release_kit/

landing.rs

//! The target-side landing model: file kinds, parameter rendering, and
//! the routing block.
//!
//! Every landable file has a declared kind — `rendered` files release-kit
//! owns and may rewrite, `seeded` files the target tunes, `state` files
//! the release automation maintains — and a `rendered` file's bytes are a
//! deterministic function of the payload plus the landing parameters, so
//! a later command can compare what is on disk against what would be
//! written. The kinds are declared here, beside the payload, never
//! inferred at runtime; a test holds the table closed over every snippet.

pub mod manifest;

use camino::Utf8Path;
use serde::{Deserialize, Serialize};

use crate::diagnostic::{Diagnostic, Reason};
use crate::error::RkError;
use crate::{atomic, embedded};

/// Who owns a landed file's bytes after landing.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum Kind {
    /// release-kit owns it: a newer payload re-renders it, and a target
    /// edit is a conflict.
    Rendered,
    /// The target owns it: a starting point the project tunes, reported
    /// and never rewritten.
    Seeded,
    /// The release automation owns it: never written after the first
    /// landing, never compared.
    State,
}

impl Kind {
    /// The wire and report form.
    #[must_use]
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::Rendered => "rendered",
            Self::Seeded => "seeded",
            Self::State => "state",
        }
    }
}

/// The declared classification: every landable destination and its kind.
/// The workflow and pipeline files carry the release automation and the
/// OIDC permission, so release-kit owns them; the tool configurations are
/// per-project judgment; the two state files are rewritten by the release
/// automation itself.
const KINDS: [(&str, Kind); 12] = [
    (".github/workflows/release-plz.yml", Kind::Rendered),
    (".github/workflows/release-please.yml", Kind::Rendered),
    (".github/workflows/release.yml", Kind::Rendered),
    (".github/workflows/pr-title.yml", Kind::Rendered),
    (".gitlab-ci.yml", Kind::Rendered),
    (".gitlab/ci/mr-title.yml", Kind::Rendered),
    ("release-plz.toml", Kind::Seeded),
    ("dist-workspace.toml", Kind::Seeded),
    ("release-please-config.json", Kind::Seeded),
    ("cliff.toml", Kind::Seeded),
    (".release-please-manifest.json", Kind::State),
    ("VERSION", Kind::State),
];

/// The declared kind of a destination, or `None` for a file the payload
/// does not classify.
#[must_use]
pub fn kind_of(destination: &str) -> Option<Kind> {
    if destination == AGENTS_DESTINATION || destination == HOOKS_DESTINATION {
        return Some(Kind::Rendered);
    }
    KINDS
        .iter()
        .find(|(name, _)| *name == destination)
        .map(|(_, kind)| *kind)
}

/// The mechanical substitution sites in `rendered` files.
///
/// Known values, substituted identically everywhere each appears. The
/// owner is derived from the landing's `repo` parameter and the two scope
/// forms from its `scopes` list, so the landed bytes stay a deterministic
/// function of payload plus parameters.
pub const OWNER_TOKEN: &[u8] = b"OWNER";

/// The scope list, comma-joined: hook arguments and prose.
pub const SCOPES_CSV_TOKEN: &[u8] = b"RK_SCOPES_CSV";

/// The scope list, pipe-joined: the title checks' regular expression.
pub const SCOPES_PIPE_TOKEN: &[u8] = b"RK_SCOPES_PIPE";

/// Substitute the landing parameters into a `rendered` file's bytes.
///
/// The repository's owner — the project path's first segment — replaces
/// every `OWNER` occurrence, and the scope list replaces the two scope
/// tokens. An empty scope list leaves the scope tokens standing, which
/// only a preview renders under; an apply refuses before reaching here.
#[must_use]
pub fn render(baseline: &[u8], repo: &str, scopes: &[String]) -> Vec<u8> {
    let owner = repo.split('/').next().unwrap_or(repo);
    let mut out = substitute(baseline, OWNER_TOKEN, owner.as_bytes());
    if !scopes.is_empty() {
        out = substitute(&out, SCOPES_CSV_TOKEN, scopes.join(",").as_bytes());
        // The pipe form drops into an extended regular expression, where a
        // dot matches any character; among the characters `parse_scopes`
        // admits, the dot is the only special one, so `api.v1` escapes to
        // match itself alone.
        let pipe: Vec<String> = scopes.iter().map(|s| s.replace('.', "\\.")).collect();
        out = substitute(&out, SCOPES_PIPE_TOKEN, pipe.join("|").as_bytes());
    }
    out
}

/// Every `token` occurrence replaced with `value`.
fn substitute(baseline: &[u8], token: &[u8], value: &[u8]) -> Vec<u8> {
    let mut out = Vec::with_capacity(baseline.len());
    let mut rest = baseline;
    while let Some(at) = find(rest, token) {
        out.extend_from_slice(&rest[..at]);
        out.extend_from_slice(value);
        rest = &rest[at + token.len()..];
    }
    out.extend_from_slice(rest);
    out
}

/// The `--scopes` argument parsed into the recorded list.
///
/// Comma-separated, each scope non-empty and made of letters, digits, and
/// `_ . / -` — a set safe for the title checks' regular expression once
/// the renderer escapes the dot, the one special character among them.
///
/// # Errors
///
/// Returns [`RkError::Usage`] naming the offending scope, or the empty
/// list.
pub fn parse_scopes(raw: &str) -> Result<Vec<String>, RkError> {
    let scopes: Vec<String> = raw
        .split(',')
        .map(str::trim)
        .filter(|scope| !scope.is_empty())
        .map(str::to_owned)
        .collect();
    if scopes.is_empty() {
        return Err(RkError::Usage(
            "--scopes names no scope; pass a comma-separated list, e.g. --scopes api,cli".into(),
        ));
    }
    for scope in &scopes {
        let clean = scope
            .chars()
            .all(|c| c.is_ascii_alphanumeric() || matches!(c, '_' | '.' | '/' | '-'));
        if !clean {
            return Err(RkError::Usage(format!(
                "the scope '{scope}' carries a character outside letters, digits, and _ . / -"
            )));
        }
    }
    Ok(scopes)
}

/// First occurrence of `needle` in `haystack`.
fn find(haystack: &[u8], needle: &[u8]) -> Option<usize> {
    haystack
        .windows(needle.len())
        .position(|window| window == needle)
}

/// The destination the routing block splices into.
pub const AGENTS_DESTINATION: &str = "AGENTS.md";

/// The block's opening marker.
pub const BLOCK_BEGIN: &str = "<!-- BEGIN release-kit -->";

/// The block's closing marker.
pub const BLOCK_END: &str = "<!-- END release-kit -->";

/// The destination the hook block splices into.
pub const HOOKS_DESTINATION: &str = ".pre-commit-config.yaml";

/// The hook block's opening marker, a YAML comment at column zero.
pub const HOOKS_BEGIN: &str = "# BEGIN release-kit";

/// The hook block's closing marker.
pub const HOOKS_END: &str = "# END release-kit";

/// The top-level key the fresh hook file carries and the skills verify on
/// an existing one: the commit-msg and pre-push hooks run only where their
/// hook types are installed.
pub const HOOK_TYPES_LINE: &str = "default_install_hook_types: [pre-commit, commit-msg, pre-push]";

/// The routing block template: the whole of target-side governance. Seven
/// lines of operational discovery — work branches before it starts, the
/// commit contract, the files are owned, a convention governs them, and
/// where the convention lives — spliced into the target's `AGENTS.md` and
/// never grown into a method chapter. The scope token renders from the
/// landing's `scopes` parameter.
const ROUTING_BLOCK: &str = "<!-- BEGIN release-kit -->

## Releases

- This repository runs the release-kit convention; `rk method invariants` states what must stay true.
- Change nothing while on `master`: work starts on a short-lived branch — `<type>/<slug>` mirroring the squash title's type, or the forge-minted `<issue-id>-<slug>` — and reaches the trunk only through its pull request. When asked to implement or change code while the checkout sits on `master`, branch first.
- Land work through squash-merged pull requests. The request's title becomes the trunk's commit message, so it MUST be a scoped Conventional Commit; the body carries the context.
- Every commit follows the same scoped convention; the landed commit-msg hook enforces it, and the scopes this project accepts are `RK_SCOPES_CSV`.
- Never author a tag, and never hand-edit a generated artifact workflow.
- Run `rk status` before changing anything under `.github/workflows/` or `.gitlab-ci.yml`, or any file `.release-kit/manifest.json` names.
- The full method is `rk method --list`; the recovery paths are `rk method recovery`.

<!-- END release-kit -->";

/// The hook block template: the commit contract and the local mirrors of
/// the forge protections, as list items under the target's `repos:` key.
/// Each hook mirrors one named rule; every mirror dies to `--no-verify`,
/// so the forge protections stay the enforcement and these exist for the
/// refusal at the desk. The third-party hooks are pinned in
/// `versions.toml`; the scope token renders from the landing's `scopes`
/// parameter.
const HOOKS_BLOCK: &str = r#"# BEGIN release-kit
# The release convention's hooks. Install every stage they run at:
# pre-commit install --hook-type pre-commit --hook-type commit-msg --hook-type pre-push
  - repo: https://github.com/compilerla/conventional-pre-commit
    rev: v4.4.0
    hooks:
      - id: conventional-pre-commit
        stages: [commit-msg]
        args: [--strict, --force-scope, --scopes, 'RK_SCOPES_CSV']
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v6.0.0
    hooks:
      - id: no-commit-to-branch
        args: [--branch, master]
  - repo: local
    hooks:
      - id: rk-branch-name
        name: rk branch name
        language: system
        always_run: true
        pass_filenames: false
        entry: sh -c 'branch=$(git symbolic-ref --quiet --short HEAD) || exit 0; [ "$branch" = master ] && exit 0; printf %s "$branch" | grep -Eq "^((build|chore|ci|docs|feat|fix|perf|refactor|revert|style|test)/[A-Za-z0-9._/-]+|([0-9]+|[A-Z][A-Z0-9]+-[0-9]+)-[A-Za-z0-9._-]+|release[-/].+)$" && exit 0; echo "branch $branch is neither <type>/<slug> nor <issue-id>-<slug>; gh issue develop <issue> --checkout or its glab counterpart mints the linked form" >&2; exit 1'
      - id: rk-no-push-to-trunk
        name: rk no push to trunk
        stages: [pre-push]
        language: system
        always_run: true
        pass_filenames: false
        entry: sh -c '[ "$PRE_COMMIT_REMOTE_BRANCH" != refs/heads/master ] || { echo "the trunk takes no direct push; it is written through squash-merged pull requests alone" >&2; exit 1; }'
      - id: rk-no-hand-authored-tag
        name: rk no hand-authored tag
        stages: [pre-push]
        language: system
        always_run: true
        pass_filenames: false
        entry: sh -c 'case "$PRE_COMMIT_REMOTE_BRANCH" in refs/tags/v*) echo "never author a tag; the release automation mints every v* tag" >&2; exit 1;; esac'
      - id: rk-status-check
        name: rk status check
        language: system
        pass_filenames: false
        entry: rk status --check --target .
        files: '^(\.github/workflows/|\.gitlab-ci\.yml$|\.gitlab/ci/|AGENTS\.md$|\.release-kit/|\.pre-commit-config\.yaml$|release-plz\.toml$|dist-workspace\.toml$|release-please-config\.json$|cliff\.toml$|\.release-please-manifest\.json$|VERSION$)'
# END release-kit"#;

/// The routing block template, markers included, without a trailing
/// newline and with its scope token unrendered.
#[must_use]
pub const fn routing_block() -> &'static str {
    ROUTING_BLOCK
}

/// The hook block template, markers included, without a trailing newline
/// and with its scope token unrendered.
#[must_use]
pub const fn hooks_block() -> &'static str {
    HOOKS_BLOCK
}

/// The markers of a block destination, or `None` for a whole-file one.
#[must_use]
pub fn block_markers(destination: &str) -> Option<(&'static str, &'static str)> {
    match destination {
        AGENTS_DESTINATION => Some((BLOCK_BEGIN, BLOCK_END)),
        HOOKS_DESTINATION => Some((HOOKS_BEGIN, HOOKS_END)),
        _ => None,
    }
}

/// The marked block inside a document, markers included, or `None` where
/// the text carries no complete block.
#[must_use]
pub fn extract_block<'a>(text: &'a str, begin: &str, end: &str) -> Option<&'a str> {
    let start = text.find(begin)?;
    let stop = text[start..].find(end)? + start + end.len();
    Some(&text[start..stop])
}

/// The whole `AGENTS.md` content after splicing the rendered block.
///
/// A fresh file where none exists, the block replaced in place where one
/// is marked, appended after the target's own content otherwise —
/// release-kit owns the lines inside the markers, not the document.
#[must_use]
pub fn splice_agents_block(existing: Option<&str>, block: &str) -> String {
    existing.map_or_else(
        || format!("{block}\n"),
        |text| {
            extract_block(text, BLOCK_BEGIN, BLOCK_END).map_or_else(
                || format!("{}\n\n{block}\n", text.trim_end()),
                |found| text.replacen(found, block, 1),
            )
        },
    )
}

/// The whole `.pre-commit-config.yaml` content after splicing the
/// rendered hook block.
///
/// A fresh file carries the hook-types key, the `repos:` key, and the
/// block; a marked file takes the block in place; an unmarked file takes
/// it directly under its `repos:` line, above the target's own hooks. An
/// unmarked file with no `repos:` line is refused by name — the block's
/// entries are list items and have nowhere honest to go.
///
/// # Errors
///
/// The reason the block has no place, for the caller's refusal to carry.
pub fn splice_hooks_block(existing: Option<&str>, block: &str) -> Result<String, String> {
    let Some(text) = existing else {
        return Ok(format!("{HOOK_TYPES_LINE}\n\nrepos:\n{block}\n"));
    };
    if let Some(defect) = hooks_marker_defect(text) {
        return Err(defect);
    }
    if let Some(found) = extract_block(text, HOOKS_BEGIN, HOOKS_END) {
        return Ok(text.replacen(found, block, 1));
    }
    let mut out = String::with_capacity(text.len() + block.len() + 1);
    let mut placed = false;
    for line in text.split_inclusive('\n') {
        out.push_str(line);
        if !placed && line.trim_end() == "repos:" {
            if !out.ends_with('\n') {
                out.push('\n');
            }
            out.push_str(block);
            out.push('\n');
            placed = true;
        }
    }
    if placed {
        Ok(out)
    } else {
        Err(format!(
            "{HOOKS_DESTINATION} exists with no repos: line, so the hook block has nowhere to land"
        ))
    }
}

/// The one definition of an ill-formed hook file, shared by the splice
/// and every reader that judges one.
///
/// The hooks between the markers execute, so ownership must be
/// unambiguous: exactly one begin marker paired with exactly one end
/// marker after it, or none of either. A second begin is a second block
/// pre-commit would still run, and a marker without its pair — or an end
/// before its begin — is a block whose extent nothing can state.
#[must_use]
pub fn hooks_marker_defect(text: &str) -> Option<String> {
    let begins = text.matches(HOOKS_BEGIN).count();
    let ends = text.matches(HOOKS_END).count();
    if begins > 1 || ends > 1 {
        return Some(format!(
            "{HOOKS_DESTINATION} carries more than one release-kit marker pair; release-kit owns exactly one block"
        ));
    }
    match (text.find(HOOKS_BEGIN), text.find(HOOKS_END)) {
        (Some(begin), Some(end)) if end > begin => None,
        (None, None) => None,
        _ => Some(format!(
            "{HOOKS_DESTINATION} carries an unmatched or misordered release-kit marker, so the block's extent is ambiguous"
        )),
    }
}

/// How a projected artifact occupies its destination.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Placement {
    /// The artifact is the whole file.
    Whole,
    /// The artifact is the marked block inside the target's `AGENTS.md`.
    Block,
}

/// One artifact of the payload projection: what would land at one
/// destination, with the payload bytes it was rendered from.
#[derive(Debug)]
pub struct Entry {
    /// The destination, relative to the target root.
    pub destination: String,
    /// The declared kind.
    pub kind: Kind,
    /// Whole file, or the marked block.
    pub placement: Placement,
    /// The payload bytes before substitution — what `baseline_sha256`
    /// digests.
    pub baseline: Vec<u8>,
    /// The bytes a landing writes: substituted for `rendered` files,
    /// identical to the baseline otherwise.
    pub rendered: Vec<u8>,
}

/// The landable files of one `(technology, forge)` pair, as
/// `(destination, payload bytes)`.
///
/// # Errors
///
/// Returns [`RkError::Usage`] naming the known bindings for an unknown
/// technology, and the supported pairs for a pair with no files.
pub fn pair_files(tech: &str, forge: &str) -> Result<Vec<(String, &'static [u8])>, RkError> {
    // The shared zone is not a technology: `_shared/<forge>` composes into
    // every pair and never names one.
    if tech.starts_with('_') || embedded::SNIPPETS.get_dir(tech).is_none() {
        let known: Vec<String> = embedded::SNIPPETS
            .dirs()
            .map(|dir| dir.path().to_string_lossy().into_owned())
            .filter(|name| !name.starts_with('_'))
            .collect();
        return Err(RkError::Usage(format!(
            "unknown tech '{tech}'; the bindings are: {}",
            known.join(", ")
        )));
    }
    let pair = format!("{tech}/{forge}");
    let pair_dir = embedded::SNIPPETS.get_dir(&pair).ok_or_else(|| {
        let known: Vec<String> = embedded::SNIPPETS
            .dirs()
            .filter(|dir| !dir.path().to_string_lossy().starts_with('_'))
            .flat_map(include_dir::Dir::dirs)
            .map(|dir| dir.path().to_string_lossy().replace('/', ", "))
            .collect();
        RkError::Usage(format!(
            "the pair ({tech}, {forge}) has no landable files; the supported pairs are: {}",
            known.join("; ")
        ))
    })?;
    // Payload paths carry their zone prefix; destinations do not. The
    // shared zone lands first, and a destination both zones ship is a
    // payload defect refused by name, never one zone silently winning.
    let mut files: Vec<(String, &'static [u8])> = Vec::new();
    let shared = format!("_shared/{forge}");
    if let Some(shared_dir) = embedded::SNIPPETS.get_dir(&shared) {
        for (path, contents) in embedded::walk(shared_dir) {
            let rel = path
                .strip_prefix(&format!("{shared}/"))
                .map_or(path.as_str(), |rel| rel)
                .to_owned();
            files.push((rel, contents));
        }
    }
    for (path, contents) in embedded::walk(pair_dir) {
        let rel = path
            .strip_prefix(&format!("{pair}/"))
            .map_or(path.as_str(), |rel| rel)
            .to_owned();
        if files.iter().any(|(existing, _)| *existing == rel) {
            return Err(anyhow::anyhow!(
                "the shared zone and the pair ({tech}, {forge}) both ship {rel}; the payload is defective"
            )
            .into());
        }
        files.push((rel, contents));
    }
    Ok(files)
}

/// The whole payload projection for one pair under the `repo` and
/// `scopes` parameters: every snippet with its kind and rendered bytes,
/// plus the routing block and the hook block, sorted by destination.
///
/// # Errors
///
/// Returns the [`pair_files`] errors, and [`RkError::Other`] for a
/// snippet destination the kind table does not classify, which is a
/// defect in this binary.
pub fn projection(
    tech: &str,
    forge: &str,
    repo: &str,
    scopes: &[String],
) -> Result<Vec<Entry>, RkError> {
    let mut entries = Vec::new();
    for (destination, baseline) in pair_files(tech, forge)? {
        let kind = kind_of(&destination).ok_or_else(|| {
            anyhow::anyhow!("the payload does not classify {destination}; the kind table is stale")
        })?;
        let rendered = match kind {
            Kind::Rendered => render(baseline, repo, scopes),
            Kind::Seeded | Kind::State => baseline.to_vec(),
        };
        entries.push(Entry {
            destination,
            kind,
            placement: Placement::Whole,
            baseline: baseline.to_vec(),
            rendered,
        });
    }
    for (destination, template) in [
        (AGENTS_DESTINATION, ROUTING_BLOCK),
        (HOOKS_DESTINATION, HOOKS_BLOCK),
    ] {
        entries.push(Entry {
            destination: destination.to_owned(),
            kind: Kind::Rendered,
            placement: Placement::Block,
            baseline: template.as_bytes().to_vec(),
            rendered: render(template.as_bytes(), repo, scopes),
        });
    }
    entries.sort_by(|a, b| a.destination.cmp(&b.destination));
    Ok(entries)
}

/// The bytes an entry's destination currently holds: the whole file, or
/// the marked block extracted from the target's `AGENTS.md`. `None` means
/// the file — or the block — is absent.
///
/// # Errors
///
/// Any read failure other than the file being absent.
pub fn read_destination(target: &Utf8Path, entry: &Entry) -> std::io::Result<Option<Vec<u8>>> {
    read_recorded(target, &entry.destination)
}

/// The bytes a recorded destination currently holds, by the placement
/// its name implies.
///
/// The marked block for `AGENTS.md` and `.pre-commit-config.yaml`, the
/// whole file otherwise. `None` means the file — or the block — is
/// absent.
///
/// # Errors
///
/// Any read failure other than the file being absent.
pub fn read_recorded(target: &Utf8Path, destination: &str) -> std::io::Result<Option<Vec<u8>>> {
    let path = target.join(destination);
    let bytes = match std::fs::read(&path) {
        Ok(bytes) => bytes,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(None),
        Err(e) => return Err(e),
    };
    if let Some((begin, end)) = block_markers(destination) {
        let text = String::from_utf8_lossy(&bytes);
        Ok(extract_block(&text, begin, end).map(|block| block.as_bytes().to_vec()))
    } else {
        Ok(Some(bytes))
    }
}

/// What one detection pass resolved for a target-side verb, with the
/// override flags applied.
#[derive(Debug)]
pub struct Resolved {
    /// The forge whose payload applies.
    pub forge: String,
    /// The project path, where a flag or the remote names one.
    pub repo: Option<String>,
}

/// Resolve forge and repository in one pass: the flags override, the
/// `origin` remote answers otherwise.
///
/// An unrecognized host refuses rather than defaulting — landing one
/// forge's files into the other forge's project is a half-configured
/// repository that looks done.
///
/// # Errors
///
/// Returns [`RkError::Usage`] for an unknown `--forge` value, and a
/// refusal naming the override when no forge resolves.
pub fn resolve(
    target: &Utf8Path,
    forge_flag: Option<&str>,
    repo_flag: Option<&str>,
) -> Result<Resolved, RkError> {
    let forge_flag = forge_flag
        .map(|name| {
            crate::detect::Forge::parse(name).ok_or_else(|| {
                RkError::Usage(format!(
                    "unknown forge '{name}'; the forges are: github, gitlab"
                ))
            })
        })
        .transpose()?;
    let detected = crate::detect::detect(target.as_std_path());
    let forge = forge_flag
        .or(detected.forge)
        .map(|forge| forge.as_str().to_owned())
        .ok_or_else(|| {
            let message = detected.host.map_or_else(
                || "no forge detected: the target has no origin remote".to_owned(),
                |host| format!("no forge detected: the host {host} is not recognized"),
            );
            RkError::refusal(
                Diagnostic::new(Reason::ForgeUndetected, message)
                    .expected("a github.com or gitlab remote, or --forge")
                    .action("pass --forge <github|gitlab>"),
            )
        })?;
    Ok(Resolved {
        forge,
        repo: repo_flag.map(str::to_owned).or(detected.repo),
    })
}

/// The refusal a verb answers when it needs the `repo` parameter and
/// neither a flag nor the remote supplies one.
#[must_use]
pub fn repo_unresolved() -> RkError {
    RkError::missing(
        Diagnostic::new(
            Reason::ForgeUndetected,
            "no repository detected: the target has no origin remote",
        )
        .expected("an origin remote naming the project")
        .action("pass --repo <path>"),
    )
}

/// Land one entry: the whole file through the temp-plus-rename writer, or
/// the block spliced into its document and the whole document rewritten
/// the same way.
///
/// # Errors
///
/// Any write failure; the destination then holds what it held. An
/// unspliceable hook file surfaces as an error here only as a backstop —
/// [`hooks_splice_refusal`] is the check a verb runs before any write.
pub fn write_destination(target: &Utf8Path, entry: &Entry) -> std::io::Result<()> {
    let path = target.join(&entry.destination);
    match entry.placement {
        Placement::Whole => atomic::write(path.as_std_path(), &entry.rendered),
        Placement::Block => {
            let existing = match std::fs::read(&path) {
                Ok(bytes) => Some(String::from_utf8_lossy(&bytes).into_owned()),
                Err(e) if e.kind() == std::io::ErrorKind::NotFound => None,
                Err(e) => return Err(e),
            };
            let block = String::from_utf8_lossy(&entry.rendered).into_owned();
            let spliced = if entry.destination == HOOKS_DESTINATION {
                splice_hooks_block(existing.as_deref(), &block).map_err(std::io::Error::other)?
            } else {
                splice_agents_block(existing.as_deref(), &block)
            };
            atomic::write(path.as_std_path(), spliced.as_bytes())
        }
    }
}

/// The hook file's defect, read from the target: `None` for a missing
/// file or one the block can land in.
///
/// The one judgment every verb shares, covering every splice refusal —
/// ill-formed markers, and an unmarked file offering the block no
/// `repos:` line. Status reports it as rendered drift, upgrade collects
/// it as a conflict in preview and apply alike so no landing dies
/// half-written, and adopt lists it with its mismatches.
///
/// # Errors
///
/// Any read failure other than the file being absent.
pub fn hooks_file_defect(target: &Utf8Path) -> std::io::Result<Option<String>> {
    let path = target.join(HOOKS_DESTINATION);
    match std::fs::read(&path) {
        Ok(bytes) => {
            let text = String::from_utf8_lossy(&bytes);
            Ok(splice_hooks_block(Some(&text), HOOKS_BLOCK).err())
        }
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(None),
        Err(e) => Err(e),
    }
}

/// The refusal a landing verb answers before writing anything, where
/// the target's hook file offers the block no place.
///
/// Checked ahead of every write so the all-or-nothing property holds and
/// no landing dies half-written into `.pre-commit-config.yaml`.
///
/// # Errors
///
/// [`RkError::Refusal`] naming the file, and any read failure.
pub fn hooks_splice_refusal(target: &Utf8Path) -> Result<(), RkError> {
    hooks_file_defect(target)?.map_or(Ok(()), |reason| {
        Err(RkError::refusal(
            Diagnostic::new(
                Reason::StateDrift,
                format!("{reason}, and nothing was written"),
            )
            .expected("a .pre-commit-config.yaml the block can land in, or none")
            .action(format!(
                "resolve it in {}, then re-run",
                target.join(HOOKS_DESTINATION)
            ))
            .target_state("unchanged"),
        ))
    })
}

#[cfg(test)]
mod tests {
    #![allow(clippy::expect_used)]

    use super::{
        AGENTS_DESTINATION, BLOCK_BEGIN, BLOCK_END, HOOK_TYPES_LINE, HOOKS_BEGIN,
        HOOKS_DESTINATION, HOOKS_END, Kind, extract_block, hooks_block, kind_of, pair_files,
        parse_scopes, projection, render, routing_block, splice_agents_block, splice_hooks_block,
    };
    use crate::embedded;

    fn scopes(list: &[&str]) -> Vec<String> {
        list.iter().map(|s| (*s).to_owned()).collect()
    }

    /// Every snippet destination has a declared kind: a new landable file
    /// without a classification fails here, not at a landing. The shared
    /// zone's files are enumerated the same way.
    #[test]
    fn the_kind_table_closes_over_every_snippet() {
        for tech_dir in embedded::SNIPPETS.dirs() {
            for pair_dir in tech_dir.dirs() {
                let prefix = format!("{}/", pair_dir.path().to_string_lossy());
                for (path, _) in embedded::walk(pair_dir) {
                    let destination = path.strip_prefix(&prefix).unwrap_or(&path);
                    assert!(
                        kind_of(destination).is_some(),
                        "{destination}: no declared kind"
                    );
                }
            }
        }
        assert_eq!(kind_of(AGENTS_DESTINATION), Some(Kind::Rendered));
        assert_eq!(kind_of(HOOKS_DESTINATION), Some(Kind::Rendered));
        assert_eq!(kind_of("something-else.txt"), None);
    }

    /// Substitution is total and derives from the repo parameter's first
    /// segment, so a nested GitLab project path still yields its root
    /// namespace; the scope list renders in both joined forms.
    #[test]
    fn rendering_substitutes_every_owner_occurrence() {
        let baseline = b"if: repository_owner == 'OWNER'\n# OWNER again: OWNER\n";
        let rendered = render(baseline, "acme/sub/widget", &[]);
        let text = String::from_utf8(rendered).expect("rendered bytes stay text");
        assert_eq!(text, "if: repository_owner == 'acme'\n# acme again: acme\n");

        let baseline = b"scopes 'RK_SCOPES_CSV' match (RK_SCOPES_PIPE)\n";
        let rendered = render(baseline, "acme/widget", &scopes(&["api", "cli"]));
        let text = String::from_utf8(rendered).expect("rendered bytes stay text");
        assert_eq!(text, "scopes 'api,cli' match (api|cli)\n");

        // A dot is the one admitted character that is special in the
        // regular expression: it escapes, so `api.v1` matches only itself.
        let rendered = render(baseline, "acme/widget", &scopes(&["api.v1"]));
        let text = String::from_utf8(rendered).expect("rendered bytes stay text");
        assert_eq!(text, "scopes 'api.v1' match (api\\.v1)\n");
    }

    /// The scope argument parses to the recorded list, refusing the empty
    /// list and any scope that would not drop into the title regex.
    #[test]
    fn scope_parsing_refuses_the_unusable() {
        assert_eq!(
            parse_scopes("api, cli,guides/release").expect("a clean list parses"),
            scopes(&["api", "cli", "guides/release"])
        );
        assert!(parse_scopes("").is_err());
        assert!(parse_scopes(" , ").is_err());
        assert!(parse_scopes("api|cli").is_err());
        assert!(parse_scopes("a b").is_err());
    }

    /// The shared zone composes into every pair, lands first, and is
    /// absent from the technology listing an unknown tech names.
    #[test]
    fn the_shared_zone_composes_into_the_pair() {
        let files = pair_files("rust", "github").expect("the pair lists");
        assert!(
            files
                .iter()
                .any(|(dest, _)| dest == ".github/workflows/pr-title.yml"),
            "the shared title check lands with the pair"
        );
        let files = pair_files("rust", "gitlab").expect("the pair lists");
        assert!(
            files
                .iter()
                .any(|(dest, _)| dest == ".gitlab/ci/mr-title.yml"),
            "the shared title job lands with the pair"
        );
        let err = pair_files("_shared", "github").expect_err("the shared zone is no tech");
        let listing = err.to_string();
        let bindings = listing
            .split("the bindings are:")
            .nth(1)
            .expect("the refusal lists the bindings");
        assert!(!bindings.contains("_shared"), "{listing}");
    }

    /// A rendered projection carries no unsubstituted token and no
    /// mechanical sentinel; the one judgment sentinel stays in its seeded
    /// file.
    #[test]
    fn a_projection_renders_owned_files_and_keeps_seeded_judgment() {
        let entries = projection("rust", "github", "acme/widget", &scopes(&["api", "cli"]))
            .expect("the pair projects");
        let workflow = entries
            .iter()
            .find(|entry| entry.destination.ends_with("release-plz.yml"))
            .expect("the workflow projects");
        assert_eq!(workflow.kind, Kind::Rendered);
        let text = String::from_utf8_lossy(&workflow.rendered);
        assert!(!text.contains("OWNER"), "an owner token survived rendering");
        assert!(text.contains("'acme'"));
        assert!(!text.contains("TODO(release-kit)"));
        let title = entries
            .iter()
            .find(|entry| entry.destination.ends_with("pr-title.yml"))
            .expect("the title check projects");
        let text = String::from_utf8_lossy(&title.rendered);
        assert!(text.contains("api|cli"), "{text}");
        assert!(
            !text.contains("RK_SCOPES"),
            "a scope token survived: {text}"
        );
        let seeded = entries
            .iter()
            .find(|entry| entry.destination == "release-plz.toml")
            .expect("the seeded file projects");
        assert_eq!(seeded.kind, Kind::Seeded);
        assert_eq!(seeded.rendered, seeded.baseline);
        assert!(String::from_utf8_lossy(&seeded.rendered).contains("TODO(release-kit)"));
        for block in [AGENTS_DESTINATION, HOOKS_DESTINATION] {
            let entry = entries
                .iter()
                .find(|entry| entry.destination == block)
                .expect("both blocks are part of the projection");
            let text = String::from_utf8_lossy(&entry.rendered);
            assert!(!text.contains("RK_SCOPES"), "{block} kept a token: {text}");
            assert!(text.contains("api,cli"), "{block} lost the scopes: {text}");
        }
    }

    #[test]
    fn the_block_splices_into_every_agents_shape() {
        let block = routing_block();
        let fresh = splice_agents_block(None, block);
        assert_eq!(fresh, format!("{block}\n"));
        assert_eq!(extract_block(&fresh, BLOCK_BEGIN, BLOCK_END), Some(block));

        let appended = splice_agents_block(Some("# My project\n\nOwn rules.\n"), block);
        assert!(appended.starts_with("# My project\n\nOwn rules.\n\n<!-- BEGIN release-kit -->"));
        assert_eq!(
            extract_block(&appended, BLOCK_BEGIN, BLOCK_END),
            Some(block)
        );

        let stale = appended.replace("Never author a tag", "Do author a tag");
        let refreshed = splice_agents_block(Some(&stale), block);
        assert_eq!(
            extract_block(&refreshed, BLOCK_BEGIN, BLOCK_END),
            Some(block)
        );
        assert!(refreshed.starts_with("# My project"));
        assert_eq!(
            refreshed.matches("BEGIN release-kit").count(),
            1,
            "a re-splice must replace, not accumulate"
        );
    }

    /// The hook block lands under `repos:` in every honest shape and
    /// refuses the one dishonest shape by name.
    #[test]
    fn the_hook_block_splices_under_repos() {
        let block = hooks_block();
        let fresh = splice_hooks_block(None, block).expect("a fresh file splices");
        assert!(fresh.starts_with(HOOK_TYPES_LINE));
        assert!(fresh.contains("\nrepos:\n# BEGIN release-kit\n"));
        assert_eq!(extract_block(&fresh, HOOKS_BEGIN, HOOKS_END), Some(block));

        let own =
            "repos:\n  - repo: https://example.com/own\n    rev: v1\n    hooks:\n      - id: own\n";
        let spliced = splice_hooks_block(Some(own), block).expect("an unmarked file splices");
        assert!(spliced.starts_with("repos:\n# BEGIN release-kit\n"));
        assert!(spliced.contains("- id: own"), "the target's hooks survive");
        assert!(
            !spliced.contains(HOOK_TYPES_LINE),
            "an existing file's top level is the skills' duty, not the splice's"
        );

        let stale = spliced.replace("--force-scope", "--no-scope");
        let refreshed = splice_hooks_block(Some(&stale), block).expect("a marked file re-splices");
        assert_eq!(
            extract_block(&refreshed, HOOKS_BEGIN, HOOKS_END),
            Some(block)
        );
        assert_eq!(refreshed.matches(HOOKS_BEGIN).count(), 1);

        let err = splice_hooks_block(Some("minimum_pre_commit_version: '3.2.0'\n"), block)
            .expect_err("no repos: line refuses");
        assert!(err.contains("repos:"), "{err}");

        // The hooks between the markers execute, so ownership is exactly
        // one well-formed block: a duplicate or an unmatched marker
        // refuses rather than leaving a stale block active.
        let doubled = format!("repos:\n{block}\n{block}\n");
        let err = splice_hooks_block(Some(&doubled), block).expect_err("a second block refuses");
        assert!(err.contains("one block"), "{err}");
        let unmatched = "repos:\n# BEGIN release-kit\n  - repo: local\n";
        let err =
            splice_hooks_block(Some(unmatched), block).expect_err("an unmatched marker refuses");
        assert!(err.contains("unmatched"), "{err}");
    }

    /// One definition of an ill-formed hook file, for every reader: the
    /// well-formed shapes pass and each ambiguous shape names a defect.
    #[test]
    fn the_hook_marker_defects_are_named() {
        use super::hooks_marker_defect;
        let block = hooks_block();
        assert_eq!(hooks_marker_defect(""), None);
        assert_eq!(hooks_marker_defect(&format!("repos:\n{block}\n")), None);
        for (case, text) in [
            (
                "a second begin",
                format!("repos:\n{block}\n# BEGIN release-kit\n"),
            ),
            (
                "a second end",
                format!("repos:\n{block}\n# END release-kit\n"),
            ),
            (
                "an unpaired begin",
                "repos:\n# BEGIN release-kit\n".to_owned(),
            ),
            ("an unpaired end", "repos:\n# END release-kit\n".to_owned()),
            (
                "an end before its begin",
                "repos:\n# END release-kit\n# BEGIN release-kit\n".to_owned(),
            ),
        ] {
            assert!(
                hooks_marker_defect(&text).is_some(),
                "{case} must be a defect"
            );
        }
    }
}