using System;
using Unity.Entities;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Slice 2 — pure mapping from a chosen class (a <see cref="CharacterId"/> byte) to its spawn-time setup: the
    /// Fire-slot ability id + the permanent trait <see cref="StatModifier"/>s (tagged with the reserved
    /// <see cref="Tuning.ClassSourceId"/> range, NEVER stripped by the generic modifier systems). Applied by
    /// GoInGameServerSystem on the just-spawned player and unit-tested. Burst-safe (byte/uint only, no managed types).
    /// <para>
    /// Trait deltas seed onto the <see cref="CharacterId.Default"/> character (no per-class blob row needed — the
    /// deltas ride the replicated StatModifier buffer, OwnerSendType.All, so the owning client folds the correct
    /// EffectiveCharacterStats). The DRG-asymmetry (operator-locked): <b>Warrior</b> = melee bruiser (tankier,
    /// slower, harder + longer-reach melee via MeleeDamage/MeleeRange); <b>Ranger</b> = ranged anchor (faster,
    /// squishier, longer projectile range + a wider auto-target assist — the co-op synergy hook the Warrior's
    /// knockback feeds). The Warrior's Fire = the aim-directed cone (<see cref="AbilityId.WarriorCone"/>); the
    /// Ranger's Fire = the default projectile (<see cref="AbilityId.Primary"/>).
    /// </para>
    /// <para>
    /// <see cref="Reapply"/> swaps an already-spawned player's class IN PLACE (strip the old class seeds, re-seed
    /// the new ones) — used by the editor-only class-switch dev tool. The single seed set lives in <see cref="Seeds"/>
    /// so the spawn path and the swap path can never drift; <see cref="ClassSeedCount"/> couples the strip range
    /// (<see cref="IsClassSeed"/>) to the number of seeds emitted.
    /// </para>
    /// </summary>
    public static class ClassTraits
    {
        public const byte WarriorClass = (byte)CharacterId.Warrior;
        public const byte RangerClass = (byte)CharacterId.Ranger;

        /// <summary>How many trait modifiers a class seeds (each on a distinct SourceId at ClassSourceId + i).</summary>
        public const int ClassSeedCount = 4;

        /// <summary>Normalize a wire ClassId to a known class (0 / unknown -> Warrior).</summary>
        public static byte Normalize(byte classId) => classId == RangerClass ? RangerClass : WarriorClass;

        /// <summary>The Fire-slot ability id for a class (Warrior = cone, Ranger = the default projectile).</summary>
        public static byte AbilityFor(byte classId)
            => classId == RangerClass ? (byte)AbilityId.Primary : (byte)AbilityId.WarriorCone;

        /// <summary>True when a modifier's SourceId is in the reserved class-seed range [ClassSourceId, +ClassSeedCount).</summary>
        public static bool IsClassSeed(uint sourceId)
            => sourceId >= Tuning.ClassSourceId && sourceId < Tuning.ClassSourceId + (uint)ClassSeedCount;

        /// <summary>
        /// The permanent trait deltas for a class — the SINGLE source shared by both the spawn path
        /// (<see cref="AppendSeeds(byte,Entity,EntityCommandBuffer)"/>) and the in-place swap path
        /// (<see cref="AppendSeeds(byte,DynamicBuffer{StatModifier})"/> / <see cref="Reapply"/>), so they can't drift.
        /// Fills exactly <see cref="ClassSeedCount"/> entries, each tagged ClassSourceId + i.
        /// </summary>
        static void Seeds(byte classId, Span<StatModifier> seeds)
        {
            uint src = Tuning.ClassSourceId;
            if (classId == RangerClass)
            {
                seeds[0] = new StatModifier { Target = (byte)StatTarget.MoveSpeed, Op = (byte)ModOp.PercentMult, Value = 0.15f, SourceId = src };
                seeds[1] = new StatModifier { Target = (byte)StatTarget.MaxHealth, Op = (byte)ModOp.PercentMult, Value = -0.15f, SourceId = src + 1u };
                seeds[2] = new StatModifier { Target = (byte)StatTarget.Range, Op = (byte)ModOp.PercentAdd, Value = 0.30f, SourceId = src + 2u };
                seeds[3] = new StatModifier { Target = (byte)StatTarget.AutoTargetRange, Op = (byte)ModOp.Flat, Value = 3f, SourceId = src + 3u };
            }
            else
            {
                seeds[0] = new StatModifier { Target = (byte)StatTarget.MaxHealth, Op = (byte)ModOp.Flat, Value = 30f, SourceId = src };
                seeds[1] = new StatModifier { Target = (byte)StatTarget.MoveSpeed, Op = (byte)ModOp.PercentMult, Value = -0.15f, SourceId = src + 1u };
                seeds[2] = new StatModifier { Target = (byte)StatTarget.MeleeDamage, Op = (byte)ModOp.Flat, Value = 6f, SourceId = src + 2u };
                seeds[3] = new StatModifier { Target = (byte)StatTarget.MeleeRange, Op = (byte)ModOp.Flat, Value = 0.8f, SourceId = src + 3u };
            }
        }

        /// <summary>Append a class's permanent trait modifiers onto a player's StatModifier buffer (via ECB at spawn).</summary>
        public static void AppendSeeds(byte classId, Entity player, EntityCommandBuffer ecb)
        {
            Span<StatModifier> seeds = stackalloc StatModifier[ClassSeedCount];
            Seeds(classId, seeds);
            for (int i = 0; i < ClassSeedCount; i++)
                ecb.AppendToBuffer(player, seeds[i]);
        }

        /// <summary>Append a class's permanent trait modifiers directly onto a live StatModifier buffer (in-place swap).</summary>
        public static void AppendSeeds(byte classId, DynamicBuffer<StatModifier> mods)
        {
            Span<StatModifier> seeds = stackalloc StatModifier[ClassSeedCount];
            Seeds(classId, seeds);
            for (int i = 0; i < ClassSeedCount; i++)
                mods.Add(seeds[i]);
        }

        /// <summary>
        /// Swap an already-spawned player's class IN PLACE: strip whatever class seeds are present, then re-seed the
        /// target class. Order-independent (StatMath folds by Target/Op), so the RemoveAtSwapBack reordering is safe,
        /// and idempotent (switching to the same class still leaves exactly <see cref="ClassSeedCount"/> seeds).
        /// Foreign modifiers (upgrades, equipment, timed buffs — all on disjoint SourceIds) are preserved.
        /// </summary>
        public static void Reapply(byte classId, DynamicBuffer<StatModifier> mods)
        {
            for (int i = mods.Length - 1; i >= 0; i--)
                if (IsClassSeed(mods[i].SourceId))
                    mods.RemoveAtSwapBack(i);
            AppendSeeds(classId, mods);
        }
    }
}