shouldbeSorted.fs

open System

type Message =
  | Default
  | Custom of string
type Person = {
  name : string
  age : int
}
let person name age = {name = name; age = age }
let imran = person "Imran" 1
let mo = person "Mo" 2
let david = person "David" 3
let byAge person = person.age
let ascending item1 item2 = item1 <= item2
let people = [| imran;  mo; david |]

let private sortChecker previousVal thisItem selector comparator message =
  let thisVal = selector thisItem
  let compare = comparator previousVal thisVal
  if compare = false then
    match message with
      | Default -> sprintf "collection is not sorted (item1: %O, item2: %O)" previousVal thisVal
      | Custom(x) -> x
    |> failwith
  thisVal

let shouldBeSorted (selector : 'TItem -> 'TProp) (comparator : 'TProp -> 'TProp -> bool) message (collection : 'TItem[]) =
  collection
  |> Array.fold (fun previous item -> sortChecker previous item selector comparator message) (selector collection.[0])
  |> ignore

people |> shouldBeSorted byAge ascending Message.Default
people |> shouldBeSorted (fun p -> p.age) (fun age1 age2 -> age1 <= age2) (Message.Custom "omg why")

// let rec whatever accum (selector : 'TItem -> 'TProp) (comparator : 'TProp -> 'TProp -> bool) (collection : List<'TItem'>) =
//   let prop = selector collection.Head
//   let compare = comparator accum prop
//   if compare = false then failwith <| sprintf "collection is not sorted (item1: %O, item2: %O)" accum prop
//   whatever prop selector comparator collection.Tail
  
// let shouldBeSorted' (selector : 'TItem -> 'TProp) (comparator : 'TProp -> 'TProp -> bool) (collection : List<'TItem'>) =
//   whatever collection.Tail selector comparator collection.Head
  
// people |> shouldBeSorted' (fun p -> p.age) (fun age1 age2 -> age1 <= age2)

// let ints = [| 1; 2; 3 |]
// ints |> shouldBeSorted (fun i -> i) (fun item1 item2 -> item1 <= item2)