using System.ComponentModel.DataAnnotations;
using System.Net;
using System.Net.Http.Json;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Polly;
using Polly.Extensions.Http;

namespace HCFS.SDK;

/// <summary>
/// Main HCFS client for .NET applications.
/// </summary>
/// <remarks>
/// This client provides both synchronous and asynchronous methods for interacting
/// with the HCFS API. It includes built-in caching, retry logic, rate limiting,
/// and comprehensive error handling.
/// 
/// <example>
/// Basic usage:
/// <code>
/// var config = new HCFSConfig
/// {
///     BaseUrl = "https://api.hcfs.dev/v1",
///     ApiKey = "your-api-key"
/// };
/// 
/// using var client = new HCFSClient(config);
/// 
/// // Create a context
/// var context = new Context
/// {
///     Path = "/docs/readme",
///     Content = "Hello, HCFS!",
///     Summary = "Getting started guide"
/// };
/// 
/// var created = await client.CreateContextAsync(context);
/// Console.WriteLine($"Created context: {created.Id}");
/// 
/// // Search contexts
/// var results = await client.SearchContextsAsync("hello world");
/// foreach (var result in results)
/// {
///     Console.WriteLine($"Found: {result.Context.Path} (score: {result.Score:F3})");
/// }
/// </code>
/// </example>
/// </remarks>
public class HCFSClient : IDisposable
{
    private const string SdkVersion = "2.0.0";
    private const string UserAgent = $"hcfs-dotnet/{SdkVersion}";
    
    private readonly HttpClient _httpClient;
    private readonly HCFSConfig _config;
    private readonly IMemoryCache? _cache;
    private readonly ILogger<HCFSClient>? _logger;
    private readonly JsonSerializerOptions _jsonOptions;
    private readonly Dictionary<string, long> _analytics;
    private readonly DateTime _sessionStart;
    private readonly SemaphoreSlim _rateLimitSemaphore;
    
    /// <summary>
    /// Initializes a new instance of the <see cref="HCFSClient"/> class.
    /// </summary>
    /// <param name="config">The client configuration.</param>
    /// <param name="httpClient">Optional HTTP client. If not provided, a new one will be created.</param>
    /// <param name="logger">Optional logger for diagnostic information.</param>
    /// <exception cref="ArgumentNullException">Thrown when config is null.</exception>
    /// <exception cref="ValidationException">Thrown when config is invalid.</exception>
    public HCFSClient(HCFSConfig config, HttpClient? httpClient = null, ILogger<HCFSClient>? logger = null)
    {
        _config = config ?? throw new ArgumentNullException(nameof(config));
        _logger = logger;
        _sessionStart = DateTime.UtcNow;
        _analytics = new Dictionary<string, long>();
        
        // Validate configuration
        ValidateConfig(_config);
        
        // Initialize JSON options
        _jsonOptions = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower,
            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
            Converters = { new JsonStringEnumConverter() }
        };
        
        // Initialize cache if enabled
        if (_config.Cache.Enabled)
        {
            var cacheOptions = new MemoryCacheOptions
            {
                SizeLimit = _config.Cache.MaxSize
            };
            _cache = new MemoryCache(cacheOptions);
        }
        
        // Initialize rate limiting
        _rateLimitSemaphore = new SemaphoreSlim(_config.RateLimit.MaxConcurrentRequests);
        
        // Initialize HTTP client
        _httpClient = httpClient ?? CreateHttpClient();
        
        _logger?.LogInformation("HCFS client initialized with base URL: {BaseUrl}", _config.BaseUrl);
    }
    
    /// <summary>
    /// Checks the API health status.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the health response.</returns>
    public async Task<HealthResponse> HealthCheckAsync(CancellationToken cancellationToken = default)
    {
        var request = new HttpRequestMessage(HttpMethod.Get, "/health");
        return await ExecuteRequestAsync<HealthResponse>(request, cancellationToken);
    }
    
    /// <summary>
    /// Creates a new context.
    /// </summary>
    /// <param name="contextData">The context data to create.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the created context.</returns>
    /// <exception cref="ArgumentNullException">Thrown when contextData is null.</exception>
    /// <exception cref="ValidationException">Thrown when contextData is invalid.</exception>
    public async Task<Context> CreateContextAsync(ContextCreate contextData, CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(contextData);
        
        if (!PathValidator.IsValid(contextData.Path))
        {
            throw new ValidationException($"Invalid context path: {contextData.Path}");
        }
        
        // Normalize path
        var normalized = contextData with { Path = PathValidator.Normalize(contextData.Path) };
        
        var request = new HttpRequestMessage(HttpMethod.Post, "/api/v1/contexts")
        {
            Content = JsonContent.Create(normalized, options: _jsonOptions)
        };
        
        var response = await ExecuteRequestAsync<ApiResponse<Context>>(request, cancellationToken);
        
        // Invalidate relevant cache entries
        InvalidateCache("/api/v1/contexts");
        
        return response.Data;
    }
    
    /// <summary>
    /// Retrieves a context by ID.
    /// </summary>
    /// <param name="contextId">The context ID.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the context.</returns>
    /// <exception cref="ArgumentException">Thrown when contextId is invalid.</exception>
    /// <exception cref="HCFSNotFoundException">Thrown when context is not found.</exception>
    public async Task<Context> GetContextAsync(int contextId, CancellationToken cancellationToken = default)
    {
        if (contextId <= 0)
        {
            throw new ArgumentException("Context ID must be positive", nameof(contextId));
        }
        
        var path = $"/api/v1/contexts/{contextId}";
        var cacheKey = $"GET:{path}";
        
        // Check cache first
        if (_cache?.TryGetValue(cacheKey, out Context? cached) == true && cached != null)
        {
            RecordAnalytics("cache_hit");
            return cached;
        }
        RecordAnalytics("cache_miss");
        
        var request = new HttpRequestMessage(HttpMethod.Get, path);
        var response = await ExecuteRequestAsync<ApiResponse<Context>>(request, cancellationToken);
        
        var context = response.Data;
        
        // Cache the result
        if (_cache != null)
        {
            var cacheEntryOptions = new MemoryCacheEntryOptions
            {
                Size = 1,
                AbsoluteExpirationRelativeToNow = _config.Cache.Ttl
            };
            _cache.Set(cacheKey, context, cacheEntryOptions);
        }
        
        return context;
    }
    
    /// <summary>
    /// Lists contexts with optional filtering and pagination.
    /// </summary>
    /// <param name="filter">The context filter (optional).</param>
    /// <param name="pagination">The pagination options (optional).</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the context list response.</returns>
    public async Task<ContextListResponse> ListContextsAsync(
        ContextFilter? filter = null,
        PaginationOptions? pagination = null,
        CancellationToken cancellationToken = default)
    {
        var queryParams = new List<string>();
        
        // Add filter parameters
        if (filter != null)
        {
            AddFilterParams(queryParams, filter);
        }
        
        // Add pagination parameters
        if (pagination != null)
        {
            AddPaginationParams(queryParams, pagination);
        }
        
        var query = queryParams.Count > 0 ? "?" + string.Join("&", queryParams) : "";
        var request = new HttpRequestMessage(HttpMethod.Get, $"/api/v1/contexts{query}");
        
        return await ExecuteRequestAsync<ContextListResponse>(request, cancellationToken);
    }
    
    /// <summary>
    /// Updates an existing context.
    /// </summary>
    /// <param name="contextId">The context ID.</param>
    /// <param name="updates">The context updates.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the updated context.</returns>
    /// <exception cref="ArgumentException">Thrown when contextId is invalid.</exception>
    /// <exception cref="ArgumentNullException">Thrown when updates is null.</exception>
    public async Task<Context> UpdateContextAsync(
        int contextId,
        ContextUpdate updates,
        CancellationToken cancellationToken = default)
    {
        if (contextId <= 0)
        {
            throw new ArgumentException("Context ID must be positive", nameof(contextId));
        }
        ArgumentNullException.ThrowIfNull(updates);
        
        var path = $"/api/v1/contexts/{contextId}";
        var request = new HttpRequestMessage(HttpMethod.Put, path)
        {
            Content = JsonContent.Create(updates, options: _jsonOptions)
        };
        
        var response = await ExecuteRequestAsync<ApiResponse<Context>>(request, cancellationToken);
        
        // Invalidate cache
        InvalidateCache($"GET:{path}");
        InvalidateCache("/api/v1/contexts");
        
        return response.Data;
    }
    
    /// <summary>
    /// Deletes a context.
    /// </summary>
    /// <param name="contextId">The context ID.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task representing the delete operation.</returns>
    /// <exception cref="ArgumentException">Thrown when contextId is invalid.</exception>
    public async Task DeleteContextAsync(int contextId, CancellationToken cancellationToken = default)
    {
        if (contextId <= 0)
        {
            throw new ArgumentException("Context ID must be positive", nameof(contextId));
        }
        
        var path = $"/api/v1/contexts/{contextId}";
        var request = new HttpRequestMessage(HttpMethod.Delete, path);
        
        await ExecuteRequestAsync<SuccessResponse>(request, cancellationToken);
        
        // Invalidate cache
        InvalidateCache($"GET:{path}");
        InvalidateCache("/api/v1/contexts");
    }
    
    /// <summary>
    /// Searches contexts using various search methods.
    /// </summary>
    /// <param name="query">The search query.</param>
    /// <param name="options">The search options (optional).</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the search results.</returns>
    /// <exception cref="ArgumentException">Thrown when query is null or empty.</exception>
    public async Task<IReadOnlyList<SearchResult>> SearchContextsAsync(
        string query,
        SearchOptions? options = null,
        CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(query))
        {
            throw new ArgumentException("Query cannot be null or empty", nameof(query));
        }
        
        var searchData = new Dictionary<string, object> { ["query"] = query };
        
        if (options != null)
        {
            AddSearchOptions(searchData, options);
        }
        
        var request = new HttpRequestMessage(HttpMethod.Post, "/api/v1/search")
        {
            Content = JsonContent.Create(searchData, options: _jsonOptions)
        };
        
        var response = await ExecuteRequestAsync<SearchResponse>(request, cancellationToken);
        return response.Data;
    }
    
    /// <summary>
    /// Creates multiple contexts in batch.
    /// </summary>
    /// <param name="contexts">The list of contexts to create.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the batch result.</returns>
    /// <exception cref="ArgumentException">Thrown when contexts is null or empty.</exception>
    /// <exception cref="ValidationException">Thrown when any context has an invalid path.</exception>
    public async Task<BatchResult> BatchCreateContextsAsync(
        IEnumerable<ContextCreate> contexts,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(contexts);
        
        var contextList = contexts.ToList();
        if (contextList.Count == 0)
        {
            throw new ArgumentException("Contexts cannot be empty", nameof(contexts));
        }
        
        var startTime = DateTime.UtcNow;
        
        // Validate and normalize all contexts
        var normalizedContexts = new List<ContextCreate>();
        foreach (var context in contextList)
        {
            if (!PathValidator.IsValid(context.Path))
            {
                throw new ValidationException($"Invalid context path: {context.Path}");
            }
            
            normalizedContexts.Add(context with { Path = PathValidator.Normalize(context.Path) });
        }
        
        var batchData = new { contexts = normalizedContexts };
        var request = new HttpRequestMessage(HttpMethod.Post, "/api/v1/contexts/batch")
        {
            Content = JsonContent.Create(batchData, options: _jsonOptions)
        };
        
        var response = await ExecuteRequestAsync<ApiResponse<BatchResult>>(request, cancellationToken);
        var result = response.Data;
        
        // Calculate additional metrics
        var executionTime = DateTime.UtcNow - startTime;
        var successRate = (double)result.SuccessCount / result.TotalItems;
        
        // Invalidate cache
        InvalidateCache("/api/v1/contexts");
        
        return result with 
        { 
            ExecutionTime = executionTime,
            SuccessRate = successRate
        };
    }
    
    /// <summary>
    /// Iterates through all contexts with automatic pagination.
    /// </summary>
    /// <param name="filter">The context filter (optional).</param>
    /// <param name="pageSize">The page size.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>An async enumerable of contexts.</returns>
    public async IAsyncEnumerable<Context> IterateContextsAsync(
        ContextFilter? filter = null,
        int pageSize = 100,
        [EnumeratorCancellation] CancellationToken cancellationToken = default)
    {
        if (pageSize <= 0) pageSize = 100;
        
        int page = 1;
        
        while (true)
        {
            var pagination = new PaginationOptions
            {
                Page = page,
                PageSize = pageSize
            };
            
            var response = await ListContextsAsync(filter, pagination, cancellationToken);
            var contexts = response.Data;
            
            if (!contexts.Any())
            {
                yield break;
            }
            
            foreach (var context in contexts)
            {
                yield return context;
            }
            
            // Check if we've reached the end
            if (contexts.Count < pageSize || !response.Pagination.HasNext)
            {
                yield break;
            }
            
            page++;
        }
    }
    
    /// <summary>
    /// Gets comprehensive system statistics.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>A task containing the statistics.</returns>
    public async Task<StatsResponse> GetStatisticsAsync(CancellationToken cancellationToken = default)
    {
        var request = new HttpRequestMessage(HttpMethod.Get, "/api/v1/stats");
        return await ExecuteRequestAsync<StatsResponse>(request, cancellationToken);
    }
    
    /// <summary>
    /// Gets client analytics and usage statistics.
    /// </summary>
    /// <returns>The analytics data.</returns>
    public IReadOnlyDictionary<string, object> GetAnalytics()
    {
        var result = new Dictionary<string, object>
        {
            ["session_start"] = _sessionStart,
            ["operation_counts"] = new Dictionary<string, long>(_analytics)
        };
        
        if (_cache != null)
        {
            // Note: MemoryCache doesn't provide detailed stats like hit rate
            // This is a simplified version
            var cacheStats = new Dictionary<string, object>
            {
                ["enabled"] = true,
                ["estimated_size"] = _cache.GetType().GetProperty("Count")?.GetValue(_cache) ?? 0
            };
            result["cache_stats"] = cacheStats;
        }
        else
        {
            result["cache_stats"] = new Dictionary<string, object> { ["enabled"] = false };
        }
        
        return result;
    }
    
    /// <summary>
    /// Clears the client cache.
    /// </summary>
    public void ClearCache()
    {
        if (_cache is MemoryCache memoryCache)
        {
            memoryCache.Compact(1.0); // Remove all entries
        }
    }
    
    /// <summary>
    /// Disposes the client and releases resources.
    /// </summary>
    public void Dispose()
    {
        _httpClient?.Dispose();
        _cache?.Dispose();
        _rateLimitSemaphore?.Dispose();
        GC.SuppressFinalize(this);
    }
    
    // Private helper methods
    
    private HttpClient CreateHttpClient()
    {
        var handler = new HttpClientHandler();
        
        var retryPolicy = HttpPolicyExtensions
            .HandleTransientHttpError()
            .Or<TaskCanceledException>()
            .WaitAndRetryAsync(
                _config.Retry.MaxAttempts,
                retryAttempt => TimeSpan.FromMilliseconds(_config.Retry.BaseDelay * Math.Pow(2, retryAttempt - 1)),
                onRetry: (outcome, timespan, retryCount, context) =>
                {
                    _logger?.LogWarning("Retry {RetryCount} for request after {Delay}ms", 
                        retryCount, timespan.TotalMilliseconds);
                });
        
        var client = new HttpClient(handler);
        client.BaseAddress = new Uri(_config.BaseUrl);
        client.Timeout = _config.Timeout;
        client.DefaultRequestHeaders.Add("User-Agent", UserAgent);
        
        if (!string.IsNullOrEmpty(_config.ApiKey))
        {
            client.DefaultRequestHeaders.Add("X-API-Key", _config.ApiKey);
        }
        if (!string.IsNullOrEmpty(_config.JwtToken))
        {
            client.DefaultRequestHeaders.Add("Authorization", $"Bearer {_config.JwtToken}");
        }
        
        return client;
    }
    
    private async Task<T> ExecuteRequestAsync<T>(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        await _rateLimitSemaphore.WaitAsync(cancellationToken);
        
        try
        {
            RecordAnalytics("request");
            
            using var response = await _httpClient.SendAsync(request, cancellationToken);
            
            if (!response.IsSuccessStatusCode)
            {
                RecordAnalytics("error");
                await HandleErrorResponseAsync(response);
            }
            
            var json = await response.Content.ReadAsStringAsync(cancellationToken);
            return JsonSerializer.Deserialize<T>(json, _jsonOptions) 
                ?? throw new HCFSException("Failed to deserialize response");
        }
        finally
        {
            _rateLimitSemaphore.Release();
        }
    }
    
    private async Task HandleErrorResponseAsync(HttpResponseMessage response)
    {
        var content = await response.Content.ReadAsStringAsync();
        
        try
        {
            var errorResponse = JsonSerializer.Deserialize<ApiErrorResponse>(content, _jsonOptions);
            var message = errorResponse?.Error ?? $"HTTP {(int)response.StatusCode} error";
            
            throw response.StatusCode switch
            {
                HttpStatusCode.BadRequest => new ValidationException(message),
                HttpStatusCode.Unauthorized => new HCFSAuthenticationException(message),
                HttpStatusCode.NotFound => new HCFSNotFoundException(message),
                HttpStatusCode.TooManyRequests => new HCFSRateLimitException(message, 
                    response.Headers.RetryAfter?.Delta?.TotalSeconds),
                HttpStatusCode.InternalServerError or 
                HttpStatusCode.BadGateway or 
                HttpStatusCode.ServiceUnavailable or 
                HttpStatusCode.GatewayTimeout => new HCFSServerException(message, (int)response.StatusCode),
                _ => new HCFSException(message)
            };
        }
        catch (JsonException)
        {
            throw new HCFSException($"HTTP {(int)response.StatusCode}: {content}");
        }
    }
    
    private static void ValidateConfig(HCFSConfig config)
    {
        if (string.IsNullOrWhiteSpace(config.BaseUrl))
        {
            throw new ValidationException("Base URL cannot be null or empty");
        }
        
        if (!Uri.TryCreate(config.BaseUrl, UriKind.Absolute, out _))
        {
            throw new ValidationException("Base URL must be a valid absolute URI");
        }
        
        if (config.Timeout <= TimeSpan.Zero)
        {
            throw new ValidationException("Timeout must be positive");
        }
    }
    
    private void AddFilterParams(List<string> queryParams, ContextFilter filter)
    {
        if (!string.IsNullOrEmpty(filter.PathPrefix))
            queryParams.Add($"path_prefix={Uri.EscapeDataString(filter.PathPrefix)}");
        if (!string.IsNullOrEmpty(filter.Author))
            queryParams.Add($"author={Uri.EscapeDataString(filter.Author)}");
        if (filter.Status.HasValue)
            queryParams.Add($"status={filter.Status}");
        if (filter.CreatedAfter.HasValue)
            queryParams.Add($"created_after={filter.CreatedAfter:O}");
        if (filter.CreatedBefore.HasValue)
            queryParams.Add($"created_before={filter.CreatedBefore:O}");
        if (!string.IsNullOrEmpty(filter.ContentContains))
            queryParams.Add($"content_contains={Uri.EscapeDataString(filter.ContentContains)}");
        if (filter.MinContentLength.HasValue)
            queryParams.Add($"min_content_length={filter.MinContentLength}");
        if (filter.MaxContentLength.HasValue)
            queryParams.Add($"max_content_length={filter.MaxContentLength}");
    }
    
    private static void AddPaginationParams(List<string> queryParams, PaginationOptions pagination)
    {
        if (pagination.Page.HasValue)
            queryParams.Add($"page={pagination.Page}");
        if (pagination.PageSize.HasValue)
            queryParams.Add($"page_size={pagination.PageSize}");
        if (!string.IsNullOrEmpty(pagination.SortBy))
            queryParams.Add($"sort_by={Uri.EscapeDataString(pagination.SortBy)}");
        if (pagination.SortOrder.HasValue)
            queryParams.Add($"sort_order={pagination.SortOrder}");
    }
    
    private static void AddSearchOptions(Dictionary<string, object> searchData, SearchOptions options)
    {
        if (options.SearchType.HasValue)
            searchData["search_type"] = options.SearchType.ToString()!.ToLowerInvariant();
        if (options.TopK.HasValue)
            searchData["top_k"] = options.TopK.Value;
        if (options.SimilarityThreshold.HasValue)
            searchData["similarity_threshold"] = options.SimilarityThreshold.Value;
        if (!string.IsNullOrEmpty(options.PathPrefix))
            searchData["path_prefix"] = options.PathPrefix;
        if (options.SemanticWeight.HasValue)
            searchData["semantic_weight"] = options.SemanticWeight.Value;
        if (options.IncludeContent.HasValue)
            searchData["include_content"] = options.IncludeContent.Value;
        if (options.IncludeHighlights.HasValue)
            searchData["include_highlights"] = options.IncludeHighlights.Value;
        if (options.MaxHighlights.HasValue)
            searchData["max_highlights"] = options.MaxHighlights.Value;
    }
    
    private void InvalidateCache(string pattern)
    {
        // Note: MemoryCache doesn't provide a way to iterate or pattern-match keys
        // This would require a custom cache implementation or a different caching library
        // For now, we'll clear the entire cache when needed
        if (pattern.Contains("/api/v1/contexts") && _cache != null)
        {
            ClearCache();
        }
    }
    
    private void RecordAnalytics(string operation)
    {
        lock (_analytics)
        {
            _analytics.TryGetValue(operation, out var count);
            _analytics[operation] = count + 1;
        }
    }
}