using System;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;

namespace MazeGen
{
    /// <summary>
    /// Drives one agent's autonomous exploration: waits out a (randomized) initial delay so
    /// many agents don't all decide in lockstep, then ticks a steady decision interval -
    /// each time it fires, picks an exit and asks the MazeAgentController to use it. Stops
    /// deciding once the agent reaches an exit room or the level has ended.
    ///
    /// Agents can "peek" into adjacent rooms before entering to see if there are monsters.
    /// Based on the perceived threat level, they may choose to retreat rather than fight.
    /// </summary>
    public class AutonomousAgentBrain : MonoBehaviour
    {
        private MazeAgentController _controller;
        private MazeGenerator _generator;
        private float _decisionInterval;
        private float _exploreChance;
        private float _retreatThreshold = 1.5f;     // CR above this = retreat (configurable)
        private Func<bool> _isLevelEnded;

        private float _timer;
        private Dictionary<int, int> _peekCount = new Dictionary<int, int>(); // Track how many times agent peeked at a room

        public void Initialize(MazeAgentController controller, MazeGenerator generator, float initialDelay, float decisionInterval, float exploreChance, float retreatThreshold, Func<bool> isLevelEnded)
        {
            _controller = controller;
            _generator = generator;
            _decisionInterval = Mathf.Max(0.05f, decisionInterval);
            _exploreChance = Mathf.Clamp01(exploreChance);
            _retreatThreshold = Mathf.Max(0, retreatThreshold);
            _isLevelEnded = isLevelEnded;
            _timer = Mathf.Max(0f, initialDelay);
        }

        private void Update()
        {
            if (_controller?.Agent == null || _controller.Agent.IsFinished || _controller.Agent.IsDead) return;
            if (_isLevelEnded != null && _isLevelEnded()) return;

            _timer -= Time.deltaTime;
            if (_timer > 0f) return;
            _timer = _decisionInterval;

            Exit choice = ChooseExit(_controller.Agent, _controller.Agent.CurrentRoom);
            if (choice != null)
                _controller.TryUseExit(choice);
        }

        /// <summary>
        /// Picks the next exit to take. Strongly prefers an unused exit (fresh, unexplored
        /// territory); failing that, prefers a used exit into a room this agent personally
        /// hasn't visited yet (following where another agent has already been); only
        /// backtracks into a room it's already visited as a last resort. `exploreChance`
        /// adds some randomness so a "follow" opportunity is occasionally taken even when
        /// exploring is available, rather than being 100% deterministic.
        ///
        /// A few anti-stuck rules keep this from looping forever around a small ring of
        /// already-explored rooms (e.g. a square formed by a loop-closing connection):
        /// - The door leading straight back to the room the agent just came from is excluded
        ///   from consideration unless it's the only door available at all, so agents don't
        ///   ping-pong between two rooms.
        /// - When forced to backtrack, exits that "peek" into a room with its own unexplored
        ///   option beyond it (an unused exit, or one leading somewhere this agent hasn't
        ///   personally seen) are preferred over ones that only lead deeper into fully-picked-
        ///   over territory - this steers the agent back out of a dead loop instead of just
        ///   circling it.
        /// - Ties are broken toward whichever room this agent has personally visited the
        ///   fewest times, so a small loop gets cycled through rather than bounced around.
        ///
        /// Also evaluates monster threats in adjacent rooms - if a room looks too dangerous,
        /// the agent will retreat (choose a different exit) if possible.
        /// </summary>
        private Exit ChooseExit(MazeAgent agent, Room room)
        {
            Exit reverseExit = FindReverseExit(agent, room);

            var explore = new List<Exit>();
            var follow = new List<Exit>();
            var backtrack = new List<Exit>();

            foreach (var exit in room.Exits)
            {
                if (exit == reverseExit) continue;
                if (exit.IsBlocked) continue; // Skip exits that are permanently unusable

                if (!exit.IsUsed)
                {
                    explore.Add(exit);
                    continue;
                }

                bool leadsToVisited = exit.ConnectedRoomId.HasValue && agent.HasVisited(exit.ConnectedRoomId.Value);
                (leadsToVisited ? backtrack : follow).Add(exit);
            }

            // Filter exits by threat level - remove dangerous ones if safer options exist
            explore = FilterByThreat(explore, agent);
            follow = FilterByThreat(follow, agent);
            backtrack = FilterByThreat(backtrack, agent);

            if (explore.Count > 0 && UnityEngine.Random.value < _exploreChance)
                return RandomPick(explore);

            if (follow.Count > 0)
                return LeastVisitedPick(agent, follow);

            if (explore.Count > 0)
                return RandomPick(explore);

            if (backtrack.Count > 0)
                return ChooseBacktrack(agent, backtrack);

            // Excluding the reverse door left nothing - it's genuinely the only way out
            // (e.g. a single-exit dead end), so take it (even if dangerous).
            return reverseExit;
        }

        /// <summary>The door in `room` that leads straight back to wherever the agent's last move came from, if any.</summary>
        private static Exit FindReverseExit(MazeAgent agent, Room room)
        {
            int? reverseExitId = agent.LastUsedExit?.ConnectedExitId;
            if (!reverseExitId.HasValue) return null;
            return room.Exits.Find(e => e.Id == reverseExitId.Value);
        }

        private Exit ChooseBacktrack(MazeAgent agent, List<Exit> backtrack)
        {
            var promising = backtrack.Where(e => LeadsTowardUnexploredOptions(agent, e)).ToList();
            return LeastVisitedPick(agent, promising.Count > 0 ? promising : backtrack);
        }

        /// <summary>
        /// One-step lookahead: does the room beyond `exit` itself have any door (other than
        /// the one leading straight back here) that's still unused or leads somewhere this
        /// agent hasn't personally been? If so, backtracking this way still has somewhere
        /// useful to go; if not, it just leads deeper into already-picked-over territory.
        /// </summary>
        private bool LeadsTowardUnexploredOptions(MazeAgent agent, Exit exit)
        {
            if (!exit.ConnectedRoomId.HasValue) return false;

            Room target = _generator.Graph.Get(exit.ConnectedRoomId.Value);
            if (target == null) return false;

            int reverseExitId = exit.ConnectedExitId ?? -1;
            foreach (var candidate in target.Exits)
            {
                if (candidate.Id == reverseExitId) continue;
                if (!candidate.IsUsed) return true;
                if (candidate.ConnectedRoomId.HasValue && !agent.HasVisited(candidate.ConnectedRoomId.Value)) return true;
            }
            return false;
        }

        private static Exit LeastVisitedPick(MazeAgent agent, List<Exit> exits)
        {
            int bestVisits = int.MaxValue;
            var bestExits = new List<Exit>();

            foreach (var exit in exits)
            {
                int visits = exit.ConnectedRoomId.HasValue ? agent.VisitCount(exit.ConnectedRoomId.Value) : 0;
                if (visits < bestVisits)
                {
                    bestVisits = visits;
                    bestExits.Clear();
                    bestExits.Add(exit);
                }
                else if (visits == bestVisits)
                {
                    bestExits.Add(exit);
                }
            }

            return RandomPick(bestExits);
        }

        private static Exit RandomPick(List<Exit> exits) => exits[UnityEngine.Random.Range(0, exits.Count)];

        /// <summary>
        /// Peek into a room (via an exit) to see if there are monsters and how many.
        /// Returns the perceived challenge rating, or 0 if no monsters/already explored.
        /// Agent sees incomplete info (60-100% of actual monsters, doesn't know about hidden ones).
        /// </summary>
        public float PeekThroughExit(Exit exit, MazeAgent agent)
        {
            if (!exit.ConnectedRoomId.HasValue)
                return 0; // Unresolved exit - can't peek yet

            Room nextRoom = _generator.Graph.Get(exit.ConnectedRoomId.Value);
            if (nextRoom == null || nextRoom.Encounter == null)
                return 0; // No encounter in this room

            return nextRoom.Encounter.GetPerceivedChallengeRating(agent.CharacterSheet);
        }

        /// <summary>
        /// Decide if an exit is worth taking based on threat level inside.
        /// Returns true if the exit is relatively safe or if the agent has no choice,
        /// false if the agent decides to retreat from this exit.
        /// </summary>
        private bool ShouldTakeExit(Exit exit, MazeAgent agent)
        {
            if (!exit.ConnectedRoomId.HasValue)
                return true; // Unresolved exit - proceed cautiously

            Room nextRoom = _generator.Graph.Get(exit.ConnectedRoomId.Value);
            if (nextRoom == null || nextRoom.Encounter == null)
                return true; // No encounter, safe to enter

            // Peek and evaluate threat
            float perceivedCR = nextRoom.Encounter.GetPerceivedChallengeRating(agent.CharacterSheet);

            // If threat is below threshold, take it. If above, retreat with some randomness.
            if (perceivedCR <= _retreatThreshold)
                return true; // Manageable threat

            // Higher difficulty = more likely to retreat, but add randomness for personality
            float retreatChance = Mathf.Clamp01((perceivedCR - _retreatThreshold) / 2.0f);
            return UnityEngine.Random.value > retreatChance;
        }

        /// <summary>
        /// Filter exits: remove those the agent wants to retreat from due to high threat.
        /// This is called during exit selection so dangerous rooms are avoided when possible.
        /// </summary>
        private List<Exit> FilterByThreat(List<Exit> exits, MazeAgent agent)
        {
            var safeExits = new List<Exit>();

            foreach (var exit in exits)
            {
                if (ShouldTakeExit(exit, agent))
                    safeExits.Add(exit);
            }

            // If all exits are dangerous, agent must take one anyway (don't get stuck)
            return safeExits.Count > 0 ? safeExits : exits;
        }
    }
}