// I learned how to use ImageSharp by reading its
// documentation and sample code.
open SixLabors.ImageSharp
open SixLabors.ImageSharp.Processing

[<EntryPoint>]
let main args =
    // make sure the user gave us an image file as input
    if args.Length <> 1 then
        printfn "Usage: dotnet run <input image>"
        exit 1

    // "use" just means "declare a variable on which we call
    // "close" when it goes out of scope;
    // Image.Load returns a "Closeable" object.
    use image = Image.Load args[0]

    // ImageSharp's Mutate method takes a function that changes
    // the image through side effects (yuck!)
    image.Mutate
        (fun x -> x.Resize(image.Width / 2, image.Height / 2).Grayscale().Rotate(45f) |> ignore)

    // We have to explicitly ask the image to save itself.
    // Here we are computing a filename based off of the original
    // one but with "-mutated.jpg" added on to the end.
    image.Save (sprintf "%s-mutated.jpg" args[0])

    0