ARK-OS/arkos/arkrt/ark.ui.basic/Sources/State/DynamicKeyPath.swift

#if canImport(Darwin)
    import func Darwin.memcmp
#elseif canImport(Glibc)
    import func Glibc.memcmp
#elseif canImport(WinSDK)
    import func WinSDK.memcmp
#elseif canImport(Android)
    import func Android.memcmp
#endif

/// A type similar to KeyPath, but that can be constructed at run time given
/// an instance of a struct, and the value of the desired property.
///
/// Construction fails if the property's in-memory representation is not unique within the
/// struct. SwiftCrossUI only uses `DynamicKeyPath` in situations where it is
/// highly likely for properties to have unique in-memory representations, such
/// as when properties have internal storage pointers.
struct DynamicKeyPath<Base, Value> {
    /// The property's offset within instances of `Base`.
    var offset: Int

    /// Constructs a key path given an instance of the base type, and the
    /// value of the desired property.
    ///
    /// The initializer will search through the base instance's in-memory
    /// representation to find the unique offset that matches the representation
    /// of the given property value. If such an offset can't be found or isn't
    /// unique, then the initialiser returns `nil`.
    ///
    /// - Parameters:
    ///   - value: The value to construct a key path to.
    ///   - base: The value to construct a key path from.
    ///   - label: The property's label, if any. Only used for debugging.
    init?(
        forProperty value: Value,
        of base: Base,
        label: String? = nil
    ) {
        let propertyAlignment = MemoryLayout<Value>.alignment
        let propertySize = MemoryLayout<Value>.size
        let baseStructSize = MemoryLayout<Base>.size

        var index = 0
        var matches: [Int] = []
        while index + propertySize <= baseStructSize {
            let isMatch =
                withUnsafeBytes(of: base) { viewPointer in
                    withUnsafeBytes(of: value) { valuePointer in
                        let viewBytes = UnsafeRawBufferPointer(start: viewPointer.baseAddress!.advanced(by: index), count: propertySize)
                        return viewBytes.elementsEqual(valuePointer)
                    }
                }
            if isMatch {
                matches.append(index)
            }
            index += propertyAlignment
        }

        guard let offset = matches.first else {
            logger.warning(
                "no offset found for dynamic property",
                metadata: ["property": "\(label ?? "<unknown>")"]
            )
            return nil
        }

        guard matches.count == 1 else {
            logger.warning(
                "multiple offsets found for dynamic property",
                metadata: ["property": "\(label ?? "<unknown>")"]
            )
            return nil
        }

        self.offset = offset
    }

    /// Gets the property's value on the given instance.
    ///
    /// - Parameter base: The instance to get the property on.
    /// - Returns: This property's value on `base`.
    func get(_ base: Base) -> Value {
        withUnsafeBytes(of: base) { buffer in
            buffer.baseAddress!.advanced(by: offset)
                .assumingMemoryBound(to: Value.self)
                .pointee
        }
    }

    /// Sets the property's value to a new value on the given instance.
    ///
    /// - Parameters:
    ///   - base: The instance to set the property on.
    ///   - newValue: The new value of the property.
    func set(_ base: inout Base, _ newValue: Value) {
        withUnsafeMutableBytes(of: &base) { buffer in
            buffer.baseAddress!.advanced(by: offset)
                .assumingMemoryBound(to: Value.self)
                .pointee = newValue
        }
    }
}