/**
 * suggest - generates a suggestor function to be used by emoji-input
 * data: object providing source information for specific types of suggestions:
 * data.emoji - optional, an array of all emoji available i.e.
 *   (useEmojiStore().standardEmojiList + state.instance.customEmoji)
 * data.users - optional, an array of all known users
 * updateUsersList - optional, a function to search and append to users
 *
 * Depending on data present one or both (or none) can be present, so if field
 * doesn't support user linking you can just provide only emoji.
 */

export default (data) => {
  const emojiCurry = suggestEmoji(data.emoji)
  const usersCurry = data.store && suggestUsers(data.store)
  return (input, nameKeywordLocalizer) => {
    const firstChar = input[0]
    if (firstChar === ':' && data.emoji) {
      return emojiCurry(input, nameKeywordLocalizer)
    }
    if (firstChar === '@' && usersCurry) {
      return usersCurry(input)
    }
    return []
  }
}

export const suggestEmoji = (emojis) => (input, nameKeywordLocalizer) => {
  const noPrefix = input.toLowerCase().substr(1)
  return emojis
    .map((emoji) => ({ ...emoji, ...nameKeywordLocalizer(emoji) }))
    .filter(
      (emoji) =>
        emoji.names
          .concat(emoji.keywords)
          .filter((kw) => kw.toLowerCase().match(noPrefix)).length,
    )
    .map((k) => {
      let score = 0

      // An exact match always wins
      score += Math.max(
        ...k.names.map((name) => (name.toLowerCase() === noPrefix ? 200 : 0)),
        0,
      )

      // Prioritize custom emoji a lot
      score += k.imageUrl ? 100 : 0

      // Prioritize prefix matches somewhat
      score += Math.max(
        ...k.names.map((kw) =>
          kw.toLowerCase().startsWith(noPrefix) ? 10 : 0,
        ),
        0,
      )

      // Sort by length
      score -= k.displayText.length

      k.score = score
      return k
    })
    .sort((a, b) => {
      // Break ties alphabetically
      const alphabetically = a.displayText > b.displayText ? 0.5 : -0.5

      return b.score - a.score + alphabetically
    })
}

export const suggestUsers = ({ dispatch, state }) => {
  // Keep some persistent values in closure, most importantly for the
  // custom debounce to work. Lodash debounce does not return a promise.
  let suggestions = []
  let previousQuery = ''
  let timeout = null
  let cancelUserSearch = null

  const userSearch = (query) => dispatch('searchUsers', { query })
  const debounceUserSearch = (query) => {
    cancelUserSearch && cancelUserSearch()
    return new Promise((resolve, reject) => {
      timeout = setTimeout(() => {
        userSearch(query).then(resolve).catch(reject)
      }, 300)
      cancelUserSearch = () => {
        clearTimeout(timeout)
        resolve([])
      }
    })
  }

  return async (input) => {
    const noPrefix = input.toLowerCase().substr(1)
    if (previousQuery === noPrefix) return suggestions

    suggestions = []
    previousQuery = noPrefix
    // Fetch more and wait, don't fetch if there's the 2nd @ because
    // the backend user search can't deal with it.
    // Reference semantics make it so that we get the updated data after
    // the await.
    if (!noPrefix.includes('@')) {
      await debounceUserSearch(noPrefix)
    }

    const newSuggestions = state.users.users
      .filter(
        (user) =>
          user.screen_name &&
          user.name &&
          (user.screen_name.toLowerCase().startsWith(noPrefix) ||
            user.name.toLowerCase().startsWith(noPrefix)),
      )
      .slice(0, 20)
      .sort((a, b) => {
        let aScore = 0
        let bScore = 0

        // Matches on screen name (i.e. user@instance) makes a priority
        aScore += a.screen_name.toLowerCase().startsWith(noPrefix) ? 2 : 0
        bScore += b.screen_name.toLowerCase().startsWith(noPrefix) ? 2 : 0

        // Matches on name takes second priority
        aScore += a.name.toLowerCase().startsWith(noPrefix) ? 1 : 0
        bScore += b.name.toLowerCase().startsWith(noPrefix) ? 1 : 0

        const diff = (bScore - aScore) * 10

        // Then sort alphabetically
        const nameAlphabetically = a.name > b.name ? 1 : -1
        const screenNameAlphabetically = a.screen_name > b.screen_name ? 1 : -1

        return diff + nameAlphabetically + screenNameAlphabetically
      })
      .map((user) => ({
        user,
        displayText: user.screen_name_ui,
        detailText: user.name,
        imageUrl: user.profile_image_url_original,
        replacement: '@' + user.screen_name + ' ',
      }))

    suggestions = newSuggestions || []
    return suggestions
  }
}