module _17

open System.Text.RegularExpressions

let rec numberToWords i =

    let firstDigit number =
        int (number.ToString().Substring(0,1))

    let remainingDigits number =
        int (number.ToString().Substring(1))

    let numberHeadTuple i =
        (firstDigit i, remainingDigits i)

    let concatWith separator s1 s2 =
        if not (System.String.IsNullOrEmpty(s2))
            then s1 + separator + s2
        else
            s1

    let hyphen = concatWith "-"

    let concatAnd = concatWith " and "

    match i.ToString().Length with
        | 1 ->
            match i with
                | 1 -> "one"
                | 2 -> "two"
                | 3 -> "three"
                | 4-> "four"
                | 5 -> "five"
                | 6 -> "six"
                | 7 -> "seven"
                | 8 -> "eight"
                | 9 -> "nine"
                | _ -> ""
        | 2 ->
            match numberHeadTuple i with
                | (1,0) -> "ten"
                | (1,1) -> "eleven"
                | (1,2) -> "twelve"
                | (1,3) -> "thirteen"
                | (1,4) -> "fourteen"
                | (1,5) -> "fifteen"
                | (1,8) -> "eighteen"
                | (1,j) -> (numberToWords j) + "teen"
                | (2,j) -> (numberToWords j) |> hyphen "twenty" 
                | (3,j) -> (numberToWords j) |> hyphen "thirty" 
                | (4,j) -> (numberToWords j) |> hyphen "forty"
                | (5,j) -> (numberToWords j) |> hyphen "fifty"
                | (6,j) -> (numberToWords j) |> hyphen "sixty"
                | (7,j) -> (numberToWords j) |> hyphen "seventy"
                | (8,j) -> (numberToWords j) |> hyphen "eighty"
                | (9,j) -> (numberToWords j) |> hyphen "ninety"
                | (_, _) -> "wtf"
        | 3 ->
            let (first,remaining) = numberHeadTuple i
            (numberToWords remaining) |> concatAnd ((numberToWords first) + " hundred") 
        | 4 -> 
            let (first,remaining) = numberHeadTuple i
            (numberToWords remaining) |> concatAnd ((numberToWords first) + " thousand") 
        | _ -> "unknown"


let getNumberWords =
    let nums = [1..1000]
    let numWords = Seq.map numberToWords nums
    //printfn "%s" (String.concat "\n" numWords)
    let strip s = Regex.Replace(s, "[^a-z]", "")
    numWords |> Seq.fold (fun acc elem -> acc + (strip elem).Length) 0
    
//let getNumberWords =
//    let nums = [1..100]
//    let strip s = Regex.Replace(s, "[^a-z]", "")
//    nums 
//    |> Seq.map (fun n -> (n, ((numberToWords >> strip) n).Length, numberToWords n))
//    |> Seq.toArray
//    |> Array.filter (fun (n, l, _) -> n % l = 0)