```powershell
<#
.SYNOPSIS
    Validates and documents expected FirewallD configuration for a CentOS 8 host.

.DESCRIPTION
    This script is a safe, non-destructive checklist helper for teams configuring FirewallD.
    It does not modify firewall rules. Instead, it helps you confirm the host state, inspect
    zones, and record the intended zone, services, ports, and optional rich rules before
    making production changes.

    The script is PowerShell-based so it can be run from an admin workstation or used as a
    structured pre-change validation aid. It assumes you will run the equivalent FirewallD
    commands on the CentOS 8 host via SSH, console, or an orchestration tool.

.NOTES
    - No destructive actions are performed.
    - No credentials or secrets are stored.
    - Adapt the placeholder values for your environment before use.

.EXAMPLE
    .\Validate-FirewalldCentOS8.ps1 -Zone public -Interface eth0 -ExpectedService ssh -ExpectedPort 8443/tcp

.EXAMPLE
    .\Validate-FirewalldCentOS8.ps1 -Zone public -Interface eth0 -ExpectedRichRule 'rule family="ipv4" source address="192.0.2.0/24" service name="ssh" accept'
#>

[CmdletBinding()]
param(
    [Parameter(Mandatory = $true)]
    [ValidateNotNullOrEmpty()]
    [string]$Zone,

    [Parameter(Mandatory = $false)]
    [ValidateNotNullOrEmpty()]
    [string]$Interface,

    [Parameter(Mandatory = $false)]
    [ValidateNotNullOrEmpty()]
    [string[]]$ExpectedService,

    [Parameter(Mandatory = $false)]
    [ValidateNotNullOrEmpty()]
    [string[]]$ExpectedPort,

    [Parameter(Mandatory = $false)]
    [ValidateNotNullOrEmpty()]
    [string[]]$ExpectedRichRule,

    [Parameter(Mandatory = $false)]
    [switch]$ShowCommands
)

Set-StrictMode -Version Latest
$ErrorActionPreference = 'Stop'

function Write-Section {
    param([Parameter(Mandatory = $true)][string]$Title)
    Write-Host "`n=== $Title ===" -ForegroundColor Cyan
}

function Write-Step {
    param([Parameter(Mandatory = $true)][string]$Text)
    Write-Host "- $Text"
}

function New-CommandLine {
    param([Parameter(Mandatory = $true)][string]$Command)
    if ($ShowCommands) {
        Write-Host "  Command: $Command" -ForegroundColor DarkGray
    }
}

function Assert-NonEmptyList {
    param(
        [string[]]$Items,
        [string]$Label
    )

    if ($null -eq $Items -or $Items.Count -eq 0) {
        Write-Host "  No expected $Label values were provided." -ForegroundColor Yellow
        return
    }

    foreach ($item in $Items) {
        if ([string]::IsNullOrWhiteSpace($item)) {
            throw "One or more $Label entries are empty."
        }
    }
}

Write-Section -Title 'Pre-change checks'
Write-Step 'Confirm you have console, out-of-band, or another reliable recovery path before changing firewall rules.'
Write-Step 'Confirm the management interface, intended zone, and required services/ports are known.'
Write-Step 'Avoid making changes over the only SSH session on the interface you plan to modify.'

Assert-NonEmptyList -Items $ExpectedService -Label 'service'
Assert-NonEmptyList -Items $ExpectedPort -Label 'port'
Assert-NonEmptyList -Items $ExpectedRichRule -Label 'rich rule'

Write-Section -Title 'Planned configuration summary'
Write-Host "Zone:        $Zone"
if ($Interface) { Write-Host "Interface:   $Interface" }
if ($ExpectedService) { Write-Host "Services:    $($ExpectedService -join ', ')" }
if ($ExpectedPort) { Write-Host "Ports:       $($ExpectedPort -join ', ')" }
if ($ExpectedRichRule) { Write-Host "Rich rules:  $($ExpectedRichRule.Count) item(s)" }

Write-Section -Title 'Suggested verification commands for CentOS 8'
$commands = @(
    'sudo firewall-cmd --state',
    'sudo firewall-cmd --get-active-zones',
    'sudo firewall-cmd --get-zones',
    ("sudo firewall-cmd --zone={0} --list-all" -f $Zone),
    ("sudo firewall-cmd --permanent --zone={0} --list-all" -f $Zone)
)
if ($Interface) {
    $commands += ("sudo firewall-cmd --permanent --zone={0} --change-interface={1}" -f $Zone, $Interface)
}
if ($ExpectedService) {
    foreach ($svc in $ExpectedService) {
        $commands += ("sudo firewall-cmd --permanent --zone={0} --add-service={1}" -f $Zone, $svc)
        $commands += ("sudo firewall-cmd --zone={0} --list-services" -f $Zone)
    }
}
if ($ExpectedPort) {
    foreach ($port in $ExpectedPort) {
        $commands += ("sudo firewall-cmd --permanent --zone={0} --add-port={1}" -f $Zone, $port)
        $commands += ("sudo firewall-cmd --zone={0} --list-ports" -f $Zone)
    }
}
if ($ExpectedRichRule) {
    foreach ($rule in $ExpectedRichRule) {
        $commands += ("sudo firewall-cmd --permanent --zone={0} --add-rich-rule='{1}'" -f $Zone, $rule)
    }
    $commands += 'sudo firewall-cmd --reload'
}

foreach ($cmd in $commands) {
    New-CommandLine -Command $cmd
}

Write-Section -Title 'Validation checklist'
Write-Step 'Verify FirewallD is running before and after changes.'
Write-Step 'Confirm the target interface belongs to the intended zone.'
Write-Step 'Choose either a service rule or a port rule that matches the application protocol.'
Write-Step 'Test runtime changes first when possible, then persist them with --permanent.'
Write-Step 'Reload FirewallD after permanent changes and re-check the zone contents.'
Write-Step 'Validate access from a trusted source before declaring the change complete.'

Write-Section -Title 'Common failure points to avoid'
Write-Step 'Adding the rule to the wrong zone while traffic enters through another zone.'
Write-Step 'Opening TCP when the application requires UDP, or vice versa.'
Write-Step 'Changing only permanent settings without reloading or checking runtime state.'
Write-Step 'Assuming SSH remains safe after modifying the interface or zone assignment.'

Write-Section -Title 'Completion note'
Write-Host 'Use this script as a pre-change and post-change validation aid. It intentionally makes no firewall modifications.' -ForegroundColor Green
```