Parse Twitch message + emote spec

tmi_emote.ts

import assert from "assert";

main();

function main(): void {
  const parsedMessage = parseEmotes(
    "Yo Kappas Kappa Kappa yo",
    {
      "25": ["10-15", "16-21"],
    },
    (e) => e,
    (emoteId) => `[${emoteId}]`
  );

  assert.deepEqual(parsedMessage, ["Yo Kappas ", "[25]", " ", "[25]", " yo"]);
}

function parseEmotes<T>(
  message: string,
  emotes: { [key: string]: string[] },
  onText: (text: string) => T,
  onEmote: (emoteId: string) => T
): T[] {
  const matches: EmoteMatch[] = [];

  for (const [emoteId, spans] of Object.entries(emotes)) {
    for (const span of spans) {
      const [startIndex, endIndex] = span.split("-").map(Number);
      matches.push({ emoteId, startIndex, endIndex });
    }
  }

  matches.sort((a, z) => a.startIndex - z.startIndex);

  const chunks: T[] = [];
  let previousMatch: EmoteMatch | null = null;

  for (const match of matches) {
    const startIndex = previousMatch?.endIndex ?? 0;
    const endIndex = match.startIndex;

    chunks.push(onText(message.substring(startIndex, endIndex)));
    chunks.push(onEmote(match.emoteId));

    previousMatch = match;
  }

  if (previousMatch != null) {
    const startIndex = previousMatch.endIndex;
    const endIndex = message.length;

    if (startIndex < endIndex) {
      chunks.push(onText(message.substring(startIndex, endIndex)));
    }
  }

  return chunks;
}

type EmoteMatch = { emoteId: string; startIndex: number; endIndex: number };