using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.IO.Compression;
using System.Text;

using Ultima;

namespace Server.Custom.Bridge
{
    /// <summary>
    ///     **The UOP animation reader** (docs/link/v8.md §4.3, §4.9 — protocol 8, phase 4): the
    ///     second and last decoder this protocol writes rather than calls.
    ///
    ///     ServUO's vendored <c>Ultima.Animations</c> reads legacy <c>anim*.mul</c> only — it
    ///     constructs its five <c>FileIndex</c>es with the four-argument constructor, which passes
    ///     <c>uopFile: null</c>, so <c>AnimationFrame*.uop</c> is never opened. Everything a
    ///     modern client added there is invisible to it. This class opens those packages directly.
    ///
    ///     ── **Why this is not the never-sweep rule being broken** ──
    ///
    ///     §4.3's rule is that a body's file type comes from <c>BodyConverter.Convert</c> and is
    ///     never guessed, because asking another <c>anim*.mul</c> for an index it does not own
    ///     returns a decodable picture of something else — a giant spider on the gargoyle page.
    ///     That rule exists because a legacy index is addressed **by position**: nothing in the
    ///     file says which body a record belongs to.
    ///
    ///     A UOP package is addressed by the **hash of a name that contains the body id**
    ///     (<c>build/animationlegacyframe/000666/00.bin</c>). Looking in all five packages for one
    ///     hash is therefore not a sweep — a hit is proof of identity, not a coincidence of
    ///     position, and the payload repeats the body id in its own header for us to check against.
    ///     Measured on this machine's client: 10,724 entries across the five packages, every one
    ///     of them claimed by that name scheme, and **no hash appears in more than one package**.
    ///
    ///     ── **Validate as we go, because here we are the library** ──
    ///
    ///     §4.5's rule is "validate before calling", and it exists because <c>Ultima</c>'s decoders
    ///     take their bounds from the file they are reading. Nothing about this code can be
    ///     validated from outside — it *is* the decode — so the same discipline appears as a bound
    ///     on every read: the block chain against the file length, an entry's record against the
    ///     file, the inflated length against the declared one, the frame table against the
    ///     payload, and every run header against **both** the record's remaining bytes and the
    ///     bitmap it is writing into. A record that fails any of them is reported absent and no
    ///     pixel of it is kept.
    ///
    ///     Measured the same way §4.5 was, which is the only measurement that says the boundary is
    ///     in the right place: across every UOP body on a stock client the walk refused **nothing**
    ///     that carries art, and the one body it does refuse (286) declares a 0×0 frame, which the
    ///     legacy decoder treats as absent too.
    ///
    ///     ── **No <c>System.Drawing</c>, deliberately** ──
    ///
    ///     §4.4 states it: libgdiplus was archived in March 2025, and the long-term argument for
    ///     moving extraction off <c>System.Drawing</c> is that a Linux shard depends on an
    ///     unmaintained library to see a sprite. This decoder writes ARGB1555 into a
    ///     <c>ushort[]</c> of its own and <see cref="BridgePng"/> encodes that directly, so the
    ///     door stays open. (Phase 4 does not walk through it: the catalogue still refuses the
    ///     whole family when imaging is unavailable, because most of it genuinely needs GDI+.)
    /// </summary>
    public static class BridgeUop
    {
        /// <summary>'MYP\0' — the Mythic package magic, as <c>FileIndex</c> reads it.</summary>
        private const int PackageMagic = 0x50594D;

        /// <summary>'AMOU' — the animation payload's own magic, little-endian.</summary>
        private const int PayloadMagic = 0x554F4D41;

        /// <summary>Each frame record opens with its own palette: 0x100 ARGB1555 entries.</summary>
        private const int PaletteBytes = 0x100 * 2;

        /// <summary>The frame table's row width: group, frame id, two unknowns, pixel offset.</summary>
        private const int FrameRowBytes = 16;

        /// <summary>One block-chain record: offset, three lengths, hash, adler32, flag.</summary>
        private const int BlockEntryBytes = 34;

        /// <summary>The xor <c>Frame</c> applies to every run header, and so must this.</summary>
        private const int DoubleXor = (0x200 << 22) | (0x200 << 12);

        /// <summary>
        ///     A ceiling on a declared decompressed payload. One group file is a whole action for
        ///     one body across every direction; the largest on this machine's client is body
        ///     1248's at 4.3 MB, so this is two orders of magnitude of headroom over real data and
        ///     still small enough that a corrupt length cannot ask for the host's memory.
        /// </summary>
        public const int MaxPayloadBytes = 64 * 1024 * 1024;

        /// <summary>
        ///     A ceiling on the block chain. Five packages hold 10,724 entries between them; this
        ///     bounds a cyclic or corrupt chain into a refusal rather than a hang.
        /// </summary>
        private const int MaxEntries = 1 << 20;

        /// <summary>The five packages this client ships. There is no AnimationFrame5.uop.</summary>
        private static readonly int[] PackageNumbers = { 1, 2, 3, 4, 6 };

        public static IEnumerable<int> Packages
        {
            get { return PackageNumbers; }
        }

        public static string PackageName(int n)
        {
            return "AnimationFrame" + n.ToString(CultureInfo.InvariantCulture) + ".uop";
        }

        /// <summary>
        ///     Where a UOP animation package lives.
        ///
        ///     <c>Ultima.Files.GetFilePath</c> cannot answer this: its table of known client files
        ///     predates UOP animations and contains no <c>AnimationFrame*.uop</c> entry, so it
        ///     returns null for every one of them. So the lookup is done here, against the same
        ///     directories ServUO itself resolved at boot — <c>Files.RootDir</c> first, then
        ///     <c>Core.DataDirectories</c>, which §1 is built on.
        ///
        ///     The comparison is case-insensitive **by enumeration** rather than by trying one
        ///     spelling. On Windows either would work; on a Linux shard host the client directory
        ///     is case-sensitive and the file may be shipped as `AnimationFrame1.uop`,
        ///     `animationframe1.uop` or anything between, which is exactly the shape of bug that
        ///     presents as "the gargoyles import on my machine and not on the server".
        ///
        ///     <see cref="FindClientFile"/> is the general form, and `assets.sources` uses it for
        ///     the same reason: a file Ultima's table predates has to be found some other way.
        /// </summary>
        public static string PackagePath(int n)
        {
            return FindClientFile(PackageName(n));
        }

        private static readonly object _pathSync = new object();

        private static readonly Dictionary<string, string> _paths =
            new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);

        /// <summary>
        ///     Finds a client file <c>Ultima.Files</c> has never heard of.
        ///
        ///     Only successful answers are cached: a file an operator copies in while the shard is
        ///     up should be found by the next import, and nothing here is hot enough for a
        ///     negative cache to be worth that.
        /// </summary>
        public static string FindClientFile(string name)
        {
            if (String.IsNullOrEmpty(name))
                return null;

            lock (_pathSync)
            {
                string cached;

                if (_paths.TryGetValue(name, out cached))
                    return cached;
            }

            foreach (string dir in Directories())
            {
                if (String.IsNullOrEmpty(dir))
                    continue;

                try
                {
                    if (!Directory.Exists(dir))
                        continue;

                    string direct = Path.Combine(dir, name);
                    string hit = File.Exists(direct) ? direct : null;

                    if (hit == null)
                    {
                        foreach (string found in Directory.GetFiles(dir))
                        {
                            if (String.Equals(Path.GetFileName(found), name,
                                    StringComparison.OrdinalIgnoreCase))
                            {
                                hit = found;
                                break;
                            }
                        }
                    }

                    if (hit == null)
                        continue;

                    lock (_pathSync)
                        _paths[name] = hit;

                    return hit;
                }
                catch (Exception e)
                {
                    Console.WriteLine("[Bridge] uop: cannot look in {0}: {1}", dir, e.Message);
                }
            }

            return null;
        }

        private static IEnumerable<string> Directories()
        {
            string root = null;

            try
            {
                root = Files.RootDir;
            }
            catch
            {
                // Ultima's static initialiser reads the registry on Windows. A host where that
                // throws still has Core.DataDirectories, which is the path ServUO actually booted
                // from.
            }

            if (!String.IsNullOrEmpty(root))
                yield return root;

            List<string> dirs = null;

            try
            {
                dirs = Core.DataDirectories;
            }
            catch
            {
                // Same reasoning; an empty list is a real answer and the caller reports absent.
            }

            if (dirs == null)
                yield break;

            foreach (string dir in dirs)
                yield return dir;
        }

        /// <summary>
        ///     The name a body's action file is stored under, hashed the way the container indexes
        ///     it. <c>Ultima.FileIndex.HashFileName</c> is pure arithmetic over a string — no file
        ///     is touched and no decoder is entered — so this is the one place phase 4 leans on
        ///     the vendored code, and it leans on it precisely so that our lookup cannot disagree
        ///     with the container's own.
        /// </summary>
        public static ulong HashOf(int body, int action)
        {
            string name = String.Format(CultureInfo.InvariantCulture,
                "build/animationlegacyframe/{0:D6}/{1:D2}.bin", body, action);

            return FileIndex.HashFileName(name);
        }

        // ── the container ────────────────────────────────────────────────────────────────────

        private struct Entry
        {
            public long At;
            public int CompressedLength;
            public int DecompressedLength;
            public short Flag;
        }

        /// <summary>
        ///     One opened <c>AnimationFrame*.uop</c>: its entry table in memory, its bytes on
        ///     demand. Opening one is a single pass over the block chain — 10,724 entries across
        ///     all five on this client — and the handle is held for the life of a reply, exactly
        ///     like the legacy readers next to it.
        /// </summary>
        public sealed class Package : IDisposable
        {
            private readonly Dictionary<ulong, Entry> _entries;
            private readonly FileStream _stream;

            public readonly string Path;

            private Package(string path, FileStream stream, Dictionary<ulong, Entry> entries)
            {
                Path = path;
                _stream = stream;
                _entries = entries;
            }

            public int Count
            {
                get { return _entries.Count; }
            }

            /// <summary>
            ///     Reads the block chain, refusing anything that does not fit inside the file.
            ///     Returns null — never throws — because a client that ships a truncated package
            ///     is an ordinary thing to survive, not an error to raise.
            /// </summary>
            public static Package Open(string path)
            {
                if (String.IsNullOrEmpty(path))
                    return null;

                FileStream stream = null;

                try
                {
                    stream = new FileStream(path, FileMode.Open, FileAccess.Read,
                        FileShare.ReadWrite);

                    long length = stream.Length;

                    var entries = new Dictionary<ulong, Entry>();

                    using (var br = new BinaryReader(stream, Encoding.UTF8, true))
                    {
                        if (length < 28 || br.ReadInt32() != PackageMagic)
                        {
                            Console.WriteLine("[Bridge] uop: {0} is not a Mythic package", path);
                            stream.Dispose();
                            return null;
                        }

                        br.ReadInt32();  // version
                        br.ReadUInt32(); // signature

                        long nextBlock = br.ReadInt64();

                        br.ReadInt32(); // block capacity
                        br.ReadInt32(); // declared file count

                        while (nextBlock > 0)
                        {
                            // A block header is 12 bytes. Anything that does not leave room for
                            // one is a corrupt or cyclic chain, and this is where it stops.
                            if (nextBlock + 12 > length)
                                break;

                            stream.Seek(nextBlock, SeekOrigin.Begin);

                            int filesCount = br.ReadInt32();
                            long following = br.ReadInt64();

                            if (filesCount < 0
                                || nextBlock + 12 + ((long)filesCount * BlockEntryBytes) > length)
                            {
                                break;
                            }

                            for (int i = 0; i < filesCount; i++)
                            {
                                long offset = br.ReadInt64();
                                int headerLength = br.ReadInt32();
                                int compressedLength = br.ReadInt32();
                                int decompressedLength = br.ReadInt32();
                                ulong hash = br.ReadUInt64();

                                br.ReadUInt32(); // adler32

                                short flag = br.ReadInt16();

                                if (offset <= 0 || headerLength < 0 || compressedLength <= 0)
                                    continue;

                                if (decompressedLength <= 0 || decompressedLength > MaxPayloadBytes)
                                    continue;

                                long at = offset + headerLength;

                                // The check FileIndex.Seek is missing, in the place it matters
                                // here too: that the record ENDS inside the file, not merely that
                                // it starts inside it (§4.5).
                                if (at < 0 || at + compressedLength > length)
                                    continue;

                                if (entries.Count >= MaxEntries)
                                    break;

                                // First writer wins. Nothing on this client produces a collision
                                // — measured: no hash appears in two packages, and none twice in
                                // one — and if a patched client ever did, taking the first is the
                                // answer that does not depend on chain order.
                                if (!entries.ContainsKey(hash))
                                    entries[hash] = new Entry
                                    {
                                        At = at,
                                        CompressedLength = compressedLength,
                                        DecompressedLength = decompressedLength,
                                        Flag = flag
                                    };
                            }

                            if (following <= nextBlock)
                                break; // a chain that does not move forward is a loop

                            nextBlock = following;
                        }
                    }

                    return new Package(path, stream, entries);
                }
                catch (Exception e)
                {
                    Console.WriteLine("[Bridge] uop: cannot open {0}: {1}: {2}",
                        path, e.GetType().Name, e.Message);

                    if (stream != null)
                    {
                        try
                        {
                            stream.Dispose();
                        }
                        catch
                        {
                            // Closing a read-only handle.
                        }
                    }

                    return null;
                }
            }

            public bool Has(ulong hash)
            {
                return _entries.ContainsKey(hash);
            }

            /// <summary>
            ///     The bytes behind one entry, decompressed. False with a reason is the ordinary
            ///     answer for "this package does not hold it".
            /// </summary>
            public bool TryRead(ulong hash, out byte[] payload, out string reason)
            {
                payload = null;
                reason = null;

                Entry entry;

                if (!_entries.TryGetValue(hash, out entry))
                {
                    reason = "not in " + System.IO.Path.GetFileName(Path);
                    return false;
                }

                byte[] raw;

                try
                {
                    _stream.Seek(entry.At, SeekOrigin.Begin);

                    raw = new byte[entry.CompressedLength];

                    if (!Fill(_stream, raw, raw.Length))
                    {
                        // The §4.5 failure, in our own code this time: a short read that nobody
                        // checked is how the library ends up decoding the previous asset.
                        reason = "record is shorter than the index claims";
                        return false;
                    }
                }
                catch (Exception e)
                {
                    reason = "read failed: " + e.GetType().Name;
                    return false;
                }

                if (entry.Flag != 1)
                {
                    if (raw.Length != entry.DecompressedLength)
                    {
                        reason = "stored record is " + raw.Length + " bytes, not the declared "
                                 + entry.DecompressedLength;
                        return false;
                    }

                    payload = raw;
                    return true;
                }

                return TryInflate(raw, entry.DecompressedLength, out payload, out reason);
            }

            public void Dispose()
            {
                try
                {
                    _stream.Dispose();
                }
                catch
                {
                    // Closing a read-only handle. Nothing useful is left to do.
                }
            }
        }

        private static bool Fill(Stream stream, byte[] into, int count)
        {
            int read = 0;

            while (read < count)
            {
                int n = stream.Read(into, read, count - read);

                if (n <= 0)
                    return false;

                read += n;
            }

            return true;
        }

        /// <summary>
        ///     zlib, which .NET Framework 4.8 does not expose — only raw deflate. The two-byte
        ///     zlib header is checked and skipped rather than assumed, because handing a
        ///     <c>DeflateStream</c> a stream that is not deflate produces garbage as readily as an
        ///     exception, and the trailing adler32 is left to the length check below: a stream
        ///     that inflates to exactly the declared number of bytes did not silently truncate.
        /// </summary>
        private static bool TryInflate(byte[] raw, int declared, out byte[] payload, out string reason)
        {
            payload = null;
            reason = null;

            if (raw.Length < 3)
            {
                reason = "compressed record is too short to be zlib";
                return false;
            }

            int cmf = raw[0];
            int flg = raw[1];

            if ((cmf & 0x0F) != 8 || (((cmf << 8) + flg) % 31) != 0 || (flg & 0x20) != 0)
            {
                reason = "compressed record is not a zlib stream";
                return false;
            }

            try
            {
                var output = new byte[declared];

                using (var source = new MemoryStream(raw, 2, raw.Length - 2, false))
                using (var inflate = new DeflateStream(source, CompressionMode.Decompress))
                {
                    int read = 0;

                    while (read < declared)
                    {
                        int n = inflate.Read(output, read, declared - read);

                        if (n <= 0)
                            break;

                        read += n;
                    }

                    if (read != declared)
                    {
                        reason = "inflated " + read + " bytes, not the declared " + declared;
                        return false;
                    }

                    // One more byte would mean the record is longer than its own header says,
                    // which is a different file from the one we were promised.
                    if (inflate.ReadByte() != -1)
                    {
                        reason = "inflated past the declared " + declared + " bytes";
                        return false;
                    }
                }

                payload = output;
                return true;
            }
            catch (Exception e)
            {
                reason = "inflate failed: " + e.GetType().Name;
                return false;
            }
        }

        // ── the payload ──────────────────────────────────────────────────────────────────────

        /// <summary>One decoded frame: ARGB1555 in our own array, no <c>Bitmap</c> anywhere.</summary>
        public sealed class Pixels
        {
            public int Width;
            public int Height;
            public int CenterX;
            public int CenterY;
            public ushort[] Argb1555;
        }

        /// <summary>
        ///     One action of one body — every direction of it, concatenated.
        ///
        ///     The legacy files address a frame as <c>index + action * 5 + direction</c>; a UOP
        ///     group file holds the whole action in one record and the directions are equal-length
        ///     runs inside its frame table. So <see cref="DirectionAt"/> is where "direction 1" is
        ///     turned into a frame number, and it is integer division exactly as the reference
        ///     implementations do it — see the note there for the nine bodies where that matters.
        /// </summary>
        public sealed class Group
        {
            private readonly byte[] _buf;
            private readonly int _dataStart;

            public readonly int FrameCount;
            public readonly int Body;

            private Group(byte[] buf, int body, int frameCount, int dataStart)
            {
                _buf = buf;
                Body = body;
                FrameCount = frameCount;
                _dataStart = dataStart;
            }

            public static bool TryOpen(byte[] buf, int expectedBody, out Group group, out string reason)
            {
                group = null;
                reason = null;

                if (buf == null || buf.Length < 40)
                {
                    reason = "payload is too short to carry a header";
                    return false;
                }

                if (BitConverter.ToInt32(buf, 0) != PayloadMagic)
                {
                    reason = "payload is not an AMOU animation record";
                    return false;
                }

                int body = BitConverter.ToInt32(buf, 12);

                // The container said which body this is, by the name it was stored under; the
                // payload says it again. They agree on every record of this client, and the day
                // they do not is the day something is being read that was not asked for.
                if (body != expectedBody)
                {
                    reason = "payload declares body " + body + ", not " + expectedBody;
                    return false;
                }

                int frameCount = BitConverter.ToInt32(buf, 32);
                int dataStart = BitConverter.ToInt32(buf, 36);

                if (frameCount <= 0 || frameCount > BridgeAssetValidator.MaxAnimFrames)
                {
                    reason = "payload declares " + frameCount + " frames";
                    return false;
                }

                if (dataStart < 40 || dataStart > buf.Length)
                {
                    reason = "frame table starts at " + dataStart + " of " + buf.Length;
                    return false;
                }

                if ((long)dataStart + ((long)frameCount * FrameRowBytes) > buf.Length)
                {
                    reason = "frame table of " + frameCount + " rows runs past the record";
                    return false;
                }

                group = new Group(buf, body, frameCount, dataStart);
                return true;
            }

            /// <summary>
            ///     Which frame of this action faces a given direction.
            ///
            ///     Five directions share the action's frames equally, so direction *d* starts at
            ///     <c>d * (FrameCount / 5)</c>. On nine of this client's 244 UOP bodies the frame
            ///     count is **not** a multiple of five (41, 42, 46…), and integer division then
            ///     lands a direction or so early in the run. That is what ClassicUO does, it is
            ///     the right trade, and the reason is §4.8's: the failure being guarded against is
            ///     a picture of the **wrong creature**, and this cannot produce one — the worst
            ///     case is the right creature at a slightly different angle, on nine bodies, where
            ///     refusing them instead would lose nine creatures outright.
            /// </summary>
            public int DirectionAt(int direction)
            {
                int perDirection = FrameCount / 5;

                if (perDirection <= 0)
                    return direction == 0 ? 0 : -1;

                if (direction < 0 || direction > 4)
                    return -1;

                int at = direction * perDirection;

                return at < FrameCount ? at : -1;
            }

            /// <summary>
            ///     Decodes one frame, bounding every read against the record and every write
            ///     against the bitmap.
            ///
            ///     The run loop is <c>Ultima.Frame</c>'s, with the two bounds it does not have.
            ///     <c>Frame</c> writes through a <c>LockBits</c> pointer whose origin comes from
            ///     two signed shorts in the file and never checks where a run lands; here a run
            ///     that would leave the bitmap, or read past the record, refuses the frame. Across
            ///     every UOP body on a stock client that refuses nothing that carries art.
            ///
            ///     A 0×0 frame returns false with <paramref name="empty"/> set: the legacy decoder
            ///     treats that as no art rather than as damage, and so must this, or body 286
            ///     would be logged as a defect on every scan.
            /// </summary>
            public bool TryDecode(int index, out Pixels pixels, out bool empty, out string reason)
            {
                pixels = null;
                empty = false;
                reason = null;

                if (index < 0 || index >= FrameCount)
                {
                    reason = "frame " + index + " of " + FrameCount;
                    return false;
                }

                int row = _dataStart + (index * FrameRowBytes);

                long at = (long)row + (uint)BitConverter.ToInt32(_buf, row + 12);

                if (at < 0 || at + PaletteBytes + 8 > _buf.Length)
                {
                    reason = "frame " + index + " points outside the record";
                    return false;
                }

                int pixelAt = (int)at;

                int centerX = BitConverter.ToInt16(_buf, pixelAt + PaletteBytes);
                int centerY = BitConverter.ToInt16(_buf, pixelAt + PaletteBytes + 2);
                int width = BitConverter.ToUInt16(_buf, pixelAt + PaletteBytes + 4);
                int height = BitConverter.ToUInt16(_buf, pixelAt + PaletteBytes + 6);

                if (width <= 0 || height <= 0)
                {
                    empty = true;
                    reason = "frame " + index + " is " + width + "x" + height;
                    return false;
                }

                if (width > BridgeAssetValidator.MaxArtDimension
                    || height > BridgeAssetValidator.MaxArtDimension)
                {
                    reason = "frame " + index + " declares " + width + "x" + height;
                    return false;
                }

                var palette = new ushort[0x100];

                for (int i = 0; i < palette.Length; i++)
                {
                    // The library's own xor: the stored entry has its alpha bit clear and every
                    // palette colour is opaque. A pixel no run covers stays zero, which is how a
                    // sprite keeps its transparent background.
                    palette[i] = (ushort)(BitConverter.ToUInt16(_buf, pixelAt + (i * 2)) ^ 0x8000);
                }

                var canvas = new ushort[width * height];

                int p = pixelAt + PaletteBytes + 8;

                int xBase = centerX - 0x200;
                int yBase = (centerY + height) - 0x200;

                while (true)
                {
                    if (p + 4 > _buf.Length)
                    {
                        reason = "frame " + index + " has no terminator inside the record";
                        return false;
                    }

                    int header = BitConverter.ToInt32(_buf, p);
                    p += 4;

                    if (header == 0x7FFF7FFF)
                        break;

                    header ^= DoubleXor;

                    int x = ((header >> 22) & 0x3FF) + xBase;
                    int y = ((header >> 12) & 0x3FF) + yBase;
                    int run = header & 0xFFF;

                    if (run == 0)
                        continue;

                    if (p + run > _buf.Length)
                    {
                        reason = "frame " + index + " has a run past the end of the record";
                        return false;
                    }

                    if (y < 0 || y >= height || x < 0 || x + run > width)
                    {
                        reason = "frame " + index + " has a run at " + x + "," + y + " of "
                                 + run + " outside " + width + "x" + height;
                        return false;
                    }

                    int cursor = (y * width) + x;

                    for (int i = 0; i < run; i++)
                        canvas[cursor + i] = palette[_buf[p + i]];

                    p += run;
                }

                pixels = new Pixels
                {
                    Width = width,
                    Height = height,
                    CenterX = centerX,
                    CenterY = centerY,
                    Argb1555 = canvas
                };

                return true;
            }
        }
    }
}