''' <summary>
''' Advanced 602TechSec client implementation with caching, logging, and performance optimizations
''' </summary>
Imports System.Collections.Concurrent
Imports System.Threading.Tasks

Public Class TechSec602AdvancedClient
    Inherits TechSec602Client

    Private ReadOnly _cache As ConcurrentDictionary(Of String, CachedResult)
    Private ReadOnly _config As TechSec602Config
    Private ReadOnly _logger As ILogger
    Private ReadOnly _circuitBreaker As TechSec602CircuitBreaker

    ''' <summary>
    ''' Parameterless constructor - reads configuration from web.config
    ''' </summary>
    Public Sub New()
        Me.New(TechSec602Config.FromAppSettings())
    End Sub

    Public Sub New(config As TechSec602Config, Optional logger As ILogger = Nothing)
        MyBase.New(config)
        _config = config
        _cache = New ConcurrentDictionary(Of String, CachedResult)()
        _logger = logger
        _circuitBreaker = New TechSec602CircuitBreaker()

        ' Start cache cleanup timer
        If config.CacheResults Then
            StartCacheCleanup()
        End If
    End Sub

    ''' <summary>
    ''' Enhanced verification with caching and performance monitoring
    ''' </summary>
    Public Shadows Async Function VerifyRequestAsync(url As String, Optional ipAddress As String = Nothing, Optional apiKey As String = Nothing) As Task(Of VerificationResult)
        Dim cacheKey = $"{url}|{ipAddress}|{apiKey}"

        ' Check cache first
        If _config.CacheResults AndAlso _cache.TryGetValue(cacheKey, CachedResult) AndAlso Not CachedResult.IsExpired Then
            _logger?.LogDebug($"Cache hit for {url}")
            Return CachedResult.Result
        End If

        Dim startTime = DateTime.UtcNow

        ' Call base verification
        Dim result = Await MyBase.VerifyRequestAsync(url, ipAddress, apiKey)

        Dim endTime = DateTime.UtcNow
        Dim duration = (endTime - startTime).TotalMilliseconds

        ' Log the request
        If _config.EnableLogging Then
            _logger?.LogInfo($"Verification: {url} | IP: {ipAddress} | Result: {result.IsAllowed} | Duration: {duration}ms | Reason: {result.Reason}")
        End If

        ' Cache successful results
        If _config.CacheResults AndAlso result.Success Then
            Dim expiry = DateTime.UtcNow.AddMinutes(_config.CacheTimeoutMinutes)
            _cache.TryAdd(cacheKey, New CachedResult With {.Result = result, .Expiry = expiry})
        End If

        Return result
    End Function

    ''' <summary>
    ''' Batch verification for multiple URLs
    ''' </summary>
    Public Async Function VerifyBatchAsync(requests As List(Of BatchVerificationRequest)) As Task(Of List(Of VerificationResult))
        Dim tasks = requests.Select(Function(req) VerifyRequestAsync(req.Url, req.IpAddress, req.ApiKey)).ToArray()
        Dim results = Await Task.WhenAll(tasks)
        Return results.ToList()
    End Function

    ''' <summary>
    ''' Pre-warm cache with common URLs
    ''' </summary>
    Public Async Function PreWarmCacheAsync(urls As List(Of String)) As Task
        Dim tasks = urls.Select(Function(url) VerifyRequestAsync(url)).ToArray()
        Await Task.WhenAll(tasks)
        _logger?.LogInfo($"Pre-warmed cache with {urls.Count} URLs")
    End Function

    ''' <summary>
    ''' Get cache statistics
    ''' </summary>
    Public Function GetCacheStats() As CacheStats
        Return New CacheStats With {
            .TotalEntries = _cache.Count,
            .ExpiredEntries = _cache.Values.Count(Function(c) c.IsExpired)
        }
    End Function

    ''' <summary>
    ''' Clear expired cache entries
    ''' </summary>
    Public Sub ClearExpiredCache()
        Dim expiredKeys = _cache.Where(Function(kvp) kvp.Value.IsExpired).Select(Function(kvp) kvp.Key).ToList()
        For Each key In expiredKeys
            _cache.TryRemove(key, Nothing)
        Next
        _logger?.LogDebug($"Cleared {expiredKeys.Count} expired cache entries")
    End Sub

    Private Sub StartCacheCleanup()
        Task.Run(Async Function()
                     While True
                         Await Task.Delay(TimeSpan.FromMinutes(1))
                         ClearExpiredCache()
                     End While
                 End Function)
    End Sub
End Class

''' <summary>
''' Cached verification result
''' </summary>
Public Class CachedResult
    Public Property Result As VerificationResult
    Public Property Expiry As DateTime

    Public ReadOnly Property IsExpired As Boolean
        Get
            Return DateTime.UtcNow > Expiry
        End Get
    End Property
End Class

''' <summary>
''' Batch verification request
''' </summary>
Public Class BatchVerificationRequest
    Public Property Url As String
    Public Property IpAddress As String
    Public Property ApiKey As String
End Class

''' <summary>
''' Cache statistics
''' </summary>
Public Class CacheStats
    Public Property TotalEntries As Integer
    Public Property ExpiredEntries As Integer
End Class

''' <summary>
''' Simple logging interface
''' </summary>
Public Interface ILogger
    Sub LogInfo(message As String)
    Sub LogDebug(message As String)
    Sub LogError(message As String)
End Interface

''' <summary>
''' Basic console logger implementation
''' </summary>
Public Class ConsoleLogger
    Implements ILogger

    Public Sub LogInfo(message As String) Implements ILogger.LogInfo
        Console.WriteLine($"[INFO] {DateTime.Now}: {message}")
    End Sub

    Public Sub LogDebug(message As String) Implements ILogger.LogDebug
        Console.WriteLine($"[DEBUG] {DateTime.Now}: {message}")
    End Sub

    Public Sub LogError(message As String) Implements ILogger.LogError
        Console.WriteLine($"[ERROR] {DateTime.Now}: {message}")
    End Sub
End Class

''' <summary>
''' Circuit breaker pattern for fault tolerance
''' </summary>
Public Class TechSec602CircuitBreaker
    Private _failureCount As Integer = 0
    Private _lastFailureTime As DateTime = DateTime.MinValue
    Private ReadOnly _failureThreshold As Integer
    Private ReadOnly _resetTimeoutMinutes As Integer

    Public Sub New(Optional failureThreshold As Integer = 5, Optional resetTimeoutMinutes As Integer = 5)
        _failureThreshold = failureThreshold
        _resetTimeoutMinutes = resetTimeoutMinutes
    End Sub

    Public ReadOnly Property IsOpen As Boolean
        Get
            If _failureCount >= _failureThreshold Then
                Return DateTime.UtcNow.Subtract(_lastFailureTime).TotalMinutes < _resetTimeoutMinutes
            End If
            Return False
        End Get
    End Property

    Public Sub RecordSuccess()
        _failureCount = 0
    End Sub

    Public Sub RecordFailure()
        _failureCount += 1
        _lastFailureTime = DateTime.UtcNow
    End Sub
End Class