using UnityEngine;
using TMPro;
using DG.Tweening;
using Ashwild.Player;

namespace Ashwild.UI
{
    /// <summary>
    /// Full-screen loading overlay shown while a session starts and the game scene loads over the
    /// network. It is deliberately NOT a UIPanel: panels live on a per-scene UIManager and are
    /// destroyed when their scene unloads, but FishNet loads the game scene with ReplaceOption.All —
    /// so the menu (and anything on it) is torn down mid-transition. This controller therefore marks
    /// itself DontDestroyOnLoad and survives the swap, covering the screen continuously from the save
    /// click until the local player has spawned. It hides the rotating menu camera and the scene
    /// switch behind a quote-cycling curtain.
    ///
    /// Place it on its own high-sorting-order Canvas in the menu scene (mirror SplashScreenController).
    /// It is driven entirely by the PlayerEvents bus: SessionStarting/SessionJoining raise it for the
    /// menu→game transition (lowered by LocalPlayerSpawned), and ReturningToMenu raises it for the
    /// game→menu transition (lowered by MenuReady once the menu has loaded). SessionError lowers it as
    /// a safety net so a failed host never leaves the player stuck behind the curtain; SessionStopped
    /// does the same except while a return-to-menu is in flight, where that teardown event is expected.
    /// </summary>
    [DisallowMultipleComponent]
    [RequireComponent(typeof(CanvasGroup))]
    public class LoadingScreen : MonoBehaviour
    {
        #region Serialized Fields

        [Header("References")]
        [Tooltip("Label that displays the current quote (and its author on a second line).")]
        [SerializeField] private TextMeshProUGUI quoteLabel;

        [Tooltip("Pool of quotes to cycle through. Assign a Loading Quotes asset.")]
        [SerializeField] private LoadingQuotes quotes;

        [Header("Curtain Fade")]
        [SerializeField] private float fadeInDuration = 0.35f;
        [SerializeField] private float fadeOutDuration = 0.5f;
        [SerializeField] private Ease fadeInEase = Ease.OutQuad;
        [SerializeField] private Ease fadeOutEase = Ease.InQuad;

        [Tooltip("Minimum time the curtain stays up once raised, so an instant load doesn't flash.")]
        [SerializeField] private float minimumDisplayTime = 1.5f;

        [Tooltip("Extra time the curtain holds after the ready signal (player spawned / menu loaded) " +
                 "before fading out, so the scene's first heavy frames (object pop-in, shader warmup) " +
                 "settle behind it instead of stuttering on screen. Stacks as the max with the " +
                 "remaining minimum display time.")]
        [SerializeField] private float settleDelay = 0.75f;

        [Header("Quote Cycling")]
        [Tooltip("How long each quote stays on screen before swapping to the next.")]
        [SerializeField] private float quoteDuration = 4f;
        [Tooltip("Cross-fade duration when swapping one quote for the next.")]
        [SerializeField] private float quoteFadeDuration = 0.4f;

        #endregion

        #region State

        /// <summary>
        /// Single persistent instance — a second copy arriving with a reloaded menu scene self-destructs.
        /// </summary>
        private static LoadingScreen instance;

        private CanvasGroup canvasGroup;

        /// <summary>
        /// True while the curtain is up (or being raised). Guards against double-show / double-hide.
        /// </summary>
        private bool isShown;

        /// <summary>
        /// Unscaled timestamp at which the curtain was raised, used to enforce the minimum display time.
        /// </summary>
        private float shownAt;

        /// <summary>
        /// True while the curtain is covering a return-to-menu transition. SessionStopped fires during
        /// that teardown, so this flag tells the curtain to ignore it and wait for MenuReady instead —
        /// otherwise the curtain would drop the instant the session stopped, before the menu has loaded.
        /// </summary>
        private bool awaitingMenu;

        /// <summary>
        /// Index of the quote currently displayed, so the next pick can avoid repeating it.
        /// </summary>
        private int currentQuoteIndex = -1;

        private Tween curtainTween;
        private Sequence quoteSequence;

        #endregion

        #region Unity Lifecycle

        /// <summary>
        /// Enforces the singleton, persists across the menu→game scene swap, and starts hidden.
        ///
        /// Detaches to a root object before <see cref="Object.DontDestroyOnLoad"/>: that call is a
        /// no-op on a child, so a nested curtain would be destroyed the moment FishNet unloads the menu
        /// (ReplaceOption.All) — leaving the load uncovered and, later, no curtain at all to raise on
        /// the return to menu. Promoting it here keeps the scene authoring free to nest it under a
        /// layout object while still guaranteeing it survives every scene swap.
        /// </summary>
        private void Awake()
        {
            if (instance != null && instance != this)
            {
                Destroy(gameObject);
                return;
            }
            instance = this;
            transform.SetParent(null, false);
            DontDestroyOnLoad(gameObject);

            canvasGroup = GetComponent<CanvasGroup>();
            canvasGroup.alpha = 0f;
            canvasGroup.blocksRaycasts = false;
            canvasGroup.interactable = false;
        }

        /// <summary>
        /// Subscribes to the session lifecycle events that raise and lower the curtain.
        /// </summary>
        private void OnEnable()
        {
            PlayerEvents.SessionStarting += HandleSessionBeginning;
            PlayerEvents.SessionJoining += HandleSessionJoining;
            PlayerEvents.LocalPlayerSpawned += HandleLocalPlayerSpawned;
            PlayerEvents.ReturningToMenu += HandleReturningToMenu;
            PlayerEvents.MenuReady += HandleMenuReady;
            PlayerEvents.SessionError += HandleSessionError;
            PlayerEvents.SessionStopped += HandleSessionStopped;
        }

        /// <summary>
        /// Unsubscribes — mirrors OnEnable exactly.
        /// </summary>
        private void OnDisable()
        {
            PlayerEvents.SessionStarting -= HandleSessionBeginning;
            PlayerEvents.SessionJoining -= HandleSessionJoining;
            PlayerEvents.LocalPlayerSpawned -= HandleLocalPlayerSpawned;
            PlayerEvents.ReturningToMenu -= HandleReturningToMenu;
            PlayerEvents.MenuReady -= HandleMenuReady;
            PlayerEvents.SessionError -= HandleSessionError;
            PlayerEvents.SessionStopped -= HandleSessionStopped;
        }

        /// <summary>
        /// Kills any running tweens so nothing animates a destroyed target on teardown.
        /// </summary>
        private void OnDestroy()
        {
            curtainTween?.Kill();
            quoteSequence?.Kill();
            if (instance == this) instance = null;
        }

        #endregion

        #region Event Handlers

        /// <summary>
        /// Raises the curtain when the local player starts hosting a session.
        /// </summary>
        private void HandleSessionBeginning()
        {
            awaitingMenu = false;
            Show();
        }

        /// <summary>
        /// Raises the curtain when the local player begins joining a remote session.
        /// </summary>
        private void HandleSessionJoining(string code)
        {
            awaitingMenu = false;
            Show();
        }

        /// <summary>
        /// Raises the curtain over a return-to-menu transition and arms the wait for MenuReady, so the
        /// upcoming SessionStopped (part of the teardown) does not drop it prematurely.
        /// </summary>
        private void HandleReturningToMenu()
        {
            awaitingMenu = true;
            Show();
        }

        /// <summary>
        /// Lowers the curtain once the local player has spawned into the loaded game scene.
        /// </summary>
        private void HandleLocalPlayerSpawned() => Hide();

        /// <summary>
        /// Lowers the curtain once the menu scene has finished loading on a return-to-menu transition.
        /// </summary>
        private void HandleMenuReady()
        {
            awaitingMenu = false;
            Hide();
        }

        /// <summary>
        /// Safety net: a connection failure must drop the curtain so the menu becomes usable again.
        /// </summary>
        private void HandleSessionError(string reason)
        {
            awaitingMenu = false;
            Hide();
        }

        /// <summary>
        /// Safety net for a session that tears down before a player spawns. Skipped while returning to
        /// the menu, where SessionStopped is expected and the curtain must stay up until MenuReady.
        /// </summary>
        private void HandleSessionStopped()
        {
            if (awaitingMenu) return;
            Hide();
        }

        #endregion

        #region Curtain

        /// <summary>
        /// Fades the curtain in (blocking input underneath) and starts cycling quotes. Ignored when
        /// already shown so re-entrant session events don't restart the animation.
        ///
        /// Raises <see cref="PlayerEvents.LoadingCurtainShown"/> only once the fade-in has fully
        /// completed: NetworkSessionManager waits for that signal before kicking off the heavy game
        /// scene load, so the unavoidable activation freeze always happens behind an already-opaque
        /// curtain instead of stalling the very frame the curtain was meant to appear on. Killing the
        /// tween early (an instant Hide) suppresses the signal, which is the intended behaviour.
        /// </summary>
        private void Show()
        {
            if (isShown) return;
            isShown = true;
            shownAt = Time.unscaledTime;

            curtainTween?.Kill();
            canvasGroup.blocksRaycasts = true;
            canvasGroup.interactable = true;

            curtainTween = canvasGroup.DOFade(1f, fadeInDuration)
                .SetEase(fadeInEase)
                .SetUpdate(true)
                .OnComplete(PlayerEvents.RaiseLoadingCurtainShown);

            ShowNextQuote(instant: true);
            StartQuoteCycle();
        }

        /// <summary>
        /// Fades the curtain out and stops the quote cycle. The fade is delayed by the larger of the
        /// remaining minimum display time (so an instant load still shows the curtain for a readable
        /// beat instead of flashing) and the settle delay (so the scene's first heavy frames after the
        /// ready signal happen behind the curtain rather than stuttering on screen).
        /// </summary>
        private void Hide()
        {
            if (!isShown) return;
            isShown = false;

            float elapsed = Time.unscaledTime - shownAt;
            float delay = Mathf.Max(settleDelay, minimumDisplayTime - elapsed);

            curtainTween?.Kill();
            curtainTween = canvasGroup.DOFade(0f, fadeOutDuration)
                .SetDelay(delay)
                .SetEase(fadeOutEase)
                .SetUpdate(true)
                .OnComplete(() =>
                {
                    canvasGroup.blocksRaycasts = false;
                    canvasGroup.interactable = false;
                    StopQuoteCycle();
                });
        }

        #endregion

        #region Quotes

        /// <summary>
        /// Builds the looping cross-fade that swaps the quote every <see cref="quoteDuration"/> seconds.
        /// Runs on unscaled time so it keeps animating even while the load freezes the timescale.
        ///
        /// Bails out (leaving the first quote shown statically) when there is nothing to cycle or when
        /// <see cref="quoteDuration"/> is not positive: a looping DOTween sequence with a zero total
        /// duration replays infinitely within a single frame and hard-freezes the editor, so the
        /// positive-duration guard here is mandatory, not cosmetic.
        /// </summary>
        private void StartQuoteCycle()
        {
            StopQuoteCycle();
            if (quotes == null || quotes.Count <= 1 || quoteLabel == null) return;
            if (quoteDuration <= 0f) return;

            float fade = Mathf.Max(0f, quoteFadeDuration);

            quoteSequence = DOTween.Sequence().SetUpdate(true);
            quoteSequence.AppendInterval(quoteDuration);
            quoteSequence.Append(quoteLabel.DOFade(0f, fade));
            quoteSequence.AppendCallback(() => ShowNextQuote(instant: false));
            quoteSequence.Append(quoteLabel.DOFade(1f, fade));
            quoteSequence.SetLoops(-1);
        }

        /// <summary>
        /// Kills the running quote cycle, if any.
        /// </summary>
        private void StopQuoteCycle()
        {
            quoteSequence?.Kill();
            quoteSequence = null;
        }

        /// <summary>
        /// Picks the next random quote and writes it to the label. When <paramref name="instant"/> is
        /// true the label is forced fully opaque (used on the very first quote, before the cross-fade
        /// loop takes over); otherwise the surrounding sequence owns the alpha.
        /// </summary>
        private void ShowNextQuote(bool instant)
        {
            if (quotes == null || !quotes.HasQuotes || quoteLabel == null) return;

            LoadingQuotes.Quote quote = quotes.GetRandom(currentQuoteIndex, out currentQuoteIndex);
            quoteLabel.text = Format(quote);

            if (instant)
            {
                Color c = quoteLabel.color;
                c.a = 1f;
                quoteLabel.color = c;
            }
        }

        /// <summary>
        /// Composes the displayed string: the quote, plus an em-dashed author line when one is set.
        /// </summary>
        private static string Format(LoadingQuotes.Quote quote)
        {
            return string.IsNullOrWhiteSpace(quote.author)
                ? quote.text
                : $"{quote.text}\n<size=80%>— {quote.author}</size>";
        }

        #endregion
    }
}