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

namespace FileShare_Services.Core
{
    /// <summary>
    /// Binds unified endpoint request models from JSON bodies or query parameters.
    /// </summary>
    internal static class ServiceRequestBinder
    {
        private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
        {
            NumberHandling = JsonNumberHandling.AllowReadingFromString,
        };

        /// <summary>
        /// Bind a JSON request body. Empty bodies are treated as an empty JSON object.
        /// </summary>
        public static T BindBody<T>(ServiceEndpointContext context)
        {
            var json = string.IsNullOrWhiteSpace(context.Body) ? "{}" : context.Body;
            return Deserialize<T>(json, "body");
        }

        /// <summary>
        /// Bind route and query parameters to a request DTO.
        /// </summary>
        public static T BindQuery<T>(ServiceEndpointContext context)
        {
            var values = new Dictionary<string, string>(context.Query, StringComparer.OrdinalIgnoreCase);
            foreach (var routeValue in context.RouteValues)
            {
                values[routeValue.Key] = routeValue.Value;
            }

            var json = JsonSerializer.Serialize(values, JsonOptions);
            return Deserialize<T>(json, "query");
        }

        /// <summary>
        /// 将 JSON 反序列化为目标类型，反序列化失败或结果为 null 时抛出 <see cref="ArgumentException"/>。
        /// </summary>
        /// <typeparam name="T">目标类型。</typeparam>
        /// <param name="json">JSON 字符串。</param>
        /// <param name="source">来源标识（body 或 query），用于异常消息。</param>
        /// <returns>反序列化后的实例。</returns>
        /// <exception cref="ArgumentException">JSON 无法绑定到目标类型时抛出。</exception>
        private static T Deserialize<T>(string json, string source)
        {
            try
            {
                return JsonSerializer.Deserialize<T>(json, JsonOptions)
                    ?? throw new ArgumentException($"Request {source} cannot be bound to {typeof(T).Name}.");
            }
            catch (JsonException ex)
            {
                throw new ArgumentException($"Request {source} cannot be bound to {typeof(T).Name}.", ex);
            }
        }
    }
}