<#
.SYNOPSIS
  Compte les packages .uasset/.umap par format (UE4 ou UE5) en lisant l'en-tete.

.DESCRIPTION
  En-tete d'un package : magic 0x9E2A83C1, puis LegacyFileVersion (int32).
  -7 = UE4 (4.27) ; -8 et moins = UE5, avec la version UE5 a l'octet 16.
  Sortie : resume, et la liste des packages UE4 ou illisibles.
  -Csv ecrit le detail complet (chemin, taille, versions, MD5 optionnel).

.EXAMPLE
  .\Tools\AssetHeaders.ps1
  .\Tools\AssetHeaders.ps1 -Root Content\BPs -Csv Docs\Migration\etat\headers_BPs.csv -Hash
#>
param(
    [string]$Root = 'Content',
    [string]$Csv,
    [switch]$Hash,
    [string]$ProjectRoot = (Split-Path $PSScriptRoot -Parent)
)
$ErrorActionPreference = 'Stop'
$base = Join-Path $ProjectRoot $Root
$buf = New-Object byte[] 24

$rows = Get-ChildItem $base -Recurse -File -Include *.uasset, *.umap | ForEach-Object {
    $fs = [IO.File]::OpenRead($_.FullName)
    try { $n = $fs.Read($buf, 0, 24) } finally { $fs.Close() }
    $magic = [BitConverter]::ToUInt32($buf, 0)
    $legacy = [BitConverter]::ToInt32($buf, 4)
    # 0x9E2A83C1 ecrit en decimal : le litteral hexadecimal serait un Int32 negatif
    $fmt = if ($n -lt 24 -or $magic -ne [uint32]2653586369) { 'ILLISIBLE' } elseif ($legacy -le -8) { 'UE5' } else { 'UE4' }
    [pscustomobject]@{
        Rel    = $_.FullName.Substring($ProjectRoot.TrimEnd('\').Length + 1)
        Format = $fmt
        Legacy = $legacy
        UE4Ver = if ($fmt -ne 'ILLISIBLE') { [BitConverter]::ToInt32($buf, 12) } else { '' }
        UE5Ver = if ($fmt -eq 'UE5') { [BitConverter]::ToInt32($buf, 16) } else { '' }
        Size   = $_.Length
        Date   = $_.LastWriteTime.ToString('s')
        MD5    = if ($Hash) { (Get-FileHash $_.FullName -Algorithm MD5).Hash } else { '' }
    }
}

$rows | Group-Object Format | ForEach-Object { '{0,-10} {1,6}' -f $_.Name, $_.Count }
$bad = $rows | Where-Object Format -ne 'UE5'
if ($bad) { "--- packages non UE5 ($(@($bad).Count), 50 premiers) :"; $bad | Select-Object -First 50 | ForEach-Object { '{0}  {1}  legacy={2} ue4={3}' -f $_.Format, $_.Rel, $_.Legacy, $_.UE4Ver } }
if ($Csv) {
    $out = Join-Path $ProjectRoot $Csv
    New-Item -ItemType Directory -Force (Split-Path $out -Parent) | Out-Null
    $rows | Export-Csv $out -NoTypeInformation -Encoding UTF8
    "detail : $out"
}