const ZWJ = 0x200d;
const VS16 = 0xfe0f;

export function twemojiUrl(emoji: string): string {
  const points = Array.from(emoji, (c) => c.codePointAt(0) ?? 0);
  const kept = points.includes(ZWJ) ? points : points.filter((p) => p !== VS16);
  return `/twemoji/${kept.map((p) => p.toString(16)).join('-')}.svg`;
}

export interface TextSegment {
  text: string;
  emoji: boolean;
}

const MAYBE_EMOJI = /\p{Extended_Pictographic}|\p{Regional_Indicator}|\u20E3/u;
const PICTOGRAPHIC = /\p{Extended_Pictographic}/u;
const EMOJI_PRESENTATION = /\p{Emoji_Presentation}/u;
const KEYCAP = /^[0-9#*]\uFE0F\u20E3$/;
const FLAG = /^\p{Regional_Indicator}{2}$/u;

let segmenter: Intl.Segmenter | null = null;

function isEmojiGrapheme(g: string): boolean {
  if (KEYCAP.test(g) || FLAG.test(g)) return true;
  return PICTOGRAPHIC.test(g) && (EMOJI_PRESENTATION.test(g) || g.includes(String.fromCodePoint(VS16)) || g.includes(String.fromCodePoint(ZWJ)));
}

export function segmentEmoji(text: string): TextSegment[] {
  if (!MAYBE_EMOJI.test(text)) return [{ text, emoji: false }];
  segmenter ??= new Intl.Segmenter(undefined, { granularity: 'grapheme' });
  const out: TextSegment[] = [];
  for (const { segment } of segmenter.segment(text)) {
    const emoji = isEmojiGrapheme(segment);
    const last = out[out.length - 1];
    if (last && !emoji && !last.emoji) last.text += segment;
    else out.push({ text: segment, emoji });
  }
  return out;
}

export function isJumbo(segments: TextSegment[]): boolean {
  let count = 0;
  for (const s of segments) {
    if (s.emoji) count += 1;
    else if (s.text.trim() !== '') return false;
  }
  return count >= 1 && count <= 3;
}