(* Tennis Kata in OCaml! *)

type player = PlayerOne | PlayerTwo


type point = Love | Fifteen | Thirty


type score =
  | Points of point * point
  | Forty of player * point
  | Duece
  | Advantage of player
  | GameOver of player


let is_player_one p =
  p = PlayerOne


let new_game =
  Points(Love, Love)


let transition_to_forty score player =
  match score with
    | Points (p1_point, p2_point) ->
      if is_player_one player then Forty(PlayerOne, p2_point)
      else Forty(PlayerTwo, p1_point)

    | _ -> score (* You can only goto Forty from Points *)


let transition_to_duece score player =
  match score with
    | Forty (player_w_forty, other_point) ->
      if player_w_forty <> player then Duece else score

    | Advantage (player_w_adv) ->
      Duece

    | _ -> score (* You can only goto Duece from Forty *)


let transition_to_advantage score player =
  match score with
    | Duece -> Advantage(player)
    | _ -> score (* You can only goto Advantage from Deuce *)


let transition_to_gameover score player =
  match score with
    | Advantage (player_w_adv) ->
      if player_w_adv = player then GameOver(player) else score

    | Forty (player_w_forty, other_point) ->
      if player_w_forty = player then GameOver(player) else score

    | _ -> score (* You can only goto GameOver from Advantage & Forty *)


let next_score_from_points point other_point player score =
  match point with
  | Love -> Points(Fifteen, other_point)
  | Fifteen -> Points(Thirty, other_point)
  | Thirty -> transition_to_forty score player


let next_score_from_forty player_w_forty point score player =
  match point with
  | Love -> Forty(player_w_forty, Fifteen)
  | Fifteen -> Forty(player_w_forty, Thirty)
  | Thirty -> transition_to_duece score player


let player_scored score player =
  match score with
    | Points (p1, p2) ->
      if is_player_one player then next_score_from_points p1 p2 player score
      else next_score_from_points p2 p1 player score

    | Forty (player_w_forty, other_point) ->
      if player_w_forty = player then transition_to_gameover score player
      else next_score_from_forty player_w_forty other_point score player

    | Duece -> transition_to_advantage score player

    | Advantage (player_w_adv) ->
      if player_w_adv = player then transition_to_gameover score player
      else transition_to_duece score player

    | GameOver (winner) -> GameOver (winner) (* Still the winner *)


(* Output as string helpers *)

let player_to_str = function
  | PlayerOne -> "Player 1"
  | PlayerTwo -> "Player 2"


let point_to_str = function
  | Love -> "love"
  | Fifteen -> "15"
  | Thirty -> "30"


let score_line p1 p2 =
  "Player 1: " ^ p1 ^ " Player 2: " ^ p2


let score_to_str = function
  | Points (p_one, p_two) ->
    score_line (point_to_str p_one) (point_to_str p_two)

  | Forty (player_w_forty, other) ->
    if is_player_one player_w_forty then score_line "40" (point_to_str other)
    else score_line (point_to_str other) "40"

  | Duece ->
    "At duece"

  | Advantage (player) ->
    "Advantage " ^ player_to_str player

  | GameOver (player) ->
    "Game over! " ^ player_to_str player ^ " has won."


(* "Test" scenarios *)
let scenario_one_player1_kills start_game =
  let score_1 = player_scored new_game PlayerOne in
  let score_2 = player_scored score_1 PlayerOne in
  let score_3 = player_scored score_2 PlayerOne in
  let score_4 = player_scored score_3 PlayerOne in
    "START\n" ^
    (score_to_str start_game) ^ "\n" ^
    (score_to_str score_1) ^ "\n" ^
    (score_to_str score_2) ^ "\n" ^
    (score_to_str score_3) ^ "\n" ^
    (score_to_str score_4) ^ "\n" ^
    "END"

let scenario_two_good_game start_game =
  let score_1 = player_scored new_game PlayerOne in
  let score_2 = player_scored score_1 PlayerOne in
  let score_3 = player_scored score_2 PlayerOne in
  let score_4 = player_scored score_3 PlayerTwo in
  let score_5 = player_scored score_4 PlayerTwo in
  let score_6 = player_scored score_5 PlayerTwo in
  let score_7 = player_scored score_6 PlayerTwo in
  let score_8 = player_scored score_7 PlayerOne in
  let score_9 = player_scored score_8 PlayerOne in
  let score_10 = player_scored score_9 PlayerOne in
      "START (scenario_two_good_game)\n" ^
      (score_to_str start_game) ^ "\n" ^
      (score_to_str score_1) ^ "\n" ^
      (score_to_str score_2) ^ "\n" ^
      (score_to_str score_3) ^ "\n" ^
      (score_to_str score_4) ^ "\n" ^
      (score_to_str score_5) ^ "\n" ^
      (score_to_str score_6) ^ "\n" ^
      (score_to_str score_7) ^ "\n" ^
      (score_to_str score_8) ^ "\n" ^
      (score_to_str score_9) ^ "\n" ^
      (score_to_str score_10) ^ "\n" ^
      "END"

let () =
  print_endline (scenario_one_player1_kills new_game)

let () =
  print_endline (scenario_two_good_game new_game)

(*
  DEBUGGIN'
  print_endline (score_to_str (Points(Love, Love)));;

  print_endline (score_to_str (Points(Love, Fifteen)));;

  print_endline (score_to_str (Forty(PlayerOne, Fifteen)));;

  print_endline (score_to_str (Forty(PlayerTwo, Thirty)));;

  print_endline (score_to_str (Advantage(PlayerTwo)));;

  print_endline (score_to_str (Advantage(PlayerOne)));;

  print_endline (score_to_str (GameOver(PlayerOne)));;

  print_endline (score_to_str (transition_to_forty (Points(Love, Fifteen)) PlayerOne));;

  print_endline (score_to_str (transition_to_forty (Points(Love, Fifteen)) PlayerTwo));;

  print_endline (score_to_str (transition_to_duece (Forty(PlayerOne, Fifteen))));;

  print_endline (score_to_str (transition_to_advantage (Duece) PlayerOne));;

  print_endline (score_to_str (transition_to_advantage (Duece) PlayerTwo));;

  print_endline (score_to_str (transition_to_gameover (Advantage(PlayerTwo)) PlayerTwo));;

  print_endline (score_to_str (transition_to_gameover (Advantage(PlayerOne)) PlayerTwo));;

  print_endline (score_to_str (transition_to_gameover (Forty(PlayerTwo, Love)) PlayerTwo));;

  print_endline (score_to_str (transition_to_gameover (Forty(PlayerOne, Fifteen)) PlayerTwo));;
*)