export interface MentionUser {
  id: number
  name: string
  color: string | null
}

export function activeMention(text: string, caret: number) {
  const before = text.slice(0, caret)
  const start = before.lastIndexOf('@')
  if (start < 0 || (start > 0 && !/[\s([{]/.test(before[start - 1]!))) return null
  const query = before.slice(start + 1)
  if (query.length > 50 || /[\r\n@]/.test(query)) return null
  return { start, end: caret, query }
}

export function mentionParts(text: string, users: MentionUser[]) {
  const names = [...users].sort((a, b) => b.name.length - a.name.length)
  const parts: { text: string, user?: MentionUser }[] = []
  let last = 0
  for (let i = 0; i < text.length; i++) {
    if (text[i] !== '@' || (i > 0 && !/[\s([{]/.test(text[i - 1]!))) continue
    const user = names.find(u => text.slice(i + 1, i + 1 + u.name.length).toLowerCase() === u.name.toLowerCase()
      && !/[\p{L}\p{N}_-]/u.test(text[i + 1 + u.name.length] ?? ''))
    if (!user) continue
    if (i > last) parts.push({ text: text.slice(last, i) })
    last = i + 1 + user.name.length
    parts.push({ text: text.slice(i, last), user })
    i = last - 1
  }
  if (last < text.length) parts.push({ text: text.slice(last) })
  return parts
}

export function mentionedUserIds(content: string, users: MentionUser[]) {
  return new Set(content.split(/https?:\/\/[^\s<>"']+/g)
    .flatMap(text => mentionParts(text, users).flatMap(part => part.user ? [part.user.id] : [])))
}