Param ([switch]$Continuous, [int]$Interval = 10, [switch]$Force)
$TimeSkew = 4
$ListUrl = "http://sharepoint/Lists/OpsMgrAlerts/AllItems.aspx"
$AlertUrl = "http://opsmgr:51908/default.aspx?DisplayMode=Pivot&AlertID="
$States = @{
0 = "New"
255 = "Resolved"
}

#Connect to SP List
Write-Host "Connecting to SharePoint List"
$DllPath = "${env:CommonProgramFiles}\Microsoft Shared\Web Server Extensions\12\ISAPI\Microsoft.SharePoint.Dll"
[System.Reflection.Assembly]::LoadFrom($DllPath) | Out-Null
$Site = New-Object -Type "Microsoft.SharePoint.SPSite" -ArgumentList "http://localhost"
$Web = $Site.OpenWeb()
$List = $Web.GetList($ListUrl)

#Connect to OpsMgr
Write-Host "Connecting to OpsMgr"
add-pssnapin Microsoft.EnterpriseManagement.OperationsManager.Client
cd "C:\Program Files\System Center Operations Manager 2007"
. .\Microsoft.EnterpriseManagement.OperationsManager.ClientShell.NonInteractiveStartup.ps1

function Sync-Alerts ([switch]$Force)
{
    if ($Force) {Write-Warning "Forced sync enabled, alerts will not sync back to OpsMgr"}
    #Get alerts from opsmgr by ids, and update status in list
    #Also sync back if Resolution is changed
    Write-Host "Updating list alerts"
    $Delete=@()
    foreach ($Item in $List.Items)
    {
        $Alert = $null
        $Alert = Get-Alert -ID $Item["OMID"]
        if ($Alert)
        {
            if (($Alert.LastModified.addhours($TimeSkew) -gt $Item["Modified"]) -or $Force)
            {
                if ($Alert.ResolutionState -eq 255)
                {
                    Write-Host "Item $($Alert.ID) is resolved in OpsMgr and marked for removal from list"
                    $Delete += $Item.Id
                }
                else
                {
                    Write-Host "Updating alert $($Alert.ID)"
                    $Item["Description"] = $Alert.Description
                    $Item["RepeatCount"] = $Alert.RepeatCount
                    $Item["Changed"] = $Alert.LastModified
                    $Item["Resolution"] = $States[[int]$Alert.ResolutionState]
                    $Item.Update()
                }
            }
            else
            {
                if ($States[[int]$Alert.ResolutionState] -ne $Item["Resolution"])
                {
                    Write-Host "Setting resolution state for item $($Alert.ID) back to OpsMgr"
                    $Alert.ResolutionState = ($States.GetEnumerator() | ?{$_.Value -eq $Item["Resolution"]}).Name
                    $Alert.Update("ResolutionState synchonized from SharePoint at $(get-date)")
                    if ($Alert.ResolutionState -eq 255)
                    {
                        Write-Host "Alert $($Alert.ID) is resolved in list and marked for removal"
                        $Delete += $Item.Id
                    }
                }
            }
        }
        else
        {
            Write-Warning "Alert with ID $($Item["OMID"]) not found in OpsMgr, marking for removal"
            $Delete += $Item.Id
        }
    }

    Write-Host "Removing resolved items from the list"
    $Delete | foreach {Write-host "Removing item $_ from list"; $list.Items.DeleteItemById($_)}

    #Get-newalerts form opsmgr, and add to list if it doenst exist
    Write-Host "Adding new alerts to list"
    foreach ($Alert in (Get-Alert -Criteria 'ResolutionState != 255'))
    {
        if (-not ($list.Items | where {$_["OMID"] -eq $Alert.ID}))
        {
            Write-host "Adding alert $($AlertID) ($($Alert.Name)) to list"
            $New = $List.Items.Add()
            $New["Title"] = $Alert.Name
            $New["OMID"] = $Alert.ID
            $New["Description"] = $Alert.Description
            $New["Computer"] = $Alert.NetbiosComputerName
            $New["FQDN"] = $Alert.PrincipalName
            $New["RepeatCount"] = $Alert.RepeatCount
            $New["Raised"] = $Alert.TimeRaised
            $New["Changed"] = $Alert.LastModified
            $New["Resolution"] = $States[[int]$Alert.ResolutionState]
            $New["Severity"] = $Alert.Severity
            $New["Priority"] = $Alert.Priority
            $New["Category"] = $Alert.Category
            $New["Link"] = $AlertUrl + $Alert.ID + ", View"
            $New.Update()
        }
    }
     
    Write-Host "Done"
}

if ($Continuous)
{
    $Counter = 0
    while ($True)
    {
        $Counter ++
        if ($Counter -eq 10)
        {
            Write-Host "`nCollecting garbage"
            [GC]::Collect()
            Write-Host "Done"
            $Counter = 0
        }
        Write-Host "`nStarting sync at $(get-date)"
        Sync-Alerts -force:$Force
        Sleep $Interval
    }
}
else
{
    Sync-Alerts -force:$Force
}