function get_param(state, arg)
    local param_mode = state.mem[state.pos] // (10 ^ (arg + 1)) % 10
    if #state.mem < state.pos + arg then
        print(string.format("Error: Opcode too short at end of memory: %d", state.pos))
        os.exit(false)
    end
    local arg = state.mem[state.pos + arg]
    if param_mode == 0 then
        arg = arg + 1
    elseif param_mode == 2 then
        arg = arg + state.relbase
    end
    return arg
end

function read_mem(state, arg)
    local param_mode = state.mem[state.pos] // (10 ^ (arg + 1)) % 10
    local arg = get_param(state, arg)
    if param_mode == 1 then
        return arg
    end
    arg = state.mem[arg]
    if not arg then
        return 0
    end
    return arg
end

function write_mem(state, arg, val)
    local param_mode = state.mem[state.pos] // (10 ^ (arg + 1)) % 10
    local arg = get_param(state, arg)
    if param_mode == 1 then
        print(string.format("Error: Invalid inmediate write: %d", arg))
    end
    state.mem[arg] = val
end

function interpret(state)
    if not state.mem then
        state.mem = state
    end
    if not state.pos then
        state.pos = 1
        state.relbase = 1
    end
    if not state.input then
        state.input = input_stdin
    end
    if not state.output then
        state.output = output_stdout
    end

    while true do
        if #state.mem < state.pos then
            print(string.format("Instruction pointer ran off of memory"))
            os.exit(false)
        end

        local opcode = state.mem[state.pos] % 100
        local instr_size = 1

        if opcode == 1 then
            write_mem(state, 3, read_mem(state, 1) + read_mem(state, 2))
            instr_size = 4
        elseif opcode == 2 then
            write_mem(state, 3, read_mem(state, 1) * read_mem(state, 2))
            instr_size = 4
        elseif opcode == 3 then
            local val = state.input()
            if not val then return true end
            write_mem(state, 1, val)
            instr_size = 2
        elseif opcode == 4 then
            state.output(read_mem(state, 1))
            instr_size = 2
        elseif opcode == 5 then
            instr_size = 3
            if read_mem(state, 1) ~= 0 then
                state.pos = read_mem(state, 2) + 1
                instr_size = 0
            end
        elseif opcode == 6 then
            instr_size = 3
            if read_mem(state, 1) == 0 then
                state.pos = read_mem(state, 2) + 1
                instr_size = 0
            end
        elseif opcode == 7 then
            write_mem(state, 3, read_mem(state, 1) < read_mem(state, 2) and 1 or 0)
            instr_size = 4
        elseif opcode == 8 then
            write_mem(state, 3, read_mem(state, 1) == read_mem(state, 2) and 1 or 0)
            instr_size = 4
        elseif opcode == 9 then
            state.relbase = state.relbase + read_mem(state, 1)
            instr_size = 2
        elseif opcode == 99 then
            return false
        else
            print(string.format("Error: Invalid opcode %d at %d", opcode, state.pos - 1))
            os.exit(false)
        end

        state.pos = state.pos + instr_size
    end
end

function input_stdin()
    io.stdout:write("> ")
    return io.stdin:read("n")
end

function output_stdout(val)
    io.stdout:write(val)
    io.stdout:write("\n")
end

function input_array(array)
    function inner()
        return table.remove(array, 1)
    end
    return inner
end

function output_array(array)
    function inner(val)
        table.insert(array, val)
    end
    return inner
end

file = io.open(arg[1])
program = {}
for num in string.gmatch(file:read(), "(-?%d+),?") do
    table.insert(program, tonumber(num))
end
file:close()

interpret(program)