import Foundation

public class SerialPort {
	var path: String
	var fileDescriptor: Int32?

	private var pollSource: DispatchSourceRead?
	private var readDataStream: AsyncStream<Data>?
	private var readBytesStream: AsyncStream<UInt8>?
	private var readLinesStream: AsyncStream<String>?

	public init(path: String) {
		self.path = path
	}

	public func openPort() throws {
		try openPort(toReceive: true, andTransmit: true)
	}

	public func openPort(toReceive receive: Bool, andTransmit transmit: Bool) throws {
		guard !path.isEmpty else {
			throw PortError.invalidPath
		}

		guard receive || transmit else {
			throw PortError.mustReceiveOrTransmit
		}

		var readWriteParam : Int32

		if receive && transmit {
			readWriteParam = O_RDWR
		} else if receive {
			readWriteParam = O_RDONLY
		} else if transmit {
			readWriteParam = O_WRONLY
		} else {
			fatalError()
		}

#if os(Linux)
		fileDescriptor = open(path, readWriteParam | O_NOCTTY)
#elseif os(OSX)
		fileDescriptor = open(path, readWriteParam | O_NOCTTY | O_EXLOCK)
#endif

		// Throw error if open() failed
		if fileDescriptor == PortError.failedToOpen.rawValue {
			throw PortError.failedToOpen
		}

		guard
			receive,
			let fileDescriptor
		else { return }
		let pollSource = DispatchSource.makeReadSource(fileDescriptor: fileDescriptor, queue: .global(qos: .default))
		let stream = AsyncStream<Data> { continuation in
			pollSource.setEventHandler {

				let bufferSize = 1024
				let buffer = UnsafeMutableRawPointer
					.allocate(byteCount: bufferSize, alignment: 8)
				let bytesRead = read(fileDescriptor, buffer, bufferSize)
				guard bytesRead > 0 else { return }
				let bytes = Data(bytes: buffer, count: bytesRead)
				continuation.yield(bytes)
			}

			pollSource.setCancelHandler {
				continuation.finish()
			}
		}
		pollSource.resume()
		self.pollSource = pollSource
		self.readDataStream = stream
	}

	public func setSettings(receiveRate: BaudRate,
							transmitRate: BaudRate,
							minimumBytesToRead: Int,
							timeout: Int = 0, /* 0 means wait indefinitely */
							parityType: ParityType = .none,
							sendTwoStopBits: Bool = false, /* 1 stop bit is the default */
							dataBitsSize: DataBitsSize = .bits8,
							useHardwareFlowControl: Bool = false,
							useSoftwareFlowControl: Bool = false,
							processOutput: Bool = false) {

		guard let fileDescriptor = fileDescriptor else {
			return
		}


		// Set up the control structure
		var settings = termios()

		// Get options structure for the port
		tcgetattr(fileDescriptor, &settings)

		// Set baud rates
		cfsetispeed(&settings, receiveRate.speedValue)
		cfsetospeed(&settings, transmitRate.speedValue)

		// Enable parity (even/odd) if needed
		settings.c_cflag |= parityType.parityValue

		// Set stop bit flag
		if sendTwoStopBits {
			settings.c_cflag |= tcflag_t(CSTOPB)
		} else {
			settings.c_cflag &= ~tcflag_t(CSTOPB)
		}

		// Set data bits size flag
		settings.c_cflag &= ~tcflag_t(CSIZE)
		settings.c_cflag |= dataBitsSize.flagValue

		//Disable input mapping of CR to NL, mapping of NL into CR, and ignoring CR
		settings.c_iflag &= ~tcflag_t(ICRNL | INLCR | IGNCR)

		// Set hardware flow control flag
#if os(Linux)
		if useHardwareFlowControl {
			settings.c_cflag |= tcflag_t(CRTSCTS)
		} else {
			settings.c_cflag &= ~tcflag_t(CRTSCTS)
		}
#elseif os(OSX)
		if useHardwareFlowControl {
			settings.c_cflag |= tcflag_t(CRTS_IFLOW)
			settings.c_cflag |= tcflag_t(CCTS_OFLOW)
		} else {
			settings.c_cflag &= ~tcflag_t(CRTS_IFLOW)
			settings.c_cflag &= ~tcflag_t(CCTS_OFLOW)
		}
#endif

		// Set software flow control flags
		let softwareFlowControlFlags = tcflag_t(IXON | IXOFF | IXANY)
		if useSoftwareFlowControl {
			settings.c_iflag |= softwareFlowControlFlags
		} else {
			settings.c_iflag &= ~softwareFlowControlFlags
		}

		// Turn on the receiver of the serial port, and ignore modem control lines
		settings.c_cflag |= tcflag_t(CREAD | CLOCAL)

		// Turn off canonical mode
		settings.c_lflag &= ~tcflag_t(ICANON | ECHO | ECHOE | ISIG)

		// Set output processing flag
		if processOutput {
			settings.c_oflag |= tcflag_t(OPOST)
		} else {
			settings.c_oflag &= ~tcflag_t(OPOST)
		}

		//Special characters
		//We do this as c_cc is a C-fixed array which is imported as a tuple in Swift.
		//To avoid hardcoding the VMIN or VTIME value to access the tuple value, we use the typealias instead
#if os(Linux)
		typealias specialCharactersTuple = (VINTR: cc_t, VQUIT: cc_t, VERASE: cc_t, VKILL: cc_t, VEOF: cc_t, VTIME: cc_t, VMIN: cc_t, VSWTC: cc_t, VSTART: cc_t, VSTOP: cc_t, VSUSP: cc_t, VEOL: cc_t, VREPRINT: cc_t, VDISCARD: cc_t, VWERASE: cc_t, VLNEXT: cc_t, VEOL2: cc_t, spare1: cc_t, spare2: cc_t, spare3: cc_t, spare4: cc_t, spare5: cc_t, spare6: cc_t, spare7: cc_t, spare8: cc_t, spare9: cc_t, spare10: cc_t, spare11: cc_t, spare12: cc_t, spare13: cc_t, spare14: cc_t, spare15: cc_t)
		var specialCharacters: specialCharactersTuple = (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) // NCCS = 32
#elseif os(OSX)
		typealias specialCharactersTuple = (VEOF: cc_t, VEOL: cc_t, VEOL2: cc_t, VERASE: cc_t, VWERASE: cc_t, VKILL: cc_t, VREPRINT: cc_t, spare1: cc_t, VINTR: cc_t, VQUIT: cc_t, VSUSP: cc_t, VDSUSP: cc_t, VSTART: cc_t, VSTOP: cc_t, VLNEXT: cc_t, VDISCARD: cc_t, VMIN: cc_t, VTIME: cc_t, VSTATUS: cc_t, spare: cc_t)
		var specialCharacters: specialCharactersTuple = (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) // NCCS = 20
#endif

		specialCharacters.VMIN = cc_t(minimumBytesToRead)
		specialCharacters.VTIME = cc_t(timeout)
		settings.c_cc = specialCharacters

		// Commit settings
		tcsetattr(fileDescriptor, TCSANOW, &settings)
	}

	public func closePort() {
		pollSource?.cancel()
		pollSource = nil

		readDataStream = nil
		readBytesStream = nil
		readLinesStream = nil

		if let fileDescriptor = fileDescriptor {
			close(fileDescriptor)
		}
		fileDescriptor = nil
	}
}

// MARK: Receiving

extension SerialPort {

	public func readBytes(into buffer: UnsafeMutablePointer<UInt8>, size: Int) throws -> Int {
		guard let fileDescriptor = fileDescriptor else {
			throw PortError.mustBeOpen
		}

		var s: stat = stat()
		fstat(fileDescriptor, &s)
		if s.st_nlink != 1 {
			throw PortError.deviceNotConnected
		}

		let bytesRead = read(fileDescriptor, buffer, size)
		return bytesRead
	}

	public func readData(ofLength length: Int) throws -> Data {
		let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: length)
		defer {
			buffer.deallocate()
		}

		let bytesRead = try readBytes(into: buffer, size: length)

		var data : Data

		if bytesRead > 0 {
			data = Data(bytes: buffer, count: bytesRead)
		} else {
			//This is to avoid the case where bytesRead can be negative causing problems allocating the Data buffer
			data = Data(bytes: buffer, count: 0)
		}

		return data
	}

	public func readString(ofLength length: Int) throws -> String {
		var remainingBytesToRead = length
		var result = ""

		while remainingBytesToRead > 0 {
			let data = try readData(ofLength: remainingBytesToRead)

			if let string = String(data: data, encoding: String.Encoding.utf8) {
				result += string
				remainingBytesToRead -= data.count
			} else {
				return result
			}
		}

		return result
	}

	public func readUntilChar(_ terminator: CChar) throws -> String {
		var data = Data()
		let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: 1)
		defer {
			buffer.deallocate()
		}

		while true {
			let bytesRead = try readBytes(into: buffer, size: 1)

			if bytesRead > 0 {
				if ( buffer[0] > 127) {
					throw PortError.unableToConvertByteToCharacter
				}
				let character = CChar(buffer[0])

				if character == terminator {
					break
				} else {
					data.append(buffer, count: 1)
				}
			}
		}

		if let string = String(data: data, encoding: String.Encoding.utf8) {
			return string
		} else {
			throw PortError.stringsMustBeUTF8
		}
	}

	public func readLine() throws -> String {
		let newlineChar = CChar(10) // Newline/Line feed character `\n` is 10
		return try readUntilChar(newlineChar)
	}

	public func readByte() throws -> UInt8 {
		let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: 1)

		defer {
			buffer.deallocate()
		}

		while true {
			let bytesRead = try readBytes(into: buffer, size: 1)

			if bytesRead > 0 {
				return buffer[0]
			}
		}
	}

	public func readChar() throws -> UnicodeScalar {
		let byteRead = try readByte()
		let character = UnicodeScalar(byteRead)
		return character
	}

	public func asyncData() throws -> AsyncStream<Data> {
		guard
			fileDescriptor != nil,
			let readDataStream
		else {
			throw PortError.mustBeOpen
		}

		return readDataStream
	}

	public func asyncBytes() throws -> AsyncStream<UInt8> {
		guard
			fileDescriptor != nil,
			let readDataStream
		else {
			throw PortError.mustBeOpen
		}

		if let existing = readBytesStream {
			return existing
		} else {
			let new = AsyncStream<UInt8> { continuation in
				Task {
					for try await data in readDataStream {
						for byte in data {
							continuation.yield(byte)
						}
					}
					continuation.finish()
				}
			}
			readBytesStream = new
			return new
		}
	}

	public func asyncLines() throws -> AsyncStream<String> {
		guard
			fileDescriptor != nil
		else {
			throw PortError.mustBeOpen
		}

		if let existing = readLinesStream {
			return existing
		} else {
			let byteStream = try asyncBytes()
			let new = AsyncStream<String> { continuation in
				Task {
					var accumulator = Data()
					for try await byte in byteStream {
						accumulator.append(byte)

						guard
							UnicodeScalar(byte) == "\n".unicodeScalars.first
						else { continue }

						defer { accumulator = Data() }
						guard
							let string = String(data: accumulator, encoding: .utf8)
						else {
							continuation.yield("Error: Non string data. Perhaps you wanted data or bytes output?")
							continue
						}
						continuation.yield(string)
					}
					continuation.finish()
				}
			}
			readLinesStream = new
			return new
		}
	}
}

// MARK: Transmitting

extension SerialPort {

	public func writeBytes(from buffer: UnsafeMutablePointer<UInt8>, size: Int) throws -> Int {
		guard let fileDescriptor = fileDescriptor else {
			throw PortError.mustBeOpen
		}

		let bytesWritten = write(fileDescriptor, buffer, size)
		return bytesWritten
	}

	public func writeData(_ data: Data) throws -> Int {
		let size = data.count
		let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: size)
		defer {
			buffer.deallocate()
		}

		data.copyBytes(to: buffer, count: size)

		let bytesWritten = try writeBytes(from: buffer, size: size)
		return bytesWritten
	}

	public func writeString(_ string: String) throws -> Int {
		guard let data = string.data(using: String.Encoding.utf8) else {
			throw PortError.stringsMustBeUTF8
		}

		return try writeData(data)
	}

	public func writeChar(_ character: UnicodeScalar) throws -> Int{
		let stringEquiv = String(character)
		let bytesWritten = try writeString(stringEquiv)
		return bytesWritten
	}
}