using System.Runtime.InteropServices;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization.Metadata;

namespace Shared.Models.Templates
{
    public static class UtilsTpl
    {
        #region HtmlEncode
        public static void HtmlEncode(ReadOnlySpan<char> value, StringBuilder sb)
        {
            foreach (var c in value)
            {
                switch (c)
                {
                    case '<': sb.Append("&lt;"); break;
                    case '>': sb.Append("&gt;"); break;
                    case '&': sb.Append("&amp;"); break;
                    case '"': sb.Append("&quot;"); break;
                    case '\'': sb.Append("&#39;"); break;
                    default: sb.Append(c); break;
                }
            }
        }
        #endregion

        #region WriteJson
        public static void WriteJson<T>(StringBuilder sb, in T value, JsonTypeInfo<T> options)
        {
            using (var msm = PoolInvk.msm.GetStream())
            {
                using (var writer = new Utf8JsonWriter((Stream)msm, new JsonWriterOptions
                {
                    Indented = false,
                    SkipValidation = true
                }))
                {
                    JsonSerializer.Serialize(writer, value, options);
                }

                if (msm.TryGetBuffer(out ArraySegment<byte> buffer))
                {
                    ReadOnlySpan<byte> utf8 = buffer.AsSpan(0, (int)msm.Length);

                    int neededChars = Encoding.UTF8.GetCharCount(utf8);

                    if (neededChars < 512)
                    {
                        Span<char> stackChars = stackalloc char[neededChars];
                        int charsWritten = Encoding.UTF8.GetChars(utf8, stackChars);
                        if (charsWritten > 0)
                            sb.Append(stackChars.Slice(0, charsWritten));
                    }
                    else
                    {
                        unsafe
                        {
                            nint rentedJsonPtr = (nint)NativeMemory.Alloc((nuint)neededChars, (nuint)sizeof(char));

                            try
                            {
                                Span<char> rentedChars = new Span<char>((void*)rentedJsonPtr, neededChars);
                                int charsWritten = Encoding.UTF8.GetChars(utf8, rentedChars);
                                if (charsWritten > 0)
                                    sb.Append(rentedChars.Slice(0, charsWritten));
                            }
                            finally
                            {
                                NativeMemory.Free((void*)rentedJsonPtr);
                            }
                        }
                    }
                }
            }
        }
        #endregion
    }
}