#434

backend/app/services/counts_candidates.rb

@@ -0,0 +1,55 @@
+# Bounded, authorised candidates at the same recorded point as the Counts query.
+class CountsCandidates
+  KEYS = ['resource', 'field', 'query', 'category', 'page', 'locale', 'at',
+          'execution_at', 'timezone'].freeze
+  LIMIT = 20
+
+  def initialize(params)
+    QueryState.validate!(params, KEYS)
+    raise ArgumentError unless params.fetch('resource') == 'posts'
+    raise ArgumentError unless ['tags', 'tags_json'].include?(params.fetch('field'))
+
+    @params = params
+    @page = Integer(params.fetch('page', '1'), 10)
+    raise ArgumentError unless @page.between?(1, 100_000)
+    raise ArgumentError if params.fetch('query', '').bytesize > 1000
+    category = params['category']
+    raise ArgumentError if category.present? && !Tag.categories.key?(category)
+  end
+
+  def call
+    options = @params.slice('locale', 'at', 'execution_at', 'timezone')
+        .merge('definition' => 'latest', 'resource' => 'tags')
+    internal = CountsPopulation.new(options)
+    external = CountsPopulation.new(options.merge('resource' => 'nico_tags',
+        'execution_at' => internal.at.iso8601(6)))
+    language = Locale.find_by!(code: @params.fetch('locale', 'ja')).language_code
+    connection = TagVersion.connection
+    path = connection.quote("$.#{ language.to_json }.name")
+    name = "COALESCE(JSON_UNQUOTE(JSON_EXTRACT(v.names, #{ path })), v.name)"
+    sources = [[internal, 'internal', name, 'v.category'],
+               [external, 'external', 'v.name', 'NULL']].map do |population, kind, title, category|
+      population.scope.except(:select).select(Arel.sql(
+          "CONCAT('#{ kind }:', v.tag_id) AS value, v.tag_id AS id, " +
+          "#{ title } AS name, #{ category } AS category, '#{ kind }' AS kind")).to_sql
+    end
+    clauses = []
+    binds = []
+    if @params['query'].present?
+      clauses << '(name LIKE ? OR CAST(id AS CHAR) = ?)'
+      binds += ["%#{ ApplicationRecord.sanitize_sql_like(@params['query']) }%", @params['query']]
+    end
+    if @params['category'].present?
+      clauses << 'category = ?'
+      binds << @params['category']
+    end
+    where = clauses.empty? ? '' : "WHERE #{ clauses.join(' AND ') }"
+    sql = <<~SQL
+      SELECT /*+ MAX_EXECUTION_TIME(10000) */ * FROM (#{ sources.join(' UNION ALL ') }) choices
+      #{ where } ORDER BY kind, id LIMIT #{ LIMIT + 1 } OFFSET #{ (@page - 1) * LIMIT }
+    SQL
+    rows = connection.select_all(ApplicationRecord.sanitize_sql_array([sql, *binds])).to_a
+    { rows: rows.first(LIMIT), page: @page, more: rows.length > LIMIT,
+      execution_at: internal.at.iso8601(6) }
+  end
+end