import { EventEmitter } from 'node:events'

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

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

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

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