Merge pull request #3847 from r888888888/intelligent-autocomplete

Intelligent autocomplete

app/logical/tag_autocomplete.rb

@@ -0,0 +1,99 @@
+module TagAutocomplete
+  extend self
+
+  PREFIX_BOUNDARIES = "(_/:;-"
+
+  class Result < Struct.new(:name, :post_count, :category, :antecedent_name)
+    def to_xml(options = {})
+      to_h.to_xml(options)
+    end
+  end
+
+  def search(query)
+    candidates = count_sort(
+      query,
+      search_prefix(query, 3) + 
+      search_fuzzy(query, 5) +
+      search_exact(query, 3) +
+      search_aliases(query, 3)
+    )
+  end
+
+  def count_sort(query, words)
+    words.uniq.sort_by do |x|
+      x.post_count
+    end.reverse
+  end
+
+  def search_exact(query, n=3)
+    Tag
+      .where("name like ? escape e'\\\\'", query.to_escaped_for_sql_like + "%")
+      .where("post_count > 0")
+      .order("post_count desc")
+      .limit(n)
+      .pluck(:name, :post_count, :category)
+      .map {|row| Result.new(*row)}
+  end
+
+  def search_fuzzy(query, n=5)
+    if query.size <= 3
+      return []
+    end
+
+    Tag
+      .where("name % ?", query)
+      .where("name like ? escape E'\\\\'", query[0].to_escaped_for_sql_like + '%')
+      .where("post_count > 0")
+      .order(Arel.sql("similarity(name, #{Tag.connection.quote(query)}) * log(10, post_count + 1) DESC"))
+      .limit(n)
+      .pluck(:name, :post_count, :category)
+      .map {|row| Result.new(*row)}
+  end
+
+  def search_prefix(query, n=3)
+    if query.size >= 5
+      return []
+    end
+
+    if query.size <= 1
+      return []
+    end
+
+    if query =~ /[-_()]/
+      return []
+    end
+
+    if query.size >= 3
+      min_post_count = 0
+    else
+      min_post_count = 5_000
+      n += 2
+    end
+
+    anchors = "^" + query.split("").map {|x| Regexp.escape(x)}.join(".*[#{PREFIX_BOUNDARIES}]")
+    Tag
+      .where("name ~ ?", anchors)
+      .where("post_count > ?", min_post_count)
+      .where("post_count > 0")
+      .order("post_count desc")
+      .limit(n)
+      .pluck(:name, :post_count, :category)
+      .map {|row| Result.new(*row)}
+  end
+
+  def search_aliases(query, n=20)
+    wildcard_name = query + "*"
+    TagAlias
+      .select("tags.name, tags.post_count, tags.category, tag_aliases.antecedent_name")
+      .joins("INNER JOIN tags ON tags.name = tag_aliases.consequent_name")
+      .where("tag_aliases.antecedent_name LIKE ? ESCAPE E'\\\\'", wildcard_name.to_escaped_for_sql_like)
+      .active
+      .where("tags.name NOT LIKE ? ESCAPE E'\\\\'", wildcard_name.to_escaped_for_sql_like)
+      .where("tag_aliases.post_count > 0")
+      .order("tag_aliases.post_count desc")
+      .limit(n)
+      .pluck(:name, :post_count, :category, :antecedent_name)
+      .map {|row| Result.new(*row)}
+  end
+end
+