using System.Buffers.Binary;
using System.Globalization;
using System.Security.Cryptography;
using System.Text;

namespace SatelliteProvider.Common.Utils;

// AZ-503: pure-C# RFC 9562 (formerly RFC 4122 §4.3) UUIDv5 implementation.
//
// .NET 10 ships Guid.CreateVersion7 but NOT a version-5 builder, so we implement
// the SHA-1-based algorithm here. Onboard `gps-denied-onboard/components/c6_tile_cache/_uuid.py`
// MUST use the same TileNamespace constant and the same algorithm (Python's stdlib
// uuid.uuid5 is identical by construction) so both sides of the wire compute
// byte-identical IDs for the same (z, x, y, source, flight_id) inputs.
//
// Cross-repo namespace coordination: TileNamespace below is THE pinned value.
// Any change here must be paired with the same change on the onboard side; the
// AZ-503 task spec requires this and AC-1 (Python reference vectors) gates it.
public static class Uuidv5
{
    // Pinned cross-repo namespace for tile identity. Must match
    // gps-denied-onboard `c6_tile_cache/_uuid.py:TILE_NAMESPACE`.
    // Chosen as a fresh random UUID (no semantic meaning beyond being a stable
    // 128-bit constant shared between the two repos).
    public static readonly Guid TileNamespace = new("5b8d0c2e-7f1a-4d3b-9c5e-1f3a8e7d2b6c");

    // AZ-505 consolidation: the canonical formula for a tile cell's
    // location_hash. Both TileRepository.GetByTileCoordinatesAsync and
    // TileService.GetInventoryAsync compute it; centralising here means the
    // cross-repo invariant (must byte-match gps-denied-onboard
    // `c6_tile_cache/_uuid.py:location_hash`) only has one source-of-truth in
    // this codebase. Format string is `"{z}/{x}/{y}"` under invariant culture —
    // matches the Python side's f-string output.
    public static Guid LocationHashForTile(int tileZoom, int tileX, int tileY)
    {
        var name = string.Create(CultureInfo.InvariantCulture, $"{tileZoom}/{tileX}/{tileY}");
        return Create(TileNamespace, name);
    }

    public static Guid Create(Guid namespaceId, string name)
    {
        ArgumentNullException.ThrowIfNull(name);

        // Namespace UUIDs are concatenated as 16 bytes in network (big-endian)
        // order. .NET's Guid.ToByteArray() returns mixed-endian (RFC 4122
        // "Microsoft" layout), so we cannot use it directly — we must rebuild
        // the byte array in big-endian order, matching what Python's
        // uuid.UUID.bytes produces.
        Span<byte> namespaceBytes = stackalloc byte[16];
        WriteGuidBigEndian(namespaceId, namespaceBytes);

        var nameBytes = Encoding.UTF8.GetBytes(name);

        Span<byte> hash = stackalloc byte[20];
        var buffer = new byte[16 + nameBytes.Length];
        namespaceBytes.CopyTo(buffer);
        Buffer.BlockCopy(nameBytes, 0, buffer, 16, nameBytes.Length);
        if (!SHA1.TryHashData(buffer, hash, out _))
        {
            throw new InvalidOperationException("SHA-1 hash computation failed.");
        }

        // Take first 16 bytes, set version to 5 (upper nibble of byte 6) and
        // variant to RFC 4122 (upper two bits of byte 8 set to `10`).
        Span<byte> uuidBytes = stackalloc byte[16];
        hash[..16].CopyTo(uuidBytes);
        uuidBytes[6] = (byte)((uuidBytes[6] & 0x0F) | 0x50);
        uuidBytes[8] = (byte)((uuidBytes[8] & 0x3F) | 0x80);

        return ReadGuidBigEndian(uuidBytes);
    }

    private static void WriteGuidBigEndian(Guid value, Span<byte> destination)
    {
        Span<byte> mixed = stackalloc byte[16];
        value.TryWriteBytes(mixed);
        // Convert from Microsoft mixed-endian (first 3 fields little-endian) to
        // network (big-endian) order.
        BinaryPrimitives.WriteUInt32BigEndian(destination[..4], BinaryPrimitives.ReadUInt32LittleEndian(mixed[..4]));
        BinaryPrimitives.WriteUInt16BigEndian(destination.Slice(4, 2), BinaryPrimitives.ReadUInt16LittleEndian(mixed.Slice(4, 2)));
        BinaryPrimitives.WriteUInt16BigEndian(destination.Slice(6, 2), BinaryPrimitives.ReadUInt16LittleEndian(mixed.Slice(6, 2)));
        mixed.Slice(8, 8).CopyTo(destination.Slice(8, 8));
    }

    private static Guid ReadGuidBigEndian(ReadOnlySpan<byte> bigEndian)
    {
        Span<byte> mixed = stackalloc byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(mixed[..4], BinaryPrimitives.ReadUInt32BigEndian(bigEndian[..4]));
        BinaryPrimitives.WriteUInt16LittleEndian(mixed.Slice(4, 2), BinaryPrimitives.ReadUInt16BigEndian(bigEndian.Slice(4, 2)));
        BinaryPrimitives.WriteUInt16LittleEndian(mixed.Slice(6, 2), BinaryPrimitives.ReadUInt16BigEndian(bigEndian.Slice(6, 2)));
        bigEndian.Slice(8, 8).CopyTo(mixed.Slice(8, 8));
        return new Guid(mixed);
    }
}
