# repair-ico.ps1 - Fix broken ICO files whose frame offsets omit the directory size.
#
# Background: some generators write ICO frame offsets starting at 0 (not accounting
# for the 6 + count*16 directory), which makes .NET Framework System.Drawing.Icon
# throw "The operation completed successfully". This script detects that pattern
# and adds the directory length to every frame offset.
#
# Usage: powershell -NoProfile -ExecutionPolicy Bypass -File repair-ico.ps1 <file.ico> [more.ico ...]
# Each file is backed up as <file>.bak-<timestamp> before being rewritten.

param([Parameter(Mandatory=$true, Position=0)][string]$IcoPath)

Add-Type -AssemblyName System.Drawing

foreach ($path in @($IcoPath)) {
  $full = (Resolve-Path $path -ErrorAction SilentlyContinue).Path
  if (-not $full -or -not (Test-Path $full)) { Write-Host "SKIP (not found): $path"; continue }
  $bytes = [System.IO.File]::ReadAllBytes($full)
  if ($bytes.Length -lt 22) { Write-Host "SKIP (too small): $path"; continue }

  $count = [BitConverter]::ToUInt16($bytes, 4)
  if ($count -lt 1 -or $count -gt 64) { Write-Host "SKIP (odd frame count $count): $path"; continue }
  $dirLen = 6 + $count * 16

  # Detect the broken pattern: first frame offset is 0 (points at the directory itself)
  $off0 = [BitConverter]::ToUInt32($bytes, 6 + 12)
  if ($off0 -ne 0) { Write-Host "OK (first offset=$off0, no fix needed): $path"; continue }

  $stamp = Get-Date -Format 'yyyyMMdd-HHmmss'
  $bak = "$full.bak-$stamp"
  Copy-Item $full $bak -Force

  $b = [byte[]]$bytes.Clone()
  for ($i = 0; $i -lt $count; $i++) {
    $o = 6 + $i * 16 + 12
    $v = [BitConverter]::ToUInt32($b, $o) + $dirLen
    [BitConverter]::GetBytes($v).CopyTo($b, $o)
  }
  [System.IO.File]::WriteAllBytes($full, $b)

  try {
    $ic = [System.Drawing.Icon]::new($full)
    $ok = "OK $($ic.Width)x$($ic.Height)"
    $ic.Dispose()
  } catch { $ok = "STILL FAILS: $($_.Exception.InnerException.Message)" }
  Write-Host "FIXED: $full (backup $bak) verify: $ok"
}