param(
    [Parameter(Mandatory=$true)] # Make parameter mandatory
    [int]$ThresholdDays
)

# Define path for HTML report (dynamic filename)
$downloadsFolder = [System.IO.Path]::Combine($env:USERPROFILE, "Downloads")
$outputFile = Join-Path -Path $downloadsFolder -ChildPath ("InactiveMailboxesReport-$($ThresholdDays)Days.html")

# Define path for server address and credentials
$serverAddressFile = ".\DefaultServer.txt"
$credentialFile = ".\AdminCredential.xml"

# --- HTML Styling (CSS) ---
$cssStyle = @"
<style>
body { font-family: Segoe UI, Calibri, Arial, sans-serif; font-size: 10pt; }
h1 { color: #2E4053; font-size: 16pt; margin-bottom: 15px;}
h2 { color: #17202A; font-size: 14pt; margin-top: 25px; border-bottom: 1px solid #AEB6BF; padding-bottom: 5px; }
table { border-collapse: collapse; width: 95%; margin-top: 10px; margin-bottom: 15px; border: 1px solid #AEB6BF; } /* Increased width */
th { background-color: #5DADE2; color: white; padding: 8px; text-align: left; border: 1px solid #AEB6BF; } /* Adjusted header color */
td { padding: 8px; text-align: left; border: 1px solid #D5DBDB; }
tr:nth-child(even) { background-color: #f2f2f2; }
tr:hover { background-color: #ddd; }
.description { margin-top: 10px; margin-bottom: 20px; padding: 10px; background-color: #f9f9f9; border-left: 4px solid #5DADE2; } /* Adjusted border color */
.description p { margin-top: 0; margin-bottom: 5px; }
.description code { font-family: Consolas, monospace; background-color: #eee; padding: 2px 4px; border-radius: 3px; }
.never-logged-on { color: #E74C3C; font-style: italic; } /* Style for 'Never' */
.status-update { margin-top: 15px; font-style: italic; color: #555; }
.error { color: red; font-weight: bold; }
.warning { color: orange; font-weight: bold; }
.success { color: green; font-weight: bold; }
.timestamp { font-size: 8pt; color: #888; margin-top: 25px; }
</style>
"@

# --- Script Logic ---
$session = $null # Initialize session variable
$inactiveUserMailboxes = @()
$inactiveSharedMailboxes = @()

# --- Initialize Report Body with Title and Descriptions ---
$thresholdDate = (Get-Date).AddDays(-$ThresholdDays)
$reportTitle = "<h1>Inactive Mailbox Report ($($ThresholdDays) Days)</h1>"
$reportDescription = @"
<div class='description'>
<p>This report lists user and shared mailboxes that have not been logged into since <strong>$($thresholdDate.ToString('yyyy-MM-dd'))</strong> (older than <code>$ThresholdDays</code> days).</p>
<p>Mailboxes listed with a 'Last Logon' date of 'Never' have potentially never been accessed or logon auditing was not enabled when they might have been accessed.</p>
<p><strong>Note:</strong> The accuracy of 'LastLogonTime' depends on Exchange auditing configurations. This report excludes Discovery and System mailboxes.</p>
</div>
"@

$reportBody = $reportTitle + $reportDescription

try {
    # Validate the ThresholdDays parameter (already handled by Mandatory attribute, but double-check > 0)
    if ($ThresholdDays -le 0) {
        throw "ThresholdDays parameter must be a positive number."
    }

    # --- Input File Validation ---
    if (-not (Test-Path $serverAddressFile)) {
        throw "Server address file not found: $serverAddressFile"
    }
    if (-not (Test-Path $credentialFile)) {
        throw "Credential file not found: $credentialFile"
    }

    # Import admin credentials
    $serverAddress = Get-Content -Path $serverAddressFile
    $credential = Import-Clixml -Path $credentialFile

    # Establish session with Exchange Server
    Write-Host "Connecting to Exchange Server: $serverAddress..."
    $session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri "http://$serverAddress/PowerShell/" -Authentication Kerberos -Credential $credential -ErrorAction Stop
    Import-PSSession $session -DisableNameChecking -ErrorAction Stop
    Write-Host "Successfully connected to Exchange." -ForegroundColor Green

    # --- Data Retrieval and Processing ---
    Write-Host "Retrieving mailboxes and checking last logon time (this may take a while)..."
    # *** CORRECTED Filter syntax using -eq and -or ***
    $mailboxesToCheck = Get-Mailbox -ResultSize Unlimited -Filter { (RecipientTypeDetails -eq 'UserMailbox') -or (RecipientTypeDetails -eq 'SharedMailbox') }

    $totalMailboxes = $mailboxesToCheck.Count
    $processedCount = 0
    $progressPercent = 0

    foreach ($mb in $mailboxesToCheck) {
        $processedCount++
        $newProgressPercent = [math]::Floor(($processedCount / $totalMailboxes) * 100)
        if ($newProgressPercent -gt $progressPercent) {
            $progressPercent = $newProgressPercent
            Write-Progress -Activity "Processing Mailboxes" -Status "Checking $($mb.PrimarySmtpAddress) ($processedCount of $totalMailboxes)" -PercentComplete $progressPercent
        }

        $lastLogonTime = $null # Reset for each mailbox
        try {
            # Get statistics - use SilentlyContinue as some mailboxes might error here but we want to continue
            $mailboxStats = Get-MailboxStatistics $mb.Identity -ErrorAction SilentlyContinue
            if ($mailboxStats) {
                $lastLogonTime = $mailboxStats.LastLogonTime
            }
        } catch {
             Write-Warning "Could not retrieve statistics for $($mb.PrimarySmtpAddress): $($_.Exception.Message)"
        }

        # Check if inactive (Never logged on OR logon time is before threshold)
        if (($null -eq $lastLogonTime) -or ($lastLogonTime -lt $thresholdDate)) {
            $mailboxData = [PSCustomObject]@{
                DisplayName   = $mb.DisplayName
                EmailAddress  = $mb.PrimarySmtpAddress
                LastLogonTime = if ($lastLogonTime) { $lastLogonTime } else { "Never" } # Store actual value or "Never"
                RecipientType = $mb.RecipientTypeDetails
            }

            if ($mailboxData.RecipientType -eq "SharedMailbox") {
                $inactiveSharedMailboxes += $mailboxData
            } else { # Assumes UserMailbox if not Shared
                $inactiveUserMailboxes += $mailboxData
            }
        }
    }
    Write-Progress -Activity "Processing Mailboxes" -Completed

    Write-Host "Finished processing mailboxes. Found $($inactiveUserMailboxes.Count) inactive user mailboxes and $($inactiveSharedMailboxes.Count) inactive shared mailboxes."

    # --- Generate User Mailboxes Table ---
    $reportBody += "<h2>Inactive User Mailboxes (Last Logon Older than $ThresholdDays days)</h2>"
    if ($inactiveUserMailboxes.Count -gt 0) {
        # Format the data for the table, handling the 'Never' case
        $formattedUsers = $inactiveUserMailboxes | Select-Object DisplayName, EmailAddress, @{Name='Last Logon'; Expression={
            if ($_.LastLogonTime -is [datetime]) {
                 # Format as date string
                 $_.LastLogonTime.ToString('yyyy-MM-dd HH:mm:ss')
            } else {
                 # Apply class for 'Never'
                 "<span class='never-logged-on'>Never</span>"
            }
        }}
        # ConvertTo-Html and Decode the 'Never' span
        $userTableHtml = $formattedUsers | Sort-Object DisplayName | ConvertTo-Html -Fragment -Property DisplayName, EmailAddress, 'Last Logon' # Added Sort-Object
        $reportBody += [System.Net.WebUtility]::HtmlDecode($userTableHtml)
    } else {
        $reportBody += "<p>No inactive user mailboxes found meeting the criteria.</p>"
    }

    # --- Generate Shared Mailboxes Table ---
    $reportBody += "<h2>Inactive Shared Mailboxes (Last Logon Older than $ThresholdDays days)</h2>"
    if ($inactiveSharedMailboxes.Count -gt 0) {
        # Format the data for the table
         $formattedShared = $inactiveSharedMailboxes | Select-Object DisplayName, EmailAddress, @{Name='Last Logon'; Expression={
            if ($_.LastLogonTime -is [datetime]) {
                 # Format as date string
                 $_.LastLogonTime.ToString('yyyy-MM-dd HH:mm:ss')
            } else {
                 # Apply class for 'Never'
                 "<span class='never-logged-on'>Never</span>"
            }
        }}
        # ConvertTo-Html and Decode the 'Never' span
        $sharedTableHtml = $formattedShared | Sort-Object DisplayName | ConvertTo-Html -Fragment -Property DisplayName, EmailAddress, 'Last Logon' # Added Sort-Object
        $reportBody += [System.Net.WebUtility]::HtmlDecode($sharedTableHtml)
    } else {
        $reportBody += "<p>No inactive shared mailboxes found meeting the criteria.</p>"
    }

    $reportBody += "<p class='status-update'>Report generation complete.</p>"

} catch {
    Write-Host "Error: $($_.Exception.Message)" -ForegroundColor Red
    # Append error details to the report body (which already has title/description)
    $reportBody += "<h2 class='error'>Script Execution Error</h2>"
    $reportBody += "<p class='error'>An error occurred while generating the inactive mailbox report.</p>"
    $reportBody += "<p class='error'><strong>Error Details:</strong><br/>$([System.Net.WebUtility]::HtmlEncode($_.Exception.Message))</p>"
    if ($_.Exception.StackTrace) {
         $reportBody += "<p class='error'><strong>Stack Trace:</strong><br/>$([System.Net.WebUtility]::HtmlEncode($_.Exception.StackTrace) -replace "`n", "<br/>")</p>"
     }
     if ($_.InvocationInfo) {
         $reportBody += "<p class='error'><strong>Script Line:</strong> $($_.InvocationInfo.ScriptLineNumber)</p>"
     }
} finally {
    # --- Generate Final HTML Report ---
    $reportFooter = "<p class='timestamp'>Report generated on: $(Get-Date -Format 'yyyy-MM-dd HH:mm:ss') by $($env:USERNAME)</p>"

    # Assemble the full HTML page
    ConvertTo-Html -Head $cssStyle `
                   -Title "Inactive Mailbox Report ($ThresholdDays Days)" `
                   -Body $reportBody `
                   -PostContent $reportFooter | Out-File $outputFile -Encoding UTF8 -ErrorAction SilentlyContinue

    # Check if the file was actually created before trying to open it
    if (Test-Path $outputFile) {
        Write-Host "HTML Report saved to: $outputFile" -ForegroundColor Green
        Invoke-Item -Path $outputFile
    } else {
         Write-Host "Failed to create the report file at: $outputFile" -ForegroundColor Red
    }

    # Clean up Exchange session
    if ($session -ne $null) {
        Write-Host "Removing Exchange PSSession..."
        Remove-PSSession $session
        Write-Host "Session removed."
    }
}