/**
 * @module storage/storageFactory
 * @description Storage adapter factory for Brainy 8.0.
 *
 * Brainy 8.0 ships **two storage adapters**:
 * - `'filesystem'` (default) — Node.js + Bun + Deno; persistent on disk.
 * - `'memory'` — in-memory; ephemeral; the right choice for tests + ephemeral
 *   workloads.
 *
 * Cloud-storage adapters (GCS, S3, R2, Azure) and the browser-only OPFS
 * adapter were removed in 8.0. The path
 * forward for cloud backup is operator tooling: persist locally with
 * `db.persist()`, sync the resulting on-disk artefact with `gsutil` /
 * `aws s3 cp` / `rclone` / `azcopy`. This is the standard pattern every
 * production database uses; bundling cloud SDKs into the library buys
 * nothing and ships ~13 K LOC of code we don't maintain well.
 */

import type { StorageAdapter } from '../coreTypes.js'
import { MemoryStorage } from './adapters/memoryStorage.js'
import type { OperationConfig } from '../utils/operationUtils.js'

/**
 * Options for creating a storage adapter (Brainy 8.0).
 */
export interface StorageOptions {
  /**
   * Storage backend to use.
   * - `'auto'` (default) — `'filesystem'` on Node-like runtimes, `'memory'`
   *   in a browser.
   * - `'memory'` — in-memory; ephemeral.
   * - `'filesystem'` — persistent disk storage; Node-like runtimes only.
   *
   * A top-level `path` implies `'filesystem'`, so `{ path: '/data' }` works
   * without an explicit `type`.
   */
  type?: 'auto' | 'memory' | 'filesystem'

  /** Force memory storage regardless of environment. */
  forceMemoryStorage?: boolean

  /** Force filesystem storage. Throws in a browser environment. */
  forceFileSystemStorage?: boolean

  /**
   * **Canonical** directory for filesystem storage. This is the one key the
   * rest of the API already speaks (`persist(path)`, `Brainy.load(path)`,
   * `asOf(path)`, `restore(path)`). Specifying it implies `type: 'filesystem'`.
   *
   * @example
   * new Brainy({ storage: { path: '/var/lib/app/data' } })
   */
  path?: string

  /**
   * @deprecated REMOVED in 8.0 — passing `rootDirectory` THROWS. Use the
   * canonical {@link StorageOptions.path} (`storage: { path: '/data' }`).
   */
  rootDirectory?: string

  /**
   * @deprecated REMOVED in 8.0 — a nested `options.path` / `options.rootDirectory`
   * THROWS. Use the top-level {@link StorageOptions.path}.
   */
  options?: {
    rootDirectory?: string
    path?: string
    [key: string]: any
  }

  /**
   * @deprecated REMOVED in 8.0 — `fileSystemStorage.path` / `.rootDirectory`
   * THROWS. Use the top-level {@link StorageOptions.path}.
   */
  fileSystemStorage?: {
    rootDirectory?: string
    path?: string
    [key: string]: any
  }

  /** Operation tuning (timeouts, retry budgets) passed through to the adapter. */
  operationConfig?: OperationConfig
}

/** Default on-disk root when a filesystem store is requested without a path. */
export const DEFAULT_FILESYSTEM_ROOT = './brainy-data'

/**
 * @description Throw a clear migration error for a removed legacy storage-config
 * key. 8.0 is a clean break: the pre-8.0 aliases were REMOVED (not deprecated),
 * so a stale config fails loudly with the exact rename rather than silently
 * writing to the wrong directory.
 * @param key - The removed key path (e.g. `'rootDirectory'`, `'options.path'`).
 * @throws Always — naming the canonical `path` replacement.
 */
function throwRemovedStorageKey(key: string): never {
  throw new Error(
    `[brainy] storage config '${key}' was removed in 8.0 — use the top-level ` +
      `'path' instead (e.g. storage: { path: '/data' }).`
  )
}

/**
 * @description Resolve any supported filesystem storage config shape to the ONE
 * canonical on-disk root, encoding the full precedence in a single place so the
 * factory, the 7.x→8.0 migration probe, and any plugin storage factory all agree
 * on the IDENTICAL directory (no `./brainy-data` split-brain).
 *
 * Behavior:
 *  1. `path` — the one supported key. Returned as-is.
 *  2. A removed pre-8.0 alias (`rootDirectory`, `options.*`, `fileSystemStorage.*`) →
 *     THROW with the exact rename (never silently fall through to the default,
 *     which would misplace a 7.x consumer's data on upgrade).
 *  3. No path at all → `./brainy-data` (the zero-config default).
 *
 * @param config - A storage config object (`StorageOptions`-shaped; tolerant of
 *   extra keys for the plugin-factory `Record<string, unknown>` contract).
 * @returns The resolved directory string.
 * @throws If a removed pre-8.0 alias is present (message names the `path` rename).
 * @example
 * resolveFilesystemRoot({ path: '/data' })          // → '/data'
 * resolveFilesystemRoot({ rootDirectory: '/data' }) // → throws (use `path`)
 * resolveFilesystemRoot({ type: 'filesystem' })     // → './brainy-data'
 */
export function resolveFilesystemRoot(
  config: StorageOptions & Record<string, unknown> = {}
): string {
  // 1. Canonical top-level path — the one and only supported key.
  if (typeof config.path === 'string' && config.path.length > 0) {
    return config.path
  }

  // 2. Removed pre-8.0 aliases → throw with the exact rename. Detect them even
  //    though they're no longer the path, so a stale config fails loudly
  //    instead of silently landing on the default and misplacing data.
  if (typeof config.rootDirectory === 'string' && config.rootDirectory.length > 0) {
    throwRemovedStorageKey('rootDirectory')
  }
  const opts = config.options
  if (
    opts &&
    typeof opts === 'object' &&
    ((typeof opts.path === 'string' && opts.path.length > 0) ||
      (typeof opts.rootDirectory === 'string' && opts.rootDirectory.length > 0))
  ) {
    throwRemovedStorageKey('options.path')
  }
  const fss = config.fileSystemStorage
  if (
    fss &&
    typeof fss === 'object' &&
    ((typeof fss.path === 'string' && fss.path.length > 0) ||
      (typeof fss.rootDirectory === 'string' && fss.rootDirectory.length > 0))
  ) {
    throwRemovedStorageKey('fileSystemStorage.path')
  }

  // 3. Zero-config default. A `type: 'filesystem'` with no path lands here
  //    intentionally ("persist, default location").
  return DEFAULT_FILESYSTEM_ROOT
}

/**
 * @description Whether a storage config (no explicit/`'auto'` type) names a
 * filesystem directory through ANY supported shape. Used by `pickAdapter` so
 * `{ path: '/data' }` (or a deprecated alias) implies filesystem on a Node
 * runtime without the caller writing `type: 'filesystem'`.
 * @param config - A storage config object.
 * @returns `true` if a directory was specified through any recognized key.
 */
function hasExplicitFilesystemPath(
  config: StorageOptions & Record<string, unknown>
): boolean {
  const nonEmpty = (v: unknown): boolean => typeof v === 'string' && v.length > 0
  return (
    nonEmpty(config.path) ||
    nonEmpty(config.rootDirectory) ||
    nonEmpty(config.options?.path) ||
    nonEmpty(config.options?.rootDirectory) ||
    nonEmpty(config.fileSystemStorage?.path) ||
    nonEmpty(config.fileSystemStorage?.rootDirectory)
  )
}

/**
 * Resolve `StorageOptions` to a concrete storage adapter.
 *
 * - `'auto'` (default) picks `FileSystemStorage`, falling back to
 *   `MemoryStorage` only if filesystem init fails (e.g. no write permission).
 * - `forceMemoryStorage: true` returns `MemoryStorage` regardless.
 * - `forceFileSystemStorage: true` returns `FileSystemStorage`.
 */
export async function createStorage(options: StorageOptions = {}): Promise<StorageAdapter> {
  return pickAdapter(options)
}

async function pickAdapter(options: StorageOptions): Promise<StorageAdapter> {
  if (options.forceMemoryStorage) {
    return new MemoryStorage()
  }

  const requestedType = options.type ?? 'auto'

  if (requestedType === 'memory') {
    return new MemoryStorage()
  }

  if (requestedType === 'filesystem' || options.forceFileSystemStorage) {
    return await createFilesystemStorage(options)
  }

  // 'auto' (or no type) with an explicit filesystem path → filesystem. A naked
  // `{ path: '/data' }` should land on disk at that path, not silently fall to
  // memory on a runtime where the `auto` filesystem attempt happens to fail.
  if (
    requestedType === 'auto' &&
    hasExplicitFilesystemPath(options as StorageOptions & Record<string, unknown>)
  ) {
    return await createFilesystemStorage(options)
  }

  // 'auto' with no path: prefer filesystem, fall back to memory if init fails.
  try {
    return await createFilesystemStorage(options)
  } catch {
    return new MemoryStorage()
  }
}

async function createFilesystemStorage(options: StorageOptions): Promise<StorageAdapter> {
  // Single source of truth for the on-disk root across every config shape.
  const rootDir = resolveFilesystemRoot(options as StorageOptions & Record<string, unknown>)

  // Dynamic import so browser bundles don't pull node:fs.
  const { FileSystemStorage } = await import('./adapters/fileSystemStorage.js')
  return new FileSystemStorage(rootDir) as unknown as StorageAdapter
}

// Re-export the surviving adapters for direct construction by callers
// that want to skip the factory.
export { MemoryStorage } from './adapters/memoryStorage.js'