/**
 * @fileoverview Validation for "create a new case in a custom folder" (`POST /api/cases` with a
 * `path`). Creating a case writes a scaffold (`CLAUDE.md`, `src/`, `.claude/settings.local.json`)
 * and registers the folder in the shared, ownerless linked-cases registry, so the target has to be
 * judged before anything is created:
 *
 *   - it must be an absolute path (a leading `~` is expanded) with no traversal and none of the shell
 *     metacharacters a session's working directory is later rejected for (`isValidWorkingDir`), so
 *     a case this accepts is one a session can actually start in;
 *   - it must not be a system directory, the home directory itself, Codeman's own data directory, or
 *     a credential/config tree (`~/.ssh`, `~/.aws`, `~/.claude`, ...). Judged on the path as typed AND on
 *     its symlink-resolved form, against both the given and the symlink-resolved roots (a home reached
 *     through a link, macOS's `/etc` -> `/private/etc`), so a link into a blocked tree is not a way
 *     around it;
 *   - it must not be, or be inside, a cases directory: a case there is a plain Create New, and the same
 *     folder listed both as a local case and as a linked one would make deleting it remove files;
 *   - its parent must already exist (one folder is created, never a whole chain), and the folder
 *     itself must not exist or must be an EMPTY directory (a folder with contents is Link Existing's
 *     job, and silently scaffolding into someone's project is the one thing this must never do);
 *   - it must not be a symlink.
 *
 * Pure except for the filesystem reads in `prepareNewCasePath`; the policy lives in `blockedReason`
 * so it can be tested without a disk.
 *
 * @module web/case-path
 */

import { promises as fs } from 'node:fs';
import { basename, dirname, join, resolve, sep } from 'node:path';
import { isValidWorkingDir } from './schemas.js';
import { describeUnknownPath, probePath } from '../utils/index.js';

/** System trees nobody creates a project in; creating one here is a mistake or an attack. */
const BLOCKED_SYSTEM_ROOTS = [
  '/bin',
  '/boot',
  '/dev',
  '/etc',
  '/lib',
  '/lib32',
  '/lib64',
  '/proc',
  '/run',
  '/sbin',
  '/sys',
  '/usr',
];

/** Home-relative trees that hold credentials or other tools' own configuration. */
const BLOCKED_HOME_DIRS = ['.ssh', '.gnupg', '.aws', '.kube', '.docker', '.claude', '.codex', '.gemini'];

export interface NewCasePathContext {
  home: string;
  /** Codeman's own state directory (`getDataDir()`), which must never become a case. */
  dataDir: string;
  /**
   * The cases directories (the caller's own and the shared one). A folder in one of them is already
   * listed as a local case, so it must not be registered as a linked one too.
   */
  casesDirs?: readonly string[];
}

export type NewCasePathResult =
  | { ok: true; path: string; existedEmpty: boolean }
  | { ok: false; code: 'INVALID' | 'BLOCKED' | 'NOT_FOUND' | 'EXISTS' | 'UNREACHABLE'; reason: string };

const isWithin = (child: string, root: string): boolean =>
  child === root || child.startsWith(root.endsWith(sep) ? root : root + sep);

/** `~` and `~/x` to the home directory; anything else is returned unchanged. */
export function expandHome(raw: string, home: string): string {
  if (raw === '~') return home;
  if (raw.startsWith('~/')) return join(home, raw.slice(2));
  return raw;
}

/**
 * Why a case may not live at this (already absolute and normalised) path, or null. `systemRoots`
 * defaults to the system trees as spelled; pass their symlink-resolved forms to judge a resolved path.
 */
export function blockedReason(
  absPath: string,
  ctx: NewCasePathContext,
  systemRoots: readonly string[] = BLOCKED_SYSTEM_ROOTS
): string | null {
  if (absPath === sep) return 'The filesystem root cannot be a case';
  for (const root of systemRoots) {
    if (isWithin(absPath, root)) return `${root} is a system directory`;
  }
  if (absPath === ctx.home) return 'The home folder itself cannot be a case; pick a folder inside it';
  for (const dir of BLOCKED_HOME_DIRS) {
    if (isWithin(absPath, join(ctx.home, dir))) return `~/${dir} holds credentials or another tool's configuration`;
  }
  if (isWithin(absPath, ctx.dataDir)) return "Codeman's own data folder cannot be a case";
  // Any Codeman instance's data dir under the home folder (~/.codeman, ~/.codeman-beta, ...), not only
  // the one this process uses.
  if (absPath.startsWith(ctx.home + sep)) {
    const firstSegment = absPath.slice(ctx.home.length + 1).split(sep)[0];
    if (/^\.codeman/.test(firstSegment)) return "Codeman's own data folder cannot be a case";
  }
  for (const dir of ctx.casesDirs ?? []) {
    if (isWithin(absPath, dir)) {
      return 'That folder is inside the cases folder; create a case there with plain Create New (no custom folder)';
    }
  }
  return null;
}

/** `p` with its symlinks resolved, or `p` itself when it does not exist (or cannot be read). */
async function realpathOr(p: string): Promise<string> {
  try {
    return await fs.realpath(p);
  } catch {
    return p;
  }
}

/** The context and system roots with their symlinks resolved, for judging a resolved path. */
async function resolvedPolicy(ctx: NewCasePathContext): Promise<[NewCasePathContext, string[]]> {
  const [home, dataDir, casesDirs, systemRoots] = await Promise.all([
    realpathOr(ctx.home),
    realpathOr(ctx.dataDir),
    Promise.all((ctx.casesDirs ?? []).map(realpathOr)),
    Promise.all(BLOCKED_SYSTEM_ROOTS.map(realpathOr)),
  ]);
  return [{ home, dataDir, casesDirs }, systemRoots];
}

/**
 * Judge `raw` as the folder for a new case and, if it is acceptable, say what to create.
 * Never creates anything.
 */
export async function prepareNewCasePath(raw: string, ctx: NewCasePathContext): Promise<NewCasePathResult> {
  const typed = raw.trim();
  if (!typed) return { ok: false, code: 'INVALID', reason: 'Enter a folder path' };
  const expanded = expandHome(typed, ctx.home);
  if (!isValidWorkingDir(expanded)) {
    return {
      ok: false,
      code: 'INVALID',
      reason: 'Use an absolute path with letters, numbers, spaces, - _ . only (no .., no shell characters)',
    };
  }

  const target = resolve(expanded);
  const typedBlock = blockedReason(target, ctx);
  if (typedBlock) return { ok: false, code: 'BLOCKED', reason: typedBlock };

  // Bounded first: the parent can sit on a network mount that stopped answering, where the
  // realpath/stat/lstat/readdir below would each hold a threadpool worker until it returns.
  // It is one folder the user named, so the probe may pass the bulk cap (never the ceiling).
  const parentState = await probePath(dirname(target), { pastCap: true });
  if (parentState === 'absent') {
    return { ok: false, code: 'NOT_FOUND', reason: `The parent folder ${dirname(target)} does not exist` };
  }
  if (parentState === 'unknown') {
    return {
      ok: false,
      code: 'UNREACHABLE',
      reason: describeUnknownPath('The parent folder', dirname(target), { pastCap: true }),
    };
  }

  // Resolve the parent's symlinks, then judge again: a link into a blocked tree must not pass.
  let realParent: string;
  try {
    realParent = await fs.realpath(dirname(target));
    if (!(await fs.stat(realParent)).isDirectory()) {
      return { ok: false, code: 'INVALID', reason: `${dirname(target)} is not a folder` };
    }
  } catch {
    return { ok: false, code: 'NOT_FOUND', reason: `The parent folder ${dirname(target)} does not exist` };
  }
  const real = join(realParent, basename(target));
  // The resolved path against the roots as given AND as resolved: with home reached through a link, a
  // link to <real home>/.ssh is only caught by the resolved home; on macOS /etc is /private/etc.
  const [resolvedCtx, resolvedSystemRoots] = await resolvedPolicy(ctx);
  const realBlock = blockedReason(real, ctx) ?? blockedReason(real, resolvedCtx, resolvedSystemRoots);
  if (realBlock) return { ok: false, code: 'BLOCKED', reason: realBlock };

  try {
    const st = await fs.lstat(real);
    if (st.isSymbolicLink()) return { ok: false, code: 'INVALID', reason: `${target} is a symbolic link` };
    if (!st.isDirectory()) return { ok: false, code: 'INVALID', reason: `${target} exists and is not a folder` };
    if ((await fs.readdir(real)).length > 0) {
      return {
        ok: false,
        code: 'EXISTS',
        reason: `${target} already has files in it. Use "Link Existing" for a project that already exists`,
      };
    }
    return { ok: true, path: real, existedEmpty: true };
  } catch (err) {
    if ((err as NodeJS.ErrnoException).code === 'ENOENT') return { ok: true, path: real, existedEmpty: false };
    return { ok: false, code: 'INVALID', reason: `Cannot read ${target}: ${(err as Error).message}` };
  }
}