Archives local files to S3bucket with verifying integrity. Powershell

Archive-FileToS3.ps1

# Archive-FileToS3 archives local files which is older than specified days in a path to S3bucket with verifying integrity of uploaded S3objects.
# The verification method is to check if an eTag of S3object matches an eTag value calculated from a local file.

# Get-S3ETagHash calculates an eTag for a local file that should match the S3 eTag of the uploaded file. 
# Credit goes to Sean Bamforth (https://gist.github.com/seanbamforth/9388507) and chrisdarth(https://gist.github.com/chrisdarth/02d030b31727d70d2c63)

function Archive-FileToS3 {
    [cmdletbinding()]
    Param (
        [Parameter(Mandatory=$true)]
        [ValidateScript({ Test-Path $_ -PathType Container })]
        [string]$Path,
        [Parameter(Mandatory=$true)]
        [ValidateScript({ $( Get-S3Bucket -BucketName $_ ) })]
        [string]$bucketname,
        [Parameter(Mandatory=$true)]
        [Int32] $Days,
        [Int32]$ConcurrentServiceRequest = 10
    )
    if ($Path[$Path.Length-1] -eq "\" ){ $Path = $Path.Substring(0,$Path.Length-1) }
    foreach ($file in $(Get-ChildItem $Path -Recurse | Where-Object{$_.Attributes -ne "directory"})){
        if ($file.LastWriteTime -lt ((Get-Date).AddDays(-$Days))){
            Write-S3Object -BucketName $bucketname -Key $file.FullName.Substring($Path.Length + 1) -File $file.FullName -ConcurrentServiceRequest $ConcurrentServiceRequest
            $s3object = Get-S3Object -BucketName $bucketname -Key $file.FullName.Substring($Path.Length + 1)
            $etag = $s3object.etag.Replace("`"","")
            $hash = $(Get-S3ETagHash($file.FullName)).Hash
            if ($etag -eq $hash){
                Remove-Item $file.FullName -Force
            }else{
                Remove-S3Object -BucketName $bucketname -Key $file.FullName.Substring($Path.Length + 1) -Force
            }
        }
    }
}

function Get-S3ETagHash {
    [cmdletbinding()]
    Param (
        [Parameter(Mandatory=$true)]
        [ValidateScript({ Test-Path $_ -PathType Leaf })]
        [string]$Path,
        [Int32]$ChunkSize = 5
    )
    $filename = Get-Item $Path
    $md5 = new-object -TypeName System.Security.Cryptography.MD5CryptoServiceProvider

    $blocksize = (1024*1024*$ChunkSize)
    $startblocks = (1024*1024*16)
    
    $lines = 0
    [byte[]] $binHash = @()
 
    $reader = [System.IO.File]::Open($filename,"OPEN","READ")
    
    if ($filename.length -ge $startblocks) {
        $buf = new-object byte[] $blocksize
        while (($read_len = $reader.Read($buf,0,$buf.length)) -ne 0){
            $lines   += 1
            $binHash += $md5.ComputeHash($buf,0,$read_len)
        }
        $binHash=$md5.ComputeHash( $binHash )
    }
    else {
        $lines   = 1
        $binHash += $md5.ComputeHash($reader)
    }
 
    $reader.Close()
    
    $hash = [System.BitConverter]::ToString( $binHash )
    $hash = $hash.Replace("-","").ToLower()
 
    if ($lines -gt 1) {
        $hash = $hash + "-$lines"
    }
    
    # Output pscustomobject, equal to Get-FileHash
    [pscustomobject]@{
        Algorithm = "S3ETag"
        Hash =$hash
        Path = $filename.FullName
    }
    return
}