using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;

namespace TrelloIntegration
{
  /// <summary>
  /// Trello-Karten-Client für WinForms-Anwendungen (.NET Framework 4.8, C# 7.3)
  /// Erstellt Karten via Trello REST API über HttpClient.
  /// </summary>
  public class TrelloCardClient : IDisposable
  {
    private readonly string _apiKey;
    private readonly string _token;
    private readonly HttpClient _httpClient;

    /// <summary>
    /// Initialisiert einen neuen TrelloCardClient.
    /// </summary>
    /// <param name="apiKey">Trello API Key</param>
    /// <param name="token">Trello API Token mit write-Recht</param>
    public TrelloCardClient(string apiKey, string token)
    {
      _apiKey = apiKey ?? throw new ArgumentNullException(nameof(apiKey));
      _token = token ?? throw new ArgumentNullException(nameof(token));

      _httpClient = new HttpClient
      {
        BaseAddress = new Uri("https://api.trello.com/1/")
      };
    }

    /// <summary>
    /// Erstellt eine neue Trello-Karte asynchron und gibt die Roh-JSON-Antwort zurück.
    /// </summary>
    /// <param name="options">Konfiguration der Karte (Name, Liste, Beschreibung, Labels, DueDate, StartDate)</param>
    /// <returns>Antwort-JSON als String (enthaltend die erstellte Karte)</returns>
    public async Task<string> CreateCardAsync(CreateCardOptions options)
    {
      ValidateOptions(options);

      var values = new Dictionary<string, string>
      {
        ["key"] = _apiKey,
        ["token"] = _token,
        ["idList"] = options.IdList,
        ["name"] = options.Name
      };

      if (!string.IsNullOrWhiteSpace(options.Desc))
        values["desc"] = options.Desc;

      if (!string.IsNullOrWhiteSpace(options.Pos))
        values["pos"] = options.Pos;

      if (options.IdLabels != null && options.IdLabels.Count > 0)
        values["idLabels"] = string.Join(",", options.IdLabels);

      if (options.DueDate.HasValue)
        values["due"] = options.DueDate.Value.ToUniversalTime().ToString("yyyy-MM-ddTHH:mm");

      if (options.StartDate.HasValue)
        values["start"] = options.StartDate.Value.ToUniversalTime().ToString("yyyy-MM-ddTHH:mm");

      var content = new FormUrlEncodedContent(values);
      var response = await _httpClient.PostAsync("cards", content);

      var responseBody = await response.Content.ReadAsStringAsync();

      if (!response.IsSuccessStatusCode)
      {
        throw new HttpRequestException(
            $"Trello API Fehler {response.StatusCode}: {responseBody}");
      }

      return responseBody;
    }

    /// <summary>
    /// Erstellt eine Karte und gibt das Ergebnis als TrelloCard-Objekt zurück.
    /// </summary>
    public async Task<TrelloCard> CreateCardAndParseAsync(CreateCardOptions options)
    {
      var json = await CreateCardAsync(options);
      return ParseTrelloCard(json);
    }

    private static TrelloCard ParseTrelloCard(string json)
    {
      // Minimaler Parser ohne System.Text.Json (für .NET Framework 4.8)
      // Extrahiert die wichtigsten Felder aus der JSON-Antwort
      var card = new TrelloCard();

      card.Id = ExtractJsonValue(json, "id");
      card.Name = ExtractJsonValue(json, "name");
      card.Desc = ExtractJsonValue(json, "desc");
      card.IdList = ExtractJsonValue(json, "idList");
      card.ShortUrl = ExtractJsonValue(json, "shortUrl");

      var due = ExtractJsonValue(json, "due");
      if (!string.IsNullOrWhiteSpace(due))
        if (DateTime.TryParse(due, out var dtDue)) card.DueDate = dtDue;
        else card.DueDate = null;

      var start = ExtractJsonValue(json, "start");
      if (!string.IsNullOrWhiteSpace(start))
        if (DateTime.TryParse(start, out var dtStart)) card.StartDate = dtStart;
        else card.StartDate = null;

      return card;
    }

    private static string ExtractJsonValue(string json, string key)
    {
      // Einfacher JSON-String-Extractor für "key": "value"
      var pattern = "\"" + key + "\"\\s*:\\s*\"";
      var startIndex = json.IndexOf(pattern, StringComparison.Ordinal);
      if (startIndex < 0)
        return null;

      startIndex += pattern.Length;
      var endIndex = json.IndexOf("\"", startIndex);
      if (endIndex < 0)
        return null;

      return json.Substring(startIndex, endIndex - startIndex);
    }

    private void ValidateOptions(CreateCardOptions options)
    {
      if (options == null)
        throw new ArgumentNullException(nameof(options));

      if (string.IsNullOrWhiteSpace(options.Name))
        throw new ArgumentException("Name ist erforderlich.", nameof(options.Name));

      if (string.IsNullOrWhiteSpace(options.IdList))
        throw new ArgumentException("IdList ist erforderlich.", nameof(options.IdList));
    }

    /// <summary>
    /// Gibt die Ressourcen des Clients frei (empiohlen).
    /// </summary>
    public void Dispose()
    {
      _httpClient?.Dispose();
    }
  }
}