private _readOrSeekTo()

in packages/selector/src/text/code-point-seeker.ts [123:188]

• 63 lines of code
• 15 McCabe index (conditional complexity)

  private _readOrSeekTo(
    read: true,
    target: number,
    roundUp?: boolean,
  ): string[];
  private _readOrSeekTo(read: false, target: number, roundUp?: boolean): void;
  private _readOrSeekTo(
    read: boolean,
    target: number,
    roundUp = false,
  ): string[] | void {
    let result: string[] = [];

    if (this.position < target) {
      let unpairedSurrogate = '';
      let characters: string[] = [];
      while (this.position < target) {
        let s = unpairedSurrogate + this.raw.read(1, true);
        if (endsWithinCharacter(s)) {
          unpairedSurrogate = s.slice(-1); // consider this half-character part of the next string.
          s = s.slice(0, -1);
        } else {
          unpairedSurrogate = '';
        }
        characters = [...s];
        this.position += characters.length;
        if (read) result = result.concat(characters);
      }
      if (unpairedSurrogate) this.raw.seekBy(-1); // align with the last complete character.
      if (!roundUp && this.position > target) {
        const overshootInCodePoints = this.position - target;
        const overshootInCodeUnits = characters
          .slice(-overshootInCodePoints)
          .join('').length;
        this.position -= overshootInCodePoints;
        this.raw.seekBy(-overshootInCodeUnits);
      }
    } else {
      // Nearly equal to the if-block, but moving backward in the text.
      let unpairedSurrogate = '';
      let characters: string[] = [];
      while (this.position > target) {
        let s = this.raw.read(-1, true) + unpairedSurrogate;
        if (startsWithinCharacter(s)) {
          unpairedSurrogate = s[0];
          s = s.slice(1);
        } else {
          unpairedSurrogate = '';
        }
        characters = [...s];
        this.position -= characters.length;
        if (read) result = characters.concat(result);
      }
      if (unpairedSurrogate) this.raw.seekBy(1);
      if (!roundUp && this.position < target) {
        const overshootInCodePoints = target - this.position;
        const overshootInCodeUnits = characters
          .slice(0, overshootInCodePoints)
          .join('').length;
        this.position += overshootInCodePoints;
        this.raw.seekBy(overshootInCodeUnits);
      }
    }

    if (read) return result;
  }