Babushka/scripts/CSharp/Common/Fight/FightHappening.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.ExceptionServices;
using System.Threading.Tasks;
using Babushka.scripts.CSharp.Common.Util;
using Godot;

namespace Babushka.scripts.CSharp.Common.Fight;

public partial class FightHappening : Node
{
    /*
    To get a visual overview of the FightHappening state machine, refer to the graph on miro:
    https://miro.com/app/board/uXjVK8YEprM=/?moveToWidget=3458764640805655262&cot=14
    */

    #region Internal Types

    public enum FightState
    {
        None,
        FightStartAnim,
        FightersEnter,
        FightersEnterAnim,
        NextFighter,
        StateCheck,
        InputActionSelect,
        ActionCheckDetails,
        InputActionDetail,
        ActionExecute,
        ActionAnim,
        EnemyActionSelect,
        PlayerWin,
        EnemyWin,
    }

    public class FightersEnterStaging
    {
        public required List<FightWorld.Fighter> enteringAllyFighters;
        public required List<FightWorld.Fighter> enteringEnemyFighters;

        public bool HasAnyToExecute()
        {
            return enteringAllyFighters.Any() || enteringEnemyFighters.Any();
        }
    }

    #endregion

    #region Settings

    private const float StartAnimationTime = 1;
    private const float FightersEnterAnimationTime = 1;

    #endregion

    #region Shortcuts

    private static FightWorld.FightHappeningData HappeningData =>
        FightWorld.Instance.fightHappeningData ?? throw new NoFightHappeningException();

    private static FightWorld.Fighter CurrentFighter => HappeningData.fighterTurn.Current;

    #endregion

    #region Events

    [Signal]
    public delegate void SignalTransitionFromStateEventHandler(FightState state);

    [Signal]
    public delegate void SignalTransitionStateEventHandler(FightState from, FightState to);

    [Signal]
    public delegate void SignalTransitionToStateEventHandler(FightState state);

    #endregion

    #region Singleton

    public static FightHappening Instance = null!;

    private void SetupInstance()
    {
        Instance = this;
    }

    #endregion

    public override void _Ready()
    {
        SetupInstance();
        StartFight();
    }

    #region Public Methods

    public void StartFight()
    {
        RequireState(FightState.None);
        ChangeState(FightState.FightStartAnim);
    }

    public void ActionSelect(FighterAction action)
    {
        RequireState(FightState.InputActionSelect);
        HappeningData.actionStaging = action;
        action.Reset();
        ChangeState(FightState.ActionCheckDetails);
    }

    public void DetailFilled()
    {
        RequireState(FightState.InputActionDetail);
        ChangeState(FightState.ActionCheckDetails);
    }

    #endregion

    #region State Machine

    private bool _inTransition = false;
    private FightState? _changeToAfterTransition = null;

    private void ChangeState(FightState nextState)
    {
        _changeToAfterTransition = null;
        if (_inTransition)
        {
            _changeToAfterTransition = nextState;
            return;
        }

        _inTransition = true;
        TransitionFromState();
        var lastState = HappeningData.fightState;
        HappeningData.fightState = nextState;
        TransitionToState(nextState);

        EmitSignalSignalTransitionFromState(lastState);
        EmitSignalSignalTransitionState(lastState, nextState);
        EmitSignalSignalTransitionToState(nextState);
        _inTransition = false;

        if (_changeToAfterTransition.HasValue)
        {
            ChangeState(_changeToAfterTransition.Value);
        }
    }

    private void TransitionFromState()
    {
        // fixed behaviour
        switch (HappeningData.fightState)
        {
            default: break;
        }
    }

    private void TransitionToState(FightState nextState)
    {
        // fixed behaviour
        switch (HappeningData.fightState)
        {
            case FightState.FightStartAnim:
                AdvanceToStateInSeconds(FightState.FightersEnter, StartAnimationTime);
                break;
            case FightState.FightersEnter:
                HappeningData.fightersEnterStaging = StageFightersEnter();
                if (HappeningData.fightersEnterStaging.HasAnyToExecute())
                {
                    ExecuteFightersEnter();
                    ChangeState(FightState.FightersEnterAnim);
                }
                else
                {
                    ChangeState(FightState.NextFighter);
                }

                break;
            case FightState.FightersEnterAnim:
                AdvanceToStateInSeconds(FightState.NextFighter, FightersEnterAnimationTime);
                break;
            case FightState.NextFighter:
                ExecuteNextFighter();
                ChangeState(FightState.StateCheck);
                break;
            case FightState.StateCheck:
                // restest action staging and fighter enter staging
                HappeningData.actionStaging = null;
                HappeningData.fightersEnterStaging = null;

                if (!FightWorld.Instance.allyFighters.IsAlive())
                {
                    ChangeState(FightState.EnemyWin);
                }
                else if (HappeningData.enemyGroup.AreAllDead())
                {
                    ChangeState(FightState.PlayerWin);
                }
                else if (CurrentFighter.actionPointsLeft <= 0)
                {
                    ChangeState(FightState.FightersEnter);
                }
                else if (CurrentFighter.IsInFormation(HappeningData.enemyFighterFormation))
                {
                    ChangeState(FightState.EnemyActionSelect);
                }
                else
                {
                    ChangeState(FightState.InputActionSelect);
                }

                break;
            case FightState.InputActionSelect:
                // wait for player input
                break;
            case FightState.ActionCheckDetails:
                RequireNotNull(HappeningData.actionStaging);

                if (ActionAbort())
                    ChangeState(FightState.InputActionSelect);
                else if (ActionNeededDetail())
                    ChangeState(FightState.InputActionDetail);
                else
                    ChangeState(FightState.ActionExecute);
                break;
            case FightState.InputActionDetail:
                // wait for player input
                break;
            case FightState.EnemyActionSelect:
                HappeningData.actionStaging = CurrentFighter.AutoSelectAction();
                ChangeState(FightState.ActionExecute);
                break;
            case FightState.ActionExecute:
                ExecuteAction();
                ChangeState(FightState.ActionAnim);
                break;
            case FightState.ActionAnim:
                var actionTime = GetActionAnimationEnd();
                if (actionTime.IsType<float>())
                {
                    AdvanceToStateInSeconds(FightState.StateCheck, actionTime);
                }
                else
                {
                    _ = AdvanceToStateWhenDone(FightState.StateCheck, actionTime);
                }

                break;
            case FightState.EnemyWin:
                // TODO: remove and find proper solution
                ReviveVesna();
                break;
            default: break;
        }
    }

    #endregion

    #region Game Logic

    private FightersEnterStaging StageFightersEnter()
    {
        // ally
        var enteringAllyFighters = new List<FightWorld.Fighter>();
        var allyFighters = FightWorld.Instance.allyFighters;
        if (!allyFighters.vesnaFighter.IsInFormation(HappeningData.allyFighterFormation))
        {
            enteringAllyFighters.Add(allyFighters.vesnaFighter);
        }

        // enemy
        const int totalEnemySpace = 3;
        var enemySpaceLeft = HappeningData.enemyFighterFormation.GetEmptySlotCount();

        return new FightersEnterStaging
        {
            enteringAllyFighters = enteringAllyFighters,
            enteringEnemyFighters = HappeningData.enemyGroup.fighters
                .WhereIsAlive()
                .WhereIsNotInFormation(HappeningData.enemyFighterFormation)
                .Take(enemySpaceLeft)
                .ToList()
        };
    }

    private void ExecuteFightersEnter()
    {
        Debug.Assert(HappeningData.fightersEnterStaging != null);
        foreach (var fighter in HappeningData.fightersEnterStaging.enteringAllyFighters)
        {
            var emptySlotIndex = HappeningData.allyFighterFormation.GetFirstEmptySlot();
            if (emptySlotIndex < 0) throw new Exception("No empty slot for ally fighter to enter");
            HappeningData.allyFighterFormation.SetFighterAtPosition(emptySlotIndex, fighter);
            HappeningData.fighterTurn.AddAsLast(fighter);
        }

        foreach (var fighter in HappeningData.fightersEnterStaging.enteringEnemyFighters)
        {
            var emptySlotIndex = HappeningData.enemyFighterFormation.GetFirstEmptySlot();
            if (emptySlotIndex < 0) throw new Exception("No empty slot for enemy fighter to enter");
            HappeningData.enemyFighterFormation.SetFighterAtPosition(emptySlotIndex, fighter);
            HappeningData.fighterTurn.AddAsLast(fighter);
        }
    }

    private void ExecuteNextFighter()
    {
        HappeningData.fighterTurn.Next();
        CurrentFighter.actionPointsLeft = FightWorld.Fighter.MaxActionPoints;
    }

    private void ExecuteAction()
    {
        Debug.Assert(HappeningData.actionStaging != null);
        HappeningData.actionStaging.ExecuteAction();
        CurrentFighter.actionPointsLeft -= HappeningData.actionStaging.GetActionPointCost();
    }

    private Variant<float, Func<bool>> GetActionAnimationEnd()
    {
        Debug.Assert(HappeningData.actionStaging != null);
        return HappeningData.actionStaging.GetAnimationEnd();
    }

    private bool ActionAbort()
    {
        Debug.Assert(HappeningData.actionStaging != null);
        return HappeningData.actionStaging.MarkedForAbort();
    }

    private bool ActionNeededDetail()
    {
        Debug.Assert(HappeningData.actionStaging != null);
        return HappeningData.actionStaging.NextDetail();
    }

    // TODO: remove
    private void ReviveVesna()
    {
        var vesnaFighter = FightWorld.Instance.allyFighters.vesnaFighter;
        vesnaFighter.health = vesnaFighter.maxHealth;
        GD.Print("Vesna has been revived. This is for the current prototype only");
    }

    #endregion // Game Logic

    #region Utility

    private void RequireState(params FightState[] states)
    {
        if (states.Contains(HappeningData.fightState))
            return;

        throw new Exception(
            $"Can not call this Method while in state {HappeningData.fightState}. Only available in {string.Join(" ,", states)}");
    }

    private void RequireNotNull(Object? o)
    {
        if (o != null)
            return;

        throw new Exception("Object must not be null to call this method");
    }

    private void AdvanceToStateInSeconds(FightState nextState, float seconds)
    {
        FightWorld.Instance.GetTree().CreateTimer(seconds).Timeout += () => ChangeState(nextState);
    }

    private async Task AdvanceToStateWhenDone(FightState nextState, Func<bool> isDone)
    {
        while (!isDone())
        {
            await FightWorld.Instance.ToSignal(FightWorld.Instance.GetTree(), SceneTree.SignalName.ProcessFrame);
        }

        ChangeState(nextState);
    }

    #endregion
}