#!/usr/bin/env ruby

def ask_type
  t = ""
  loop do
    STDERR.print "Choose a format {R,I,J}[R]: "
    t = STDIN.gets.chomp
    if "RIJrij".include?(t)
      break
    else
      STDERR.puts "That's not recognized as a format"
    end
  end
  if( t.empty? )
    t = "r"
  end
  STDERR.puts "Format chosen: #{t}"
  t.downcase
end

def ask_op(prompt,min,max)
  #STDERR.puts "You can either supply one in decimal or hexadecimal format."
  op = 0
  loop do
    STDERR.print prompt
    op = STDIN.gets.chomp.to_i(16)
    if op > max
      STDERR.puts "That's larger than allowed. Maximum value 0x#{max.to_s(16)}."
    elsif op < min
      STDERR.puts "That's less than allowed. Minimum value 0x#{min.to_s(16)}."
    else
      break
    end
  end
  op
end


STDERR.puts <<eoh
This is a small script for creating properly formated MIPS-instructions.
You will be asked a number of questions and then rewarded with a 4-byte
instruction in hexadecimal and decimal format. Have fun!

eoh

loop do
  t = ask_type

  op = ask_op("        Choose an op-code {0x00-0x3f}[0x00]: ",0x00,0x3f)
  fu = ask_op("   Choose a function-code {0x00-0x3f}[0x00]: ",0x00,0x3f) if t == 'r'
  rs = ask_op("       Choose rs-register {0x00-0x1f}[0x00]: ",0x00,0x1f) if t != 'j'
  rt = ask_op("       Choose rt-register {0x00-0x1f}[0x00]: ",0x00,0x1f) if t != 'j'
  ta = ask_op("Choose target-address {0x0-0x2000000}[0x00]: ",0x00,0x2000000) if t == 'j'
  im = ask_op("  Choose immediate value {0x0-0x8000}[0x00]: ",0x00,0x8000) if t == 'i'
  rd = ask_op("       Choose rd-register {0x00-0x1f}[0x00]: ",0x00,0x1f) if t == 'r'
  sh = ask_op("      Choose shift-amount {0x00-0x1f}[0x00]: ",0x00,0x1f) if t == 'r'
  case
    when 'j' == t
      instruction = (op<<26) + ta
    when 'i' == t
      instruction = (op<<26) + (rs<<21) + (rt<<16) + im
    when 'r' == t
      instruction = (op<<26) + (rs<<21) + (rt<<16) + (rd<<11) + (sh<<6) + fu
  end

  STDOUT.printf( "instruction:\t0x%08x\t%d\n",  instruction,instruction)
end