import {
  closeSync,
  constants,
  fstatSync,
  lstatSync,
  openSync,
  readSync,
  realpathSync,
} from "node:fs";
import type { Stats } from "node:fs";
import { dirname, isAbsolute, join, normalize } from "node:path";
import { parseDocument } from "yaml";
import { z } from "zod";
import { isValidPasswordHash, verifyPassword, verifyWithDummy } from "./password.js";
import type { LoadedAuthConfig, Role } from "./types.js";
import { createWindowsAuthStorageBridge, type WindowsAuthStorageBridge } from "./windows-auth-storage.js";

const MAX_USERS_YAML_BYTES = 1 << 20;
const USERNAME_PATTERN = /^[A-Za-z0-9][A-Za-z0-9._@-]{2,63}$/;
const UUID_V4_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
const ROLES = ["user", "admin"] as const;
const invalid = (): Error => new Error("local_user_registry_invalid");

function runtimeOwner(): number {
  if (process.platform === "win32" || typeof process.geteuid !== "function") throw invalid();
  const owner = process.geteuid();
  if (!Number.isSafeInteger(owner) || owner < 0) throw invalid();
  return owner;
}

export interface LocalUserRecord {
  id: string;
  username: string;
  normalizedUsername: string;
  displayName?: string;
  passwordHash: string;
  roles: readonly Role[];
  enabled: boolean;
  authRevision: number;
}

export interface LocalUserRegistry {
  /** Safe production diagnostic probe; never returns user records or hashes. */
  hasEnabledAdmin(): Promise<boolean>;
  findByUsername(username: string): Promise<LocalUserRecord | undefined>;
  findBySubject(id: string): Promise<LocalUserRecord | undefined>;
  verify(user: LocalUserRecord | undefined, password: string): Promise<boolean>;
}

/** Keeps only the registry named by the current coherent authentication-config snapshot. */
export interface CurrentLocalUserRegistryResolver {
  resolve(loaded: LoadedAuthConfig): LocalUserRegistry | undefined;
}

/** Native Windows obtains protected registry bytes only from the hidden tht bridge. */
export interface LocalUserRegistryOptions {
  windowsStorageBridge?: Pick<WindowsAuthStorageBridge, "readLocalUsers">;
}

interface FileIdentity {
  dev: number;
  ino: number;
  uid: number;
  size: number;
  mtimeMs: number;
}

interface DirectoryIdentity {
  dev: number;
  ino: number;
  uid: number;
  mode: number;
}

interface RegistryIdentity {
  file: FileIdentity;
  directory: DirectoryIdentity;
}

const roleSchema = z.enum(ROLES);
const userSchema = z.strictObject({
  id: z.string().regex(UUID_V4_PATTERN),
  username: z.string().regex(USERNAME_PATTERN),
  displayName: z.string().optional().refine((value) => value === undefined || !/\p{Cc}/u.test(value)),
  passwordHash: z.string().refine(isValidPasswordHash),
  roles: z.array(roleSchema).min(1).superRefine((roles, context) => {
    if (new Set(roles).size !== roles.length) context.addIssue({ code: "custom", message: "duplicate role" });
  }),
  enabled: z.boolean(),
  authRevision: z.number().int().positive().safe(),
});
const registrySchema = z.strictObject({ version: z.literal(1), users: z.array(userSchema).min(1) });

function normalizeUsername(username: string): string {
  return username.replace(/[A-Z]/g, (character) => character.toLowerCase());
}

function sameFileIdentity(left: FileIdentity, right: FileIdentity): boolean {
  return left.dev === right.dev && left.ino === right.ino && left.uid === right.uid
    && left.size === right.size && left.mtimeMs === right.mtimeMs;
}

function sameDirectoryIdentity(left: DirectoryIdentity, right: DirectoryIdentity): boolean {
  return left.dev === right.dev && left.ino === right.ino && left.uid === right.uid && left.mode === right.mode;
}

function sameIdentity(left: RegistryIdentity, right: RegistryIdentity): boolean {
  return sameFileIdentity(left.file, right.file) && sameDirectoryIdentity(left.directory, right.directory);
}

function validateCanonicalPath(path: string): void {
  if (typeof path !== "string" || path.length === 0 || path.includes("\0") || !isAbsolute(path) || normalize(path) !== path) throw invalid();
  const parent = dirname(path);
  if (realpathSync(parent) !== parent) throw invalid();
}

function fileMetadata(info: Stats, owner: number): FileIdentity {
  if (!info.isFile() || info.uid !== owner || info.nlink !== 1 || (info.mode & 0o7777) !== 0o600) throw invalid();
  if (info.size < 0 || info.size > MAX_USERS_YAML_BYTES) throw invalid();
  return { dev: info.dev, ino: info.ino, uid: info.uid, size: info.size, mtimeMs: info.mtimeMs };
}

function directoryMetadata(info: Stats, owner: number): DirectoryIdentity {
  if (!info.isDirectory() || info.uid !== owner || (info.mode & 0o7777) !== 0o700) throw invalid();
  return { dev: info.dev, ino: info.ino, uid: info.uid, mode: info.mode & 0o7777 };
}

function directoryIdentity(path: string, owner: number): DirectoryIdentity {
  const parent = dirname(path);
  if (realpathSync(parent) !== parent) throw invalid();
  return directoryMetadata(lstatSync(parent) as Stats, owner);
}

function registryIdentity(path: string, owner: number): RegistryIdentity {
  validateCanonicalPath(path);
  const info = lstatSync(path);
  return { file: fileMetadata(info as Stats, owner), directory: directoryIdentity(path, owner) };
}

function openDirectoryDescriptor(path: string): number | undefined {
  if (process.platform === "win32") return undefined;
  const flags = constants.O_RDONLY
    | (constants.O_DIRECTORY ?? 0)
    | (constants.O_NOFOLLOW ?? 0)
    | (constants.O_NONBLOCK ?? 0);
  return openSync(path, flags);
}

function readBounded(path: string, owner: number): { source: string; identity: RegistryIdentity } {
  validateCanonicalPath(path);
  const beforeDirectory = directoryIdentity(path, owner);
  const beforePath = lstatSync(path);
  const before = fileMetadata(beforePath as Stats, owner);
  let directoryDescriptor: number | undefined;
  let descriptor: number | undefined;
  try {
    directoryDescriptor = openDirectoryDescriptor(dirname(path));
    const openedDirectory = directoryDescriptor === undefined
      ? beforeDirectory
      : directoryMetadata(fstatSync(directoryDescriptor) as Stats, owner);
    if (!sameDirectoryIdentity(beforeDirectory, openedDirectory)) throw invalid();
    descriptor = openSync(path, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK);
    const opened = fileMetadata(fstatSync(descriptor) as Stats, owner);
    if (!sameFileIdentity(before, opened)) throw invalid();
    const buffer = Buffer.allocUnsafe(MAX_USERS_YAML_BYTES + 1);
    let offset = 0;
    while (offset < buffer.length) {
      const bytesRead = readSync(descriptor, buffer, offset, buffer.length - offset, null);
      if (bytesRead === 0) break;
      offset += bytesRead;
    }
    if (offset > MAX_USERS_YAML_BYTES) throw invalid();
    const after = fileMetadata(fstatSync(descriptor) as Stats, owner);
    const afterPath = fileMetadata(lstatSync(path) as Stats, owner);
    const afterDirectory = directoryMetadata(lstatSync(dirname(path)) as Stats, owner);
    const afterOpenedDirectory = directoryDescriptor === undefined
      ? afterDirectory
      : directoryMetadata(fstatSync(directoryDescriptor) as Stats, owner);
    if (!sameFileIdentity(opened, after) || !sameFileIdentity(after, afterPath)
      || !sameDirectoryIdentity(beforeDirectory, afterDirectory)
      || !sameDirectoryIdentity(openedDirectory, afterOpenedDirectory)) throw invalid();
    const source = new TextDecoder("utf-8", { fatal: true }).decode(buffer.subarray(0, offset));
    return { source, identity: { file: after, directory: afterDirectory } };
  } catch {
    throw invalid();
  } finally {
    if (descriptor !== undefined) {
      try { closeSync(descriptor); } catch { /* sanitized by design */ }
    }
    if (directoryDescriptor !== undefined) {
      try { closeSync(directoryDescriptor); } catch { /* sanitized by design */ }
    }
  }
}

function parseRegistry(source: string): LocalUserRecord[] {
  try {
    const document = parseDocument(source, { uniqueKeys: true });
    if (document.errors.length > 0 || document.warnings.length > 0) throw invalid();
    const parsed = registrySchema.parse(document.toJSON());
    const ids = new Set<string>();
    const usernames = new Set<string>();
    const records = parsed.users.map((user) => {
      const normalizedUsername = normalizeUsername(user.username);
      if (ids.has(user.id) || usernames.has(normalizedUsername)) throw invalid();
      ids.add(user.id);
      usernames.add(normalizedUsername);
      return Object.freeze({
        id: user.id,
        username: user.username,
        normalizedUsername,
        ...(user.displayName === undefined ? {} : { displayName: user.displayName }),
        passwordHash: user.passwordHash,
        roles: Object.freeze([...user.roles]) as readonly Role[],
        enabled: user.enabled,
        authRevision: user.authRevision,
      });
    });
    return records;
  } catch {
    throw invalid();
  }
}

function load(path: string, owner: number): { records: LocalUserRecord[]; identity: RegistryIdentity } {
  const read = readBounded(path, owner);
  return { records: parseRegistry(read.source), identity: read.identity };
}

export function createLocalUserRegistry(usersPath: string, options: LocalUserRegistryOptions = {}): LocalUserRegistry {
  let cached: { records: LocalUserRecord[]; identity: RegistryIdentity } | undefined;
  const windowsStorage = process.platform === "win32"
    ? options.windowsStorageBridge ?? createWindowsAuthStorageBridge()
    : undefined;

  function currentPosix(): LocalUserRecord[] {
    try {
      const owner = runtimeOwner();
      const before = registryIdentity(usersPath, owner);
      if (cached && sameIdentity(cached.identity, before)) return cached.records;
      for (let attempt = 0; attempt < 2; attempt += 1) {
        const loaded = load(usersPath, owner);
        if (sameIdentity(loaded.identity, registryIdentity(usersPath, owner))) {
          cached = loaded;
          return loaded.records;
        }
      }
    } catch {
      throw invalid();
    }
    throw invalid();
  }

  async function current(): Promise<LocalUserRecord[]> {
    if (process.platform !== "win32") return currentPosix();
    try {
      if (!windowsStorage) throw invalid();
      const contents = await windowsStorage.readLocalUsers(usersPath);
      if (!Buffer.isBuffer(contents) || contents.length === 0 || contents.length > MAX_USERS_YAML_BYTES) throw invalid();
      return parseRegistry(new TextDecoder("utf-8", { fatal: true }).decode(contents));
    } catch {
      throw invalid();
    }
  }

  async function operationalRecords(): Promise<LocalUserRecord[]> {
    const records = await current();
    if (!records.some((user) => user.enabled && user.roles.includes("admin"))) throw invalid();
    return records;
  }

  return {
    async hasEnabledAdmin(): Promise<boolean> {
      return (await current()).some((user) => user.enabled && user.roles.includes("admin"));
    },
    async findByUsername(username: string): Promise<LocalUserRecord | undefined> {
      const normalized = normalizeUsername(username);
      return (await operationalRecords()).find((user) => user.normalizedUsername === normalized);
    },
    async findBySubject(id: string): Promise<LocalUserRecord | undefined> {
      return (await operationalRecords()).find((user) => user.id === id);
    },
    async verify(user: LocalUserRecord | undefined, password: string): Promise<boolean> {
      if (!user || !user.enabled) {
        await verifyWithDummy(password);
        return false;
      }
      return await verifyPassword(password, user.passwordHash);
    },
  };
}

export function createCurrentLocalUserRegistryResolver(options: LocalUserRegistryOptions = {}): CurrentLocalUserRegistryResolver {
  let current: { usersPath: string; registry: LocalUserRegistry } | undefined;
  return {
    resolve(loaded: LoadedAuthConfig): LocalUserRegistry | undefined {
      if (loaded.value.mode !== "local") return undefined;
      const usersPath = join(dirname(loaded.sourcePath), loaded.value.local.usersFile);
      if (current?.usersPath === usersPath) return current.registry;
      const registry = createLocalUserRegistry(usersPath, options);
      current = { usersPath, registry };
      return registry;
    },
  };
}