module _59

open System
open System.IO

let cypher = 
    let encrypted = 
        File.ReadAllLines(@"59_cipher1.txt") 
        |> Array.collect (fun line -> line.Split(',') |> Array.map uint16)
    
    let decrypt f message key =
        let repeatedKey = seq { while true do yield! key }
        Seq.map2 f message repeatedKey

    let decryptXor = decrypt (^^^)

    let decriptMessage = decryptXor encrypted

    let de = encrypted |> Seq.distinct |> Seq.toArray
    
    let filteri f s =
        seq {
            for i in 0..((s |> Seq.length) - 1) do
                let si = Seq.nth i s
                if f i si then yield si
        }

    let validKeys encryptedSymbols = 
        let lowercase = [97us..122us] |> List.toArray
        let validSymbols = [32us..122us] |> List.toArray
        
        let isValidChar i =
            Array.exists ((=) i) validSymbols

        [0..2]
        |> List.map (fun offset ->
            lowercase
            |> Seq.filter (fun lc ->
                encryptedSymbols 
                |> filteri (fun i e -> i % 3 = offset)
                |> Seq.forall (fun e -> (e ^^^ lc) |> isValidChar))
            )

    let messageToText message =
        message
        |> Seq.map (char >> string)
        |> Seq.fold (fun acc e -> acc + e) ""

    validKeys encrypted
    |> common.slottedPermutations
    |> Seq.map (fun p -> (p, (decriptMessage >> messageToText) p))
    |> Seq.find (fun p -> (snd p).Contains(" the "))
    |> (fst >> decriptMessage)
    |> Seq.map (int)
    |> Seq.sum