using System.Buffers;
using System.Buffers.Text;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace IdentityShroud.Core.Messages;

// https://www.rfc-editor.org/rfc/rfc7517.html


public class JsonWebKey
{
    [JsonPropertyName("kty")]
    public string KeyType { get; set; } = "RSA";
    
    // Common values sig(nature) enc(ryption)
    [JsonPropertyName("use")]
    public string? Use { get; set; } = "sig"; // "sig" for signature, "enc" for encryption
    
    // Per standard this field is optional, commented out for now as it seems not 
    // have any good use in an identity server. Anyone validating tokens should use
    // the algorithm specified in the header of the token.
    // [JsonPropertyName("alg")]
    // public string? Algorithm { get; set; } = "RS256";
    
    [JsonPropertyName("kid")]
    public required string KeyId { get; set; }
    
    // RSA Public Key Components
    [JsonPropertyName("n")]
    public string? Modulus { get; set; }
    
    [JsonPropertyName("e")]
    public string? Exponent { get; set; }
    
    // ECdsa
    public string? Curve { get; set; }
    [JsonConverter(typeof(Base64UrlConverter))]
    public byte[]? X { get; set; }
    [JsonConverter(typeof(Base64UrlConverter))]
    public byte[]? Y { get; set; }
    
    // Optional fields
    // [JsonPropertyName("x5c")]
    // [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    // public List<string>? X509CertificateChain { get; set; }
    //
    // [JsonPropertyName("x5t")]
    // [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    // public string? X509CertificateThumbprint { get; set; }    
}

public class Base64UrlConverter : JsonConverter<byte[]>
{
    public override byte[] Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        // GetValueSpan gives you the raw UTF-8 bytes of the JSON string value
        if (reader.HasValueSequence)
        {
            var valueSequence = reader.ValueSequence.ToArray();
            return Base64Url.DecodeFromUtf8(valueSequence);
        }
        return Base64Url.DecodeFromUtf8(reader.ValueSpan);
    }

    public override void Write(Utf8JsonWriter writer, byte[] value, JsonSerializerOptions options)
    {
        int encodedLength = Base64Url.GetEncodedLength(value.Length);
        Span<byte> buffer = encodedLength <= 256 ? stackalloc byte[encodedLength] : new byte[encodedLength];
        Base64Url.EncodeToUtf8(value, buffer);
        writer.WriteStringValue(buffer);
    }
}