param(
    [PSCredential]
    $Credential
)

$headers = @{}
if($Credential)
{
    $networkCredential = $Credential.GetNetworkCredential()
    $user = $networkCredential.Username
    $pass = $networkCredential.Password

    $pair = "${user}:${pass}"

    $bytes = [System.Text.Encoding]::ASCII.GetBytes($pair)
    $base64 = [System.Convert]::ToBase64String($bytes)
    $basicAuthValue = "Basic $base64"
    $headers = @{ Authorization = $basicAuthValue }
}

$last = 0
if(Test-Path repositories.csv)
{
    $lastItem = Get-Content repositories.csv -Tail 1 | ConvertFrom-Csv -Header Id,Name,html_url,description,languages
    $last = $lastItem.Id
}

function Ensure-RateLimit
{
    do
    {
        $limit = (Invoke-RestMethod -uri "https://api.github.com/rate_limit" -Headers $headers).Rate

        if(([int] $limit.Remaining) -lt 10)
        {
            Write-Progress ("Waiting. Rate limit resets in: " +
                ([System.DateTimeOffset]::FromUnixTimeSeconds($limit.Reset).ToLocalTime().DateTime - (Get-Date)))
            Start-Sleep -Seconds 60
        }
    } while($limit.Remaining -lt 10)
}

while($true)
{
    Ensure-RateLimit
    $repositories = Invoke-RestMethod -uri "https://api.github.com/repositories?since=$last" -Headers $headers
    if(-not $repositories)
    {
        break
    }

    $firstRepository = $repositories[0]
    Write-Progress ("Processing repository {0}: {1} - {2}" -f $firstRepository.Id,$firstRepository.Name,$firstRepository.Description)

    foreach($repository in $repositories)
    {
        Ensure-RateLimit
        $outputObject = $repository | Select-Object Id,Name,html_url,Description,Languages
        $languages = (Invoke-RestMethod $repository.languages_url -Headers $headers).PSObject.Properties.Name -join ":"
        $outputObject.Languages = $languages

        $outputObject | Export-Csv repositories.csv -Append -NoTypeInformation
        $last = $repository.id
    }
}