using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

namespace MarketAlly.AIPlugin.Refactoring.Plugins
{
	public static class InputValidator
	{
		private static readonly HashSet<string> DangerousFileExtensions = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
		{
			".exe", ".dll", ".bat", ".cmd", ".ps1", ".vbs", ".js", ".jar", ".msi", ".scr"
		};

		private static readonly Regex SafeFilePathPattern = new Regex(@"^[a-zA-Z]:[\\\/](?:[^<>:""|?*\r\n]+[\\\/])*[^<>:""|?*\r\n]*$", RegexOptions.Compiled);
		private static readonly Regex SafeIdentifierPattern = new Regex(@"^[a-zA-Z_][a-zA-Z0-9_]*$", RegexOptions.Compiled);

		public class ValidationResult
		{
			public bool IsValid { get; set; }
			public string ErrorMessage { get; set; }
			public List<string> Warnings { get; set; } = new List<string>();
		}

		public static ValidationResult ValidateFilePath(string filePath, bool mustExist = true, bool allowDirectories = true)
		{
			var result = new ValidationResult();

			if (string.IsNullOrWhiteSpace(filePath))
			{
				result.ErrorMessage = "File path cannot be null or empty";
				return result;
			}

			// Check for path traversal attempts
			if (filePath.Contains("..") || filePath.Contains("~"))
			{
				result.ErrorMessage = "Path traversal attempts are not allowed";
				return result;
			}

			// Validate path format
			if (!SafeFilePathPattern.IsMatch(filePath))
			{
				result.ErrorMessage = "Invalid file path format";
				return result;
			}

			// Check for dangerous file extensions
			var extension = Path.GetExtension(filePath);
			if (DangerousFileExtensions.Contains(extension))
			{
				result.ErrorMessage = $"File extension '{extension}' is not allowed for security reasons";
				return result;
			}

			// Check existence if required
			if (mustExist)
			{
				if (allowDirectories && Directory.Exists(filePath))
				{
					result.IsValid = true;
					return result;
				}
				
				if (File.Exists(filePath))
				{
					result.IsValid = true;
					return result;
				}

				result.ErrorMessage = "File or directory does not exist";
				return result;
			}

			// Check if parent directory exists for new files
			var parentDir = Path.GetDirectoryName(filePath);
			if (!string.IsNullOrEmpty(parentDir) && !Directory.Exists(parentDir))
			{
				result.ErrorMessage = "Parent directory does not exist";
				return result;
			}

			result.IsValid = true;
			return result;
		}

		public static ValidationResult ValidateIdentifier(string identifier, string context = "identifier")
		{
			var result = new ValidationResult();

			if (string.IsNullOrWhiteSpace(identifier))
			{
				result.ErrorMessage = $"{context} cannot be null or empty";
				return result;
			}

			if (!SafeIdentifierPattern.IsMatch(identifier))
			{
				result.ErrorMessage = $"{context} contains invalid characters";
				return result;
			}

			// Check for C# reserved keywords
			var reservedKeywords = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
			{
				"abstract", "as", "base", "bool", "break", "byte", "case", "catch", "char", "checked",
				"class", "const", "continue", "decimal", "default", "delegate", "do", "double", "else",
				"enum", "event", "explicit", "extern", "false", "finally", "fixed", "float", "for",
				"foreach", "goto", "if", "implicit", "in", "int", "interface", "internal", "is", "lock",
				"long", "namespace", "new", "null", "object", "operator", "out", "override", "params",
				"private", "protected", "public", "readonly", "ref", "return", "sbyte", "sealed", "short",
				"sizeof", "stackalloc", "static", "string", "struct", "switch", "this", "throw", "true",
				"try", "typeof", "uint", "ulong", "unchecked", "unsafe", "ushort", "using", "virtual",
				"void", "volatile", "while"
			};

			if (reservedKeywords.Contains(identifier))
			{
				result.ErrorMessage = $"{context} cannot be a C# reserved keyword";
				return result;
			}

			result.IsValid = true;
			return result;
		}

		public static ValidationResult ValidateNumericRange<T>(T value, T min, T max, string parameterName) where T : IComparable<T>
		{
			var result = new ValidationResult();

			if (value.CompareTo(min) < 0 || value.CompareTo(max) > 0)
			{
				result.ErrorMessage = $"{parameterName} must be between {min} and {max}";
				return result;
			}

			result.IsValid = true;
			return result;
		}

		public static ValidationResult ValidateString(string value, string parameterName, int minLength = 0, int maxLength = int.MaxValue, bool allowEmpty = false)
		{
			var result = new ValidationResult();

			if (string.IsNullOrEmpty(value))
			{
				if (!allowEmpty)
				{
					result.ErrorMessage = $"{parameterName} cannot be null or empty";
					return result;
				}
			}
			else
			{
				if (value.Length < minLength)
				{
					result.ErrorMessage = $"{parameterName} must be at least {minLength} characters long";
					return result;
				}

				if (value.Length > maxLength)
				{
					result.ErrorMessage = $"{parameterName} cannot exceed {maxLength} characters";
					return result;
				}

				// Check for potentially dangerous content
				if (value.Contains('\0'))
				{
					result.ErrorMessage = $"{parameterName} contains null characters";
					return result;
				}
			}

			result.IsValid = true;
			return result;
		}

		public static ValidationResult ValidateCollection<T>(IEnumerable<T> collection, string parameterName, int minCount = 0, int maxCount = int.MaxValue)
		{
			var result = new ValidationResult();

			if (collection == null)
			{
				result.ErrorMessage = $"{parameterName} cannot be null";
				return result;
			}

			var count = collection.Count();
			if (count < minCount)
			{
				result.ErrorMessage = $"{parameterName} must contain at least {minCount} items";
				return result;
			}

			if (count > maxCount)
			{
				result.ErrorMessage = $"{parameterName} cannot contain more than {maxCount} items";
				return result;
			}

			result.IsValid = true;
			return result;
		}

		public static ValidationResult ValidateUrl(string url, string parameterName, bool requireHttps = true)
		{
			var result = new ValidationResult();

			if (string.IsNullOrWhiteSpace(url))
			{
				result.ErrorMessage = $"{parameterName} cannot be null or empty";
				return result;
			}

			if (!Uri.TryCreate(url, UriKind.Absolute, out var uri))
			{
				result.ErrorMessage = $"{parameterName} is not a valid URL";
				return result;
			}

			if (requireHttps && uri.Scheme.ToLower() != "https")
			{
				result.ErrorMessage = $"{parameterName} must use HTTPS";
				return result;
			}

			if (uri.Scheme.ToLower() != "http" && uri.Scheme.ToLower() != "https")
			{
				result.ErrorMessage = $"{parameterName} must use HTTP or HTTPS scheme";
				return result;
			}

			result.IsValid = true;
			return result;
		}

		public static void ThrowIfInvalid(ValidationResult result)
		{
			if (!result.IsValid)
			{
				throw new ArgumentException(result.ErrorMessage);
			}
		}

		public static ValidationResult CombineResults(params ValidationResult[] results)
		{
			var combinedResult = new ValidationResult { IsValid = true };
			var errors = new List<string>();
			var warnings = new List<string>();

			foreach (var result in results)
			{
				if (!result.IsValid)
				{
					combinedResult.IsValid = false;
					if (!string.IsNullOrEmpty(result.ErrorMessage))
					{
						errors.Add(result.ErrorMessage);
					}
				}
				warnings.AddRange(result.Warnings);
			}

			if (!combinedResult.IsValid)
			{
				combinedResult.ErrorMessage = string.Join("; ", errors);
			}
			combinedResult.Warnings = warnings;

			return combinedResult;
		}
	}
}