module _50

let sumOfConsequitivePrimes =
    let ceiling = 1000000
    let primes = common.primeArray ceiling
    let isPrime = common.isPrimeFunByArray primes

    let primeSumUnderCeilingIndex =
        primes
        |> Seq.scan (fun state p -> p + state) 0
        |> Seq.findIndex (fun s -> s > ceiling)
        |> (+) -1

    let indiciesOfDecendingLength max =
        seq {
            for l in max .. -1 .. 0 do
                for o in 0 .. (max - l) do
                    yield (o, l)
        }

    indiciesOfDecendingLength primeSumUnderCeilingIndex
    |> Seq.map (fun (start,len) -> Array.sub primes start len |> Array.sum)
    |> Seq.find isPrime