tga 10.3.0

//! The tga → trusty-review authorship artifact (#5453, #6004).
//!
//! Why: owner ruling 2026-08-18 — the DD report needs a dedicated Authorship &
//! Key-Person Risk section carrying ownership concentration, bus factor,
//! single-author subsystems, and a high-level trailing-12-month trajectory.
//! #5468 (CLOSED) ruled all contributor-profiling derivation lives in tga,
//! never trusty-review — this module is that derivation. It mirrors
//! [`super::ticketing`]'s read-side shape (a pure query-and-serialize builder;
//! the caller writes the file), but is PER-REPOSITORY rather than
//! engagement-wide, because `commits.repository` distinguishes repositories
//! within tga's one-database-per-engagement audit flow and ownership is a
//! per-codebase question — mirrors the precedent
//! `RepositoryEntry.velocity: Option<PathBuf>` (DOC-67 §8 velocity spec) sets
//! for a per-repo artifact field, rather than ticketing's engagement-wide one.
//!
//! ## The five data traps (issue #5453) — what this module handles vs. caveats
//!
//! - **Bot commits** — HANDLED. [`is_bot`] excludes machine-authored commits
//!   (`dependabot`, `renovate[bot]`, `github-actions[bot]`, and similar) by a
//!   name/email pattern match before any aggregation runs.
//! - **Merge commits** — HANDLED. The query filters `is_merge = 0`; an
//!   inflated merger count never reaches the aggregation.
//! - **Identity aliases** — HANDLED, partially. Authors are grouped by the
//!   collection pass's own identity resolver
//!   (`collect::identity::IdentityResolver`, which populates
//!   `commits.author_id → authors.canonical_email`), so one person committing
//!   under several names or emails collapses to one author. A commit the
//!   resolver never linked (`author_id IS NULL`) is then routed through the
//!   CONFIRMED merges recorded in `authors.aliases` (#6142), so a merge an
//!   operator accepted applies to every figure here without a separate manual
//!   step. What stays split is an identity that is neither resolved nor
//!   merged — [`AuthorshipSummary::unresolved_authors`] counts exactly those,
//!   which is the honesty gate issue #5453 asked for. An identity that a
//!   HIGH-confidence suggestion would merge, but nobody has confirmed, is
//!   never merged silently; it raises
//!   [`AuthorshipSummary::identity_merge_risk`] instead (#6142).
//! - **Squash-merge attribution, vendored-path exclusion** — NOT handled (each
//!   needs, respectively: nothing extra for GitHub squash since
//!   `commits.author_name`/`author_email` already read the PR author verbatim,
//!   per issue #5453's own finding — the residual risk is a LOCAL `git merge
//!   --squash` by a human, which this derivation cannot distinguish from a
//!   real commit; and a vendored-path filter, which needs a configurable
//!   ignore-list this module does not have). Named explicitly in [`CAVEATS`],
//!   which the report section renders verbatim rather than silently omitting
//!   the limitation.
//!
//! What: [`AuthorshipSummary`], [`build_authorship_summary`] which reads it
//! from an open database for one repository, and
//! [`AuthorshipSummary::to_json`].
//! Test: `super::authorship_tests`.

use std::collections::{BTreeMap, HashMap};

use rusqlite::{params, Connection};
use serde::Serialize;

use crate::collect::identity::suggest::{detect_from_authors, Suggestion, HIGH_CONFIDENCE_CUTOFF};
use crate::core::errors::Result;

/// Schema tag written into the artifact — pairs with trusty-review's
/// `report::authorship::SUPPORTED_SCHEMA_MAJOR`.
pub const AUTHORSHIP_SCHEMA_VERSION: &str = "v0";

/// One repository's ownership/bus-factor/trajectory figures.
///
/// Why: this is the whole tga→trusty-review authorship seam. Every figure is
/// derived from `commits JOIN files`, never invented or estimated beyond the
/// stated approximations (see field docs).
/// What: `bus_factor` — the smallest number of top-touching authors whose
/// combined share reaches 50% of all counted file-touches; `top_author_share`
/// — the single largest author's share of all touches, as a percentage;
/// `single_author_subsystems` — top-level path segments touched by exactly
/// one non-bot author; `distinct_authors` and `monthly_trajectory` feed the
/// report's Key Facts block and the trailing-12-month narrative.
/// Test: `super::authorship_tests::builds_from_seeded_commits`.
#[derive(Debug, Clone, Default, PartialEq, Serialize)]
#[non_exhaustive]
pub struct AuthorshipSummary {
    /// Artifact schema tag; always [`AUTHORSHIP_SCHEMA_VERSION`].
    pub schema_version: String,
    /// The repository name these figures describe (matches `commits.repository`).
    pub repository: String,
    /// Distinct non-bot authors with at least one non-merge commit.
    pub distinct_authors: u64,
    /// Smallest number of top-touching authors whose combined file-touch
    /// share reaches 50%. `0` when there is no data.
    pub bus_factor: u64,
    /// The single largest author's share of all file-touches, in `0.0..=100.0`.
    pub top_author_share_pct: f64,
    /// Top-level path segments (e.g. `src`, `docs`) touched by exactly one
    /// non-bot author, sorted.
    pub single_author_subsystems: Vec<String>,
    /// One entry per active month in the trailing 12 months, oldest first.
    pub monthly_trajectory: Vec<MonthlyActivity>,
    /// Distinct raw commit identities the identity resolver never linked to an
    /// `authors` row (`commits.author_id IS NULL`) — issue #5453's honesty gate.
    ///
    /// Why: every such identity is grouped by its raw commit email instead of a
    /// canonical one, so its aliases stay split and concentration/bus factor
    /// read LOWER than reality. A nonzero count is the caveat a reader needs to
    /// discount the figures by; zero means every counted commit went through
    /// the resolver.
    /// Test: `super::authorship_tests::unresolved_authors_are_counted_and_caveated`.
    pub unresolved_authors: u64,
    /// Set when unconfirmed high-confidence alias suggestions touch the
    /// authors that determine this repository's concentration figures (#6142).
    ///
    /// Why: a confirmed merge is applied before the figures are computed, but
    /// a merge nobody has accepted yet is not — and silently auto-merging a
    /// suggestion would invent an identity the operator never approved. The
    /// flag is how the figures stay honest without that: it names the metrics
    /// at risk, the number of identities involved, and the command that
    /// resolves them.
    /// Test: `super::authorship_tests::suggested_but_unmerged_identity_raises_a_risk_flag`.
    pub identity_merge_risk: Option<IdentityMergeRisk>,
    /// Data-trap limitations this run did NOT correct for (issue #5453) —
    /// rendered verbatim by the report section's caption.
    pub caveats: Vec<String>,
}

/// The risk flag a report carries when suggested-but-unmerged identities
/// touch its concentration metrics (#6142).
///
/// Why: bus factor and top-author share are the two figures a split identity
/// distorts, and both distort in the same direction — they read LOWER than
/// reality. A reader needs to know which figures are affected, by how many
/// identities, and what to run.
/// What: the count of distinct suggested-but-unmerged source identities
/// touching the top-N authors, the names of the metrics they affect, and the
/// resolving command.
/// Test: `super::authorship_tests::suggested_but_unmerged_identity_raises_a_risk_flag`.
#[derive(Debug, Clone, Default, PartialEq, Serialize)]
#[non_exhaustive]
pub struct IdentityMergeRisk {
    /// Distinct identities suggested for merge, at or above
    /// [`crate::collect::identity::suggest::HIGH_CONFIDENCE_CUTOFF`], that no
    /// operator has confirmed and that touch a top-N author.
    pub suggested_unmerged: u64,
    /// Field names of the affected metrics on [`AuthorshipSummary`].
    pub affected_metrics: Vec<String>,
    /// The command that lists the suggestions so an operator can confirm them.
    pub resolve_command: String,
}

/// How many of the ranked authors count as "top-N" for the risk flag (#6142).
///
/// Why: bus factor and top-author share are determined by the head of the
/// ranked list, so a suggestion touching a long-tail author cannot move
/// either figure enough to warrant a flag. Ten is generous relative to the
/// bus-factor cohort a real repository produces, which keeps the flag from
/// under-reporting.
/// Test: `super::authorship_tests::a_long_tail_suggestion_does_not_flag`.
const TOP_N_AUTHORS: usize = 10;

/// The metric fields a split identity distorts, named in the risk flag.
const RISK_AFFECTED_METRICS: &[&str] = &["bus_factor", "top_author_share_pct"];

/// The command a reader runs to resolve the flagged suggestions.
const RISK_RESOLVE_COMMAND: &str = "tga aliases suggest";

/// One month's active-author/commit-volume figures.
#[derive(Debug, Clone, Default, PartialEq, Serialize)]
#[non_exhaustive]
pub struct MonthlyActivity {
    /// `YYYY-MM`.
    pub month: String,
    /// Distinct non-bot authors with a non-merge commit in this month.
    pub active_authors: u64,
    /// Distinct non-merge, non-bot commits in this month.
    ///
    /// Why: the source query returns one row per file a commit touched, so
    /// this figure is a count of distinct `commits.id` values, never of rows
    /// (#6082 — a row count reported ~10x reality on a repository whose
    /// commits average ten files each).
    /// Test: `super::authorship_tests::commits_count_commits_not_file_touches`.
    pub commits: u64,
}

/// The standing caveats every artifact this module writes carries (#5453).
const CAVEATS: &[&str] = &[
    "Squash-merge attribution: a GitHub squash-merge preserves the PR author, but a local \
     `git merge --squash` by a human does not — this run cannot distinguish the two.",
    "Identity aliases are merged only as far as the collection pass resolved them: authors \
     are grouped by `authors.canonical_email` where the resolver linked the commit, and by the \
     raw commit email where it did not.",
    "No vendored-path exclusion: a checked-in vendor/dependency directory can make its \
     committer look like the sole owner of thousands of paths.",
];

/// The caveat naming an unresolved-identity count, for a run that has one.
///
/// Why: a standing caveat a reader sees on every report teaches them to skip
/// it; this one appears only when the figure is nonzero, and carries the
/// figure. Splitting an author across aliases lowers every concentration
/// number, so the direction of the error is stated too.
fn unresolved_caveat(count: u64) -> String {
    format!(
        "{count} commit identity/identities in this repository were never linked to a resolved \
         author, so their aliases stay split — concentration and bus factor read LOWER than \
         reality by that much."
    )
}

/// The caveat naming the suggested-but-unmerged identities (#6142).
///
/// Why: the structured [`IdentityMergeRisk`] is what a machine reads; a
/// renderer that only prints [`AuthorshipSummary::caveats`] would otherwise
/// drop the flag entirely.
fn suggested_merge_caveat(risk: &IdentityMergeRisk) -> String {
    format!(
        "{count} identity/identities are suggested for merge but not confirmed, and they touch \
         the authors behind {metrics} — both read LOWER than reality until the merges are \
         accepted. Run `{command}` to review them; nothing is merged automatically.",
        count = risk.suggested_unmerged,
        metrics = risk.affected_metrics.join(" and "),
        command = risk.resolve_command,
    )
}

/// Map every CONFIRMED alias to the canonical email that owns it (#6142).
///
/// Why: `tga aliases merge` records an accepted merge two ways — it reassigns
/// `commits.author_id` for the commits present at merge time, and it appends
/// the source email to the destination's `authors.aliases`. Only the second
/// survives a later collect that re-observes the source email on new commits
/// the resolver does not link, so a report reading `author_id` alone lets a
/// confirmed merge silently come apart. Reading the alias list closes that.
/// What: one lowercased `alias → canonical_email` entry per element of every
/// row's `aliases` JSON array. Malformed JSON yields no entries for that row
/// rather than failing the report. Suggestions are never in this map — only
/// merges an operator accepted.
/// Test: `super::authorship_tests::confirmed_alias_merge_collapses_the_authorship_metric`.
///
/// # Errors
///
/// Propagates [`crate::core::errors::TgaError::DbError`].
fn confirmed_alias_map(conn: &Connection) -> Result<HashMap<String, String>> {
    let mut stmt = conn.prepare("SELECT canonical_email, aliases FROM authors")?;
    let rows = stmt.query_map([], |row| {
        Ok((
            row.get::<_, String>(0)?,
            row.get::<_, Option<String>>(1)?.unwrap_or_default(),
        ))
    })?;

    let mut map: HashMap<String, String> = HashMap::new();
    for row in rows {
        let (canonical, aliases_json) = row?;
        if canonical.is_empty() {
            continue;
        }
        // #6142 review: a row whose `aliases` value will not parse is treated
        // as having none, which silently un-applies a merge the operator
        // accepted. The fallback stays — one bad row must not fail the whole
        // report — but it is named on stderr with the author it belongs to.
        let aliases: Vec<String> = match serde_json::from_str(&aliases_json) {
            Ok(aliases) => aliases,
            Err(e) => {
                if !aliases_json.trim().is_empty() {
                    tracing::warn!(
                        author = %canonical,
                        error = %e,
                        "authors.aliases is not a JSON array of strings; this author's confirmed \
                         merges are not applied to the authorship figures"
                    );
                }
                Vec::new()
            }
        };
        for alias in aliases {
            let key = alias.to_lowercase();
            if key.is_empty() || key == canonical.to_lowercase() {
                continue;
            }
            map.insert(key, canonical.clone());
        }
    }
    Ok(map)
}

/// Every high-confidence merge suggestion the `authors` table alone supports.
///
/// Why (#6142 review): the suggestion scan cross-joins every distinct email
/// against every other to compute Levenshtein distances, so it costs O(n²) in
/// identities. `build_authorship_summary` runs once per REPOSITORY but the
/// `authors` table is shared across all of them, so calling it inside the
/// summary paid that cost once per repository for an identical answer. The
/// caller runs this once per audit and passes the result to every repository.
/// What: the author-table passes at [`HIGH_CONFIDENCE_CUTOFF`]. The commit-SHA
/// pass is deliberately excluded — it scans every row of `commits`, which a
/// report cannot afford on a large extract database. `canonical_domain`
/// enables the `.local` / GitHub-noreply / domain-typo signals; passing `None`
/// mutes exactly the signals issue #6142 names, so a caller with a configured
/// domain must thread it through.
/// Test: `super::authorship_tests::the_configured_domain_reaches_the_risk_flag`.
///
/// # Errors
///
/// Propagates [`crate::core::errors::TgaError::DbError`].
pub fn merge_suggestions(
    conn: &Connection,
    canonical_domain: Option<&str>,
) -> Result<Vec<Suggestion>> {
    detect_from_authors(conn, canonical_domain, HIGH_CONFIDENCE_CUTOFF)
}

/// The risk flag for suggested-but-unmerged identities touching `ranked`.
///
/// Why (#6142): only a suggestion that would move `ranked`'s head can move
/// bus factor or top-author share, so a flag naming every suggestion in the
/// database would be noise a reader learns to skip.
/// What: keeps the [`merge_suggestions`] pairs with either endpoint among the
/// first [`TOP_N_AUTHORS`] ranked authors, drops any whose source is already a
/// confirmed alias of its destination, and counts the distinct source
/// identities. Returns `None` when that count is zero.
/// Test: `super::authorship_tests::{suggested_but_unmerged_identity_raises_a_risk_flag,
/// a_long_tail_suggestion_does_not_flag}`.
fn identity_merge_risk(
    suggestions: &[Suggestion],
    alias_map: &HashMap<String, String>,
    ranked: &[(&String, &u64)],
) -> Option<IdentityMergeRisk> {
    let top: std::collections::BTreeSet<String> = ranked
        .iter()
        .take(TOP_N_AUTHORS)
        .map(|(email, _)| email.to_lowercase())
        .collect();
    if top.is_empty() {
        return None;
    }

    let touching: std::collections::BTreeSet<String> = suggestions
        .iter()
        // A pair the operator already merged is not "unmerged", however the
        // detector still scores it (#6142 review).
        .filter(|s| !alias_map.contains_key(&s.src.to_lowercase()))
        .filter(|s| top.contains(&s.src.to_lowercase()) || top.contains(&s.dst.to_lowercase()))
        .map(|s| s.src.to_lowercase())
        .collect();

    if touching.is_empty() {
        return None;
    }
    Some(IdentityMergeRisk {
        suggested_unmerged: touching.len() as u64,
        affected_metrics: RISK_AFFECTED_METRICS
            .iter()
            .map(|s| s.to_string())
            .collect(),
        resolve_command: RISK_RESOLVE_COMMAND.to_string(),
    })
}

/// Name/email substrings identifying a machine-authored commit (issue #5453).
///
/// Why: a case-insensitive substring match is deliberately permissive — a
/// missed bot inflates a human's apparent ownership, which is the more
/// dangerous direction of error for a key-man risk figure.
const BOT_MARKERS: &[&str] = &[
    "[bot]",
    "dependabot",
    "renovate",
    "github-actions",
    "gitlab-ci",
    "greenkeeper",
];

/// True when `name` or `email` identifies a machine author.
fn is_bot(name: &str, email: &str) -> bool {
    let name = name.to_ascii_lowercase();
    let email = email.to_ascii_lowercase();
    BOT_MARKERS
        .iter()
        .any(|m| name.contains(m) || email.contains(m))
}

/// The top-level path segment of a file path — this module's "subsystem".
fn subsystem_of(path: &str) -> String {
    path.split('/').next().unwrap_or(path).to_string()
}

/// The `YYYY-MM` key of an ISO-8601 timestamp (first 7 characters).
fn month_of(timestamp: &str) -> Option<String> {
    timestamp.get(0..7).map(str::to_string)
}

/// [`build_authorship_summary_with`] for a caller that has no suggestion set.
///
/// Why (#6142 review): the suggestion set became a required parameter when the
/// scan moved out to the audit caller, which would break every existing caller
/// of this function. Keeping the previous signature working keeps tga's public
/// surface additive.
/// What: runs [`merge_suggestions`] itself, then delegates. That scan is O(n²)
/// in identities, so this wrapper pays one full scan PER CALL — a caller
/// summarising several repositories from one database should call
/// [`build_authorship_summary_with`] with a set scanned once. It also passes
/// `None` for the canonical domain, which mutes the `.local`, GitHub-noreply
/// and domain-typo signals; a caller with a configured domain must use
/// [`build_authorship_summary_with`].
/// Test: `super::authorship_tests::the_wrapper_scans_its_own_suggestions`.
///
/// # Errors
///
/// Propagates [`crate::core::errors::TgaError::DbError`] from the scan or the
/// summary queries.
pub fn build_authorship_summary(conn: &Connection, repository: &str) -> Result<AuthorshipSummary> {
    let suggestions = merge_suggestions(conn, None)?;
    build_authorship_summary_with(conn, repository, &suggestions)
}

/// Build one repository's authorship summary from an open database.
///
/// Why: the single function that reads `commits JOIN files` for this artifact
/// — every other item in this module is a pure helper it calls.
/// What: reads every non-merge commit for `repository`, drops bot-authored
/// rows (issue #5453), then aggregates: per-author file-touch counts (for
/// bus factor / concentration), per-subsystem author sets (for single-author
/// subsystems), and per-month distinct-author/commit counts limited to the
/// most recent 12 active months (for the trajectory).
///
/// The `JOIN files` returns one row per file a commit touched, so every
/// per-COMMIT figure deduplicates on `commits.id` while every per-TOUCH figure
/// counts rows (#6082).
///
/// Authors are keyed on `authors.canonical_email` via a LEFT JOIN on
/// `commits.author_id` — the identity resolver's own output (#5453 requires
/// reusing it rather than re-grouping raw commit emails). A commit the resolver
/// never linked keeps its raw email as the key and is counted into
/// [`AuthorshipSummary::unresolved_authors`].
/// `suggestions` comes from [`merge_suggestions`] and is supplied by the
/// caller rather than computed here: the scan is O(n²) in identities and the
/// `authors` table is shared across every repository in one database, so
/// computing it per repository paid that cost repeatedly for one answer
/// (#6142 review).
/// Test: `super::authorship_tests::{builds_from_seeded_commits,
/// bots_and_merges_are_excluded, shared_subsystem_is_not_single_author,
/// aliases_collapse_through_the_identity_resolver,
/// unresolved_authors_are_counted_and_caveated}`.
///
/// # Errors
///
/// Propagates [`crate::core::errors::TgaError::DbError`] from either query.
pub fn build_authorship_summary_with(
    conn: &Connection,
    repository: &str,
    suggestions: &[Suggestion],
) -> Result<AuthorshipSummary> {
    // #6142: confirmed merges are applied before any figure is computed;
    // unconfirmed suggestions never are — they only raise the risk flag below.
    let alias_map = confirmed_alias_map(conn)?;
    let mut stmt = conn.prepare(
        "SELECT c.id, c.author_name, c.author_email, a.canonical_email, c.timestamp, f.path \
         FROM commits c \
         JOIN files f ON f.commit_id = c.id \
         LEFT JOIN authors a ON a.id = c.author_id \
         WHERE c.repository = ?1 AND c.is_merge = 0",
    )?;
    let rows = stmt.query_map(params![repository], |row| {
        Ok((
            row.get::<_, i64>(0)?,
            row.get::<_, String>(1)?,
            row.get::<_, String>(2)?,
            row.get::<_, Option<String>>(3)?,
            row.get::<_, String>(4)?,
            row.get::<_, String>(5)?,
        ))
    })?;

    let mut touches_by_author: BTreeMap<String, u64> = BTreeMap::new();
    let mut authors_by_subsystem: BTreeMap<String, std::collections::BTreeSet<String>> =
        BTreeMap::new();
    let mut months: BTreeMap<String, std::collections::BTreeSet<String>> = BTreeMap::new();
    // #6082: keyed on `commits.id`, not incremented per row — one row arrives
    // per file touched, so a counter here reports file-touches as commits.
    let mut month_commits: BTreeMap<String, std::collections::BTreeSet<i64>> = BTreeMap::new();
    let mut unresolved: std::collections::BTreeSet<String> = std::collections::BTreeSet::new();

    for row in rows {
        let (commit_id, name, email, canonical_email, timestamp, path) = row?;
        if is_bot(&name, &email) {
            continue;
        }
        let raw_key = if email.is_empty() {
            name.clone()
        } else {
            email.clone()
        };
        // A CONFIRMED merge (#6142) outranks the resolver on both paths.
        //
        // The resolver's answer is routed through the alias map too (#6142
        // review): `upsert_observed_authors` relinks every `author_id IS NULL`
        // commit on each collect, and a commit re-observed under a merged-away
        // email gets a freshly created row for that email — so the resolver
        // answers with the SOURCE address the merge deleted, and reading it
        // uncritically lets the merge come apart. An unlinked commit is routed
        // through the same map on its raw email. Only when both miss does the
        // commit keep its raw identity and count as an honesty caveat (#5453).
        let resolved = canonical_email.filter(|e| !e.is_empty());
        let author_key = match resolved {
            Some(canonical) => match alias_map.get(&canonical.to_lowercase()) {
                Some(merged) => merged.clone(),
                None => canonical,
            },
            None => match alias_map.get(&raw_key.to_lowercase()) {
                Some(canonical) => canonical.clone(),
                None => {
                    unresolved.insert(raw_key.clone());
                    raw_key
                }
            },
        };
        *touches_by_author.entry(author_key.clone()).or_insert(0) += 1;
        authors_by_subsystem
            .entry(subsystem_of(&path))
            .or_default()
            .insert(author_key.clone());
        if let Some(month) = month_of(&timestamp) {
            months.entry(month.clone()).or_default().insert(author_key);
            month_commits.entry(month).or_default().insert(commit_id);
        }
    }

    let total_touches: u64 = touches_by_author.values().sum();
    let mut ranked: Vec<(&String, &u64)> = touches_by_author.iter().collect();
    ranked.sort_by_key(|(_, n)| std::cmp::Reverse(**n));

    let top_author_share_pct = match ranked.first() {
        Some((_, n)) if total_touches > 0 => (**n as f64 / total_touches as f64) * 100.0,
        _ => 0.0,
    };
    let bus_factor = bus_factor_of(&ranked, total_touches);

    let mut single_author_subsystems: Vec<String> = authors_by_subsystem
        .into_iter()
        .filter(|(_, authors)| authors.len() == 1)
        .map(|(subsystem, _)| subsystem)
        .collect();
    single_author_subsystems.sort();

    // Trailing 12 active months, oldest first — matches the report's
    // "trajectory by month" framing without depending on wall-clock "now",
    // which would make two runs of the same database disagree.
    let mut month_keys: Vec<String> = months.keys().cloned().collect();
    month_keys.sort();
    let recent: Vec<String> = month_keys.into_iter().rev().take(12).rev().collect();
    let monthly_trajectory = recent
        .into_iter()
        .map(|month| MonthlyActivity {
            active_authors: months.get(&month).map(|s| s.len() as u64).unwrap_or(0),
            commits: month_commits
                .get(&month)
                .map(|s| s.len() as u64)
                .unwrap_or(0),
            month,
        })
        .collect();

    let unresolved_authors = unresolved.len() as u64;
    let mut caveats: Vec<String> = CAVEATS.iter().map(|s| s.to_string()).collect();
    if unresolved_authors > 0 {
        caveats.push(unresolved_caveat(unresolved_authors));
    }

    // #6142: the flag sits beside the metrics it names, and never merges.
    let merge_risk = identity_merge_risk(suggestions, &alias_map, &ranked);
    if let Some(risk) = &merge_risk {
        caveats.push(suggested_merge_caveat(risk));
    }

    Ok(AuthorshipSummary {
        schema_version: AUTHORSHIP_SCHEMA_VERSION.to_string(),
        repository: repository.to_string(),
        distinct_authors: touches_by_author.len() as u64,
        bus_factor,
        top_author_share_pct,
        single_author_subsystems,
        monthly_trajectory,
        unresolved_authors,
        identity_merge_risk: merge_risk,
        caveats,
    })
}

/// True when at least one commit row carries `repository` as its name.
///
/// Why (#5453 review): `build_authorship_summary` cannot tell "this repository
/// genuinely has no commits" from "the name the manifest used never matched a
/// `commits.repository` value" — both aggregate zero rows and both would render
/// as a confident "0 authors, bus factor 0". The caller needs the difference to
/// choose between an artifact and a named gap, so the probe is its own query.
/// What: a bare `SELECT 1 … LIMIT 1` existence check, merges included, because
/// the question is whether the NAME matched anything at all.
/// Test: `super::authorship_tests::a_name_that_matches_nothing_is_detectable`.
///
/// # Errors
///
/// Propagates [`crate::core::errors::TgaError::DbError`].
pub fn repository_has_commits(conn: &Connection, repository: &str) -> Result<bool> {
    let mut stmt = conn.prepare("SELECT 1 FROM commits WHERE repository = ?1 LIMIT 1")?;
    Ok(stmt.exists(params![repository])?)
}

/// Every distinct `commits.repository` value in the database, sorted.
///
/// Why: when a manifest name matched nothing, the gap line is only actionable
/// if it names what IS present — "no commits under 'acme-web' (the database
/// holds: acme_web)" points straight at the drift, where a bare "no commits"
/// does not.
/// Test: `super::authorship_tests::a_name_that_matches_nothing_is_detectable`.
///
/// # Errors
///
/// Propagates [`crate::core::errors::TgaError::DbError`].
pub fn recorded_repository_names(conn: &Connection) -> Result<Vec<String>> {
    let mut stmt = conn.prepare("SELECT DISTINCT repository FROM commits ORDER BY repository")?;
    let rows = stmt.query_map([], |row| row.get::<_, String>(0))?;
    let mut names = Vec::new();
    for row in rows {
        names.push(row?);
    }
    Ok(names)
}

/// The smallest number of top-ranked authors whose combined share reaches 50%.
///
/// Why: the classic "bus factor" heuristic — how many people, if all left,
/// would take half the project's institutional knowledge with them.
/// What: `0` with no data; otherwise walks `ranked` (already sorted
/// descending) accumulating touches until the running total reaches half of
/// `total`.
fn bus_factor_of(ranked: &[(&String, &u64)], total: u64) -> u64 {
    if total == 0 {
        return 0;
    }
    let half = total as f64 / 2.0;
    let mut running = 0u64;
    for (i, (_, n)) in ranked.iter().enumerate() {
        running += **n;
        if running as f64 >= half {
            return (i + 1) as u64;
        }
    }
    ranked.len() as u64
}

impl AuthorshipSummary {
    /// Serialize to the JSON text trusty-review's loader reads.
    ///
    /// Why: keeping serialization here means the artifact's shape is testable
    /// without touching disk, exactly as [`super::ticketing`] does.
    /// What: `serde_json::to_string_pretty` over the declared field order.
    ///
    /// # Errors
    ///
    /// [`crate::core::errors::TgaError`] when serialization fails.
    pub fn to_json(&self) -> Result<String> {
        Ok(serde_json::to_string_pretty(self)?)
    }
}

#[cfg(test)]
#[path = "authorship_tests.rs"]
mod authorship_tests;