module DirectiveRecord
  module Query
    class SQL

      def initialize(base)
        @base = base
      end

      def to_sql(*args)
        options = extract_options(args)
        validate_options! options

        optimize_query! options

        prepare_options! options
        normalize_options! options

        parse_joins! options

        prepend_base_alias! options
        finalize_options! options

        compose_sql options
      end

    private

      def path_delimiter
        raise NotImplementedError
      end

      def aggregate_delimiter
        raise NotImplementedError
      end

      def group_by_all_sql
        raise NotImplementedError
      end

      def select_aggregate_sql(method, path)
        "#{method.to_s.upcase}(#{path})"
      end

      def select_aggregate_sql_alias(method, path)
        quote_alias("#{method}#{aggregate_delimiter}#{path}")
      end

      def base
        @base
      end

      def base_alias
        @base_alias ||= quote_alias(base.table_name.split("_").collect{|x| x[0]}.join(""))
      end

      def quote_alias(sql_alias)
        sql_alias
      end

      def extract_options(args)
        options = args.extract_options!.deep_dup
        options.reverse_merge! :select => (args.empty? ? "*" : args)
        options
      end

      def validate_options!(options)
        options.assert_valid_keys :select, :where, :group_by, :order_by, :limit, :offset, :aggregates, :numerize_aliases
      end

      def optimize_query!(options)
        select = [options[:select]].flatten
        if options[:where] && (select != %w(id)) && select.any?{|x| x.match(/^\w+(\.\w+)+$/)}
          ids = base.connection.select_values(to_sql(options.merge(:select => "id"))).uniq + [0]
          options[:where] = ["id IN (#{ids.join(", ")})"]
          options.delete :limit
          options.delete :offset
        end
      end

      def prepare_options!(options); end

      def normalize_options!(options)
        normalize_select!(options)
        normalize_where!(options)
        normalize_group_by!(options)
        normalize_order_by!(options)
        options.reject!{|k, v| v.blank?}
      end

      def normalize_select!(options)
        select = to_array! options, :select
        select.uniq!

        options[:scales] = select.inject({}) do |hash, sql|
          if scale = column_for(sql).try(:scale)
            hash[sql] = scale
          end
          hash
        end

        options[:aggregated] = {}
        options[:aliases] = {}

        options[:select] = options[:select].inject([]) do |array, path|
          sql, sql_alias = ((path == ".*") ? "#{base_alias}.*" : path), nil

          if aggregate_method = (options[:aggregates] || {})[path]
            sql = select_aggregate_sql(aggregate_method, path)
            sql_alias = options[:aggregated][path] = select_aggregate_sql_alias(aggregate_method, path)
          end
          if scale = options[:scales][path]
            sql = "ROUND(#{sql}, #{scale})"
            sql_alias ||= quote_alias(path)
          end
          if options[:numerize_aliases]
            sql = sql.gsub(/ AS .*$/, "")
            sql_alias = options[:aliases][prepend_base_alias(sql_alias || sql)] = "c#{array.size + 1}"
          end

          array << [sql, sql_alias].compact.join(" AS ")
          array
        end
      end

      def normalize_where!(options)
        regexp = /^\S+/

        where, having = (to_array!(options, :where) || []).partition do |statement|
          !options[:aggregated].keys.include?(statement.strip.match(regexp).to_s) &&
          statement.downcase.gsub(/((?<![\\])['"])((?:.(?!(?<![\\])\1))*.?)\1/, " ")
                            .scan(/([a-zA-Z_\.]+)?\s*(=|<=>|>=|>|<=|<|<>|!=|is|like|rlike|regexp|in|between|not|sounds|soundex)(\b|\s)/)
                            .all? do |(path, operator)|
            path && column_for(path)
          end
        end

        unless (attrs = base.scope_attributes).blank?
          sql = base.send(:sanitize_sql_for_conditions, attrs, "").gsub(/``.`(\w+)`/) { $1 }
          where << sql
        end

        options[:where], options[:having] = where, having.collect do |statement|
          statement.strip.gsub(regexp){|path| options[:aggregated][path] || path}
        end

        [:where, :having].each do |key|
          value = options[key]
          options[key] = (value.collect{|x| "(#{x})"}.join(" AND ") unless value.empty?)
        end
      end

      def normalize_group_by!(options)
        group_by = to_array! options, :group_by
        group_by.clear.push(group_by_all_sql) if group_by == [:all]
      end

      def normalize_order_by!(options)
        options[:order_by] ||= (options[:group_by] || []).collect do |path|
          direction = "DESC" if path.to_s == "date"
          "#{path} #{direction}".strip
        end

        to_array!(options, :order_by).collect! do |x|
          segments = x.split " "
          direction = segments.pop if %w(asc desc).include?(segments[-1].downcase)
          path = segments.join " "

          if path != group_by_all_sql
            scale = options[:scales][path]
            select = begin
              if aggregate_method = (options[:aggregates] || {})[path]
                select_aggregate_sql(aggregate_method, path)
              else
                path
              end
            end
            "#{scale ? "ROUND(#{select}, #{scale})" : select} #{direction.upcase if direction}".strip
          end
        end

        options[:order_by].compact!
      end

      def to_array!(options, key)
        if value = options[key]
          options[key] = [value].flatten
        end
      end

      def column_for(path)
        segments = path.split(".")
        column = segments.pop
        model = segments.inject(base) do |klass, association|
          klass.reflect_on_association(association.to_sym).klass
        end
        model.columns_hash[column]
      rescue
        nil
      end

      def parse_joins!(options)
        return if (paths = extract_paths(options)).empty?

        regexp = /INNER JOIN `([^`]+)`( `[^`]+`)? ON `[^`]+`.`([^`]+)` = `[^`]+`.`([^`]+)`/

        options[:joins] = paths.collect do |path|
          joins, associations = [], []
          path.split(".").inject(base) do |klass, association|
            association = association.to_sym

            table_joins = klass.joins(association).to_sql.scan regexp
            concerns_bridge_table = table_joins.size == 2
            bridge_table_as = nil

            table_joins.each_with_index do |table_join, index|
              concerns_bridge_table_join = concerns_bridge_table && index == 0
              join_table, possible_alias, join_table_column, table_column = table_join

              table_as = (klass == base) ? base_alias : quote_alias(associations.join(path_delimiter))
              join_table_as = quote_alias((associations + [association]).join(path_delimiter))

              if concerns_bridge_table
                if concerns_bridge_table_join
                  join_table_as = bridge_table_as = quote_alias("#{(associations + [association]).join(path_delimiter)}_bridge_table")
                else
                  table_as = bridge_table_as
                end
              end

              joins.push "LEFT JOIN #{join_table} #{join_table_as} ON #{join_table_as}.#{join_table_column} = #{table_as}.#{table_column}"
            end

            associations << association
            klass.reflect_on_association(association).klass
          end
          joins
        end.flatten.uniq.join("\n")
      end

      def extract_paths(options)
        [:select, :where, :group_by, :having, :order_by].inject([]) do |paths, key|
          if value = options[key]
            value = value.join " " if value.is_a?(Array)
            paths.concat value.gsub(/((?<![\\])['"])((?:.(?!(?<![\\])\1))*.?)\1/, " ").scan(/[a-zA-Z_]+\.[a-zA-Z_\.]+/).collect{|x| x.split(".")[0..-2].join "."}
          else
            paths
          end
        end.uniq
      end

      def prepend_base_alias!(options)
        [:select, :where, :group_by, :having, :order_by].each do |key|
          if value = options[key]
            options[key] = prepend_base_alias value, options[:aliases]
          end
        end
      end

      def prepend_base_alias(sql, aliases = {})
        columns = base.columns_hash.keys
        sql = sql.join ", " if sql.is_a?(Array)
        sql.gsub(/("[^"]*"|'[^']*'|`[^`]*`|[a-zA-Z_#{aggregate_delimiter}]+(\.[a-zA-Z_\*]+)*)/) do
          columns.include?($1) ? "#{base_alias}.#{$1}" : begin
            if (string = $1).match /^([a-zA-Z_\.]+)\.([a-zA-Z_\*]+)$/
              path, column = $1, $2
              "#{quote_alias path.gsub(".", path_delimiter)}.#{column}"
            else
              string
            end
          end
        end
      end

      def finalize_options!(options); end

      def compose_sql(options)
        sql = ["SELECT #{options[:select]}", "FROM #{base.table_name} #{base_alias}", options[:joins]].compact

        [:where, :group_by, :having, :order_by, :limit, :offset].each do |key|
          unless (value = options[key]).blank?
            keyword = key.to_s.upcase.gsub("_", " ")
            sql << "#{keyword} #{value}"
          end
        end

        sql.join "\n"
      end

    end
  end
end