cargo_coupling/

history.rs

//! Time-series coupling analysis.
//!
//! Re-runs snapshot-equivalent balance analysis at past git revisions using
//! disposable `git worktree`s, producing a chronological health timeline. This is
//! the data foundation for *observing* how a codebase's coupling evolves over
//! time, rather than inspecting a single snapshot.
//!
//! Each sampled revision is analyzed with AST structure, git-churn volatility,
//! temporal coupling, and config volatility/subdomain overrides so the timeline
//! score uses the same methodology as the snapshot report for that revision.

use std::path::{Path, PathBuf};
use std::process::Command;
use std::sync::atomic::{AtomicUsize, Ordering};

use crate::balance::grade::{HealthGrade, ProjectBalanceReport};
use crate::balance::project::analyze_project_balance_with_thresholds;
use crate::balance::severity::Severity;
use crate::config::CompiledConfig;
use crate::metrics::project::ProjectMetrics;
use crate::{IssueThresholds, VolatilityAnalyzer, analyze_workspace_with_config};

static WORKTREE_SEQ: AtomicUsize = AtomicUsize::new(0);

/// One sampled point in the coupling timeline.
#[derive(Debug, Clone)]
pub struct HistoryPoint {
    /// Abbreviated commit hash.
    pub commit: String,
    /// Committer date in ISO-8601 (e.g. `2026-05-20`).
    pub date: String,
    /// Overall project health grade at this revision.
    pub grade: HealthGrade,
    /// Average balance score (0.0 - 1.0).
    pub average_score: f64,
    /// Number of detected couplings.
    pub total_couplings: usize,
    /// Number of analyzed modules.
    pub module_count: usize,
    /// Critical-severity issue count.
    pub critical: usize,
    /// High-severity issue count.
    pub high: usize,
}

/// A revision that was sampled but could not be analyzed.
#[derive(Debug, Clone)]
pub struct SkippedRevision {
    /// Abbreviated commit hash.
    pub commit: String,
    /// Committer date in ISO-8601.
    pub date: String,
    /// Human-readable reason analysis did not complete.
    pub reason: String,
}

/// Result of a history analysis run.
#[derive(Debug, Default)]
pub struct HistoryReport {
    /// Points in chronological order (oldest first).
    pub points: Vec<HistoryPoint>,
    /// Revisions that were sampled but skipped, with reasons.
    pub skipped: Vec<SkippedRevision>,
    /// Look-back window in months that was requested.
    pub months: usize,
}

/// Snapshot-equivalent analysis result for a single git ref.
#[derive(Debug)]
pub struct RefAnalysis {
    /// The git ref that was analyzed.
    pub git_ref: String,
    /// Snapshot-equivalent project metrics for the ref.
    pub metrics: ProjectMetrics,
    /// Full balance report for the ref.
    pub report: ProjectBalanceReport,
    /// Number of Rust files analyzed.
    pub total_files: usize,
    /// Number of modules analyzed.
    pub module_count: usize,
    /// Number of couplings found.
    pub total_couplings: usize,
}

impl HistoryReport {
    /// Oldest and newest analyzed points, if any exist.
    pub fn endpoints(&self) -> Option<(&HistoryPoint, &HistoryPoint)> {
        match (self.points.first(), self.points.last()) {
            (Some(first), Some(last)) => Some((first, last)),
            _ => None,
        }
    }
}

/// Errors that can occur during history analysis.
#[derive(Debug)]
pub enum HistoryError {
    /// The analysis path is not inside a git repository.
    NotGitRepo,
    /// A git command failed.
    Git(String),
    /// An I/O error occurred.
    Io(std::io::Error),
    /// No commits were found in the requested window.
    NoCommits,
    /// Coupling analysis failed at a git revision/ref.
    Analysis(String),
}

impl std::fmt::Display for HistoryError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            HistoryError::NotGitRepo => write!(f, "path is not inside a git repository"),
            HistoryError::Git(msg) => write!(f, "git command failed: {}", msg),
            HistoryError::Io(e) => write!(f, "I/O error: {}", e),
            HistoryError::NoCommits => write!(f, "no commits found in the requested time window"),
            HistoryError::Analysis(msg) => write!(f, "analysis failed: {}", msg),
        }
    }
}

impl std::error::Error for HistoryError {}

impl From<std::io::Error> for HistoryError {
    fn from(e: std::io::Error) -> Self {
        HistoryError::Io(e)
    }
}

/// Analyze the coupling health of a project across its recent git history.
///
/// Samples up to `max_points` commits evenly across the last `months` months,
/// re-running snapshot-equivalent analysis at each via a disposable worktree.
pub fn analyze_history(
    path: &Path,
    config: &CompiledConfig,
    thresholds: &IssueThresholds,
    months: usize,
    max_points: usize,
) -> Result<HistoryReport, HistoryError> {
    let repo_root = repo_root(path)?;
    let subpath = relative_subpath(&repo_root, path)?;

    let commits = list_commits(&repo_root, months)?;
    if commits.is_empty() {
        return Err(HistoryError::NoCommits);
    }

    let sampled = sample_evenly(commits.len(), max_points);

    let mut report = HistoryReport {
        months,
        ..Default::default()
    };

    for (idx, &i) in sampled.iter().enumerate() {
        let (commit, date) = &commits[i];
        match analyze_revision(
            &repo_root, &subpath, commit, config, thresholds, months, idx,
        ) {
            Ok(point) => report.points.push(HistoryPoint {
                date: date.clone(),
                ..point
            }),
            Err(reason) => report.skipped.push(SkippedRevision {
                commit: short_hash(commit),
                date: date.clone(),
                reason,
            }),
        }
    }

    Ok(report)
}

/// Analyze a project at an arbitrary git ref using a disposable worktree.
///
/// The analysis path is mapped relative to the current repository root into the
/// worktree, then analyzed with the same structural, git-volatility, and config
/// override methodology used for history snapshots.
pub fn analyze_ref(
    path: &Path,
    config: &CompiledConfig,
    thresholds: &IssueThresholds,
    git_ref: &str,
    months: usize,
    use_git: bool,
) -> Result<RefAnalysis, HistoryError> {
    let repo_root = repo_root(path)?;
    let subpath = relative_subpath(&repo_root, path)?;
    let seq = WORKTREE_SEQ.fetch_add(1, Ordering::Relaxed);
    analyze_ref_in_repo(
        &repo_root,
        &subpath,
        git_ref,
        RefAnalysisParams {
            config,
            thresholds,
            months,
            use_git,
            seq,
        },
    )
}

/// Resolve the git repository root containing `path`.
fn repo_root(path: &Path) -> Result<PathBuf, HistoryError> {
    let output = Command::new("git")
        .args(["rev-parse", "--show-toplevel"])
        .current_dir(path)
        .output()?;

    if !output.status.success() {
        return Err(HistoryError::NotGitRepo);
    }

    let root = String::from_utf8_lossy(&output.stdout).trim().to_string();
    if root.is_empty() {
        return Err(HistoryError::NotGitRepo);
    }
    let root = PathBuf::from(root);
    // Canonicalize so it matches the canonicalized analysis path in
    // `relative_subpath` (e.g. macOS `/var` -> `/private/var`).
    Ok(root.canonicalize().unwrap_or(root))
}

/// Compute the analysis path relative to the repo root (for use inside a worktree).
fn relative_subpath(repo_root: &Path, path: &Path) -> Result<PathBuf, HistoryError> {
    let abs = path.canonicalize().unwrap_or_else(|_| path.to_path_buf());
    abs.strip_prefix(repo_root)
        .map(|p| p.to_path_buf())
        .map_err(|_| {
            HistoryError::Analysis(format!(
                "analysis path '{}' is not under git repository root '{}'",
                abs.display(),
                repo_root.display()
            ))
        })
}

/// List `(hash, iso-date)` of `.rs`-touching commits in the window, oldest first.
fn list_commits(repo_root: &Path, months: usize) -> Result<Vec<(String, String)>, HistoryError> {
    let output = Command::new("git")
        .args([
            "log",
            "--reverse",
            "--pretty=format:%H|%cs",
            &format!("--since={} months ago", months),
            "--",
            "*.rs",
        ])
        .current_dir(repo_root)
        .output()?;

    if !output.status.success() {
        return Err(HistoryError::Git(
            String::from_utf8_lossy(&output.stderr).trim().to_string(),
        ));
    }

    let commits = String::from_utf8_lossy(&output.stdout)
        .lines()
        .filter_map(|line| {
            let (hash, date) = line.split_once('|')?;
            if hash.is_empty() {
                return None;
            }
            Some((hash.to_string(), date.to_string()))
        })
        .collect();

    Ok(commits)
}

/// Analyze a single revision inside a disposable worktree.
fn analyze_revision(
    repo_root: &Path,
    subpath: &Path,
    commit: &str,
    config: &CompiledConfig,
    thresholds: &IssueThresholds,
    months: usize,
    seq: usize,
) -> Result<HistoryPoint, String> {
    let analysis = analyze_ref_in_repo(
        repo_root,
        subpath,
        commit,
        RefAnalysisParams {
            config,
            thresholds,
            months,
            use_git: true,
            seq,
        },
    )
    .map_err(|e| e.to_string())?;
    let report = analysis.report;
    let critical = *report
        .issues_by_severity
        .get(&Severity::Critical)
        .unwrap_or(&0);
    let high = *report.issues_by_severity.get(&Severity::High).unwrap_or(&0);

    Ok(HistoryPoint {
        commit: short_hash(commit),
        date: String::new(), // filled in by caller
        grade: report.health_grade,
        average_score: report.average_score,
        total_couplings: analysis.total_couplings,
        module_count: analysis.module_count,
        critical,
        high,
    })
}

struct RefAnalysisParams<'a> {
    config: &'a CompiledConfig,
    thresholds: &'a IssueThresholds,
    months: usize,
    use_git: bool,
    seq: usize,
}

fn analyze_ref_in_repo(
    repo_root: &Path,
    subpath: &Path,
    git_ref: &str,
    params: RefAnalysisParams<'_>,
) -> Result<RefAnalysis, HistoryError> {
    let worktree = Worktree::add(repo_root, git_ref, params.seq)?;

    let analysis_path = worktree.dir.join(subpath);
    if !analysis_path.exists() {
        return Err(HistoryError::Analysis(
            "analysis path does not exist at this revision".to_string(),
        ));
    }

    let mut config = rebase_config_root(params.config, repo_root, &worktree.dir);
    let mut metrics = analyze_workspace_with_config(&analysis_path, &config)
        .map_err(|e| HistoryError::Analysis(e.to_string()))?;

    // Drift notes assert "the CURRENT config is stale". Historical revisions are
    // analyzed with today's config against an old tree, so an unmatched pattern
    // there says nothing about config rot — suppress to avoid false positives.
    metrics.dead_config_patterns.clear();

    if metrics.modules.is_empty() {
        return Err(HistoryError::Analysis(
            "no modules found at this revision".to_string(),
        ));
    }

    if params.use_git {
        let mut volatility = VolatilityAnalyzer::new(params.months);
        if volatility.analyze(&analysis_path).is_ok() {
            if let Ok(temporal) = volatility.analyze_temporal_coupling(&analysis_path) {
                metrics.temporal_couplings = temporal;
            }
            metrics.file_changes = volatility.file_changes;
            metrics.update_volatility_from_git();
        }
    }

    if config.has_volatility_overrides() || config.has_subdomain_config() {
        metrics.apply_config_volatility_overrides(&mut config);
    }

    let report = analyze_project_balance_with_thresholds(&metrics, params.thresholds);
    rebase_metrics_paths(&mut metrics, &worktree.dir, repo_root);

    let total_files = metrics.total_files;
    let module_count = metrics.modules.len();
    let total_couplings = metrics.couplings.len();

    Ok(RefAnalysis {
        git_ref: git_ref.to_string(),
        metrics,
        report,
        total_files,
        module_count,
        total_couplings,
    })
}

fn rebase_metrics_paths(metrics: &mut ProjectMetrics, worktree_root: &Path, repo_root: &Path) {
    for module in metrics.modules.values_mut() {
        if let Ok(relative) = module.path.strip_prefix(worktree_root) {
            module.path = repo_root.join(relative);
        }
    }

    for coupling in &mut metrics.couplings {
        if let Some(path) = &coupling.location.file_path
            && let Ok(relative) = path.strip_prefix(worktree_root)
        {
            coupling.location.file_path = Some(repo_root.join(relative));
        }
    }
}

fn rebase_config_root(
    config: &CompiledConfig,
    repo_root: &Path,
    worktree_root: &Path,
) -> CompiledConfig {
    let mut config = config.clone();
    let Some(config_root) = config.config_root() else {
        return config;
    };

    if let Ok(relative) = config_root.strip_prefix(repo_root) {
        config.set_config_root(Some(worktree_root.join(relative)));
    }

    config
}

/// A git worktree that is removed when dropped.
struct Worktree {
    repo_root: PathBuf,
    dir: PathBuf,
}

impl Worktree {
    fn add(repo_root: &Path, commit: &str, seq: usize) -> Result<Self, HistoryError> {
        let dir = std::env::temp_dir().join(format!(
            "cargo-coupling-hist-{}-{}-{}",
            std::process::id(),
            seq,
            short_hash(commit)
        ));

        let output = Command::new("git")
            .args(["worktree", "add", "--detach"])
            .arg(&dir)
            .arg(commit)
            .current_dir(repo_root)
            .output()?;

        if !output.status.success() {
            return Err(HistoryError::Git(
                String::from_utf8_lossy(&output.stderr).trim().to_string(),
            ));
        }

        Ok(Worktree {
            repo_root: repo_root.to_path_buf(),
            dir,
        })
    }
}

impl Drop for Worktree {
    fn drop(&mut self) {
        let _ = Command::new("git")
            .args(["worktree", "remove", "--force"])
            .arg(&self.dir)
            .current_dir(&self.repo_root)
            .output();
    }
}

/// Abbreviate a commit/ref to a path-safe 7-character label.
fn short_hash(hash: &str) -> String {
    hash.chars()
        .take(7)
        .map(|c| {
            if c.is_ascii_alphanumeric() || matches!(c, '_' | '.' | '-') {
                c
            } else {
                '_'
            }
        })
        .collect()
}

/// Pick up to `max` evenly-spaced indices from `[0, len)`.
///
/// Always includes the first and last index when `len >= 2` so the endpoints
/// of the timeline are preserved. Returns all indices when `len <= max`.
pub(crate) fn sample_evenly(len: usize, max: usize) -> Vec<usize> {
    // Covers the empty cases too: `len <= max` is true when `len == 0`, and the
    // loop below produces nothing when `max == 0`, so no separate guard is needed.
    if len <= max {
        return (0..len).collect();
    }
    if max == 1 {
        return vec![len - 1];
    }

    let mut indices = Vec::with_capacity(max);
    for k in 0..max {
        // Spread k across [0, len-1] inclusive.
        let idx = k * (len - 1) / (max - 1);
        if indices.last() != Some(&idx) {
            indices.push(idx);
        }
    }
    indices
}

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

    #[test]
    fn sample_returns_all_when_under_limit() {
        assert_eq!(sample_evenly(3, 10), vec![0, 1, 2]);
        assert_eq!(sample_evenly(5, 5), vec![0, 1, 2, 3, 4]);
    }

    #[test]
    fn sample_includes_endpoints() {
        let s = sample_evenly(100, 5);
        assert_eq!(s.first(), Some(&0));
        assert_eq!(s.last(), Some(&99));
        assert!(s.len() <= 5);
    }

    #[test]
    fn sample_is_monotonic_and_unique() {
        let s = sample_evenly(50, 8);
        for w in s.windows(2) {
            assert!(w[0] < w[1], "indices must be strictly increasing: {:?}", s);
        }
    }

    #[test]
    fn sample_edge_cases() {
        assert_eq!(sample_evenly(0, 5), Vec::<usize>::new());
        assert_eq!(sample_evenly(5, 0), Vec::<usize>::new());
        assert_eq!(sample_evenly(10, 1), vec![9]);
        assert_eq!(sample_evenly(1, 5), vec![0]);
    }

    #[test]
    fn short_hash_truncates() {
        assert_eq!(short_hash("0123456789abcdef"), "0123456");
        assert_eq!(short_hash("abc"), "abc");
        assert_eq!(short_hash("feat/foo"), "feat_fo");
    }

    #[test]
    fn error_display_messages() {
        assert_eq!(
            HistoryError::NotGitRepo.to_string(),
            "path is not inside a git repository"
        );
        assert_eq!(
            HistoryError::NoCommits.to_string(),
            "no commits found in the requested time window"
        );
        assert!(
            HistoryError::Git("boom".into())
                .to_string()
                .contains("boom")
        );
    }

    #[test]
    fn relative_subpath_strips_root() {
        // `/repo` does not exist, so canonicalize falls back to the path as-is
        // (`/repo/src`), and strip_prefix then yields the relative `src`.
        let sub = relative_subpath(Path::new("/repo"), Path::new("/repo/src")).unwrap();
        assert_eq!(sub, Path::new("src"));
    }

    #[test]
    fn relative_subpath_errors_outside_root() {
        let err = relative_subpath(Path::new("/repo"), Path::new("/elsewhere/src")).unwrap_err();
        assert!(err.to_string().contains("is not under git repository root"));
    }
}