// =============================================================================
// TeslaLauncher — MiniZip
// =============================================================================
// Minimal ZIP extractor for net40: System.IO.Compression.ZipFile/ZipArchive are
// net45+, so they do not exist on the XP-compatible framework. This reads the
// archive via the central directory and supports exactly what the Console's
// install packages use:
//   - compression methods 0 (stored) and 8 (deflate; DeflateStream is net20+)
//   - UTF-8 (general-purpose flag bit 11) or ANSI/CP437 entry names
//   - ZIP64 sizes/offsets/entry counts (archives > 4 GB or > 65535 entries)
// CRC is not verified — archives arrive from our own Console over the
// OFB-encrypted link, and the install already fails loudly on truncation.
// =============================================================================

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

namespace Tesla.Launcher
{
    internal static class MiniZip
    {
        /// <summary>Extracts every entry of <paramref name="zipPath"/> under
        /// <paramref name="destDir"/> (existing files overwritten), reporting
        /// (entriesDone, entriesTotal) after each entry. Entries that would
        /// escape the destination directory (zip-slip) are skipped.</summary>
        public static void ExtractToDirectory(string zipPath, string destDir, Action<int, int> onEntry)
        {
            using (var fs = new FileStream(zipPath, FileMode.Open, FileAccess.Read, FileShare.Read))
            {
                var entries  = ReadCentralDirectory(fs);
                var destRoot = Path.GetFullPath(destDir).TrimEnd('\\');
                int done = 0;
                foreach (var e in entries)
                {
                    ExtractEntry(fs, e, destRoot);
                    done++;
                    if (onEntry != null) onEntry(done, entries.Count);
                }
            }
        }

        private sealed class Entry
        {
            public string Name;
            public int    Method;
            public long   CompressedSize;
            public long   LocalHeaderOffset;
        }

        // ── Central directory ─────────────────────────────────────────────────

        private static List<Entry> ReadCentralDirectory(FileStream fs)
        {
            // End-of-central-directory record: fixed 22 bytes + up to 64K comment.
            long fileLen = fs.Length;
            int  maxScan = (int)Math.Min(fileLen, 22 + 65535);
            var  tail    = new byte[maxScan];
            fs.Seek(fileLen - maxScan, SeekOrigin.Begin);
            ReadExact(fs, tail, maxScan);

            int eocd = -1;
            for (int i = maxScan - 22; i >= 0; i--)
            {
                if (tail[i] == 0x50 && tail[i + 1] == 0x4B &&
                    tail[i + 2] == 0x05 && tail[i + 3] == 0x06) { eocd = i; break; }
            }
            if (eocd < 0) throw new IOException("Not a ZIP archive (no end-of-central-directory record).");

            long eocdPos      = fileLen - maxScan + eocd;
            long totalEntries = BitConverter.ToUInt16(tail, eocd + 10);
            long cdOffset     = BitConverter.ToUInt32(tail, eocd + 16);

            // ZIP64: any maxed-out field means the real values live in the
            // ZIP64 EOCD record, found via the locator 20 bytes before EOCD.
            if (totalEntries == 0xFFFF || cdOffset == 0xFFFFFFFF)
            {
                long locPos = eocdPos - 20;
                if (locPos >= 0)
                {
                    var loc = new byte[20];
                    fs.Seek(locPos, SeekOrigin.Begin);
                    ReadExact(fs, loc, 20);
                    if (loc[0] == 0x50 && loc[1] == 0x4B && loc[2] == 0x06 && loc[3] == 0x07)
                    {
                        long z64Pos = BitConverter.ToInt64(loc, 8);
                        var z64 = new byte[56];
                        fs.Seek(z64Pos, SeekOrigin.Begin);
                        ReadExact(fs, z64, 56);
                        if (!(z64[0] == 0x50 && z64[1] == 0x4B && z64[2] == 0x06 && z64[3] == 0x06))
                            throw new IOException("Corrupt ZIP64 end-of-central-directory record.");
                        totalEntries = BitConverter.ToInt64(z64, 32);
                        cdOffset     = BitConverter.ToInt64(z64, 48);
                    }
                }
            }

            var list = new List<Entry>((int)totalEntries);
            fs.Seek(cdOffset, SeekOrigin.Begin);
            var br = new BinaryReader(fs);   // not disposed — would close fs

            for (long i = 0; i < totalEntries; i++)
            {
                if (br.ReadUInt32() != 0x02014B50)
                    throw new IOException("Corrupt central directory (bad entry signature).");

                br.ReadUInt16();                    // version made by
                br.ReadUInt16();                    // version needed
                ushort flags   = br.ReadUInt16();
                ushort method  = br.ReadUInt16();
                br.ReadUInt32();                    // DOS mod time/date
                br.ReadUInt32();                    // CRC-32
                long comp      = br.ReadUInt32();
                long uncomp    = br.ReadUInt32();
                ushort nameLen    = br.ReadUInt16();
                ushort extraLen   = br.ReadUInt16();
                ushort commentLen = br.ReadUInt16();
                br.ReadUInt16();                    // disk number start
                br.ReadUInt16();                    // internal attributes
                br.ReadUInt32();                    // external attributes
                long lho       = br.ReadUInt32();

                byte[] nameBytes = br.ReadBytes(nameLen);
                byte[] extra     = br.ReadBytes(extraLen);
                if (commentLen > 0) br.ReadBytes(commentLen);

                // ZIP64 extended-information extra field (id 0x0001): 8-byte
                // values present, in order, only for headers that were 0xFFFFFFFF.
                int p = 0;
                while (p + 4 <= extra.Length)
                {
                    ushort id = BitConverter.ToUInt16(extra, p);
                    ushort sz = BitConverter.ToUInt16(extra, p + 2);
                    if (id == 0x0001)
                    {
                        int q = p + 4;
                        if (uncomp == 0xFFFFFFFF && q + 8 <= p + 4 + sz) { uncomp = BitConverter.ToInt64(extra, q); q += 8; }
                        if (comp   == 0xFFFFFFFF && q + 8 <= p + 4 + sz) { comp   = BitConverter.ToInt64(extra, q); q += 8; }
                        if (lho    == 0xFFFFFFFF && q + 8 <= p + 4 + sz) { lho    = BitConverter.ToInt64(extra, q); }
                    }
                    p += 4 + sz;
                }

                bool utf8 = (flags & 0x0800) != 0;
                var name = (utf8 ? Encoding.UTF8 : Encoding.Default).GetString(nameBytes);

                list.Add(new Entry
                {
                    Name              = name,
                    Method            = method,
                    CompressedSize    = comp,
                    LocalHeaderOffset = lho
                });
            }
            return list;
        }

        // ── Entry extraction ──────────────────────────────────────────────────

        private static void ExtractEntry(FileStream fs, Entry e, string destRoot)
        {
            if (string.IsNullOrEmpty(e.Name)) return;

            string destPath;
            try { destPath = Path.GetFullPath(Path.Combine(destRoot, e.Name.Replace('/', '\\'))); }
            catch { return; }   // illegal characters in name — skip

            // Zip-slip protection: never write outside the destination root.
            if (!destPath.StartsWith(destRoot + "\\", StringComparison.OrdinalIgnoreCase)
                && !destPath.Equals(destRoot, StringComparison.OrdinalIgnoreCase))
                return;

            if (e.Name.EndsWith("/") || e.Name.EndsWith("\\"))
            {
                Directory.CreateDirectory(destPath);
                return;
            }

            // Local header: its name/extra lengths can differ from the central
            // directory's, so read them from the local header itself.
            fs.Seek(e.LocalHeaderOffset, SeekOrigin.Begin);
            var lh = new byte[30];
            ReadExact(fs, lh, 30);
            if (!(lh[0] == 0x50 && lh[1] == 0x4B && lh[2] == 0x03 && lh[3] == 0x04))
                throw new IOException("Corrupt local header for entry '" + e.Name + "'.");
            int lNameLen  = BitConverter.ToUInt16(lh, 26);
            int lExtraLen = BitConverter.ToUInt16(lh, 28);
            fs.Seek(lNameLen + lExtraLen, SeekOrigin.Current);

            Directory.CreateDirectory(Path.GetDirectoryName(destPath));
            using (var outFs = File.Create(destPath))
            {
                if (e.Method == 0)          // stored
                {
                    CopyExactly(fs, outFs, e.CompressedSize);
                }
                else if (e.Method == 8)     // deflate
                {
                    var limited = new LimitedReadStream(fs, e.CompressedSize);
                    using (var inflate = new DeflateStream(limited, CompressionMode.Decompress, leaveOpen: true))
                        inflate.CopyTo(outFs);
                }
                else
                {
                    throw new IOException(string.Format(
                        "Unsupported compression method {0} for entry '{1}'.", e.Method, e.Name));
                }
            }
        }

        private static void CopyExactly(Stream src, Stream dst, long count)
        {
            var buffer = new byte[65536];
            while (count > 0)
            {
                int n = src.Read(buffer, 0, (int)Math.Min(buffer.Length, count));
                if (n == 0) throw new IOException("Unexpected end of archive.");
                dst.Write(buffer, 0, n);
                count -= n;
            }
        }

        private static void ReadExact(Stream stream, byte[] buf, int count)
        {
            int off = 0;
            while (off < count)
            {
                int n = stream.Read(buf, off, count - off);
                if (n == 0) throw new IOException("Unexpected end of archive.");
                off += n;
            }
        }

        /// <summary>Caps reads at N bytes of the underlying stream so DeflateStream's
        /// read-ahead cannot consume the next entry's bytes. Does not own the inner
        /// stream.</summary>
        private sealed class LimitedReadStream : Stream
        {
            private readonly Stream _inner;
            private long _remaining;

            public LimitedReadStream(Stream inner, long limit)
            {
                _inner     = inner;
                _remaining = limit;
            }

            public override int Read(byte[] buffer, int offset, int count)
            {
                if (_remaining <= 0) return 0;
                int n = _inner.Read(buffer, offset, (int)Math.Min(count, _remaining));
                _remaining -= n;
                return n;
            }

            public override bool CanRead  => true;
            public override bool CanWrite => false;
            public override bool CanSeek  => false;
            public override void Flush() { }
            public override long Length   => throw new NotSupportedException();
            public override long Position
            {
                get => throw new NotSupportedException();
                set => throw new NotSupportedException();
            }
            public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
            public override void SetLength(long value)                 => throw new NotSupportedException();
            public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
        }
    }
}