module AlgoliaSearchableResource
  extend ActiveSupport::Concern

  class_methods do
    attr_reader :_algolia_index, :_query_fields

    # Declare the Algolia index to use when searching this resource
    def algolia_index(index)
      @_algolia_index = index
    end

    def inherited(subclass)
      subclass.instance_variable_set(:@_algolia_index, @_algolia_index)
      subclass.instance_variable_set(:@_query_fields, @_query_fields.deep_dup)
      super
    end

    # Declare the fields to query, and how to query them
    def query(field, opts = {})
      field = field.to_sym

      # For some reason, #filter(verify:) is supposed to return the values to
      # use.  I cannot honestly figure out why this is the case, so we provide
      # #query(valid:) instead.  #query(valid:) lambdas receive a value+context
      # and return a boolean.  If all values in a field are valid, the whole
      # is assumed valid.
      #
      # If you must, you can still use #filter(verify:) to handle the entire
      # array all at once, or to modify values.
      filter field, verify: opts[:verify] || ->(values, context) do
        if opts[:valid]
          values if values.all? { |v| opts[:valid].call(v, context) }
        else
          values
        end
      end

      @_query_fields ||= {}
      @_query_fields[field] = opts
    end

    # Determine if an Algolia hit is required
    def should_query?(filters)
      return false unless filters.respond_to?(:keys)
      return false unless @_query_fields
      filters.keys.any? { |key| @_query_fields.include?(key) }
    end

    # Override the #find_records method to search when called upon
    def find_records(filters, opts = {})
      return super(filters, opts) unless should_query?(filters)
      return [] if filters.values.any?(&:nil?)

      # Apply scopes and load
      load_query_records(apply_scopes(filters, opts), opts)
    end

    def find_serialized_with_caching(filters, serializer, opts = {})
      return super(filters, serializer, opts) unless should_query?(filters)
      records = find_records(filters, opts).reject(&:nil?)
      cached_resources_for(records, serializer, opts)
    end

    def load_query_records(query, opts = {})
      include_directives = opts[:include_directives]
      unless include_directives
        return @_search_service ? query.to_a : query.load.to_a
      end

      model_includes = resolve_relationship_names_to_relations(self,
        include_directives.model_includes, opts)

      if @_search_service
        query.includes(model_includes).to_a
      else
        query.load(scope: -> { includes(model_includes) }).to_a
      end
    end

    # Count all search results
    def find_count(filters, opts = {})
      return super(filters, opts) unless should_query?(filters)
      return 0 if filters.values.any?(&:nil?)
      apply_scopes(filters, opts).total_count
    end

    # Allow sorting on anything queryable + _score
    def sortable_fields(context = nil)
      @_query_fields ||= {}
      if searchable?
        super(context) + @_query_fields.keys + ['_score']
      else
        super(context)
      end
    end

    def searchable?
      @_query_fields.present?
    end

    private

    def pluck_arel_attributes(relation, *attrs)
      if relation.is_a?(Chewy::Query)
        attr_names = attrs.map { |a| a.name.to_s }
        relation = relation.only(*attr_names)
        relation.map { |row| row.attributes.values_at(*attr_names) }
      elsif relation.is_a?(Array)
        attr_names = attrs.map { |a| a.name.to_s }
        relation.map { |row| row.attributes.values_at(*attr_names) }
      else
        conn = relation.connection
        quoted_attrs = attrs.map do |attr|
          quoted_table = conn.quote_table_name(attr.relation.table_alias || attr.relation.name)
          quoted_column = conn.quote_column_name(attr.name)
          Arel.sql("#{quoted_table}.#{quoted_column}")
        end
        relation.pluck(*quoted_attrs)
      end
    end

    def apply_scopes(filters, opts = {})
      context = opts[:context]
      if @_search_service
        # Separate queries from filters
        queries = filters.select { |f| @_query_fields.include?(f) }
        filters = filters.reject { |f| @_query_fields.include?(f) }
        # Set up the search service
        query = @_search_service.new(queries, filters)
      else
        # Generate query
        query = generate_query(filters)
        query = query.reduce(@_chewy_index) do |scope, subquery|
          scope.public_send(*subquery.values_at(:mode, :query))
        end
      end
      # Pagination
      query = opts[:paginator].apply(query, {}) if opts[:paginator]
      # Sorting
      if opts[:sort_criteria]
        query = opts[:sort_criteria].reduce(query) do |scope, sort|
          field = sort[:field] == 'id' ? '_score' : sort[:field]
          scope.order(field => sort[:direction])
        end
      else
        query = query.order('_score' => :desc)
      end
      # Policy Scope
      query = search_policy_scope.new(context[:current_user], query).resolve
      context[:policy_used]&.call

      query
    end

    def preload_included_fragments(resources, records, serializer, options)
      return unless records.is_a?(ActiveRecord::Relation)
      super(resources, records, serializer, options)
    end

    def search_policy_scope
      Pundit::PolicyFinder.new(_model_class.new).scope!
    end

    def generate_query(filters)
      # For each queryable field, attempt to apply.  If there's no apply
      # specified, use auto_query to generate one.
      queries = @_query_fields.map do |field, opts|
        next unless filters.key?(field) # Skip if we don't have a filter

        filter = filters[field]
        filter = opts[:apply].call(filter, {}) if opts[:apply]

        { mode: opts[:mode] || :filter, query: auto_query(field, filter) }
      end
      queries.compact
    end

    def auto_query(field, value)
      case value
      when String, Integer, Float, Date
        { match: { field => value } }
      when Range
        { range: { field => { gte: value.min, lte: value.max } } }
      when Array
        # Array<String|Fixnum|Float> get shorthanded to a single match query
        if value.all? { |v| v.is_a?(String) || v.is_a?(Numeric) }
          auto_query(field, value.join(' '))
        else
          matchers = value.map { |v| auto_query(field, v) }
          { bool: { should: matchers } }
        end
      when Hash
        value.deep_transform_keys { |key| key.to_s == '$field' ? field : key }
      else
        value
      end
    end
  end
end
