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

namespace MediaBrowser.Common.Json.Converters
{
    /// <summary>
    /// Parse JSON string as nullable long.
    /// Javascript does not support 64-bit integers.
    /// </summary>
    public class JsonNullableInt64Converter : JsonConverter<long?>
    {
        /// <summary>
        /// Read JSON string as int64.
        /// </summary>
        /// <param name="reader"><see cref="Utf8JsonReader"/>.</param>
        /// <param name="type">Type.</param>
        /// <param name="options">Options.</param>
        /// <returns>Parsed value.</returns>
        public override long? Read(ref Utf8JsonReader reader, Type type, JsonSerializerOptions options)
        {
            if (reader.TokenType == JsonTokenType.Null)
            {
                return null;
            }

            if (reader.TokenType == JsonTokenType.String)
            {
                // try to parse number directly from bytes
                var span = reader.HasValueSequence ? reader.ValueSequence.ToArray() : reader.ValueSpan;
                if (Utf8Parser.TryParse(span, out long number, out var bytesConsumed) && span.Length == bytesConsumed)
                {
                    return number;
                }

                var stringValue = reader.GetString().AsSpan();

                // value is null or empty, just return null.
                if (stringValue.IsEmpty)
                {
                    return null;
                }

                // try to parse from a string if the above failed, this covers cases with other escaped/UTF characters
                if (long.TryParse(stringValue, out number))
                {
                    return number;
                }
            }

            // fallback to default handling
            return reader.GetInt64();
        }

        /// <summary>
        /// Write long to JSON long.
        /// </summary>
        /// <param name="writer"><see cref="Utf8JsonWriter"/>.</param>
        /// <param name="value">Value to write.</param>
        /// <param name="options">Options.</param>
        public override void Write(Utf8JsonWriter writer, long? value, JsonSerializerOptions options)
        {
            if (value is null)
            {
                writer.WriteNullValue();
            }
            else
            {
                writer.WriteNumberValue(value.Value);
            }
        }
    }
}