<#
.SYNOPSIS
    Hyper-V Replica Prometheus Metrics Exporter
.DESCRIPTION
    Prometheus exporter for Hyper-V Replica - replication health, state, last
    replication time, replication frequency, pending bytes, missed replications,
    VM replication count, and failover readiness. Exports metrics as
    Prometheus-compatible text format.
.PARAMETER Mode
    Output mode: 'stdout' (default), 'textfile', or 'http'
.PARAMETER Port
    HTTP port for http mode (default: 9517)
.PARAMETER TextfileDir
    Directory for textfile collector output (default: C:\ProgramData\node_exporter)
.PARAMETER InstallScheduledTask
    Switch to create a scheduled task for auto-start on system boot
.PARAMETER TaskIntervalMinutes
    Interval in minutes for the scheduled task (default: 2)
.NOTES
    Author:  Phil Connor
    Contact: contact@mylinux.work
    Website: https://mylinux.work
    License: MIT
    Version: 1.0

    Metrics Exported:
      Core Status:
        - hyperv_replica_up
        - hyperv_replica_exporter_info{version}

      Per-VM Replication:
        - hyperv_replica_vm_state{vm, state}
        - hyperv_replica_vm_health{vm, health}
        - hyperv_replica_vm_last_replication_timestamp{vm}
        - hyperv_replica_vm_frequency_seconds{vm}
        - hyperv_replica_vm_pending_bytes{vm}
        - hyperv_replica_vm_missed_count{vm}
        - hyperv_replica_vm_failover_ready{vm}
        - hyperv_replica_vm_role{vm, role}

      Totals:
        - hyperv_replica_total_vms
        - hyperv_replica_healthy_vms

      Exporter:
        - hyperv_replica_exporter_duration_seconds
        - hyperv_replica_exporter_last_run_timestamp
#>

param(
    [ValidateSet('stdout', 'textfile', 'http')]
    [string]$Mode = 'stdout',

    [int]$Port = 9517,

    [string]$TextfileDir = 'C:\ProgramData\node_exporter',

    [switch]$InstallScheduledTask,

    [int]$TaskIntervalMinutes = 2
)

# Create a scheduled task to run this script every $TaskIntervalMinutes minutes
if ($InstallScheduledTask) {
    $taskName = "HyperVReplicaMetricsExporter"
    $existingTask = Get-ScheduledTask -TaskName $taskName -ErrorAction SilentlyContinue

    if (-not $existingTask) {
        $taskAction = New-ScheduledTaskAction -Execute "powershell.exe" -Argument "-NoProfile -ExecutionPolicy Bypass -File `"$($MyInvocation.MyCommand.Path)`" -Mode textfile"

        if (-not $TaskIntervalMinutes -or $TaskIntervalMinutes -le 0) {
            throw "TaskIntervalMinutes must be a positive integer"
        }

        $taskTrigger = New-ScheduledTaskTrigger -Once -At (Get-Date).AddMinutes(1) -RepetitionInterval (New-TimeSpan -Minutes $TaskIntervalMinutes) -RepetitionDuration (New-TimeSpan -Days 365)
        $taskPrincipal = New-ScheduledTaskPrincipal -UserId "SYSTEM" -LogonType ServiceAccount -RunLevel Highest

        try {
            Write-Host "Creating scheduled task: $taskName"
            Register-ScheduledTask -TaskName $taskName -Action $taskAction -Trigger $taskTrigger -Principal $taskPrincipal -Description "Exports Hyper-V Replica metrics for Prometheus every $TaskIntervalMinutes minutes"

            $createdTask = Get-ScheduledTask -TaskName $taskName -ErrorAction SilentlyContinue
            if (-not $createdTask) {
                throw "Failed to verify scheduled task creation"
            }
            Write-Host "Successfully created scheduled task: $taskName" -ForegroundColor Green
        } catch {
            Write-Error "Failed to create scheduled task: $($_.Exception.Message)"
            throw
        }
    } else {
        Write-Host "Scheduled task '$taskName' already exists, skipping creation"
    }
}

$ErrorActionPreference = 'SilentlyContinue'

# ============================================================================
# HELPER FUNCTIONS
# ============================================================================

function Get-UnixTimestamp {
    [int][double]::Parse((Get-Date -UFormat '%s'))
}

function Format-MetricValue {
    param([double]$Value, [int]$Decimals = 2)
    [math]::Round($Value, $Decimals)
}

# ============================================================================
# HYPER-V REPLICA METRICS
# ============================================================================

function Get-HyperVReplicaMetrics {
    $sb = [System.Text.StringBuilder]::new()

    try {
        $replicas = @(Get-VMReplication -ErrorAction Stop)
    } catch {
        $replicas = @()
    }

    $replicationStates = @('Replicating', 'Suspended', 'WaitingForInitialReplication', 'WaitingForStartResynchronize', 'Resynchronizing', 'ResynchronizeSuspended', 'WaitingForUpdateCompletion', 'WaitingForRepurposeCompletion', 'ReadyForInitialReplication', 'FailedOver', 'NotApplicable')
    $healthStates = @('Normal', 'Warning', 'Critical')

    # --- hyperv_replica_vm_state ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_state Replication state of VM (1=current state)')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_state gauge')
    try {
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $currentState = $vm.State.ToString()
            foreach ($state in $replicationStates) {
                $val = if ($state -eq $currentState) { 1 } else { 0 }
                [void]$sb.AppendLine("hyperv_replica_vm_state{vm=`"$vmName`",state=`"$state`"} $val")
            }
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_state 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_vm_health ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_health Replication health of VM (1=current health)')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_health gauge')
    try {
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $currentHealth = $vm.Health.ToString()
            foreach ($health in $healthStates) {
                $val = if ($health -eq $currentHealth) { 1 } else { 0 }
                [void]$sb.AppendLine("hyperv_replica_vm_health{vm=`"$vmName`",health=`"$health`"} $val")
            }
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_health 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_vm_last_replication_timestamp ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_last_replication_timestamp Unix timestamp of last successful replication')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_last_replication_timestamp gauge')
    try {
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $lastReplTime = $vm.LastReplicationTime
            if ($lastReplTime) {
                $epoch = [int][double]::Parse((Get-Date $lastReplTime -UFormat '%s'))
                [void]$sb.AppendLine("hyperv_replica_vm_last_replication_timestamp{vm=`"$vmName`"} $epoch")
            } else {
                [void]$sb.AppendLine("hyperv_replica_vm_last_replication_timestamp{vm=`"$vmName`"} 0")
            }
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_last_replication_timestamp 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_vm_frequency_seconds ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_frequency_seconds Replication frequency in seconds')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_frequency_seconds gauge')
    try {
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $freqSec = $vm.FrequencySec
            if (-not $freqSec) { $freqSec = 0 }
            [void]$sb.AppendLine("hyperv_replica_vm_frequency_seconds{vm=`"$vmName`"} $freqSec")
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_frequency_seconds 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_vm_pending_bytes ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_pending_bytes Pending replication data in bytes')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_pending_bytes gauge')
    try {
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $pending = $vm.PendingReplicationSize
            if (-not $pending) { $pending = 0 }
            [void]$sb.AppendLine("hyperv_replica_vm_pending_bytes{vm=`"$vmName`"} $pending")
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_pending_bytes 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_vm_missed_count ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_missed_count Number of missed replication cycles')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_missed_count gauge')
    try {
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $missed = $vm.MissedReplicationCount
            if (-not $missed) { $missed = 0 }
            [void]$sb.AppendLine("hyperv_replica_vm_missed_count{vm=`"$vmName`"} $missed")
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_missed_count 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_vm_failover_ready ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_failover_ready Test replica available for failover (1=yes, 0=no)')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_failover_ready gauge')
    try {
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $testReplicaAvailable = $vm.TestReplicaObject
            $val = if ($testReplicaAvailable) { 1 } else { 0 }
            [void]$sb.AppendLine("hyperv_replica_vm_failover_ready{vm=`"$vmName`"} $val")
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_failover_ready 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_vm_role ---
    [void]$sb.AppendLine('# HELP hyperv_replica_vm_role Replication role of VM (1=current role)')
    [void]$sb.AppendLine('# TYPE hyperv_replica_vm_role gauge')
    try {
        $roles = @('Primary', 'Replica')
        foreach ($vm in $replicas) {
            $vmName = $vm.VMName
            $currentRole = $vm.ReplicationMode.ToString()
            foreach ($role in $roles) {
                $val = if ($role -eq $currentRole) { 1 } else { 0 }
                [void]$sb.AppendLine("hyperv_replica_vm_role{vm=`"$vmName`",role=`"$role`"} $val")
            }
        }
    } catch {
        [void]$sb.AppendLine("hyperv_replica_vm_role 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_total_vms ---
    [void]$sb.AppendLine('# HELP hyperv_replica_total_vms Total VMs with replication configured')
    [void]$sb.AppendLine('# TYPE hyperv_replica_total_vms gauge')
    try {
        $totalVms = $replicas.Count
        [void]$sb.AppendLine("hyperv_replica_total_vms $totalVms")
    } catch {
        [void]$sb.AppendLine("hyperv_replica_total_vms 0")
    }
    [void]$sb.AppendLine('')

    # --- hyperv_replica_healthy_vms ---
    [void]$sb.AppendLine('# HELP hyperv_replica_healthy_vms VMs with Normal replication health')
    [void]$sb.AppendLine('# TYPE hyperv_replica_healthy_vms gauge')
    try {
        $healthyCount = ($replicas | Where-Object { $_.Health.ToString() -eq 'Normal' } | Measure-Object).Count
        [void]$sb.AppendLine("hyperv_replica_healthy_vms $healthyCount")
    } catch {
        [void]$sb.AppendLine("hyperv_replica_healthy_vms 0")
    }
    [void]$sb.AppendLine('')

    $sb.ToString()
}

# ============================================================================
# COLLECT ALL METRICS
# ============================================================================

function Get-AllMetrics {
    $scriptStart = Get-Date
    $sb = [System.Text.StringBuilder]::new()

    # Exporter up
    [void]$sb.AppendLine('# HELP hyperv_replica_up Hyper-V Replica exporter status (1=up, 0=down)')
    [void]$sb.AppendLine('# TYPE hyperv_replica_up gauge')
    try {
        $vmms = Get-Service -Name vmms -ErrorAction Stop
        $upVal = if ($vmms.Status -eq 'Running') { 1 } else { 0 }
        [void]$sb.AppendLine("hyperv_replica_up $upVal")
    } catch {
        [void]$sb.AppendLine("hyperv_replica_up 0")
    }
    [void]$sb.AppendLine('')

    # Exporter info
    [void]$sb.AppendLine('# HELP hyperv_replica_exporter_info Exporter version information')
    [void]$sb.AppendLine('# TYPE hyperv_replica_exporter_info gauge')
    [void]$sb.AppendLine('hyperv_replica_exporter_info{version="1.0"} 1')
    [void]$sb.AppendLine('')

    # Collect Hyper-V Replica metrics
    [void]$sb.Append((Get-HyperVReplicaMetrics))

    # Exporter runtime
    $scriptEnd = Get-Date
    $duration = Format-MetricValue ($scriptEnd - $scriptStart).TotalSeconds
    $timestamp = Get-UnixTimestamp

    [void]$sb.AppendLine('# HELP hyperv_replica_exporter_duration_seconds Time to generate all metrics')
    [void]$sb.AppendLine('# TYPE hyperv_replica_exporter_duration_seconds gauge')
    [void]$sb.AppendLine("hyperv_replica_exporter_duration_seconds $duration")
    [void]$sb.AppendLine('')
    [void]$sb.AppendLine('# HELP hyperv_replica_exporter_last_run_timestamp Unix timestamp of last successful run')
    [void]$sb.AppendLine('# TYPE hyperv_replica_exporter_last_run_timestamp gauge')
    [void]$sb.AppendLine("hyperv_replica_exporter_last_run_timestamp $timestamp")
    [void]$sb.AppendLine('')

    $sb.ToString()
}

# ============================================================================
# HTTP SERVER MODE
# ============================================================================

function Start-HttpServer {
    param([int]$ListenPort)

    $prefix = "http://+:$ListenPort/"
    $listener = [System.Net.HttpListener]::new()
    $listener.Prefixes.Add($prefix)

    try {
        $listener.Start()
        Write-Host "Starting Hyper-V Replica metrics exporter on port $ListenPort..." -ForegroundColor Green
        Write-Host "Metrics available at http://localhost:$ListenPort/metrics"

        while ($listener.IsListening) {
            $context  = $listener.GetContext()
            $request  = $context.Request
            $response = $context.Response

            if ($request.Url.AbsolutePath -eq '/metrics') {
                $metrics = Get-AllMetrics
                $buffer  = [System.Text.Encoding]::UTF8.GetBytes($metrics)
                $response.ContentType = 'text/plain; version=0.0.4; charset=utf-8'
            }
            else {
                $html = @"
<!DOCTYPE html>
<html>
<head><title>Hyper-V Replica Metrics Exporter v1.0</title></head>
<body>
<h1>Hyper-V Replica Metrics Exporter v1.0</h1>
<p><a href="/metrics">Metrics</a></p>
<h2>Metrics</h2>
<ul>
<li>Per-VM replication state and health</li>
<li>Last replication time and frequency</li>
<li>Pending replication bytes</li>
<li>Missed replication count</li>
<li>Failover readiness</li>
<li>Replication role (Primary/Replica)</li>
<li>Total and healthy VM counts</li>
</ul>
</body>
</html>
"@
                $buffer = [System.Text.Encoding]::UTF8.GetBytes($html)
                $response.ContentType = 'text/html; charset=utf-8'
            }

            $response.ContentLength64 = $buffer.Length
            $response.OutputStream.Write($buffer, 0, $buffer.Length)
            $response.OutputStream.Close()
        }
    }
    catch {
        Write-Error "HTTP server error: $_"
        Write-Error "If access denied, run: netsh http add urlacl url=http://+:$ListenPort/ user=Everyone"
    }
    finally {
        if ($listener.IsListening) {
            $listener.Stop()
        }
    }
}

# ============================================================================
# MAIN EXECUTION
# ============================================================================

switch ($Mode) {
    'http' {
        Start-HttpServer -ListenPort $Port
    }
    'textfile' {
        $OutputFile = Join-Path $TextfileDir 'hyperv_replica_metrics.prom'

        $outputDir = Split-Path $OutputFile -Parent
        if (-not (Test-Path $outputDir)) {
            New-Item -Path $outputDir -ItemType Directory -Force | Out-Null
        }

        $tempFile = Join-Path $outputDir ".hyperv_replica_metrics.$PID.tmp"

        try {
            $metrics = Get-AllMetrics
            $metrics | Out-File -FilePath $tempFile -Encoding utf8 -NoNewline

            $lineCount = ($metrics -split "`n").Count
            if ($lineCount -lt 10) {
                Remove-Item -Path $tempFile -Force -ErrorAction SilentlyContinue
                Write-Error "Metrics file too small ($lineCount lines), keeping previous"
                exit 1
            }

            Move-Item -Path $tempFile -Destination $OutputFile -Force
            Write-Host "Metrics written to $OutputFile ($lineCount lines)" -ForegroundColor Green
        }
        catch {
            Remove-Item -Path $tempFile -Force -ErrorAction SilentlyContinue
            Write-Error "Failed to generate metrics: $_"
            exit 1
        }
    }
    default {
        Get-AllMetrics | Write-Output
    }
}