[CmdletBinding()]
param(
    [Parameter(Mandatory = $true)]
    [string]$ConfigurationTemplate
)

$ErrorActionPreference = "Stop"
$serviceName = "telegraf"
$installRoot = "C:\Program Files\NDC\Mission Core\Telegraf"
$configurationRoot = "C:\ProgramData\NDC\MissionCore\telemetry-agent"
$configurationPath = Join-Path $configurationRoot "telegraf.conf"
$executable = Join-Path $installRoot "telegraf.exe"
$serviceRegistryPath = "HKLM:\SYSTEM\CurrentControlSet\Services\$serviceName"

$service = Get-Service -Name $serviceName -ErrorAction Stop
if (-not (Test-Path -LiteralPath $executable -PathType Leaf)) {
    throw "NDC Mission Core Telegraf executable is missing"
}
if (-not (Test-Path -LiteralPath $ConfigurationTemplate -PathType Leaf)) {
    throw "Configuration template not found: $ConfigurationTemplate"
}

foreach ($entry in @((Get-ItemProperty -Path $serviceRegistryPath).Environment)) {
    $name, $value = $entry -split "=", 2
    if ($name -and $value) {
        Set-Item -Path "Env:$name" -Value $value
    }
}

$temporaryRoot = Join-Path $env:TEMP "ndc-mission-core-telegraf-update-$([Guid]::NewGuid().ToString('N'))"
$validationOutput = Join-Path $temporaryRoot "validation.out.log"
$validationError = Join-Path $temporaryRoot "validation.error.log"
$backupRoot = Join-Path $configurationRoot "backups"
$backupPath = Join-Path $backupRoot "telegraf-$([DateTime]::UtcNow.ToString('yyyyMMddTHHmmssZ')).conf"
try {
    New-Item -ItemType Directory -Path $temporaryRoot, $backupRoot -Force | Out-Null
    $validation = Start-Process -FilePath $executable `
        -ArgumentList @("--config", $ConfigurationTemplate, "--test") `
        -NoNewWindow -Wait -PassThru `
        -RedirectStandardOutput $validationOutput `
        -RedirectStandardError $validationError
    if ($validation.ExitCode -ne 0) {
        $validationDetail = Get-Content -LiteralPath $validationError -Tail 8 |
            Out-String
        throw "Telegraf configuration validation failed: $validationDetail"
    }

    Copy-Item -LiteralPath $configurationPath -Destination $backupPath
    Stop-Service -Name $serviceName
    try {
        Copy-Item -LiteralPath $ConfigurationTemplate -Destination $configurationPath
        Start-Service -Name $serviceName
        $service = Get-Service -Name $serviceName
        $service.WaitForStatus(
            [ServiceProcess.ServiceControllerStatus]::Running,
            [TimeSpan]::FromSeconds(20)
        )
    }
    catch {
        Copy-Item -LiteralPath $backupPath -Destination $configurationPath
        Start-Service -Name $serviceName
        throw
    }

    [ordered]@{
        SchemaVersion = "missioncore.telemetry-agent-config-result/v1"
        ServiceName = $serviceName
        Status = (Get-Service -Name $serviceName).Status.ToString()
        Configuration = $configurationPath
        Backup = $backupPath
    } | ConvertTo-Json -Compress
}
finally {
    Remove-Item -LiteralPath $temporaryRoot -Recurse -Force -ErrorAction SilentlyContinue
}