install required .NET SDK

build.ps1

@@ -32,6 +32,35 @@ function Task {
     }
 }
 
+Task "install-dotnet" $true {
+    $path = $PSScriptRoot
+
+    # Ensures that .net core is up to date.
+    # first get the required version from global.json
+    $json = ConvertFrom-Json (Get-Content "$path/global.json" -Raw)
+    $required_version = $json.sdk.version
+
+    # Running dotnet --version stupidly fails if the required SDK version is higher
+    # than the currently installed version. So move global.json out the way
+    # and then put it back again
+    Rename-Item "$path/global.json" "$path/global.json.bak"
+    $current_version = (dotnet --version)
+    Rename-Item "$path/global.json.bak" "$path/global.json"
+    Write-Host "Required .NET version: $required_version Installed: $current_version"
+
+    if ($current_version -lt $required_version) {
+        # Current installed version is too low.
+        # Install new version as a local only dependency.
+        $urlCurrent = "https://dotnetcli.blob.core.windows.net/dotnet/Sdk/$required_version/dotnet-sdk-$required_version-win-x64.zip"
+        Write-Host "Installing .NET Core $required_version from $urlCurrent"
+        $env:DOTNET_INSTALL_DIR = "$path/.dotnetsdk"
+        New-Item -Type Directory $env:DOTNET_INSTALL_DIR -Force | Out-Null
+        (New-Object System.Net.WebClient).DownloadFile($urlCurrent, "dotnet.zip")
+        Write-Host "Unzipping to $env:DOTNET_INSTALL_DIR"
+        Add-Type -AssemblyName System.IO.Compression.FileSystem; [System.IO.Compression.ZipFile]::ExtractToDirectory("dotnet.zip", $env:DOTNET_INSTALL_DIR)
+    }
+}
+
 
 Task "Init" $true {