// Read-only file access for approved Pi session roots (#1507, CHAT-02).
//
// A root is <projectRoot>/.pi/state/<seat>/sessions. The project root comes
// from the board's own configuration and is trusted as given (it may itself
// be a symlink, like the compatibility path to this checkout). Every
// component below it must be a real directory, never a symlink, and a
// session file must be a regular file directly inside the root.
//
// A file is opened O_RDONLY | O_NOFOLLOW | O_NONBLOCK, and the descriptor's
// (dev, ino) must match the lstat taken before the open. Node has no openat,
// so a directory component swapped between the checks and the open is caught
// by re-checking the components after the open, not prevented outright. The
// seat that owns a root can write there anyway; the checks keep anything
// outside the root from being read through it.
//
// Nothing here writes, renames, creates or migrates a file.

import { lstatSync, openSync, fstatSync, readSync, closeSync, readdirSync, constants } from "node:fs";
import { join, relative, isAbsolute, sep, basename } from "node:path";

export class Refusal extends Error {
  constructor(code, message, { reconcile = false } = {}) {
    super(message);
    this.code = code;
    this.reconcile = reconcile;
  }
}

// Refusals of the CHAT-03 control layer (controller, claims, guard, engine
// pin). They reach a socket client, never the reader's HTTP routes, so the
// control board's status map covers only the reader's own codes.
export class ControlRefusal extends Refusal {}

const SESSION_NAME = /^[A-Za-z0-9][A-Za-z0-9._:-]*\.jsonl$/;

// Permission errors inside a root are one conversation's problem, not the
// catalogue's: they become a refusal instead of a thrown error.
function denied(err, what) {
  if (err.code === "EACCES" || err.code === "EPERM") return new Refusal("unreadable", `${what} is not readable`);
  return err;
}

// A directory above the file without search permission is refused the same
// way, so one bad root does not fail the catalogue.
function lstatOrNull(path) {
  try {
    return lstatSync(path, { bigint: true });
  } catch (err) {
    if (err.code === "ENOENT" || err.code === "ENOTDIR") return null;
    throw denied(err, "a session path component");
  }
}

// Every component from the project root down to the sessions directory must
// be a real directory.
export function checkRoot(root) {
  const rel = relative(root.projectRoot, root.dir);
  if (!rel || rel.startsWith("..") || isAbsolute(rel)) throw new Refusal("unsafe-path", "session root is outside its project");
  let path = root.projectRoot;
  for (const part of rel.split(sep)) {
    path = join(path, part);
    const st = lstatOrNull(path);
    if (!st) throw new Refusal("unavailable", "session root does not exist");
    if (st.isSymbolicLink()) throw new Refusal("unsafe-path", "session root contains a symlink");
    if (!st.isDirectory()) throw new Refusal("unsafe-path", "session root is not a directory");
  }
}

// Session files directly inside a root, by name. Symlinks and anything that
// is not a regular *.jsonl file are reported, never followed.
export function listSessionFiles(root) {
  checkRoot(root);
  const files = [], refused = [];
  let dirents;
  try {
    dirents = readdirSync(root.dir, { withFileTypes: true });
  } catch (err) {
    throw denied(err, "session root");
  }
  for (const dirent of dirents) {
    if (!dirent.name.endsWith(".jsonl")) continue;
    if (!SESSION_NAME.test(dirent.name)) refused.push({ name: dirent.name, code: "unsafe-path" });
    else if (dirent.isSymbolicLink()) refused.push({ name: dirent.name, code: "unsafe-path" });
    else if (dirent.isFile()) files.push(dirent.name);
  }
  return { files: files.sort(), refused };
}

// Opens one session file read-only. The caller must close the returned fd.
export function openSessionFile(root, name) {
  if (typeof name !== "string" || name !== basename(name) || !SESSION_NAME.test(name)) throw new Refusal("unsafe-path", "not a session file name");
  checkRoot(root);
  const path = join(root.dir, name);
  const before = lstatOrNull(path);
  if (!before) throw new Refusal("unknown-conversation", "session file no longer exists", { reconcile: true });
  if (before.isSymbolicLink()) throw new Refusal("unsafe-path", "session file is a symlink");
  if (!before.isFile()) throw new Refusal("unsafe-path", "session file is not a regular file");
  let fd;
  try {
    fd = openSync(path, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK);
  } catch (err) {
    if (err.code === "ELOOP") throw new Refusal("unsafe-path", "session file became a symlink");
    if (err.code === "ENOENT") throw new Refusal("unknown-conversation", "session file no longer exists", { reconcile: true });
    throw denied(err, "session file");
  }
  try {
    const st = fstatSync(fd, { bigint: true });
    if (!st.isFile() || st.dev !== before.dev || st.ino !== before.ino) throw new Refusal("unsafe-path", "session file changed while it was opened");
    checkRoot(root);
    return { fd, dev: st.dev.toString(), ino: st.ino.toString(), size: Number(st.size) };
  } catch (err) {
    closeSync(fd);
    throw err;
  }
}

export function readRange(fd, start, length) {
  const buf = Buffer.alloc(length);
  let done = 0;
  while (done < length) {
    const n = readSync(fd, buf, done, length - done, start + done);
    if (n === 0) break;
    done += n;
  }
  return done === length ? buf : buf.subarray(0, done);
}

export { closeSync };