Function mark

src/common/syntax-highlighter.ts:420–476

(line: StyledSpan[], mark: string)

}

export function mark(line: StyledSpan[], mark: string): StyledSpan[] {
  // Mark is of the form "1-3" and indicates a range of characters to mark
  const [start, end_] = mark.split('-').map((x) => parseInt(x));
  let end = end_;
  if (end === undefined) end = start + 1;
  if (start >= end) end = start + 1;

  let pos = 0;

  const markSpan = (span: StyledSpan): StyledSpan[] => {
    const content = span.content;

    const spanStart = pos;
    const spanEnd = pos + content.length - 1;

    pos += content.length;

    // Is the span entirely outside the marked range?
    if (spanEnd < start || end < spanStart) return [span];

    // Is the span entirely inside the marked range?
    if (spanStart >= start && spanEnd <= end)
      return [{ ...span, ...DEFAULT_THEME.mark }];

    // Is the start of the span in the marked range?
    if (spanStart >= start && spanEnd > end) {
      const before = content.slice(0, end + 1 - pos);
      const after = content.slice(end + 1 - pos);
      return [
        { ...span, content: before, ...DEFAULT_THEME.mark },
        { ...span, content: after },
      ];
    }

    // Is the end of the span in the marked range?
    if (start >= spanStart && end >= spanEnd) {
      const before = content.slice(0, start - pos);
      const after = content.slice(start - pos);
      return [
        { ...span, content: before },
        { ...span, content: after, ...DEFAULT_THEME.mark },
      ];
    }

    // The span is entirely inside the marked range
    const before = content.slice(0, start - pos);
    const marked = content.slice(start - pos, end - pos + 1);
    const after = content.slice(end - pos + 1);
    return [
      { ...span, content: before },
      { ...span, content: marked, ...DEFAULT_THEME.mark },
      { ...span, content: after },
    ];
  };

  return line.flatMap((span) => markSpan(span));
}