SnapKit/Source/Constraint.swift

//
//  Snap
//
//  Copyright (c) 2011-2015 Masonry Team - https://github.com/Masonry
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.

#if os(iOS)
import UIKit
#else
import AppKit
#endif

public class Constraint {
    
    public func install() -> [LayoutConstraint] {
        return self.installOnView(updateExisting: false)
    }
    
    public func uninstall() {
        self.uninstallFromView()
    }
    
    public func activate() {
        if NSLayoutConstraint.respondsToSelector("activateConstraints:") && self.installInfo != nil {
            let layoutConstraints = self.installInfo!.layoutConstraints.allObjects as! [LayoutConstraint]
            if layoutConstraints.count > 0 {
                NSLayoutConstraint.activateConstraints(layoutConstraints)
            }
        } else {
            self.install()
        }
    }
    
    public func deactivate() {
        if NSLayoutConstraint.respondsToSelector("deactivateConstraints:") && self.installInfo != nil {
            let layoutConstraints = self.installInfo!.layoutConstraints.allObjects as! [LayoutConstraint]
            if layoutConstraints.count > 0 {
                NSLayoutConstraint.deactivateConstraints(layoutConstraints)
            }
        } else {
            self.uninstall()
        }
    }
    
    private let fromItem: ConstraintItem
    private let toItem: ConstraintItem
    private let relation: ConstraintRelation
    private var constant: Any
    private var multiplier: Float
    private var priority: Float
    
    private var installInfo: ConstraintInstallInfo? = nil
    
    internal init(fromItem: ConstraintItem, toItem: ConstraintItem, relation: ConstraintRelation, constant: Any, multiplier: Float, priority: Float) {
        self.fromItem = fromItem
        self.toItem = toItem
        self.relation = relation
        self.constant = constant
        self.multiplier = multiplier
        self.priority = priority
    }
    
    internal func installOnView(updateExisting: Bool = false) -> [LayoutConstraint] {
        var installOnView: View? = nil
        if self.toItem.view != nil {
            installOnView = closestCommonSuperviewBetween(self.fromItem.view, self.toItem.view)
            if installOnView == nil {
                NSException(name: "Cannot Install Constraint", reason: "No common superview between views", userInfo: nil).raise()
                return []
            }
        } else {
            installOnView = self.fromItem.view?.superview
            if installOnView == nil {
                if self.fromItem.attributes == ConstraintAttributes.Width || self.fromItem.attributes == ConstraintAttributes.Height {
                    installOnView = self.fromItem.view
                }
                
                if installOnView == nil {
                    NSException(name: "Cannot Install Constraint", reason: "Missing superview", userInfo: nil).raise()
                    return []
                }
            }
        }
        
        if let installedOnView = self.installInfo?.view {
            if installedOnView != installOnView {
                NSException(name: "Cannot Install Constraint", reason: "Already installed on different view.", userInfo: nil).raise()
                return []
            }
            return self.installInfo?.layoutConstraints.allObjects as? [LayoutConstraint] ?? []
        }
        
        var newLayoutConstraints = [LayoutConstraint]()
        let layoutFromAttributes = self.fromItem.attributes.layoutAttributes
        let layoutToAttributes = self.toItem.attributes.layoutAttributes
        
        // get layout from
        let layoutFrom: View? = self.fromItem.view
        
        // get layout relation
        let layoutRelation: NSLayoutRelation = self.relation.layoutRelation
        
        for layoutFromAttribute in layoutFromAttributes {
            // get layout to attribute
            let layoutToAttribute = (layoutToAttributes.count > 0) ? layoutToAttributes[0] : layoutFromAttribute
            
            // get layout constant
            var layoutConstant: CGFloat = layoutToAttribute.snp_constantForValue(self.constant)
            
            // get layout to
            var layoutTo: View? = self.toItem.view
            if layoutTo == nil && layoutToAttribute != .Width && layoutToAttribute != .Height {
                layoutTo = installOnView
            }
            
            // create layout constraint
            let layoutConstraint = LayoutConstraint(
                item: layoutFrom!,
                attribute: layoutFromAttribute,
                relatedBy: layoutRelation,
                toItem: layoutTo,
                attribute: layoutToAttribute,
                multiplier: CGFloat(self.multiplier),
                constant: layoutConstant)
            
            // set priority
            layoutConstraint.priority = self.priority
            
            // set constraint
            layoutConstraint.snp_constraint = self
            
            newLayoutConstraints.append(layoutConstraint)
        }
        
        // special logic for updating
        if updateExisting {
            // get existing constraints for this view
            let existingLayoutConstraints = reverse(layoutFrom!.snp_installedLayoutConstraints)
            
            // array that will contain only new layout constraints to keep
            var newLayoutConstraintsToKeep = [LayoutConstraint]()
            
            // begin looping
            for layoutConstraint in newLayoutConstraints {
                // layout constraint that should be updated
                var updateLayoutConstraint: LayoutConstraint? = nil
                
                // loop through existing and check for match
                for existingLayoutConstraint in existingLayoutConstraints {
                    if existingLayoutConstraint == layoutConstraint {
                        updateLayoutConstraint = existingLayoutConstraint
                        break
                    }
                }
                
                // if we have existing one lets just update the constant
                if updateLayoutConstraint != nil {
                    updateLayoutConstraint!.constant = layoutConstraint.constant
                }
                    // otherwise add this layout constraint to new keep list
                else {
                    newLayoutConstraintsToKeep.append(layoutConstraint)
                }
            }
            
            // set constraints to only new ones
            newLayoutConstraints = newLayoutConstraintsToKeep
        }
        
        // add constraints
        installOnView!.addConstraints(newLayoutConstraints)
        
        // set install info
        self.installInfo = ConstraintInstallInfo(view: installOnView, layoutConstraints: NSHashTable.weakObjectsHashTable())
        
        // store which layout constraints are installed for this constraint
        for layoutConstraint in newLayoutConstraints {
            self.installInfo!.layoutConstraints.addObject(layoutConstraint)
        }
        
        // store the layout constraints against the layout from view
        layoutFrom!.snp_installedLayoutConstraints += newLayoutConstraints
        
        // return the new constraints
        return newLayoutConstraints
    }
    
    internal func uninstallFromView() {
        if let installInfo = self.installInfo,
            let installedLayoutConstraints = installInfo.layoutConstraints.allObjects as? [LayoutConstraint] {
                
                if installedLayoutConstraints.count > 0 {
                    
                    if let installedOnView = installInfo.view {
                        // remove the constraints from the UIView's storage
                        installedOnView.removeConstraints(installedLayoutConstraints)
                    }
                    
                    // remove the constraints from the from item view
                    if let fromView = self.fromItem.view {
                        fromView.snp_installedLayoutConstraints = fromView.snp_installedLayoutConstraints.filter {
                            return !contains(installedLayoutConstraints, $0)
                        }
                    }
                }
                
        }
        self.installInfo = nil
    }
    
}

private struct ConstraintInstallInfo {
    
    weak var view: View? = nil
    let layoutConstraints: NSHashTable
    
}

private extension NSLayoutAttribute {
    
    private func snp_constantForValue(value: Any?) -> CGFloat {
        // Float
        if let float = value as? Float {
            return CGFloat(float)
        }
            // Double
        else if let double = value as? Double {
            return CGFloat(double)
        }
            // UInt
        else if let int = value as? Int {
            return CGFloat(int)
        }
            // Int
        else if let uint = value as? UInt {
            return CGFloat(uint)
        }
            // CGFloat
        else if let float = value as? CGFloat {
            return float
        }
            // CGSize
        else if let size = value as? CGSize {
            if self == .Width {
                return size.width
            } else if self == .Height {
                return size.height
            }
        }
            // CGPoint
        else if let point = value as? CGPoint {
            #if os(iOS)
                switch self {
                case .Left, .CenterX, .LeftMargin, .CenterXWithinMargins: return point.x
                case .Top, .CenterY, .TopMargin, .CenterYWithinMargins, .Baseline, .FirstBaseline: return point.y
                case .Right, .RightMargin: return point.x
                case .Bottom, .BottomMargin: return point.y
                case .Leading, .LeadingMargin: return point.x
                case .Trailing, .TrailingMargin: return point.x
                case .Width, .Height, .NotAnAttribute: return CGFloat(0)
                }
                #else
                switch self {
                case .Left, .CenterX: return point.x
                case .Top, .CenterY, .Baseline: return point.y
                case .Right: return point.x
                case .Bottom: return point.y
                case .Leading: return point.x
                case .Trailing: return point.x
                case .Width, .Height, .NotAnAttribute: return CGFloat(0)
                }
            #endif
        }
            // EdgeInsets
        else if let insets = value as? EdgeInsets {
            #if os(iOS)
                switch self {
                case .Left, .CenterX, .LeftMargin, .CenterXWithinMargins: return insets.left
                case .Top, .CenterY, .TopMargin, .CenterYWithinMargins, .Baseline, .FirstBaseline: return insets.top
                case .Right, .RightMargin: return insets.right
                case .Bottom, .BottomMargin: return insets.bottom
                case .Leading, .LeadingMargin: return  (Config.interfaceLayoutDirection == .LeftToRight) ? insets.left : -insets.right
                case .Trailing, .TrailingMargin: return  (Config.interfaceLayoutDirection == .LeftToRight) ? insets.right : -insets.left
                case .Width, .Height, .NotAnAttribute: return CGFloat(0)
                }
                #else
                switch self {
                case .Left, .CenterX: return insets.left
                case .Top, .CenterY, .Baseline: return insets.top
                case .Right: return insets.right
                case .Bottom: return insets.bottom
                case .Leading, .LeadingMargin: return  (Config.interfaceLayoutDirection == .LeftToRight) ? insets.left : -insets.right
                case .Trailing, .TrailingMargin: return  (Config.interfaceLayoutDirection == .LeftToRight) ? insets.right : -insets.left
                case .Width, .Height, .NotAnAttribute: return CGFloat(0)
                }
            #endif
        }
        
        return CGFloat(0);
    }
}

private func closestCommonSuperviewBetween(fromView: View?, toView: View?) -> View? {
    var views = Set<View>()
    var fromView = fromView
    var toView = toView
    do {
        if let view = toView {
            if views.contains(view) {
                return view
            }
            views.insert(view)
            toView = view.superview
        }
        if let view = fromView {
            if views.contains(view) {
                return view
            }
            views.insert(view)
            fromView = view.superview
        }
    } while (fromView != nil || toView != nil)
    
    return nil
}

private func ==(left: Constraint, right: Constraint) -> Bool {
    return (left.fromItem == right.fromItem &&
            left.toItem == right.toItem &&
            left.relation == right.relation &&
            left.multiplier == right.multiplier &&
            left.priority == right.priority)
}

//public protocol Constraint: class {
//    
//    func install() -> [LayoutConstraint]
//    func uninstall() -> Void
//    func activate() -> Void
//    func deactivate() -> Void
//    
//}