# 設定編碼以防中文亂碼
[Console]::OutputEncoding = [System.Text.Encoding]::UTF8
Clear-Host

# 記錄原本的視窗顏色，以便離開時還原
$originalBg = $host.UI.RawUI.BackgroundColor
$originalFg = $host.UI.RawUI.ForegroundColor

try {
    $failStage = $null
    $isOnline = $false

    # 快速通道：直接 Ping 外部 DNS (1.1.1.1) 測試網際網路是否暢通
    $quickPing = Test-Connection -ComputerName "1.1.1.1" -Count 1 -Quiet

    if ($quickPing) {
        $isOnline = $true
    } else {
        # 如果快速檢測失敗，才執行詳細的逐層排查
        # 步驟 1: 檢查 IP 位址 (只要有一個非 169.254 的 IP 即視為正常)
        $activeInterfaceIndex = $(Get-NetConnectionProfile -ErrorAction SilentlyContinue | Select-Object -ExpandProperty InterfaceIndex)
        $allIps = @()

        if ($activeInterfaceIndex) {
            $allIps = Get-NetIPAddress -AddressFamily IPv4 -InterfaceIndex $activeInterfaceIndex -ErrorAction SilentlyContinue | Select-Object -ExpandProperty IPAddress
        }

        if (-not $allIps) {
            $allIps = Get-NetIPAddress -AddressFamily IPv4 -ErrorAction SilentlyContinue | Where-Object { $_.IPAddress -ne "127.0.0.1" } | Select-Object -ExpandProperty IPAddress
        }

        $validIps = $allIps | Where-Object { $_ -notlike "169.254.*" }

        if ($validIps) {
            $ipAddress = $validIps[0]
        } else {
            $apipaIps = $allIps | Where-Object { $_ -like "169.254.*" }
            if ($apipaIps) {
                $failStage = "IP_APIPA (DHCP 伺服器無回應，取得無效的 169.254 網段)"
            } else {
                $failStage = "IP_Missing (未取得任何 IPv4 位址)"
            }
        }

        # 步驟 2: 檢查閘道器 (Gateway) 是否通
        if (-not $failStage) {
            $gateway = $null
            if ($activeInterfaceIndex) {
                $gateway = (Get-NetRoute -DestinationPrefix "0.0.0.0/0" -ErrorAction SilentlyContinue | Where-Object { $_.InterfaceIndex -in $activeInterfaceIndex } | Select-Object -ExpandProperty NextHop | Select-Object -First 1)
            }
            
            if (-not $gateway) {
                $gateway = (Get-NetRoute -DestinationPrefix "0.0.0.0/0" -ErrorAction SilentlyContinue | Select-Object -ExpandProperty NextHop | Where-Object { $_ -and $_ -ne "0.0.0.0" } | Select-Object -First 1)
            }
            
            if ($gateway) {
                $pingGw = Test-Connection -ComputerName $gateway -Count 1 -Quiet
                if (-not $pingGw) {
                    $failStage = "Gateway_Unreachable (有取得 IP 但無法連線至閘道器，實體線路或交換器異常)"
                }
            } else {
                $failStage = "Gateway_NotFound (找不到預設閘道器)"
            }
        }

        # 步驟 3: 檢查外網 IP 是否真不通 (二次確認)
        if (-not $failStage) {
            $pingExt = Test-Connection -ComputerName "8.8.8.8" -Count 1 -Quiet
            if (-not $pingExt) {
                $failStage = "External_Network_Fail (閘道器通，但無法連線至外網，可能路由器斷線或外線掉線)"
            }
        }

        # 步驟 4: 檢查 DNS 解析是否正常
        if (-not $failStage) {
            try {
                $resolve = Resolve-DnsName -Name "google.com" -ErrorAction Stop
            } catch {
                $failStage = "DNS_Fail (外網可通，但無法解析網域名稱，請檢查 DNS 設定)"
            }
        }
    }

    # 根據檢測結果設定 PowerShell 視窗背景與字體顏色
    if ($isOnline -or -not $failStage) {
        $host.UI.RawUI.BackgroundColor = "DarkGreen"
        $host.UI.RawUI.ForegroundColor = "White"
    } else {
        $host.UI.RawUI.BackgroundColor = "DarkRed"
        $host.UI.RawUI.ForegroundColor = "White"
    }
    Clear-Host

    # 渲染美化的輸出畫面
    Write-Host "=========================================" -ForegroundColor Cyan
    Write-Host "      端點網路狀態快速診斷工具          " -ForegroundColor Cyan
    Write-Host "=========================================" -ForegroundColor Cyan
    Write-Host ""

    if ($isOnline) {
        Write-Host "[*] 快速檢測對外連線 (1.1.1.1)... [ 成功 ]" -ForegroundColor Green
    } else {
        Write-Host "[*] 快速檢測對外連線 (1.1.1.1)... [ 失敗 ]" -ForegroundColor Red
        Write-Host "[!] 開始進行詳細診斷..." -ForegroundColor Yellow
        Write-Host ""
        
        if ($validIps) {
            Write-Host "[*] 檢查本機 IP 設定... [ 成功 ]" -ForegroundColor Green
            Write-Host "    -> 目前 IP: $ipAddress"
        } else {
            Write-Host "[*] 檢查本機 IP 設定... [ 失敗 ]" -ForegroundColor Red
        }

        if ($gateway) {
            Write-Host "[*] 檢查區域網路閘道器 (Gateway)... [ 成功 ] ($gateway)" -ForegroundColor Green
        } elseif (-not $failStage -or $failStage -like "Gateway*") {
            Write-Host "[*] 檢查區域網路閘道器 (Gateway)... [ 失敗 ]" -ForegroundColor Red
        }

        Write-Host "[*] 檢查外網與 DNS 狀態..." -NoNewline
        if (-not $failStage) {
            Write-Host " [ 成功 ]" -ForegroundColor Green
        } else {
            Write-Host " [ 失敗 ]" -ForegroundColor Red
        }
    }

    Write-Host ""
    Write-Host "=========================================" -ForegroundColor Cyan
    if ($isOnline -or -not $failStage) {
        Write-Host " 檢測結果：網路完全正常！ (OK)" -ForegroundColor Green
    } else {
        Write-Host " 檢測結果：網路異常" -ForegroundColor Red
        Write-Host " 故障點：$failStage" -ForegroundColor Yellow
    }
    Write-Host "=========================================" -ForegroundColor Cyan
    Write-Host ""

    # 等待按 Enter 鍵
    Read-Host "請檢視上方結果，按下 Enter 鍵關閉視窗..."

} finally {
    # 無論如何（包含正常結束、異常、或中斷），離開前一定會將顏色還原回預設值
    $host.UI.RawUI.BackgroundColor = $originalBg
    $host.UI.RawUI.ForegroundColor = $originalFg
    Clear-Host
}