/**
 * @fileoverview `git fetch` for the repositories the Git panel shows, on the user's click
 * (`POST /api/sessions/:id/git-fetch`) or on an interval the user turned on
 * (`src/git-fetch-scheduler.ts`).
 *
 * The status module (src/git-workspace-status.ts) is deliberately offline: "behind" is as of the last
 * fetch, so a number that is stale can only be made current by fetching. This is the only git command the
 * Git panel runs that writes, and the only git command Codeman runs on a timer. Cloning a repository and
 * managing worktrees write too, but those are things the user asked for at the moment they asked; this is
 * the one that can happen later, by itself. Nothing here commits, checks out, merges or touches the working
 * tree: `git fetch` updates remote-tracking
 * refs and nothing else, and `FETCH_CONFIG_ARGS` keeps it from starting a gc in a repository an agent is
 * already using. It is not harmless in the way a read is: a fetch holds git's ref lock, so an agent's own
 * `git pull` in the same clone can collide with it (`cannot lock ref`), which is why one folder is fetched
 * by at most one run at a time (`fetchWorkspaceOnce`).
 *
 * Same split as git-clone.ts: the pure half (`buildFetchArgs`, `describeFetchFailure`, `fetchEnvFor`,
 * `gitFetchSettingsFrom`, `gitFetchStatusFrom`) holds every decision and tests without spawning, and the IO
 * half runs one bounded `git fetch --quiet` per repository.
 *
 * Rules the code keeps and the tests pin:
 *   - The repository set is `resolveWorkspaceRepos`, the single source the panel and the diff route
 *     already use, so Fetch cannot reach a repository the panel would not show. The Docker rule is
 *     checked before any git runs: a repository a container can write to is refused outright, because a
 *     planted config would run on the host, and `git fetch` is exactly the command that can run a
 *     repository's own hooks (`reference-transaction`, and `pre-auto-gc` through the automatic maintenance
 *     that follows a fetch) and its config commands such as `credential.helper`, which is why a timer only
 *     runs it after the user opts in.
 *   - One run per folder at a time: `fetchWorkspaceOnce` joins a run already going for the same folder
 *     instead of starting a second one, because two fetches in one clone collide on the ref lock.
 *   - Bounded: the git timeout from Settings → Bottom bar per repository, `MAX_REPOS_LIMIT` repositories at
 *     most, a hard wall-clock bound on each spawn, and `FETCH_CONCURRENCY` git processes at a time for the
 *     whole run: one `Limiter`, shared by the scheduler's tick, not one bound per folder.
 *   - Non-interactive: `GIT_TERMINAL_PROMPT=0` and BatchMode ssh, so a private repository that needs a
 *     login fails fast instead of hanging the request on an invisible username prompt. Codeman collects
 *     no credentials; a repository the user's own git is already signed in to works because that is the
 *     user's existing setup, so unlike a clone no credential helper is disabled here. That BatchMode ssh is
 *     a default, never an override: `fetchEnvFor` keeps whatever the repository's `core.sshCommand`, the
 *     user's own `GIT_SSH_COMMAND` or a `GIT_SSH` already says, because on a machine with several ssh setups
 *     that choice is usually the one that works. ⚠️ The default still leaves a record: `StrictHostKeyChecking=accept-new`
 *     writes an unknown host key into `~/.ssh/known_hosts` without asking: BatchMode stops a prompt, not a
 *     write.
 *   - The timeout kills the PROCESS GROUP, not just the `git` parent. A fetch over http spawns
 *     `git-remote-http` children, and `execFile`'s `timeout` signals the parent only, so the answer can go
 *     out while a helper is still running, and on a timer that repeats every tick with nobody watching.
 *     `spawn` with `detached: true` puts the tree in its own group so the escalation (SIGTERM, then SIGKILL
 *     `FETCH_KILL_ESCALATION_MS` later) reaches the children too, which is why the negative pid is used
 *     rather than `child.kill()`. Same shape as `runGit` in git-clone.ts, without that module's slot queue:
 *     fetch is bounded by `FETCH_CONCURRENCY`, not by a clone queue.
 *   - Failure text reaching a client is control-stripped and credential-redacted (`sanitizeGitOutput`),
 *     and the browser writes it with `textContent` only.
 *
 * @module git-fetch
 */

import { execFile, spawn } from 'node:child_process';
import { basename, relative, resolve } from 'node:path';
import { promisify } from 'node:util';
import { classifyGitFailure, gitNonInteractiveEnv, sanitizeGitOutput, type GitFailureCode } from './git-clone.js';
import {
  createLimiter,
  DEFAULT_GIT_TIMEOUT_MS,
  type Limiter,
  resolveOverviewLimits,
  resolveWorkspaceRepos,
  type GitRunner,
} from './git-workspace-status.js';
import { gitMissingError, gitSpawnAllowed } from './utils/git-availability.js';

const execFileAsync = promisify(execFile);

/**
 * Git processes in flight at once, for one run, and for a whole scheduler tick, because the tick hands ONE
 * bound to every run (see `createLimiter`): each fetch is one git process, and a folder can hold up to
 * `MAX_REPOS_LIMIT`. The tick bounds its folders separately, because the same semaphore cannot serve both
 * levels: a folder holding a slot would then wait for a slot its own fetch needs.
 */
export const FETCH_CONCURRENCY = 4;
/** A fetch on a busy remote can print a lot; a bound on what we will hold. */
const MAX_FETCH_OUTPUT_BYTES = 2 * 1024 * 1024;
/** git's stderr is kept as a bounded tail (as in git-clone.ts): enough for the reason, not the whole stream. */
const MAX_FETCH_STDERR_BYTES = 8_192;
/** A `git config --get` answer is one line; this is a sanity cap, not an expected size. */
const MAX_SSH_COMMAND_BYTES = 4_096;
/**
 * How long the process group gets to answer SIGTERM before the same escalation goes to SIGKILL. Kept as a
 * const so a test can say how long it is willing to wait for the group to actually die.
 */
export const FETCH_KILL_ESCALATION_MS = 3_000;

/**
 * Config overrides set ahead of the argv, so an unattended fetch cannot do more than move refs: no
 * fsmonitor hook, and no automatic maintenance or gc. A fetch is the git command that can run a
 * repository's own hooks (`reference-transaction`, and `pre-auto-gc` through the maintenance that follows a
 * fetch), and a gc started by a timer in a repository an agent is working in is exactly the kind of extra
 * write this module must not do. Kept as a const so a test can pin it without spawning git.
 */
export const FETCH_CONFIG_ARGS = ['-c', 'core.fsmonitor=false', '-c', 'maintenance.auto=false', '-c', 'gc.auto=0'];

/** The interval the user can turn on (Settings → Bottom bar, and Session Options → Git): bounds and default. */
export const DEFAULT_GIT_FETCH_INTERVAL_SECONDS = 300;
export const MIN_GIT_FETCH_INTERVAL_SECONDS = 30;
export const MAX_GIT_FETCH_INTERVAL_SECONDS = 3600;

export interface GitFetchSettings {
  enabled: boolean;
  intervalSeconds: number;
}

/**
 * A settings object as the scheduler should read it: absent means OFF, because nothing runs on a timer
 * until the user turns this on, and a number outside the schema's bounds is clamped rather than trusted.
 * Pure, so the reading itself is testable without a settings file.
 */
export function gitFetchSettingsFrom(settings: Record<string, unknown> | undefined): GitFetchSettings {
  const raw = settings?.gitFetchIntervalSeconds;
  const seconds =
    typeof raw === 'number' && Number.isFinite(raw) ? Math.round(raw) : DEFAULT_GIT_FETCH_INTERVAL_SECONDS;
  return {
    enabled: settings?.gitFetchEnabled === true,
    intervalSeconds: Math.min(MAX_GIT_FETCH_INTERVAL_SECONDS, Math.max(MIN_GIT_FETCH_INTERVAL_SECONDS, seconds)),
  };
}

/**
 * The only git command this module runs. Kept as a function so a test can pin the verb: nothing here
 * commits, checks out, merges or prunes, and no operand is interpolated: the repository is the process
 * `cwd` and the argv is fixed.
 */
export function buildFetchArgs(): string[] {
  return ['fetch', '--quiet'];
}

/**
 * The `git` process also gets the `FETCH_CONFIG_ARGS` overrides ahead of this argv; they are kept separate
 * so pinning the verb here does not have to say anything about maintenance, and so both can be tested
 * without spawning.
 *
 * A repository with no remote is a fact, not a fault. Git's wordings for it differ by version (2.47
 * exits quietly and this code is never reached, older git says "no default remote repository"), so the
 * branch is pinned on literal fixtures and the code the panel shows is the code this writes.
 */
export type FetchFailureCode = GitFailureCode | 'NO_REMOTE';

export interface FetchFailure {
  code: FetchFailureCode;
  /** User-facing summary. */
  message: string;
  /** Tail of git's own stderr, control-stripped and credential-redacted. */
  stderr: string;
}

/**
 * A thrown git error as the panel should show it. `classifyGitFailure` (git-clone.ts) already knows the
 * network reasons (auth, an unreachable host, a missing git), so they are reused here; only its timeout
 * wording is written for clones, so the fetch path replaces it with what the user can actually do.
 */
export function describeFetchFailure(err: unknown): FetchFailure {
  const e = err as { code?: unknown; stderr?: unknown; message?: string; killed?: boolean };
  const stderr = typeof e.stderr === 'string' ? e.stderr : '';
  const spawnError = typeof e.message === 'string' ? e.message : undefined;
  const clean = sanitizeGitOutput(stderr);
  const lower = `${clean}\n${spawnError ?? ''}`.toLowerCase();
  if (/no default remote repository|no remote configured|nothing to fetch/.test(lower)) {
    return {
      code: 'NO_REMOTE',
      message: 'This repository has no remote, so there is nothing to fetch.',
      stderr: clean,
    };
  }
  const timedOut = e.code === 'ETIMEDOUT' || e.killed === true;
  const failure = classifyGitFailure(stderr, timedOut, spawnError);
  if (failure.code === 'TIMEOUT')
    failure.message = 'Git timed out. Raise “Git status: git timeout” in Settings → Bottom bar, or fetch from a shell.';
  return failure;
}

/**
 * The environment a fetch gets, as a pure decision so it can be pinned without spawning git.
 *
 * `gitNonInteractiveEnv` supplies the BatchMode default, and the default is only a default: git reads
 * `GIT_SSH_COMMAND` from the environment ahead of the repository's `core.sshCommand`, so setting it would
 * override a repository that already chose its own ssh (an alternative host, an identity file, a jump box)
 * and break a setup that works today. The server's own `GIT_SSH` is the same kind of answer: git reads it
 * after both of those (`GIT_SSH_COMMAND`, then `core.sshCommand`, then `GIT_SSH`), so a written default would
 * hide it too. That is the only case where this module makes an ssh choice on the user's behalf, so it is the
 * whole decision here: the caller supplies the value it read, and this decides between the user's
 * environment and the repository's own answer.
 */
export function fetchEnvFor(base: NodeJS.ProcessEnv, repoSshCommand: string | null): NodeJS.ProcessEnv {
  const env = gitNonInteractiveEnv(base);
  // `gitNonInteractiveEnv` only writes the default when the environment had nothing, so this is exactly the
  // case where it was a choice rather than a pass-through, and the repository's own answer, or a `GIT_SSH` in
  // the environment, wins over it.
  if (!base.GIT_SSH_COMMAND && (repoSshCommand || base.GIT_SSH)) delete env.GIT_SSH_COMMAND;
  return env;
}

/**
 * The repository's own `core.sshCommand`, or null. One bounded, read-only `git config --get` per fetch:
 * git would honour that config itself if we did not write `GIT_SSH_COMMAND` over it, so honouring it means
 * not writing one. `--get` reads local and global config, which is the value git would have used, and no
 * hook or filter runs on the way to it.
 *
 * The read happens inside the same slot and the same wall-clock bound as the fetch it serves, so it cannot
 * add a fifth git process or push a fetch past the user's timeout: it spends part of it.
 */
export async function readRepoSshCommand(cwd: string, timeoutMs: number): Promise<string | null> {
  if (!gitSpawnAllowed()) return null;
  try {
    const { stdout } = await execFileAsync('git', ['config', '--get', 'core.sshCommand'], {
      cwd,
      timeout: timeoutMs,
      maxBuffer: MAX_SSH_COMMAND_BYTES,
      env: gitNonInteractiveEnv(),
    });
    return stdout.trim() || null;
  } catch {
    // A repository with no such setting, or a read that could not finish: the default is what git would have
    // used anyway, and a fetch must not fail because the check for a config value failed.
    return null;
  }
}

/**
 * Fetch is allowed to write refs, so this runner does not carry `--no-optional-locks`: fetch takes a
 * required lock anyway.
 *
 * `spawn`, not `execFile`, because the bound has to reach the whole tree (see the fileoverview): the
 * caller is answered at the timeout, and the SIGTERM → SIGKILL escalation is deliberately NOT cancelled
 * when the answer goes out, because the promise is a promise about the answer while the group still has to
 * die. That is the difference from `runGit` in git-clone.ts, which disarms the escalation at `finish` and so
 * can leave a `git-remote-http` child running after a timed-out call.
 *
 * The thrown error keeps the shape `describeFetchFailure` reads: `stderr` for the reason, `message` for a
 * spawn failure (`spawn git ENOENT` → GIT_MISSING), `killed` and `code` for the timeout. A non-zero exit
 * rejects the way `execFile` would (`code` is then the exit code), because resolving it would report a real
 * failure as a clean run with an empty reason.
 *
 * `timeoutMs` bounds the `core.sshCommand` read and the fetch TOGETHER: the spawn is armed with what the read
 * left, so a `git` that never answers costs one timeout, not two. A read that used the whole bound answers
 * as a timeout without starting the fetch.
 */
export const runFetch: GitRunner = async (cwd, args, opts) => {
  // Never Apple's placeholder git on a Mac without developer tools: answered as GIT_MISSING.
  if (!gitSpawnAllowed()) throw gitMissingError();
  const timeoutMs = opts?.timeoutMs ?? DEFAULT_GIT_TIMEOUT_MS;
  const startedAt = Date.now();
  const env = fetchEnvFor(process.env, await readRepoSshCommand(cwd, timeoutMs));
  const remainingMs = timeoutMs - (Date.now() - startedAt);
  if (remainingMs <= 0) {
    throw Object.assign(new Error(`Command failed: git ${args.join(' ')}`), {
      stderr: '',
      killed: true,
      code: 'ETIMEDOUT',
    });
  }

  return new Promise<string>((resolve, reject) => {
    let child: ReturnType<typeof spawn>;
    try {
      child = spawn('git', [...FETCH_CONFIG_ARGS, ...args], {
        cwd,
        env,
        stdio: ['ignore', 'pipe', 'pipe'],
        detached: true,
      });
    } catch (err) {
      reject(err);
      return;
    }

    let stdout = '';
    let stderr = '';
    let stdoutBytes = 0;
    let timedOut = false;
    let settled = false;
    let killTimer: NodeJS.Timeout | undefined;

    const killTree = (signal: NodeJS.Signals) => {
      try {
        if (child.pid) process.kill(-child.pid, signal);
      } catch {
        try {
          child.kill(signal);
        } catch {
          /* already gone */
        }
      }
    };

    const fail = (spawnError?: string, exitCode?: number | null) => {
      if (settled) return;
      settled = true;
      // Only the timeout timer is disarmed here. On a timeout the escalation is what the caller is waiting
      // for, and cancelling it is the bug this runner exists to fix.
      clearTimeout(timeoutTimer);
      reject(
        Object.assign(new Error(spawnError ?? `Command failed: git ${args.join(' ')}`), {
          stderr,
          killed: timedOut,
          code: timedOut ? 'ETIMEDOUT' : (exitCode ?? undefined),
        })
      );
    };

    const timeoutTimer = setTimeout(() => {
      timedOut = true;
      killTree('SIGTERM');
      killTimer = setTimeout(() => killTree('SIGKILL'), FETCH_KILL_ESCALATION_MS);
      fail();
    }, remainingMs);

    child.stdout?.on('data', (chunk: Buffer) => {
      stdoutBytes += chunk.length;
      if (stdoutBytes <= MAX_FETCH_OUTPUT_BYTES) stdout += chunk.toString('utf-8');
    });
    child.stderr?.on('data', (chunk: Buffer) => {
      stderr += chunk.toString('utf-8');
      if (stderr.length > MAX_FETCH_STDERR_BYTES * 2) stderr = stderr.slice(-MAX_FETCH_STDERR_BYTES);
    });

    const finish = (code: number | null) => {
      if (settled) return;
      // execFile's contract, which `describeFetchFailure` depends on: a non-zero exit rejects, so a real
      // git failure keeps its reason in `stderr` instead of becoming a green row with an empty one. `null`
      // means a signal, reachable only when something outside this runner killed the group: our own timeout
      // has already answered by then, and `settled` above is what keeps that answer the answer.
      if (code !== 0) return fail(undefined, code);
      settled = true;
      clearTimeout(timeoutTimer);
      if (killTimer) clearTimeout(killTimer);
      resolve(stdout);
    };

    child.on('error', (err) => fail(String(err)));
    child.on('close', (code) => finish(code));
  });
};

export interface GitFetchEntry {
  /** Folder name of the repository (its root's basename), as the panel names it. */
  name: string;
  /** The repository root relative to the working directory: `.`, `..`, `api`, `apps/web`. */
  path: string;
  ok: boolean;
  failure?: FetchFailure;
}

export interface GitFetchReport {
  /** `ok` when at least one repository was fetched (or attempted); the other states are as in the overview. */
  state: 'ok' | 'not-a-repo' | 'unsupported' | 'error';
  reason?: 'remote' | 'docker' | 'adopted';
  error?: string;
  /** One entry per repository fetched, in the same order the panel lists them. */
  repos: GitFetchEntry[];
  /** More than `repoLimit` repositories were found; only the first were fetched. */
  reposTruncated: boolean;
  /** The most repositories this fetch would list (the caller's setting, or `MAX_REPOS`). */
  repoLimit?: number;
  /** When the last repository finished, so the panel can say what the "behind" number is now based on. */
  fetchedAt: number;
}

/**
 * What one run did, in the shape a session keeps and the Session Options Git row shows. `trigger` says
 * whether the user clicked or the interval fired, because a number the user did not ask for should read
 * differently from one they did.
 */
/** What a run was, and why it happened. */
export type GitFetchTrigger = 'click' | 'interval';

export interface GitFetchStatus {
  ranAt: number;
  trigger: GitFetchTrigger;
  /** As in the report: `ok`, or the state that stopped the run. */
  state: GitFetchReport['state'];
  /** Repositories this run covered. */
  repos: number;
  /** How many of them could not be fetched. */
  failed: number;
  /** The first failure, named: enough for one row without reprinting the whole list. */
  firstFailure?: { name: string; code: FetchFailureCode };
}

/**
 * One run, with the trigger that caused it. A joiner gets the run already going, so what it reports is that
 * run's trigger rather than the one that made it ask: a click that joins an interval run did not fetch
 * anything itself, and the row the panel shows has to describe the fetch that actually happened.
 */
export interface GitFetchRun {
  report: GitFetchReport;
  trigger: GitFetchTrigger;
}

export function gitFetchStatusFrom(report: GitFetchReport, trigger: GitFetchTrigger): GitFetchStatus {
  const failed = report.repos.filter((r) => !r.ok);
  const status: GitFetchStatus = {
    ranAt: report.fetchedAt,
    trigger,
    state: report.state,
    repos: report.repos.length,
    failed: failed.length,
  };
  const first = failed[0];
  if (first?.failure) status.firstFailure = { name: first.name, code: first.failure.code };
  return status;
}

/** Options for the fetch path: the same repository rules and limits as an overview, without its cache clock. */
export interface GitFetchOptions {
  git?: GitRunner;
  home?: string;
  dockerWorkspaces?: string[];
  maxRepos?: number;
  timeoutMs?: number;
  /**
   * The shared slot count for a whole scheduler tick. Passed in so `FETCH_CONCURRENCY` bounds the tick
   * rather than each folder separately; without it, a tick over more than `FETCH_CONCURRENCY` folders could
   * have that many git processes going at once inside each one.
   */
  limiter?: Limiter;
}

export const emptyReport = (state: GitFetchReport['state'], extra: Partial<GitFetchReport> = {}): GitFetchReport => ({
  state,
  repos: [],
  reposTruncated: false,
  fetchedAt: Date.now(),
  ...extra,
});

async function fetchOne(dir: string, git: GitRunner, timeoutMs: number): Promise<FetchFailure | null> {
  try {
    await git(dir, buildFetchArgs(), { timeoutMs });
    return null;
  } catch (err) {
    return describeFetchFailure(err);
  }
}

/**
 * Fetch every repository the panel would show for `cwd`, through the same resolver so the two cannot
 * disagree. A repository that failed keeps its row with the reason, exactly as an unreadable repository
 * stays in the status list: the panel must show that something was not fetched rather than quietly skip it.
 */
export async function fetchGitWorkspaceOverview(cwd: string, opts: GitFetchOptions = {}): Promise<GitFetchReport> {
  const where = await resolveWorkspaceRepos(cwd, opts);
  if (where.kind === 'docker') return emptyReport('unsupported', { reason: 'docker' });
  if (where.kind === 'error') return emptyReport('error', { error: where.error });
  const dirs = where.kind === 'enclosing' ? [where.root] : where.dirs;
  if (!dirs.length) return emptyReport('not-a-repo');
  const { timeoutMs } = resolveOverviewLimits(opts);
  const runner = opts.git ?? runFetch;
  const run = opts.limiter ?? createLimiter(FETCH_CONCURRENCY);
  const failures = await run(dirs, (dir) => fetchOne(dir, runner, timeoutMs));
  const repos: GitFetchEntry[] = dirs.map((dir, i) => {
    const base = { name: basename(dir), path: relative(cwd, dir) || '.' };
    const failure = failures[i];
    return failure ? { ...base, ok: false, failure } : { ...base, ok: true };
  });
  return {
    state: 'ok',
    repos,
    reposTruncated: where.kind === 'children' ? where.truncated : false,
    repoLimit: resolveOverviewLimits(opts).maxRepos,
    fetchedAt: Date.now(),
  };
}

/**
 * Runs already going, keyed by the resolved folder. A request for a folder another run is already working on
 * JOINS that run instead of starting a second `git fetch` in the same clone: two fetches there collide on
 * git's ref lock (`cannot lock ref 'refs/remotes/origin/main'`), which is what a click during a tick would
 * otherwise do. A joiner gets the run already going's answer, including its limits and its trigger: the point
 * is not to fetch twice, not to fetch with the freshest options, and a click that fetched nothing cannot
 * report itself as the fetch.
 *
 * Keyed by `resolve`, not `realpath`, because `realpath` is itself one of the unbounded fs calls rule #516
 * bounds for user-chosen paths; the scheduler probes the folder bounded and calls this. Two paths that
 * resolve the same are the same folder here; a workspace reached through a symlink resolves to the link, so
 * a link and its target can be fetched by two runs, the accepted trade for keeping the probe bounded.
 */
const lane = new Map<string, Promise<GitFetchRun>>();

export async function fetchWorkspaceOnce(
  folder: string,
  opts: GitFetchOptions = {},
  trigger: GitFetchTrigger
): Promise<GitFetchRun> {
  const key = resolve(folder);
  const going = lane.get(key);
  // The joiner is handed the run already going as it is, trigger included: it did not cause that fetch, so it
  // must not report itself as having.
  if (going) return going;
  const run: Promise<GitFetchRun> = fetchGitWorkspaceOverview(key, opts)
    .then((report) => ({ report, trigger }))
    .finally(() => {
      // Only the run that is still the lane's own: a later run for the same folder must not be dropped by an
      // earlier one finishing late.
      if (lane.get(key) === run) lane.delete(key);
    });
  lane.set(key, run);
  return run;
}

/** Test seam: an in-memory lane is not cleared by stopping the scheduler, so a test has to clear it itself. */
export function clearGitFetchLane(): void {
  lane.clear();
}