ConstraintMakerRelatable.swift

//
//  SnapKit
//
//  Copyright (c) 2011-Present SnapKit Team - https://github.com/SnapKit
//
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//  of this software and associated documentation files (the "Software"), to deal
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//  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.
//
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//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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#if os(iOS) || os(tvOS)
    import UIKit
#else
    import AppKit
#endif


public class ConstraintMakerRelatable {
    
    internal let description: ConstraintDescription
    
    internal init(_ description: ConstraintDescription) {
        self.description = description
    }
    
    internal func relatedTo(_ other: ConstraintRelatableTarget, relation: ConstraintRelation, file: String, line: UInt) -> ConstraintMakerEditable {
        let related: ConstraintItem
        let constant: ConstraintConstantTarget
        
        if let other = other as? ConstraintItem {
            guard other.attributes == ConstraintAttributes.none ||
                  other.attributes.layoutAttributes.count <= 1 ||
                  other.attributes.layoutAttributes == self.description.attributes.layoutAttributes ||
                  other.attributes == .edges && self.description.attributes == .margins ||
                  other.attributes == .margins && self.description.attributes == .edges else {
                fatalError("Cannot constraint to multiple non identical attributes. (\(file), \(line))");
            }
            
            related = other
            constant = 0.0
        } else if let other = other as? ConstraintView {
            related = ConstraintItem(target: other, attributes: ConstraintAttributes.none)
            constant = 0.0
        } else if let other = other as? ConstraintConstantTarget {
            related = ConstraintItem(target: nil, attributes: ConstraintAttributes.none)
            constant = other
        } else if #available(iOS 9.0, OSX 10.11, *), let other = other as? ConstraintLayoutGuide {
            related = ConstraintItem(target: other, attributes: ConstraintAttributes.none)
            constant = 0.0
        } else {
            fatalError("Invalid constraint. (\(file), \(line))")
        }
        
        let editable = ConstraintMakerEditable(self.description)
        editable.description.sourceLocation = (file, line)
        editable.description.relation = relation
        editable.description.related = related
        editable.description.constant = constant
        return editable
    }
    
    @discardableResult
    public func equalTo(_ other: ConstraintRelatableTarget, _ file: String = #file, _ line: UInt = #line) -> ConstraintMakerEditable {
        return self.relatedTo(other, relation: .equal, file: file, line: line)
    }
    
    @discardableResult
    public func equalToSuperview(_ file: String = #file, _ line: UInt = #line) -> ConstraintMakerEditable {
        guard let other = self.description.item.superview else {
            fatalError("Expected superview but found nil when attempting make constraint `equalToSuperview`.")
        }
        return self.relatedTo(other, relation: .equal, file: file, line: line)
    }
    
    @discardableResult
    public func lessThanOrEqualTo(_ other: ConstraintRelatableTarget, _ file: String = #file, _ line: UInt = #line) -> ConstraintMakerEditable {
        return self.relatedTo(other, relation: .lessThanOrEqual, file: file, line: line)
    }
    
    @discardableResult
    public func lessThanOrEqualToSuperview(_ file: String = #file, _ line: UInt = #line) -> ConstraintMakerEditable {
        guard let other = self.description.item.superview else {
            fatalError("Expected superview but found nil when attempting make constraint `lessThanOrEqualToSuperview`.")
        }
        return self.relatedTo(other, relation: .lessThanOrEqual, file: file, line: line)
    }
    
    @discardableResult
    public func greaterThanOrEqualTo(_ other: ConstraintRelatableTarget, _ file: String = #file, line: UInt = #line) -> ConstraintMakerEditable {
        return self.relatedTo(other, relation: .greaterThanOrEqual, file: file, line: line)
    }
    
    @discardableResult
    public func greaterThanOrEqualToSuperview(_ file: String = #file, line: UInt = #line) -> ConstraintMakerEditable {
        guard let other = self.description.item.superview else {
            fatalError("Expected superview but found nil when attempting make constraint `greaterThanOrEqualToSuperview`.")
        }
        return self.relatedTo(other, relation: .greaterThanOrEqual, file: file, line: line)
    }
}