import { EventEmitter } from 'node:events'

export class JSONParser extends EventEmitter {
  #buff = Buffer.from('')
  #byteLen = 0

  initLength(length) {
    this.#byteLen = length
  }

  write(buffer) {
    this.#buff = Buffer.concat([this.#buff, buffer])
  }

  end() {
    if (this.#buff.length === this.#byteLen) {
      let data = this.#buff.toString()
      let fields = data
      try {
        fields = JSON.parse(data)
      } catch (e) {
        try{
          // 非标准的json语法,尝试用 Function 解析
          fields = Function(`try{return ${data}}catch(e){}`)()
        }catch(err){}
      }

      this.emit('field', false, fields)
      this.emit('end')

      this.#buff = null
    } else {
      this.emit('error', new Error(`The uploaded data is incomplete. Expected ${this.#byteLen}, Received ${this.#buff.length} .`))
    }
  }
}