function Get-TemporaryDirectory {
  $parent = [System.IO.Path]::GetTempPath()
  do {
    $name = [System.IO.Path]::GetRandomFileName()
    $item = New-Item -Path $parent -Name $name -ItemType "directory" -ErrorAction SilentlyContinue
  } while (-not $item)
  return $item.FullName
}

function Get-TemporaryFile {
  param(
	[string]$extension
  )
  $parent = [System.IO.Path]::GetTempPath()
  do {
    $name = [System.IO.Path]::GetRandomFileName() + $extension
    $item = New-Item -Path $parent -Name $name -ItemType "file" -ErrorAction SilentlyContinue
  } while (-not $item)
  return $item.FullName
}

function Get-Mscx-Content {
  param(
	[string]$mscz_file
  )
    # First rename (a copy) of the original score (=.mscz) to ".zip" to be able to unzip
    $tmpZIP = Get-TemporaryFile ".zip"
    Copy-Item $mscz_file $tmpZIP
    # uncompress score
    $uncompressed = Get-TemporaryDirectory
    Expand-Archive $tmpZIP -DestinationPath $uncompressed
    Remove-Item $tmpZIP
    $mscx = Get-ChildItem -Path $uncompressed -Filter "*.mscx"
    $content = Get-Content $mscx.FullName
    Remove-Item $uncompressed -Recurse
    return $content
}

function Start-of-staffs {
  param(
	[System.Object[]]$content_mscx
  )
    $line_no = 0
    $found = $false
    while ( -not $found -and $line_no -lt $content_mscx.Count ) {
        $line = $content_mscx[$line_no++]
        if ( $line -imatch "<Part id=") {
            $inPart = $true
        } elseif ( $line -imatch "</Part>") {
            $inPart = $false
        } elseif ( $line -imatch "<Staff id=" -and -not $inPart ) {
            $found = $true
        }
    }
  return $line_no
}

function Setup-initial-meged-score {
    param(
    [string]$new_uncompressed,
    [string]$first_score
    )
    # Unzip first score as working base
        # First rename (a copy) of the original score (=.mscz) to ".zip" to be able to unzip
        $tmpZIP = Get-TemporaryFile ".zip"
        Copy-Item $first_score $tmpZIP
    # uncompress score
    Expand-Archive $tmpZIP -DestinationPath $new_uncompressed
        Remove-Item $tmpZIP
    $mscx_file_name = (Get-ChildItem $new_uncompressed -Filter "*.mscx").FullName
    Remove-Item $mscx_file_name
    return $mscx_file_name
}

[System.Collections.ArrayList]$content_of_scores = @()
[System.Collections.ArrayList]$line_no_in_score = @()

if ( $args.Count -lt 2 ) {
    Write-Host -ForegroundColor Red "ERROR: provide at least two scores to combine!"
    exit 1
}

"Combinging " + $args.Count + " scores created by 'musescore'"

foreach ( $score in $args ) {
    "> extracting score '" + $score + "'"
    # extend content array
    $c = Get-Mscx-Content $score 
    $null = $content_of_scores.Add( $c )
    # remember line number of each score file
    $null = $line_no_in_score.Add(0)
}

[System.Collections.ArrayList]$new_score = @()
# where do all the staffs begin in scores?
for ( $score_no = 0 ; $score_no -lt $content_of_scores.Count ; $score_no++ ) {
    $line_no_in_score[$score_no] = Start-of-staffs $content_of_scores[$score_no]
}

# take header of first score till start of staffs
for ( $i = 0; $i -lt $line_no_in_score[0]; $i++ ) {
    $null = $new_score.Add($content_of_scores[0][$i])
}

while ( $line_no_in_score[0] -lt $content_of_scores[0].Count -and $content_of_scores[0][$line_no_in_score[0]] -inotmatch "</Score>" ) {
    # insert staffs of other score
    for ( $score_no = 0 ; $score_no -lt $content_of_scores.Count ; $score_no++ ) {
        # take stuff till </Staff>"
        do {
            $inner_line = $content_of_scores[$score_no][$line_no_in_score[$score_no]++]
            if ( $score_no -eq ($content_of_scores.Count-1) -or $inner_line -inotmatch "</Staff>" ) {
                $null = $new_score.Add($inner_line)
            } else {
                # add staff line "end" and page break at end of score if not last one
                if ( $score_no -lt ($content_of_scores.Count - 1) ) {
                    # "end" must be before </voice>
                    $null = $new_score.Insert($new_score.Count-2, "          <BarLine>")
                    $null = $new_score.Insert($new_score.Count-2, "            <subtype>end</subtype>")
                    $null = $new_score.Insert($new_score.Count-2, "            </BarLine>")
                    # page and sectin break must be before </measure>
                    $null = $new_score.Insert($new_score.Count-1, "        <LayoutBreak>")
                    $null = $new_score.Insert($new_score.Count-1, "          <subtype>section</subtype>")
                    $null = $new_score.Insert($new_score.Count-1, "          </LayoutBreak>")
                    $null = $new_score.Insert($new_score.Count-1, "        <LayoutBreak>")
                    $null = $new_score.Insert($new_score.Count-1, "          <subtype>page</subtype>")
                    $null = $new_score.Insert($new_score.Count-1, "          </LayoutBreak>")
                }
            }
        } while ( $line_no_in_score[$score_no] -lt $content_of_scores[$score_no].Count -and $inner_line -inotmatch "</Staff>" )
        # find next line starting a staff (may not be necessary for first staff)
        if ( $score_no -ne 0 -and $content_of_scores[$score_no][$line_no_in_score[$score_no]] -imatch "<Staff id=" ) {
            $line_no_in_score[$score_no]++
        }
    }
}
# take rest of first score
for ( $i = $line_no_in_score[0]; $i -lt $content_of_scores[0].Count; $i++ ) {
    $null = $new_score.Add($content_of_scores[0][$i])
}

$combined = "MergedSore"
$target_score= $combined + ".mscz"
If( test-path $target_score ) {
    $decision = $Host.UI.PromptForChoice('Target score "' + $target_score + '" already exists', "Overwrite?", ("&yes", "&no" ), 1)
    if ($decision -eq 0) {
        Remove-Item $target_score
    }
    else {
        Write-Host -ForegroundColor Red "ABORT: nothing exported"
        exit 1
    }
}

# create new score based on first score
$new_uncompressed = Get-TemporaryDirectory
$mscx_file_name = Setup-initial-meged-score $new_uncompressed $args[0]
$new_score | Out-File -Encoding "ASCII" -FilePath $mscx_file_name

# do it a .mscz (i. e. renamed .zip)
$new_zip = Get-TemporaryFile ".zip"
Compress-Archive $new_uncompressed\* $new_zip -Force
Remove-Item -Recurse $new_uncompressed
Copy-Item $new_zip $target_score
Remove-Item $new_zip