/**
 * MCP Auth Storage Module
 *
 * Handles secure storage of OAuth credentials, tokens, client information,
 * and legacy PKCE state for MCP servers.
 *
 * Persistent OAuth entries are stored in the operating system credential store.
 * Legacy plaintext entries are imported from $MCP_OAUTH_DIR/sha256-<server-hash>/tokens.json
 * when set, otherwise <Pi agent dir>/mcp-oauth/sha256-<server-hash>/tokens.json,
 * then the plaintext file is removed.
 */

import { createHash } from 'crypto';
import { createRequire } from 'module';
import { readFileSync, existsSync, rmSync } from 'fs';
import { join } from 'path';
import { getAgentPath } from './agent-dir.ts';
import { resolveConfiguredOAuthDir } from './config.ts';

const require = createRequire(import.meta.url);
const AUTH_SECRET_SERVICE = 'pi-mcp-adapter.oauth';
const TEST_AUTH_STORE_ENV = 'PI_MCP_ADAPTER_TEST_AUTH_STORE';

/** OAuth token storage format */
export interface StoredTokens {
  accessToken: string;
  refreshToken?: string;
  expiresAt?: number; // Unix timestamp in seconds
  scope?: string;
  /** SEP-2352 authorization-server issuer stamp from the SDK */
  issuer?: string;
}

/** OAuth client information from dynamic or static registration */
export interface StoredClientInfo {
  clientId: string;
  clientSecret?: string;
  clientIdIssuedAt?: number;
  clientSecretExpiresAt?: number;
  redirectUris?: string[];
  /** SEP-2352 authorization-server issuer stamp from the SDK */
  issuer?: string;
  /**
   * True when this entry is a secretless SEP-2352 issuer stub persisted for a
   * config-pre-registered client (written by the config-clientId path of
   * saveClientInformation). Such a stub is only usable when paired with the
   * config that supplies the client secret; it must never be served as
   * standalone client information.
   */
  configPreRegistered?: boolean;
}

/** Complete auth entry for a server */
export interface AuthEntry {
  tokens?: StoredTokens;
  clientInfo?: StoredClientInfo;
  codeVerifier?: string;
  oauthState?: string;
  serverUrl?: string; // Track the URL these credentials are for
}

export interface AuthStorageOptions {
  /** Legacy plaintext import directory. Persistent secrets no longer use this as their store. */
  baseDir?: string;
}

interface KeyringEntry {
  getPassword(): string | null;
  setPassword(password: string): void;
  deleteCredential(): boolean;
}

type KeyringEntryConstructor = new (service: string, account: string) => KeyringEntry;

interface AuthSecretStore {
  read(account: string): string | undefined;
  write(account: string, payload: string): void;
  remove(account: string): void;
}

let KeyringEntryClass: KeyringEntryConstructor | undefined;
const memoryAuthEntries = new Map<string, string>();

const memoryAuthSecretStore: AuthSecretStore = {
  read(account) {
    return memoryAuthEntries.get(account);
  },
  write(account, payload) {
    memoryAuthEntries.set(account, payload);
  },
  remove(account) {
    memoryAuthEntries.delete(account);
  },
};

const keyringAuthSecretStore: AuthSecretStore = {
  read(account) {
    return getKeyringEntry(account).getPassword() ?? undefined;
  },
  write(account, payload) {
    getKeyringEntry(account).setPassword(payload);
  },
  remove(account) {
    getKeyringEntry(account).deleteCredential();
  },
};

const unavailableAuthSecretStore: AuthSecretStore = {
  read() {
    throw new Error('simulated secure credential store unavailable');
  },
  write() {
    throw new Error('simulated secure credential store unavailable');
  },
  remove() {
    throw new Error('simulated secure credential store unavailable');
  },
};

export function resetTestAuthSecretStore(): void {
  memoryAuthEntries.clear();
}

function getAuthSecretStore(): AuthSecretStore {
  if (process.env[TEST_AUTH_STORE_ENV] === 'memory') return memoryAuthSecretStore;
  if (process.env[TEST_AUTH_STORE_ENV] === 'unavailable') return unavailableAuthSecretStore;
  return keyringAuthSecretStore;
}

function getKeyringEntry(account: string): KeyringEntry {
  try {
    KeyringEntryClass ??= (require('@napi-rs/keyring') as { Entry: KeyringEntryConstructor }).Entry;
    return new KeyringEntryClass(AUTH_SECRET_SERVICE, account);
  } catch (error) {
    throw new Error('OAuth secure credential storage is unavailable. Configure the OS credential store and retry authentication.', { cause: error });
  }
}

export function getAuthStorageOptions(oauthDir: unknown, cwd = process.cwd()): AuthStorageOptions {
  const baseDir = resolveConfiguredOAuthDir(oauthDir, cwd);
  return baseDir ? { baseDir } : {};
}

export function getAuthBaseDir(options: AuthStorageOptions = {}): string {
  const override = process.env.MCP_OAUTH_DIR?.trim();
  if (override) return override;
  return options.baseDir ?? getAgentPath('mcp-oauth');
}

/**
 * Get the legacy server-specific directory path.
 */
function getServerDir(serverName: string, options?: AuthStorageOptions): string {
  if (typeof serverName !== 'string') {
    throw new Error(`Invalid MCP server name: ${JSON.stringify(serverName)}`);
  }
  const storageKey = getAuthEntryAccount(serverName);
  return join(getAuthBaseDir(options), storageKey);
}

function getAuthEntryAccount(serverName: string): string {
  if (typeof serverName !== 'string') {
    throw new Error(`Invalid MCP server name: ${JSON.stringify(serverName)}`);
  }
  return `sha256-${createHash('sha256').update(serverName, 'utf8').digest('hex')}`;
}

/**
 * Get the legacy plaintext tokens file path for a server.
 */
export function getAuthEntryFilePath(serverName: string, options?: AuthStorageOptions): string {
  return join(getServerDir(serverName, options), 'tokens.json');
}

function parseAuthEntryPayload(serverName: string, payload: string, source: string): AuthEntry {
  try {
    return JSON.parse(payload) as AuthEntry;
  } catch (error) {
    throw new Error(`Failed to parse OAuth credentials for ${serverName} from ${source}`, { cause: error });
  }
}

function readLegacyAuthEntry(serverName: string, options?: AuthStorageOptions): AuthEntry | undefined {
  const filePath = getAuthEntryFilePath(serverName, options);
  if (!existsSync(filePath)) return undefined;
  const data = readFileSync(filePath, 'utf-8');
  return parseAuthEntryPayload(serverName, data, filePath);
}

function removeLegacyAuthEntry(serverName: string, options?: AuthStorageOptions): void {
  const filePath = getAuthEntryFilePath(serverName, options);
  if (!existsSync(filePath)) return;
  try {
    rmSync(filePath, { force: true });
  } catch (error) {
    throw new Error(`Failed to remove legacy plaintext OAuth credentials for ${serverName} at ${filePath}`, { cause: error });
  }

  const dir = getServerDir(serverName, options);
  try {
    rmSync(dir, { recursive: true });
  } catch {
    // Directory may contain future non-secret metadata; the plaintext file was already removed.
  }
}

function writeSecureAuthEntry(serverName: string, entry: AuthEntry): void {
  const account = getAuthEntryAccount(serverName);
  try {
    getAuthSecretStore().write(account, JSON.stringify(entry, null, 2));
  } catch (error) {
    throw new Error(`Failed to write OAuth credentials for ${serverName} to the OS secure credential store`, { cause: error });
  }
}

/**
 * Read the auth entry for a server from the OS secure store, importing and
 * deleting a legacy plaintext entry when present.
 */
function readAuthEntry(serverName: string, options?: AuthStorageOptions): AuthEntry | undefined {
  const account = getAuthEntryAccount(serverName);
  let payload: string | undefined;
  try {
    payload = getAuthSecretStore().read(account);
  } catch (error) {
    throw new Error(`Failed to read OAuth credentials for ${serverName} from the OS secure credential store`, { cause: error });
  }

  if (payload !== undefined) {
    const entry = parseAuthEntryPayload(serverName, payload, 'OS secure credential store');
    removeLegacyAuthEntry(serverName, options);
    return entry;
  }

  const legacyEntry = readLegacyAuthEntry(serverName, options);
  if (!legacyEntry) return undefined;
  writeSecureAuthEntry(serverName, legacyEntry);
  removeLegacyAuthEntry(serverName, options);
  return legacyEntry;
}

/**
 * Get auth entry for a server.
 */
export function getAuthEntry(serverName: string, options?: AuthStorageOptions): AuthEntry | undefined {
  return readAuthEntry(serverName, options);
}

/**
 * Get auth entry and validate it's for the correct URL.
 * Returns undefined if URL has changed (credentials are invalid).
 */
export function getAuthForUrl(serverName: string, serverUrl: string, options?: AuthStorageOptions): AuthEntry | undefined {
  const entry = getAuthEntry(serverName, options);
  if (!entry) return undefined;

  // If no serverUrl is stored, this is from an old version - consider it invalid
  if (!entry.serverUrl) return undefined;

  // If URL has changed, credentials are invalid
  if (entry.serverUrl !== serverUrl) return undefined;

  return entry;
}

/**
 * Save auth entry for a server.
 */
export function saveAuthEntry(serverName: string, entry: AuthEntry, serverUrl?: string, options?: AuthStorageOptions): void {
  // Always update serverUrl if provided
  if (serverUrl) {
    entry.serverUrl = serverUrl;
  }
  writeSecureAuthEntry(serverName, entry);
  removeLegacyAuthEntry(serverName, options);
}

/**
 * Remove auth entry for a server.
 */
export function removeAuthEntry(serverName: string, options?: AuthStorageOptions): void {
  const account = getAuthEntryAccount(serverName);
  try {
    getAuthSecretStore().remove(account);
  } catch (error) {
    throw new Error(`Failed to remove OAuth credentials for ${serverName} from the OS secure credential store`, { cause: error });
  }
  removeLegacyAuthEntry(serverName, options);
}

/**
 * Update tokens for a server.
 */
export function updateTokens(
  serverName: string,
  tokens: StoredTokens,
  serverUrl?: string,
  options?: AuthStorageOptions
): void {
  const entry = getAuthEntry(serverName, options) ?? {};
  if (serverUrl && entry.serverUrl !== serverUrl) {
    delete entry.clientInfo;
    delete entry.codeVerifier;
    delete entry.oauthState;
  }
  entry.tokens = tokens;
  saveAuthEntry(serverName, entry, serverUrl, options);
}

/**
 * Update client info for a server.
 */
export function updateClientInfo(
  serverName: string,
  clientInfo: StoredClientInfo,
  serverUrl?: string,
  options?: AuthStorageOptions
): void {
  const entry = getAuthEntry(serverName, options) ?? {};
  if (serverUrl && entry.serverUrl !== serverUrl) {
    delete entry.tokens;
    delete entry.codeVerifier;
    delete entry.oauthState;
  }
  entry.clientInfo = clientInfo;
  saveAuthEntry(serverName, entry, serverUrl, options);
}

/**
 * Update code verifier for a server.
 */
export function updateCodeVerifier(serverName: string, codeVerifier: string, serverUrl?: string, options?: AuthStorageOptions): void {
  const entry = getAuthEntry(serverName, options) ?? {};
  if (serverUrl && entry.serverUrl !== serverUrl) {
    delete entry.tokens;
    delete entry.clientInfo;
    delete entry.oauthState;
  }
  entry.codeVerifier = codeVerifier;
  saveAuthEntry(serverName, entry, serverUrl, options);
}

/**
 * Clear code verifier for a server.
 */
export function clearCodeVerifier(serverName: string, options?: AuthStorageOptions): void {
  const entry = getAuthEntry(serverName, options);
  if (entry) {
    delete entry.codeVerifier;
    saveAuthEntry(serverName, entry, undefined, options);
  }
}

/**
 * Update OAuth state for a server.
 */
export function updateOAuthState(serverName: string, state: string, serverUrl?: string, options?: AuthStorageOptions): void {
  const entry = getAuthEntry(serverName, options) ?? {};
  if (serverUrl && entry.serverUrl !== serverUrl) {
    delete entry.tokens;
    delete entry.clientInfo;
    delete entry.codeVerifier;
  }
  entry.oauthState = state;
  saveAuthEntry(serverName, entry, serverUrl, options);
}

/**
 * Get OAuth state for a server.
 */
export function getOAuthState(serverName: string, options?: AuthStorageOptions): string | undefined {
  const entry = getAuthEntry(serverName, options);
  return entry?.oauthState;
}

/**
 * Clear OAuth state for a server.
 */
export function clearOAuthState(serverName: string, options?: AuthStorageOptions): void {
  const entry = getAuthEntry(serverName, options);
  if (entry) {
    delete entry.oauthState;
    saveAuthEntry(serverName, entry, undefined, options);
  }
}

/**
 * Check if stored tokens are expired.
 * Returns null if no tokens exist, false if no expiry or not expired, true if expired.
 */
export function isTokenExpired(serverName: string, options?: AuthStorageOptions): boolean | null {
  const entry = getAuthEntry(serverName, options);
  if (!entry?.tokens) return null;
  if (!entry.tokens.expiresAt) return false;
  return entry.tokens.expiresAt < Date.now() / 1000;
}

/**
 * Check if a server has stored tokens.
 */
export function hasStoredTokens(serverName: string, options?: AuthStorageOptions): boolean {
  const entry = getAuthEntry(serverName, options);
  return !!entry?.tokens;
}

/**
 * Clear all credentials for a server.
 */
export function clearAllCredentials(serverName: string, options?: AuthStorageOptions): void {
  removeAuthEntry(serverName, options);
}

/**
 * Clear only client info for a server.
 */
export function clearClientInfo(serverName: string, options?: AuthStorageOptions): void {
  const entry = getAuthEntry(serverName, options);
  if (entry) {
    delete entry.clientInfo;
    saveAuthEntry(serverName, entry, undefined, options);
  }
}

/**
 * Clear only tokens for a server.
 */
export function clearTokens(serverName: string, options?: AuthStorageOptions): void {
  const entry = getAuthEntry(serverName, options);
  if (entry) {
    delete entry.tokens;
    saveAuthEntry(serverName, entry, undefined, options);
  }
}