swift-foundation/Sources/FoundationEssentials/String/String+Essentials.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 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
//
//===----------------------------------------------------------------------===//

@available(macOS 10.10, iOS 8.0, watchOS 2.0, tvOS 9.0, *)
extension String {
    func _capitalized() -> String {
        var new = ""
        new.reserveCapacity(utf8.count)

        let uppercaseSet = BuiltInUnicodeScalarSet.uppercaseLetters
        let lowercaseSet = BuiltInUnicodeScalarSet.lowercaseLetters
        let cfcaseIgnorableSet = BuiltInUnicodeScalarSet.caseIgnorables

        var isLastCased = false
        for scalar in unicodeScalars {
            let properties = scalar.properties
            if uppercaseSet.contains(scalar) {
                new += isLastCased ? properties.lowercaseMapping  : String(scalar)
                isLastCased = true
            } else if lowercaseSet.contains(scalar) {
                new += isLastCased ? String(scalar) : properties.titlecaseMapping
                isLastCased = true
            } else if !cfcaseIgnorableSet.contains(scalar) {
                // We only use a subset of case-ignorable characters as defined in CF instead of the full set of characters satisfying `property.isCaseIgnorable` for compatibility reasons
                new += String(scalar)
                isLastCased = false
            } else {
                new += String(scalar)
            }
        }

        return new
    }

    // MARK: - Public API

    /// Creates a new string equivalent to the given bytes interpreted in the
    /// specified encoding.
    ///
    /// - Parameters:
    ///   - bytes: A sequence of bytes to interpret using `encoding`.
    ///   - encoding: The encoding to use to interpret `bytes`.
    public init?<S: Sequence>(bytes: __shared S, encoding: Encoding)
        where S.Iterator.Element == UInt8
    {
#if FOUNDATION_FRAMEWORK // TODO: Move init?(bytes:encoding) to Swift
        func makeString(bytes: UnsafeBufferPointer<UInt8>) -> String? {
            if encoding == .utf8 || encoding == .ascii,
               let str = String._tryFromUTF8(bytes) {
                if encoding == .utf8 || (encoding == .ascii && str._guts._isContiguousASCII) {
                    return str
                }
            }

            if let ns = NSString(
                bytes: bytes.baseAddress.unsafelyUnwrapped, length: bytes.count, encoding: encoding.rawValue) {
                return String._unconditionallyBridgeFromObjectiveC(ns)
            } else {
                return nil
            }
        }
        if let string = (bytes.withContiguousStorageIfAvailable(makeString) ??
                         Array(bytes).withUnsafeBufferPointer(makeString)) {
            self = string
        } else {
            return nil
        }
#else
        guard encoding == .utf8 || encoding == .ascii else {
            return nil
        }
        func makeString(buffer: UnsafeBufferPointer<UInt8>) -> String? {
            if let string = String._tryFromUTF8(buffer),
               (encoding == .utf8 || (encoding == .ascii && string._guts._isContiguousASCII)) {
                return string
            }

            return buffer.withMemoryRebound(to: CChar.self) { ptr in
                guard let address = ptr.baseAddress else {
                    return nil
                }
                return String(validatingUTF8: address)
            }
        }

        if let string = bytes.withContiguousStorageIfAvailable(makeString) ??
            Array(bytes).withUnsafeBufferPointer(makeString) {
            self = string
        } else {
            return nil
        }
#endif // FOUNDATION_FRAMEWORK
    }

    /// Returns a `String` initialized by converting given `data` into
    /// Unicode characters using a given `encoding`.
    public init?(data: __shared Data, encoding: Encoding) {
        if encoding == .utf8 || encoding == .ascii,
        let str = data.withUnsafeBytes({
            $0.withMemoryRebound(to: UInt8.self, String._tryFromUTF8(_:))
        }) {
            if encoding == .utf8 || (encoding == .ascii && str._guts._isContiguousASCII) {
                self = str
                return
            }
        }
#if FOUNDATION_FRAMEWORK
        guard let s = NSString(data: data, encoding: encoding.rawValue) else { return nil }
        self = String._unconditionallyBridgeFromObjectiveC(s)
#else
        return nil
#endif // FOUNDATION_FRAMEWORK
    }
}