using System.Collections.Generic;
using SepCore.CustomComponent;
using SepCore.Definition;

namespace SepCore.Battle
{
    /// <summary>
    /// 当前战斗的事实唯一来源，仅战斗期间存在。
    /// 调度、指令校验、效果、状态和敌人决策共享同一实例，不复制单位、轮次和状态集合；
    /// 内部不为函数调用建立请求/响应 DTO，玩家与敌人的行动都走同一条执行管线并产生同一组 BattleEvent。
    /// M1 只支持 1 名玩家与 1 名敌人的普通攻击闭环。
    /// </summary>
    internal sealed class BattleRuntime
    {
        /// <summary>
        /// 触发本场战斗的遭遇 ID，用于结果回写关联地图敌人。
        /// </summary>
        public readonly int EncounterId;

        /// <summary>
        /// 本场全部单位，创建顺序即稳定显示顺序（玩家在前）。
        /// </summary>
        public readonly BattleUnit[] Units;

        /// <summary>
        /// 是否为本场先制战斗（只影响第一轮；M1 未启用）。
        /// </summary>
        public readonly bool IsPreemptive;

        /// <summary>
        /// 当前轮次，从 1 开始。
        /// </summary>
        public int RoundNumber = 1;

        /// <summary>
        /// 当前行动者；无行动者或战斗完成时为 0。
        /// </summary>
        public int CurrentActorUnitId;

        /// <summary>
        /// 本轮已获得行动机会的单位 ID。
        /// </summary>
        public readonly HashSet<int> ActedUnitIds = new HashSet<int>();

        /// <summary>
        /// 本次推进产生的待展示行动记录，推进结束时被 BattleStep 取走。
        /// </summary>
        public readonly List<BattleEvent> PendingEvents = new List<BattleEvent>();

        /// <summary>
        /// 战斗结束后的结果；非 null 即表示战斗已完成。
        /// </summary>
        public BattleResult Result;

        private readonly IRunRandomSource _random;
        private readonly IBattleConfigProvider _config;

        /// <summary>
        /// 是否已完成。
        /// </summary>
        public bool IsCompleted => Result != null;

        /// <summary>
        /// 当前行动者单位；无行动者时返回 null。
        /// </summary>
        public BattleUnit CurrentActor => GetUnit(CurrentActorUnitId);

        private BattleRuntime(int encounterId, BattleUnit[] units, bool isPreemptive,
            IRunRandomSource random, IBattleConfigProvider config)
        {
            EncounterId = encounterId;
            Units = units;
            IsPreemptive = isPreemptive;
            _random = random;
            _config = config;
        }

        /// <summary>
        /// 从遭遇、单局玩家状态、配置和本局随机源创建唯一战斗运行时。
        /// 任一必要输入缺失或配置缺失时返回 null，表示启动失败且不产生任何副作用。
        /// </summary>
        public static BattleRuntime Create(BattleEncounter encounter, IReadOnlyList<RunPlayerState> players,
            IBattleConfigProvider config, IRunRandomSource random)
        {
            if (encounter == null || players == null || players.Count == 0 || config == null || random == null)
            {
                return null;
            }

            EnemyPartyConfig party = config.GetEnemyParty(encounter.EnemyPartyConfigId);
            if (party == null || party.EnemyIds == null || party.EnemyIds.Count == 0)
            {
                return null;
            }

            List<BattleUnit> units = new List<BattleUnit>(players.Count + party.EnemyIds.Count);
            int nextId = 1;

            foreach (RunPlayerState state in players)
            {
                if (state == null)
                {
                    return null;
                }

                BattleUnit unit = new BattleUnit(nextId++, BattleFaction.Player, state.CharacterId, state.PartyOrder,
                    state.CurrentHp, state.MaxHp, state.CurrentMp, state.MaxMp,
                    state.Atk, state.Mat, state.Speed);
                if (state.AttackActionId != 0)
                {
                    unit.ActionIds.Add(state.AttackActionId);
                }

                if (state.SkillActionId != 0)
                {
                    unit.ActionIds.Add(state.SkillActionId);
                }

                units.Add(unit);
            }

            int enemyOrder = 1;
            foreach (int enemyId in party.EnemyIds)
            {
                EnemyConfig enemy = config.GetEnemy(enemyId);
                if (enemy == null)
                {
                    return null;
                }

                BattleUnit unit = new BattleUnit(nextId++, BattleFaction.Enemy, enemy.Id, enemyOrder++,
                    enemy.MaxHp, enemy.MaxHp, enemy.MaxMp, enemy.MaxMp, enemy.Atk, enemy.Mat, enemy.Speed);
                if (enemy.ActionIds != null)
                {
                    unit.ActionIds.AddRange(enemy.ActionIds);
                }

                units.Add(unit);
            }

            BattleRuntime runtime = new BattleRuntime(encounter.EncounterId, units.ToArray(),
                encounter.IsPreemptive, random, config);
            runtime.SelectNextActor();
            return runtime;
        }

        /// <summary>
        /// 按运行时 ID 获取单位；不存在时返回 null。
        /// </summary>
        public BattleUnit GetUnit(int unitId)
        {
            foreach (BattleUnit unit in Units)
            {
                if (unit.UnitId == unitId)
                {
                    return unit;
                }
            }

            return null;
        }

        /// <summary>
        /// 单位是否仍在战斗中（未阵亡且未逃跑）。
        /// </summary>
        public static bool IsActive(BattleUnit unit)
        {
            return unit != null && !unit.IsDefeated && !unit.IsEscaped;
        }

        /// <summary>
        /// 校验并执行当前玩家指令（单次行动）。
        /// 非法指令不消耗 MP、行动机会或随机数；玩家行动后仅选择下一个行动者，
        /// 不自动推进敌人回合——间歇节奏由组件在外部编排。
        /// </summary>
        public BattleStep SubmitCommand(BattleCommand command)
        {
            if (!ValidatePlayerCommand(command))
            {
                return new BattleStep(new BattleEvent[0], BuildViewState(), null);
            }

            PendingEvents.Clear();

            BattleUnit actor = GetUnit(command.ActorUnitId);
            ExecuteAction(actor, command.CommandType, command.ActionConfigId, command.TargetUnitIds);
            MarkActed(command.ActorUnitId);
            CheckBattleEnd();

            if (!IsCompleted)
            {
                SelectNextActor();
            }

            return new BattleStep(DrainEvents(), BuildViewState(), Result);
        }

        /// <summary>
        /// 推进当前敌人行动者的自动回合（单次行动）。
        /// 当前行动者不是敌人、没有行动者或战斗已完成时返回无变化步骤；
        /// 与玩家指令共用同一执行管线并产生同一组 BattleEvent。
        /// </summary>
        public BattleStep AdvanceEnemyTurn()
        {
            BattleUnit actor = CurrentActor;
            if (actor == null || actor.Faction != BattleFaction.Enemy || IsCompleted)
            {
                return new BattleStep(new BattleEvent[0], BuildViewState(), null);
            }

            PendingEvents.Clear();

            ExecuteEnemyTurn(actor);
            MarkActed(actor.UnitId);
            CheckBattleEnd();

            if (!IsCompleted)
            {
                SelectNextActor();
            }

            return new BattleStep(DrainEvents(), BuildViewState(), Result);
        }

        /// <summary>
        /// 构建当前只读视图。
        /// </summary>
        public BattleViewState BuildViewState()
        {
            List<BattleUnitView> unitViews = new List<BattleUnitView>(Units.Length);
            foreach (BattleUnit unit in Units)
            {
                List<BattleStatusView> statusViews = new List<BattleStatusView>(unit.Statuses.Count);
                foreach (BattleStatus status in unit.Statuses)
                {
                    statusViews.Add(new BattleStatusView(status.Type, status.RemainingRounds));
                }

                unitViews.Add(new BattleUnitView(unit.UnitId, unit.Faction, unit.ConfigId, unit.PartyOrder,
                    unit.CurrentHp, unit.MaxHp, unit.CurrentMp, unit.MaxMp, unit.Speed,
                    unit.IsDefeated, unit.IsEscaped, statusViews));
            }

            List<int> remainingOrder = new List<int>();
            if (!IsCompleted)
            {
                foreach (BattleUnit unit in Units)
                {
                    if (IsActive(unit) && !ActedUnitIds.Contains(unit.UnitId))
                    {
                        remainingOrder.Add(unit.UnitId);
                    }
                }
            }

            List<int> availableActions = new List<int>();
            BattleUnit actor = CurrentActor;
            if (actor != null && actor.Faction == BattleFaction.Player)
            {
                availableActions.AddRange(actor.ActionIds);
            }

            return new BattleViewState(RoundNumber, CurrentActorUnitId, unitViews, remainingOrder, availableActions);
        }

        private bool ValidatePlayerCommand(BattleCommand command)
        {
            if (command == null || IsCompleted)
            {
                return false;
            }

            if (command.ActorUnitId != CurrentActorUnitId)
            {
                return false;
            }

            BattleUnit actor = GetUnit(command.ActorUnitId);
            if (actor == null || actor.Faction != BattleFaction.Player)
            {
                return false;
            }

            if (command.CommandType != BattleActionType.Attack)
            {
                return false;
            }

            BattleActionConfig action = _config.GetAction(command.ActionConfigId);
            if (action == null || action.ActionType != BattleActionType.Attack)
            {
                return false;
            }

            if (actor.CurrentMp < action.MpCost)
            {
                return false;
            }

            return TryResolvePlayerTargets(command, actor, action);
        }

        private bool TryResolvePlayerTargets(BattleCommand command, BattleUnit actor, BattleActionConfig action)
        {
            if (action.TargetType != BattleTargetType.SingleEnemy)
            {
                return false;
            }

            if (command.TargetUnitIds == null || command.TargetUnitIds.Count != 1)
            {
                return false;
            }

            BattleUnit target = GetUnit(command.TargetUnitIds[0]);
            return target != null && target.Faction != actor.Faction && IsActive(target);
        }

        private void ExecuteAction(BattleUnit actor, BattleActionType commandType, int actionConfigId,
            IReadOnlyList<int> targetUnitIds)
        {
            BattleActionConfig action = _config.GetAction(actionConfigId);
            if (action == null)
            {
                return;
            }

            if (action.MpCost > 0 && actor.CurrentMp >= action.MpCost)
            {
                actor.CurrentMp -= action.MpCost;
            }

            foreach (int targetUnitId in targetUnitIds)
            {
                BattleUnit target = GetUnit(targetUnitId);
                if (target == null)
                {
                    continue;
                }

                foreach (BattleEffect effect in action.Effects)
                {
                    ApplyEffect(actor, target, commandType, actionConfigId, effect);
                }
            }
        }

        private void ApplyEffect(BattleUnit actor, BattleUnit target, BattleActionType commandType,
            int actionConfigId, BattleEffect effect)
        {
            int sourceValue = GetStatValue(actor, effect.SourceStat);
            int change = effect.FlatValue + sourceValue * effect.SourceScalePermille / 1000;

            int beforeHp = target.CurrentHp;
            int beforeMp = target.CurrentMp;

            switch (effect.TargetStat)
            {
                case BattleStatType.HP:
                    target.CurrentHp = Clamp(target.CurrentHp + change, 0, target.MaxHp);
                    if (target.CurrentHp <= 0)
                    {
                        target.CurrentHp = 0;
                        target.IsDefeated = true;
                    }

                    break;
                case BattleStatType.MP:
                    target.CurrentMp = Clamp(target.CurrentMp + change, 0, target.MaxMp);
                    break;
                default:
                    // M1 不处理速度/上限等目标属性修改与状态施加
                    break;
            }

            PendingEvents.Add(new BattleEvent(actor.UnitId, commandType, actionConfigId, target.UnitId,
                beforeHp, target.CurrentHp, beforeMp, target.CurrentMp,
                BattleStatusType.None, 0));
        }

        private static int GetStatValue(BattleUnit unit, BattleStatType stat)
        {
            switch (stat)
            {
                case BattleStatType.HP:
                    return unit.CurrentHp;
                case BattleStatType.MP:
                    return unit.CurrentMp;
                case BattleStatType.MaxHP:
                    return unit.MaxHp;
                case BattleStatType.MaxMP:
                    return unit.MaxMp;
                case BattleStatType.ATK:
                    return unit.Atk;
                case BattleStatType.MAT:
                    return unit.Mat;
                case BattleStatType.Speed:
                    return unit.Speed;
                default:
                    return 0;
            }
        }

        private static int Clamp(int value, int min, int max)
        {
            return value < min ? min : (value > max ? max : value);
        }

        private void MarkActed(int unitId)
        {
            ActedUnitIds.Add(unitId);
        }

        /// <summary>
        /// 选择本轮下一个未行动的活跃单位；全部行动过则进入下一轮。
        /// M1 按单位创建顺序（玩家在前）轮流，每轮每个单位最多行动一次；
        /// M2 起由完整调度规则（速度、阵营、队伍顺序、先制）替换。
        /// </summary>
        private void SelectNextActor()
        {
            if (IsCompleted)
            {
                CurrentActorUnitId = 0;
                return;
            }

            BattleUnit next = FindNextActor();
            if (next == null)
            {
                RoundNumber++;
                ActedUnitIds.Clear();
                next = FindNextActor();
            }

            CurrentActorUnitId = next != null ? next.UnitId : 0;
        }

        private BattleUnit FindNextActor()
        {
            foreach (BattleUnit unit in Units)
            {
                if (IsActive(unit) && !ActedUnitIds.Contains(unit.UnitId))
                {
                    return unit;
                }
            }

            return null;
        }

        /// <summary>
        /// 敌人随机决策并执行：从 MP 足够的行动中等概率选择，单体行动从合法目标中等概率选择；
        /// 没有可执行行动或合法目标时跳过本次机会。
        /// </summary>
        private void ExecuteEnemyTurn(BattleUnit enemy)
        {
            List<int> usableActions = new List<int>();
            foreach (int actionId in enemy.ActionIds)
            {
                BattleActionConfig action = _config.GetAction(actionId);
                if (action != null && enemy.CurrentMp >= action.MpCost)
                {
                    usableActions.Add(actionId);
                }
            }

            if (usableActions.Count == 0)
            {
                return;
            }

            int chosenActionId = PickOne(usableActions);
            BattleActionConfig chosen = _config.GetAction(chosenActionId);

            List<int> targets = new List<int>();
            foreach (BattleUnit unit in Units)
            {
                if (unit.Faction != enemy.Faction && IsActive(unit))
                {
                    targets.Add(unit.UnitId);
                }
            }

            if (targets.Count == 0)
            {
                return;
            }

            int targetUnitId = PickOne(targets);
            ExecuteAction(enemy, chosen.ActionType, chosenActionId, new[] { targetUnitId });
        }

        /// <summary>
        /// 等概率选一；只有一项时直接返回，不消费随机数。
        /// </summary>
        private int PickOne(IReadOnlyList<int> candidates)
        {
            if (candidates.Count == 1)
            {
                return candidates[0];
            }

            return candidates[_random.NextInt(0, candidates.Count)];
        }

        private void CheckBattleEnd()
        {
            if (Result != null)
            {
                return;
            }

            bool allEnemiesDefeated = true;
            bool allPlayersDefeated = true;
            foreach (BattleUnit unit in Units)
            {
                if (IsActive(unit))
                {
                    if (unit.Faction == BattleFaction.Enemy)
                    {
                        allEnemiesDefeated = false;
                    }
                    else
                    {
                        allPlayersDefeated = false;
                    }
                }
            }

            BattleOutcome outcome;
            if (allEnemiesDefeated)
            {
                outcome = BattleOutcome.Victory;
            }
            else if (allPlayersDefeated)
            {
                outcome = BattleOutcome.TotalDefeat;
            }
            else
            {
                return;
            }

            List<BattlePlayerResult> players = new List<BattlePlayerResult>();
            foreach (BattleUnit unit in Units)
            {
                if (unit.Faction == BattleFaction.Player)
                {
                    players.Add(new BattlePlayerResult(unit.ConfigId, unit.CurrentHp, unit.CurrentMp,
                        unit.IsDefeated, unit.IsEscaped));
                }
            }

            Result = new BattleResult(EncounterId, outcome, players);
            CurrentActorUnitId = 0;
        }

        private List<BattleEvent> DrainEvents()
        {
            List<BattleEvent> drained = new List<BattleEvent>(PendingEvents);
            PendingEvents.Clear();
            return drained;
        }
    }
}