# CSPT13 Computer Architecture I

import sys

# a machine that simply executes an instruction

# op-code - they represent the instruction that is supposed to be executed
PRINT_HI = 1
HALT = 2
PRINT_NUM = 3
SAVE = 4 # save a value in a given register
PRINT_REGISTER = 5 # print value stored in register
ADD = 6 # takes in two registers, A and B and adds both values contained in the registers and stores it in reg A

memory = [
    PRINT_HI,
    SAVE, # SAVE 65 2 means save the value 65 into reg 2
    65,
    2,
    SAVE, # SAVE 20 3 means save the value 20 into reg 3
    20,
    3,
    ADD, # ADD 2 3 means add the values stored in reg 2 and reg 3 and store the result in reg 2
    2,
    3,
    PRINT_REGISTER, # PRINT_REGISTER 2 means print the value stored in register 2
    2,
    HALT,
]

program_counter = 0 # points to the current instruction we need to execute next
running = True
registers = [0] * 8

# keep looping while not halted
while running:
    command_to_execute = memory[program_counter]

    if command_to_execute == PRINT_HI:
        print("hi")
        program_counter += 1
    elif command_to_execute == PRINT_NUM:
        number_to_print = memory[program_counter + 1]
        print(f"{number_to_print}")
        program_counter += 2
    elif command_to_execute == HALT:
        running = False
        program_counter += 1
    elif command_to_execute == SAVE:
        value_to_save = memory[program_counter + 1]
        register_to_save_it_in = memory[program_counter + 2]
        registers[register_to_save_it_in] = value_to_save
        program_counter += 3
    elif command_to_execute == PRINT_REGISTER:
        register_to_print = memory[program_counter + 1]
        print(f"{registers[register_to_print]}")
        program_counter += 2
    elif command_to_execute == ADD:
        register_a = memory[program_counter + 1]
        register_b = memory[program_counter + 2]
        sum_of_registers = registers[register_a] + registers[register_b]
        registers[register_a] = sum_of_registers
        program_counter += 3
    else:
        print(f"Unknown instruction {command_to_execute}")
        sys.exit(1)