/*

    Copyright (C) 2016 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    Contains the definition for `CenteringClipView` which is a specialized clip view subclass to center its document.

*/

import Cocoa

/**

    `CenteringClipView` is a clip view subclass that centers smaller documents views

    within its inset clip bounds (as described by the set `contentInsets`).

*/

class CenteringClipView: NSClipView {

    override func constrainBoundsRect(_ proposedBounds: NSRect) -> NSRect {

        guard let documentView = documentView else { return super.constrainBoundsRect(proposedBounds) }

        var newClipBoundsRect = super.constrainBoundsRect(proposedBounds)

        // Get the `contentInsets` scaled to the future bounds size.

        let insets = convertedContentInsetsToProposedBoundsSize(newClipBoundsRect.size)

        // Get the insets in terms of the view geometry edges, accounting for flippedness.

        let minYInset = isFlipped ? insets.top : insets.bottom

        let maxYInset = isFlipped ? insets.bottom : insets.top

        let minXInset = insets.left

        let maxXInset = insets.right

        /*

            Get and outset the `documentView`'s frame by the scaled contentInsets.

            The outset frame is used to align and constrain the `newClipBoundsRect`.

        */

        let documentFrame = documentView.frame

        let outsetDocumentFrame = NSRect(x: documentFrame.minX - minXInset,

                                         y: documentFrame.minY - minYInset,

                                     width: (documentFrame.width + (minXInset + maxXInset)),

                                    height: documentFrame.height + (minYInset + maxYInset))

        if newClipBoundsRect.width > outsetDocumentFrame.width {

            /*

                If the clip bounds width is larger than the document, center the

                bounds around the document.

            */

            newClipBoundsRect.origin.x = outsetDocumentFrame.minX - (newClipBoundsRect.width - outsetDocumentFrame.width) / 2.0

        }

        else if newClipBoundsRect.width < outsetDocumentFrame.width {

            /*

                Otherwise, the document is wider than the clip rect. Make sure that 

                the clip rect stays within the document frame.

            */

            if newClipBoundsRect.maxX > outsetDocumentFrame.maxX {

                // The clip rect is outside the maxX edge of the document, bring it in.

                newClipBoundsRect.origin.x = outsetDocumentFrame.maxX - newClipBoundsRect.width

            }

            else if newClipBoundsRect.minX < outsetDocumentFrame.minX {

                // The clip rect is outside the minX edge of the document, bring it in.

                newClipBoundsRect.origin.x = outsetDocumentFrame.minX

            }

        }

        if newClipBoundsRect.height > outsetDocumentFrame.height {

            /*

                If the clip bounds height is larger than the document, center the 

                bounds around the document.

            */

            newClipBoundsRect.origin.y = outsetDocumentFrame.minY - (newClipBoundsRect.height - outsetDocumentFrame.height) / 2.0

        }

        else if newClipBoundsRect.height < outsetDocumentFrame.height {

            /*

                Otherwise, the document is taller than the clip rect. Make sure 

                that the clip rect stays within the document frame.

            */

            if newClipBoundsRect.maxY > outsetDocumentFrame.maxY {

                // The clip rect is outside the maxY edge of the document, bring it in.

                newClipBoundsRect.origin.y = outsetDocumentFrame.maxY - newClipBoundsRect.height

            }

            else if newClipBoundsRect.minY < outsetDocumentFrame.minY {

                // The clip rect is outside the minY edge of the document, bring it in.

                newClipBoundsRect.origin.y = outsetDocumentFrame.minY

            }

        }

        return backingAlignedRect(newClipBoundsRect, options: .alignAllEdgesNearest)

    }

    /**

        The `contentInsets` scaled to the scale factor of a new potential bounds

        rect. Used by `constrainBoundsRect(NSRect)`.

    */

    fileprivate func convertedContentInsetsToProposedBoundsSize(_ proposedBoundsSize: NSSize) -> EdgeInsets {

        // Base the scale factor on the width scale factor to the new proposedBounds.

        let fromBoundsToProposedBoundsFactor = bounds.width > 0 ? (proposedBoundsSize.width / bounds.width) : 1.0

        // Scale the set `contentInsets` by the width scale factor.

        var newContentInsets = contentInsets

        newContentInsets.top *= fromBoundsToProposedBoundsFactor

        newContentInsets.left *= fromBoundsToProposedBoundsFactor

        newContentInsets.bottom *= fromBoundsToProposedBoundsFactor

        newContentInsets.right *= fromBoundsToProposedBoundsFactor

        return newContentInsets

    }

}