DB transform algorithm

db_transform.rb

require 'pp'

SPEC = {
  identity_idx: 0,
  columns: [
    :id,
    :title,
    {
      name: :author,
      identity_idx: 0,
      columns: [:id, :name]
    }
  ]
}

def get_next_column_value
  @counter ||= 0
  @counter += 1
end

def get_column_value(idx)
  get_next_column_value
end

def process(row_hash, spec)
  spec[:columns].each do |c|
    case c
    when Hash
      relation_hash = row_hash[c[:name]] = {}
      process(relation_hash, c)
    else
      row_hash[c] = get_next_column_value
    end
  end
end

def prepare_spec(spec)
  if spec[:identity_idx]
    spec[:id_map] = {}
  end
  spec[:columns].each do |c|
    prepare_spec(c) if c.is_a?(Hash)
  end
end

def process(spec)
  id = get_column_value(spec[:identity_idx])
  if (row = spec[:id_map][id])
    return row
  end

  row = {}
  populate_row(row, spec)
  row
end

def populate_row(row, spec)
  spec[:columns].each_with_index do |c, i|
    case c
    when Hash
      row[c[:name]] = process(c)
    else
      value = row[c] = get_next_column_value
      if i == spec[:identity_idx]
        spec[:id_map][value] = row
      end
    end
  end
end


prepare_spec(SPEC)
puts "row:"
p process(SPEC)
puts
puts "SPEC:"
pp SPEC