require 'rom/sql/header'

require 'rom/sql/relation/class_methods'
require 'rom/sql/relation/inspection'
require 'rom/sql/relation/associations'

module ROM
  module SQL
    # Sequel-specific relation extensions
    #
    class Relation < ROM::Relation
      extend ClassMethods

      include Inspection
      include Associations

      attr_reader :header, :table

      # @api private
      def initialize(dataset, registry = {})
        super
        @table = dataset.opts[:from].first
      end

      # Return a header for this relation
      #
      # @return [Header]
      #
      # @api private
      def header
        @header ||= Header.new(dataset.opts[:select] || dataset.columns, table)
      end

      # Return raw column names
      #
      # @return [Array<Symbol>]
      #
      # @api private
      def columns
        dataset.columns
      end

      # @api public
      def project(*names)
        select(*header.project(*names))
      end

      # @api public
      def rename(options)
        select(*header.rename(options))
      end

      # @api public
      def prefix(name = Inflector.singularize(table))
        rename(header.prefix(name).to_h)
      end

      # @api public
      def qualified
        select(*qualified_columns)
      end

      # @api public
      def qualified_columns
        header.qualified.to_a
      end

      # Get first tuple from the relation
      #
      # @example
      #   users.first
      #
      # @return [Relation]
      #
      # @api public
      def first
        dataset.first
      end

      # Get last tuple from the relation
      #
      # @example
      #   users.first
      #
      # @return [Relation]
      #
      # @api public
      def last
        dataset.last
      end

      # Return relation count
      #
      # @example
      #   users.count # => 12
      #
      # @return [Relation]
      #
      # @api public
      def count
        dataset.count
      end

      # Select specific columns for select clause
      #
      # @example
      #   users.select(:id, :name)
      #
      # @return [Relation]
      #
      # @api public
      def select(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Append specific columns to select clause
      #
      # @example
      #   users.select(:id, :name).select_append(:email)
      #
      # @return [Relation]
      #
      # @api public
      def select_append(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Restrict a relation to match criteria
      #
      # @example
      #   users.where(name: 'Jane')
      #
      # @return [Relation]
      #
      # @api public
      def where(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Set order for the relation
      #
      # @example
      #   users.order(:name)
      #
      # @return [Relation]
      #
      # @api public
      def order(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Reverse the order of the relation
      #
      # @example
      #   users.order(:name).reverse
      #
      # @return [Relation]
      #
      # @api public
      def reverse(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Limit a relation to a specific number of tuples
      #
      # @example
      #   users.limit(1)
      #
      # @return [Relation]
      #
      # @api public
      def limit(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Set offset for the relation
      #
      # @example
      #   users.limit(10).offset(2)
      #
      # @return [Relation]
      #
      # @api public
      def offset(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Map tuples from the relation
      #
      # @example
      #   users.map { |user| ... }
      #
      # @api public
      def map(&block)
        to_enum.map(&block)
      end

      # Join other relation using inner join
      #
      # @param [Symbol] relation name
      # @param [Hash] join keys
      #
      # @return [Relation]
      #
      # @api public
      def inner_join(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Join other relation using left outer join
      #
      # @param [Symbol] relation name
      # @param [Hash] join keys
      #
      # @return [Relation]
      #
      # @api public
      def left_join(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Group by specific columns
      #
      # @example
      #   tasks.group(:user_id)
      #
      # @return [Relation]
      #
      # @api public
      def group(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Group by specific columns and count by group
      #
      # @example
      #   tasks.group_and_count(:user_id)
      #   # => [{ user_id: 1, count: 2 }, { user_id: 2, count: 3 }]
      #
      # @return [Relation]
      #
      # @api public
      def group_and_count(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Select and group by specific columns
      #
      # @example
      #   tasks.select_group(:user_id)
      #   # => [{ user_id: 1 }, { user_id: 2 }]
      #
      # @return [Relation]
      #
      # @api public
      def select_group(*args, &block)
        __new__(dataset.__send__(__method__, *args, &block))
      end

      # Insert tuple into relation
      #
      # @example
      #   users.insert(name: 'Jane')
      #
      # @param [Hash] tuple
      #
      # @return [Relation]
      #
      # @api public
      def insert(*args, &block)
        dataset.insert(*args, &block)
      end

      # Update tuples in the relation
      #
      # @example
      #   users.update(name: 'Jane')
      #   users.where(name: 'Jane').update(name: 'Jane Doe')
      #
      # @return [Relation]
      #
      # @api public
      def update(*args, &block)
        dataset.update(*args, &block)
      end

      # Delete tuples from the relation
      #
      # @example
      #   users.delete # deletes all
      #   users.where(name: 'Jane').delete # delete tuples
      #                                      from restricted relation
      #
      # @return [Relation]
      #
      # @api public
      def delete(*args, &block)
        dataset.delete(*args, &block)
      end

      # Return if a restricted relation has 0 tuples
      #
      # @example
      #   users.unique?(email: 'jane@doe.org') # true
      #
      #   users.insert(email: 'jane@doe.org')
      #
      #   users.unique?(email: 'jane@doe.org') # false
      #
      # @param [Hash] criteria hash for the where clause
      #
      # @return [Relation]
      #
      # @api public
      def unique?(criteria)
        where(criteria).count.zero?
      end
    end
  end
end