/**
 * @fileoverview Periodic GC for paste-image files.
 *
 * Without cleanup, /api/sessions/:id/paste-image accumulates files indefinitely
 * under {workingDir}/.claude-images/. The route only triggers cleanup on
 * killMux=true session deletion, so long-lived sessions can fill disk under
 * heavy pasting. This sweeper bounds disk use by deleting `paste-*` files
 * older than MAX_AGE_MS from each live session's image dir on an interval.
 *
 * Conservative defaults — only files matching the `paste-` prefix are
 * considered, and we lstat (not stat) so a planted symlink cannot escape the
 * image dir.
 */
import fs from 'node:fs/promises';
import { realpathSync } from 'node:fs';
import { join, resolve } from 'node:path';
import type { SessionPort } from './ports/index.js';

const MAX_AGE_MS = 7 * 24 * 60 * 60 * 1000; // 7 days
const SWEEP_INTERVAL_MS = 60 * 60 * 1000; // 1 hour
const INITIAL_DELAY_MS = 30 * 1000; // 30s after startup

export async function sweepPasteImagesOnce(
  ctx: Pick<SessionPort, 'sessions'>,
  now: number = Date.now()
): Promise<{ scanned: number; deleted: number }> {
  const cutoff = now - MAX_AGE_MS;
  let scanned = 0;
  let deleted = 0;
  for (const session of ctx.sessions.values()) {
    const dir = join(session.workingDir, '.claude-images');
    let entries: string[];
    try {
      entries = await fs.readdir(dir);
    } catch {
      continue; // dir absent — nothing to do
    }
    for (const name of entries) {
      if (!name.startsWith('paste-')) continue;
      const p = join(dir, name);
      scanned += 1;
      try {
        const st = await fs.lstat(p);
        if (!st.isFile()) continue;
        if (st.mtimeMs < cutoff) {
          await fs.unlink(p);
          deleted += 1;
        }
      } catch {
        // best-effort: skip permission/race errors silently
      }
    }
  }
  return { scanned, deleted };
}

/**
 * The path two sessions must share to share a paste-image dir: the canonical
 * path when it can be resolved, so a sibling that reaches the same directory
 * through a symlink matches, and the normalised path otherwise (a directory
 * that no longer exists has nothing left to protect).
 */
function canonicalDir(dir: string): string {
  try {
    return realpathSync(dir);
  } catch {
    return resolve(dir);
  }
}

/** One session the paste-image guard weighs: its id, directory and, for a persisted record, its status. */
export interface PasteImageDirUser {
  id: string;
  workingDir: string;
  status?: string;
}

/**
 * Does another live session still use this working directory's paste-image
 * dir? Deleting a session removes `{workingDir}/.claude-images` recursively,
 * and several sessions routinely share one case directory, so without this
 * check closing one session deletes the pasted images a sibling in the same
 * case still refers to.
 *
 * Two kinds of sibling count as live:
 *
 * - a session in the server's map, unless it is itself being killed;
 * - a persisted record whose status is not `stopped`. That covers a session
 *   detached with `killMux=false`, which leaves the server's map while its
 *   tmux pane keeps running, and a session whose detach is still in progress.
 *
 * A session being KILLED does not count. Without that exemption, killing two
 * sessions of one case concurrently (a bulk delete, or the exited-agent sweep
 * closing two panes on one tick) would have each defer to the other, and
 * neither would remove the dir.
 *
 * Erring toward "in use" only costs a missed deletion, which the periodic
 * sweep above ages out. A pinned record whose tmux session is gone keeps its
 * status through boot pruning, so it holds the dir this way until unpinned.
 */
export function pasteImageDirInUseByOtherSession(input: {
  live: Iterable<PasteImageDirUser>;
  persisted: Iterable<PasteImageDirUser>;
  closingId: string;
  workingDir: string;
  killing: ReadonlySet<string>;
}): boolean {
  const target = canonicalDir(input.workingDir);
  const matches = (user: PasteImageDirUser): boolean =>
    user.id !== input.closingId &&
    !input.killing.has(user.id) &&
    !!user.workingDir &&
    canonicalDir(user.workingDir) === target;
  for (const user of input.live) {
    if (matches(user)) return true;
  }
  for (const user of input.persisted) {
    if (user.status === 'stopped') continue;
    if (matches(user)) return true;
  }
  return false;
}

export function startPasteImageGc(ctx: Pick<SessionPort, 'sessions'>): () => void {
  const initial = setTimeout(() => {
    void sweepPasteImagesOnce(ctx);
  }, INITIAL_DELAY_MS);
  const interval = setInterval(() => {
    void sweepPasteImagesOnce(ctx);
  }, SWEEP_INTERVAL_MS);
  if (typeof initial.unref === 'function') initial.unref();
  if (typeof interval.unref === 'function') interval.unref();
  return (): void => {
    clearTimeout(initial);
    clearInterval(interval);
  };
}