module internal ImageServices

    open System.IO
    open System.Drawing
    open System.Drawing.Imaging
    open DeathSocket
    open ColourServices
    open SkiaSharp
    open System

    let setLineThickness pDimension aDimension lineWidth =
        if (pDimension <= 0.0 || aDimension <= 0.0 || lineWidth <= 0.0) then
            raise (new DivideByZeroException ("[ERROR] The images height and width must be greater than 0."))
        else lineWidth / (pDimension / aDimension)

    // SkiaSharp Functions
    // ========================================================================

    let createSKHorizontalLines width height rows =
        let interval = float32 (height / rows)
        [|for point in 1 .. (rows - 1) ->
            [| SKPoint ((float32 0), (interval * (float32 point)))
               SKPoint ((float32 width), (interval * (float32 point)))|]|]

    let createSKVerticalLines width height columns =
        let interval = float32 (width / columns)
        [| for point in 1 .. (columns - 1) ->
            [| SKPoint ((interval * (float32 point)), (float32 0))
               SKPoint ((interval * (float32 point)), (float32 height))|]|]

    let determineSkiaDimensions filePath =
        use fileStream = File.Open (filePath, FileMode.Open)
        use skStream = new SKManagedStream (fileStream)
        use bitmap = SKBitmap.Decode (skStream)
        (bitmap.Width, bitmap.Height)

    // Does not work when using SkiaSharp NuGet v. 1.68
    let drawSkiaGrid (spec: SkiaSpec) =
        use fileStream = File.Open (spec.originalPath, FileMode.Open)
        use skStream = new SKManagedStream (fileStream)
        use bitmap = SKBitmap.Decode (skStream)
        use shader =
            SKShader.CreateBitmap (bitmap, SKShaderTileMode.Mirror, SKShaderTileMode.Mirror)
        let imageInfo = new SKImageInfo (bitmap.Width, bitmap.Height)
        use surface = SKSurface.Create (imageInfo)
        use canvas = surface.Canvas
        canvas.Clear (SKColors.White)

        use imageFill = new SKPaint ()
        imageFill.Style <- SKPaintStyle.Fill
        imageFill.Shader <- shader
        canvas.DrawPaint (imageFill)

        use stroke = new SKPaint ()
        stroke.Style <- SKPaintStyle.Stroke
        stroke.StrokeWidth <- spec.penWidth
        stroke.Color <- spec.skColour
        let horizontalLines =
            createSKHorizontalLines (bitmap.Width) (bitmap.Height) (spec.rows)
        let verticalLines =
            createSKVerticalLines (bitmap.Width) (bitmap.Height) (spec.columns)
        for hLine in horizontalLines do
            canvas.DrawLine (hLine.[0], hLine.[1], stroke)
        for vLine in verticalLines do
            canvas.DrawLine (vLine.[0], vLine.[1], stroke)

        use snapshot = surface.Snapshot ()
        use data =
            match Path.GetExtension (spec.savePath) with
            | ".jpg" | ".JPG" -> snapshot.Encode (SKEncodedImageFormat.Jpeg, 100)
            | ".png"| ".PNG" -> snapshot.Encode (SKEncodedImageFormat.Png, 100)
            | _ -> invalidArg "savePath" "The file type must be a .jpg or .png file."
        use saveStream = File.OpenWrite (spec.savePath)
        data.SaveTo (saveStream)

    // Does not work when using SkiaSharp NuGet v. 1.68
    let drawSkiaRGBGrid spec =
        use fileStream = File.Open (spec.originalPath, FileMode.Open)
        use skStream = new SKManagedStream (fileStream)
        use bitmap = SKBitmap.Decode (skStream)
        use shader =
            SKShader.CreateBitmap (bitmap, SKShaderTileMode.Mirror, SKShaderTileMode.Mirror)
        let imageInfo = new SKImageInfo (bitmap.Width, bitmap.Height)
        use surface = SKSurface.Create (imageInfo)
        use canvas = surface.Canvas
        canvas.Clear (SKColors.White)

        use imageFill = new SKPaint ()
        imageFill.Style <- SKPaintStyle.Fill
        imageFill.Shader <- shader
        canvas.DrawPaint (imageFill)

        use stroke = new SKPaint ()
        stroke.Style <- SKPaintStyle.Stroke
        stroke.StrokeWidth <- spec.penWidth
        stroke.Color <-
            new SKColor ((byte spec.red), (byte spec.green), (byte spec.blue))
        let horizontalLines =
            createSKHorizontalLines (bitmap.Width) (bitmap.Height) (spec.rows)
        let verticalLines =
            createSKVerticalLines (bitmap.Width) (bitmap.Height) (spec.columns)
        for hLine in horizontalLines do
            canvas.DrawLine (hLine.[0], hLine.[1], stroke)
        for vLine in verticalLines do
            canvas.DrawLine (vLine.[0], vLine.[1], stroke)

        use snapshot = surface.Snapshot ()
        use data =
            match Path.GetExtension (spec.savePath) with
            | ".jpg" | ".JPG" -> snapshot.Encode (SKEncodedImageFormat.Jpeg, 100)
            | ".png"| ".PNG" -> snapshot.Encode (SKEncodedImageFormat.Png, 100)
            | _ -> invalidArg "savePath" "The file type must be a .jpg or .png file."
        use saveStream = File.OpenWrite (spec.savePath)
        data.SaveTo (saveStream)

    // System.Drawing Functions
    // ========================================================================

    let createHorizontalLines width height rows =
        let interval = height / rows
        [| for point in 1 .. (rows - 1) ->
            [|Point (0, (interval * point))
              Point (width, (interval * point) )|]|]

    let createVerticalLines width height columns =
        let interval = width / columns
        [| for point in 1 .. (columns - 1) ->
            [| Point ((interval * point), 0)
               Point ((interval * point), height)|]|]

    let determineSystemDrawingDimensions filePath =
        use bitmap = Bitmap.FromFile filePath
        (bitmap.Width, bitmap.Height)

    (* Note on Use of Temp. File in Functions which Add A Grid Overlay
    ===========================================================================
    The temp. file is used in the functions below are there to convert images
    with indexed pixels. Instead of listing them all, just assume any function
    with a "*Spec" type as a parameter will use this "temp" file. *)

    let drawBrushSpecGrid (spec: BrushSpec) =
        use original = Bitmap.FromFile spec.originalPath
        use temp = new Bitmap(original)
        use clone = temp.Clone(new Rectangle(0, 0, temp.Width, temp.Height), PixelFormat.Format32bppArgb)
        use graphics = Graphics.FromImage(clone)
        use pen = new Pen (spec.colour, width = spec.penWidth)
        graphics.DrawImage(original,new Rectangle(0, 0, clone.Width, clone.Height))
        let horizontalLines =
            createHorizontalLines (clone.Size.Width) (clone.Size.Height) (spec.rows)
        let verticalLines =
            createVerticalLines (clone.Size.Width) (clone.Size.Height) (spec.columns)
        for line in horizontalLines do graphics.DrawLines (pen, line)
        for line in verticalLines do graphics.DrawLines (pen, line)
        clone.Save (spec.savePath)

    let drawRGBAGrid (spec: RGBASpec) =
        use original = Bitmap.FromFile spec.originalPath
        use temp = new Bitmap (original)
        use clone = temp.Clone (new Rectangle(0, 0, temp.Width, temp.Height), PixelFormat.Format32bppArgb)
        use graphics = Graphics.FromImage(clone)
        use pen = new Pen ((makeBrushFromRGBASpec spec), width = spec.penWidth)
        graphics.DrawImage (original,new Rectangle(0, 0, clone.Width, clone.Height))
        let horizontalLines =
            createHorizontalLines (clone.Size.Width) (clone.Size.Height) (spec.rows)
        let verticalLines =
            createVerticalLines (clone.Size.Width) (clone.Size.Height) (spec.columns)
        for line in horizontalLines do graphics.DrawLines (pen, line)
        for line in verticalLines do graphics.DrawLines (pen, line)
        clone.Save (spec.savePath)