const CUSTOM_EMOJI = /^<a?:([^:]+):(\d+)>$/
const UNICODE_EMOJI =
  /^\p{Extended_Pictographic}[\u{1F3FB}-\u{1F3FF}]?(?:\u200D\p{Extended_Pictographic}[\u{1F3FB}-\u{1F3FF}]?)*$/u

// discord sends some unicode emoji with and some without a variation
// selector, so we strip it on both sides to keep comparisons stable
const stripVariation = (emoji: string): string => emoji.replace(/\uFE0F/g, '')

/** Normalizes a unicode emoji or a `<a:name:id>` mention to the `name:id` /
 *  unicode form the reactions API expects. Returns undefined for anything else. */
export function normalizeEmoji(input: string): string | undefined {
  const trimmed = input.trim()
  const custom = CUSTOM_EMOJI.exec(trimmed)
  if (custom !== null) return `${custom[1]}:${custom[2]}`
  const unicode = stripVariation(trimmed)
  return UNICODE_EMOJI.test(unicode) ? unicode : undefined
}

/** Reaction key for an event emoji, matching `normalizeEmoji` output. */
export function reactionKey(emoji: { id: string | null; name: string | null }): string | undefined {
  if (emoji.name === null) return undefined
  return emoji.id === null ? stripVariation(emoji.name) : `${emoji.name}:${emoji.id}`
}