cs193p-emojiart/EmojiArt/UtilityExtensions.swift

//
//  UtilityExtensions.swift
//  EmojiArt
//
//  Created by CS193p Instructor on 4/26/21.
//  Copyright © 2021 Stanford University. All rights reserved.
//

import SwiftUI

// in a Collection of Identifiables
// we often might want to find the element that has the same id
// as an Identifiable we already have in hand
// we name this index(matching:) instead of firstIndex(matching:)
// because we assume that someone creating a Collection of Identifiable
// is usually going to have only one of each Identifiable thing in there
// (though there's nothing to restrict them from doing so; it's just a naming choice)

extension Collection where Element: Identifiable {
    func index(matching element: Element) -> Self.Index? {
        firstIndex(where: { $0.id == element.id })
    }
}

// we could do the same thing when it comes to removing an element
// but we have to add that to a different protocol
// because Collection works for immutable collections of things
// the "mutable" one is RangeReplaceableCollection
// not only could we add remove
// but we could add a subscript which takes a copy of one of the elements
// and uses its Identifiable-ness to subscript into the Collection
// this is an awesome way to create Bindings into an Array in a ViewModel
// (since any Published var in an ObservableObject can be bound to via $)
// (even vars on that Published var or subscripts on that var)
// (or subscripts on vars on that var, etc.)

extension RangeReplaceableCollection where Element: Identifiable {
    mutating func remove(_ element: Element) {
        if let index = index(matching: element) {
            remove(at: index)
        }
    }

    subscript(_ element: Element) -> Element {
        get {
            if let index = index(matching: element) {
                return self[index]
            } else {
                return element
            }
        }
        set {
            if let index = index(matching: element) {
                replaceSubrange(index...index, with: [newValue])
            }
        }
    }
}

// if you use a Set to represent the selection of emoji in HW5
// then you might find this syntactic sugar function to be of use

extension Set where Element: Identifiable {
    mutating func toggleMembership(of element: Element) {
        if let index = index(matching: element) {
            remove(at: index)
        } else {
            insert(element)
        }
    }
}

// some extensions to String and Character
// to help us with managing our Strings of emojis
// we want them to be "emoji only"
// (thus isEmoji below)
// and we don't want them to have repeated emojis
// (thus withNoRepeatedCharacters below)

extension String {
    var withNoRepeatedCharacters: String {
        var uniqued = ""
        for ch in self {
            if !uniqued.contains(ch) {
                uniqued.append(ch)
            }
        }
        return uniqued
    }
}

extension Character {
    var isEmoji: Bool {
        // Swift does not have a way to ask if a Character isEmoji
        // but it does let us check to see if our component scalars isEmoji
        // unfortunately unicode allows certain scalars (like 1)
        // to be modified by another scalar to become emoji (e.g. 1️⃣)
        // so the scalar "1" will report isEmoji = true
        // so we can't just check to see if the first scalar isEmoji
        // the quick and dirty here is to see if the scalar is at least the first true emoji we know of
        // (the start of the "miscellaneous items" section)
        // or check to see if this is a multiple scalar unicode sequence
        // (e.g. a 1 with a unicode modifier to force it to be presented as emoji 1️⃣)
        if let firstScalar = unicodeScalars.first, firstScalar.properties.isEmoji {
            return (firstScalar.value >= 0x238d || unicodeScalars.count > 1)
        } else {
            return false
        }
    }
}

// extracting the actual url to an image from a url that might contain other info
// (essentially looking for the imgurl key)
// imgurl is a "well known" key that can be embedded in a url that says what the actual image url is

extension URL {
    var imageURL: URL {
        for query in query?.components(separatedBy: "&") ?? [] {
            let queryComponents = query.components(separatedBy: "=")
            if queryComponents.count == 2 {
                if queryComponents[0] == "imgurl", let url = URL(string: queryComponents[1].removingPercentEncoding ?? "") {
                    return url
                }
            }
        }
        return baseURL ?? self
    }
}

// convenience functions for adding/subtracting CGPoints and CGSizes
// might come in handy when doing gesture handling
// because we do a lot of converting between coordinate systems and such
// notice that type types of the lhs and rhs arguments vary below
// thus you can offset a CGPoint by the width and height of a CGSize, for example

extension DragGesture.Value {
    var distance: CGSize { location - startLocation }
}

extension CGRect {
    var center: CGPoint {
        CGPoint(x: midX, y: midY)
    }
}

extension CGPoint {
    static func -(lhs: Self, rhs: Self) -> CGSize {
        CGSize(width: lhs.x - rhs.x, height: lhs.y - rhs.y)
    }
    static func +(lhs: Self, rhs: CGSize) -> CGPoint {
        CGPoint(x: lhs.x + rhs.width, y: lhs.y + rhs.height)
    }
    static func -(lhs: Self, rhs: CGSize) -> CGPoint {
        CGPoint(x: lhs.x - rhs.width, y: lhs.y - rhs.height)
    }
    static func *(lhs: Self, rhs: CGFloat) -> CGPoint {
        CGPoint(x: lhs.x * rhs, y: lhs.y * rhs)
    }
    static func /(lhs: Self, rhs: CGFloat) -> CGPoint {
        CGPoint(x: lhs.x / rhs, y: lhs.y / rhs)
    }
}

extension CGSize {
    // the center point of an area that is our size
    var center: CGPoint {
        CGPoint(x: width/2, y: height/2)
    }
    static func +(lhs: Self, rhs: Self) -> CGSize {
        CGSize(width: lhs.width + rhs.width, height: lhs.height + rhs.height)
    }
    static func -(lhs: Self, rhs: Self) -> CGSize {
        CGSize(width: lhs.width - rhs.width, height: lhs.height - rhs.height)
    }
    static func *(lhs: Self, rhs: CGFloat) -> CGSize {
        CGSize(width: lhs.width * rhs, height: lhs.height * rhs)
    }
    static func /(lhs: Self, rhs: CGFloat) -> CGSize {
        CGSize(width: lhs.width/rhs, height: lhs.height/rhs)
    }
}

// add RawRepresentable protocol conformance to CGSize and CGFloat
// so that they can be used with @SceneStorage
// we do this by first providing default implementations of rawValue and init(rawValue:)
//   in RawRepresentable when the thing in question is Codable (which both CGFloat and CGSize are)
// then all it takes to make something that is Codable be RawRepresentable is to declare it to be so
// (it will then get the default implementions needed to be a RawRepresentable)

extension RawRepresentable where Self: Codable {
    public var rawValue: String {
        if let json = try? JSONEncoder().encode(self), let string = String(data: json, encoding: .utf8) {
            return string
        } else {
            return ""
        }
    }
    public init?(rawValue: String) {
        if let value = try? JSONDecoder().decode(Self.self, from: Data(rawValue.utf8)) {
            self = value
        } else {
            return nil
        }
    }
}

extension CGSize: RawRepresentable { }
extension CGFloat: RawRepresentable { }

// convenience functions for [NSItemProvider] (i.e. array of NSItemProvider)
// makes the code for  loading objects from the providers a bit simpler
// NSItemProvider is a holdover from the Objective-C (i.e. pre-Swift) world
// you can tell by its very name (starts with NS)
// so unfortunately, dealing with this API is a little bit crufty
// thus I recommend you just accept that these loadObjects functions will work and move on
// it's a rare case where trying to dive in and understand what's going on here
// would probably not be a very efficient use of your time
// (though I'm certainly not going to say you shouldn't!)
// (just trying to help you optimize your valuable time this quarter)

extension Array where Element == NSItemProvider {
    func loadObjects<T>(ofType theType: T.Type, firstOnly: Bool = false, using load: @escaping (T) -> Void) -> Bool where T: NSItemProviderReading {
        if let provider = first(where: { $0.canLoadObject(ofClass: theType) }) {
            provider.loadObject(ofClass: theType) { object, error in
                if let value = object as? T {
                    DispatchQueue.main.async {
                        load(value)
                    }
                }
            }
            return true
        }
        return false
    }
    func loadObjects<T>(ofType theType: T.Type, firstOnly: Bool = false, using load: @escaping (T) -> Void) -> Bool where T: _ObjectiveCBridgeable, T._ObjectiveCType: NSItemProviderReading {
        if let provider = first(where: { $0.canLoadObject(ofClass: theType) }) {
            let _ = provider.loadObject(ofClass: theType) { object, error in
                if let value = object {
                    DispatchQueue.main.async {
                        load(value)
                    }
                }
            }
            return true
        }
        return false
    }
    func loadFirstObject<T>(ofType theType: T.Type, using load: @escaping (T) -> Void) -> Bool where T: NSItemProviderReading {
        loadObjects(ofType: theType, firstOnly: true, using: load)
    }
    func loadFirstObject<T>(ofType theType: T.Type, using load: @escaping (T) -> Void) -> Bool where T: _ObjectiveCBridgeable, T._ObjectiveCType: NSItemProviderReading {
        loadObjects(ofType: theType, firstOnly: true, using: load)
    }
}