// Package gs232 drives rotator controllers that speak the Yaesu GS-232A
// protocol, over a raw TCP socket or a serial COM port. The target device is
// the microHAM ARCO: both its LAN "CONTROL PROTOCOL" setting (a TCP port) and
// its USB port ("USB CONTROL PROTOCOL", a virtual COM where the baud rate is
// irrelevant) can be set to speak Yaesu GS-232A — so OpsLog controls it
// directly, no PstRotator in between. ARCO accepts up to four parallel LAN
// connections, and commands are single CR-terminated lines, so short
// per-call connections (same idiom as the other rotator backends) work fine.
//
// GS-232A subset used:
//
//	Maaa<CR>  move to azimuth aaa (000-450)
//	S<CR>     stop rotation
//	C<CR>     query azimuth — replies "+0aaa" (GS-232A) or "AZ=aaa" (GS-232B
//	          flavour); both are parsed.
package gs232

import (
	"fmt"
	"io"
	"net"
	"regexp"
	"strconv"
	"strings"
	"time"

	"go.bug.st/serial"
)

const (
	dialTimeout = 3 * time.Second
	ioTimeout   = 2 * time.Second
)

// Client is a stateless per-call sender, mirroring the pst/rotgenius idiom.
// Exactly one of (Host, Port) or ComPort is used, per Transport.
type Client struct {
	Host    string
	Port    int
	ComPort string // serial transport: "COM5" etc. (ARCO USB virtual COM — any baud)
}

// New returns a TCP Client with sane defaults applied for empty fields. There
// is no standard port: the number is whatever the user typed into the ARCO's
// LAN CONTROL PROTOCOL setting — 4001 is only a placeholder.
func New(host string, port int) *Client {
	if host == "" {
		host = "127.0.0.1"
	}
	if port <= 0 || port > 65535 {
		port = 4001
	}
	return &Client{Host: host, Port: port}
}

// NewSerial returns a Client talking over the ARCO's USB virtual COM port. The
// baud rate is irrelevant on USB per the ARCO manual (8N1 framing matters); we
// open at 9600 which also suits a real RS-232 hookup left at its default.
func NewSerial(comPort string) *Client {
	return &Client{ComPort: comPort}
}

// roundTrip opens a connection (TCP or serial per the client's config), sends
// one CR-terminated command and (when wantReply) reads one CR/LF-terminated
// reply line.
func (c *Client) roundTrip(cmd string, wantReply bool) (string, error) {
	var conn io.ReadWriteCloser
	if c.ComPort != "" {
		sp, err := serial.Open(c.ComPort, &serial.Mode{BaudRate: 9600})
		if err != nil {
			return "", fmt.Errorf("open ARCO %s: %w", c.ComPort, err)
		}
		_ = sp.SetReadTimeout(200 * time.Millisecond)
		conn = sp
	} else {
		nc, err := net.DialTimeout("tcp", net.JoinHostPort(c.Host, strconv.Itoa(c.Port)), dialTimeout)
		if err != nil {
			return "", fmt.Errorf("connect ARCO %s:%d: %w", c.Host, c.Port, err)
		}
		_ = nc.SetDeadline(time.Now().Add(ioTimeout))
		conn = nc
	}
	defer conn.Close()
	if _, err := conn.Write([]byte(cmd + "\r")); err != nil {
		return "", fmt.Errorf("send %q: %w", cmd, err)
	}
	if !wantReply {
		return "", nil
	}
	buf := make([]byte, 64)
	var sb strings.Builder
	deadline := time.Now().Add(ioTimeout)
	for time.Now().Before(deadline) {
		n, err := conn.Read(buf)
		if n > 0 {
			sb.Write(buf[:n])
			if strings.ContainsAny(sb.String(), "\r\n") {
				break
			}
		}
		// A serial read that times out returns (0, nil) — keep polling until the
		// overall deadline; a real error ends the read.
		if err != nil {
			break
		}
	}
	line := strings.TrimSpace(sb.String())
	if line == "" {
		return "", fmt.Errorf("no reply to %q", cmd)
	}
	return line, nil
}

// GoTo points the antenna at the given azimuth (0-359). GS-232A takes M000-M450
// (overlap rotators accept >360); we normalise to [0,360).
func (c *Client) GoTo(az int) error {
	az = ((az % 360) + 360) % 360
	_, err := c.roundTrip(fmt.Sprintf("M%03d", az), false)
	return err
}

// Stop interrupts any in-progress rotation.
func (c *Client) Stop() error {
	_, err := c.roundTrip("S", false)
	return err
}

// azRe matches both reply flavours: "+0aaa" (GS-232A) and "AZ=aaa" (GS-232B).
var azRe = regexp.MustCompile(`(?:\+0|AZ=)(\d{3})`)

// Heading queries the current azimuth. Returns the raw reply for diagnostics.
func (c *Client) Heading() (az int, raw string, err error) {
	raw, err = c.roundTrip("C", true)
	if err != nil {
		return 0, raw, err
	}
	m := azRe.FindStringSubmatch(raw)
	if m == nil {
		return 0, raw, fmt.Errorf("unrecognised azimuth reply %q", raw)
	}
	az, _ = strconv.Atoi(m[1])
	return az % 360, raw, nil
}