require 'singleton'

class SafeHash < BasicObject
  attr_reader :hash
  
  def initialize hash = {}
    reinitialize hash
  end
  
  def []= key, value
    value = SafeHash.new value if value.is_a? Hash
    @hash[key.to_s] = value
  end
  
  def include? key
    @hash.include? key.to_s
  end
  
  def [] key, *args     
    key = key.to_s
    if key.last == '!'
      key = key[0..-2]
      if @hash.include? key
        @hash[key]
      else
        raise "No key #{key}"
      end
    elsif key.last == '?'
      key = key[0..-2]
      @hash.include? key
    else
      if @hash.include? key
        @hash[key]
      elsif args.empty?
        SafeNil.instance
      else
        return *args
      end
    end
  end
  
  def reinitialize hash
    @hash = {}
    hash.each do |k, v|
      v = SafeHash.new v if v.is_a? Hash 
      @hash[k.to_s] = v
    end
    # @hash.freeze
  end
  
  def method_missing m, *args
    m = m.to_s
    if m.last == '='
      self[m[0..-2]] = *args
    else
      self[m, *args]
    end
  end
  
  def to_yaml *args
    @hash.to_yaml *args
  end
  
  def inspect
    @hash.inspect
  end
  
  def delete key
    @hash.delete key.to_s
  end
  
  # deep conversion, check and converts nested SafeHashes to Hashes
  def to_hash    
    r = {}
    @hash.each do |k, v|
      r[k] = if v.respond_to :is_a_safe_hash?
        v.to_hash
      else
        v
      end
    end
    r
  end
  alias_method :to_h, :to_hash
  
  def is_a_safe_hash?
    true
  end
  
  class SafeNil < BasicObject
    include Singleton

    def [] key, *args
      key = key.to_s
      if key.last == '!'
        raise "No key #{key}"
      elsif key.last == '?'
        false
      elsif args.empty?
        SafeNil.instance
      else
        return *args
      end
    end

    def method_missing m, *args
      m = m.to_s
      if m.last == '='
        raise "No such key!"
      else
        self[m, *args]
      end
    end
    
    def include? key
      false
    end
    
    def to_b
      false
    end
    
    def to_yaml *args
      nil.to_yaml *args
    end
    
    def to_h
      {}
    end
    
    def inspect
      nil.inspect
    end
  end
end