import { Transform, TransformCallback } from 'stream'
import makeSourceEnvelope from './makeSourceEnvelope'

/**
 * Stream that reads a string and writes a single Source message.
 */
export default class SourceMessageStream extends Transform {
  private buffer = Buffer.alloc(0)

  constructor(private readonly uri: string) {
    super({ readableObjectMode: true, writableObjectMode: false })
  }

  public _transform(
    chunk: Buffer,
    encoding: string,
    callback: TransformCallback
  ) {
    this.buffer = Buffer.concat([this.buffer, chunk])
    callback()
  }

  public _flush(callback: TransformCallback) {
    const data = this.buffer.toString('UTF-8')
    const chunk = makeSourceEnvelope(data, this.uri)
    this.push(chunk)
    callback()
  }
}