$GithubAPIBaseURI = "https://api.github.com/repos"

function Get-GitHubHeaders ($token) {
  $headers = @{
    Authorization = "bearer $token"
  }
  return $headers
}

function Invoke-GitHubAPIPost {
  param (
    [Parameter(Mandatory = $true)]
    $apiURI,
    [Parameter(Mandatory = $true)]
    $body,
    [Parameter(Mandatory = $true)]
    $token
  )

  $resp = Invoke-RestMethod `
    -Method POST `
    -Body ($body | ConvertTo-Json) `
    -Uri $apiURI `
    -Headers (Get-GitHubHeaders -token $token) `
    -MaximumRetryCount 3

  return $resp
}

function Invoke-GitHubAPIPatch {
  param (
    [Parameter(Mandatory = $true)]
    $apiURI,
    [Parameter(Mandatory = $true)]
    $body,
    [Parameter(Mandatory = $true)]
    $token
  )

  $resp = Invoke-RestMethod `
    -Method PATCH `
    -Body ($body | ConvertTo-Json) `
    -Uri $apiURI `
    -Headers (Get-GitHubHeaders -token $token) `
    -MaximumRetryCount 3

  return $resp
}

function Invoke-GitHubAPIGet {
  param (
    [Parameter(Mandatory = $true)]
    $apiURI,
    $token
  )

  if ($token)
  {
    $resp = Invoke-RestMethod `
      -Method GET `
      -Uri $apiURI `
      -Headers (Get-GitHubHeaders -token $token) `
      -MaximumRetryCount 3
  }
  else {
    $resp = Invoke-RestMethod `
      -Method GET `
      -Uri $apiURI `
      -MaximumRetryCount 3
  }

  return $resp
}

function SplitMembers ($membersString)
{
  if (!$membersString) { return $null }
  return @($membersString.Split(",") | % { $_.Trim() } | ? { return $_ })
}

function List-PullRequests {
  param (
    [Parameter(Mandatory = $true)]
    $RepoOwner,
    [Parameter(Mandatory = $true)]
    $RepoName,
    [ValidateSet("open","closed","all")]
    $State = "open",
    $Head,
    $Base,
    [ValidateSet("created","updated","popularity","long-running")]
    $Sort,
    [ValidateSet("asc","desc")]
    $Direction
  )

  $uri = "$GithubAPIBaseURI/$RepoOwner/$RepoName/pulls"
  if ($State -or $Head -or $Base -or $Sort -or $Direction) { $uri += '?'}
  if ($State) { $uri += "state=$State&" }
  if ($Head) { $uri += "head=$Head&" }
  if ($Base) { $uri += "base=$Base&" }
  if ($Sort) { $uri += "sort=$Sort&" }
  if ($Direction){ $uri += "direction=$Direction&" }

  return Invoke-GitHubAPIGet -apiURI $uri
}

function Add-IssueComment {
  param (
    [Parameter(Mandatory = $true)]
    $RepoOwner,
    [Parameter(Mandatory = $true)]
    $RepoName,
    [Parameter(Mandatory = $true)]
    $IssueNumber,
    [Parameter(Mandatory = $true)]
    $Comment,
    [Parameter(Mandatory = $true)]
    $AuthToken

  )
  $uri = "$GithubAPIBaseURI/$RepoOwner/$RepoName/issues/$IssueNumber/comments"

  $parameters = @{
    body = $Comment
  }

  return Invoke-GitHubAPIPost -apiURI $uri -body $parameters -token $AuthToken
}

# Will add labels to existing labels on the issue
function Add-IssueLabels {
  param (
    [Parameter(Mandatory = $true)]
    $RepoOwner,
    [Parameter(Mandatory = $true)]
    $RepoName,
    [Parameter(Mandatory = $true)]
    $IssueNumber,
    [ValidateNotNullOrEmpty()]
    [Parameter(Mandatory = $true)]
    $Labels,
    [Parameter(Mandatory = $true)]
    $AuthToken
  )

  if ($Labels.Trim().Length -eq 0)
  {
    throw "The 'Labels' parameter should not not be whitespace..`
    You can use the 'Update-Issue' function if you plan to reset the labels"
  }

  $uri = "$GithubAPIBaseURI/$RepoOwner/$RepoName/issues/$IssueNumber/labels"
  $labelAdditions = SplitMembers -membersString $Labels
  $parameters = @{
    labels = @($labelAdditions)
  }

  return Invoke-GitHubAPIPost -apiURI $uri -body $parameters -token $AuthToken
}

# Will add assignees to existing assignees on the issue
function Add-IssueAssignees {
  param (
    [Parameter(Mandatory = $true)]
    $RepoOwner,
    [Parameter(Mandatory = $true)]
    $RepoName,
    [Parameter(Mandatory = $true)]
    $IssueNumber,
    [ValidateNotNullOrEmpty()]
    [Parameter(Mandatory = $true)]
    $Assignees,
    [Parameter(Mandatory = $true)]
    $AuthToken
  )

  if ($Assignees.Trim().Length -eq 0)
  {
    throw "The 'Assignees' parameter should not be whitespace.`
    You can use the 'Update-Issue' function if you plan to reset the Assignees"
  }

  $uri = "$GithubAPIBaseURI/$RepoOwner/$RepoName/issues/$IssueNumber/assignees"
  $assigneesAdditions = SplitMembers -membersString $Assignees
  $parameters = @{
    assignees = @($assigneesAdditions)
  }

  return Invoke-GitHubAPIPost -apiURI $uri -body $parameters -token $AuthToken
}

# For labels and assignee pass comma delimited string, to replace existing labels or assignees.
# Or pass white space " " to remove all labels or assignees
function Update-Issue {
  param (
    [Parameter(Mandatory = $true)]
    $RepoOwner,
    [Parameter(Mandatory = $true)]
    $RepoName,
    [Parameter(Mandatory = $true)]
    $IssueNumber,
    [string]$Title,
    [string]$Body,
    [ValidateSet("open","closed")]
    [string]$State,
    [int]$Milestome,
    [ValidateNotNullOrEmpty()]
    [string]$Labels,
    [ValidateNotNullOrEmpty()]
    [string]$Assignees,
    [Parameter(Mandatory = $true)]
    $AuthToken
  )

  $uri = "$GithubAPIBaseURI/$RepoOwner/$RepoName/issues/$IssueNumber"
  $parameters = @{}
  if ($Title) { $parameters["title"] = $Title }
  if ($Body) { $parameters["body"] = $Body }
  if ($State) { $parameters["state"] = $State }
  if ($Milestone) { $parameters["milestone"] = $Milestone }
  if ($Labels) { 
    $labelAdditions = SplitMembers -membersString $Labels
    $parameters["labels"] = @($labelAdditions)
  }
  if ($Assignees) { 
    $assigneesAdditions = SplitMembers -membersString $Assignees
    $parameters["assignees"] = @($assigneesAdditions)
  }

  return Invoke-GitHubAPIPatch -apiURI $uri -body $parameters -token $AuthToken
}