package usb

import (
	"errors"
)

var (
	ErrUARTInvalidPort = errors.New("invalid USB port")
	ErrUARTEmptyBuffer = errors.New("USB receive buffer empty")
)

// UART represents a virtual serial (UART) device emulation using the USB
// CDC-ACM device class driver.
type UART struct {
	// Port is the MCU's native USB core number. If in doubt, leave it
	// uninitialized for default (0).
	Port int
	core *core
}

type UARTConfig struct {
	BusSpeed Speed
}

func (uart *UART) Configure(config UARTConfig) error {

	c := class{id: classDeviceCDCACM, config: 1}

	// verify we have a free USB port and take ownership of it
	var st status
	uart.core, st = initCore(uart.Port, config.BusSpeed, c)
	if !st.ok() {
		return ErrUARTInvalidPort
	}
	return nil
}

func (uart *UART) Ready() bool {
	return uart.core.dc.uartReady()
}

// Buffered returns the number of bytes currently stored in the RX buffer.
func (uart *UART) Buffered() int {
	for !uart.Ready() {
	}
	return uart.core.dc.uartAvailable()
}

// ReadByte reads a single byte from the RX buffer.
// If there is no data in the buffer, returns an error.
func (uart *UART) ReadByte() (byte, error) {
	for !uart.Ready() {
	}
	n, ok := uart.core.dc.uartReadByte()
	if !ok {
		return 0, ErrUARTEmptyBuffer
	}
	return n, nil
}

// Read from the RX buffer.
func (uart *UART) Read(data []byte) (n int, err error) {
	for !uart.Ready() {
	}
	return uart.core.dc.uartRead(data)
}

// WriteByte writes a single byte of data to the UART interface.
func (uart *UART) WriteByte(c byte) error {
	for !uart.Ready() {
	}
	return uart.core.dc.uartWriteByte(c)
}

// Write data to the UART.
func (uart *UART) Write(data []byte) (n int, err error) {
	for !uart.Ready() {
	}
	return uart.core.dc.uartWrite(data)
}