Install-TerraformPlugin.ps1

<#
.SYNOPSIS
    Installs a given terraform plugin/provider from github
.EXAMPLE
    PS C:\> ./Install-TerraformPlugin -GitHubPath Mastercard/terraform-provider-restapi
    Install-TerraformPlugin will search github the repo: Mastercard/terraform-provider-restapi
    foo and check if the latest version has been added to the local terraform
    plugins dir. If not, it will downlaod and install it.
.NOTES
  - Only supports Windows at the moment. 
  - Only tested on Windows 10 1809 so far. 
  - License: MIT
  - Copywrite 2018-Present - George Bowen
#>

[CmdletBinding( PositionalBinding )]
param (

    # name of the plugin in as a github path such as Mastercard/terraform-provider-restapi
    # also excepts and array for plugins
    [Parameter( Mandatory )]
    [ValidatePattern( "^\w+\/\.?" )]
    [string[]]
    $GitHubPath,

    # Directory where terraform will store plugins
    [Parameter()]
    [ValidateScript( { Test-Path $_ })]
    [string]
    $PluginDir = "$env:APPDATA/terraform.d/plugins/windows_amd64",

    # The extenion that the plugin will have. .exe for Windows
    [Parameter( DontShow )]
    [string]
    $PluginExt = ".exe"

)

begin {

    Set-StrictMode -Version 2.0

    $ErrorActionPreference = "Stop"

    DATA LogMessages {

        ConvertFrom-StringData @'

        #culture="en-US"
        FailedCreatePluginDir = Failed to verify or create plugin dir at path: {0}
        ResolvingPath  = Resolving plugin path for: {0}...
        EnsureDirExists = Ensuring plugin directory exists at path: {0}...
        DownloadingPlugin = Downloading plugin from source: {0} to dest: {1}...

'@

    }

    # Create the plugin dir if missing
    function Assert-PluginDirExists ( $PluginDir ) {

        try {

            New-Directory $PluginDir

        }
        catch {

            Write-Warning ( $LogMessages.FailedCreatePluginDir -f $PluginDir )
            throw $_

        }

    }

    # Create a dir if missing
    function New-Directory ( $Path ) {

        if ( Test-DirectoryExists $Path ) {

            return $null

        }

        New-Item $Path -ItemType Directory -Force |
            Out-Null

    }

    # Test if a given directory exiss
    function Test-DirectoryExists ( $Path ) {

        Test-Path $Path

    }

    # Gets the path that a web request is attempting to be redirected too
    function Get-RedirectedUrl ( $Url ) {

        $WebReqArgs = @{

            Method             = "HEAD"
            UseBasicParsing    = $true
            Uri                = $Url
            MaximumRedirection = 0
            Verbose            = $false
            ErrorAction        = "Stop" # Will throw an error if attempted to be redirected
            OutVariable        = "Response"

        }

        try {

            Invoke-WebRequest @WebReqArgs | Out-Null

        }
        catch {

            if ( $Response.StatusCode -eq 302 ) {

                # return the location that the redirect was attempted
                return $Response.Headers.location

            }
            else {

                throw $_

            }

        }

    }

    # resolves a plugin path into the github maintainer, repo name,
    # url to latest, binaries
    function Resolve-PluginPath ( $PluginPath ) {

        $Plugin = [PSCustomObject]@{

            Maintainer = $null
            ProjName   = $null
            Binaries   = @()

        }

        $Plugin.Maintainer, $Plugin.ProjName = $PluginPath -split "\/"
        $Plugin.Binaries = Get-PluginBinaries $Plugin.Maintainer $Plugin.ProjName

        return $Plugin

    }

    # Get the download URL for terraform plugin from github release page
    function Get-PluginBinaries ( $Maintainer, $ProjectName ) {

        $GithubUrl = "https://github.com"
        $SearchUrl = (
            $GithubUrl + "/" +
            $Maintainer + "/" +
            $ProjectName + "/releases/latest"
        )

        $LatestReleasesUrl = Get-RedirectedUrl $SearchUrl

        $Bins = Get-GithubReleaseBins $LatestReleasesUrl | Where-Object {

            $_ -match $Maintainer -AND
            $_ -match $ProjectName -AND
            $_ -match "\/releases\/download\/.*.\/terraform-provider-.*.-windows-amd64"

        }

        # prefix gituhub domain to urls
        $Bins | ForEach-Object {

            $GithubUrl + $_

        }

    }

    # return a list of binaries from a github releases page
    function Get-GithubReleaseBins ( $Url ) {

        $WebReqArgs = @{

            Method          = "GET"
            Uri             = $Url
            Verbose         = $false
            TimeoutSec      = 5
            UseBasicParsing = $true

        }

        $Response = Invoke-WebRequest @WebReqArgs

        # Using the css class fine all links that contain bins
        $Releases = $Response.Links | Where-Object {
            ( $_ | Get-Member -Name class ) -AND
            $_.class -match "d-flex flex-items-center"
        }
        $Releases.href

    }

    function Invoke-PluginDownload ( $Url, $Dest ) {

        if ( -not ( Test-Path $Dest )) {

            # Invoke web request is slow, using webclient class
            [System.Net.WebClient]::new().DownloadFile( $Url, $Dest)

        }

    }

}

process {

    Write-Verbose ( $LogMessages.EnsureDirExists -f $PluginDir )
    Assert-PluginDirExists $PluginDir

    foreach ( $Plugin in $GitHubPath ) {

        Write-Host ( $LogMessages.ResolvingPath -f $Plugin )
        $Plugin = Resolve-PluginPath $Plugin

        foreach ( $Bin in $Plugin.Binaries ) {

            $BinName = Split-Path $Bin -Leaf
            $BinName = $BinName -replace '-windows-amd64'
            $BinName = $BinName + $PluginExt
            $DestinationPath = Join-Path $PluginDir $BinName
            Write-Host ( $LogMessages.DownloadingPlugin -f $Bin, $DestinationPath)
            Invoke-PluginDownload $Bin $DestinationPath

        }

    }

}