const {
  validateUsername,
  USERNAME_MIN_LENGTH,
  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 padBase = (base) => {
  let value = base.replace(/[^a-zA-Z0-9._-]/g, '')
  if (!/^[a-zA-Z0-9]/.test(value)) value = `u${value}`
  while (value.length < USERNAME_MIN_LENGTH - 2) {
    value = `${value}0`
  }
  return value.slice(0, Math.max(USERNAME_MIN_LENGTH - 2, 1))
}

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

  const builders = [
    () => `${stem}${random2()}`,
    () => `${stem}_${random2()}`,
    () => `${stem}.${random2()}`,
    () => `${stem}-${random2()}`,
    () => `${stem}${random3()}`,
    () => `${stem.slice(0, Math.max(USERNAME_MIN_LENGTH - 3, 1))}${random3()}`,
  ]

  return builders[attempt % builders.length]()
}

const trimToMax = (value) =>
  value.length > USERNAME_MAX_LENGTH ? value.slice(0, USERNAME_MAX_LENGTH) : value

const generateUsernameSuggestions = async (UserModel, baseUserName, excludeUserId) => {
  const base = trimToMax(baseUserName.trim().toLowerCase())
  const suggestions = []
  let attempt = 0

  while (suggestions.length < 3 && attempt < 40) {
    const candidate = trimToMax(buildCandidates(base, attempt))
    attempt += 1

    if (validateUsername(candidate)) continue
    if (suggestions.includes(candidate)) continue
    if (await isUsernameTaken(UserModel, candidate, excludeUserId)) continue

    suggestions.push(candidate)
  }

  return suggestions
}

module.exports = {
  generateUsernameSuggestions,
}