class ReeHash::HashKeysContract

def self.message(value, name, lvl = 1)
  "expected #{to_s}, got => #{truncate(value.inspect)}"
end

def self.to_s
  "[:key0, .., :keyM => [:keyN, .., :keyZ]]"
end

def self.valid?(obj)
  return false if !obj.is_a?(Array)
  return false if obj.any? { !valid_item?(_1) }
  true
end

def self.valid_item?(obj)
  return true if obj.is_a?(Symbol)
  return false if !obj.is_a?(Hash)  
  obj.each do |k, v|
    return false if !k.is_a?(Symbol)
    return false if !v.is_a?(Array)
    return false if v.any? { !valid_item?(_1) }
  end
  true
end