param(
  [string]$TemplatePath = 'D:\project\deployment\alertmanager\alertmanager.yml',
  [string]$OutputPath,
  [string]$EnvFilePath = ''
)

$ErrorActionPreference = 'Stop'

if ([string]::IsNullOrWhiteSpace($OutputPath)) {
  throw 'OutputPath is required'
}

if (-not (Test-Path $TemplatePath)) {
  throw "template not found: $TemplatePath"
}

if (-not [string]::IsNullOrWhiteSpace($EnvFilePath)) {
  if (-not (Test-Path $EnvFilePath)) {
    throw "env file not found: $EnvFilePath"
  }

  Get-Content $EnvFilePath -Encoding UTF8 | ForEach-Object {
    $line = $_.Trim()
    if ($line -eq '' -or $line.StartsWith('#')) {
      return
    }
    $parts = $line -split '=', 2
    if ($parts.Count -ne 2) {
      throw "invalid env line: $line"
    }
    [Environment]::SetEnvironmentVariable($parts[0].Trim(), $parts[1].Trim(), 'Process')
  }
}

$content = Get-Content $TemplatePath -Raw -Encoding UTF8
$matches = [regex]::Matches($content, '\$\{(?<name>[A-Z0-9_]+)\}')
$variables = @($matches | ForEach-Object { $_.Groups['name'].Value } | Sort-Object -Unique)
$missing = @()

foreach ($name in $variables) {
  $value = [Environment]::GetEnvironmentVariable($name, 'Process')
  if ([string]::IsNullOrWhiteSpace($value)) {
    $missing += $name
    continue
  }
  $escapedToken = [regex]::Escape('${' + $name + '}')
  $escapedValue = $value -replace '\\', '\\'
  $content = [regex]::Replace($content, $escapedToken, [System.Text.RegularExpressions.MatchEvaluator]{ param($m) $value })
}

if ($missing.Count -gt 0) {
  throw "missing required alertmanager environment variables: $($missing -join ', ')"
}

if ($content -match '\$\{[A-Z0-9_]+\}') {
  throw 'rendered alertmanager config still contains unresolved placeholders'
}

$outputDir = Split-Path $OutputPath -Parent
if (-not [string]::IsNullOrWhiteSpace($outputDir)) {
  New-Item -ItemType Directory -Force $outputDir | Out-Null
}

Set-Content -Path $OutputPath -Value $content -Encoding UTF8
Get-Content $OutputPath