import { ansiParser } from "./ansi.ts";

/** Append coloured output snapshots, restarting when the result replaces or truncates the stream. */
export function ansiOutput(element: HTMLElement): (source: string) => void {
  let parser = ansiParser();
  let previous = "";
  let tail: Text | null = null;
  let tailStyle = "";
  element.hidden = true;

  return (source) => {
    if (source === previous) return;
    if (!source.startsWith(previous)) {
      parser = ansiParser();
      previous = "";
      tail = null;
      element.replaceChildren();
    }
    const fragment = document.createDocumentFragment();
    for (const { text, style } of parser.write(source.slice(previous.length))) {
      const key = JSON.stringify(style);
      let offset = 0;
      while (offset < text.length) {
        // bound text-node edits without making a new span for every streaming chunk
        if (tail === null || key !== tailStyle || tail.length >= 16384) {
          const span = document.createElement("span");
          for (const [property, value] of Object.entries(style)) {
            span.style.setProperty(property, value);
          }
          tail = document.createTextNode("");
          tailStyle = key;
          span.append(tail);
          fragment.append(span);
        }
        let end = Math.min(text.length, offset + 16384 - tail.length);
        if (
          end < text.length && text.charCodeAt(end - 1) >= 0xd800 &&
          text.charCodeAt(end - 1) <= 0xdbff && text.charCodeAt(end) >= 0xdc00 &&
          text.charCodeAt(end) <= 0xdfff
        ) end++;
        tail.appendData(text.slice(offset, end));
        offset = end;
      }
    }
    element.append(fragment);
    element.hidden = source === "";
    previous = source;
  };
}