// adpated from https://github.com/sebastianseilund/node-json-socket

import {StringDecoder} from 'string_decoder'
import EventEmitter from 'events'
import btc from 'better-try-catch'

const decoder = new StringDecoder()

export default class JsonStream extends EventEmitter{
  constructor(opts={}){
    super()
    this._contentLength = null
    this._buffer = ''
    this._delimeter = opts.delimiter || '#'
    this.onData = this.onData.bind(this)
    this.serialize = this.serialize.bind(this)
  }


  onData (data) {
    // console.log('a chunk arrived', data)
    data = decoder.write(data)
    try {
      this._handleData(data)
    } catch (e) {
      this.emit('error', { error: e })
    }
  }

  async serialize(message) {
    return new Promise( (resolve,reject) => {
      let [err,messageData] = btc(JSON.stringify)(message)
      if (err) reject(err)
      let [err2,length] = btc(Buffer.byteLength)(messageData, 'utf8')
      if (err2) reject(err2)
      let data = length + this._delimeter + messageData
      // console.log('serialized',data)
      resolve(data)
    })
  }

  _handleData (data) {
    this._buffer += data
    if (this._contentLength == null) {
      var i = this._buffer.indexOf(this._delimeter)
      //Check if the buffer has a this._opts.delimeter or "#", if not, the end of the buffer string might be in the middle of a content length string
      if (i !== -1) {
        var rawContentLength = this._buffer.substring(0, i)
        this._contentLength = parseInt(rawContentLength)
        if (isNaN(this._contentLength)) {
          this._contentLength = null
          this._buffer = ''
          var err = new Error('Invalid content length supplied ('+rawContentLength+') in: '+this._buffer)
          err.code = 'E_INVALID_CONTENT_LENGTH'
          throw err
        }
        this._buffer = this._buffer.substring(i+1)
      }
    }
    if (this._contentLength != null) {
      var length = Buffer.byteLength(this._buffer, 'utf8')
      if (length == this._contentLength) {
        this._handleMessage(this._buffer)
      } else if (length > this._contentLength) {
        var message = this._buffer.substring(0, this._contentLength)
        var rest = this._buffer.substring(this._contentLength)
        this._handleMessage(message)
        this.onData(rest)
      }
    }
  }

  _handleMessage (data) {
    this._contentLength = null
    this._buffer = ''
    var message
    try {
      message = JSON.parse(data)
    } catch (e) {
      var err = new Error('Could not parse JSON: '+e.message+'\nRequest data: '+data)
      err.code = 'E_INVALID_JSON'
      throw err
    }
    message = message || {}
    this.emit('message', message)
  }

}