<#
.SYNOPSIS
Classify text files by encoding under the current subtree, respecting .gitignore.

.DESCRIPTION
Enumerates tracked files and untracked-but-not-ignored files (via Git) beneath
PWD. Skips likely-binary files (NUL probe). Classifies remaining files as:
  - 'utf8'          : valid UTF-8 (no BOM) or empty file
  - 'utf8-with-bom' : starts with UTF-8 BOM (EF BB BF)
  - 'other'         : text but not valid UTF-8 (e.g., UTF-16/ANSI)

Outputs:
  1) Relative paths of files classified as 'other'
  2) A table by extension: UTF8 / UTF8-with-BOM / Other / Total

Notes:
  - Read-only: this script makes no changes.
  - Requires Git and must be run inside a Git work tree.
#>

[CmdletBinding()]
param()

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

# --- Git enumeration ---------------------------------------------------------
function Assert-InGitWorkTree {
  # Throws if not inside a Git work tree.
  $inside = (& git rev-parse --is-inside-work-tree 2>$null).Trim()
  if ($LASTEXITCODE -ne 0 -or $inside -ne 'true') {
    throw 'Not in a Git work tree.'
  }
}

function Get-GitFilesUnderPwd {
  <#
    Returns full paths to tracked + untracked-not-ignored files under PWD.
  #>
  Assert-InGitWorkTree

  $repoRoot = (& git rev-parse --show-toplevel).Trim()
  $pwdPath  = (Get-Location).Path

  # cached (tracked) + others (untracked not ignored)
  $nulSeparated = & git -C $repoRoot ls-files -z --cached --others --exclude-standard

  $relativePaths = $nulSeparated.Split(
    [char]0, [System.StringSplitOptions]::RemoveEmptyEntries)

  foreach ($relPath in $relativePaths) {
    $fullPath = Join-Path $repoRoot $relPath

    # Only include files under the current subtree.
    if ($fullPath.StartsWith($pwdPath,
         [System.StringComparison]::OrdinalIgnoreCase)) {
      if (Test-Path -LiteralPath $fullPath -PathType Leaf) { $fullPath }
    }
  }
}

# --- Probes ------------------------------------------------------------------
function Test-ProbablyBinary {
  # Heuristic: treat as binary if the first 8 KiB contains any NUL byte.
  param([Parameter(Mandatory)][string]$Path)

  try {
    $stream = [System.IO.File]::Open($Path,'Open','Read','ReadWrite')
    try {
      $len = [int][Math]::Min(8192,$stream.Length)
      if ($len -le 0) { return $false }

      $buffer = [byte[]]::new($len)
      [void]$stream.Read($buffer,0,$len)
      return ($buffer -contains 0)
    }
    finally { $stream.Dispose() }
  }
  catch { return $false }
}

function Get-TextEncodingCategory {
  # Returns 'utf8', 'utf8-with-bom', 'other', or $null for likely-binary.
  param([Parameter(Mandatory)][string]$Path)

  $stream = [System.IO.File]::Open($Path,'Open','Read','ReadWrite')
  try {
    $fileLength = $stream.Length
    if ($fileLength -eq 0) { return 'utf8' }

    # BOM check (EF BB BF)
    $header = [byte[]]::new([Math]::Min(3,$fileLength))
    [void]$stream.Read($header,0,$header.Length)
    if ($header.Length -ge 3 -and
        $header[0] -eq 0xEF -and $header[1] -eq 0xBB -and $header[2] -eq 0xBF) {
      return 'utf8-with-bom'
    }

    # Quick binary probe before expensive decoding
    $stream.Position = 0
    $sampleLen = [int][Math]::Min(8192,$fileLength)
    $sample = [byte[]]::new($sampleLen)
    [void]$stream.Read($sample,0,$sampleLen)
    if ($sample -contains 0) { return $null }
  }
  finally { $stream.Dispose() }

  # Validate UTF-8 by decoding with throw-on-invalid option (no BOM).
  try {
    $bytes = [System.IO.File]::ReadAllBytes($Path)
    $utf8 = [System.Text.UTF8Encoding]::new($false,$true)
    [void]$utf8.GetString($bytes)
    return 'utf8'
  }
  catch { return 'other' }
}

# --- Main --------------------------------------------------------------------
$otherFiles  = @()
$byExtension = @{}

$allFiles = Get-GitFilesUnderPwd

foreach ($fullPath in $allFiles) {
  # Avoid decoding likely-binary files.
  if (Test-ProbablyBinary $fullPath) { continue }

  $category = Get-TextEncodingCategory $fullPath
  if (-not $category) { continue }

  $ext = [IO.Path]::GetExtension($fullPath).ToLower()
  if (-not $byExtension.ContainsKey($ext)) {
    $byExtension[$ext] = @{ 'utf8' = 0; 'utf8-with-bom' = 0; 'other' = 0 }
  }

  $byExtension[$ext][$category]++

  if ($category -eq 'other') {
    $otherFiles += (Resolve-Path -LiteralPath $fullPath -Relative)
  }
}

# 1) Files in 'other'
if ($otherFiles.Count -gt 0) {
  'Files classified as ''other'':'
  $otherFiles | Sort-Object | ForEach-Object { "  $_" }
  ''
}

# 2) Table by extension
$rows = foreach ($kv in $byExtension.GetEnumerator()) {
  $ext = if ($kv.Key) { $kv.Key } else { '[noext]' }
  $u   = [int]$kv.Value['utf8']
  $b   = [int]$kv.Value['utf8-with-bom']
  $o   = [int]$kv.Value['other']

  [PSCustomObject]@{
    Extension       = $ext
    UTF8            = $u
    'UTF8-with-BOM' = $b
    Other           = $o
    Total           = $u + $b + $o
  }
}

$rows |
  Sort-Object -Property (
  	@{Expression='Total';Descending=$true},
    @{Expression='Extension';Descending=$false}
  ) |
  Format-Table -AutoSize