using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace Lskj.AgentBridge
{
    public static class BridgeRequestParser
    {
        private static readonly ISet<string> AllowedProperties =
            new HashSet<string>(new[]
            {
                "protocolVersion",
                "requestId",
                "correlationId",
                "clientSessionId",
                "sessionScopeToken",
                "method",
                "payload",
                "uatGrant"
            }, StringComparer.Ordinal);

        public static BridgeRequest Parse(string json)
        {
            if (string.IsNullOrWhiteSpace(json))
                throw new JsonSerializationException("桥请求 JSON 不能为空。");
            JObject root;
            using (StringReader text = new StringReader(json))
            using (StrictJsonTextReader reader = new StrictJsonTextReader(text))
            {
                root = JObject.Load(reader, new JsonLoadSettings
                {
                    CommentHandling = CommentHandling.Ignore,
                    LineInfoHandling = LineInfoHandling.Ignore,
                    DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error
                });
                if (reader.Read())
                    throw new JsonSerializationException("桥请求包含多个 JSON 根值。");
            }
            foreach (JProperty property in root.Properties())
            {
                if (!AllowedProperties.Contains(property.Name))
                    throw new JsonSerializationException(
                        "桥请求包含未知字段：" + property.Name);
            }
            RequireStringWhenPresent(root, "protocolVersion");
            RequireStringWhenPresent(root, "requestId");
            RequireStringWhenPresent(root, "correlationId");
            RequireStringWhenPresent(root, "clientSessionId");
            RequireStringWhenPresent(root, "sessionScopeToken");
            RequireStringWhenPresent(root, "method");
            JToken payload = root["payload"];
            if (payload != null && payload.Type != JTokenType.Object)
                throw new JsonSerializationException("桥请求 payload 必须是 JSON 对象。");
            JToken uatGrant = root["uatGrant"];
            if (uatGrant != null)
            {
                JObject grant = uatGrant as JObject;
                if (grant == null)
                    throw new JsonSerializationException(
                        "桥请求 uatGrant 必须是 JSON 对象。");
                ISet<string> grantFields = new HashSet<string>(
                    new[] { "authorizationId", "caseCode", "token" },
                    StringComparer.Ordinal);
                foreach (JProperty property in grant.Properties())
                {
                    if (!grantFields.Contains(property.Name))
                        throw new JsonSerializationException(
                            "桥请求 uatGrant 包含未知字段："
                            + property.Name);
                }
                if (grant.Properties().Count() != 3)
                    throw new JsonSerializationException(
                        "桥请求 uatGrant 必须完整包含三个字段。");
                RequireStringWhenPresent(grant, "authorizationId");
                RequireStringWhenPresent(grant, "caseCode");
                RequireStringWhenPresent(grant, "token");
            }
            BridgeRequest request = root.ToObject<BridgeRequest>();
            if (request == null)
                throw new JsonSerializationException("桥请求无法反序列化。");
            return request;
        }

        private static void RequireStringWhenPresent(JObject root, string name)
        {
            JToken value = root[name];
            if (value != null && value.Type != JTokenType.String)
                throw new JsonSerializationException(
                    "桥请求字段必须是字符串：" + name);
        }

        private sealed class StrictJsonTextReader : JsonTextReader
        {
            public StrictJsonTextReader(TextReader reader)
                : base(reader)
            {
                DateParseHandling = DateParseHandling.None;
                FloatParseHandling = FloatParseHandling.Decimal;
                MaxDepth = 64;
                SupportMultipleContent = false;
            }

            public override bool Read()
            {
                bool available = base.Read();
                if (available && TokenType == JsonToken.Comment)
                    throw new JsonReaderException("桥请求不允许 JSON 注释。");
                return available;
            }
        }
    }
}