using System;
using System.Collections.Generic;
using System.Linq;
using AcDream.Core.World;
using DatReaderWriter;
using DatReaderWriter.Options;
using DatReaderWriter.Enums;
using DatGfxObj = DatReaderWriter.DBObjs.GfxObj;
using DatGfxObjDegradeInfo = DatReaderWriter.DBObjs.GfxObjDegradeInfo;
using DatSetup = DatReaderWriter.DBObjs.Setup;
using DatRegion = DatReaderWriter.DBObjs.Region;
using DatLandBlock = DatReaderWriter.DBObjs.LandBlock;
using DatLandBlockInfo = DatReaderWriter.DBObjs.LandBlockInfo;
using Xunit;
using Xunit.Abstractions;

namespace AcDream.Core.Tests.Conformance;

/// <summary>
/// DISTANCE-DEGRADE design probe (2026-06-23, throwaway). Answers the single
/// load-bearing question for the FPS distance-degrade port: do the GfxObjs that
/// a dense town actually DRAWS (procedural scenery + placed stabs) even carry a
/// <c>DIDDegrade</c> table, and if so, at what distance does retail HIDE them
/// (last non-zero slot's <c>MaxDist</c>, since past that the table degrades to
/// gfxobj id 0)? This decides whether the recommended "hide-only" phase 1 is the
/// real FPS win for scenery or a no-op. Output-only — no assertions. Delete after
/// the design lands. Run with the real client dats present (ACDREAM_DAT_DIR).
/// </summary>
public sealed class DegradeCoverageProbeTests
{
    private readonly ITestOutputHelper _out;
    public DegradeCoverageProbeTests(ITestOutputHelper output) => _out = output;

    private const uint RegionDatId = 0x13000000u;
    private const float Inf = float.PositiveInfinity;

    // Per-GfxObj degrade summary.
    private readonly record struct GfxDeg(bool HasTable, bool DegradesToHidden, float HideDist, int NumSlots, float Slot0Max);

    [Fact]
    public void Probe_DenseTown_Holtburg_DegradeCoverage()
    {
        var datDir = ConformanceDats.ResolveDatDir();
        if (datDir is null) { _out.WriteLine("SKIP: dats unavailable"); return; }
        using var dats = new DatCollection(datDir, DatAccessType.Read);

        var region = dats.Get<DatRegion>(RegionDatId);
        if (region is null) { _out.WriteLine("SKIP: Region 0x13000000 missing"); return; }

        // 3x3 landblock neighbourhood centred on Holtburg 0xA9B4 — approximates the
        // scenery volume that gets drawn when facing the town.
        byte[] xs = { 0xA8, 0xA9, 0xAA };
        byte[] ys = { 0xB3, 0xB4, 0xB5 };

        // GfxObj-level degrade cache.
        var gfxCache = new Dictionary<uint, GfxDeg>();
        GfxDeg DegOf(uint gfxId)
        {
            if (gfxCache.TryGetValue(gfxId, out var c)) return c;
            var g = dats.Get<DatGfxObj>(gfxId);
            GfxDeg r;
            if (g is null || !g.Flags.HasFlag(GfxObjFlags.HasDIDDegrade) || g.DIDDegrade == 0)
                r = new GfxDeg(false, false, Inf, 0, Inf);
            else
            {
                var info = dats.Get<DatGfxObjDegradeInfo>(g.DIDDegrade);
                if (info is null || info.Degrades.Count == 0)
                    r = new GfxDeg(false, false, Inf, 0, Inf);
                else
                {
                    int n = info.Degrades.Count;
                    int hideSlot = -1;
                    for (int i = 0; i < n; i++)
                        if ((uint)info.Degrades[i].Id == 0u) { hideSlot = i; break; }
                    float slot0Max = info.Degrades[0].MaxDist;
                    if (hideSlot < 0)
                        r = new GfxDeg(true, false, Inf, n, slot0Max);          // LOD-only, never hides
                    else if (hideSlot == 0)
                        r = new GfxDeg(true, true, 0f, n, slot0Max);            // editor-only marker
                    else
                        r = new GfxDeg(true, true, info.Degrades[hideSlot - 1].MaxDist, n, slot0Max);
                }
            }
            gfxCache[gfxId] = r;
            return r;
        }

        // Resolve an object id (Setup 0x02 or GfxObj 0x01) to its part GfxObj ids.
        var partsCache = new Dictionary<uint, List<uint>>();
        List<uint> PartsOf(uint objId)
        {
            if (partsCache.TryGetValue(objId, out var c)) return c;
            var list = new List<uint>();
            if ((objId >> 24) == 0x02u)
            {
                var s = dats.Get<DatSetup>(objId);
                if (s is not null) foreach (var p in s.Parts) list.Add((uint)p);
            }
            else if ((objId >> 24) == 0x01u)
                list.Add(objId);
            partsCache[objId] = list;
            return list;
        }

        // Per-entity (object) hide distance = MAX over parts' hide dist (entity is
        // fully hidden only when EVERY part has degraded to nothing). A part with no
        // table / no hidden slot contributes +inf → entity never fully hides.
        var entityHideCache = new Dictionary<uint, (float hideDist, bool anyTable)>();
        (float hideDist, bool anyTable) EntityHide(uint objId)
        {
            if (entityHideCache.TryGetValue(objId, out var c)) return c;
            var parts = PartsOf(objId);
            float maxHide = 0f; bool anyTable = false; bool sawNonHiding = false;
            if (parts.Count == 0) { var e0 = (Inf, false); entityHideCache[objId] = e0; return e0; }
            foreach (var pid in parts)
            {
                var d = DegOf(pid);
                if (d.HasTable) anyTable = true;
                if (d.DegradesToHidden) maxHide = MathF.Max(maxHide, d.HideDist);
                else sawNonHiding = true;
            }
            float hide = sawNonHiding ? Inf : maxHide;
            var e = (hide, anyTable);
            entityHideCache[objId] = e;
            return e;
        }

        // Tally scenery placements (weighted by count) + stabs.
        var sceneryCount = new Dictionary<uint, int>();
        var stabCount = new Dictionary<uint, int>();
        int lbWithTerrain = 0;

        foreach (var x in xs)
        foreach (var y in ys)
        {
            uint lbId = ((uint)x << 24) | ((uint)y << 16);
            var block = dats.Get<DatLandBlock>(lbId | 0xFFFFu);
            if (block is null || block.Terrain is null || block.Terrain.Length == 0) continue;
            lbWithTerrain++;

            var spawns = SceneryGenerator.Generate(dats, region, block, lbId);
            foreach (var sp in spawns)
                sceneryCount[sp.ObjectId] = sceneryCount.GetValueOrDefault(sp.ObjectId) + 1;

            var info = dats.Get<DatLandBlockInfo>(lbId | 0xFFFEu);
            if (info?.Objects is not null)
                foreach (var stab in info.Objects)
                    stabCount[stab.Id] = stabCount.GetValueOrDefault(stab.Id) + 1;
        }

        _out.WriteLine($"=== Dense-town degrade coverage (3x3 around Holtburg 0xA9B4, {lbWithTerrain}/9 lb w/ terrain) ===");

        Summarize("PROCEDURAL SCENERY (the bulk)", sceneryCount, EntityHide);
        Summarize("PLACED STABS (LandBlockInfo.Objects)", stabCount, EntityHide);

        // GfxObj-level coverage across every unique part seen.
        var allObjIds = sceneryCount.Keys.Concat(stabCount.Keys).Distinct();
        var allGfx = allObjIds.SelectMany(PartsOf).Distinct().ToList();
        int gfxWithTable = allGfx.Count(g => DegOf(g).HasTable);
        int gfxHides = allGfx.Count(g => DegOf(g).DegradesToHidden);
        _out.WriteLine($"\n[GfxObj-level] unique part GfxObjs={allGfx.Count}  withDegradeTable={gfxWithTable} ({Pct(gfxWithTable, allGfx.Count)})  degradesToHidden={gfxHides} ({Pct(gfxHides, allGfx.Count)})");

        // Sample the top scenery objects with their tables.
        _out.WriteLine("\n[Top scenery objects by placement count]");
        foreach (var kv in sceneryCount.OrderByDescending(k => k.Value).Take(20))
        {
            var (hide, anyTable) = EntityHide(kv.Key);
            string hideStr = float.IsPositiveInfinity(hide) ? "NEVER" : $"{hide:F0}m";
            var parts = PartsOf(kv.Key);
            string slots = parts.Count > 0
                ? string.Join(",", parts.Take(3).Select(p => { var d = DegOf(p); return d.HasTable ? $"{d.NumSlots}sl/hide={(float.IsPositiveInfinity(d.HideDist) ? "inf" : d.HideDist.ToString("F0"))}" : "noTable"; }))
                : "(unresolved)";
            _out.WriteLine($"  0x{kv.Key:X8} x{kv.Value,-5} parts={parts.Count} hideDist={hideStr,-7} [{slots}]");
        }

        // LOD ladder with poly counts for the top 6 scenery objects: quantifies the
        // per-slot triangle savings (the LOD-degrade win) and at what distances the
        // swaps land.
        int PolyCount(uint gfxId)
        {
            var g = dats.Get<DatGfxObj>(gfxId);
            return g?.Polygons?.Count ?? -1;
        }
        _out.WriteLine("\n[LOD ladder — top scenery objects, per part: slot=(Id polys min/ideal/max mode)]");
        foreach (var kv in sceneryCount.OrderByDescending(k => k.Value).Take(6))
        {
            _out.WriteLine($"  OBJ 0x{kv.Key:X8} (x{kv.Value}):");
            foreach (var pid in PartsOf(kv.Key).Distinct())
            {
                var g = dats.Get<DatGfxObj>(pid);
                int basePolys = g?.Polygons?.Count ?? -1;
                if (g is null || !g.Flags.HasFlag(GfxObjFlags.HasDIDDegrade) || g.DIDDegrade == 0)
                { _out.WriteLine($"    part 0x{pid:X8} polys={basePolys} : NO TABLE (always full detail)"); continue; }
                var info = dats.Get<DatGfxObjDegradeInfo>(g.DIDDegrade);
                if (info is null || info.Degrades.Count == 0)
                { _out.WriteLine($"    part 0x{pid:X8} polys={basePolys} : empty table"); continue; }
                var ladder = string.Join("  ", info.Degrades.Select((d, i) =>
                {
                    uint sid = (uint)d.Id;
                    int p = sid == 0 ? 0 : PolyCount(sid);
                    return $"[{i}]={(sid == 0 ? "HIDE" : $"0x{sid:X8}/{p}p")} {d.MinDist:F0}/{d.IdealDist:F0}/{d.MaxDist:F0} m{d.DegradeMode}";
                }));
                _out.WriteLine($"    part 0x{pid:X8} base{basePolys}p : {ladder}");
            }
        }
    }

    private void Summarize(string label, Dictionary<uint, int> counts, Func<uint, (float hideDist, bool anyTable)> entityHide)
    {
        int total = counts.Values.Sum();
        if (total == 0) { _out.WriteLine($"\n[{label}] no placements"); return; }

        int placementsWithTable = 0, placementsHide = 0;
        var hideBuckets = new int[] { 0, 0, 0, 0, 0, 0 }; // <25, <50, <75, <100, <150, >=150
        int hideTotalPlacements = 0;
        foreach (var (id, cnt) in counts)
        {
            var (hide, anyTable) = entityHide(id);
            if (anyTable) placementsWithTable += cnt;
            if (!float.IsPositiveInfinity(hide))
            {
                placementsHide += cnt;
                hideTotalPlacements += cnt;
                int b = hide < 25 ? 0 : hide < 50 ? 1 : hide < 75 ? 2 : hide < 100 ? 3 : hide < 150 ? 4 : 5;
                hideBuckets[b] += cnt;
            }
        }

        _out.WriteLine($"\n[{label}] uniqueObjs={counts.Count} totalPlacements={total}");
        _out.WriteLine($"  placements whose obj has a degrade table : {placementsWithTable} ({Pct(placementsWithTable, total)})");
        _out.WriteLine($"  placements that HIDE at finite distance   : {placementsHide} ({Pct(placementsHide, total)})");
        if (hideTotalPlacements > 0)
            _out.WriteLine($"  hide-distance histogram (placements): <25m={hideBuckets[0]} <50m={hideBuckets[1]} <75m={hideBuckets[2]} <100m={hideBuckets[3]} <150m={hideBuckets[4]} >=150m={hideBuckets[5]}");
    }

    private static string Pct(int n, int d) => d == 0 ? "n/a" : $"{100.0 * n / d:F1}%";
}