swift-foundation/Sources/FoundationEssentials/AttributedString/AttributedStringAttribute.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2020 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

// MARK: AttributedStringKey API

@available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
extension AttributedString {
    public enum AttributeRunBoundaries : Hashable, Sendable {
        case paragraph

        // FIXME: This is semantically wrong. We do not ever want to constrain attributes on
        // characters (i.e., grapheme clusters) -- they are way too vague, and way
        // too eager to accidentally merge with neighboring string data. (And they're also way
        // too slow for this use case.)
        //
        // The entire point of this feature is to anchor attributes that describe attachments like
        // custom views that should be embedded in the text. We do not _ever_ want the anchor text
        // to accidentally compose with a subsequent combining character, losing the attachment.
        //
        // This needs to be deprecated and replaced by `case unicodeScalar(UnicodeScalar)`.
        //
        // The current implementation already works like that -- it ignores all but the first scalar
        // of the specified `Character`, and does not engage in normalization or grapheme breaking.
        case character(Character)
    }
}

@available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
extension AttributedString.AttributeRunBoundaries {
    var _isScalarConstrained: Bool {
        if case .character = self { return true }
        return false
    }

    var _constrainedScalar: Unicode.Scalar? {
        switch self {
        case .character(let char): return char.unicodeScalars.first
        default: return nil
        }
    }
}

@available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
extension AttributedString {
    public struct AttributeInvalidationCondition : Hashable, Sendable {
        private enum _Storage : Hashable {
            case textChanged
            case attributeChanged(String)
        }
        
        private let storage: _Storage
        
        private init(_ storage: _Storage) {
            self.storage = storage
        }

        var isAttribute: Bool {
            guard case .attributeChanged = storage else { return false }
            return true
        }

        var attributeKey: String? {
            switch storage {
            case .textChanged:
                return nil
            case .attributeChanged(let string):
                return string
            }
        }
        
        public static let textChanged = Self(.textChanged)

        public static func attributeChanged<T: AttributedStringKey>(_ key: T.Type) -> Self {
            Self(.attributeChanged(key.name))
        }

        public static func attributeChanged<T: AttributedStringKey>(_ key: KeyPath<AttributeDynamicLookup, T>) -> Self {
            Self(.attributeChanged(T.name))
        }
        
        static func attributeChanged(_ name: String) -> Self {
            Self(.attributeChanged(name))
        }
    }
}

// Developers define new attributes by implementing AttributeKey.
@available(macOS 12, iOS 15, tvOS 15, watchOS 8, *)
public protocol AttributedStringKey {
    associatedtype Value : Hashable
    static var name : String { get }
    
    @available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
    static var runBoundaries : AttributedString.AttributeRunBoundaries? { get }
    
    @available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
    static var inheritedByAddedText : Bool { get }
    
    @available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
    static var invalidationConditions : Set<AttributedString.AttributeInvalidationCondition>? { get }
}

@available(macOS 12, iOS 15, tvOS 15, watchOS 8, *)
extension AttributedStringKey {
    public var description: String { Self.name }

    @available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
    public static var runBoundaries : AttributedString.AttributeRunBoundaries? { nil }

    @available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
    public static var inheritedByAddedText : Bool { true }

    @available(macOS 13, iOS 16, tvOS 16, watchOS 9, *)
    public static var invalidationConditions : Set<AttributedString.AttributeInvalidationCondition>? { nil }
}

// MARK: Attribute Scopes

@dynamicMemberLookup @frozen
@available(macOS 12, iOS 15, tvOS 15, watchOS 8, *)
public enum AttributeDynamicLookup {
    public subscript<T: AttributedStringKey>(_: T.Type) -> T {
        get { fatalError("Called outside of a dynamicMemberLookup subscript overload") }
    }
}

@available(macOS, unavailable, introduced: 12.0)
@available(iOS, unavailable, introduced: 15.0)
@available(tvOS, unavailable, introduced: 15.0)
@available(watchOS, unavailable, introduced: 8.0)
@available(*, unavailable)
extension AttributeDynamicLookup : Sendable {}

@dynamicMemberLookup
@available(macOS 12, iOS 15, tvOS 15, watchOS 8, *)
public struct ScopedAttributeContainer<S: AttributeScope> : Sendable {
    internal var storage : AttributedString._AttributeStorage
    
    // Record the most recently deleted key for use in AttributedString mutation subscripts that use _modify
    // Note: if ScopedAttributeContainer ever adds a mutating function that can mutate multiple attributes, this will need to record multiple removed keys
    internal var removedKey : String?

    @preconcurrency
    public subscript<T: AttributedStringKey>(dynamicMember keyPath: KeyPath<S, T>) -> T.Value? where T.Value : Sendable {
        get { storage[T.self] }
        set {
            storage[T.self] = newValue
            if newValue == nil {
                removedKey = T.name
            }
        }
    }

    internal init(_ storage : AttributedString._AttributeStorage = .init()) {
        self.storage = storage
    }
    
#if FOUNDATION_FRAMEWORK
    // TODO: Support scope-specific equality/attributes in FoundationPreview
    internal func equals(_ other: Self) -> Bool {
        for (name, _) in S.attributeKeyTypes() {
            if self.storage[name] != other.storage[name] {
                return false
            }
        }
        return true
    }

    internal var attributes : AttributeContainer {
        var contents = AttributedString._AttributeStorage()
        for (name, _) in S.attributeKeyTypes() {
            contents[name] = self.storage[name]
        }
        return AttributeContainer(contents)
    }
    
#endif // FOUNDATION_FRAMEWORK
}


// MARK: Internals

#if FOUNDATION_FRAMEWORK

internal extension AttributedStringKey {
    static func _convertToObjectiveCValue(_ value: Value) throws -> AnyObject {
        if let convertibleType = Self.self as? any ObjectiveCConvertibleAttributedStringKey.Type {
            func project<K: ObjectiveCConvertibleAttributedStringKey>(_: K.Type) throws -> AnyObject {
                try K.objectiveCValue(for: value as! K.Value)
            }
            return try project(convertibleType)
        } else {
            return value as AnyObject
        }
    }
    
    static func _convertFromObjectiveCValue(_ value: AnyObject) throws -> Value {
        if let convertibleType = Self.self as? any ObjectiveCConvertibleAttributedStringKey.Type {
            func project<K: ObjectiveCConvertibleAttributedStringKey>(_: K.Type) throws -> Value {
                guard let objcValue = value as? K.ObjectiveCValue else {
                    throw CocoaError(.coderInvalidValue)
                }
                return try K.value(for: objcValue) as! Value
            }
            return try project(convertibleType)
        } else if let trueValue = value as? Value {
            return trueValue
        } else {
            throw CocoaError(.coderInvalidValue)
        }
    }
}
#endif // FOUNDATION_FRAMEWORK