
    fn sharpen_basic() {
        let p = parse(&to_vec(&["a.png", "-sharpen", "1x0.5", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Sharpen { radius: 1, sigma }] => assert!((sigma - 0.5).abs() < 1e-6),
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn sharpen_radius_only_defaults_sigma() {
        let p = parse(&to_vec(&["a.png", "-sharpen", "4", "b.png"])).unwrap();
        // Sigma defaults to radius/2 (matches IM and parse_blur).
        assert_eq!(
            p.ops,
            vec![Op::Sharpen {
                radius: 4,
                sigma: 2.0
            }]
        );
    }

    #[test]
    fn unsharp_full_grammar() {
        let p = parse(&to_vec(&["a.png", "-unsharp", "2x1.5+0.8+5", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Unsharp {
                radius: 2,
                sigma,
                amount,
                threshold: 5,
            }] => {
                assert!((sigma - 1.5).abs() < 1e-6);
                assert!((amount - 0.8).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn unsharp_partial_defaults() {
        let p = parse(&to_vec(&["a.png", "-unsharp", "3", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Unsharp {
                radius: 3,
                sigma,
                amount,
                threshold: 0,
            }] => {
                assert!((sigma - 1.5).abs() < 1e-6, "sigma = {sigma}");
                assert!((amount - 1.0).abs() < 1e-6, "amount = {amount}");
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn gamma_basic() {
        let p = parse(&to_vec(&["a.png", "-gamma", "1.8", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Gamma { value }] => assert!((value - 1.8).abs() < 1e-6),
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn gamma_zero_rejected() {
        let err = parse(&to_vec(&["a.png", "-gamma", "0", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("must be > 0"));
    }

    #[test]
    fn gamma_negative_rejected() {
        let err = parse(&to_vec(&["a.png", "-gamma", "-1.5", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("must be > 0"));
    }

    #[test]
    fn brightness_contrast_basic_comma() {
        let p = parse(&to_vec(&["a.png", "-brightness-contrast", "10,5", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::BrightnessContrast {
                brightness: 10.0,
                contrast: 5.0
            }]
        );
    }

    #[test]
    fn brightness_contrast_basic_x_separator() {
        let p = parse(&to_vec(&[
            "a.png",
            "-brightness-contrast",
            "20x-15",
            "b.png",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![Op::BrightnessContrast {
                brightness: 20.0,
                contrast: -15.0
            }]
        );
    }

    #[test]
    fn brightness_contrast_brightness_only() {
        let p = parse(&to_vec(&["a.png", "-brightness-contrast", "30", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::BrightnessContrast {
                brightness: 30.0,
                contrast: 0.0
            }]
        );
    }

    #[test]
    fn brightness_contrast_out_of_range_rejected() {
        let err = parse(&to_vec(&[
            "a.png",
            "-brightness-contrast",
            "150,0",
            "b.png",
        ]))
        .unwrap_err();
        assert!(format!("{err:?}").contains("out of range"));
    }

    #[test]
    fn contrast_step_default_one() {
        let p = parse(&to_vec(&["a.png", "-contrast", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Contrast { delta: 1 }]);
    }

    #[test]
    fn contrast_repeated_accumulates_via_chain() {
        // IM accumulates `-contrast` across repeated flags. We capture
        // each as a separate Op; the executor sums them.
        let p = parse(&to_vec(&["a.png", "-contrast", "-contrast", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Contrast { delta: 1 }, Op::Contrast { delta: 1 }]
        );
    }

    #[test]
    fn sepia_percent_form() {
        let p = parse(&to_vec(&["a.png", "-sepia", "80%", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Sepia { threshold }] => assert!((threshold - 0.8).abs() < 1e-6),
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn sepia_unit_form() {
        let p = parse(&to_vec(&["a.png", "-sepia", "0.5", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Sepia { threshold }] => assert!((threshold - 0.5).abs() < 1e-6),
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn modulate_full_triplet() {
        let p = parse(&to_vec(&["a.png", "-modulate", "120,80,150", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Modulate {
                brightness: 120.0,
                saturation: 80.0,
                hue: 150.0,
            }]
        );
    }

    #[test]
    fn modulate_brightness_only_defaults_other_components() {
        let p = parse(&to_vec(&["a.png", "-modulate", "150", "b.png"])).unwrap();
        assert_eq!(
            p.ops,
            vec![Op::Modulate {
                brightness: 150.0,
                saturation: 100.0,
                hue: 100.0,
            }]
        );
    }

    #[test]
    fn level_full_triplet() {
        let p = parse(&to_vec(&["a.png", "-level", "10/1.2/250", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Level {
                black: 10,
                gamma,
                white: 250,
            }] => assert!((gamma - 1.2).abs() < 1e-6),
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn level_percent_endpoints() {
        let p = parse(&to_vec(&["a.png", "-level", "10%/1.0/90%", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Level {
                black,
                gamma: _,
                white,
            }] => {
                // 10% of 255 ≈ 26; 90% ≈ 230.
                assert_eq!(*black, 26);
                assert_eq!(*white, 230);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn level_inverted_endpoints_rejected() {
        let err = parse(&to_vec(&["a.png", "-level", "200/1.0/100", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("must be <="));
    }

    #[test]
    fn normalize_is_valueless() {
        let p = parse(&to_vec(&["a.png", "-normalize", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Normalize]);
    }

    #[test]
    fn threshold_percent() {
        let p = parse(&to_vec(&["a.png", "-threshold", "50%", "b.png"])).unwrap();
        // 50% of 255 ≈ 128.
        assert_eq!(p.ops, vec![Op::Threshold { value: 128 }]);
    }

    #[test]
    fn threshold_byte() {
        let p = parse(&to_vec(&["a.png", "-threshold", "200", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Threshold { value: 200 }]);
    }

    #[test]
    fn posterize_basic() {
        let p = parse(&to_vec(&["a.png", "-posterize", "4", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Posterize { levels: 4 }]);
    }

    #[test]
    fn posterize_one_rejected() {
        let err = parse(&to_vec(&["a.png", "-posterize", "1", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("levels must be >= 2"));
    }

    #[test]
    fn solarize_percent() {
        let p = parse(&to_vec(&["a.png", "-solarize", "100", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Solarize { value: 100 }]);
    }

    #[test]
    fn colorspace_gray_recognised() {
        let p = parse(&to_vec(&["a.png", "-colorspace", "Gray", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Colorspace("Gray".into())]);
    }

    #[test]
    fn colorspace_rgb_recognised() {
        let p = parse(&to_vec(&["a.png", "-colorspace", "rgb", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Colorspace("rgb".into())]);
    }

    #[test]
    fn colorspace_unsupported_rejected() {
        let err = parse(&to_vec(&["a.png", "-colorspace", "CMYK", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("not yet wired"));
    }

    #[test]
    fn unknown_flag_errors() {
        let err = parse(&to_vec(&["a.png", "-fnord", "42", "b.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(msg.contains("unknown flag"));
        // `-fnord` isn't close enough to any known flag — no hint clause.
        assert!(
            !msg.contains("did you mean"),
            "distant token should not get a hint, got: {msg}"
        );
    }

    #[test]
    fn unknown_flag_typo_suggests_close_match() {
        // Single-letter transposition of `-quality`.
        let err = parse(&to_vec(&["a.png", "-quailty", "90", "b.jpg"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(msg.contains("unknown flag"), "got: {msg}");
        assert!(
            msg.contains("did you mean '-quality'?"),
            "expected quality suggestion, got: {msg}"
        );
    }

    #[test]
    fn unknown_flag_typo_preserves_single_vs_double_dash() {
        // `--prbe` is a 1-edit miss of `--probe`. The suggestion must
        // reattach the same `--` lead the user typed, not a single dash.
        let err = parse(&to_vec(&["--prbe", "in.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(msg.contains("unknown flag"), "got: {msg}");
        assert!(
            msg.contains("did you mean '--probe'?"),
            "expected --probe suggestion with two dashes, got: {msg}"
        );
    }

    #[test]
    fn unknown_flag_typo_resize_transposition() {
        let err = parse(&to_vec(&["a.png", "-reszie", "100x100", "b.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("did you mean '-resize'?"),
            "expected resize suggestion, got: {msg}"
        );
    }

    #[test]
    fn missing_output_errors() {
        let err = parse(&to_vec(&["in.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("no output file given"));
    }

    #[test]
    fn quality_strip() {
        let p = parse(&to_vec(&["a.png", "-quality", "85", "-strip", "b.jpg"])).unwrap();
        assert_eq!(p.ops, vec![Op::Quality(85), Op::Strip]);
    }

    #[test]
    fn quality_zero_and_hundred_accepted() {
        // Endpoints stay accepted: 0 is JPEG's "smallest acceptable",
        // 100 is "highest"; both round-trip through the parser.
        let p0 = parse(&to_vec(&["a.png", "-quality", "0", "b.jpg"])).unwrap();
        assert_eq!(p0.ops, vec![Op::Quality(0)]);
        let p100 = parse(&to_vec(&["a.png", "-quality", "100", "b.jpg"])).unwrap();
        assert_eq!(p100.ops, vec![Op::Quality(100)]);
    }

    #[test]
    fn quality_out_of_range_rejected() {
        // The common typo case (1000 instead of 100); without this
        // guard the encoder silently dropped the over-range value.
        let err = parse(&to_vec(&["a.png", "-quality", "1000", "b.jpg"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("-quality") && msg.contains("out of range"),
            "got: {msg}"
        );
        assert!(
            msg.contains("0..=100"),
            "must point at the legal range; got: {msg}"
        );
        // And the tame just-over-100 case (150 instead of 100):
        let err = parse(&to_vec(&["a.png", "-quality", "150", "b.jpg"])).unwrap_err();
        assert!(format!("{err:?}").contains("out of range"));
    }

    #[test]
    fn quality_non_numeric_rejected() {
        // Negative integers + non-numeric strings still hit the
        // pre-cap parse-error branch with the existing message.
        let err = parse(&to_vec(&["a.png", "-quality", "-5", "b.jpg"])).unwrap_err();
        assert!(format!("{err:?}").contains("not a non-negative integer"));
        let err = parse(&to_vec(&["a.png", "-quality", "high", "b.jpg"])).unwrap_err();
        assert!(format!("{err:?}").contains("not a non-negative integer"));
    }

    #[test]
    fn density_background_alpha_chain() {
        let p = parse(&to_vec(&[
            "in.pdf",
            "-density",
            "300",
            "-background",
            "white",
            "-alpha",
            "remove",
            "-alpha",
            "off",
            "page-%03d.png",
        ]))
        .unwrap();
        assert_eq!(p.input, "in.pdf");
        assert_eq!(p.output, "page-%03d.png");
        assert_eq!(
            p.ops,
            vec![
                Op::Density(300),
                Op::Background([255, 255, 255, 255]),
                Op::Alpha(AlphaOp::Remove),
                Op::Alpha(AlphaOp::Off),
            ]
        );
    }

    #[test]
    fn density_zero_rejected() {
        let err = parse(&to_vec(&["a.png", "-density", "0", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("-density must be > 0"));
    }

    #[test]
    fn alpha_unknown_subcommand_rejected() {
        let err = parse(&to_vec(&["a.png", "-alpha", "fnord", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("unknown subcommand"));
    }

    #[test]
    fn background_hex_color() {
        let p = parse(&to_vec(&["a.png", "-background", "#ff8000", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Background([255, 128, 0, 255])]);
    }

    #[test]
    fn background_hex_with_alpha() {
        let p = parse(&to_vec(&["a.png", "-background", "#80808040", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Background([128, 128, 128, 64])]);
    }

    #[test]
    fn printf_template_zero_padded() {
        let t = parse_printf_template("page-%03d.png").unwrap().unwrap();
        assert_eq!(t.prefix, "page-");
        assert_eq!(t.width, 3);
        assert_eq!(t.suffix, ".png");
    }

    #[test]
    fn printf_template_unpadded() {
        let t = parse_printf_template("out%d.jpg").unwrap().unwrap();
        assert_eq!(t.prefix, "out");
        assert_eq!(t.width, 0);
        assert_eq!(t.suffix, ".jpg");
    }

    #[test]
    fn printf_template_absent_returns_none() {
        assert!(parse_printf_template("out.png").unwrap().is_none());
        assert!(parse_printf_template("/some/dir/out.jpg")
            .unwrap()
            .is_none());
    }

    #[test]
    fn printf_template_multiple_d_rejected() {
        let err = parse_printf_template("page-%d-frame-%d.png").unwrap_err();
        assert!(format!("{err:?}").contains("more than one"));
    }

    #[test]
    fn printf_template_unsupported_specifier_rejected() {
        let err = parse_printf_template("out-%s.png").unwrap_err();
        assert!(format!("{err:?}").contains("unsupported format specifier"));
    }

    #[test]
    fn parse_populates_output_template_when_present() {
        let p = parse(&to_vec(&["in.pdf", "page-%02d.png"])).unwrap();
        let t = p.output_template.unwrap();
        assert_eq!(t.prefix, "page-");
        assert_eq!(t.width, 2);
        assert_eq!(t.suffix, ".png");
    }

    #[test]
    fn parse_leaves_output_template_none_for_literal_path() {
        let p = parse(&to_vec(&["in.png", "out.jpg"])).unwrap();
        assert!(p.output_template.is_none());
    }

    #[test]
    fn ping_flag_off_by_default() {
        let p = parse(&to_vec(&["in.png", "out.jpg"])).unwrap();
        assert!(!p.ping);
    }

    #[test]
    fn ping_flag_set_when_present() {
        let p = parse(&to_vec(&["-ping", "in.png", "out.jpg"])).unwrap();
        assert!(p.ping);
    }

    #[test]
    fn ping_makes_output_optional() {
        let p = parse(&to_vec(&["-ping", "in.png"])).unwrap();
        assert!(p.ping);
        assert_eq!(p.output, "");
        assert!(p.output_template.is_none());
    }

    #[test]
    fn missing_output_without_ping_still_errors() {
        let err = parse(&to_vec(&["in.png"])).unwrap_err();
        // Should be Invalid, not Unsupported.
        assert!(format!("{err:?}").contains("no output file"));
    }

    #[test]
    fn input_selector_single_page() {
        let (path, sel) = split_input_selector("input.pdf[0]").unwrap();
        assert_eq!(path, "input.pdf");
        assert_eq!(sel, Some(PageSelector::Single(0)));
    }

    #[test]
    fn input_selector_range() {
        let (path, sel) = split_input_selector("foo.pdf[2-5]").unwrap();
        assert_eq!(path, "foo.pdf");
        assert_eq!(sel, Some(PageSelector::Range(2, 5)));
    }

    #[test]
    fn input_selector_absent_passes_through() {
        let (path, sel) = split_input_selector("plain.pdf").unwrap();
        assert_eq!(path, "plain.pdf");
        assert_eq!(sel, None);
    }

    #[test]
    fn input_selector_empty_brackets_rejected() {
        assert!(split_input_selector("foo.pdf[]").is_err());
    }

    #[test]
    fn input_selector_non_numeric_rejected() {
        assert!(split_input_selector("foo.pdf[abc]").is_err());
        assert!(split_input_selector("foo.pdf[1-x]").is_err());
    }

    #[test]
    fn input_selector_extra_dash_rejected() {
        assert!(split_input_selector("foo.pdf[1-2-3]").is_err());
    }

    #[test]
    fn parse_pulls_selector_into_input_pages() {
        let p = parse(&to_vec(&["in.pdf[0]", "out.png"])).unwrap();
        assert_eq!(p.input, "in.pdf");
        assert_eq!(p.input_pages, Some(PageSelector::Single(0)));
    }

    #[test]
    fn parse_pulls_range_selector_into_input_pages() {
        let p = parse(&to_vec(&["in.pdf[2-4]", "page-%02d.png"])).unwrap();
        assert_eq!(p.input, "in.pdf");
        assert_eq!(p.input_pages, Some(PageSelector::Range(2, 4)));
        assert!(p.output_template.is_some());
    }

    // ---- Round-after-next: comma-separated and negative page indices ----

    #[test]
    fn input_selector_negative_index_parses() {
        let (path, sel) = split_input_selector("foo.pdf[-1]").unwrap();
        assert_eq!(path, "foo.pdf");
        assert_eq!(sel, Some(PageSelector::Single(-1)));
    }

    #[test]
    fn input_selector_negative_range_endpoint_parses() {
        // `5--1` = page 5 through the last page.
        let (path, sel) = split_input_selector("foo.pdf[5--1]").unwrap();
        assert_eq!(path, "foo.pdf");
        assert_eq!(sel, Some(PageSelector::Range(5, -1)));
    }

    #[test]
    fn input_selector_negative_range_both_endpoints() {
        // `-3--1` = last three pages.
        let (path, sel) = split_input_selector("foo.pdf[-3--1]").unwrap();
        assert_eq!(path, "foo.pdf");
        assert_eq!(sel, Some(PageSelector::Range(-3, -1)));
    }

    #[test]
    fn input_selector_comma_list_of_singles() {
        let (path, sel) = split_input_selector("foo.pdf[0,2,4]").unwrap();
        assert_eq!(path, "foo.pdf");
        assert_eq!(
            sel,
            Some(PageSelector::List(vec![
                PageAtom::Single(0),
                PageAtom::Single(2),
                PageAtom::Single(4),
            ]))
        );
    }

    #[test]
    fn input_selector_comma_list_with_ranges_and_negatives() {
        // `0-2,5,-1` = "pages 0..=2, plus 5, plus the last page".
        let (path, sel) = split_input_selector("foo.pdf[0-2,5,-1]").unwrap();
        assert_eq!(path, "foo.pdf");
        assert_eq!(
            sel,
            Some(PageSelector::List(vec![
                PageAtom::Range(0, 2),
                PageAtom::Single(5),
                PageAtom::Single(-1),
            ]))
        );
    }

    #[test]
    fn input_selector_single_atom_list_collapses_to_single_variant() {
        // A list with exactly one atom collapses to the single-atom
        // variant — most callers only ever inspect Single/Range.
        let (_, sel) = split_input_selector("foo.pdf[3]").unwrap();
        assert!(matches!(sel, Some(PageSelector::Single(3))));
    }

    #[test]
    fn input_selector_empty_atom_in_list_rejected() {
        assert!(split_input_selector("foo.pdf[0,,1]").is_err());
        assert!(split_input_selector("foo.pdf[,0]").is_err());
        assert!(split_input_selector("foo.pdf[0,]").is_err());
    }

    #[test]
    fn input_selector_bare_dash_rejected() {
        assert!(split_input_selector("foo.pdf[-]").is_err());
    }

    #[test]
    fn page_selector_negative_single_resolves_to_last_page() {
        let s = PageSelector::Single(-1);
        assert_eq!(s.resolve(5).unwrap(), vec![4]);
        let s = PageSelector::Single(-2);
        assert_eq!(s.resolve(5).unwrap(), vec![3]);
        // Negative index out of range.
        assert!(PageSelector::Single(-6).resolve(5).is_err());
    }

    #[test]
    fn page_selector_negative_range_endpoint_resolves() {
        // `5--1` against 8 pages → 5..=7.
        let s = PageSelector::Range(5, -1);
        assert_eq!(s.resolve(8).unwrap(), vec![5, 6, 7]);
        // `-3--1` against 8 pages → 5..=7 (last three).
        let s = PageSelector::Range(-3, -1);
        assert_eq!(s.resolve(8).unwrap(), vec![5, 6, 7]);
    }

    #[test]
    fn page_selector_list_resolves_in_source_order() {
        let s = PageSelector::List(vec![
            PageAtom::Single(0),
            PageAtom::Single(2),
            PageAtom::Range(4, 5),
            PageAtom::Single(-1),
        ]);
        assert_eq!(s.resolve(8).unwrap(), vec![0, 2, 4, 5, 7]);
    }

    #[test]
    fn page_selector_list_preserves_duplicates() {
        // IM convention: `[0,0,0]` writes the same page three times.
        let s = PageSelector::List(vec![
            PageAtom::Single(0),
            PageAtom::Single(0),
            PageAtom::Single(0),
        ]);
        assert_eq!(s.resolve(3).unwrap(), vec![0, 0, 0]);
    }

    #[test]
    fn page_selector_list_propagates_out_of_range() {
        let s = PageSelector::List(vec![PageAtom::Single(0), PageAtom::Single(99)]);
        assert!(s.resolve(3).is_err());
    }

    // ---- Round-after-next: -vignette / -colorize / -equalize / -auto-gamma ----

    #[test]
    fn vignette_radius_only_defaults_sigma_and_centre() {
        let p = parse(&to_vec(&["a.png", "-vignette", "50", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Vignette {
                radius,
                sigma,
                x,
                y,
            }] => {
                assert!((radius - 50.0).abs() < 1e-6);
                // Sigma defaults to radius / 2.
                assert!((sigma - 25.0).abs() < 1e-6);
                // X/Y default to image centre (0.5, 0.5).
                assert!((x - 0.5).abs() < 1e-6);
                assert!((y - 0.5).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn vignette_radius_and_sigma() {
        let p = parse(&to_vec(&["a.png", "-vignette", "50+10", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Vignette {
                radius,
                sigma,
                x,
                y,
            }] => {
                assert!((radius - 50.0).abs() < 1e-6);
                assert!((sigma - 10.0).abs() < 1e-6);
                assert!((x - 0.5).abs() < 1e-6);
                assert!((y - 0.5).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn vignette_full_grammar_with_xy() {
        let p = parse(&to_vec(&["a.png", "-vignette", "50+10+0.25+0.75", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Vignette {
                radius,
                sigma,
                x,
                y,
            }] => {
                assert!((radius - 50.0).abs() < 1e-6);
                assert!((sigma - 10.0).abs() < 1e-6);
                assert!((x - 0.25).abs() < 1e-6);
                assert!((y - 0.75).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn vignette_too_many_components_rejected() {
        let err = parse(&to_vec(&["a.png", "-vignette", "1+2+3+4+5", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("more than 4"));
    }

    #[test]
    fn vignette_negative_radius_rejected() {
        let err = parse(&to_vec(&["a.png", "-vignette", "-5", "b.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(msg.contains("not a finite float radius") || msg.contains("must be >= 0"));
    }

    #[test]
    fn colorize_named_color_with_percent_amount() {
        let p = parse(&to_vec(&["a.png", "-colorize", "red/40%", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Colorize { color, amount }] => {
                assert_eq!(*color, [255, 0, 0, 255]);
                assert!((amount - 0.4).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn colorize_hex_color() {
        let p = parse(&to_vec(&["a.png", "-colorize", "#ff8000/50%", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Colorize { color, amount }] => {
                assert_eq!(*color, [255, 128, 0, 255]);
                assert!((amount - 0.5).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn colorize_per_channel_triplet() {
        let p = parse(&to_vec(&["a.png", "-colorize", "200x100x50/25%", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Colorize { color, amount }] => {
                assert_eq!(*color, [200, 100, 50, 255]);
                assert!((amount - 0.25).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn colorize_single_channel_replicated() {
        // `100/50%` → no `x`, but contains `/`. The colour is the
        // string before `/`; "100" lacks `x`, so we fall through to
        // parse_color which won't match (it's not named / hex). Test
        // that we get a clean error.
        let err = parse(&to_vec(&["a.png", "-colorize", "100/50%", "b.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(msg.contains("unknown colour") || msg.contains("not a valid hex"));
    }

    #[test]
    fn colorize_per_channel_one_value_replicates() {
        // `100x` (or `100xx`) — single value means R = G = B = 100.
        let p = parse(&to_vec(&["a.png", "-colorize", "100x100x100/30%", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Colorize { color, amount: _ }] => {
                assert_eq!(*color, [100, 100, 100, 255]);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn colorize_amount_only_defaults_white() {
        // `/40%` form — IM accepts it; default colour is white.
        let p = parse(&to_vec(&["a.png", "-colorize", "/40%", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Colorize { color, amount }] => {
                assert_eq!(*color, [255, 255, 255, 255]);
                assert!((amount - 0.4).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn colorize_amount_unit_scalar() {
        // Without `%`, parse_percent_or_unit accepts a unit scalar.
        let p = parse(&to_vec(&["a.png", "-colorize", "red/0.6", "b.png"])).unwrap();
        match p.ops.as_slice() {
            [Op::Colorize { color, amount }] => {
                assert_eq!(*color, [255, 0, 0, 255]);
                assert!((amount - 0.6).abs() < 1e-6);
            }
            other => panic!("unexpected ops: {other:?}"),
        }
    }

    #[test]
    fn colorize_out_of_range_channel_rejected() {
        let err = parse(&to_vec(&["a.png", "-colorize", "300x0x0/50%", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("out of range"));
    }

    #[test]
    fn equalize_is_valueless() {
        let p = parse(&to_vec(&["a.png", "-equalize", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Equalize]);
    }

    #[test]
    fn auto_gamma_is_valueless() {
        let p = parse(&to_vec(&["a.png", "-auto-gamma", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::AutoGamma]);
    }

    #[test]
    fn vignette_rejects_negative_sigma() {
        let err = parse(&to_vec(&["a.png", "-vignette", "5+-1", "b.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("not a finite float sigma") || msg.contains("must be >= 0"),
            "unexpected message: {msg}"
        );
    }

    // ---- Per-format encoder option flags (`-stl-format`,
    //      `-gltf-format`). End-to-end coverage lives in
    //      `tests/format_flags.rs`; the unit tests here only check
    //      that the parser populates `ConvertPlan::mesh3d_options`
    //      correctly and rejects malformed values up-front. ----

    #[test]
    fn stl_format_default_is_none() {
        let p = parse(&to_vec(&["in.stl", "out.stl"])).unwrap();
        assert!(p.mesh3d_options.stl_format.is_none());
        assert!(p.ops.is_empty(), "no -stl-format → no Op pushed");
    }

    #[test]
    fn stl_format_ascii_parses() {
        let p = parse(&to_vec(&["in.stl", "-stl-format", "ascii", "out.stl"])).unwrap();
        assert_eq!(p.mesh3d_options.stl_format, Some(StlFormatChoice::Ascii));
    }

    #[test]
    fn stl_format_binary_parses() {
        let p = parse(&to_vec(&["in.stl", "-stl-format", "binary", "out.stl"])).unwrap();
        assert_eq!(p.mesh3d_options.stl_format, Some(StlFormatChoice::Binary));
    }

    #[test]
    fn stl_format_aliases_parse() {
        // `bin` → Binary, `text` → Ascii.
        let p = parse(&to_vec(&["in.stl", "-stl-format", "bin", "out.stl"])).unwrap();
        assert_eq!(p.mesh3d_options.stl_format, Some(StlFormatChoice::Binary));
        let p = parse(&to_vec(&["in.stl", "-stl-format", "text", "out.stl"])).unwrap();
        assert_eq!(p.mesh3d_options.stl_format, Some(StlFormatChoice::Ascii));
    }

    #[test]
    fn stl_format_case_insensitive() {
        let p = parse(&to_vec(&["in.stl", "-stl-format", "ASCII", "out.stl"])).unwrap();
        assert_eq!(p.mesh3d_options.stl_format, Some(StlFormatChoice::Ascii));
    }

    #[test]
    fn stl_format_unknown_value_rejected() {
        let err = parse(&to_vec(&["in.stl", "-stl-format", "xml", "out.stl"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("unknown flavour 'xml'") && msg.contains("expected 'binary'"),
            "unexpected message: {msg}"
        );
    }

    #[test]
    fn stl_format_missing_value_rejected() {
        let err = parse(&to_vec(&["in.stl", "-stl-format"])).unwrap_err();
        assert!(format!("{err:?}").contains("-stl-format: missing value"));
    }

    #[test]
    fn gltf_format_default_is_none() {
        let p = parse(&to_vec(&["in.stl", "out.gltf"])).unwrap();
        assert!(p.mesh3d_options.gltf_format.is_none());
    }

    #[test]
    fn gltf_format_glb_parses() {
        let p = parse(&to_vec(&["in.stl", "-gltf-format", "glb", "out.glb"])).unwrap();
        assert_eq!(p.mesh3d_options.gltf_format, Some(GltfFormatChoice::Glb));
    }

    #[test]
    fn gltf_format_embedded_parses() {
        let p = parse(&to_vec(&["in.stl", "-gltf-format", "embedded", "out.gltf"])).unwrap();
        assert_eq!(
            p.mesh3d_options.gltf_format,
            Some(GltfFormatChoice::JsonEmbedded)
        );
    }

    #[test]
    fn gltf_format_external_parses_even_though_runtime_rejects() {
        // The parser accepts the token; runtime emits the gltf-rN
        // follow-up message. Decouples the user-facing error from the
        // arg parser's "unknown flag" path.
        let p = parse(&to_vec(&["in.stl", "-gltf-format", "external", "out.gltf"])).unwrap();
        assert_eq!(
            p.mesh3d_options.gltf_format,
            Some(GltfFormatChoice::JsonExternal)
        );
    }

    #[test]
    fn gltf_format_aliases_parse() {
        // `binary` → Glb (matches IM-style synonym tolerance).
        let p = parse(&to_vec(&["in.stl", "-gltf-format", "binary", "out.glb"])).unwrap();
        assert_eq!(p.mesh3d_options.gltf_format, Some(GltfFormatChoice::Glb));
        // `json-embedded` → JsonEmbedded.
        let p = parse(&to_vec(&[
            "in.stl",
            "-gltf-format",
            "json-embedded",
            "out.gltf",
        ]))
        .unwrap();
        assert_eq!(
            p.mesh3d_options.gltf_format,
            Some(GltfFormatChoice::JsonEmbedded)
        );
    }

    #[test]
    fn gltf_format_unknown_value_rejected() {
        let err = parse(&to_vec(&["in.stl", "-gltf-format", "obj", "out.gltf"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("unknown flavour 'obj'") && msg.contains("expected 'glb'"),
            "unexpected message: {msg}"
        );
    }

    #[test]
    fn render_gouraud_parses() {
        let p = parse(&to_vec(&["in.stl", "-render", "gouraud", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::Gouraud)
        );
    }

    #[test]
    fn render_phong_parses() {
        let p = parse(&to_vec(&["in.stl", "-render", "phong", "out.png"])).unwrap();
        assert_eq!(p.mesh3d_options.render_mode, Some(Mesh3DRenderMode::Phong));
    }

    #[test]
    fn render_wire_alias_parses() {
        let p = parse(&to_vec(&["in.stl", "-render", "wire", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::Wireframe)
        );
    }

    #[test]
    fn render_unknown_mode_rejected_lists_all_options() {
        let err = parse(&to_vec(&["in.stl", "-render", "raytrace", "out.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("unknown mode 'raytrace'")
                && msg.contains("'gouraud'")
                && msg.contains("'phong'"),
            "unexpected message: {msg}"
        );
    }

    #[test]
    fn light_parses_three_components() {
        let p = parse(&to_vec(&["in.stl", "-light", "30,45,1.5", "out.png"])).unwrap();
        let light = p.mesh3d_options.light.expect("-light should populate");
        assert_eq!(light.azimuth_deg, 30.0);
        assert_eq!(light.elevation_deg, 45.0);
        assert_eq!(light.intensity, 1.5);
    }

    #[test]
    fn light_rejects_negative_intensity() {
        let err = parse(&to_vec(&["in.stl", "-light", "0,0,-1", "out.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("intensity"));
    }

    #[test]
    fn light_rejects_two_component_input() {
        let err = parse(&to_vec(&["in.stl", "-light", "30,45", "out.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("AZIMUTH,ELEVATION,INTENSITY"),
            "expected grammar hint, got: {msg}"
        );
    }

    #[test]
    fn camera_parses_three_components() {
        let p = parse(&to_vec(&["in.stl", "-camera", "20,30,2.0", "out.png"])).unwrap();
        let cam = p.mesh3d_options.camera.expect("-camera should populate");
        assert_eq!(cam.elevation_deg, 20.0);
        assert_eq!(cam.azimuth_deg, 30.0);
        assert_eq!(cam.distance, 2.0);
    }

    #[test]
    fn camera_rejects_zero_distance() {
        let err = parse(&to_vec(&["in.stl", "-camera", "0,0,0", "out.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("distance"));
    }

    #[test]
    fn projection_orthographic_parses() {
        let p = parse(&to_vec(&[
            "in.stl",
            "-projection",
            "orthographic",
            "out.png",
        ]))
        .unwrap();
        assert_eq!(
            p.mesh3d_options.projection,
            Some(ProjectionMode::Orthographic)
        );
    }

    #[test]
    fn projection_perspective_default_is_unset() {
        let p = parse(&to_vec(&["in.stl", "out.png"])).unwrap();
        assert!(p.mesh3d_options.projection.is_none());
    }

    #[test]
    fn projection_alias_parses() {
        let p = parse(&to_vec(&["in.stl", "-projection", "ortho", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.projection,
            Some(ProjectionMode::Orthographic)
        );
    }

    #[test]
    fn projection_unknown_rejected() {
        let err = parse(&to_vec(&["in.stl", "-projection", "isometric", "out.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("unknown mode 'isometric'"));
    }

    #[test]
    fn fov_parses_within_range() {
        let p = parse(&to_vec(&["in.stl", "-fov", "45", "out.png"])).unwrap();
        assert_eq!(p.mesh3d_options.fov_deg, Some(45.0));
    }

    #[test]
    fn fov_rejects_zero() {
        let err = parse(&to_vec(&["in.stl", "-fov", "0", "out.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("(0, 180)"));
    }

    #[test]
    fn fov_rejects_180_or_above() {
        let err = parse(&to_vec(&["in.stl", "-fov", "180", "out.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("(0, 180)"));
    }

    #[test]
    fn bg_named_colour_parses() {
        let p = parse(&to_vec(&["in.stl", "-bg", "black", "out.png"])).unwrap();
        assert_eq!(p.mesh3d_options.bg, Some([0, 0, 0, 255]));
    }

    #[test]
    fn bg_hex_colour_parses() {
        let p = parse(&to_vec(&["in.stl", "-bg", "#abcdef", "out.png"])).unwrap();
        assert_eq!(p.mesh3d_options.bg, Some([0xab, 0xcd, 0xef, 255]));
    }

    #[test]
    fn bg_transparent_parses() {
        let p = parse(&to_vec(&["in.stl", "-bg", "transparent", "out.png"])).unwrap();
        assert_eq!(p.mesh3d_options.bg, Some([0, 0, 0, 0]));
    }

    #[test]
    fn mesh3d_flags_can_appear_before_input() {
        // IM grammar lets ops appear on either side of the positional;
        // confirm the per-format flags follow the same rule.
        let p = parse(&to_vec(&[
            "-stl-format",
            "ascii",
            "-gltf-format",
            "glb",
            "in.stl",
            "out.stl",
        ]))
        .unwrap();
        assert_eq!(p.mesh3d_options.stl_format, Some(StlFormatChoice::Ascii));
        assert_eq!(p.mesh3d_options.gltf_format, Some(GltfFormatChoice::Glb));
        assert_eq!(p.input, "in.stl");
        assert_eq!(p.output, "out.stl");
    }

    // ---- Round 45: -render normal-debug / depth-debug + -aa N --------

    #[test]
    fn render_normal_debug_parses() {
        let p = parse(&to_vec(&["in.stl", "-render", "normal-debug", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::NormalDebug)
        );
    }

    #[test]
    fn render_depth_debug_parses() {
        let p = parse(&to_vec(&["in.stl", "-render", "depth-debug", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::DepthDebug)
        );
    }

    #[test]
    fn render_normal_alias_parses() {
        // `normal` (singular) and `normals` (plural) both map to
        // NormalDebug; convenience for the common typo.
        let p = parse(&to_vec(&["in.stl", "-render", "normal", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::NormalDebug)
        );
        let p = parse(&to_vec(&["in.stl", "-render", "normals", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::NormalDebug)
        );
    }

    #[test]
    fn render_depth_alias_parses() {
        let p = parse(&to_vec(&["in.stl", "-render", "depth", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::DepthDebug)
        );
        let p = parse(&to_vec(&["in.stl", "-render", "z", "out.png"])).unwrap();
        assert_eq!(
            p.mesh3d_options.render_mode,
            Some(Mesh3DRenderMode::DepthDebug)
        );
    }

    #[test]
    fn render_unknown_mode_lists_debug_modes() {
        // Round 45 added two new modes; the error message should
        // mention them so users don't have to grep the docs.
        let err = parse(&to_vec(&["in.stl", "-render", "raytrace", "out.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("normal-debug") && msg.contains("depth-debug"),
            "expected new debug-mode names in error, got: {msg}"
        );
    }

    #[test]
    fn aa_default_is_unset() {
        let p = parse(&to_vec(&["in.stl", "out.png"])).unwrap();
        assert!(p.mesh3d_options.aa.is_none());
    }

    #[test]
    fn aa_factor_parses() {
        let p = parse(&to_vec(&["in.stl", "-aa", "4", "out.png"])).unwrap();
        assert_eq!(p.mesh3d_options.aa, Some(4));
    }

    #[test]
    fn aa_factor_one_is_allowed_meaning_no_supersampling() {
        // 1× is the documented "off" value — allowed so callers can
        // unconditionally set the flag from a config without special-
        // casing the disabled state.
        let p = parse(&to_vec(&["in.stl", "-aa", "1", "out.png"])).unwrap();
        assert_eq!(p.mesh3d_options.aa, Some(1));
    }

    #[test]
    fn aa_factor_zero_rejected() {
        let err = parse(&to_vec(&["in.stl", "-aa", "0", "out.png"])).unwrap_err();
        let msg = format!("{err:?}");
        assert!(
            msg.contains("out of range") && msg.contains("1..=8"),
            "expected range hint, got: {msg}"
        );
    }

    #[test]
    fn aa_factor_above_cap_rejected() {
        let err = parse(&to_vec(&["in.stl", "-aa", "16", "out.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("1..=8"));
    }

    #[test]
    fn aa_non_integer_rejected() {
        let err = parse(&to_vec(&["in.stl", "-aa", "2.5", "out.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("not a positive integer"));
    }

    // ---- -trim / -fuzz ----

    /// Bare `-trim` (no preceding `-fuzz`) lands as `Op::Trim { fuzz: 0 }` —
    /// IM's default exact-match background detection.
    #[test]
    fn trim_default_fuzz_is_zero() {
        let p = parse(&to_vec(&["a.png", "-trim", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Trim { fuzz: 0 }]);
    }

    /// `-fuzz N` updates state but emits no op of its own; the next
    /// `-trim` captures the value.
    #[test]
    fn fuzz_byte_then_trim_captures_value() {
        let p = parse(&to_vec(&["a.png", "-fuzz", "12", "-trim", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Trim { fuzz: 12 }]);
    }

    /// `-fuzz N%` accepts the IM percent grammar and maps `100%` to
    /// `255`. `10%` ≈ `26` (`10 × 2.55` rounded).
    #[test]
    fn fuzz_percent_then_trim_captures_scaled_value() {
        let p = parse(&to_vec(&["a.png", "-fuzz", "10%", "-trim", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Trim { fuzz: 26 }]);
        let p = parse(&to_vec(&["a.png", "-fuzz", "100%", "-trim", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Trim { fuzz: 255 }]);
    }

    /// A `-fuzz` placed AFTER a `-trim` does NOT retroactively rewrite
    /// the earlier trim's tolerance (source-order semantics, identical to
    /// `-background` + `-extent`). The second `-trim` then captures the
    /// new fuzz.
    #[test]
    fn fuzz_after_trim_only_affects_following_trim() {
        let p = parse(&to_vec(&[
            "a.png", "-fuzz", "5", "-trim", "-fuzz", "20", "-trim", "b.png",
        ]))
        .unwrap();
        assert_eq!(p.ops, vec![Op::Trim { fuzz: 5 }, Op::Trim { fuzz: 20 }]);
    }

    /// `-fuzz` with no preceding-or-following `-trim` is a recorded
    /// state-only setting — no Op emitted, no error.
    #[test]
    fn fuzz_without_trim_is_no_op() {
        let p = parse(&to_vec(&["a.png", "-fuzz", "30", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![]);
    }

    /// `-fuzz` requires a value; missing → clean "missing value" error.
    #[test]
    fn fuzz_missing_value_rejected() {
        let err = parse(&to_vec(&["a.png", "-fuzz"])).unwrap_err();
        assert!(format!("{err:?}").contains("missing value"));
    }

    /// `-fuzz` rejects garbage with the same shape as `-threshold`.
    #[test]
    fn fuzz_garbage_rejected() {
        let err = parse(&to_vec(&["a.png", "-fuzz", "xyz", "-trim", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("-fuzz"));
    }

    /// `-fuzz N%` with `N` outside `[0, 100]` is rejected (same shape as
    /// `-threshold` / `-solarize`).
    #[test]
    fn fuzz_percent_out_of_range_rejected() {
        let err = parse(&to_vec(&["a.png", "-fuzz", "150%", "-trim", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("out of range"));
    }

    /// `-fuzz N` with `N > 255` is rejected (raw bytes only go up to
    /// `255`; the percent grammar is the documented escape hatch).
    #[test]
    fn fuzz_byte_above_255_rejected() {
        let err = parse(&to_vec(&["a.png", "-fuzz", "300", "-trim", "b.png"])).unwrap_err();
        assert!(format!("{err:?}").contains("out of range"));
    }

    /// `-trim` composes with surrounding ops in source order — typical
    /// IM idiom `convert in.png -trim +repage out.png` would land trim
    /// between any prior `-resize` and a downstream `-strip`. Pins the
    /// no-implicit-reorder contract.
    #[test]
    fn trim_keeps_source_order_with_neighbours() {
        let p = parse(&to_vec(&[
            "a.png", "-resize", "100x100", "-fuzz", "8", "-trim", "-strip", "b.png",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![
                Op::Resize {
                    width: 100,
                    height: 100,
                    mode: ResizeMode::Default,
                },
                Op::Trim { fuzz: 8 },
                Op::Strip,
            ]
        );
    }

    // ---- -roll +X+Y ----

    /// Plain `-roll +X+Y` lands as `Op::Roll { dx, dy }` with both
    /// offsets positive.
    #[test]
    fn roll_positive_offsets() {
        let p = parse(&to_vec(&["a.png", "-roll", "+5+10", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Roll { dx: 5, dy: 10 }]);
    }

    /// `-roll -X-Y` accepts negative offsets unchanged — the inline
    /// shift handles the modulo wrap, so the args layer doesn't
    /// normalise.
    #[test]
    fn roll_negative_offsets() {
        let p = parse(&to_vec(&["a.png", "-roll", "-3-7", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Roll { dx: -3, dy: -7 }]);
    }

    /// Mixed signs (`+X-Y`, `-X+Y`) ride through the same
    /// `parse_extent_offsets` helper as `-extent`.
    #[test]
    fn roll_mixed_signs() {
        let p = parse(&to_vec(&["a.png", "-roll", "+5-10", "b.png"])).unwrap();
        assert_eq!(p.ops, vec![Op::Roll { dx: 5, dy: -10 }]);
    }

    /// Single-offset `+X` is rejected — IM requires both X and Y
    /// signed. Mirrors the `-extent +X` rejection path.
    #[test]
    fn roll_single_offset_rejected() {
        let err = parse(&to_vec(&["a.png", "-roll", "+5", "b.png"])).unwrap_err();
        assert!(
            format!("{err:?}").contains("single offset"),
            "unexpected error: {err:?}"
        );
    }

    /// Empty value (e.g. `-roll ""`) is rejected with a clear
    /// message rather than silently treated as `0,0`.
    #[test]
    fn roll_empty_value_rejected() {
        let err = parse(&to_vec(&["a.png", "-roll", "", "b.png"])).unwrap_err();
        assert!(
            format!("{err:?}").contains("empty offset"),
            "unexpected error: {err:?}"
        );
    }

    /// Unsigned `5+10` (missing leading sign) is rejected with the
    /// IM "must start with `+` or `-`" message — IM grammar requires
    /// the explicit sign.
    #[test]
    fn roll_unsigned_value_rejected() {
        let err = parse(&to_vec(&["a.png", "-roll", "5+10", "b.png"])).unwrap_err();
        let s = format!("{err:?}");
        assert!(
            s.contains("must start with `+` or `-`") || s.contains("not a signed integer"),
            "unexpected error: {err:?}"
        );
    }

    /// `-roll` preserves source order alongside neighbours — same
    /// no-reorder contract as `-trim` / `-flip` / `-extent`.
    #[test]
    fn roll_keeps_source_order_with_neighbours() {
        let p = parse(&to_vec(&[
            "a.png", "-resize", "100x100", "-roll", "+5+5", "-strip", "b.png",
        ]))
        .unwrap();
        assert_eq!(
            p.ops,
            vec![
                Op::Resize {
                    width: 100,
                    height: 100,
                    mode: ResizeMode::Default,
                },
                Op::Roll { dx: 5, dy: 5 },
                Op::Strip,
            ]
        );
    }
}