//
//  SocketUtils.swift
//  BlueSocket
//
//  Created by Bill Abt on 11/19/15.
//  Copyright © 2016 IBM. All rights reserved.
//
// 	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.
//

#if os(macOS) || os(iOS) || os(tvOS)
import Darwin
#elseif os(Linux)
import Glibc
#endif

import Foundation

//
// Great help with this from
// https://blog.obdev.at/representing-socket-addresses-in-swift-using-enums/
//
extension Socket.Address {
	
	///
	/// Call a low level socket function using the specified socket address pointer.
	///
	/// - Parameters:
	///		- body:		The closure containing the call to the low level function.
	///
	///	- Returns:		The result of executing the closure.
	///
	func withSockAddrPointer<Result>(body: (UnsafePointer<sockaddr>, socklen_t) throws -> Result) rethrows -> Result {
		
		///
		/// Internal function to call do the cast and call to the closure.
		///
		/// - Parameter:	Closure body.
		///
		///	- Returns:		Result of executing the closure.
		///
		func castAndCall<T>(_ address: T, _ body: (UnsafePointer<sockaddr>, socklen_t) throws -> Result) rethrows -> Result {
			var localAddress = address // We need a `var` here for the `&`.
			return try withUnsafePointer(to: &localAddress) {
				return try $0.withMemoryRebound(to: sockaddr.self, capacity: 1, {
					return try body($0, socklen_t(MemoryLayout<T>.size))
				})
			}
		}
		
		switch self {
			
		case .ipv4(let address):
			return try castAndCall(address, body)
			
		case .ipv6(let address):
			return try castAndCall(address, body)
			
		case .unix(let address):
			return try castAndCall(address, body)
			
		}
	}
}

extension Socket.Address {
	
	///
	/// Creates a Socket.Address
	///
	/// - Parameters:
	///		- addressProvider:    Tuple containing pointers to the sockaddr and its length.
	///
	///	- Returns:                Newly initialized Socket.Address.
	///
	init?(addressProvider: (UnsafeMutablePointer<sockaddr>, UnsafeMutablePointer<socklen_t>) throws -> Void) rethrows {
		
		var addressStorage = sockaddr_storage()
		var addressStorageLength = socklen_t(MemoryLayout.size(ofValue: addressStorage))
		try withUnsafeMutablePointer(to: &addressStorage) {
			try $0.withMemoryRebound(to: sockaddr.self, capacity: 1) { addressPointer in
				try withUnsafeMutablePointer(to: &addressStorageLength) { addressLengthPointer in
					try addressProvider(addressPointer, addressLengthPointer)
				}
			}
		}
		
		switch Int32(addressStorage.ss_family) {
		case AF_INET:
			self = withUnsafePointer(to: &addressStorage) {
				return $0.withMemoryRebound(to: sockaddr_in.self, capacity: 1) {
					return Socket.Address.ipv4($0.pointee)
				}
			}
		case AF_INET6:
			self = withUnsafePointer(to: &addressStorage) {
				return $0.withMemoryRebound(to: sockaddr_in6.self, capacity: 1) {
					return Socket.Address.ipv6($0.pointee)
				}
			}
		case AF_UNIX:
			self = withUnsafePointer(to: &addressStorage) {
				return $0.withMemoryRebound(to: sockaddr_un.self, capacity: 1) {
					return Socket.Address.unix($0.pointee)
				}
			}
		default:
			return nil
		}
	}
}

#if os(Linux)

	/// Arm archictecture only allows for 16 fds.
	#if arch(arm)
		let __fd_set_count = 16
	#else
		let __fd_set_count = 32
	#endif

	extension fd_set {
	
		@inline(__always)
		mutating func withCArrayAccess<T>(block: (UnsafeMutablePointer<Int32>) throws -> T) rethrows -> T {
			return try withUnsafeMutablePointer(to: &__fds_bits) {
				try block(UnsafeMutableRawPointer($0).assumingMemoryBound(to: Int32.self))
			}
		}
	}

#else   // not Linux on ARM

	// __DARWIN_FD_SETSIZE is number of *bits*, so divide by number bits in each element to get element count
	// at present this is 1024 / 32 == 32
	let __fd_set_count = Int(__DARWIN_FD_SETSIZE) / 32

	extension fd_set {
	
		@inline(__always)
		mutating func withCArrayAccess<T>(block: (UnsafeMutablePointer<Int32>) throws -> T) rethrows -> T {
			return try withUnsafeMutablePointer(to: &fds_bits) {
				try block(UnsafeMutableRawPointer($0).assumingMemoryBound(to: Int32.self))
			}
		}
	}

#endif

extension fd_set {
	
	@inline(__always)
	private static func address(for fd: Int32) -> (Int, Int32) {
		var intOffset = Int(fd) / __fd_set_count
		#if _endian(big)
		if intOffset % 2 == 0 {
			intOffset += 1
		} else {
			intOffset -= 1
		}
		#endif
		let bitOffset = Int(fd) % __fd_set_count
		let mask = Int32(bitPattern: UInt32(1 << bitOffset))
		return (intOffset, mask)
	}
	
	///
	/// Zero the fd_set
	///
	public mutating func zero() {
		#if swift(>=4.1)
		withCArrayAccess { $0.initialize(repeating: 0, count: __fd_set_count) }
		#else
		withCArrayAccess { $0.initialize(to: 0, count: __fd_set_count) }
		#endif
	}
	
	///
	/// Set an fd in an fd_set
	///
	/// - Parameter fd:	The fd to add to the fd_set
	///
	public mutating func set(_ fd: Int32) {
		let (index, mask) = fd_set.address(for: fd)
		withCArrayAccess { $0[index] |= mask }
	}
	
	///
	/// Clear an fd from an fd_set
	///
	/// - Parameter fd:	The fd to clear from the fd_set
	///
	public mutating func clear(_ fd: Int32) {
		let (index, mask) = fd_set.address(for: fd)
		withCArrayAccess { $0[index] &= ~mask }
	}
	
	///
	/// Check if an fd is present in an fd_set
	///
	/// - Parameter fd:	The fd to check
	///
	///	- Returns:	`True` if present, `false` otherwise.
	///
	public mutating func isSet(_ fd: Int32) -> Bool {
		let (index, mask) = fd_set.address(for: fd)
		return withCArrayAccess { $0[index] & mask != 0 }
	}
}