//! Headless DeckCraft.
//!
//! ```text
//! deckcraft-cli info FILE                       # slides, titles, layouts (JSON)
//! deckcraft-cli render (FILE | --sample) [--slide N | --all] [--scale S] OUT.png|OUT_DIR
//! N starts at 0. --all writes slide-01.png, slide-02.png, …
//! deckcraft-cli render-transition FILE --slide N --t T[,T…] [--width PX] OUT.png   # transition frame(s)
//! deckcraft-cli convert IN OUT                  # .deckcraft ⇄ .pptx, outline .txt, .png (first slide)
//! deckcraft-cli run [--in FILE | --sample] [--cmd ID[=JSON]]... [--save OUT] [--export OUT] [--print]
//! deckcraft-cli commands [FILTER]               # list commands (JSON)
//! deckcraft-cli describe ID                     # one command
//! deckcraft-cli app [--port PORT] COMMAND [JSON] | --method METHOD [JSON]   # drive the running app
//! deckcraft-cli mcp [--connect PORT] [--sample] # MCP server over stdio
//! deckcraft-cli bench [FILE | --sample] [--runs N] [--json]   # time open, render, save, export
//! deckcraft-cli links | --version
//! ```
#![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
#![forbid(unsafe_code)]

use std::process::ExitCode;

use deckcraft_engine::Session;
use serde_json::{Value, json};

macro_rules! outln {
    ($($arg:tt)*) => {{
        use std::io::Write as _;
        if let Err(e) = writeln!(std::io::stdout(), $($arg)*) {
            if e.kind() == std::io::ErrorKind::BrokenPipe {
                std::process::exit(0);
            }
            eprintln!("deckcraft-cli: can't write to stdout: {e}");
            std::process::exit(1);
        }
    }};
}

const USAGE: &str = "usage: deckcraft-cli info FILE
       deckcraft-cli render (FILE | --sample) [--slide N | --all] [--scale S] [--edit] OUT
       N starts at 0 (the first slide). --all writes slide-01.png, slide-02.png, …
       deckcraft-cli render-transition FILE --slide N --t T[,T...] [--width PX] OUT.png
       deckcraft-cli convert IN OUT
       deckcraft-cli run [--in FILE | --sample] [--cmd ID[=JSON]]... [--save OUT] [--export OUT] [--print]
       deckcraft-cli commands [FILTER]
       deckcraft-cli describe COMMAND
       deckcraft-cli app [--port PORT] COMMAND [JSON] | --method METHOD [JSON]
       deckcraft-cli mcp [--connect PORT] [--sample]
       deckcraft-cli bench [FILE | --sample] [--runs N] [--json]
       deckcraft-cli links | --version";

fn main() -> ExitCode {
    let args: Vec<String> = std::env::args().skip(1).collect();
    let rest = args.get(1..).unwrap_or(&[]);
    match args.first().map(String::as_str) {
        Some("--version" | "-V" | "version") => {
            outln!("deckcraft-cli {}", env!("CARGO_PKG_VERSION"));
            ExitCode::SUCCESS
        }
        Some("info") => report(info(rest)),
        Some("bench") => report(bench(rest)),
        Some("render") => report(render(rest)),
        Some("render-transition") => report(render_transition(rest)),
        Some("convert") => report(convert(rest)),
        Some("run") => report(run(rest)),
        Some("--help" | "-h" | "help") => {
            outln!("{USAGE}");
            ExitCode::SUCCESS
        }
        Some("commands") if rest.first().is_some_and(|a| is_help(a)) => {
            outln!("{USAGE}");
            ExitCode::SUCCESS
        }
        Some("commands") => {
            let s = Session::new();
            let f = rest.first().map(|x| x.to_lowercase());
            let list: Vec<Value> = s
                .commands()
                .into_iter()
                .filter(|c| f.as_ref().is_none_or(|f| c.id.to_lowercase().contains(f.as_str()) || c.label.to_lowercase().contains(f.as_str())))
                .map(|c| serde_json::to_value(c).unwrap_or_default())
                .collect();
            outln!("{}", serde_json::to_string_pretty(&list).unwrap_or_default());
            ExitCode::SUCCESS
        }
        Some("describe") => report(describe(rest.first().map(String::as_str))),
        Some("app") => report(app(rest)),
        Some("mcp") => report(mcp(rest)),
        Some("links") => {
            use deckcraft_engine::links::*;
            outln!("Discord   {DISCORD}\nWebsite   {WEBSITE}\nApp page  {APP_PAGE}\nGitHub    {GITHUB}");
            ExitCode::SUCCESS
        }
        _ => {
            eprintln!("{USAGE}");
            eprintln!("\nCommunity: {}  ·  {}", deckcraft_engine::links::DISCORD, deckcraft_engine::links::APP_PAGE);
            ExitCode::FAILURE
        }
    }
}

fn is_help(arg: &str) -> bool {
    matches!(arg, "--help" | "-h")
}

fn report(r: Result<(), String>) -> ExitCode {
    match r {
        Ok(()) => ExitCode::SUCCESS,
        Err(e) => {
            eprintln!("deckcraft-cli: {e}");
            ExitCode::FAILURE
        }
    }
}

fn open(s: &mut Session, input: Option<&str>, sample: bool) -> Result<(), String> {
    if sample {
        return deckcraft_engine::sample::open_sample(s).map_err(|e| e.to_string());
    }
    match input {
        Some(p) => s.execute("file.open", &json!({"path": p})).map(|_| ()).map_err(|e| e.to_string()),
        None => s.execute("file.new", &json!({})).map(|_| ()).map_err(|e| e.to_string()),
    }
}

/// Median and slowest of `runs` timings of `f`, in milliseconds.
fn time_ms(runs: usize, mut f: impl FnMut() -> Result<(), String>) -> Result<(f64, f64), String> {
    let mut ms = Vec::with_capacity(runs);
    for _ in 0..runs.max(1) {
        let t = std::time::Instant::now();
        f()?;
        ms.push(t.elapsed().as_secs_f64() * 1000.0);
    }
    ms.sort_by(f64::total_cmp);
    let median = ms.get(ms.len() / 2).copied().unwrap_or(0.0);
    Ok((median, ms.last().copied().unwrap_or(0.0)))
}

/// Peak resident memory of this process in MiB (Linux `VmHWM`); `None` elsewhere.
fn peak_rss_mib() -> Option<f64> {
    let s = std::fs::read_to_string("/proc/self/status").ok()?;
    let kb: f64 = s.lines().find_map(|l| l.strip_prefix("VmHWM:"))?.trim().trim_end_matches("kB").trim().parse().ok()?;
    Some(kb / 1024.0)
}

/// The performance baseline (docs/gaps.md "No baseline"): how long a deck takes to open, to
/// render each slide, to save and to export, and the peak memory, as JSON or a table.
fn bench(args: &[String]) -> Result<(), String> {
    use deckcraft_engine::cmd::file::{open_presentation, save_bytes};
    let mut input = None;
    let mut sample = false;
    let mut runs = 5usize;
    let mut as_json = false;
    let mut it = args.iter();
    while let Some(a) = it.next() {
        match a.as_str() {
            "--sample" => sample = true,
            "--json" => as_json = true,
            "--runs" => {
                runs = it.next().and_then(|v| v.parse().ok()).filter(|n| (1..=1000).contains(n)).ok_or("--runs needs a number from 1 to 1000")?
            }
            f if !f.starts_with("--") && input.is_none() => input = Some(f.to_string()),
            o => return Err(format!("bench: unknown argument `{o}`")),
        }
    }
    if input.is_none() && !sample {
        return Err("bench needs a FILE or --sample".into());
    }
    let mut s = Session::new();
    let (name, bytes) = match &input {
        Some(p) => (p.clone(), std::fs::read(p).map_err(|e| format!("{p}: {e}"))?),
        None => {
            open(&mut s, None, true)?;
            let doc = &s.doc().map_err(|e| e.to_string())?.doc;
            ("sample.deckcraft".to_string(), save_bytes(doc, "deckcraft").map_err(|e| e.to_string())?)
        }
    };
    let e = |x: deckcraft_engine::EngineError| x.to_string();
    let doc = open_presentation(&name, &bytes).map_err(e)?;
    let slides = doc.slides.len();
    let open = time_ms(runs, || open_presentation(&name, &bytes).map(|_| ()).map_err(e))?;
    let opts = deckcraft_engine::render::RenderOpts { scale: 1.0, ..Default::default() };
    let mut per_slide = vec![];
    for i in 0..slides {
        per_slide.push(time_ms(runs, || {
            deckcraft_engine::render::render_slide(&doc, i, &opts);
            Ok(())
        })?);
    }
    let pptx = save_bytes(&doc, "pptx").map_err(e)?;
    let mut steps = vec![
        ("open", open),
        ("save .deckcraft", time_ms(runs, || save_bytes(&doc, "deckcraft").map(|_| ()).map_err(e))?),
        ("save .pptx", time_ms(runs, || save_bytes(&doc, "pptx").map(|_| ()).map_err(e))?),
        ("open .pptx", time_ms(runs, || open_presentation("bench.pptx", &pptx).map(|_| ()).map_err(e))?),
        ("export .pdf", time_ms(runs.min(3), || save_bytes(&doc, "pdf").map(|_| ()).map_err(e))?),
    ];
    let render_total: f64 = per_slide.iter().map(|m| m.0).sum();
    let render_max = per_slide.iter().map(|m| m.1).fold(0.0, f64::max);
    steps.insert(1, ("render all slides (1×)", (render_total, render_max)));
    let peak = peak_rss_mib();
    if as_json {
        let v = json!({
            "file": name,
            "bytes": bytes.len(),
            "slides": slides,
            "runs": runs,
            "steps": steps.iter().map(|(k, (m, x))| json!({"step": k, "medianMs": m, "maxMs": x})).collect::<Vec<_>>(),
            "renderMsPerSlide": per_slide.iter().map(|m| m.0).collect::<Vec<_>>(),
            "peakRssMiB": peak,
        });
        outln!("{}", serde_json::to_string_pretty(&v).unwrap_or_default());
    } else {
        outln!("{name}: {slides} slides, {} KiB, median of {runs} runs", bytes.len() / 1024);
        for (k, (m, x)) in &steps {
            outln!("  {k:<24} {m:>9.1} ms   (slowest {x:.1} ms)");
        }
        if let Some((i, m)) = per_slide.iter().enumerate().max_by(|a, b| a.1.0.total_cmp(&b.1.0)) {
            outln!("  slowest slide            {:>9.1} ms   (slide {})", m.0, i + 1);
        }
        if let Some(p) = peak {
            outln!("  peak memory              {p:>9.1} MiB");
        }
    }
    Ok(())
}

fn info(args: &[String]) -> Result<(), String> {
    if args.first().is_some_and(|a| is_help(a)) {
        outln!("{USAGE}");
        return Ok(());
    }
    let path = args.first().ok_or("info needs a FILE")?;
    let mut s = Session::new();
    open(&mut s, Some(path), false)?;
    let v = s.execute("document.inspect", &json!({})).map_err(|e| e.to_string())?;
    outln!("{}", serde_json::to_string_pretty(&v).unwrap_or_default());
    Ok(())
}

fn render(args: &[String]) -> Result<(), String> {
    let mut input = None;
    let mut sample = false;
    let mut slide: Option<usize> = None;
    let mut all = false;
    let mut scale = 2.0;
    let mut edit = false;
    let mut out = None;
    let mut it = args.iter();
    while let Some(a) = it.next() {
        match a.as_str() {
            "--sample" => sample = true,
            "--slide" => slide = Some(it.next().and_then(|v| v.parse().ok()).ok_or("--slide needs a number")?),
            "--all" => all = true,
            "--edit" => edit = true,
            "--scale" => scale = it.next().and_then(|v| v.parse().ok()).ok_or("--scale needs a number")?,
            "--help" | "-h" => {
                outln!("{USAGE}");
                return Ok(());
            }
            other if other.starts_with('-') => return Err(format!("unknown option `{other}`")),
            other
                if input.is_none()
                    && !sample
                    && !other.starts_with("--")
                    && out.is_none()
                    && !(other.ends_with(".png") || other.ends_with(".jpg"))
                    || (input.is_none() && !sample && std::path::Path::new(other).is_file()) =>
            {
                input = Some(other.to_string())
            }
            other => out = Some(other.to_string()),
        }
    }
    let out = out.ok_or("render needs an output path")?;
    let mut s = Session::new();
    open(&mut s, input.as_deref(), sample)?;
    let st = s.doc().map_err(|e| e.to_string())?;
    let n = st.doc.slides.len();
    let list = slide_indices(n, all, slide)?;
    if all {
        std::fs::create_dir_all(&out).map_err(|e| format!("{out}: {e}"))?;
    }
    for i in list {
        let (png, w, h) = deckcraft_engine::cmd::file::render_png(&st.doc, i, scale, edit);
        let path = if all { format!("{out}/slide-{:02}.png", i + 1) } else { out.clone() };
        std::fs::write(&path, png).map_err(|e| format!("{path}: {e}"))?;
        outln!("{path} ({w}×{h})");
    }
    Ok(())
}

/// Slides `--slide` asks for. `N` is a 0-based index, the same one `slide.go` uses.
/// `--all` still names files from 1 (`slide-01.png`), which is PowerPoint's slide number.
fn slide_indices(n: usize, all: bool, slide: Option<usize>) -> Result<Vec<usize>, String> {
    if all {
        return Ok((0..n).collect());
    }
    let i = slide.unwrap_or(0);
    if i >= n {
        return Err(missing_slide(i, n));
    }
    Ok(vec![i])
}

fn missing_slide(i: usize, n: usize) -> String {
    match n {
        0 => format!("no slide index {i} (this deck has no slides)"),
        1 => format!("no slide index {i} (this deck has 1 slide, index 0, which --all names slide-01.png)"),
        n => {
            let last = n - 1;
            format!(
                "no slide index {i} (this deck has {n} slides, numbered 0 through {last}; --all names them slide-01.png through slide-{n:02}.png)"
            )
        }
    }
}

/// Frames of slide N's transition (0-based N; from slide N-1, or black for the first slide) at
/// the given progress values. With several values, OUT gets `-t<value>` before its extension.
fn render_transition(args: &[String]) -> Result<(), String> {
    use deckcraft_engine::render;
    let mut input = None;
    let mut slide: Option<usize> = None;
    let mut ts: Vec<f64> = Vec::new();
    let mut width: Option<f64> = None;
    let mut out = None;
    let mut it = args.iter();
    while let Some(a) = it.next() {
        match a.as_str() {
            "--slide" => slide = Some(it.next().and_then(|v| v.parse().ok()).ok_or("--slide needs a number")?),
            "--t" => {
                let v = it.next().ok_or("--t needs a value")?;
                for x in v.split(',') {
                    let t: f64 = x.trim().parse().map_err(|_| format!("bad --t value `{x}`"))?;
                    if !t.is_finite() {
                        return Err(format!("bad --t value `{x}`"));
                    }
                    ts.push(t);
                }
            }
            "--width" => {
                width = Some(it.next().and_then(|v| v.parse().ok()).filter(|w: &f64| w.is_finite() && *w >= 1.0).ok_or("--width needs pixels")?)
            }
            other if input.is_none() => input = Some(other.to_string()),
            other => out = Some(other.to_string()),
        }
    }
    let input = input.ok_or("render-transition needs a FILE")?;
    let out = out.ok_or("render-transition needs an output path")?;
    let i = slide.ok_or("render-transition needs --slide N")?;
    if ts.is_empty() {
        return Err("render-transition needs --t".into());
    }
    let mut s = Session::new();
    open(&mut s, Some(&input), false)?;
    let st = s.doc().map_err(|e| e.to_string())?;
    let doc = &st.doc;
    let n = doc.slides.len();
    let Some(sl) = doc.slides.get(i) else { return Err(format!("no slide {i} (the deck has {n})")) };
    let sw = doc.slide_size.width.max(1.0);
    let w = width.unwrap_or(sw * 2.0).min(render::MAX_SIDE as f64);
    let opts = render::RenderOpts { scale: w / sw, ..Default::default() };
    let tr = sl.transition.clone().unwrap_or_default();
    // Render both slides once and composite every frame from them (morph re-renders per frame).
    let prev = i.checked_sub(1);
    let cached = (tr.kind != "morph").then(|| {
        let parts = render::uses_slide_parts(&tr.kind, &tr.option).then(|| render::SlideParts::render(doc, prev, i, &opts));
        (prev.map(|p| render::render_slide(doc, p, &opts)), render::render_slide(doc, i, &opts), parts)
    });
    let aspect = sw / doc.slide_size.height.max(1.0);
    for t in &ts {
        let img = match &cached {
            Some((old, new, parts)) => {
                render::composite_transition(old.as_ref(), new, parts.as_ref(), &render::transition_frame(&tr.kind, &tr.option, *t, aspect))
            }
            None => render::render_transition(doc, i, *t, &opts),
        };
        let path = if ts.len() == 1 {
            out.clone()
        } else {
            let p = std::path::Path::new(&out);
            let stem = p.file_stem().and_then(|x| x.to_str()).unwrap_or("frame");
            let name = format!("{stem}-t{t:.3}.png");
            p.with_file_name(name).to_string_lossy().into_owned()
        };
        std::fs::write(&path, img.to_png_at(render::dpi_for_scale(opts.scale))).map_err(|e| format!("{path}: {e}"))?;
        outln!("{path} ({}×{}) {} {} t={t}", img.width, img.height, tr.kind, tr.option);
    }
    Ok(())
}

fn convert(args: &[String]) -> Result<(), String> {
    if args.first().is_some_and(|a| is_help(a)) {
        outln!("{USAGE}");
        return Ok(());
    }
    let (Some(input), Some(out)) = (args.first(), args.get(1)) else { return Err("convert needs IN and OUT".into()) };
    let fmt = output_format(out)?;
    let mut s = Session::new();
    open(&mut s, Some(input), false)?;
    let r = if matches!(fmt, "png" | "jpeg") {
        s.execute("file.export", &json!({"path": out, "slide": 0}))
    } else {
        s.execute("file.saveAs", &json!({"path": out}))
    };
    r.map_err(|e| e.to_string())?;
    outln!("{out}");
    Ok(())
}

/// The format `convert`, `run --save` and `run --export` write to `path`, or an error naming the
/// supported extensions when `path`'s extension isn't one (rather than native bytes under that name).
fn output_format(path: &str) -> Result<&'static str, String> {
    use deckcraft_engine::cmd::file::{WRITABLE_EXTENSIONS, writable_format_for_path};
    writable_format_for_path(path).ok_or_else(|| {
        let ext = std::path::Path::new(path).extension().map(|e| format!(".{}", e.to_string_lossy())).unwrap_or_else(|| "(none)".into());
        format!("{path}: unsupported output format {ext} (supported: .{})", WRITABLE_EXTENSIONS.join(", ."))
    })
}

fn run(args: &[String]) -> Result<(), String> {
    let mut input = None;
    let mut sample = false;
    let mut cmds = vec![];
    let mut save = None;
    let mut export = None;
    let mut print = false;
    let mut it = args.iter();
    while let Some(a) = it.next() {
        match a.as_str() {
            "--in" => input = Some(it.next().cloned().ok_or("--in needs a file")?),
            "--sample" => sample = true,
            "--cmd" => cmds.push(it.next().cloned().ok_or("--cmd needs ID[=JSON]")?),
            "--save" => save = Some(it.next().cloned().ok_or("--save needs a path")?),
            "--export" => export = Some(it.next().cloned().ok_or("--export needs a path")?),
            "--print" => print = true,
            "--help" | "-h" => {
                outln!("{USAGE}");
                return Ok(());
            }
            other => return Err(format!("unknown option `{other}`")),
        }
    }
    for p in save.iter().chain(&export) {
        output_format(p)?;
    }
    let mut s = Session::new();
    open(&mut s, input.as_deref(), sample)?;
    for c in cmds {
        let (id, p) = match c.split_once('=') {
            Some((id, j)) => (id.to_string(), serde_json::from_str::<Value>(j).map_err(|e| format!("{id}: bad JSON: {e}"))?),
            None => (c.clone(), json!({})),
        };
        let r = s.execute(&id, &p).map_err(|e| e.to_string())?;
        if print {
            outln!("{id} → {r}");
        }
    }
    if let Some(p) = save {
        s.execute("file.saveAs", &json!({"path": p})).map_err(|e| e.to_string())?;
    }
    if let Some(p) = export {
        s.execute("file.export", &json!({"path": p})).map_err(|e| e.to_string())?;
    }
    Ok(())
}

fn describe(id: Option<&str>) -> Result<(), String> {
    if id.is_some_and(is_help) {
        outln!("{USAGE}");
        return Ok(());
    }
    let id = id.ok_or("describe needs a command id")?;
    let c = deckcraft_engine::find_command(id).ok_or_else(|| format!("unknown command `{id}`"))?;
    outln!("{}  —  {}\n  where:    {}\n  shortcut: {}\n  params:   {}", c.id, c.label, c.menu.join(" ▸ "), c.shortcut.unwrap_or("—"), c.params);
    Ok(())
}

fn app(args: &[String]) -> Result<(), String> {
    use deckcraft_mcp::{Backend, Remote, control_addr};
    let mut port = deckcraft_mcp::DEFAULT_PORT.to_string();
    let mut method: Option<String> = None;
    let mut rest = vec![];
    let mut it = args.iter();
    while let Some(a) = it.next() {
        match a.as_str() {
            "--port" => port = it.next().cloned().ok_or("--port needs a value")?,
            "--method" => method = Some(it.next().cloned().ok_or("--method needs a name")?),
            "--help" | "-h" => {
                outln!("{USAGE}");
                return Ok(());
            }
            other => rest.push(other.to_string()),
        }
    }
    let mut r = Remote::connect(&control_addr(&port))
        .map_err(|e| format!("no DeckCraft app on port {port} ({e}); start it with `deckcraft --control {port}`"))?;
    let parse = |s: Option<&String>| -> Result<Value, String> {
        s.map(|j| serde_json::from_str(j).map_err(|e| format!("bad JSON: {e}"))).transpose().map(|v| v.unwrap_or(json!({})))
    };
    let v = match method {
        Some(m) => r.call(&m, parse(rest.first())?)?,
        None => {
            let id = rest.first().ok_or("app needs a COMMAND or --method")?;
            r.call("engine.execute", json!({"command": id, "params": parse(rest.get(1))?}))?
        }
    };
    outln!("{}", serde_json::to_string_pretty(&v).unwrap_or_default());
    Ok(())
}

fn mcp(args: &[String]) -> Result<(), String> {
    use deckcraft_mcp::{Backend, Headless, Remote, Server, control_addr};
    let mut connect: Option<String> = None;
    let mut sample = false;
    let mut it = args.iter();
    while let Some(a) = it.next() {
        match a.as_str() {
            "--connect" => connect = Some(it.next().cloned().ok_or("--connect needs a port or host:port")?),
            "--sample" => sample = true,
            "--help" | "-h" => {
                outln!("{USAGE}");
                return Ok(());
            }
            other => return Err(format!("unknown mcp option `{other}`")),
        }
    }
    let backend: Box<dyn Backend> = match connect {
        Some(c) => Box::new(Remote::connect(&control_addr(&c)).map_err(|e| format!("can't reach the app at {c}: {e}"))?),
        None => {
            let mut h = Headless::new();
            if sample {
                deckcraft_engine::sample::open_sample(&mut h.session).map_err(|e| e.to_string())?;
            }
            Box::new(h)
        }
    };
    let mut server = Server::new(backend);
    let stdin = std::io::stdin();
    server.serve(stdin.lock(), std::io::stdout()).map_err(|e| e.to_string())
}

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

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

    #[test]
    fn render_help_prints_usage_and_writes_nothing() {
        assert!(render(&args(&["--help"])).is_ok());
        assert!(render(&args(&["-h"])).is_ok());
        assert!(!std::path::Path::new("--help").exists());
    }

    #[test]
    fn render_rejects_unknown_flag() {
        let err = render(&args(&["--sample", "--scael", "2", "out.png"])).unwrap_err();
        assert_eq!(err, "unknown option `--scael`");
        assert!(!std::path::Path::new("--scael").exists());
    }

    #[test]
    fn other_subcommands_accept_help() {
        assert!(info(&args(&["--help"])).is_ok());
        assert!(convert(&args(&["-h"])).is_ok());
        assert!(run(&args(&["--help"])).is_ok());
        assert!(describe(Some("--help")).is_ok());
        assert!(mcp(&args(&["-h"])).is_ok());
    }
}

#[cfg(test)]
mod slide_index_tests {
    use super::{missing_slide, slide_indices};

    #[test]
    fn slide_numbers_start_at_zero_and_files_at_one() {
        assert_eq!(slide_indices(8, false, None).ok().as_deref(), Some(&[0][..]));
        assert_eq!(slide_indices(8, false, Some(0)).ok().as_deref(), Some(&[0][..]));
        assert_eq!(slide_indices(8, false, Some(7)).ok().as_deref(), Some(&[7][..]));
        assert_eq!(slide_indices(8, true, None).ok().as_deref(), Some(&[0, 1, 2, 3, 4, 5, 6, 7][..]));
        let err = slide_indices(8, false, Some(8)).err().unwrap_or_default();
        assert!(!err.is_empty(), "index 8 was accepted");
        assert!(err.contains("numbered 0 through 7"), "{err}");
        assert!(err.contains("slide-01.png"), "{err}");
        assert!(err.contains("slide-08.png"), "{err}");
        assert!(missing_slide(0, 0).contains("no slides"));
        assert!(missing_slide(1, 1).contains("index 0"));
    }
}