//
//  Utilities.swift
//  Cryptor
//
// 	Licensed under the Apache License, Version 2.0 (the "License");
// 	you may not use this file except in compliance with the License.
// 	You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// 	Unless required by applicable law or agreed to in writing, software
// 	distributed under the License is distributed on an "AS IS" BASIS,
// 	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// 	See the License for the specific language governing permissions and
// 	limitations under the License.
//

import Foundation

//
//	Replaces Swift's native `fatalError` function to allow redirection
//	For more details about how this all works see:
//	  https://marcosantadev.com/test-swift-fatalerror/
//
func fatalError(_ message: @autoclosure () -> String = "", file: StaticString = #file, line: UInt = #line) -> Never {
	
	FatalErrorUtil.fatalErrorClosure(message(), file, line)
}

// Convert an UnsafeMutablePointer<Int8>? to a String, providing a
// default value of empty string if the pointer is nil.
//
//	- Parameter ptr: Pointer to string to be converted.
//
//	- Returns: Converted string.
//
func errToString(_ ptr: UnsafeMutablePointer<Int8>?) -> String {
    if let ptr = ptr {
        return String(cString: ptr)
    } else {
        return ""
    }
}

///
/// Allows redirection of `fatalError` for Unit Testing or for
/// library users that want to handle such errors in another way.
///
struct FatalErrorUtil {
	
	static var fatalErrorClosure: (String, StaticString, UInt) -> Never = defaultFatalErrorClosure
	private static let defaultFatalErrorClosure = { Swift.fatalError($0, file: $1, line: $2) }
	static func replaceFatalError(closure: @escaping (String, StaticString, UInt) -> Never) {
		fatalErrorClosure = closure
	}
	static func restoreFatalError() {
		fatalErrorClosure = defaultFatalErrorClosure
	}
	
}

///
/// Various utility functions for conversions
///
public struct CryptoUtils {

	///
	/// Converts a single hexadecimal digit encoded as a Unicode Scalar to it's corresponding value.
	///
	/// - Parameter digit: A Unicode scalar in the set 0..9a..fA..F
	///
	/// - Returns: The hexadecimal value of the digit
	///
	static func convert(hexDigit digit: UnicodeScalar) -> UInt8? {
		
		switch digit {
			
		case UnicodeScalar(unicodeScalarLiteral:"0")...UnicodeScalar(unicodeScalarLiteral:"9"):
			return UInt8(digit.value - UnicodeScalar(unicodeScalarLiteral:"0").value)
			
		case UnicodeScalar(unicodeScalarLiteral:"a")...UnicodeScalar(unicodeScalarLiteral:"f"):
			return UInt8(digit.value - UnicodeScalar(unicodeScalarLiteral:"a").value + 0xa)
			
		case UnicodeScalar(unicodeScalarLiteral:"A")...UnicodeScalar(unicodeScalarLiteral:"F"):
			return UInt8(digit.value - UnicodeScalar(unicodeScalarLiteral:"A").value + 0xa)
			
		default:
			return nil 
		}
	}
	
	///
	/// Converts a string of hexadecimal digits to a byte array.
	///
	/// - Parameter string: The hex string (must contain an even number of digits)
	///
	/// - Returns: A byte array or [] if the input is not valid hexadecimal
	///
	public static func byteArray(fromHex string: String) -> [UInt8] {
		
		var iterator = string.unicodeScalars.makeIterator()
		var byteArray: [UInt8] = []
		while let msn = iterator.next() {
			
			if let lsn = iterator.next(),
				let hexMSN = convert(hexDigit: msn) ,
				let hexLSN = convert(hexDigit: lsn)	{
				
				byteArray += [ (hexMSN << 4 | hexLSN) ]
				
			} else {
				
				// @TODO: In the next major release this function should throw instead of returning an empty array.
				return []
			}
		}
		return byteArray
	}
	
	///
	/// Converts a UTF-8 String to a byte array.
	///
	/// - Parameter string: the string
	///
	/// - Returns: A byte array
	///
	public static func byteArray(from string: String) -> [UInt8] {
		
		let array = [UInt8](string.utf8)
		return array
	}
	
	///
	/// Converts a string of hexadecimal digits to an `NSData` object.
	///
	/// - Parameter string: The hex string (must contain an even number of digits)
	///
	/// - Returns: An `NSData` object
	///
	public static func data(fromHex string: String) -> NSData {
		
		let a = byteArray(fromHex: string)
		return NSData(bytes:a, length:a.count)
	}
	
	///
	/// Converts a string of hexadecimal digits to an `Data` object.
	///
	/// - Parameter string: The hex string (must contain an even number of digits)
	///
	/// - Returns: An `Data` object
	///
	public static func data(fromHex string: String) -> Data {
		
		let a = byteArray(fromHex: string)
		return Data(bytes: a, count: a.count)
	}
	
	///
	/// Converts a byte array to an `NSData` object.
	///
	/// - Parameter byteArray: The byte array
	///
	/// - Returns: An `NSData` object
	///
	public static func data(from byteArray: [UInt8]) -> NSData {
		
		return NSData(bytes:byteArray, length:byteArray.count)
	}
	
	///
	/// Converts a byte array to an `Data` object.
	///
	/// - Parameter byteArray: The byte array
	///
	/// - Returns: An `Data` object
	///
	public static func data(from byteArray: [UInt8]) -> Data {
		
		return Data(bytes: byteArray, count: byteArray.count)
	}
	
	///
	/// Converts a byte array to a string of hexadecimal digits.
	///
	/// - Parameters:
 	///		- byteArray: The Swift array
	/// 	- uppercase: True to use uppercase for letter digits, lowercase otherwise
	///
	/// - Returns: A String
	///
	public static func hexString(from byteArray: [UInt8], uppercase: Bool = false) -> String {
		
		return byteArray.map() { String(format: (uppercase) ? "%02X" : "%02x", $0) }.reduce("", +)
	}
	
	///
	/// Converts a Swift array to an `NSString` object.
	///
	/// - Parameters:
 	///		- byteArray: The Swift array
	/// 	- uppercase: True to use uppercase for letter digits, lowercase otherwise
	///
	/// - Returns: An `NSString` object
	///
	public static func hexNSString(from byteArray: [UInt8], uppercase: Bool = false) -> NSString {
		
		let formatString = (uppercase) ? "%02X" : "%02x"
		#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
			return byteArray.map() { String(format: formatString, $0) }.reduce("", +) as NSString
		#else
			let aString = byteArray.map() { String(format: formatString, $0) }.reduce("", +)
			return NSString(string: aString)
		#endif
	}
	
	///
	/// Converts a byte array to a String containing a comma separated list of bytes.
	/// This is used to generate test data programmatically.
	///
	/// - Parameter byteArray: The byte array
	///
	/// - Returns: A String
	///
	public static func hexList(from byteArray: [UInt8]) -> String {
		
		return byteArray.map() { String(format:"0x%02x, ", $0) }.reduce("", +)
	}
	
	///
	/// Zero pads a byte array such that it is an integral number of `blockSizeinBytes` long.
	///
	/// - Parameters:
 	///		- byteArray: 		The byte array
	/// 	- blockSizeInBytes: The block size in bytes.
	///
	/// - Returns: A Swift string
	///
	public static func zeroPad(byteArray: [UInt8], blockSize: Int) -> [UInt8] {
		
		let pad = blockSize - (byteArray.count % blockSize)
		guard pad != 0 else {
			return byteArray
		}
		return byteArray + Array<UInt8>(repeating: 0, count: pad)
	}
	
	///
	/// Zero pads a String (after UTF8 conversion)  such that it is an integral number of `blockSizeinBytes` long.
	///
	/// - Parameters:
 	///		- string: 			The String
	/// 	- blockSizeInBytes:	The block size in bytes
	///
	/// - Returns: A byte array
	///
	public static func zeroPad(string: String, blockSize: Int) -> [UInt8] {
		
		return zeroPad(byteArray: Array<UInt8>(string.utf8), blockSize: blockSize)
	}
	
}