whenwas.fsx

whenwas.fsx

#!/usr/bin/env fsharpi --exec

open System

type DateScale = Hour | Hours | Day | Days | Week | Weeks
type DateDirection = Ago | Forward

let parseDirection strInput =
    match strInput with 
        | "forward" | "from now"  -> Forward
        | "ago" | "back"          -> Ago
        | _                       -> failwith "Unrecognized direction"
;;

let parseScale strInput =
    match strInput with
        | "hour"      -> Hour
        | "hours"     -> Hours
        | "day"       -> Day
        | "days"      -> Days
        | "week"      -> Week
        | "weeks"     -> Weeks
        | _           -> failwith "Unrecognized interval"
;;

let getDate interval scale direction =
    let hoursToAdd = match scale with
                        | Hour  | Hours -> interval
                        | Day   | Days  -> interval * 24
                        | Week  | Weeks -> interval * 24 * 7
    in
    let signedHours = match direction with
                        | Ago       -> -1 * hoursToAdd
                        | Forward   -> hoursToAdd
    in
    signedHours
    |> float
    |> System.DateTime.Now.AddHours
;;

let main (args: string[]) = 
    if args.Length <> 3 then
        printfn "USAGE: whenwas N UNITS (ago|forward)"
        1
    else
        let intervalAsNumber = int args.[0]
        let parsedScale      = args.[1].ToLower() |> parseScale 
        let parsedDirection  = args.[2].ToLower() |> parseDirection 

        let computedDate = getDate intervalAsNumber parsedScale parsedDirection

        printfn "%A" computedDate
        0

fsi.CommandLineArgs 
|> Array.toList 
|> List.tail 
|> List.toArray 
|> main