(*
Copyright (C) 2023  Florian Brinkmeyer

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.
*)

namespace GameFramework

open System

type NegaMax (player : int, searchDepth : int) =
    interface AI_Agent with
        member x.Player = player
        member x.MakeMove mutableGame game =
            let makeMove =
                async {
                    let state = game :?> ImmutableGame
                    let rec helper step (state : ImmutableGame) =
                        let numberOfPossibleMoves = state.NumberOfPossibleMoves
                        if (step = 0) || (numberOfPossibleMoves = 0)  then
                            state.ZSValue
                        else 
                            [0..(numberOfPossibleMoves-1)] |> List.map (fun move -> -(helper (step-1) (state.NthMove move))) |> List.max
                    let chosenMove = [0..(state.NumberOfPossibleMoves-1)] |> List.maxBy (fun move -> -(helper (searchDepth-1) (state.NthMove move)))
                    mutableGame.MakeMove chosenMove
                }
            makeMove |> Async.Start