# File path to store disk space usage CSV
$outFile = "C:\disks.txt"

# Set delta threshold in percentage
# E.g.: 5 means a change in free space of more than 5% will trigger warning
$deltaThresholdPercent = 1

# Set delta threshold in GB
# E.g.: 5 means a change in free space of more than 5 GB will trigger warning
$deltaThresholdSpace = 1

# Absolute threshold in percentage
# E.g.: 20 means free space below 20% will trigger warning
$absoluteThresholdPercent = 20

# Absolute threshold in GB
# E.g.: 10 means free space below 10GB will trigger warning
$absoluteThresholdSpace = 10



# Initialize warning; assume false
$warning = $false

# Get hostname
$computerName = Get-Content Env:\COMPUTERNAME

# Email subject line
$subj = "Disk Usage Report for " + $computerName + "."

# Start email message body
$msg = "`r`n=== Disk Usage Report for " + $computerName + " ===`n`n"

# Email recipients
[String[]] $recipients = "[email protected]"

# Load all local volumes
$disks = Get-WmiObject Win32_LogicalDisk | Where-Object {$_.DriveType -eq 3}

# Iterate over volumes
foreach ($disk in $disks)
{

    $volumeLetter = $disk.DeviceID
    $totalSize = ($disk.Size/1GB)

    [double]$currentFreeSpace = [System.Math]::Round(($disk.FreeSpace/1GB), 2)
    [double]$currentFreePercent = [System.Math]::Round(($currentFreeSpace/$totalSize) * 100, 2)

    # Run absolute free space check
    if (100 - $currentFreePercent -le $absoluteThresholdPercent -or $currentFreeSpace -le $absoluteThresholdSpace)
    {
        # Trigger warning
        $warning = $true
        $msg += $volumeLetter + " has " + $currentFreeSpace + "GB (" + $currentFreePercent + "%) disk space remaining.`r`n"
        $msg += "Total free space less than " + $absoluteThresholdSpace + "GB or " + $absoluteThresholdPercent + "% triggers this warning.`r`n"
    }

    # Don't run relative check if comparison data doesn't exist
    if ((Test-Path $outFile) -eq $true)
    {
        # Read CSV
        $csvIn = Import-Csv $outFile -Header("volume","freeSpace")
        foreach ($row in $csvIn)
        {
            if ($row.volume -eq $volumeLetter)
            {
                [double]$oldFreePercent = [System.Math]::Round(($row.freeSpace/$totalSize) * 100, 2)
                [double]$oldFreeSpace = $row.freeSpace
            }
        }

        # Calculate deltas
        [double]$deltaFreePercent = [System.Math]::Round((([math]::abs($currentFreeSpace - $oldFreeSpace))/$totalSize) * 100, 2)
        [double]$deltaFreeSpace = [System.Math]::Round(([math]::abs($currentFreeSpace - $oldFreeSpace)), 2)

        # Run relative free space check
        if (($deltaFreePercent -ge $deltaThresholdPercent) -or ($deltaFreeSpace -ge $deltaThresholdSpace))
        {
            $warning = $true
            $lastWriteTime = (Get-Item $outFile).LastWriteTime
            $msg += $volumeLetter + " has lost " + $deltaFreeSpace + "GB (" + $deltaFreePercent + "%) free space since " + $lastWriteTime + "`r`n"
            $msg += $volumeLetter + " currently has " + $currentFreeSpace + "GB (" + $currentFreePercent + "%) free space.`r`n"
            $msg += "Free space losses in excess of " + $deltaThresholdSpace + "GB or " + $deltaThresholdPercent + "% trigger this warning.`r`n"
        }
    }

    # Update CSV with new disk usage
    $csv += $volumeLetter + "," + $currentFreeSpace + "`r`n"
}
echo $csv | Out-File $outFile
echo $msg

# :TODO: Send warning email