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 splitBaseAndSuffix = (value) => {
  const match = value.match(/^(.*?)(\d+)$/)
  if (!match || !match[1]) {
    return { core: value, suffix: null }
  }
  return { core: match[1], suffix: Number.parseInt(match[2], 10) }
}

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

/** پیشنهادهای مشابه: amiri2 → amiri3, amiri5, amiiri3, amiri334 */
const buildCandidates = (base) => {
  const { core, suffix } = splitBaseAndSuffix(base)
  const candidates = []

  if (suffix !== null && !Number.isNaN(suffix)) {
    candidates.push(`${core}${suffix + 1}`)
    candidates.push(`${core}${suffix + 3}`)
    candidates.push(`${core}${suffix}${Math.floor(Math.random() * 9 + 1)}`)
  }

  const numericSuffixes = [3, 5, 7, 12, 21, 34, 99, 334, 567]
  numericSuffixes.forEach((num) => {
    candidates.push(`${core}${num}`)
  })

  for (let i = 1; i < Math.min(core.length, 5); i += 1) {
    const ch = core[i]
    if (!ch) continue
    const doubled = `${core.slice(0, i)}${ch}${core.slice(i)}`
    candidates.push(`${doubled}${suffix !== null ? suffix + 1 : 3}`)
    candidates.push(`${doubled}${Math.floor(Math.random() * 90 + 10)}`)
  }

  candidates.push(`${core}_${suffix !== null ? suffix + 1 : 1}`)
  candidates.push(`${core}.${Math.floor(Math.random() * 900 + 100)}`)
  candidates.push(`${core}-${Math.floor(Math.random() * 90 + 10)}`)

  return [...new Set(candidates.map(trimToMax))]
}

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

  for (let attempt = 0; attempt < 80 && suggestions.length < count; attempt += 1) {
    const candidates = buildCandidates(base)

    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)
    }

    if (suggestions.length < count) {
      const fallback = trimToMax(`${base}${Math.floor(Math.random() * 9000 + 1000)}`)
      if (!tried.has(fallback) && !validateUsername(fallback)) {
        tried.add(fallback)
        const taken = await isUsernameTaken(UserModel, fallback, excludeUserId)
        if (!taken) suggestions.push(fallback)
      }
    }
  }

  return suggestions
}

module.exports = {
  generateUsernameSuggestions,
  isUsernameTaken
}