d2s1.jl

using OffsetArrays
using Test

const input = parse.(Int, split(read("2_input", String), ','))

const instructions = Dict(
    1 => +,
    2 => *,
)

function main(input)
    intcode = OffsetVector(copy(input), 0:length(input) - 1)

    # 1202 program alarm
    intcode[1] = 12
    intcode[2] = 2

    i = 0
    while intcode[i] != 99
        intcode[intcode[i + 3]] = instructions[intcode[i]](intcode[intcode[i + 1]], intcode[intcode[i + 2]])
        i += 4
    end
    return intcode
end

function tests()
    @test main([1,0,0,0,99]) == [2,0,0,0,99]
    @test main([2,3,0,3,99]) == [2,3,0,6,99]
    @test main([2,4,4,5,99,0]) == [2,4,4,5,99,9801]
    @test main([1,1,1,4,99,5,6,0,99]) == [30,1,1,4,2,5,6,0,99]
end