const fs = require('fs/promises')
const path = require('path')
const { createWriteStream } = require('fs')
const zlib = require('zlib')
const stream = require('stream/promises')
const nbt = require('prismarine-nbt')
const fileExists = require('./file_exists')

class PersistentData {
  #endianness
  data = null

  constructor (filepath) {
    this.filepath = filepath
    this.loaded = false
  }

  async load () {
    const { parsed, type } = await this.#loadData(this.filepath, true)

    this.data = this.parse(parsed)
    this.#endianness = type
    this.loaded = true
  }

  async #loadData (filepath, tryBackup) {
    if (!await fileExists(filepath)) {
      return { parsed: nbt.comp({}), type: 'big' }
    }

    const buffer = await fs.readFile(filepath)

    try {
      return nbt.parse(buffer)
    } catch (error) {
      if (tryBackup) return this.#loadData(filepath + '_old', false)
      throw error
    }
  }

  async save () {
    await fs.mkdir(path.dirname(this.filepath), { recursive: true })

    const data = this.unparse(this.data)
    if (await fileExists(this.filepath)) await fs.copyFile(this.filepath, this.filepath + '_old') // Back up our data before a save

    const gzip = zlib.createGzip()
    const out = createWriteStream(this.filepath)

    gzip.pipe(out)
    gzip.write(nbt.writeUncompressed(data))
    gzip.end()

    await stream.finished(gzip)
  }

  async unload (save) {
    if (save) await this.save()

    this.data = null
    this.#endianness = undefined
    this.loaded = false
  }

  parse (data) {
    return data
  }

  unparse (data) {
    return data
  }
}

module.exports = PersistentData