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

namespace Cepis;

/// <summary>
/// Reads any scalar as a string, and a JSON <c>null</c> as the empty string.
/// </summary>
/// <remarks>
/// The API documents every text field as a string and an absent one as
/// <c>""</c>, never null. This converter makes a client that meets a
/// <c>null</c>, or a code sent as a number, degrade to the documented shape
/// instead of throwing: none of those is worth failing a whole lookup over.
/// </remarks>
internal sealed class LenientStringConverter : JsonConverter<string>
{
    public override bool HandleNull => true;

    public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        switch (reader.TokenType)
        {
            case JsonTokenType.String:
                return reader.GetString() ?? "";
            case JsonTokenType.Null:
                return "";
            case JsonTokenType.True:
                return "true";
            case JsonTokenType.False:
                return "false";
            case JsonTokenType.Number:
                var raw = reader.HasValueSequence
                    ? reader.ValueSequence.ToArray()
                    : reader.ValueSpan.ToArray();
                return Encoding.UTF8.GetString(raw);
            default:
                throw new JsonException($"expected a string, got {reader.TokenType}");
        }
    }

    public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options)
    {
        ArgumentNullException.ThrowIfNull(writer);
        writer.WriteStringValue(value);
    }

    public override string ReadAsPropertyName(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) =>
        reader.GetString() ?? "";

    public override void WriteAsPropertyName(Utf8JsonWriter writer, string value, JsonSerializerOptions options)
    {
        ArgumentNullException.ThrowIfNull(writer);
        writer.WritePropertyName(value);
    }
}