<#
.SYNOPSIS
  Compare health metrics across all Exchange mailbox databases

.DESCRIPTION
  Generates a comparison report of database sizes, whitespace, mount status,
  backup age, and circular logging settings. Alerts on databases exceeding
  thresholds or with configuration issues.

.PARAMETER WhitespaceThresholdGB
  Alert if available whitespace exceeds this value (default: 50)

.PARAMETER BackupAgeThresholdDays
  Alert if last backup is older than this many days (default: 2)

.PARAMETER OutputFolder
  Destination folder for reports. Default: .\DatabaseComparison-<date>

.NOTES
  ⚠️  AI-GENERATED SCRIPT - UNTESTED
  This script was generated by Claude AI and has not been tested in production.
  Review and test thoroughly in a non-production environment before use.

  - Run in Exchange Management Shell with appropriate RBAC permissions
  - Requires -Status parameter support (Get-MailboxDatabase -Status)
  - Tested compatibility: Exchange 2013/2016/2019 (not validated)

.EXAMPLE
  .\Compare-MailboxDatabases.ps1

.EXAMPLE
  .\Compare-MailboxDatabases.ps1 -WhitespaceThresholdGB 100 -BackupAgeThresholdDays 1
#>

[CmdletBinding()]
param(
    [int]$WhitespaceThresholdGB = 50,
    [int]$BackupAgeThresholdDays = 2,
    [string]$OutputFolder = (Join-Path -Path (Get-Location) -ChildPath ("DatabaseComparison-" + (Get-Date -Format "yyyyMMdd-HHmm")))
)

function NowTag { (Get-Date).ToString("yyyy-MM-dd HH:mm:ss") }

function Convert-BytesToGB([string]$sizeStr) {
    if (-not $sizeStr) { return 0 }
    try {
        if ($sizeStr -match "([\d\.,]+)\s*(KB|MB|GB|TB)") {
            $num = [double]($matches[1] -replace ',', '.')
            $bytes = switch ($matches[2].ToUpper()) {
                "KB" { $num * 1KB }
                "MB" { $num * 1MB }
                "GB" { $num * 1GB }
                "TB" { $num * 1TB }
            }
            return [math]::Round($bytes / 1GB, 2)
        }
    } catch {}
    return 0
}

Write-Host "[$(NowTag)] ⚠️  AI-GENERATED SCRIPT - UNTESTED" -ForegroundColor Yellow
Write-Host "[$(NowTag)] Starting database comparison analysis..." -ForegroundColor Green

# Create output folder
New-Item -ItemType Directory -Path $OutputFolder -Force | Out-Null

# Get all databases with status
Write-Host "[$(NowTag)] Retrieving mailbox databases..."
$databases = Get-MailboxDatabase -Status -ErrorAction SilentlyContinue | Sort-Object Name

$dbCount = ($databases | Measure-Object).Count
Write-Host "[$(NowTag)] Found $dbCount databases"

# Analyze each database
$dbAnalysis = @()
$alerts = @()

foreach ($db in $databases) {
    Write-Host "[$(NowTag)] Analyzing $($db.Name)..."

    $dbSizeGB = Convert-BytesToGB ([string]$db.DatabaseSize)
    $whitespaceGB = Convert-BytesToGB ([string]$db.AvailableNewMailboxSpace)

    $backupAge = $null
    $backupStatus = "Unknown"
    if ($db.LastFullBackup) {
        $backupAge = [int]((Get-Date) - $db.LastFullBackup).TotalDays
        $backupStatus = if ($backupAge -le $BackupAgeThresholdDays) { "OK" } else { "OLD" }
    } else {
        $backupStatus = "NEVER"
    }

    # Generate alerts
    $dbAlerts = @()

    if (-not $db.Mounted) {
        $dbAlerts += "Database is DISMOUNTED"
        $alerts += [PSCustomObject]@{
            Database = $db.Name
            Severity = "CRITICAL"
            Alert    = "Database is dismounted"
        }
    }

    if ($whitespaceGB -gt $WhitespaceThresholdGB) {
        $dbAlerts += "Excessive whitespace: $whitespaceGB GB"
        $alerts += [PSCustomObject]@{
            Database = $db.Name
            Severity = "WARNING"
            Alert    = "Excessive whitespace: $whitespaceGB GB (threshold: $WhitespaceThresholdGB GB)"
        }
    }

    if ($backupStatus -eq "NEVER") {
        $dbAlerts += "Never backed up"
        $alerts += [PSCustomObject]@{
            Database = $db.Name
            Severity = "CRITICAL"
            Alert    = "Database has never been backed up"
        }
    } elseif ($backupStatus -eq "OLD") {
        $dbAlerts += "Backup is $backupAge days old"
        $alerts += [PSCustomObject]@{
            Database = $db.Name
            Severity = "WARNING"
            Alert    = "Last backup is $backupAge days old (threshold: $BackupAgeThresholdDays days)"
        }
    }

    if ($db.CircularLoggingEnabled) {
        $dbAlerts += "Circular logging enabled"
        $alerts += [PSCustomObject]@{
            Database = $db.Name
            Severity = "INFO"
            Alert    = "Circular logging is enabled"
        }
    }

    $dbAnalysis += [PSCustomObject]@{
        Database              = $db.Name
        Server                = $db.Server
        Mounted               = $db.Mounted
        DatabaseSizeGB        = $dbSizeGB
        WhitespaceGB          = $whitespaceGB
        WhitespacePercent     = if ($dbSizeGB -gt 0) { [math]::Round(($whitespaceGB / $dbSizeGB) * 100, 2) } else { 0 }
        CircularLogging       = $db.CircularLoggingEnabled
        LastFullBackup        = $db.LastFullBackup
        BackupAgeDays         = $backupAge
        BackupStatus          = $backupStatus
        EdbFilePath           = $db.EdbFilePath
        LogFolderPath         = $db.LogFolderPath
        Alerts                = ($dbAlerts -join "; ")
    }
}

# Export full analysis
$csvFile = Join-Path $OutputFolder "Database-Comparison.csv"
$dbAnalysis | Export-Csv -NoTypeInformation -Encoding UTF8 -Path $csvFile
Write-Host "[$(NowTag)] Database analysis exported: $csvFile" -ForegroundColor Green

# Export alerts
if ($alerts.Count -gt 0) {
    $alertsFile = Join-Path $OutputFolder "Database-Alerts.csv"
    $alerts | Export-Csv -NoTypeInformation -Encoding UTF8 -Path $alertsFile
    Write-Host "[$(NowTag)] Alerts exported: $alertsFile" -ForegroundColor Yellow

    Write-Host "`nALERTS FOUND:" -ForegroundColor Yellow
    $alerts | Group-Object Severity | ForEach-Object {
        Write-Host "  $($_.Name): $($_.Count) alert(s)" -ForegroundColor $(
            switch ($_.Name) {
                "CRITICAL" { "Red" }
                "WARNING" { "Yellow" }
                default { "Cyan" }
            }
        )
    }
} else {
    Write-Host "`n[$(NowTag)] No alerts found - all databases healthy!" -ForegroundColor Green
}

# Summary statistics
Write-Host "`nDATABASE SUMMARY:" -ForegroundColor Cyan
Write-Host "  Total Databases: $dbCount"
Write-Host "  Mounted: $(($dbAnalysis | Where-Object Mounted).Count)"
Write-Host "  Dismounted: $(($dbAnalysis | Where-Object { -not $_.Mounted }).Count)"
Write-Host "  Total Size: $([math]::Round(($dbAnalysis | Measure-Object DatabaseSizeGB -Sum).Sum, 2)) GB"
Write-Host "  Total Whitespace: $([math]::Round(($dbAnalysis | Measure-Object WhitespaceGB -Sum).Sum, 2)) GB"
Write-Host "  Circular Logging Enabled: $(($dbAnalysis | Where-Object CircularLogging).Count)"

Write-Host "`n[$(NowTag)] Analysis complete! Output folder: $OutputFolder"