#!/usr/bin/env ruby

require 'optparse'

def eval_h
  puts "Hello, world!"
end

def eval_q(script_string)
  puts script_string
end

def eval_9

  def multibeer(n)
    n = n.to_i
    case n
    when 0 then 'no more bottles'
    when 1 then '1 bottle'
    else "#{n} bottles"
    end
  end
  99.downto(1) do |i|
    puts <<-BOTTLES
#{multibeer(i)} of beer on the wall, #{multibeer(i)} of beer.
Take one down and pass it around, #{multibeer(i-1)} of beer on the wall.

    BOTTLES
  end

    puts <<-BOTTLES_ENDING
No more bottles of beer on the wall, no more bottles of beer.
Go to the store and buy some more, 99 bottles of beer on the wall.
    BOTTLES_ENDING
end

$i = 0
def eval_plus
  $i += 1
end

def show_usage
  puts <<-USAGE
Usage:

  -h, --help    - show help
  -e SCRIPT     - execute script

  no arguments  - fall back to interactive mode
  USAGE
end

def show_greeting
  puts <<-GREETING
--- Welcome to hquby interactive mode!
--- hquby is an implementation of HQ9+ interpreter.
--- Type ':help' or '?' for more options.
  GREETING
end

def show_help
  puts <<-HELP
\nAvailable options:

:help, ?          - show this help
:setprompt PROMPT - set new prompt
:examine          - print hidden variable value for debug purposes
:quit             - get me out of here!\n
  HELP
end

def eval_config(str)
  words = str.split(/\s+/)
  case words[0]
  when /\?|:help/   then show_help()
  when ':setprompt' then $prompt = words[1].nil? ? DEFAULT_PROMPT : "#{words[1]} "
  when ':quit'      then exit(0)
  when ':examine'   then puts "#{$i}"
  else puts "~ Error! Unknown statement: '#{words[0]}'"
  end
end

def eval_string(str)
  str.strip!

  # eval config
  if $is_interactive and [':', '?'].include?(str[0])
    eval_config(str)
    return
  end

  str.downcase!
  str.gsub!(/\s+/, '')
  commands = str.split('')

  # check commands
  commands.each_index do |c|
    if not ['h', 'q', '9', '+'].include?(commands[c])
      $stderr.puts "~ Error! Unknown symbol: '#{commands[c]}' (:#{c})"
      return
    end
  end

  # exec
  commands.each do |x|
    case x
    when 'h' then eval_h
    when 'q' then eval_q(str)
    when '9' then eval_9
    when '+' then eval_plus
    else puts "~ Error! This is awkward..."
    end
  end
end


########
# MAIN #
########

optparse = OptionParser.new do |opts|
  opts.on('-h', '--help', 'Display usage') do
    show_usage()
    exit(0)
  end

  opts.on('-e SCRIPT', 'Execute script from command line') do |scr|
    eval_string(scr)
    exit(0)
  end
end
optparse.parse!


$is_interactive = false
# Read from scripts or STDIN
if not ARGV.empty? or not $stdin.tty?
  ARGF.each do |line|
    eval_string(line.chomp)
  end
  exit(0)
end

# Fall back to interactive mode
# TODO Check 'Readline' support!
require 'readline'
$stdout.sync = true

DEFAULT_PROMPT = '>> '
$prompt = DEFAULT_PROMPT
$is_interactive = true

# Catch Ctrl-C
trap('INT') do
  puts "\n~ Interrupt"
  print $prompt
end

LIST = [
  ':help', ':setprompt',
  ':quit', ':examine',
].sort

comp = proc { |s| LIST.grep( /^#{Regexp.escape(s)}/ ) }

Readline.completion_append_character = " "
Readline.completion_proc = comp

show_greeting()
while line = Readline.readline($prompt, true)
  eval_string(line.chomp)
end