param(
    [int]$Port = 8789
)

$ErrorActionPreference = "Stop"

function Get-Percent {
    param([double]$Value)
    if ([double]::IsNaN($Value) -or [double]::IsInfinity($Value)) {
        return 0
    }
    $rounded = [math]::Round($Value)
    if ($rounded -lt 0) { return 0 }
    if ($rounded -gt 100) { return 100 }
    return [int]$rounded
}

function Get-SystemMetrics {
    $cpu = Get-CimInstance Win32_PerfFormattedData_PerfOS_Processor |
        Where-Object { $_.Name -eq "_Total" } |
        Select-Object -First 1

    $os = Get-CimInstance Win32_OperatingSystem
    $totalMemory = [double]$os.TotalVisibleMemorySize
    $freeMemory = [double]$os.FreePhysicalMemory
    $memoryPercent = if ($totalMemory -gt 0) {
        (($totalMemory - $freeMemory) / $totalMemory) * 100
    } else {
        0
    }

    $disk = Get-CimInstance Win32_LogicalDisk -Filter "DeviceID='C:'"
    $diskPercent = if ($disk -and [double]$disk.Size -gt 0) {
        (([double]$disk.Size - [double]$disk.FreeSpace) / [double]$disk.Size) * 100
    } else {
        0
    }

    $network = Get-CimInstance Win32_PerfFormattedData_Tcpip_NetworkInterface |
        Where-Object {
            $_.Name -notmatch "Loopback|isatap|Teredo" -and
            ([double]$_.BytesReceivedPersec -gt 0 -or [double]$_.BytesSentPersec -gt 0)
        }

    $rxBytes = 0.0
    $txBytes = 0.0
    foreach ($adapter in $network) {
        $rxBytes += [double]$adapter.BytesReceivedPersec
        $txBytes += [double]$adapter.BytesSentPersec
    }

    return [ordered]@{
        cpu  = Get-Percent ([double]$cpu.PercentProcessorTime)
        mem  = Get-Percent $memoryPercent
        disk = Get-Percent $diskPercent
        rx   = [int][math]::Max(0, [math]::Round($rxBytes / 1024))
        tx   = [int][math]::Max(0, [math]::Round($txBytes / 1024))
    }
}

function Get-MetricsLine {
    $m = Get-SystemMetrics
    return "SYS,$($m.cpu),$($m.mem),$($m.disk),$($m.rx),$($m.tx)"
}

function Send-Response {
    param(
        [System.Net.Sockets.TcpClient]$Client,
        [string]$Status,
        [string]$ContentType,
        [string]$Body
    )

    $bodyBytes = [System.Text.Encoding]::UTF8.GetBytes($Body)
    $header = "HTTP/1.1 $Status`r`nContent-Type: $ContentType; charset=utf-8`r`nContent-Length: $($bodyBytes.Length)`r`nConnection: close`r`nCache-Control: no-store`r`n`r`n"
    $headerBytes = [System.Text.Encoding]::ASCII.GetBytes($header)
    $stream = $Client.GetStream()
    $stream.Write($headerBytes, 0, $headerBytes.Length)
    $stream.Write($bodyBytes, 0, $bodyBytes.Length)
    $stream.Flush()
}

$listener = [System.Net.Sockets.TcpListener]::new([System.Net.IPAddress]::Any, $Port)
$listener.Start()
Write-Host "PC metrics HTTP server listening on 0.0.0.0:$Port"
Write-Host "Text endpoint: /metrics.txt"
Write-Host "JSON endpoint: /metrics.json"

try {
    while ($true) {
        $client = $listener.AcceptTcpClient()
        try {
            $stream = $client.GetStream()
            $buffer = New-Object byte[] 2048
            $read = $stream.Read($buffer, 0, $buffer.Length)
            $request = [System.Text.Encoding]::ASCII.GetString($buffer, 0, $read)
            $firstLine = ($request -split "`r?`n")[0]
            $path = "/"
            if ($firstLine -match "^[A-Z]+\\s+([^\\s]+)") {
                $path = $Matches[1]
            }

            if ($path -eq "/health") {
                Send-Response $client "200 OK" "text/plain" "ok`n"
            } elseif ($path -eq "/metrics.json") {
                $metrics = Get-SystemMetrics
                Send-Response $client "200 OK" "application/json" (($metrics | ConvertTo-Json -Compress) + "`n")
            } elseif ($path -eq "/" -or $path -eq "/metrics.txt") {
                Send-Response $client "200 OK" "text/plain" ((Get-MetricsLine) + "`n")
            } else {
                Send-Response $client "404 Not Found" "text/plain" "not found`n"
            }
        } catch {
            try {
                Send-Response $client "500 Internal Server Error" "text/plain" "error`n"
            } catch {
            }
        } finally {
            $client.Close()
        }
    }
} finally {
    $listener.Stop()
}