import { execFile, spawn, type ChildProcessWithoutNullStreams } from "node:child_process";
import { lstatSync, mkdirSync } from "node:fs";
import { mkdir } from "node:fs/promises";
import { isAbsolute, join } from "node:path";
import { promisify, TextDecoder } from "node:util";
import type { WorkspaceErrorCode, WorkspaceRegistryConfig } from "./types.js";

const execFileAsync = promisify(execFile);

export interface GitStatus {
  branch: string;
  repository?: WorkspaceRepositoryIdentity;
  head?: string;
  ahead: number;
  behind: number;
  degraded: boolean;
  lastError?: WorkspaceErrorCode;
}

export interface WorkspaceRepositoryIdentity {
  host: string;
  repository: string;
  transport: "https" | "ssh" | "local";
}

export interface EvidenceTreeObject {
  mode: "100644" | "100755";
  oid: string;
  posixPath: string;
}

export class WorkspaceRegistryError extends Error {
  constructor(readonly code: WorkspaceErrorCode, message: string) {
    super(message);
    this.name = "WorkspaceRegistryError";
  }
}

function invalidRemote(): never {
  throw new WorkspaceRegistryError("workspace_invalid", "Workspace Git remote is invalid");
}

function safeRepositoryPath(raw: string): string {
  let decoded: string;
  try {
    decoded = decodeURIComponent(raw).replace(/^\/+/, "").replace(/\/+$/, "").replace(/\.git$/, "");
  } catch {
    return invalidRemote();
  }
  if (
    decoded.length === 0
    || decoded.includes("\\")
    || decoded.split("/").some((part) => part === "" || part === "." || part === "..")
    || /[\p{Cc}\s?#]/u.test(decoded)
  ) return invalidRemote();
  return decoded;
}

/** Convert a configured remote to the only repository identity safe for API/UI responses. */
export function normalizeRepositoryIdentity(remote: string): WorkspaceRepositoryIdentity {
  if (remote.length === 0 || remote.trim() !== remote || remote.includes("\0")) return invalidRemote();
  if (isAbsolute(remote) || remote.startsWith("file://")) {
    return { host: "local", repository: "configured-repository", transport: "local" };
  }
  const scp = /^git@([^:/\s]+):(.+)$/.exec(remote);
  if (scp) {
    return { host: scp[1].toLowerCase(), repository: safeRepositoryPath(scp[2]), transport: "ssh" };
  }
  let parsed: URL;
  try {
    parsed = new URL(remote);
  } catch {
    return invalidRemote();
  }
  if (parsed.search || parsed.hash || !parsed.hostname || parsed.port) return invalidRemote();
  if (parsed.protocol === "https:") {
    if (parsed.username || parsed.password) return invalidRemote();
    return {
      host: parsed.hostname.toLowerCase(),
      repository: safeRepositoryPath(parsed.pathname),
      transport: "https",
    };
  }
  if (parsed.protocol === "ssh:") {
    if (parsed.password || (parsed.username !== "" && parsed.username !== "git")) return invalidRemote();
    return {
      host: parsed.hostname.toLowerCase(),
      repository: safeRepositoryPath(parsed.pathname),
      transport: "ssh",
    };
  }
  return invalidRemote();
}

function isMissing(path: string): boolean {
  try {
    lstatSync(path);
    return false;
  } catch {
    return true;
  }
}

function assertDirectory(path: string): void {
  const entry = lstatSync(path);
  if (!entry.isDirectory() || entry.isSymbolicLink()) {
    throw new WorkspaceRegistryError("git_unavailable", "Workspace registry path is unavailable");
  }
}

function isValidUtf8(buffer: Buffer): boolean {
  try {
    new TextDecoder("utf-8", { fatal: true }).decode(buffer);
    return true;
  } catch {
    return false;
  }
}

function gitErrorCode(error: unknown): WorkspaceErrorCode {
  const detail = [
    error instanceof Error ? error.message : "",
    typeof error === "object" && error !== null && "stderr" in error
      ? String((error as { stderr?: unknown }).stderr ?? "")
      : "",
  ].join("\n").toLowerCase();
  if (/authentication failed|could not read username|permission denied|publickey/.test(detail)) {
    return "git_auth_failed";
  }
  if (/non-fast-forward|not possible to fast-forward|fast-forward/.test(detail)) {
    return "git_non_fast_forward";
  }
  return "git_unavailable";
}

/**
 * A persistent checkout that executes Git only through fixed argument vectors. Git's stdout and
 * stderr are intentionally never exposed: they can contain remote URLs or credential hints.
 */
export class GitWorkspaceRepository {
  readonly root: string;
  readonly repoPath: string;
  readonly snapshotsPath: string;
  readonly statePath: string;
  readonly locksPath: string;
  private readonly hooksPath: string;
  private readonly identity?: WorkspaceRepositoryIdentity;

  constructor(private readonly config: WorkspaceRegistryConfig) {
    if (!isAbsolute(config.root)) {
      throw new WorkspaceRegistryError("git_unavailable", "Workspace registry root is unavailable");
    }
    this.root = config.root;
    this.repoPath = join(this.root, "repo");
    this.snapshotsPath = join(this.root, "snapshots");
    this.statePath = join(this.root, "state");
    this.locksPath = join(this.root, "locks");
    this.hooksPath = join(this.locksPath, "empty-hooks");
    this.identity = config.remoteUrl === undefined
      ? undefined
      : normalizeRepositoryIdentity(config.remoteUrl);
  }

  async ensureLayout(): Promise<void> {
    try {
      for (const path of [this.root, this.snapshotsPath, this.statePath, this.locksPath, this.hooksPath]) {
        await mkdir(path, { recursive: true, mode: 0o700 });
        assertDirectory(path);
      }
    } catch (error) {
      if (error instanceof WorkspaceRegistryError) throw error;
      throw new WorkspaceRegistryError("git_unavailable", "Workspace registry storage is unavailable");
    }
  }

  async bootstrap(): Promise<GitStatus> {
    await this.ensureLayout();
    if (isMissing(this.repoPath)) {
      if (!this.config.remoteUrl) {
        throw new WorkspaceRegistryError("git_unavailable", "Workspace registry remote is unavailable");
      }
      await this.clone();
    } else {
      assertDirectory(this.repoPath);
      await this.refresh();
    }
    return await this.status();
  }

  async pull(): Promise<GitStatus> {
    await this.ensureLayout();
    if (isMissing(this.repoPath)) return await this.bootstrap();
    assertDirectory(this.repoPath);
    await this.refresh();
    return await this.status();
  }

  async status(): Promise<GitStatus> {
    const head = (await this.git(["rev-parse", "HEAD"])).trim();
    const tracking = await this.gitOptional(["rev-list", "--left-right", "--count", "HEAD...@{upstream}"]);
    const [ahead = "0", behind = "0"] = tracking ? tracking.trim().split(/\s+/) : [];
    return {
      branch: this.config.branch,
      ...(this.identity ? { repository: this.identity } : {}),
      head,
      ahead: Number(ahead),
      behind: Number(behind),
      degraded: false,
    };
  }

  async workspaceDirectories(): Promise<string[]> {
    const output = await this.git(["ls-tree", "-d", "--name-only", "HEAD"]);
    const directories = output.trim() === "" ? [] : output.trim().split("\n");
    for (const id of directories) {
      if (id === "workspace-docs") continue;
      if (!/^[a-z][a-z0-9-]{2,62}$/.test(id)) {
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace repository contains an invalid path");
      }
    }
    return directories.filter((id) => id !== "workspace-docs").sort();
  }

  async workspacePaths(): Promise<string[]> {
    const paths: string[] = [];
    for (const id of await this.workspaceDirectories()) {
      const path = `${id}/workspace.yaml`;
      const type = await this.gitOptional(["cat-file", "-t", `HEAD:${path}`]);
      if (type === undefined) continue;
      if (type.trim() !== "blob") {
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace descriptor is invalid");
      }
      paths.push(path);
    }
    return paths.sort();
  }

  async readCatalog(revision = "HEAD"): Promise<string> {
    return await this.git(["show", `${revision}:thoth-workspaces.yaml`], {}, "Workspace catalog is invalid");
  }

  async catalogBlob(revision = "HEAD"): Promise<string> {
    return (await this.git(["rev-parse", `${revision}:thoth-workspaces.yaml`], {},
      "Workspace catalog is invalid")).trim();
  }

  async readWorkspace(path: string, revision = "HEAD"): Promise<string> {
    if (!/^(?!workspace-docs\/)[a-z][a-z0-9-]{2,62}\/workspace\.yaml$/.test(path)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace repository path is invalid");
    }
    return await this.git(["show", `${revision}:${path}`]);
  }

  async blob(path: string, revision = "HEAD"): Promise<string> {
    if (!/^(?!workspace-docs\/)[a-z][a-z0-9-]{2,62}\/workspace\.yaml$/.test(path)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace repository path is invalid");
    }
    return (await this.git(["rev-parse", `${revision}:${path}`])).trim();
  }

  /** Read-only object type at an exact revision, or undefined when absent. */
  async gitObjectType(revision: string, path: string): Promise<string | undefined> {
    if (!/^[0-9a-f]{40}$/.test(revision)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace revision is invalid");
    }
    if (!/^[a-z][a-z0-9-]{2,62}\/workspace\.yaml$/.test(path)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace repository path is invalid");
    }
    return await this.gitOptional(["cat-file", "-t", `${revision}:${path}`]);
  }

  /** Read a generated-doc blob at an exact revision, or undefined when absent. */
  async readObjectOrAbsent(revision: string, path: string): Promise<string | undefined> {
    if (!/^[0-9a-f]{40}$/.test(revision)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace revision is invalid");
    }
    if (!/^workspace-docs\/[a-z][a-z0-9-]{2,62}\/(?:contract\.env\.example|README\.md)$/.test(path)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace repository path is invalid");
    }
    const output = await this.gitOptional(["show", `${revision}:${path}`]);
    return output === undefined ? undefined : output;
  }

  /** List committed generated-doc paths at an exact revision. */
  async workspaceDocsPaths(revision: string): Promise<string[]> {
    if (!/^[0-9a-f]{40}$/.test(revision)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace revision is invalid");
    }
    const output = await this.git(["ls-tree", "-r", "--name-only", revision, "--", "workspace-docs"]);
    if (output.trim() === "") return [];
    const paths = output.trim().split("\n");
    for (const path of paths) {
      if (!/^workspace-docs\/[a-z][a-z0-9-]{2,62}\/(?:contract\.env\.example|README\.md)$/.test(path)) {
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace repository contains an invalid docs path");
      }
    }
    return paths;
  }

  /** Assert that a canonical Evidence root is a Git tree at an exact commit. */
  async assertTreeAtRevision(revision: string, repoRelativePath: string): Promise<void> {
    if (!/^[0-9a-f]{40}$/.test(revision)
      || !/^[a-z][a-z0-9-]{2,62}\/evidence$/.test(repoRelativePath)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence revision is invalid");
    }
    const type = (await this.git(
      ["cat-file", "-t", `${revision}:${repoRelativePath}`],
      {},
      "Workspace Evidence root is invalid",
    )).trim();
    if (type !== "tree") {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence root is invalid");
    }
  }

  /** Read the curated FK annotations object at an exact commit, or undefined when absent. */
  async annotationsObject(revision: string, id: string): Promise<{ blobId: string; contents: Buffer } | undefined> {
    if (!/^[0-9a-f]{40}$/.test(revision)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace annotations revision is invalid");
    }
    if (!/^[a-z][a-z0-9-]{2,62}$/.test(id) || id === "workspace-docs") {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace annotations path is invalid");
    }
    const path = `${id}/schema/annotations.yaml`;
    // ls-tree -z reports the exact object at the path (or its children when the path is a tree).
    const listing = await this.git(["ls-tree", "-z", "--full-tree", revision, "--", path]);
    const entries = listing.split("\0").filter((entry) => entry.length > 0);
    if (entries.length === 0) return undefined;
    const exact = entries.find((entry) => entry.slice(entry.lastIndexOf("\t") + 1) === path);
    if (exact === undefined) {
      // The path resolves to a tree (its children are listed) or another non-blob object.
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace annotations object is invalid");
    }
    const match = /^([0-9]{6})\s+(blob|tree|commit)\s+([0-9a-f]{40})\t/.exec(exact);
    // Only regular Git blobs are accepted: symlinks (120000) and gitlinks (160000) are refused.
    if (match === null || match[2] !== "blob" || (match[1] !== "100644" && match[1] !== "100755")) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace annotations object is invalid");
    }
    const blobId = match[3];
    const contents = await this.gitBlobBytes(blobId, 16 * 1024 * 1024, "annotations");
    if (!isValidUtf8(contents)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace annotations object is not valid UTF-8");
    }
    return { blobId, contents };
  }

  /**
   * Recursively enumerate a canonical `<id>/evidence` tree at an exact commit as regular Git blobs.
   * Symlinks (120000), gitlinks (160000), non-regular modes, non-blob types, traversal/absolute/
   * duplicate/cross-namespace paths, and NUL/newline-bearing names are refused.
   */
  async evidenceTreeObjects(revision: string, id: string): Promise<EvidenceTreeObject[]> {
    if (!/^[0-9a-f]{40}$/.test(revision)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence revision is invalid");
    }
    if (!/^[a-z][a-z0-9-]{2,62}$/.test(id)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence path is invalid");
    }
    const prefix = `${id}/evidence`;
    const listing = await this.git(["ls-tree", "-r", "-z", "--full-tree", revision, "--", prefix]);
    const entries = listing.split("\0").filter((entry) => entry.length > 0);
    const seen = new Set<string>();
    const objects: EvidenceTreeObject[] = [];
    for (const entry of entries) {
      const tab = entry.lastIndexOf("\t");
      if (tab < 0) throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence object is invalid");
      const name = entry.slice(tab + 1);
      const meta = entry.slice(0, tab);
      const match = /^([0-9]{6}) (blob|commit|tree) ([0-9a-f]{40})$/.exec(meta);
      if (match === null || match[2] !== "blob" || (match[1] !== "100644" && match[1] !== "100755")) {
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence object is invalid");
      }
      if (name === prefix) {
        // The Evidence root resolves to a single regular blob (or symlink/gitlink already refused above).
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence root is invalid");
      }
      if (!name.startsWith(`${prefix}/`)) {
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence object escapes its namespace");
      }
      const rel = name.slice(prefix.length + 1);
      if (rel.length === 0 || rel.includes("\0") || rel.includes("\n") || rel.includes("\r")) {
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence path is invalid");
      }
      const segments = rel.split("/");
      if (segments.some((segment) => segment === "" || segment === "." || segment === "..")) {
        throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence path is invalid");
      }
      if (seen.has(rel)) throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence path is duplicated");
      seen.add(rel);
      objects.push({ mode: match[1] as "100644" | "100755", oid: match[3], posixPath: rel });
    }
    return objects;
  }

  /** Read one Evidence blob with a per-object byte bound. */
  evidenceBlobBytes(objectId: string, maxBytes: number): Promise<Buffer> {
    return this.gitBlobBytes(objectId, maxBytes, "Evidence");
  }

  /** Return the 40-hex tree id of a canonical Evidence root at an exact commit. */
  async evidenceTreeId(revision: string, id: string): Promise<string> {
    if (!/^[0-9a-f]{40}$/.test(revision) || !/^[a-z][a-z0-9-]{2,62}$/.test(id)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence revision is invalid");
    }
    const objectId = (await this.git(["rev-parse", `${revision}:${id}/evidence`])).trim();
    const type = (await this.git(["cat-file", "-t", objectId])).trim();
    if (!/^[0-9a-f]{40}$/.test(objectId) || type !== "tree") {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence root is invalid");
    }
    return objectId;
  }

  /** Return the byte size of one Git object without reading its contents. */
  async gitObjectSize(objectId: string): Promise<number> {
    if (!/^[0-9a-f]{40}$/.test(objectId)) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence object is invalid");
    }
    const raw = (await this.git(["cat-file", "-s", objectId])).trim();
    const size = Number(raw);
    if (!Number.isSafeInteger(size) || size < 0) {
      throw new WorkspaceRegistryError("workspace_invalid", "Workspace Evidence object size is invalid");
    }
    return size;
  }

  private async gitBlobBytes(objectId: string, maxBytes: number, label: string): Promise<Buffer> {
    if (!/^[0-9a-f]{40}$/.test(objectId)) {
      throw new WorkspaceRegistryError("workspace_invalid", `Workspace ${label} object is invalid`);
    }
    try {
      const { stdout } = await execFileAsync(
        "git",
        ["-c", `core.hooksPath=${this.hooksPath}`, "cat-file", "blob", objectId],
        {
          cwd: this.repoPath,
          env: { ...process.env, GIT_TERMINAL_PROMPT: "0" },
          encoding: "buffer",
          maxBuffer: maxBytes + 1024 * 1024,
        },
      );
      if (stdout.length > maxBytes) {
        throw new WorkspaceRegistryError("workspace_invalid", `Workspace ${label} object is too large`);
      }
      return stdout;
    } catch (error) {
      if (error instanceof WorkspaceRegistryError) throw error;
      const detail = error instanceof Error ? error.message : "";
      if (/maxBuffer|stdout maxBuffer/i.test(detail)) {
        throw new WorkspaceRegistryError("workspace_invalid", `Workspace ${label} object is too large`);
      }
      throw this.sanitizeGitError(error);
    }
  }

  private async clone(): Promise<void> {
    try {
      await execFileAsync("git", [
        "-c", `core.hooksPath=${this.hooksPath}`,
        "clone", "--branch", this.config.branch, "--single-branch", "--", this.config.remoteUrl!, this.repoPath,
      ], { cwd: this.root, env: { ...process.env, GIT_TERMINAL_PROMPT: "0" } });
      assertDirectory(this.repoPath);
    } catch (error) {
      throw this.sanitizeGitError(error);
    }
  }

  private async refresh(): Promise<void> {
    if ((await this.git(["status", "--porcelain"])).trim() !== "") {
      throw new WorkspaceRegistryError("workspace_stale", "Workspace checkout has local changes");
    }
    if (this.config.remoteUrl) {
      await this.git(["remote", "set-url", "origin", "--", this.config.remoteUrl]);
    }
    await this.git(["fetch", "--no-tags", "origin", this.config.branch]);
    const remoteHead = (await this.git(["rev-parse", "FETCH_HEAD"])).trim();
    const localHead = (await this.git(["rev-parse", "HEAD"])).trim();
    if (localHead !== remoteHead) {
      const commonAncestor = (await this.git(["merge-base", "HEAD", "FETCH_HEAD"])).trim();
      if (commonAncestor !== localHead) {
        throw new WorkspaceRegistryError("git_non_fast_forward", "Workspace checkout diverged from remote");
      }
      await this.git(["merge", "--ff-only", "FETCH_HEAD"]);
    }
    if ((await this.git(["rev-parse", "HEAD"])).trim() !== remoteHead) {
      throw new WorkspaceRegistryError("git_non_fast_forward", "Workspace checkout does not match remote");
    }
  }

  private async git(
    args: string[],
    env: NodeJS.ProcessEnv = {},
    invalidObjectMessage?: string,
  ): Promise<string> {
    try {
      const { stdout } = await execFileAsync(
        "git",
        ["-c", `core.hooksPath=${this.hooksPath}`, ...args],
        { cwd: this.repoPath, env: { ...process.env, GIT_TERMINAL_PROMPT: "0", ...env } },
      );
      return stdout;
    } catch (error) {
      const stderr = typeof error === "object" && error !== null && "stderr" in error
        && typeof error.stderr === "string" ? error.stderr : "";
      if (invalidObjectMessage
        && /^fatal: path '[^']+' does not exist in '[0-9a-f]{40}'\s*$/u.test(stderr)) {
        throw new WorkspaceRegistryError("workspace_invalid", invalidObjectMessage);
      }
      throw this.sanitizeGitError(error);
    }
  }

  private async gitOptional(args: string[]): Promise<string | undefined> {
    try {
      return await this.git(args);
    } catch (error) {
      if (error instanceof WorkspaceRegistryError && error.code === "git_unavailable") return undefined;
      throw error;
    }
  }

  private sanitizeGitError(error: unknown): WorkspaceRegistryError {
    return new WorkspaceRegistryError(gitErrorCode(error), "Workspace Git operation failed");
  }
}

export class WorkspaceRepositoryLock {
  private queue = Promise.resolve();

  constructor(private readonly locksPath: string) {}

  async run<T>(operation: () => Promise<T>): Promise<T> {
    const previous = this.queue;
    let releaseQueue!: () => void;
    this.queue = new Promise<void>((resolve) => { releaseQueue = resolve; });
    await previous;

    let holder: ChildProcessWithoutNullStreams | undefined;
    const lockPath = join(this.locksPath, "repository.lock");
    try {
      try {
        mkdirSync(this.locksPath, { recursive: true, mode: 0o700 });
        assertDirectory(this.locksPath);
      } catch (error) {
        throw new WorkspaceRegistryError("git_unavailable", "Workspace registry lock is unavailable");
      }
      try {
        holder = await this.acquire(lockPath);
      } catch (error) {
        throw this.lockError(error);
      }
      return await operation();
    } finally {
      try {
        if (holder !== undefined) await this.release(holder);
      } finally {
        releaseQueue();
      }
    }
  }

  private async acquire(lockPath: string): Promise<ChildProcessWithoutNullStreams> {
    try {
      const entry = lstatSync(lockPath);
      if (!entry.isFile() || entry.isSymbolicLink()) throw new Error("invalid lock path");
    } catch (error) {
      if (!(typeof error === "object" && error !== null && "code" in error && error.code === "ENOENT")) {
        throw error;
      }
    }
    const holder = spawn("python3", ["-c", WorkspaceRepositoryLock.HOLDER_PROGRAM, lockPath], {
      stdio: ["pipe", "pipe", "pipe"],
    });
    await new Promise<void>((resolve, reject) => {
      let output = "";
      const fail = (error: WorkspaceRegistryError) => {
        holder.stdout.removeAllListeners("data");
        reject(error);
      };
      holder.once("error", () => fail(new WorkspaceRegistryError("git_unavailable", "Workspace registry lock is unavailable")));
      holder.once("exit", (code) => {
        fail(new WorkspaceRegistryError(
          code === 73 ? "workspace_stale" : "git_unavailable",
          code === 73 ? "Workspace registry is busy" : "Workspace registry lock is unavailable",
        ));
      });
      holder.stdout.on("data", (chunk: Buffer) => {
        output += chunk.toString("utf8");
        if (output === "locked\n") {
          holder.stdout.removeAllListeners("data");
          resolve();
        }
      });
    });
    return holder;
  }

  private async release(holder: ChildProcessWithoutNullStreams): Promise<void> {
    if (!holder.stdin.destroyed) holder.stdin.end();
    await new Promise<void>((resolve) => holder.once("exit", () => resolve()));
  }

  private lockError(error: unknown): WorkspaceRegistryError {
    if (error instanceof WorkspaceRegistryError) return error;
    if (typeof error === "object" && error !== null && "code" in error && error.code === "EEXIST") {
      return new WorkspaceRegistryError("workspace_stale", "Workspace registry is busy");
    }
    return new WorkspaceRegistryError("git_unavailable", "Workspace registry lock is unavailable");
  }

  private static readonly HOLDER_PROGRAM = [
    "import fcntl, os, sys",
    "fd = os.open(sys.argv[1], os.O_RDWR | os.O_CREAT | getattr(os, 'O_NOFOLLOW', 0), 0o600)",
    "try:",
    "    fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)",
    "except BlockingIOError:",
    "    sys.exit(73)",
    "sys.stdout.write('locked\\n')",
    "sys.stdout.flush()",
    "sys.stdin.buffer.read()",
  ].join("\n");
}