ace-of-base/lib/ace_of_base/query.rb

# frozen_string_literal: true

module AceOfBase
  # A query builder for querying our data.
  class Query
    require 'ace_of_base/query/operator'
    require 'ace_of_base/query/or'
    require 'ace_of_base/query/and'
    require 'ace_of_base/query/eq'

    include ValidField

    INVALID_AGGREGATION_MESSAGE = 'Operation %s is not a valid aggregation'
    VALID_AGGREGATIONS = %i[min max sum count collect].freeze

    def initialize(storage)
      @fields = []
      @order_bys = []
      @filters = []
      @aggregations = {}
      @group_bys = []
      @storage = storage
    end

    def select(*fields)
      ensure_valid_fields!(fields)
      @fields = fields

      self
    end

    def aggregate(aggregations)
      ensure_valid_fields!(aggregations.keys)
      ensure_valid_aggregations!(aggregations.values)
      @aggregations = aggregations

      self
    end

    def group_by(*fields)
      ensure_valid_fields!(fields)
      @group_bys = fields

      self
    end

    def order_by(*fields)
      ensure_valid_fields!(fields)
      @order_bys = fields
      self
    end

    def filter(*filters)
      @filters = filters
      self
    end

    def execute
      collection = @storage
      collection = apply_filters(collection)
      collection = apply_aggregations(collection)
      collection = apply_sorts(collection)
      collection = take_fields(collection)
      collection.to_a
    end

    private

    attr_reader :fields, :order_bys, :filters, :storage, :group_bys, :aggregations

    def ensure_valid_aggregations!(aggregations)
      aggregations.each do |op|
        raise ArgumentError, format(INVALID_AGGREGATION_MESSAGE, op) unless VALID_AGGREGATIONS.include?(op.to_sym)
      end
    end

    def apply_filters(collection)
      return collection if filters.empty?

      collection.select do |record|
        filters.all? do |filter|
          filter.match?(record)
        end
      end
    end

    def apply_sorts(collection)
      return collection if order_bys.empty?

      collection.sort do |lhs, rhs|
        order_bys
          .lazy
          .map { |attr| lhs.public_send(attr) <=> rhs.public_send(attr) }
          .find(-> { 0 }, &:nonzero?)
      end
    end

    def apply_aggregations(results)
      return results if group_bys.empty?

      results
        .group_by { |record| group_bys.map { |attr| record.public_send(attr) } }
        .values
        .map { |records| AggregatedRecord.new(records, aggregations) }
    end

    def take_fields(collection)
      collection.map do |record|
        selected_fields.map { |field| record.public_send(field) }
      end
    end

    def selected_fields
      return Record::ATTRIBUTES if fields.empty?

      fields
    end
  end
end