$compileHashFile = "compilehashes.xml"

if (Get-ChildItem -File $compileHashFile -ErrorAction SilentlyContinue) {
    $hashes = Import-Clixml $compileHashFile
} else {
    $hashes = @{}
}

function CompileShader($fileName) {
    $spvFileName = "$fileName.spv"
    $newHash = Get-FileHash -Path $fileName -Algorithm SHA1

    $spvExists = $false
    if (Get-ChildItem -File $spvFileName -ErrorAction SilentlyContinue) {
        $spvExists = $true
    }
    
    if ($spvExists -and $hashes.ContainsKey($fileName) -and $hashes[$fileName] -eq $newHash.Hash) {
        Write-Output "Skipping $fileName"
    } else {
        glslangValidator -V $fileName -o $spvFileName
        $hashes.$fileName = $newHash.Hash
    }
}

Get-ChildItem -Filter *.vert | ForEach-Object {
    CompileShader $_.Name
}
Get-ChildItem -Filter *.frag | ForEach-Object {
    CompileShader $_.Name
}

Export-Clixml -Path $compileHashFile -InputObject $hashes