module GraphQL::Analysis

def analyze_query(query, analyzers)
  analyzers_and_values = analyzers.map { |r| initialize_reducer(r, query) }
  irep = query.internal_representation
  irep.each do |name, op_node|
    reduce_node(op_node, analyzers_and_values)
  end
  analyzers_and_values.map { |(r, value)| finalize_reducer(r, value) }
end

def finalize_reducer(reducer, reduced_value)
  if reducer.respond_to?(:final_value)
    reducer.final_value(reduced_value)
  else
    reduced_value
  end
end

def initialize_reducer(reducer, query)
  if reducer.respond_to?(:initial_value)
    [reducer, reducer.initial_value(query)]
  else
    [reducer, nil]
  end
end

def reduce_node(irep_node, analyzers_and_values)
  visit_analyzers(:enter, irep_node, analyzers_and_values)
  irep_node.children.each do |name, child_irep_node|
    reduce_node(child_irep_node, analyzers_and_values)
  end
  visit_analyzers(:leave, irep_node, analyzers_and_values)
end

def visit_analyzers(visit_type, irep_node, analyzers_and_values)
  analyzers_and_values.each do |reducer_and_value|
    reducer = reducer_and_value[0]
    memo = reducer_and_value[1]
    next_memo = reducer.call(memo, visit_type, irep_node)
    reducer_and_value[1] = next_memo
  end
end