Delete-Duplicates.ps1

[CmdletBinding(
    SupportsShouldProcess = $true,
    ConfirmImpact = "High"
)]
param(
    [string]
    $GoodDirectory,

    [string]
    $TargetDirectory
);

@"
Comparing:
    $GoodDirectory
to:
    $TargetDirectory
"@ | Write-Host;

$actualGood = (Resolve-Path -LiteralPath $GoodDirectory);
$actualTarget = (Resolve-Path -LiteralPath $TargetDirectory);

Push-Location $GoodDirectory
    $goodHashes = @{};
    $filesInGood = Get-ChildItem -File -Recurse -LiteralPath $actualGood `
        | Where-Object { -not $_.PSIsContainer } `
        | ForEach-Object {
            Resolve-Path -Relative -LiteralPath $_.FullName
        };
    $filesInGood | ForEach-Object {
        $prog = $goodHashes.Count / $filesInGood.Length;
        Write-Progress -Activity "Hashing good directory..." -Status "$prog" -PercentComplete (100 * $prog);
        $goodHashes.Add($_, (Get-FileHash -LiteralPath $_ -Algorithm SHA256).Hash);
    };
Pop-Location

Push-Location $TargetDirectory
    $filesInTarget = Get-ChildItem -File -Recurse -LiteralPath $actualTarget `
        | Where-Object { -not $_.PSIsContainer } `
        | ForEach-Object { Resolve-Path -Relative -LiteralPath $_.FullName }
    "${$filesInTarget.Length} files in target directory."  | Write-Host;
    $nTargetFilesProcessed = 0;
    $filesSafelyInTarget = $filesInTarget `
        | Where-Object {
            $prog = $nTargetFilesProcessed / $filesInTarget.Length;
            Write-Progress -Activity "Hashing target directory..." -Status "$prog" -PercentComplete (100 * $prog);
            # First check if this filename is in the good hashes or not.
            if ($goodHashes.ContainsKey($_)) {
                # Next, check that the hash was OK.
                $goodHash = $goodHashes[$_];
                $thisHash = (Get-FileHash -LiteralPath $_ -Algorithm SHA256).Hash;
                if ($thisHash -eq $goodHash) {
                    $true | Write-Output;
                } else {
                    "Hashes ${$thisHash} and ${$goodHash} for $_ did not match." | Write-Host;
                    $false | Write-Output;
                }
            } else {
                $false | Write-Output;
            }
            $nTargetFilesProcessed += 1;
        };
Pop-Location

"$($filesSafelyInTarget.Length) out of $($filesInGood.Length) safely in target." | Write-Host;

Push-Location $GoodDirectory
    $nOriginalsDeleted = 0;
    $filesSafelyInTarget | ForEach-Object {
        $prog = $nOriginalsDeleted / $filesSafelyInTarget.Length;
        Write-Progress `
            -Activity "Deleting originals for files safely in target..." `
            -Status "$prog" `
            -PercentComplete (100 * $prog)
        $itemToRemove = (Resolve-Path -LiteralPath $_ -ErrorAction SilentlyContinue);
        if ($itemToRemove -and $PSCmdlet.ShouldProcess($itemToRemove)) {
            Remove-Item -LiteralPath $itemToRemove;
        }
        $nOriginalsDeleted += 1;
    }
Pop-Location