using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

namespace MarketAlly.AIPlugin.Analysis.Infrastructure
{
    /// <summary>
    /// Input validation and security service for analysis operations
    /// </summary>
    public class InputValidator
    {
        private readonly ILogger<InputValidator>? _logger;
        private static readonly HashSet<string> AllowedFileExtensions = new(StringComparer.OrdinalIgnoreCase)
        {
            ".cs", ".csproj", ".sln", ".json", ".xml", ".config", ".md", ".txt",
            ".dll", ".exe", ".pdb", ".nuspec", ".props", ".targets"
        };

        private static readonly Regex SafePathRegex = new(@"^[a-zA-Z0-9\\\/:._\-\s]+$", RegexOptions.Compiled);
        private static readonly Regex DangerousPatternRegex = new(@"(\.\.[\\/]|<script|javascript:|vbscript:|onload=|onerror=)", 
            RegexOptions.Compiled | RegexOptions.IgnoreCase);

        public InputValidator(ILogger<InputValidator>? logger = null)
        {
            _logger = logger;
        }

        /// <summary>
        /// Validates and sanitizes a file path
        /// </summary>
        public ValidationResult ValidateFilePath(string? filePath)
        {
            if (string.IsNullOrWhiteSpace(filePath))
            {
                return ValidationResult.Failure("File path cannot be null or empty");
            }

            // Check for dangerous patterns
            if (DangerousPatternRegex.IsMatch(filePath))
            {
                _logger?.LogWarning("Dangerous pattern detected in file path: {FilePath}", filePath);
                return ValidationResult.Failure("File path contains potentially dangerous patterns");
            }

            // Validate path format
            if (!SafePathRegex.IsMatch(filePath))
            {
                return ValidationResult.Failure("File path contains invalid characters");
            }

            // Check for path traversal attempts
            var normalizedPath = Path.GetFullPath(filePath);
            if (filePath.Contains("..") && !normalizedPath.StartsWith(Path.GetFullPath(".")))
            {
                _logger?.LogWarning("Path traversal attempt detected: {FilePath}", filePath);
                return ValidationResult.Failure("Path traversal detected");
            }

            // Validate file extension
            var extension = Path.GetExtension(filePath);
            if (!string.IsNullOrEmpty(extension) && !AllowedFileExtensions.Contains(extension))
            {
                return ValidationResult.Failure($"File extension '{extension}' is not allowed");
            }

            return ValidationResult.Success(normalizedPath);
        }

        /// <summary>
        /// Validates plugin parameters for security issues
        /// </summary>
        public ValidationResult ValidatePluginParameters(Dictionary<string, object>? parameters)
        {
            if (parameters == null)
            {
                return ValidationResult.Success();
            }

            foreach (var kvp in parameters)
            {
                // Validate parameter name
                if (string.IsNullOrWhiteSpace(kvp.Key) || !IsValidParameterName(kvp.Key))
                {
                    return ValidationResult.Failure($"Invalid parameter name: {kvp.Key}");
                }

                // Validate parameter value
                var valueValidation = ValidateParameterValue(kvp.Key, kvp.Value);
                if (!valueValidation.IsValid)
                {
                    return valueValidation;
                }
            }

            return ValidationResult.Success();
        }

        /// <summary>
        /// Validates analysis configuration settings
        /// </summary>
        public ValidationResult ValidateConfiguration(AnalysisConfiguration? config)
        {
            if (config == null)
            {
                return ValidationResult.Failure("Configuration cannot be null");
            }

            // Validate timeout values
            if (config.DefaultTimeout <= TimeSpan.Zero || config.DefaultTimeout > TimeSpan.FromHours(1))
            {
                return ValidationResult.Failure("Default timeout must be between 1 second and 1 hour");
            }

            // Validate concurrency limits
            if (config.MaxConcurrentAnalyses < 1 || config.MaxConcurrentAnalyses > Environment.ProcessorCount * 4)
            {
                return ValidationResult.Failure($"Max concurrent analyses must be between 1 and {Environment.ProcessorCount * 4}");
            }

            // Validate cache settings
            if (config.CacheExpirationTime < TimeSpan.FromMinutes(1) || config.CacheExpirationTime > TimeSpan.FromDays(7))
            {
                return ValidationResult.Failure("Cache expiration time must be between 1 minute and 7 days");
            }

            // Validate security settings
            if (config.AllowDynamicPluginLoading && string.IsNullOrWhiteSpace(config.TrustedPluginDirectory))
            {
                return ValidationResult.Failure("Trusted plugin directory must be specified when dynamic plugin loading is enabled");
            }

            return ValidationResult.Success();
        }

        /// <summary>
        /// Sanitizes string input to remove potentially dangerous content
        /// </summary>
        public string SanitizeInput(string? input)
        {
            if (string.IsNullOrEmpty(input))
            {
                return string.Empty;
            }

            // Remove or escape potentially dangerous characters
            var sanitized = input
                .Replace("<", "&lt;")
                .Replace(">", "&gt;")
                .Replace("&", "&amp;")
                .Replace("\"", "&quot;")
                .Replace("'", "&#x27;")
                .Replace("/", "&#x2F;");

            // Remove null bytes and control characters (except common whitespace)
            sanitized = Regex.Replace(sanitized, @"[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]", "");

            return sanitized.Trim();
        }

        /// <summary>
        /// Validates that a directory path is safe and accessible
        /// </summary>
        public ValidationResult ValidateDirectoryPath(string? directoryPath)
        {
            if (string.IsNullOrWhiteSpace(directoryPath))
            {
                return ValidationResult.Failure("Directory path cannot be null or empty");
            }

            var pathValidation = ValidateFilePath(directoryPath);
            if (!pathValidation.IsValid)
            {
                return pathValidation;
            }

            try
            {
                var fullPath = Path.GetFullPath(directoryPath);
                
                // Check if directory exists and is accessible
                if (!Directory.Exists(fullPath))
                {
                    return ValidationResult.Failure("Directory does not exist");
                }

                // Basic permission check
                try
                {
                    Directory.GetFiles(fullPath, "*", SearchOption.TopDirectoryOnly);
                }
                catch (UnauthorizedAccessException)
                {
                    _logger?.LogWarning("Access denied to directory: {DirectoryPath}", fullPath);
                    return ValidationResult.Failure("Access denied to directory");
                }

                return ValidationResult.Success(fullPath);
            }
            catch (Exception ex)
            {
                _logger?.LogError(ex, "Error validating directory path: {DirectoryPath}", directoryPath);
                return ValidationResult.Failure("Invalid directory path");
            }
        }

        private bool IsValidParameterName(string parameterName)
        {
            // Parameter names should only contain alphanumeric characters, underscores, and dots
            return Regex.IsMatch(parameterName, @"^[a-zA-Z0-9_\.]+$");
        }

        private ValidationResult ValidateParameterValue(string parameterName, object? value)
        {
            if (value == null)
            {
                return ValidationResult.Success();
            }

            // Check for potentially dangerous string values
            if (value is string stringValue)
            {
                if (DangerousPatternRegex.IsMatch(stringValue))
                {
                    _logger?.LogWarning("Dangerous pattern detected in parameter {ParameterName}: {Value}", 
                        parameterName, stringValue);
                    return ValidationResult.Failure($"Parameter '{parameterName}' contains potentially dangerous content");
                }

                // Check string length limits
                if (stringValue.Length > 10000)
                {
                    return ValidationResult.Failure($"Parameter '{parameterName}' exceeds maximum length (10000 characters)");
                }
            }

            // Validate file paths in parameters
            if (parameterName.EndsWith("Path", StringComparison.OrdinalIgnoreCase) && value is string pathValue)
            {
                var pathValidation = ValidateFilePath(pathValue);
                if (!pathValidation.IsValid)
                {
                    return ValidationResult.Failure($"Invalid file path in parameter '{parameterName}': {pathValidation.ErrorMessage}");
                }
            }

            return ValidationResult.Success();
        }
    }

    /// <summary>
    /// Result of input validation operation
    /// </summary>
    public class ValidationResult
    {
        public bool IsValid { get; private set; }
        public string? ErrorMessage { get; private set; }
        public string? SanitizedValue { get; private set; }

        private ValidationResult(bool isValid, string? errorMessage = null, string? sanitizedValue = null)
        {
            IsValid = isValid;
            ErrorMessage = errorMessage;
            SanitizedValue = sanitizedValue;
        }

        public static ValidationResult Success(string? sanitizedValue = null)
        {
            return new ValidationResult(true, sanitizedValue: sanitizedValue);
        }

        public static ValidationResult Failure(string errorMessage)
        {
            return new ValidationResult(false, errorMessage);
        }
    }
}