using System;
using System.Collections.Generic;

namespace ProjectI.Enemies
{
    // Shared frame cap; queued FIFO grants are reserved before repeat requests use spare capacity.
    public sealed class EnemyQueryBudget
    {
        private readonly LinkedList<ulong> waiting = new LinkedList<ulong>();
        private readonly HashSet<ulong> queued = new HashSet<ulong>(), grants = new HashSet<ulong>();
        private readonly Dictionary<ulong, double> enqueuedAt = new Dictionary<ulong, double>();
        private readonly Dictionary<ulong, int> lastRequested = new Dictionary<ulong, int>();
        private readonly List<ulong> abandoned = new List<ulong>();
        private int frame = -1;
        public int QueriesPerFrame { get; }
        public int UsedThisFrame { get; private set; }
        public int WaitingCount => waiting.Count;
#if UNITY_EDITOR || DEVELOPMENT_BUILD
        public int InspectionPendingCount => enqueuedAt.Count;
        public double MaximumServicedAge { get; private set; }
#endif
        public EnemyQueryBudget(int queriesPerFrame = 8)
        {
            if (queriesPerFrame < 0 || queriesPerFrame > 32) throw new ArgumentOutOfRangeException(nameof(queriesPerFrame));
            QueriesPerFrame = queriesPerFrame;
        }
        public bool TrySpend(ulong request, int currentFrame, double now)
        {
            if (request == 0 || currentFrame < 0 || !EnemyObservationRules.Finite(now) || now < 0) return false;
            if (currentFrame != frame)
            {
                abandoned.Clear();
                foreach (var pair in lastRequested) if (currentFrame - pair.Value > 2) abandoned.Add(pair.Key);
                foreach (ulong stale in abandoned) Cancel(stale);
                // Unused grants retain their old FIFO priority; no valid but inactive head can block a frame.
                foreach (ulong previous in grants) { waiting.AddFirst(previous); queued.Add(previous); }
                grants.Clear(); frame = currentFrame; UsedThisFrame = 0;
                GrantWaiting();
            }
            if (!grants.Contains(request) && !queued.Contains(request))
            {
                if (enqueuedAt.Count >= 64) return false;
                waiting.AddLast(request); queued.Add(request); enqueuedAt[request] = now;
            }
            lastRequested[request] = currentFrame;
            GrantWaiting();
            if (!grants.Remove(request)) return false;
            UsedThisFrame++;
#if UNITY_EDITOR || DEVELOPMENT_BUILD
            MaximumServicedAge = Math.Max(MaximumServicedAge, now - enqueuedAt[request]);
#endif
            enqueuedAt.Remove(request); lastRequested.Remove(request); return true;
        }
        private void GrantWaiting()
        {
            while (waiting.Count > 0 && grants.Count + UsedThisFrame < QueriesPerFrame)
            {
                ulong request = waiting.First.Value; waiting.RemoveFirst(); queued.Remove(request); grants.Add(request);
            }
        }
        public void Cancel(ulong request)
        {
            waiting.Remove(request); queued.Remove(request); grants.Remove(request); enqueuedAt.Remove(request); lastRequested.Remove(request);
        }
    }
}