// Copyright 2016 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Polyfill for TextEncoderStream and TextDecoderStream
// Modified by Sukka (https://skk.moe) to increase compatibility and performance with Bun.

export class PolyfillTextDecoderStream extends TransformStream<Uint8Array, string> {
  readonly fatal: boolean;
  readonly ignoreBOM: boolean;

  constructor(
    public readonly encoding: Bun.Encoding = 'utf-8',
    {
      fatal = false,
      ignoreBOM = false
    }: ConstructorParameters<typeof TextDecoder>[1] = {}
  ) {
    const decoder = new TextDecoder(encoding, { fatal, ignoreBOM });

    const nonLastChunkDecoderOpt: TextDecodeOptions = { stream: true };

    super({
      transform(chunk: Uint8Array, controller: TransformStreamDefaultController<string>) {
        const decoded = decoder.decode(chunk, nonLastChunkDecoderOpt);
        controller.enqueue(decoded);
      },
      flush(controller: TransformStreamDefaultController<string>) {
        // If {fatal: false} is in options (the default), then the final call to
        // decode() can produce extra output (usually the unicode replacement
        // character 0xFFFD). When fatal is true, this call is just used for its
        // side-effect of throwing a TypeError exception if the input is
        // incomplete.
        const output = decoder.decode();
        if (output.length > 0) {
          controller.enqueue(output);
        }
      }
    });

    this.fatal = fatal;
    this.ignoreBOM = ignoreBOM;
  }
}