module GdsApi::PartMethods

def find_part(slug)
  return nil unless index = part_index(slug)
  parsed_content['parts'][index]
end

def has_next_part?(part)
  index = part_index(part['slug'])
  !! (index && (index + 1) < parsed_content['parts'].length)
end

def has_parts?(part)
  !! (has_previous_part?(part) || has_next_part?(part))
end

def has_previous_part?(part)
  index = part_index(part['slug'])
  !! (index && index > 0)
end

def part_after(part)
  part_at(part, 1)
end

def part_at(part, relative_offset)
  current_index = part_index(part['slug'])
  return nil unless current_index
  other_index = current_index + relative_offset
  return nil unless (0...parsed_content['parts'].length).cover?(other_index)
  parsed_content['parts'][other_index]
end

def part_before(part)
  part_at(part, -1)
end

def part_index(slug)
  parsed_content['parts'].index { |p| p['slug'] == slug }
end