function Write-Win11ISOLog {
    <#
    .SYNOPSIS
        Appends a timestamped message to the Win11ISO status log TextBox.
    .PARAMETER Message
        The message to append.
    #>
    param([string]$Message)
    $timestamp = (Get-Date).ToString("HH:mm:ss")
    $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
        $current = $sync["WPFWin11ISOStatusLog"].Text
        if ($current -eq "Ready. Please select a Windows 11 ISO to begin.") {
            $sync["WPFWin11ISOStatusLog"].Text = "[$timestamp] $Message"
        } else {
            $sync["WPFWin11ISOStatusLog"].Text += "`n[$timestamp] $Message"
        }
        $sync["WPFWin11ISOStatusLog"].CaretIndex = $sync["WPFWin11ISOStatusLog"].Text.Length
        $sync["WPFWin11ISOStatusLog"].ScrollToEnd()
    })
}

function Invoke-WinUtilISOBrowse {
    <#
    .SYNOPSIS
        Opens an OpenFileDialog so the user can choose a Windows 11 ISO file.
        Populates WPFWin11ISOPath and reveals the Mount & Verify section (Step 2).
    #>
    Add-Type -AssemblyName System.Windows.Forms

    $dlg = [System.Windows.Forms.OpenFileDialog]::new()
    $dlg.Title  = "Select Windows 11 ISO"
    $dlg.Filter = "ISO files (*.iso)|*.iso|All files (*.*)|*.*"
    $dlg.InitialDirectory = [System.Environment]::GetFolderPath("Desktop")

    if ($dlg.ShowDialog() -ne [System.Windows.Forms.DialogResult]::OK) { return }

    $isoPath = $dlg.FileName

    # ── Basic size sanity-check (a Win11 ISO is typically > 4 GB) ──
    $fileSizeGB = [math]::Round((Get-Item $isoPath).Length / 1GB, 2)

    $sync["WPFWin11ISOPath"].Text = $isoPath
    $sync["WPFWin11ISOFileInfo"].Text      = "File size: $fileSizeGB GB"
    $sync["WPFWin11ISOFileInfo"].Visibility = "Visible"

    # Reveal Step 2
    $sync["WPFWin11ISOMountSection"].Visibility = "Visible"

    # Collapse all later steps whenever a new ISO is chosen
    $sync["WPFWin11ISOVerifyResultPanel"].Visibility = "Collapsed"
    $sync["WPFWin11ISOModifySection"].Visibility     = "Collapsed"
    $sync["WPFWin11ISOOutputSection"].Visibility     = "Collapsed"

    Write-Win11ISOLog "ISO selected: $isoPath  ($fileSizeGB GB)"
}

function Invoke-WinUtilISOMountAndVerify {
    <#
    .SYNOPSIS
        Mounts the selected ISO, verifies it is a valid Windows 11 image,
        and populates the edition list.  Reveals Step 3 on success.
    #>
    $isoPath = $sync["WPFWin11ISOPath"].Text

    if ([string]::IsNullOrWhiteSpace($isoPath) -or $isoPath -eq "No ISO selected...") {
        [System.Windows.MessageBox]::Show(
            "Please select an ISO file first.",
            "No ISO Selected", "OK", "Warning")
        return
    }

    Write-Win11ISOLog "Mounting ISO: $isoPath"
    Set-WinUtilProgressBar -Label "Mounting ISO..." -Percent 10

    try {
        # Mount the ISO
        $diskImage = Mount-DiskImage -ImagePath $isoPath -PassThru -ErrorAction Stop
        $driveLetter = ($diskImage | Get-Volume).DriveLetter + ":"
        Write-Win11ISOLog "Mounted at drive $driveLetter"

        Set-WinUtilProgressBar -Label "Verifying ISO contents..." -Percent 30

        # ── Verify install.wim / install.esd presence ──
        $wimPath = Join-Path $driveLetter "sources\install.wim"
        $esdPath = Join-Path $driveLetter "sources\install.esd"

        if (-not (Test-Path $wimPath) -and -not (Test-Path $esdPath)) {
            Dismount-DiskImage -ImagePath $isoPath | Out-Null
            Write-Win11ISOLog "ERROR: install.wim/install.esd not found — not a valid Windows ISO."
            [System.Windows.MessageBox]::Show(
                "This does not appear to be a valid Windows ISO.`n`ninstall.wim / install.esd was not found.",
                "Invalid ISO", "OK", "Error")
            Set-WinUtilProgressBar -Label "" -Percent 0
            return
        }

        $activeWim = if (Test-Path $wimPath) { $wimPath } else { $esdPath }

        # ── Read edition / architecture info ──
        Set-WinUtilProgressBar -Label "Reading image metadata..." -Percent 55

        $imageInfo = Get-WindowsImage -ImagePath $activeWim | Select-Object ImageIndex, ImageName

        # ── Verify at least one Win11 edition is present ──
        $isWin11 = $imageInfo | Where-Object { $_.ImageName -match "Windows 11" }
        if (-not $isWin11) {
            Dismount-DiskImage -ImagePath $isoPath | Out-Null
            Write-Win11ISOLog "ERROR: No 'Windows 11' edition found in the image."
            [System.Windows.MessageBox]::Show(
                "No Windows 11 edition was found in this ISO.`n`nOnly official Windows 11 ISOs are supported.",
                "Not a Windows 11 ISO", "OK", "Error")
            Set-WinUtilProgressBar -Label "" -Percent 0
            return
        }

        # Store edition info for later index lookup
        $sync["Win11ISOImageInfo"] = $imageInfo

        # ── Populate UI ──
        $sync["WPFWin11ISOMountDriveLetter"].Text = "Mounted at: $driveLetter   |   Image file: $(Split-Path $activeWim -Leaf)"
        $sync["WPFWin11ISOEditionComboBox"].Dispatcher.Invoke([action]{
            $sync["WPFWin11ISOEditionComboBox"].Items.Clear()
            foreach ($img in $imageInfo) {
                [void]$sync["WPFWin11ISOEditionComboBox"].Items.Add("$($img.ImageIndex): $($img.ImageName)")
            }
            if ($sync["WPFWin11ISOEditionComboBox"].Items.Count -gt 0) {
                $sync["WPFWin11ISOEditionComboBox"].SelectedIndex = 0
            }
        })
        $sync["WPFWin11ISOVerifyResultPanel"].Visibility = "Visible"

        # Store for later steps
        $sync["Win11ISODriveLetter"] = $driveLetter
        $sync["Win11ISOWimPath"]     = $activeWim
        $sync["Win11ISOImagePath"]   = $isoPath

        # Reveal Step 3
        $sync["WPFWin11ISOModifySection"].Visibility = "Visible"

        Set-WinUtilProgressBar -Label "ISO verified ✔" -Percent 100
        Write-Win11ISOLog "ISO verified OK.  Editions found: $($imageInfo.Count)"
    }
    catch {
        Write-Win11ISOLog "ERROR during mount/verify: $_"
        [System.Windows.MessageBox]::Show(
            "An error occurred while mounting or verifying the ISO:`n`n$_",
            "Error", "OK", "Error")
    }
    finally {
        Start-Sleep -Milliseconds 800
        Set-WinUtilProgressBar -Label "" -Percent 0
    }
}

function Invoke-WinUtilISOModify {
    <#
    .SYNOPSIS
        Extracts ISO contents to a temp working directory, modifies install.wim,
        then repackages the image.  Reveals Step 4 (output options) on success.

    .NOTES
        This function runs inside a PowerShell runspace so the UI stays responsive.
        Placeholder modification logic is provided; extend as needed.
    #>

    $isoPath    = $sync["Win11ISOImagePath"]
    $driveLetter= $sync["Win11ISODriveLetter"]
    $wimPath    = $sync["Win11ISOWimPath"]

    if (-not $isoPath) {
        [System.Windows.MessageBox]::Show(
            "No verified ISO found.  Please complete Steps 1 and 2 first.",
            "Not Ready", "OK", "Warning")
        return
    }

    # ── Resolve selected edition index from the ComboBox ──
    $selectedItem = $sync["WPFWin11ISOEditionComboBox"].SelectedItem
    $selectedWimIndex = 1  # default fallback
    if ($selectedItem -and $selectedItem -match '^(\d+):') {
        $selectedWimIndex = [int]$Matches[1]
    } elseif ($sync["Win11ISOImageInfo"]) {
        $selectedWimIndex = $sync["Win11ISOImageInfo"][0].ImageIndex
    }
    $selectedEditionName = if ($selectedItem) { ($selectedItem -replace '^\d+:\s*', '') } else { "Unknown" }
    Write-Win11ISOLog "Selected edition: $selectedEditionName (Index $selectedWimIndex)"

    # Disable the modify button to prevent double-click
    $sync["WPFWin11ISOModifyButton"].IsEnabled = $false

    $existingWorkDir = Get-Item -Path (Join-Path $env:TEMP "WinUtil_Win11ISO*") -ErrorAction SilentlyContinue |
        Where-Object { $_.PSIsContainer } |
        Sort-Object LastWriteTime -Descending |
        Select-Object -First 1

    $workDir = if ($existingWorkDir) {
        Write-Win11ISOLog "Reusing existing temp directory: $($existingWorkDir.FullName)"
        $existingWorkDir.FullName
    } else {
        Join-Path $env:TEMP "WinUtil_Win11ISO_$(Get-Date -Format 'yyyyMMdd_HHmmss')"
    }

    # ── Resolve autounattend.xml content ──────────────────────────────────────
    # Compiled winutil.ps1 sets $WinUtilAutounattendXml before main.ps1 runs.
    # In dev/source mode fall back to reading tools\autounattend.xml directly.
    $autounattendContent = if ($WinUtilAutounattendXml) {
        $WinUtilAutounattendXml
    } else {
        $toolsXml = Join-Path $PSScriptRoot "..\..\tools\autounattend.xml"
        if (Test-Path $toolsXml) { Get-Content $toolsXml -Raw } else { "" }
    }

    # ── Run modification in a background runspace ──
    $runspace = [Management.Automation.Runspaces.RunspaceFactory]::CreateRunspace()
    $runspace.ApartmentState = "STA"
    $runspace.ThreadOptions  = "ReuseThread"
    $runspace.Open()
    $runspace.SessionStateProxy.SetVariable("sync",                $sync)
    $runspace.SessionStateProxy.SetVariable("isoPath",             $isoPath)
    $runspace.SessionStateProxy.SetVariable("driveLetter",         $driveLetter)
    $runspace.SessionStateProxy.SetVariable("wimPath",             $wimPath)
    $runspace.SessionStateProxy.SetVariable("workDir",             $workDir)
    $runspace.SessionStateProxy.SetVariable("selectedWimIndex",    $selectedWimIndex)
    $runspace.SessionStateProxy.SetVariable("selectedEditionName", $selectedEditionName)
    $runspace.SessionStateProxy.SetVariable("autounattendContent", $autounattendContent)

    # Serialize functions so they are available inside the runspace
    $isoScriptFuncDef = "function Invoke-WinUtilISOScript {`n" + `
        ${function:Invoke-WinUtilISOScript}.ToString() + "`n}"
    $runspace.SessionStateProxy.SetVariable("isoScriptFuncDef", $isoScriptFuncDef)

    $win11ISOLogFuncDef = "function Write-Win11ISOLog {`n" + `
        ${function:Write-Win11ISOLog}.ToString() + "`n}"
    $runspace.SessionStateProxy.SetVariable("win11ISOLogFuncDef", $win11ISOLogFuncDef)

    $refreshUSBFuncDef = "function Invoke-WinUtilISORefreshUSBDrives {`n" + `
        ${function:Invoke-WinUtilISORefreshUSBDrives}.ToString() + "`n}"
    $runspace.SessionStateProxy.SetVariable("refreshUSBFuncDef", $refreshUSBFuncDef)

    $script = [Management.Automation.PowerShell]::Create()
    $script.Runspace = $runspace
    $script.AddScript({

        # Import helper functions into this runspace
        . ([scriptblock]::Create($isoScriptFuncDef))
        . ([scriptblock]::Create($win11ISOLogFuncDef))
        . ([scriptblock]::Create($refreshUSBFuncDef))

        function Log($msg) {
            $ts = (Get-Date).ToString("HH:mm:ss")
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                $sync["WPFWin11ISOStatusLog"].Text += "`n[$ts] $msg"
                $sync["WPFWin11ISOStatusLog"].CaretIndex = $sync["WPFWin11ISOStatusLog"].Text.Length
                $sync["WPFWin11ISOStatusLog"].ScrollToEnd()
            })
        }

        function SetProgress($label, $pct) {
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                $sync.progressBarTextBlock.Text    = $label
                $sync.progressBarTextBlock.ToolTip = $label
                $sync.ProgressBar.Value            = [Math]::Max($pct, 5)
            })
        }

        try {
            # ── Hide Steps 1-3 while modification is running; expand log to fill screen ──
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                $sync["WPFWin11ISOSelectSection"].Visibility  = "Collapsed"
                $sync["WPFWin11ISOMountSection"].Visibility   = "Collapsed"
                $sync["WPFWin11ISOModifySection"].Visibility  = "Collapsed"
                $expandedHeight = [Math]::Max(400, $sync["Form"].ActualHeight - 100)
                $sync["WPFWin11ISOStatusLog"].Height = $expandedHeight
                $sync["Win11ISOLogExpanded"] = $true
                # Register the resize handler once so the log tracks window resizes
                if (-not $sync["Win11ISOResizeHandlerAdded"]) {
                    $sync["Form"].add_SizeChanged({
                        if ($sync["Win11ISOLogExpanded"]) {
                            $sync["WPFWin11ISOStatusLog"].Height = [Math]::Max(400, $sync["Form"].ActualHeight - 100)
                            $sync["WPFWin11ISOStatusLog"].CaretIndex = $sync["WPFWin11ISOStatusLog"].Text.Length
                            $sync["WPFWin11ISOStatusLog"].ScrollToEnd()
                        }
                    })
                    $sync["Win11ISOResizeHandlerAdded"] = $true
                }
            })

            # ── 1. Create working directory structure ──
            Log "Creating working directory: $workDir"
            $isoContents = Join-Path $workDir "iso_contents"
            $mountDir     = Join-Path $workDir "wim_mount"
            New-Item -ItemType Directory -Path $isoContents, $mountDir -Force | Out-Null
            SetProgress "Copying ISO contents..." 10

            # ── 2. Copy all ISO contents to the working directory ──
            Log "Copying ISO contents from $driveLetter to $isoContents..."
            $robocopyArgs = @($driveLetter, $isoContents, "/E", "/NFL", "/NDL", "/NJH", "/NJS")
            & robocopy @robocopyArgs | Out-Null
            Log "ISO contents copied."
            SetProgress "Mounting install.wim..." 25

            # ── 3. Copy install.wim to working dir (it may be read-only on the DVD) ──
            $localWim = Join-Path $isoContents "sources\install.wim"
            if (-not (Test-Path $localWim)) {
                # ESD path
                $localWim = Join-Path $isoContents "sources\install.esd"
            }
            # Ensure the file is writable
            Set-ItemProperty -Path $localWim -Name IsReadOnly -Value $false

            # ── 4. Mount the selected edition of install.wim ──
            Log "Mounting install.wim (Index ${selectedWimIndex}: $selectedEditionName) at $mountDir..."
            Mount-WindowsImage -ImagePath $localWim -Index $selectedWimIndex -Path $mountDir -ErrorAction Stop | Out-Null
            SetProgress "Modifying install.wim..." 45

            # ── Apply all WinUtil modifications via Invoke-WinUtilISOScript ──
            Log "Applying WinUtil modifications to install.wim..."
            Invoke-WinUtilISOScript -ScratchDir $mountDir -ISOContentsDir $isoContents -AutoUnattendXml $autounattendContent -Log { param($m) Log $m }

            # ── 4b. DISM component store cleanup ──
            # /ResetBase removes all superseded component versions from WinSxS,
            # which is the single largest space saving possible (typically 300–800 MB).
            # This must be done while the image is still mounted.
            SetProgress "Cleaning up component store (WinSxS)..." 56
            Log "Running DISM component store cleanup (/ResetBase)..."
            & dism /English "/image:$mountDir" /Cleanup-Image /StartComponentCleanup /ResetBase | ForEach-Object { Log $_ }
            Log "Component store cleanup complete."

            # ── 5. Save and dismount the WIM ──
            SetProgress "Saving modified install.wim..." 65
            Log "Dismounting and saving install.wim. This will take several minutes..."
            Dismount-WindowsImage -Path $mountDir -Save -ErrorAction Stop | Out-Null
            Log "install.wim saved."

            # ── 5b. Strip unused editions — export only the selected index ──
            # A standard multi-edition install.wim can be 4–5 GB; exporting a
            # single index typically drops it to ~3 GB, saving 1–2 GB in the ISO.
            SetProgress "Removing unused editions from install.wim..." 70
            Log "Exporting edition '$selectedEditionName' (Index $selectedWimIndex) to a single-edition install.wim..."
            $exportWim = Join-Path $isoContents "sources\install_export.wim"
            Export-WindowsImage `
                -SourceImagePath $localWim `
                -SourceIndex     $selectedWimIndex `
                -DestinationImagePath $exportWim `
                -ErrorAction Stop | Out-Null
            Remove-Item -Path $localWim -Force
            Rename-Item -Path $exportWim -NewName "install.wim" -Force
            # Update local path so later steps (e.g. ISO build) reference the new file
            $localWim = Join-Path $isoContents "sources\install.wim"
            Log "Unused editions removed.  install.wim now contains only '$selectedEditionName'."

            SetProgress "Dismounting source ISO..." 80

            # ── 6. Dismount the original ISO ──
            Log "Dismounting original ISO..."
            Dismount-DiskImage -ImagePath $isoPath | Out-Null

            # Store work directory for output steps
            $sync["Win11ISOWorkDir"]      = $workDir
            $sync["Win11ISOContentsDir"]  = $isoContents

            SetProgress "Modification complete ✔" 100
            Log "install.wim modification complete.  Choose an output option in Step 4."

            # ── Reveal Step 4 on the UI thread ──
            # Note: USB drive enumeration (Get-Disk) is intentionally deferred to
            # when the user explicitly selects the USB option, to avoid blocking
            # the UI thread here.
            $sync["WPFWin11ISOOutputSection"].Dispatcher.Invoke([action]{
                $sync["WPFWin11ISOOutputSection"].Visibility = "Visible"
            })
        }
        catch {
            Log "ERROR during modification: $_"

            # ── Cleanup: dismount WIM if still mounted ──
            try {
                if (Test-Path $mountDir) {
                    $mountedImages = Get-WindowsImage -Mounted -ErrorAction SilentlyContinue |
                                     Where-Object { $_.Path -eq $mountDir }
                    if ($mountedImages) {
                        Log "Cleaning up: dismounting install.wim (discarding changes)..."
                        Dismount-WindowsImage -Path $mountDir -Discard -ErrorAction SilentlyContinue | Out-Null
                    }
                }
            } catch {
                Log "Warning: could not dismount install.wim during cleanup: $_"
            }

            # ── Cleanup: dismount the source ISO ──
            try {
                $mountedISO = Get-DiskImage -ImagePath $isoPath -ErrorAction SilentlyContinue
                if ($mountedISO -and $mountedISO.Attached) {
                    Log "Cleaning up: dismounting source ISO..."
                    Dismount-DiskImage -ImagePath $isoPath -ErrorAction SilentlyContinue | Out-Null
                }
            } catch {
                Log "Warning: could not dismount ISO during cleanup: $_"
            }

            # ── Cleanup: remove temp working directory ──
            try {
                if (Test-Path $workDir) {
                    Log "Cleaning up: removing temp directory $workDir..."
                    Remove-Item -Path $workDir -Recurse -Force -ErrorAction SilentlyContinue
                }
            } catch {
                Log "Warning: could not remove temp directory during cleanup: $_"
            }

            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                [System.Windows.MessageBox]::Show(
                    "An error occurred during install.wim modification:`n`n$_",
                    "Modification Error", "OK", "Error")
            })
        }
        finally {
            Start-Sleep -Milliseconds 800
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                $sync.progressBarTextBlock.Text = ""
                $sync.progressBarTextBlock.ToolTip = ""
                $sync.ProgressBar.Value = 0
                $sync["WPFWin11ISOModifyButton"].IsEnabled = $true
                # ── Only restore steps 1-3 if Step 4 was NOT successfully shown ──
                # When modification succeeds, Step 4 is visible and steps 1-3 stay
                # hidden until the user clicks Clean & Reset.
                if ($sync["WPFWin11ISOOutputSection"].Visibility -ne "Visible") {
                    $sync["WPFWin11ISOSelectSection"].Visibility = "Visible"
                    $sync["WPFWin11ISOMountSection"].Visibility  = "Visible"
                    $sync["WPFWin11ISOModifySection"].Visibility = "Visible"
                }
                $sync["Win11ISOLogExpanded"] = $false
                $sync["WPFWin11ISOStatusLog"].Height = 140
            })
        }
    }) | Out-Null

    $script.BeginInvoke() | Out-Null
}

function Invoke-WinUtilISOCleanAndReset {
    <#
    .SYNOPSIS
        Deletes the temporary working directory created during ISO modification
        and resets the entire ISO UI back to its initial state (Step 1 only).
    #>

    $workDir = $sync["Win11ISOWorkDir"]

    if ($workDir -and (Test-Path $workDir)) {
        $confirm = [System.Windows.MessageBox]::Show(
            "This will delete the temporary working directory:`n`n$workDir`n`nAnd reset the interface back to the start.`n`nContinue?",
            "Clean & Reset", "YesNo", "Warning")
        if ($confirm -ne "Yes") { return }

        try {
            Write-Win11ISOLog "Deleting temp directory: $workDir"
            Remove-Item -Path $workDir -Recurse -Force -ErrorAction Stop
            Write-Win11ISOLog "Temp directory deleted."
        } catch {
            Write-Win11ISOLog "WARNING: could not fully delete temp directory: $_"
        }
    }

    # Clear all stored ISO state
    $sync["Win11ISOWorkDir"]     = $null
    $sync["Win11ISOContentsDir"] = $null
    $sync["Win11ISOImagePath"]   = $null
    $sync["Win11ISODriveLetter"] = $null
    $sync["Win11ISOWimPath"]     = $null
    $sync["Win11ISOImageInfo"]   = $null
    $sync["Win11ISOUSBDisks"]    = $null

    # Reset the UI to the initial state
    $sync["WPFWin11ISOPath"].Text                     = "No ISO selected..."
    $sync["WPFWin11ISOFileInfo"].Visibility            = "Collapsed"
    $sync["WPFWin11ISOVerifyResultPanel"].Visibility   = "Collapsed"
    $sync["WPFWin11ISOOptionUSB"].Visibility           = "Collapsed"
    $sync["WPFWin11ISOOutputSection"].Visibility       = "Collapsed"
    $sync["WPFWin11ISOModifySection"].Visibility       = "Collapsed"
    $sync["WPFWin11ISOMountSection"].Visibility        = "Collapsed"
    $sync["WPFWin11ISOSelectSection"].Visibility       = "Visible"
    $sync["WPFWin11ISOStatusLog"].Text                 = "Ready. Please select a Windows 11 ISO to begin."
    $sync["WPFWin11ISOStatusLog"].Height               = 140
    $sync["WPFWin11ISOModifyButton"].IsEnabled         = $true
}

function Invoke-WinUtilISOExport {
    <#
    .SYNOPSIS
        Saves the modified ISO contents as a new bootable ISO file.
        Uses oscdimg.exe (part of the Windows ADK) if present; falls back
        to a reminder message if not installed.
    #>
    $contentsDir = $sync["Win11ISOContentsDir"]

    if (-not $contentsDir -or -not (Test-Path $contentsDir)) {
        [System.Windows.MessageBox]::Show(
            "No modified ISO content found.  Please complete Steps 1–3 first.",
            "Not Ready", "OK", "Warning")
        return
    }

    Add-Type -AssemblyName System.Windows.Forms

    $dlg = [System.Windows.Forms.SaveFileDialog]::new()
    $dlg.Title            = "Save Modified Windows 11 ISO"
    $dlg.Filter           = "ISO files (*.iso)|*.iso"
    $dlg.FileName         = "Win11_Modified_$(Get-Date -Format 'yyyyMMdd').iso"
    $dlg.InitialDirectory = [System.Environment]::GetFolderPath("Desktop")

    if ($dlg.ShowDialog() -ne [System.Windows.Forms.DialogResult]::OK) { return }

    $outputISO = $dlg.FileName
    Write-Win11ISOLog "Exporting to ISO: $outputISO"
    Set-WinUtilProgressBar -Label "Building ISO..." -Percent 10

    # Locate oscdimg.exe (Windows ADK)
    $oscdimg = Get-ChildItem "C:\Program Files (x86)\Windows Kits" -Recurse -Filter "oscdimg.exe" -ErrorAction SilentlyContinue |
               Select-Object -First 1 -ExpandProperty FullName

    if (-not $oscdimg) {
        Write-Win11ISOLog "oscdimg.exe not found.  Attempting to install via winget..."
        Set-WinUtilProgressBar -Label "Installing oscdimg..." -Percent 5
        try {
            $winget = Get-Command winget -ErrorAction Stop
            $result = & $winget install -e --id Microsoft.OSCDIMG --accept-package-agreements --accept-source-agreements 2>&1
            Write-Win11ISOLog "winget output: $result"
            # Re-scan for oscdimg after install
            $oscdimg = Get-ChildItem "C:\Program Files (x86)\Windows Kits" -Recurse -Filter "oscdimg.exe" -ErrorAction SilentlyContinue |
                       Select-Object -First 1 -ExpandProperty FullName
        } catch {
            Write-Win11ISOLog "winget not available or install failed: $_"
        }

        if (-not $oscdimg) {
            Set-WinUtilProgressBar -Label "" -Percent 0
            Write-Win11ISOLog "oscdimg.exe still not found after install attempt."
            [System.Windows.MessageBox]::Show(
                "oscdimg.exe could not be found or installed automatically.`n`nPlease install it manually:`n  winget install -e --id Microsoft.OSCDIMG`n`nOr install the Windows ADK from:`nhttps://learn.microsoft.com/windows-hardware/get-started/adk-install",
                "oscdimg Not Found", "OK", "Warning")
            return
        }
        Write-Win11ISOLog "oscdimg.exe installed successfully."
    }

    # Build boot parameters (BIOS + UEFI dual-boot)
    $bootData   = "2#p0,e,b`"$contentsDir\boot\etfsboot.com`"#pEF,e,b`"$contentsDir\efi\microsoft\boot\efisys.bin`""
    $oscdimgArgs = @(
        "-m",           # ignore source path max size
        "-o",           # optimise storage
        "-u2",          # UDF 2.01
        "-udfver102",
        "-bootdata:$bootData",
        "-l`"CTOS_MODIFIED`"",
        "`"$contentsDir`"",
        "`"$outputISO`""
    )

    try {
        Write-Win11ISOLog "Running oscdimg..."
        $proc = Start-Process -FilePath $oscdimg -ArgumentList $oscdimgArgs -Wait -PassThru -NoNewWindow
        if ($proc.ExitCode -eq 0) {
            Set-WinUtilProgressBar -Label "ISO exported ✔" -Percent 100
            Write-Win11ISOLog "ISO exported successfully: $outputISO"
            [System.Windows.MessageBox]::Show(
                "ISO exported successfully!`n`n$outputISO",
                "Export Complete", "OK", "Info")
        } else {
            Write-Win11ISOLog "oscdimg exited with code $($proc.ExitCode)."
            [System.Windows.MessageBox]::Show(
                "oscdimg exited with code $($proc.ExitCode).`nCheck the status log for details.",
                "Export Error", "OK", "Error")
        }
    }
    catch {
        Write-Win11ISOLog "ERROR during ISO export: $_"
        [System.Windows.MessageBox]::Show("ISO export failed:`n`n$_","Error","OK","Error")
    }
    finally {
        Start-Sleep -Milliseconds 800
        Set-WinUtilProgressBar -Label "" -Percent 0
    }
}

function Invoke-WinUtilISORefreshUSBDrives {
    <#
    .SYNOPSIS
        Populates the USB drive ComboBox with all currently attached removable drives.
    #>
    $combo = $sync["WPFWin11ISOUSBDriveComboBox"]
    $combo.Items.Clear()

    $removable = Get-Disk | Where-Object { $_.BusType -eq "USB" } | Sort-Object Number

    if ($removable.Count -eq 0) {
        $combo.Items.Add("No USB drives detected")
        $combo.SelectedIndex = 0
        Write-Win11ISOLog "No USB drives detected."
        return
    }

    foreach ($disk in $removable) {
        $sizeGB    = [math]::Round($disk.Size / 1GB, 1)
        $label     = "Disk $($disk.Number): $($disk.FriendlyName)  [$sizeGB GB]  — $($disk.PartitionStyle)"
        $combo.Items.Add($label)
    }
    $combo.SelectedIndex = 0
    Write-Win11ISOLog "Found $($removable.Count) USB drive(s)."

    # Store disk objects for later use
    $sync["Win11ISOUSBDisks"] = $removable
}

function Invoke-WinUtilISOWriteUSB {
    <#
    .SYNOPSIS
        Erases the selected USB drive and writes the modified Windows 11 ISO
        content as a bootable installation drive (using DISM / robocopy approach).
    #>
    $contentsDir = $sync["Win11ISOContentsDir"]
    $usbDisks    = $sync["Win11ISOUSBDisks"]

    if (-not $contentsDir -or -not (Test-Path $contentsDir)) {
        [System.Windows.MessageBox]::Show(
            "No modified ISO content found.  Please complete Steps 1–3 first.",
            "Not Ready", "OK", "Warning")
        return
    }

    $selectedIndex = $sync["WPFWin11ISOUSBDriveComboBox"].SelectedIndex
    if ($selectedIndex -lt 0 -or -not $usbDisks -or $selectedIndex -ge $usbDisks.Count) {
        [System.Windows.MessageBox]::Show(
            "Please select a USB drive from the dropdown.",
            "No Drive Selected", "OK", "Warning")
        return
    }

    $targetDisk = $usbDisks[$selectedIndex]
    $diskNum    = $targetDisk.Number
    $sizeGB     = [math]::Round($targetDisk.Size / 1GB, 1)

    $confirm = [System.Windows.MessageBox]::Show(
        "ALL data on Disk $diskNum ($($targetDisk.FriendlyName), $sizeGB GB) will be PERMANENTLY ERASED.`n`nAre you sure you want to continue?",
        "Confirm USB Erase", "YesNo", "Warning")

    if ($confirm -ne "Yes") {
        Write-Win11ISOLog "USB write cancelled by user."
        return
    }

    $sync["WPFWin11ISOWriteUSBButton"].IsEnabled = $false
    Write-Win11ISOLog "Starting USB write to Disk $diskNum..."

    $runspace = [Management.Automation.Runspaces.RunspaceFactory]::CreateRunspace()
    $runspace.ApartmentState = "STA"
    $runspace.ThreadOptions  = "ReuseThread"
    $runspace.Open()
    $runspace.SessionStateProxy.SetVariable("sync",         $sync)
    $runspace.SessionStateProxy.SetVariable("diskNum",      $diskNum)
    $runspace.SessionStateProxy.SetVariable("contentsDir",  $contentsDir)

    $script = [Management.Automation.PowerShell]::Create()
    $script.Runspace = $runspace
    $script.AddScript({

        function Log($msg) {
            $ts = (Get-Date).ToString("HH:mm:ss")
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                $sync["WPFWin11ISOStatusLog"].Text += "`n[$ts] $msg"
                $sync["WPFWin11ISOStatusLog"].CaretIndex = $sync["WPFWin11ISOStatusLog"].Text.Length
                $sync["WPFWin11ISOStatusLog"].ScrollToEnd()
            })
        }
        function SetProgress($label, $pct) {
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                $sync.progressBarTextBlock.Text    = $label
                $sync.progressBarTextBlock.ToolTip = $label
                $sync.ProgressBar.Value            = [Math]::Max($pct, 5)
            })
        }

        try {
            SetProgress "Formatting USB drive..." 10

            # ── Diskpart script: clean, GPT, create ESP + data partitions ──
            $dpScript = @"
select disk $diskNum
clean
convert gpt
create partition efi size=512
format quick fs=fat32 label="SYSTEM"
assign
create partition primary
format quick fs=fat32 label="WINPE"
assign
exit
"@
            $dpFile = Join-Path $env:TEMP "winutil_diskpart_$(Get-Random).txt"
            $dpScript | Set-Content -Path $dpFile -Encoding ASCII
            Log "Running diskpart on Disk $diskNum..."
            diskpart /s $dpFile | Out-Null
            Remove-Item $dpFile -Force

            SetProgress "Identifying USB partitions..." 30
            Start-Sleep -Seconds 3   # let Windows assign drive letters

            # Find newly assigned drive letter for the data partition
            $usbVol = Get-Partition -DiskNumber $diskNum |
                      Where-Object { $_.Type -eq "Basic" } |
                      Get-Volume |
                      Where-Object { $_.FileSystemLabel -eq "WINPE" } |
                      Select-Object -First 1

            if (-not $usbVol) {
                throw "Could not locate the formatted USB data partition.  Drive letter may not have been assigned automatically."
            }

            $usbDrive = "$($usbVol.DriveLetter):"
            Log "USB data partition: $usbDrive"
            SetProgress "Copying Windows 11 files to USB..." 45

            # ── Copy files (split large install.wim if > 4 GB for FAT32) ──
            $installWim = Join-Path $contentsDir "sources\install.wim"
            if (Test-Path $installWim) {
                $wimSizeMB = [math]::Round((Get-Item $installWim).Length / 1MB)
                if ($wimSizeMB -gt 3800) {
                    # FAT32 limit – split with DISM
                    Log "install.wim is $wimSizeMB MB – splitting for FAT32 compatibility..."
                    $splitDest = Join-Path $usbDrive "sources\install.swm"
                    New-Item -ItemType Directory -Path (Split-Path $splitDest) -Force | Out-Null
                    Split-WindowsImage -ImagePath $installWim `
                                       -SplitImagePath $splitDest `
                                       -FileSize 3800 -CheckIntegrity | Out-Null
                    Log "install.wim split complete."

                    # Copy everything else (exclude install.wim)
                    $robocopyArgs = @($contentsDir, $usbDrive, "/E", "/XF", "install.wim", "/NFL", "/NDL", "/NJH", "/NJS")
                    & robocopy @robocopyArgs | Out-Null
                } else {
                    & robocopy $contentsDir $usbDrive /E /NFL /NDL /NJH /NJS | Out-Null
                }
            } else {
                & robocopy $contentsDir $usbDrive /E /NFL /NDL /NJH /NJS | Out-Null
            }

            SetProgress "Finalising USB drive..." 90
            Log "Files copied to USB."

            SetProgress "USB write complete ✔" 100
            Log "USB drive is ready for use."

            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                [System.Windows.MessageBox]::Show(
                    "USB drive created successfully!`n`nYou can now boot from this drive to install Windows 11.",
                    "USB Ready", "OK", "Info")
            })
        }
        catch {
            Log "ERROR during USB write: $_"
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                [System.Windows.MessageBox]::Show(
                    "USB write failed:`n`n$_",
                    "USB Write Error", "OK", "Error")
            })
        }
        finally {
            Start-Sleep -Milliseconds 800
            $sync["WPFWin11ISOStatusLog"].Dispatcher.Invoke([action]{
                $sync.progressBarTextBlock.Text = ""
                $sync.progressBarTextBlock.ToolTip = ""
                $sync.ProgressBar.Value = 0
                $sync["WPFWin11ISOWriteUSBButton"].IsEnabled = $true
            })
        }
    }) | Out-Null

    $script.BeginInvoke() | Out-Null
}