param(
  [Parameter(Mandatory)]
  [ValidateScript({ Test-Path -LiteralPath $_ })]
  [string]$SourceA,

  [Parameter(Mandatory)]
  [ValidateScript({ Test-Path -LiteralPath $_ })]
  [string]$TargetB
)
$outputA    = $SourceA -Replace ".xls", "_diff.xls"
$outputB    = $targetB -Replace ".xls", "_diff.xls"

$ErrorActionPreference = 'Stop'

$yellow = 65535     #vbYellow
$red    = 255       #vbRed
$cyan   = 16776960  #vbCyan

if (Test-Path $outputA) {
  Remove-Item $outputA -Force
}
if (Test-Path $outputB) {
  Remove-Item $outputB -Force
}

$excel = New-Object -ComObject Excel.Application
$excel.Visible = $false
$excel.DisplayAlerts = $false

$wbA = $null
$wbB = $null

try {
  $wbA = $excel.Workbooks.Open($sourceA)
  $wbB = $excel.Workbooks.Open($targetB)

  $mapA = @{}
  foreach ($ws in $wbA.Worksheets) { $mapA[$ws.Name] = $ws }

  $mapB = @{}
  foreach ($ws in $wbB.Worksheets) { $mapB[$ws.Name] = $ws }

  $commonNames = @($mapA.Keys | Where-Object { $mapB.ContainsKey($_) } | Sort-Object -Descending)
  if ($commonNames.Count -eq 0) {
    throw "同名のシートが見つかりませんでした。"
  }

  foreach ($name in $commonNames) {
    $wsA = $mapA[$name]
    $wsB = $mapB[$name]
　　Write-Host "比較中 - シート名: $($name)"

    $endRow = [Math]::Max(
      $wsA.UsedRange.Row + $wsA.UsedRange.Rows.Count - 1,
      $wsB.UsedRange.Row + $wsB.UsedRange.Rows.Count - 1
    )
    $endCol = [Math]::Max(
      $wsA.UsedRange.Column + $wsA.UsedRange.Columns.Count - 1,
      $wsB.UsedRange.Column + $wsB.UsedRange.Columns.Count - 1
    )

    $hasDiff = $false
    $hasDiffAll = $false

    for ($r = 1; $r -le $endRow; $r++) {
      for ($c = 1; $c -le $endCol; $c++) {
        $v1 = $wsA.Cells.Item($r, $c).Value2
        $v2 = $wsB.Cells.Item($r, $c).Value2
　　
        if (("$v1") -ne ("$v2")) {
          $addr = $wsB.Cells.Item($r, $c).Address($false, $false) 
　　　　　Write-Host "    不一致セル $($addr): $($v1) != $($v2)"
          $hasDiff = $true
          $hasDiffAll = $true
          $wsA.Cells.Item($r, $c).Interior.Color = $yellow
          $wsB.Cells.Item($r, $c).Interior.Color = $yellow
        }
      }
    }

    if ($hasDiff) {
　　　Write-Host "    差分あり"
      $wsA.Tab.Color = $yellow
      $wsB.Tab.Color = $yellow
    } else {
　　　Write-Host "    差分なし"
      $wsA.Tab.Color = $cyan
      $wsB.Tab.Color = $cyan
    }
  }

  Write-Host "比較中 - シートの有無..."
  foreach ($ws in $wbA.Worksheets) {
    $wsA = $mapA[$ws.Name]
    if (($wsA.Tab.Color -eq $yellow) -or ($wsA.Tab.Color -eq $cyan)) {
      # 確認済みシート
    } else {
      # 未確認シート（Bに存在しない）
      $hasDiffAll = $true
      $wsA.Tab.Color = $red
      Write-Host "'$(Split-Path -Path $SourceA -Leaf)' のシート名 '$($ws.Name)' は、'$(Split-Path -Path $TargetB -Leaf)' に存在しません。"
    }
  }
  foreach ($ws in $wbB.Worksheets) {
    $wsB = $mapB[$ws.Name]
    if (($wsB.Tab.Color -eq $yellow) -or ($wsB.Tab.Color -eq $cyan)) {
      # 確認済みシート
    } else {
      # 未確認シート（Aに存在しない）
      $hasDiffAll = $true
      $wsB.Tab.Color = $red
      Write-Host "'$(Split-Path -Path $targetB -Leaf)' のシート名 '$($ws.Name)' は、'$(Split-Path -Path $SourceA -Leaf)' に存在しません。"
    }
  }

  if ($hasDiffAll) {
    $xlOpenXMLWorkbook = 51  # xlsx
    $wbA.SaveAs($outputA, $xlOpenXMLWorkbook)
    $wbB.SaveAs($outputB, $xlOpenXMLWorkbook)
  } 
}
finally {
  if ($wbA) { $wbA.Close($false) | Out-Null }
  if ($wbB) { $wbB.Close($false) | Out-Null }
  if ($excel) { $excel.Quit() | Out-Null }

  foreach ($o in @($wbA, $wbB, $excel)) {
    if ($null -ne $o) { [void][System.Runtime.InteropServices.Marshal]::ReleaseComObject($o) }
  }
  [GC]::Collect()
  [GC]::WaitForPendingFinalizers()
}
if ($hasDiffAll) {
  Write-Host ("差分を次のファイルに保存しました。 {0}" -f $outputA)
  Write-Host ("差分を次のファイルに保存しました。 {0}" -f $outputB)
} else {
  Write-Host "差分はありません。"
}