using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
using UnityEngine;
using UnityEngine.Networking;
using Vanguard.Api.Contracts;
using Vanguard.App;
using Vanguard.Auth;

namespace Vanguard.Api
{
    /// <summary>
    /// HTTP/JSON клиент мета-API. UnityWebRequest работает только на главном
    /// потоке, поэтому все вызовы должны идти из Unity-кода; continuation после
    /// await тоже возвращается на главный поток.
    /// </summary>
    public sealed class ApiClient
    {
        private static readonly JsonSerializerSettings JsonSettings = new JsonSerializerSettings
        {
            ContractResolver = new CamelCasePropertyNamesContractResolver(),
            NullValueHandling = NullValueHandling.Ignore,
            DateParseHandling = DateParseHandling.DateTimeOffset,
        };

        private readonly AppConfig _config;
        private readonly TokenStore _tokens;

        public ApiClient(AppConfig config, TokenStore tokens)
        {
            _config = config;
            _tokens = tokens;
        }

        public string BaseUrl => _config.ServerBaseUrl;

        public async Task<T> GetAsync<T>(string path, bool authenticated = true)
        {
            var body = await SendAsync("GET", path, null, authenticated);
            if (string.IsNullOrEmpty(body))
                return default;

            return JsonConvert.DeserializeObject<T>(body, JsonSettings);
        }

        public async Task<T> PostAsync<T>(string path, object body, bool authenticated = true)
        {
            var response = await SendAsync("POST", path, body, authenticated);
            if (string.IsNullOrEmpty(response))
                return default;

            return JsonConvert.DeserializeObject<T>(response, JsonSettings);
        }

        public Task PostAsync(string path, object body, bool authenticated = true) =>
            SendAsync("POST", path, body, authenticated);

        private async Task<string> SendAsync(
            string method,
            string path,
            object body,
            bool authenticated)
        {
            var url = _config.ServerBaseUrl + path;

            using (var request = new UnityWebRequest(url, method))
            {
                request.downloadHandler = new DownloadHandlerBuffer();
                request.timeout = Mathf.CeilToInt(_config.RequestTimeoutSeconds);
                request.SetRequestHeader("Accept", "application/json");

                if (body != null)
                {
                    var json = JsonConvert.SerializeObject(body, JsonSettings);
                    request.uploadHandler = new UploadHandlerRaw(Encoding.UTF8.GetBytes(json));
                    request.SetRequestHeader("Content-Type", "application/json");
                }

                if (authenticated && !string.IsNullOrEmpty(_tokens.AccessToken))
                    request.SetRequestHeader("Authorization", "Bearer " + _tokens.AccessToken);

                await SendRequestAsync(request);

                var text = request.downloadHandler != null ? request.downloadHandler.text : string.Empty;

                if (request.responseCode == 0)
                {
                    var reason = string.IsNullOrEmpty(request.error)
                        ? "Нет связи с сервером."
                        : request.error;
                    throw new ApiException(0, "network", reason);
                }

                if (request.responseCode >= 400)
                    throw ParseError(request.responseCode, text);

                return text;
            }
        }

        private static Task SendRequestAsync(UnityWebRequest request)
        {
            var completion = new TaskCompletionSource<bool>();
            var operation = request.SendWebRequest();
            operation.completed += _ => completion.TrySetResult(true);
            return completion.Task;
        }

        private static ApiException ParseError(long statusCode, string body)
        {
            ApiErrorDto error = null;
            try
            {
                if (!string.IsNullOrWhiteSpace(body))
                    error = JsonConvert.DeserializeObject<ApiErrorDto>(body, JsonSettings);
            }
            catch (JsonException)
            {
                // Ниже отдадим общий текст: тело не JSON.
            }

            if (error == null)
            {
                return new ApiException(
                    statusCode,
                    "http." + statusCode,
                    "Сервер вернул ошибку " + statusCode + ".");
            }

            var violations = new List<ApiViolation>();
            if (error.Violations != null)
            {
                foreach (var violation in error.Violations)
                    violations.Add(new ApiViolation(violation.Code, violation.Message));
            }

            var message = string.IsNullOrWhiteSpace(error.Message)
                ? "Сервер вернул ошибку " + statusCode + "."
                : error.Message;

            return new ApiException(statusCode, error.Error, message, violations);
        }
    }
}