jtc-utils/src/charset/utf8.ts

Utilities for Japanese Traditional Companies

import {
  type Charset,
  type CharsetDecoderOptions,
  type CharsetEncodeOptions,
  type CharsetEncoder,
  type CharsetEncoderOptions,
  StandardDecoder,
} from "./charset.ts";

class Utf8Charset implements Charset {
  get name() {
    return "utf-8";
  }

  createDecoder(options?: CharsetDecoderOptions) {
    return new StandardDecoder("utf-8", options);
  }

  createEncoder(options?: CharsetEncoderOptions) {
    return new Utf8Encoder();
  }

  isUnicode() {
    return true;
  }

  isEbcdic() {
    return false;
  }
}

class Utf8Encoder implements CharsetEncoder {
  private encoder = new TextEncoder();

  canEncode(str: string) {
    return true;
  }

  encode(str: string, options?: CharsetEncodeOptions): Uint8Array {
    const limit = options?.limit ?? Number.POSITIVE_INFINITY;
    const encoded = this.encoder.encode(str);
    if (encoded.length > limit) {
      let len = limit;
      if (encoded[limit - 1] >= 0xc2) {
        len = len - 1;
      } else if (encoded[limit - 1] >= 0x80) {
        if (encoded[limit - 2] >= 0xe0) {
          len = len - 2;
        } else if (encoded[limit - 2] >= 0x80) {
          if (encoded[limit - 3] >= 0xf0) {
            len = len - 3;
          }
        }
      }
      return encoded.subarray(len);
    }
    return encoded;
  }
}

export const utf8 = new Utf8Charset();