prov-graph 0.8.0

//! Documents — a plaintext file with an embedded metadata block and a body,
//! or a config file whose *entire content* is the metadata.
//!
//! The two shapes are one model: a config file is simply a document whose
//! metadata carrier is the whole file and whose body is empty. Both parse to
//! the same [`Document`], link through the same relations, and participate in
//! traversal, validation, and mutation identically — which is what lets a
//! workspace mix prose documents and config documents in one tree.

use std::path::{Path, PathBuf};

use crate::error::Result;
use crate::meta::{self, Value};

/// The embed archetype a fenced metadata block was found in. Re-exported from
/// `fig`, which owns both detection (`fig::detect`) and the fence/format
/// coupling ([`EmbedType::inner_format`]).
pub use fig::EmbedType;

/// A document's prose body, and the file it was read from.
///
/// The two halves travel together because a *separated* document keeps them in
/// different files: the text comes from the `content` target while the metadata
/// stays in the node, so a caller that renders the prose needs to know which
/// path declares its grammar. For a combined document [`path`](Body::path) is
/// simply the document's own.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Body {
    /// The prose itself. Empty for a document that has none — a config
    /// document standing for itself, or a manifest node standing for a
    /// directory.
    pub text: String,
    /// The file the prose lives in: the document's own path when combined, its
    /// [`content_path`](Document::content_path) when separated. What
    /// [`ContentFormat::from_extension`](crate::content::ContentFormat::from_extension)
    /// should be asked about.
    pub path: PathBuf,
}

/// Where a document's metadata physically lives — recorded at parse time so a
/// write can preserve the original carrier exactly (a ```` ```fig ```` block is
/// never rewritten as `---` YAML; a bare `.yaml` file never grows fences).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MetaCarrier {
    /// A fenced block inside a host file (`---` YAML, `;;;` JSON,
    /// ```` ```fig ````, endmatter), with the prose body around it.
    Fenced(EmbedType),
    /// The entire file is the metadata (a config document); the body is empty.
    /// The format comes from the file extension.
    WholeFile(fig::Format),
}

impl MetaCarrier {
    /// The format the metadata is written in.
    pub fn format(&self) -> fig::Format {
        match self {
            MetaCarrier::Fenced(kind) => kind.inner_format(),
            MetaCarrier::WholeFile(format) => *format,
        }
    }
}

/// The whole-file metadata format implied by `path`'s extension, if any.
/// These are the extensions prov treats as config documents.
///
/// Each extension is recognized only when its format feature is compiled in: a
/// `.json` file is a config document under the `json` feature, and an ordinary
/// (metadata-less) prose document without it. This keeps prov from claiming
/// to read a format whose parser was left out of the build.
pub fn whole_file_format(path: &Path) -> Option<fig::Format> {
    match path.extension()?.to_str()? {
        #[cfg(feature = "yaml")]
        "yaml" | "yml" => Some(fig::Format::Yaml),
        #[cfg(feature = "json")]
        "json" => Some(fig::Format::Json),
        #[cfg(feature = "toml")]
        "toml" => Some(fig::Format::Toml),
        #[cfg(feature = "fig-lang")]
        "fig" | "figl" => Some(fig::Format::Fig),
        _ => None,
    }
}

/// Enforce that a **record store** at `path` (the id registry, the recycle-bin
/// index, a flat vocabulary) is a whole-file config document, returning its
/// format. A [`MetaCarrier::Fenced`] carrier — markdown frontmatter — is
/// rejected with [`Error::MarkdownStore`](crate::error::Error::MarkdownStore): prov re-lays-out these stores as a
/// sorted record list (DESIGN §5), so human prose has no stable home in them and
/// unambiguous extension→format sniffing depends on the carrier being whole-file.
/// The single choke point every store loader passes through, so the rule cannot
/// be enforced in one place and forgotten in another.
pub fn require_whole_file(path: &Path, carrier: MetaCarrier) -> Result<fig::Format> {
    match carrier {
        MetaCarrier::WholeFile(format) => Ok(format),
        MetaCarrier::Fenced(_) => Err(crate::error::Error::MarkdownStore(path.to_path_buf())),
    }
}

/// Whether prov can read `path` as text — a recognized body format
/// (Markdown/Djot/HTML) or a whole-file metadata format (YAML/JSON/…). Its
/// negation is an **opaque payload**: a file prov treats as bytes (an image,
/// a PDF, a font, any binary) and never parses. An *attachment* is exactly a
/// whole-file metadata sidecar whose `content` points at such a payload, which
/// is how an arbitrary file gains workspace-linked metadata without being able
/// to carry frontmatter itself.
pub fn is_opaque_payload(path: &Path) -> bool {
    crate::content::ContentFormat::from_extension(path).is_none()
        && whole_file_format(path).is_none()
}

/// The canonical whole-file extension for a metadata `format` — the inverse of
/// [`whole_file_format`]. Used when materializing a whole-file metadata document
/// (a config/registry sidecar, or the metadata half of a *separated* document):
/// `yaml`, `json`, `figl`. A format whose feature is not compiled falls back to
/// `yaml` (the always-present default).
pub fn whole_file_extension(format: fig::Format) -> &'static str {
    match format {
        #[cfg(feature = "json")]
        fig::Format::Json => "json",
        #[cfg(feature = "toml")]
        fig::Format::Toml => "toml",
        #[cfg(feature = "fig-lang")]
        fig::Format::Fig => "figl",
        _ => "yaml",
    }
}

/// The fenced-frontmatter carrier for `format` — the archetype a new document
/// gets when it inherits no parent block and the workspace default is `format`.
/// A format whose feature is not compiled falls back to YAML frontmatter (which
/// the default `yaml` feature always provides).
pub fn frontmatter_carrier(format: fig::Format) -> MetaCarrier {
    let embed = match format {
        #[cfg(feature = "json")]
        fig::Format::Json => EmbedType::FrontmatterJson,
        #[cfg(feature = "toml")]
        fig::Format::Toml => EmbedType::PlusToml,
        #[cfg(feature = "fig-lang")]
        fig::Format::Fig => EmbedType::FrontmatterFig,
        _ => EmbedType::FrontmatterYaml,
    };
    MetaCarrier::Fenced(embed)
}

/// The archetype *family* a workspace authors embedded metadata in — the
/// "embed type" the CLI's `init` prompts for, one level above the concrete
/// [`EmbedType`]. A family plus a metadata [`fig::Format`] resolves to a
/// carrier through [`embed_carrier`]: e.g. (`CodeBlock`, YAML) is a
/// ```` ```yaml ```` block, (`Delimited`, TOML) is a `+++` block, and
/// (`Separate`, JSON) is a whole-file `.json` sidecar. It is what the config
/// document records (via `prov`'s `WorkspaceConfig`) so a
/// workspace stays self-describing about *how* its metadata is embedded, not
/// just which format it is written in.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum EmbedStyle {
    /// Character-delimited frontmatter: `---` YAML, `+++` TOML, `;;;` JSON. A
    /// Markdown convention; the fig dialect has no delimiter form.
    Delimited,
    /// A typed fenced code block — ```` ```yaml ````, ```` ```toml ````,
    /// ```` ```json ````, ```` ```fig ```` — that renders as a visible block in
    /// Markdown or Djot.
    CodeBlock,
    /// An HTML `<script type="application/…">` data island (not rendered).
    HtmlScript,
    /// An HTML `<pre><code class="language-…">` visible code block.
    HtmlCode,
    /// Metadata kept in a sibling *whole-file* document, joined to a plain body
    /// file by a `content` attribute — neither file carries fences.
    Separate,
}

impl EmbedStyle {
    /// The `embed_type` config-document spelling for this style.
    pub fn as_config_str(self) -> &'static str {
        match self {
            EmbedStyle::Delimited => "delimited",
            EmbedStyle::CodeBlock => "code_block",
            EmbedStyle::HtmlScript => "html_script",
            EmbedStyle::HtmlCode => "html_code",
            EmbedStyle::Separate => "separate",
        }
    }

    /// Parse an `embed_type` config value. Unknown → `None` (keep the default).
    pub fn from_config_str(value: &str) -> Option<Self> {
        Some(match value {
            "delimited" => EmbedStyle::Delimited,
            "code_block" => EmbedStyle::CodeBlock,
            "html_script" => EmbedStyle::HtmlScript,
            "html_code" => EmbedStyle::HtmlCode,
            "separate" => EmbedStyle::Separate,
            _ => return None,
        })
    }
}

/// The [`EmbedStyle`] *family* a concrete [`EmbedType`] belongs to — the inverse
/// (on the style axis) of [`embed_carrier`], which resolves a `(style, format)`
/// pair back to a carrier. Pairing it with a new metadata format is how a
/// *format conversion* keeps a document's embedding shape while changing only its
/// frontmatter language: classify the current archetype, then [`embed_carrier`]
/// the same style with the target format.
///
/// The bare delimiter frontmatters (`---`/`+++`/`;;;`) and the labeled markdown
/// frontmatters (`---json`/`---toml`/`---fig`) are all [`Delimited`](EmbedStyle::Delimited);
/// [`embed_carrier`] then lands each format on prov's canonical delimiter
/// spelling. Endmatter is grouped with the fenced [`CodeBlock`](EmbedStyle::CodeBlock)
/// forms (it is a trailing ```` ```endmatter ```` block); converting it to another
/// format therefore moves it to a leading fenced block, since only YAML has an
/// endmatter archetype.
pub fn embed_style_of(kind: EmbedType) -> EmbedStyle {
    use EmbedType as E;
    match kind {
        E::FrontmatterYaml
        | E::FrontmatterJson
        | E::PlusToml
        | E::MdFrontmatterJson
        | E::MdFrontmatterToml
        | E::MdFrontmatterFig => EmbedStyle::Delimited,
        E::EndmatterYaml | E::FencedYaml | E::FencedJson | E::FencedToml | E::FrontmatterFig => {
            EmbedStyle::CodeBlock
        }
        E::HtmlScriptYaml | E::HtmlScriptJson | E::HtmlScriptToml | E::HtmlScriptFig => {
            EmbedStyle::HtmlScript
        }
        E::HtmlCodeYaml | E::HtmlCodeJson | E::HtmlCodeToml | E::HtmlCodeFig => {
            EmbedStyle::HtmlCode
        }
        // `EmbedType` is `#[non_exhaustive]`: a fig version newer than this crate
        // may detect an archetype prov doesn't know yet. Guessing a style here
        // would risk silently misclassifying a real document mid-`convert`, so
        // this needs an actual case added (here, `embed_carrier`, and the prose
        // in `about.rs`/`history/docs.rs`) before such a document can be handled.
        _ => unreachable!("unhandled fig::EmbedType variant — add a case in embed_style_of"),
    }
}

/// Resolve an [`EmbedStyle`] + metadata `format` to the carrier a new document
/// should get. `Separate` maps to a whole-file sidecar in `format`; every other
/// style maps to the concrete [`EmbedType`] for that `(style, format)` pair.
/// `None` for a combination that has no archetype — notably `Delimited` + fig
/// (the dialect has no `---`-style delimiter) and any fenced style paired with a
/// format fig cannot fence (`Zon`).
pub fn embed_carrier(style: EmbedStyle, format: fig::Format) -> Option<MetaCarrier> {
    use EmbedType as E;
    use fig::Format as F;
    // JSON's three dialects share one fenced/frontmatter archetype.
    let is_json = matches!(format, F::Json | F::Jsonc | F::Json5);
    let kind = match style {
        EmbedStyle::Separate => return Some(MetaCarrier::WholeFile(format)),
        EmbedStyle::Delimited => match format {
            F::Yaml => E::FrontmatterYaml,
            F::Toml => E::PlusToml,
            _ if is_json => E::FrontmatterJson,
            _ => return None,
        },
        EmbedStyle::CodeBlock => match format {
            F::Yaml => E::FencedYaml,
            F::Toml => E::FencedToml,
            F::Fig => E::FrontmatterFig,
            _ if is_json => E::FencedJson,
            _ => return None,
        },
        EmbedStyle::HtmlScript => match format {
            F::Yaml => E::HtmlScriptYaml,
            F::Toml => E::HtmlScriptToml,
            F::Fig => E::HtmlScriptFig,
            _ if is_json => E::HtmlScriptJson,
            _ => return None,
        },
        EmbedStyle::HtmlCode => match format {
            F::Yaml => E::HtmlCodeYaml,
            F::Toml => E::HtmlCodeToml,
            F::Fig => E::HtmlCodeFig,
            _ if is_json => E::HtmlCodeJson,
            _ => return None,
        },
    };
    Some(MetaCarrier::Fenced(kind))
}

/// A parsed document: its path, its embedded metadata, and its body text.
///
/// Metadata is stored as a dynamic [`Value`] (a mapping, or [`Value::Null`] when
/// the document has no frontmatter) because link fields are configurable and
/// therefore accessed dynamically.
#[derive(Debug, Clone)]
pub struct Document {
    /// Path this document was read from (workspace-relative or absolute — the
    /// caller decides; prov does not interpret it here).
    pub path: PathBuf,
    /// Parsed embedded metadata.
    pub meta: Value,
    /// Everything outside the metadata block (the host prose). Empty for a
    /// config document.
    pub body: String,
    /// Where the metadata was found, or `None` when the document has no
    /// (well-formed) metadata. Preserved on write.
    pub carrier: Option<MetaCarrier>,
}

impl Document {
    /// Parse a document from its full text.
    ///
    /// If `path` has a config extension (`.yaml`, `.yml`, `.json`, `.fig`,
    /// `.figl`), the entire text is the metadata and the body is empty.
    /// Otherwise the embedded metadata block is auto-detected via
    /// `fig::detect` — any archetype fig knows (`---` YAML, `;;;` JSON,
    /// ```` ```fig ````, ```` ```endmatter ````) — and parsed in that
    /// archetype's inner format. If there is no (well-formed) block, `meta`
    /// is [`Value::Null`] and the whole text is the body. An unterminated
    /// opening fence is treated as no metadata — we do not guess where it
    /// ends.
    pub fn parse(path: impl Into<PathBuf>, text: &str) -> Result<Self> {
        let path = path.into();
        if let Some(format) = whole_file_format(&path) {
            let meta = meta::parse_value(text, format)?;
            return Ok(Self {
                path,
                meta,
                body: String::new(),
                carrier: Some(MetaCarrier::WholeFile(format)),
            });
        }
        let (meta, body, carrier) = match fig::detect(text) {
            Some(kind) => match fig::Embed::extract(text, kind) {
                Ok(found) => (
                    meta::parse_value(found.content(), kind.inner_format())?,
                    // *Both* host sides, in file order. A block at an edge leaves
                    // one of them empty, which is every markdown document; a
                    // mid-document block — an HTML `<script>` island below a
                    // `<head>` — leaves text on both, and taking fig's one-sided
                    // `body()` view there silently drops everything above the
                    // island. What that cost: a body write losing the `<head>`,
                    // and `content_hash` covering a suffix while reporting that
                    // it covered the document (fig 3.3 exposes both sides).
                    [found.host_before(), found.host_after()].concat(),
                    Some(MetaCarrier::Fenced(kind)),
                ),
                // Detected by its open delimiter but with no matching close:
                // recognized-but-malformed degrades to "no metadata".
                Err(_) => (Value::Null, text.to_owned(), None),
            },
            None => (Value::Null, text.to_owned(), None),
        };
        Ok(Self {
            path,
            meta,
            body,
            carrier,
        })
    }

    /// Zero-copy counterpart to [`parse`](Self::parse): locate a fenced
    /// metadata block in `text` without parsing it, returning the
    /// [`MetaCarrier`] found and the three slices it borrows from `text` —
    /// `(meta_block, body_before, body_after)`. Mirrors
    /// `fig::detect`/`fig::Embed::extract` composed into one step, the same
    /// primitives `parse` builds its owned, parsed [`Value`] from.
    ///
    /// The body comes back in **two** pieces because a block need not sit at an
    /// edge. Frontmatter leaves `body_before` empty and endmatter leaves
    /// `body_after` empty, but an HTML `<script>` data island below a `<head>`
    /// has host text on both sides, and a single slice cannot name both — the
    /// one-sided view this used to return dropped whichever side it could not
    /// see. Concatenated in order they are [`Document::body`]; a caller
    /// splicing text back together wants them separate, since only their
    /// offsets say where the block sat.
    ///
    /// Only recognizes a *fenced* carrier — a whole-file (config) document has
    /// no split to offer, since its entire text already is the metadata; a
    /// caller steering by path extension (as `parse` does via
    /// [`whole_file_format`]) should check that first. Returns `None` when
    /// `text` opens no known archetype, or its opening fence has no matching
    /// close (an unterminated fence degrades to "no metadata", matching
    /// `parse`).
    ///
    /// The caller who wants the parsed [`Value`] should use [`parse`](Self::parse)
    /// instead; this exists for one who wants to defer parsing to their own
    /// deserializer, or just needs the raw borrowed text (e.g. to detect which
    /// archetype a document uses without allocating).
    pub fn split(text: &str) -> Option<(MetaCarrier, &str, &str, &str)> {
        let kind = fig::detect(text)?;
        let found = fig::Embed::extract(text, kind).ok()?;
        Some((
            MetaCarrier::Fenced(kind),
            found.content(),
            found.host_before(),
            found.host_after(),
        ))
    }

    /// The document's path.
    pub fn path(&self) -> &Path {
        &self.path
    }

    /// `true` if the document declares any embedded metadata mapping.
    pub fn has_meta(&self) -> bool {
        self.meta.as_mapping().is_some()
    }

    /// The raw `content` attribute — the relative path to a *separated*
    /// document's body file — or `None` for an ordinary (combined) document
    /// whose body is [`self.body`](Document::body). A separated document is a
    /// whole-file metadata document (`.yaml`/`.json`/`.figl`) that points at its
    /// prose body in a sibling file, keeping both halves plain text and linked.
    pub fn content_attr(&self) -> Option<&str> {
        self.meta.get("content").and_then(Value::as_str)
    }

    /// The raw `manifest` attribute — the relative path to the manifest
    /// document listing the files this node stands for — or `None` for a node
    /// that stands for itself.
    ///
    /// The bulk counterpart of [`content_attr`](Document::content_attr) and
    /// **mutually exclusive** with it: a node covers one payload or a set of
    /// them, never both. See [`manifest`](crate::manifest) for the record shape.
    pub fn manifest_attr(&self) -> Option<&str> {
        self.meta
            .get(crate::manifest::MANIFEST_KEY)
            .and_then(Value::as_str)
    }

    /// `true` when this document is a **manifest node**: it declares a
    /// `manifest` pointer, so the files it stands for are listed there rather
    /// than being a single `content` payload.
    pub fn is_manifest_node(&self) -> bool {
        self.manifest_attr().is_some()
    }

    /// `true` when this document declares *both* `content` and `manifest` —
    /// a node claiming to be a single payload's sidecar and a whole
    /// directory's at once. Neither reading is safe to pick, so the pair is
    /// reported rather than resolved.
    pub fn manifest_conflicts(&self) -> bool {
        self.content_attr().is_some() && self.manifest_attr().is_some()
    }

    /// The path of this document's separated body file — its `content` target
    /// joined onto its own directory — or `None` for a combined document, whose
    /// prose is [`self.body`](Document::body).
    ///
    /// Plain path joining, deliberately: `content` names a file *beside* the
    /// node (§5's placement rule), so this is the one link-ish value with no
    /// root-absolute spelling to honour, and staying free of the workspace-root
    /// coordinate is what lets a caller holding a real filesystem path — the
    /// CLI reading a file it was handed — resolve it the same way a caller
    /// holding a workspace-relative one does. Matches the resolution
    /// `attach`'s reverse lookup and the mutation verbs already make.
    pub fn content_path(&self, doc_path: &Path) -> Option<PathBuf> {
        let dir = doc_path.parent().unwrap_or(Path::new(""));
        Some(crate::link::normalize(dir.join(self.content_attr()?)))
    }

    /// The path of the file that actually holds this document's prose: its
    /// [`content_path`](Document::content_path) when separated, and `doc_path`
    /// itself when combined.
    ///
    /// This is the path whose extension declares the body's grammar
    /// ([`ContentFormat::from_extension`](crate::content::ContentFormat::from_extension)).
    /// Reading that off a separated document's *own* path asks a `.yaml` node
    /// what grammar its prose is in, and the honest answer — "none, a config
    /// file has no body" — is the wrong question rather than a wrong answer.
    pub fn body_path(&self, doc_path: &Path) -> PathBuf {
        self.content_path(doc_path)
            .unwrap_or_else(|| doc_path.to_path_buf())
    }

    /// `true` when this document is an **attachment sidecar**: a whole-file
    /// metadata document whose `content` points at an [opaque
    /// payload](is_opaque_payload) rather than a prose body. Recognized two ways,
    /// so a hand-written sidecar need not be verbose: an explicit `attachment:
    /// true` flag (what `prov`'s `Workspace::attach` writes),
    /// **or** a `content` target whose extension prov cannot read as text.
    ///
    /// A *separated prose* document (`content` → a `.md`/`.dj`/`.html` body) is
    /// deliberately **not** an attachment: its body is a prov document in its
    /// own right, scanned for links and titles; an attachment's payload is bytes
    /// prov never opens.
    pub fn is_attachment(&self) -> bool {
        match self.content_attr() {
            None => false,
            Some(content) => {
                self.meta.get("attachment").and_then(Value::as_bool) == Some(true)
                    || is_opaque_payload(Path::new(content))
            }
        }
    }
}

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

    #[cfg(feature = "yaml")]
    #[test]
    fn content_path_joins_the_target_onto_the_node_s_own_directory() {
        let doc = Document::parse("notes/a.yaml", "title: A\ncontent: a.md\n").unwrap();
        assert_eq!(
            doc.content_path(Path::new("notes/a.yaml")),
            Some(PathBuf::from("notes/a.md"))
        );
        assert_eq!(
            doc.body_path(Path::new("notes/a.yaml")),
            PathBuf::from("notes/a.md")
        );
    }

    /// The CLI resolves by real filesystem path, so the join must not assume a
    /// workspace-root coordinate.
    #[cfg(feature = "yaml")]
    #[test]
    fn content_path_resolves_an_absolute_node_path_as_absolute() {
        let doc = Document::parse("/vault/notes/a.yaml", "title: A\ncontent: a.md\n").unwrap();
        assert_eq!(
            doc.content_path(Path::new("/vault/notes/a.yaml")),
            Some(PathBuf::from("/vault/notes/a.md"))
        );
    }

    #[cfg(feature = "yaml")]
    #[test]
    fn a_combined_document_has_no_content_path_and_is_its_own_body_path() {
        let doc = Document::parse("notes/a.md", "---\ntitle: A\n---\nprose\n").unwrap();
        assert_eq!(doc.content_path(Path::new("notes/a.md")), None);
        assert_eq!(
            doc.body_path(Path::new("notes/a.md")),
            PathBuf::from("notes/a.md")
        );
    }

    #[cfg(feature = "yaml")]
    #[test]
    fn parses_yaml_frontmatter_and_body() {
        let text = "---\ntitle: Root\ncontents:\n- a.md\n---\n# Body\n\nhello\n";
        let doc = Document::parse("index.md", text).unwrap();
        assert_eq!(doc.meta.get("title").and_then(Value::as_str), Some("Root"));
        assert_eq!(doc.body, "# Body\n\nhello\n");
        assert_eq!(
            doc.carrier,
            Some(MetaCarrier::Fenced(EmbedType::FrontmatterYaml))
        );
        assert!(doc.has_meta());
    }

    #[cfg(feature = "fig-lang")]
    #[test]
    fn parses_fig_fenced_frontmatter() {
        let text = "```fig\ntitle = prov\ncontents = [docs/design.md]\n```\n# Body\n";
        let doc = Document::parse("README.md", text).unwrap();
        assert_eq!(doc.meta.get("title").and_then(Value::as_str), Some("prov"));
        assert_eq!(doc.body, "# Body\n");
        assert_eq!(
            doc.carrier,
            Some(MetaCarrier::Fenced(EmbedType::FrontmatterFig))
        );
        assert!(doc.has_meta());
    }

    #[cfg(feature = "json")]
    #[test]
    fn parses_json_frontmatter() {
        let text = ";;;\n{\"title\": \"Root\"}\n;;;\nbody\n";
        let doc = Document::parse("note.md", text).unwrap();
        assert_eq!(doc.meta.get("title").and_then(Value::as_str), Some("Root"));
        assert_eq!(
            doc.carrier,
            Some(MetaCarrier::Fenced(EmbedType::FrontmatterJson))
        );
    }

    #[cfg(feature = "yaml")]
    #[test]
    fn parses_yaml_endmatter() {
        let text = "# Body first\n```endmatter\ntitle: Tail\n```\n";
        let doc = Document::parse("note.md", text).unwrap();
        assert_eq!(doc.meta.get("title").and_then(Value::as_str), Some("Tail"));
        assert_eq!(doc.body, "# Body first\n");
        assert_eq!(
            doc.carrier,
            Some(MetaCarrier::Fenced(EmbedType::EndmatterYaml))
        );
    }

    #[cfg(feature = "yaml")]
    #[test]
    fn a_config_file_is_a_document_whose_content_is_all_metadata() {
        let text = "title: ID registry\npart_of: index.md\nregistry:\n  abc: a.md\n";
        let doc = Document::parse("registry.yaml", text).unwrap();
        assert_eq!(
            doc.meta.get("title").and_then(Value::as_str),
            Some("ID registry")
        );
        assert_eq!(
            doc.meta.get("part_of").and_then(Value::as_str),
            Some("index.md")
        );
        assert_eq!(doc.body, "");
        assert_eq!(doc.carrier, Some(MetaCarrier::WholeFile(fig::Format::Yaml)));
        assert!(doc.has_meta());
    }

    #[cfg(feature = "fig-lang")]
    #[test]
    fn a_fig_config_file_parses_the_dialect() {
        let text = "title = settings\npart_of = index.md\n";
        let doc = Document::parse("settings.figl", text).unwrap();
        assert_eq!(
            doc.meta.get("title").and_then(Value::as_str),
            Some("settings")
        );
        assert_eq!(doc.carrier, Some(MetaCarrier::WholeFile(fig::Format::Fig)));
    }

    #[test]
    fn embed_style_config_str_round_trips() {
        for style in [
            EmbedStyle::Delimited,
            EmbedStyle::CodeBlock,
            EmbedStyle::HtmlScript,
            EmbedStyle::HtmlCode,
            EmbedStyle::Separate,
        ] {
            assert_eq!(
                EmbedStyle::from_config_str(style.as_config_str()),
                Some(style)
            );
        }
        assert_eq!(EmbedStyle::from_config_str("nonsense"), None);
    }

    #[test]
    fn embed_carrier_resolves_style_and_format_to_a_carrier() {
        use fig::Format;
        let fenced = |k| Some(MetaCarrier::Fenced(k));
        // Delimited: the three delimiter formats, but the fig dialect has none.
        assert_eq!(
            embed_carrier(EmbedStyle::Delimited, Format::Yaml),
            fenced(EmbedType::FrontmatterYaml)
        );
        assert_eq!(
            embed_carrier(EmbedStyle::Delimited, Format::Toml),
            fenced(EmbedType::PlusToml)
        );
        assert_eq!(
            embed_carrier(EmbedStyle::Delimited, Format::Json),
            fenced(EmbedType::FrontmatterJson)
        );
        assert_eq!(embed_carrier(EmbedStyle::Delimited, Format::Fig), None);
        // Code block: fig lands in the ```fig block; the rest in ```lang blocks.
        assert_eq!(
            embed_carrier(EmbedStyle::CodeBlock, Format::Fig),
            fenced(EmbedType::FrontmatterFig)
        );
        assert_eq!(
            embed_carrier(EmbedStyle::CodeBlock, Format::Yaml),
            fenced(EmbedType::FencedYaml)
        );
        // HTML islands, both shapes.
        assert_eq!(
            embed_carrier(EmbedStyle::HtmlScript, Format::Json),
            fenced(EmbedType::HtmlScriptJson)
        );
        assert_eq!(
            embed_carrier(EmbedStyle::HtmlCode, Format::Toml),
            fenced(EmbedType::HtmlCodeToml)
        );
        // Separate is a whole-file sidecar in the chosen format (any format).
        assert_eq!(
            embed_carrier(EmbedStyle::Separate, Format::Yaml),
            Some(MetaCarrier::WholeFile(Format::Yaml))
        );
        assert_eq!(
            embed_carrier(EmbedStyle::Separate, Format::Fig),
            Some(MetaCarrier::WholeFile(Format::Fig))
        );
    }

    #[test]
    fn no_frontmatter_is_all_body() {
        let doc = Document::parse("note.md", "# Just a note\n").unwrap();
        assert!(doc.meta.is_null());
        assert_eq!(doc.body, "# Just a note\n");
        assert_eq!(doc.carrier, None);
        assert!(!doc.has_meta());
    }

    #[test]
    fn unterminated_fence_is_not_frontmatter() {
        let text = "---\ntitle: oops\nno closing fence\n";
        let doc = Document::parse("x.md", text).unwrap();
        assert!(doc.meta.is_null());
        assert_eq!(doc.body, text);
        assert_eq!(doc.carrier, None);
    }

    #[cfg(feature = "yaml")]
    #[test]
    fn split_borrows_yaml_frontmatter_and_body_without_parsing() {
        let text = "---\ntitle: Root\n---\n# Body\n\nhello\n";
        let (carrier, meta, before, after) = Document::split(text).unwrap();
        assert_eq!(carrier, MetaCarrier::Fenced(EmbedType::FrontmatterYaml));
        assert_eq!(meta, "title: Root\n");
        assert_eq!(before, "", "frontmatter has no host text above it");
        assert_eq!(after, "# Body\n\nhello\n");
        let body = after;
        // Byte-identical to what `parse` extracts, just unparsed and borrowed.
        let doc = Document::parse("x.md", text).unwrap();
        assert_eq!(doc.body, body);
    }

    #[cfg(feature = "yaml")]
    #[test]
    fn split_handles_crlf_line_endings() {
        let text = "---\r\ntitle: Root\r\n---\r\nbody\r\n";
        let (carrier, meta, before, after) = Document::split(text).unwrap();
        assert_eq!(carrier, MetaCarrier::Fenced(EmbedType::FrontmatterYaml));
        assert_eq!(meta, "title: Root\r\n");
        assert_eq!(before, "");
        assert_eq!(after, "body\r\n");
    }

    #[test]
    fn split_is_none_with_no_frontmatter() {
        assert_eq!(Document::split("# Just a note\n"), None);
    }

    #[test]
    fn split_is_none_for_an_unterminated_fence() {
        let text = "---\ntitle: oops\nno closing fence\n";
        assert_eq!(Document::split(text), None);
    }

    #[cfg(feature = "fig-lang")]
    #[test]
    fn split_recognizes_a_non_yaml_carrier() {
        let text = "```fig\ntitle = prov\n```\n# Body\n";
        let (carrier, meta, before, after) = Document::split(text).unwrap();
        assert_eq!(carrier, MetaCarrier::Fenced(EmbedType::FrontmatterFig));
        assert_eq!(meta, "title = prov\n");
        assert_eq!(before, "");
        assert_eq!(after, "# Body\n");
    }

    #[cfg(feature = "json")]
    #[test]
    fn split_recognizes_json_frontmatter() {
        let text = ";;;\n{\"title\": \"Root\"}\n;;;\nbody\n";
        let (carrier, meta, before, after) = Document::split(text).unwrap();
        assert_eq!(carrier, MetaCarrier::Fenced(EmbedType::FrontmatterJson));
        assert_eq!(meta, "{\"title\": \"Root\"}\n");
        assert_eq!(before, "");
        assert_eq!(after, "body\n");
    }

    /// A `<script>` island below a `<head>` has host text on *both* sides. fig's
    /// one-sided `body()` view returned only the tail, so the whole document head
    /// vanished from `doc.body` — and from everything reading it: a separated
    /// document's prose file, `prov body`, and the bytes `content_hash` covers.
    #[cfg(feature = "yaml")]
    #[test]
    fn a_mid_document_island_keeps_the_host_text_on_both_sides() {
        let text = concat!(
            "<!doctype html>\n",
            "<html><head><title>KEEP ME</title></head>\n",
            "<body>\n",
            "<script type=\"application/yaml\">\n",
            "title: Mid\n",
            "</script>\n",
            "<p>tail</p>\n",
            "</html>\n",
        );
        let doc = Document::parse("page.html", text).unwrap();
        assert_eq!(doc.meta.get("title").and_then(Value::as_str), Some("Mid"));
        assert!(
            doc.body.contains("KEEP ME"),
            "the head above the island was dropped: {:?}",
            doc.body
        );
        assert!(doc.body.contains("<p>tail</p>"), "the tail was dropped");

        // The two sides, in file order, and nothing of the block itself.
        let (_, meta, before, after) = Document::split(text).unwrap();
        assert_eq!(doc.body, format!("{before}{after}"));
        assert!(
            !doc.body.contains("<script"),
            "the island leaked into the body"
        );
        assert_eq!(meta, "title: Mid\n");
    }

    #[cfg(feature = "yaml")]
    #[test]
    fn crlf_fences_are_handled() {
        let text = "---\r\ntitle: Root\r\n---\r\nbody\r\n";
        let doc = Document::parse("x.md", text).unwrap();
        assert_eq!(
            doc.carrier,
            Some(MetaCarrier::Fenced(EmbedType::FrontmatterYaml))
        );
        assert_eq!(doc.body, "body\r\n");
        // Exact scalar — fig ≥ 2.1.1 treats \r\n as a single line break.
        assert_eq!(doc.meta.get("title").and_then(Value::as_str), Some("Root"));
    }
}