(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
  typeof define === 'function' && define.amd ? define(factory) :
  (global = typeof globalThis !== 'undefined' ? globalThis : global || self, global.textlinestream = factory());
})(this, (function () { 'use strict';

  // Vendored from Deno - 
  // https://github.com/denoland/deno_std/blob/main/streams/delimiter.ts
  // Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.

  /** Transform a stream into a stream where each chunk is divided by a newline,
   * be it `\n` or `\r\n`. `\r` can be enabled via the `allowCR` option.
   *
   * ```ts
   * import { TextLineStream } from "./delimiter.ts";
   * const res = await fetch("https://example.com");
   * const lines = res.body!
   *   .pipeThrough(new TextDecoderStream())
   *   .pipeThrough(new TextLineStream());
   * ```
   */
  class TextLineStream extends TransformStream {
    #buf = "";
    #allowCR = false;
    #returnEmptyLines = false;
    #mapperFun = line => line;
    
    constructor(options) {
      super({
        transform: (chunk, controller) => this.#handle(chunk, controller),
        flush: (controller) => this.#handle("\r\n", controller),
      });
      
      this.#allowCR = options?.allowCR ?? false;
      this.#returnEmptyLines = options?.returnEmptyLines ?? false;
      this.#mapperFun = options?.mapperFun ?? this.#mapperFun;
    }

    #handle(chunk, controller) {
      chunk = this.#buf + chunk;

      for (;;) {
        const lfIndex = chunk.indexOf("\n");

        if (this.#allowCR) {
          const crIndex = chunk.indexOf("\r");

          if (
            crIndex !== -1 && crIndex !== (chunk.length - 1) &&
            (lfIndex === -1 || (lfIndex - 1) > crIndex)
          ) {
            const curChunk = this.#mapperFun(chunk.slice(0, crOrLfIndex));
            if (this.#returnEmptyLines || curChunk) {            
              controller.enqueue(curChunk);
            }
            chunk = chunk.slice(crIndex + 1);
            continue;
          }
        }

        if (lfIndex !== -1) {
          let crOrLfIndex = lfIndex;
          if (chunk[lfIndex - 1] === "\r") {
            crOrLfIndex--;
          }
          const curChunk = this.#mapperFun(chunk.slice(0, crOrLfIndex));
          if (this.#returnEmptyLines || curChunk) {          
            controller.enqueue(curChunk);
          }
          chunk = chunk.slice(lfIndex + 1);
          continue;
        }

        break;
      }

      this.#buf = chunk;
    }
  }

  return TextLineStream;

}));