password.fs

#light
open System

let conc ls :string =
  if List.length ls = 0 then ""
  else List.reduce (fun x y -> x + y) ls

let av_chars = ["0"; "1"; "2"; "3"; "4"; "5"; "6"; "7"; "8"; "9"; "A"; "B"; "C"; "D"; "E"; "F"; "G"; "H"; "I"; "J"; "K"; "L"; "M"; "N"; "O"; "P"; "Q"; "R"; "S"; "T"; "U"; "V"; "W"; "X"; "Y"; "Z"; "a"; "b"; "c"; "d"; "e"; "f"; "g"; "h"; "i"; "j"; "k"; "l"; "m"; "n"; "o"; "p"; "q"; "r"; "s"; "t"; "u"; "v"; "w"; "x"; "y"; "z";]
let special_chars = ["!"; "#"; "$"; "%"; "&"; "*"; "+"; "-"; "_"; "?"; "@";]

let getPass stringPart randLen specialLen =
  let rnd = System.Random()
  let rand = List.init randLen (fun i -> av_chars.[rnd.Next(List.length av_chars)])
  let spec = List.init specialLen (fun i -> special_chars.[rnd.Next(List.length special_chars)])
  stringPart + conc rand + conc spec

let usage x =
  "usage: password first random special\ne.g. 'password ted 4 3' -> " + (getPass "ted" 4 3) + " or 'password milk 7 2' -> " + (getPass "milk" 7 2)

let validate (stringPart:string) (randLen:string) (specialLen:string) =
  let randValid, randNum = Int32.TryParse(randLen)
  let specialValid, specialNum = Int32.TryParse(specialLen)
  match randNum, specialNum with
  | y, z when y > 0 && z > 0 -> getPass stringPart y z
  | y, _ when y > 0 -> getPass stringPart y 0
  | y, z when y <= 0 -> "must be at least one random element\n" + usage()
  | _ -> "invalid entry\n" + usage()

[<EntryPoint>]
let main args =
  match args with
  | [|_;_;_;|] -> printfn "%s" (validate args.[0] args.[1] args.[2])
  | _ | [|"--help";_;_;|] | [|"-h";_;_;|] | [|"?";_;_;|] | [|"/?";_;_;|] -> printfn "%s" (usage 0)
  0