gistfile1.txt

def expand input
  
  quote = nil
  prev = nil
  prevprev = nil
  escape = "\\"
  dq = "\""
  sq = "'"  
  state = "code"
  string = ""
  ret = ""
  interp = ""
  braces = nil
  interp_quote = nil
  add_bracket = false
  code = "#"
  
  add_brackets = false
  
  input.split("").each do |ch| 
    case state
    when "code"
      if (ch == dq || ch == sq) && prev != escape
        quote = ch
        state = "string"
        string = ch
      else
        ret += ch
      end
    when "string"
      if ch == "{" && prevprev != escape && prev == code
        state = "interp"
        interp = ""
        braces = 1
        interp_quote = nil
        string = string.slice(0,string.length - 1)
      elsif ch == quote && prev != escape
        state = "code"
        ret = ret + string + ch # nothing for the minute ! 
        ret += ")" if add_bracket && add_brackets
        add_bracket = false
        string = ""
        quote = nil
      elsif prev==code && prevprev != escape && ch.match(/[a-zA-Z_\$]/)
        state = "interp_var"
        interp = ch
      string = string.slice(0,string.length - 1)
      else
        string += ch
      end
    when "interp_var"
      if ch.match(/[a-zA-Z_\$0-9]/)
        interp += ch
      else
        string += "#{quote}+(#{interp})+#{quote}"
        interp = ""
        state = "string"
      end
    when "interp"
      
      if interp_quote
        if ch == interp_quote && prev != escape
          interp_quote = nil
        end
      else
        if ch == "{"
          braces += 1
        elsif ch == "}"
          braces -= 1
        elsif (ch == dq || ch == sq) && prev != escape
          interp_quote = ch
        end
      end
      
      if braces == 0
        if add_brackets
          string = "(" + string + "#{quote})+(#{interp})+(#{quote}"
        else
          string = string + "#{quote}+(#{interp})+#{quote}"
        end  
        add_bracket = true
        interp_quote = nil
        state = "string"
      else
        interp += ch
      end
    end
    
    prevprev = prev
    prev = ch
  end
  
  ret
end

def exterpolate string
  puts "in:  " + string 
  
  while true
    expanded = expand(string)
  
    if expanded == string
      puts "out: " + string
      puts
      return expanded 
    end
    string = expanded
    #puts "transform => " + string
  end
  
end

coffee =<<EOF
x: "1 + 2"
x: "1 + \\"2"
y: "1 + ${x}"
y: "1 + $myvar + $someothervar \\${helo}"
y: "1 + \\${x}"
z: "2 + ${fn ? 3 : 2} + etc"
"1 + ${x}"
z: "${join({a:1})} + etc"
z: '${join({a:1})}'
z: '1 + ${if x then join {a: "hello"} }'
z: '1 + ${ {a: "hel${X}lo"}.keys }'
z: '${"${"${"${"${"${"hello!"}"}"}"}"}"}'
z: "${{}"
z: "hello: ${\}}"
'"${x ? y : "${z || '${1 + "${2}" + 1}'}" }"'
EOF

coffee.gsub("$", "#").split("\n").each do |line|
  exterpolate(line)
end