require "readline"
require "yaml"

command_tree = {"pet"=>
  {"buy"=>{"dog"=>nil, "cat"=>nil},
   "sell"=>{"bird"=>nil, "fox"=>nil},
   "sellGroup"=>{"pig"=>nil, "kingfisher"=>nil},
   "list"=>{"all"=>nil, "filter_by"=>nil}},
 "store"=>
  {"find"=>{"by_name"=>nil, "by_tag"=>nil, "by_address"=>nil}, "list"=>nil},
 "user"=>{"login"=>nil, "logout"=>nil, "sign_up"=>nil},
 "petGroup"=>{"login"=>nil, "loout"=>nil, "sign_up"=>nil},
}

pp command_tree

def get_current_option(command_tree, line_buffer)
  current_option = command_tree.keys
  commands = line_buffer.split

  commands.each_with_index do |command, i|

    # Don't go down to the lower level(and return current_option) in case current command matches two candidates such as "pet" and "petGroup" 
    return current_option if i == commands.size-1 and !line_buffer.end_with?("\s")

    # Go down  
    if command_tree.has_key?(command) 
      if command_tree[command].nil? # invalid command or key at leaf
        current_option = []
      else
        command_tree = command_tree[command] 
        current_option = command_tree.keys
      end
    end
  end
  current_option
end

# Evaluate the proc when pressing <tab>
comp = proc do |input|
  get_current_option(command_tree, Readline.line_buffer).select { |name| name.to_s.start_with?(input) }
end

Readline.completion_proc = comp
#Readline.completion_append_character = " "

while input = Readline.readline("$ ", true)
  break if input == "q"
  p Readline.line_buffer.split if !input.empty?
end