import type { Track } from './types'

type CacheServerDescriptor = {
  id: string
  host: string
  port?: string | number
  ssl?: boolean
}

type PersistedTrack = Omit<Track, 'id'>

type LibraryCacheRecord = {
  cacheKey: string
  updatedAt: number
  tracks: PersistedTrack[]
  searchCache: Record<string, number[]>
}

export type LibraryCacheSnapshot = {
  tracks: PersistedTrack[]
  searchCache: Record<string, number[]>
}

export type LibraryCacheStats = {
  snapshotCount: number
  staleSnapshotCount: number
  totalBytes: number
  activeBytes: number
  trackCount: number
  searchEntryCount: number
  updatedAt: number | null
}

const DATABASE_NAME = 'api-mediaplayer-library-cache'
const DATABASE_VERSION = 1
const STORE_NAME = 'snapshots'
const MAX_TRACKS = 5000
const MAX_SEARCHES = 250
const textEncoder = typeof TextEncoder !== 'undefined' ? new TextEncoder() : null

export function buildLibraryCacheKey(servers: CacheServerDescriptor[]) {
  return servers.map((server) => `${server.id}:${server.host}:${server.port ?? ''}:${server.ssl ? 'https' : 'http'}`).join('|')
}

function openLibraryCacheDatabase() {
  return new Promise<IDBDatabase>((resolve, reject) => {
    const request = indexedDB.open(DATABASE_NAME, DATABASE_VERSION)

    request.onupgradeneeded = () => {
      const database = request.result
      if (!database.objectStoreNames.contains(STORE_NAME)) {
        database.createObjectStore(STORE_NAME, { keyPath: 'cacheKey' })
      }
    }

    request.onsuccess = () => resolve(request.result)
    request.onerror = () => reject(request.error ?? new Error('Failed to open library cache database'))
  })
}

function withStore<T>(mode: IDBTransactionMode, handler: (store: IDBObjectStore) => IDBRequest<T>) {
  return new Promise<T>((resolve, reject) => {
    openLibraryCacheDatabase()
      .then((database) => {
        const transaction = database.transaction(STORE_NAME, mode)
        const store = transaction.objectStore(STORE_NAME)
        const request = handler(store)

        request.onsuccess = () => resolve(request.result)
        request.onerror = () => reject(request.error ?? new Error('IndexedDB request failed'))

        transaction.oncomplete = () => database.close()
        transaction.onerror = () => reject(transaction.error ?? new Error('IndexedDB transaction failed'))
        transaction.onabort = () => reject(transaction.error ?? new Error('IndexedDB transaction aborted'))
      })
      .catch(reject)
  })
}

function estimateRecordBytes(record: LibraryCacheRecord) {
  const payload = JSON.stringify(record)
  if (!textEncoder) return payload.length
  return textEncoder.encode(payload).length
}

async function listLibraryCacheRecords(): Promise<LibraryCacheRecord[]> {
  if (typeof indexedDB === 'undefined') return []
  const records = await withStore<LibraryCacheRecord[]>('readonly', (store) => store.getAll())
  return Array.isArray(records) ? records : []
}

export async function loadLibraryCache(cacheKey: string): Promise<LibraryCacheSnapshot | null> {
  if (!cacheKey || typeof indexedDB === 'undefined') return null

  const record = await withStore<LibraryCacheRecord | undefined>('readonly', (store) => store.get(cacheKey))
  if (!record) return null

  return {
    tracks: Array.isArray(record.tracks) ? record.tracks : [],
    searchCache: record.searchCache && typeof record.searchCache === 'object' ? record.searchCache : {},
  }
}

export async function pruneLibraryCache(activeCacheKey: string) {
  if (!activeCacheKey || typeof indexedDB === 'undefined') return 0

  const records = await listLibraryCacheRecords()
  const staleKeys = records
    .map((record) => record.cacheKey)
    .filter((cacheKey) => cacheKey !== activeCacheKey)

  if (staleKeys.length === 0) return 0

  await Promise.all(staleKeys.map((cacheKey) => withStore('readwrite', (store) => store.delete(cacheKey))))
  return staleKeys.length
}

export async function getLibraryCacheStats(activeCacheKey: string): Promise<LibraryCacheStats> {
  if (!activeCacheKey || typeof indexedDB === 'undefined') {
    return {
      snapshotCount: 0,
      staleSnapshotCount: 0,
      totalBytes: 0,
      activeBytes: 0,
      trackCount: 0,
      searchEntryCount: 0,
      updatedAt: null,
    }
  }

  const records = await listLibraryCacheRecords()
  const activeRecord = records.find((record) => record.cacheKey === activeCacheKey)

  return {
    snapshotCount: records.length,
    staleSnapshotCount: records.filter((record) => record.cacheKey !== activeCacheKey).length,
    totalBytes: records.reduce((sum, record) => sum + estimateRecordBytes(record), 0),
    activeBytes: activeRecord ? estimateRecordBytes(activeRecord) : 0,
    trackCount: activeRecord?.tracks.length ?? 0,
    searchEntryCount: activeRecord ? Object.keys(activeRecord.searchCache || {}).length : 0,
    updatedAt: activeRecord?.updatedAt ?? null,
  }
}

export async function saveLibraryCache(cacheKey: string, tracks: Track[], searchCache: Record<string, number[]>) {
  if (!cacheKey || typeof indexedDB === 'undefined') return

  const trimmedTracks = tracks
    .filter((track) => track.serverId && track.fileId != null && track.url)
    .slice(-MAX_TRACKS)
    .map(({ id: _id, ...track }) => track)

  const trimmedSearchCache = Object.fromEntries(Object.entries(searchCache).slice(-MAX_SEARCHES))

  const record: LibraryCacheRecord = {
    cacheKey,
    updatedAt: Date.now(),
    tracks: trimmedTracks,
    searchCache: trimmedSearchCache,
  }

  await withStore('readwrite', (store) => store.put(record))
  await pruneLibraryCache(cacheKey)
}