const { validateUsername, USERNAME_MAX_LENGTH } = require('./usernameValidation')

const escapeRegex = (value) => value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')

const isUsernameTaken = async (UserModel, userName, excludeUserId) => {
  const existing = await UserModel.findOne({
    user_name: { $regex: new RegExp(`^${escapeRegex(userName)}$`, 'i') }
  })

  if (!existing) return false
  if (excludeUserId && existing._id.toString() === excludeUserId) return false
  return true
}

const buildCandidates = (base, attempt) => {
  const random2 = () => String(Math.floor(Math.random() * 90 + 10))
  const random3 = () => String(Math.floor(Math.random() * 900 + 100))
  const random4 = () => String(Math.floor(Math.random() * 9000 + 1000))

  const builders = [
    (b) => `${b}${random2()}`,
    (b) => `${b}_${random3()}`,
    (b) => `${b}.${random2()}`,
    (b) => `${b}-${random2()}`,
    (b) => `${b}${random4()}`,
    (b) => `${b}_m${random2()}`,
    (b) => `${b}${attempt}`,
  ]

  return builders.map((fn) => {
    let candidate = fn(base)
    if (candidate.length > USERNAME_MAX_LENGTH) {
      candidate = candidate.slice(0, USERNAME_MAX_LENGTH)
    }
    return candidate
  })
}

const generateUsernameSuggestions = async (
  UserModel,
  baseUsername,
  excludeUserId,
  count = 3
) => {
  const base = baseUsername.trim().toLowerCase()
  const suggestions = []
  const tried = new Set([base])

  for (let attempt = 1; attempt <= 60 && suggestions.length < count; attempt++) {
    const candidates = buildCandidates(base, attempt)

    for (const candidate of candidates) {
      if (suggestions.length >= count) break
      if (tried.has(candidate)) continue
      tried.add(candidate)
      if (validateUsername(candidate)) continue

      const taken = await isUsernameTaken(UserModel, candidate, excludeUserId)
      if (!taken) suggestions.push(candidate)
    }
  }

  return suggestions
}

module.exports = {
  generateUsernameSuggestions,
  isUsernameTaken
}