// Package gs232 drives rotator controllers that speak the Yaesu GS-232A
// protocol, over a raw TCP socket or a serial COM port.
//
// Any controller set to GS-232A works, which is most of them: the microHAM ARCO
// natively, and the ERC family (Easy Rotor Control — ERC Mini, ERC interface),
// which EMULATES GS-232A/B over its USB port. An ERC can also be configured for
// Hy-Gain DCU-1, a different command set entirely, so it must be set to GS-232.
//
// On the 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)
//	Waaa eee<CR>  move to azimuth aaa AND elevation eee (az/el controllers)
//	S<CR>         stop rotation
//	C<CR>         query azimuth — replies "+0aaa" (GS-232A) or "AZ=aaa" (GS-232B
//	              flavour); both are parsed.
//	C2<CR>        query both axes — "+0aaa+0eee" / "AZ=aaa EL=eee"
//	B<CR>         query elevation alone, for the controllers that do not answer C2
package gs232

import (
	"fmt"
	"io"
	"net"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"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.
	// Baud matters on some controllers. An ARCO's USB virtual COM ignores it, but
	// an ERC (Easy Rotor Control) runs at whatever rate its own configuration
	// sets — commonly 9600 or 19200 — and a mismatch reads as a dead rotator.
	// Zero keeps the historical 9600.
	Baud int
}

// 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, baud int) *Client {
	return &Client{ComPort: comPort, Baud: baud}
}

// bootSettle is how long a freshly opened serial port is left alone before the
// first command.
//
// An Arduino-based controller — K3NG's firmware, the ERC family — RESETS when
// the serial port is opened: the DTR line pulses its reset pin, and the
// bootloader then holds the processor for a second or more. A command sent into
// that window is simply lost, which is exactly how a controller that answers
// PuTTY perfectly reports "no reply" here.
const bootSettle = 2 * time.Second

// heldPort is an open serial port, kept between calls.
//
// The package holds it rather than the Client because the callers build a FRESH
// Client for every poll (one per heading request), and the port has to outlive
// them. Reopening per command is what made an Arduino controller reboot several
// times a second and never answer anything. A serial port is a single-owner
// resource in any case: two clients for COM5 would be two handles on one cable.
type heldPort struct {
	p        serial.Port
	openedAt time.Time
}

var (
	portsMu   sync.Mutex
	openPorts = map[string]*heldPort{}
)

// acquire returns the open port for com, opening it if needed.
func acquire(com string, baud int) (*heldPort, error) {
	portsMu.Lock()
	defer portsMu.Unlock()
	if h, ok := openPorts[com]; ok && h.p != nil {
		return h, nil
	}
	if baud <= 0 {
		baud = 9600
	}
	sp, err := serial.Open(com, &serial.Mode{BaudRate: baud})
	if err != nil {
		return nil, fmt.Errorf("open rotator %s @ %d baud: %w", com, baud, err)
	}
	_ = sp.SetReadTimeout(200 * time.Millisecond)
	h := &heldPort{p: sp, openedAt: time.Now()}
	openPorts[com] = h
	return h, nil
}

// drop closes and forgets a port, so the next call opens a fresh one. Called
// when an exchange fails: a half-spoken conversation is worse than a new one.
func drop(com string) {
	portsMu.Lock()
	defer portsMu.Unlock()
	if h, ok := openPorts[com]; ok {
		if h.p != nil {
			_ = h.p.Close()
		}
		delete(openPorts, com)
	}
}

// roundTrip sends one CR-terminated command and (when wantReply) reads one
// CR/LF-terminated reply line. Serial keeps its port open between calls; TCP
// dials per call, which is what the ARCO's LAN side expects.
func (c *Client) roundTrip(cmd string, wantReply bool) (string, error) {
	var conn io.ReadWriteCloser
	if c.ComPort != "" {
		h, err := acquire(c.ComPort, c.Baud)
		if err != nil {
			return "", err
		}
		// Let a just-reset controller finish booting before speaking to it.
		if wait := bootSettle - time.Since(h.openedAt); wait > 0 {
			time.Sleep(wait)
		}
		conn = h.p
		// Whatever is already in the buffer belongs to the last exchange — the
		// trailing LF of the previous reply, or a line the controller volunteered
		// while nobody was reading. Read as the answer to THIS command it would
		// be an answer to the wrong question.
		drain(h.p)
	} 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))
		defer nc.Close()
		conn = nc
	}
	if _, err := conn.Write([]byte(cmd + "\r")); err != nil {
		if c.ComPort != "" {
			drop(c.ComPort)
		}
		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 == "" {
		// Silence may mean the port is fine and the controller is not, or that
		// the handle is stale (a USB adapter unplugged and replugged). Let go of
		// it so the next attempt starts from a clean open rather than repeating
		// the same silence for ever.
		if c.ComPort != "" {
			drop(c.ComPort)
		}
		return "", fmt.Errorf("no reply to %q", cmd)
	}
	return line, nil
}

// drain empties whatever is waiting, without blocking for long.
func drain(sp serial.Port) {
	buf := make([]byte, 128)
	for i := 0; i < 4; i++ {
		n, err := sp.Read(buf)
		if n == 0 || err != nil {
			return
		}
	}
}

// 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
}

// --- Elevation: the az/el controllers ---
//
// The ERC-M (Easy Rotor Control, DF9GR) is the reason this half exists. It
// drives a Yaesu G-5500 — the az/el pair most satellite stations own — and
// emulates GS-232 over its USB port, so the same three commands that already
// pointed an azimuth rotator point a satellite antenna once elevation is added.
//
// A plain ERC or a microHAM ARCO answers the azimuth commands and ignores
// these; that is why the elevation capability is a property of the configured
// TYPE and not something probed at runtime. Asking a controller with no
// elevation motor where its elevation is gets an answer, and the answer is
// zero, for ever.

// GoToAzEl points an az/el controller at both axes in one command. GS-232's W
// takes the two angles separated by a space, azimuth first.
//
// Elevation is clamped to 0-180 rather than 0-90: a G-5500 goes past the zenith
// and keeps counting, which is how an overhead pass is followed without swinging
// the azimuth 180° through the middle of it.
func (c *Client) GoToAzEl(az, el int) error {
	az = ((az % 360) + 360) % 360
	if el < 0 {
		el = 0
	}
	if el > 180 {
		el = 180
	}
	_, err := c.roundTrip(fmt.Sprintf("W%03d %03d", az, el), false)
	return err
}

// elRe matches the elevation half of a reply, in either flavour. The GS-232A
// form of C2 is "+0aaa+0eee" — two identically-shaped groups — so the azimuth
// is taken from the first match and the elevation from the second, which is
// what bothRe below does; this one is for the reply to a bare B.
var elRe = regexp.MustCompile(`(?:\+0|EL=)(\d{3})`)

// bothRe pulls both angles out of a C2 reply.
var bothRe = regexp.MustCompile(`(?:\+0|AZ=)(\d{3})[^0-9+]*(?:\+0|EL=)(\d{3})`)

// Position queries both axes.
//
// C2 first, because one exchange is one chance for a serial line to go quiet.
// Controllers that answer C2 with the azimuth alone — some ERC firmware does —
// fall through to the two separate queries rather than reporting an elevation
// of zero, which would read as "the antenna is on the horizon" and is the one
// wrong answer that looks plausible.
func (c *Client) Position() (az, el int, raw string, err error) {
	raw, err = c.roundTrip("C2", true)
	if err == nil {
		if m := bothRe.FindStringSubmatch(raw); m != nil {
			a, _ := strconv.Atoi(m[1])
			e, _ := strconv.Atoi(m[2])
			return a % 360, e, raw, nil
		}
	}
	a, azRaw, aerr := c.Heading()
	if aerr != nil {
		return 0, 0, azRaw, aerr
	}
	e, elRaw, eerr := c.Elevation()
	if eerr != nil {
		return a, 0, azRaw + " " + elRaw, eerr
	}
	return a, e, azRaw + " " + elRaw, nil
}

// Elevation queries the elevation axis alone.
func (c *Client) Elevation() (el int, raw string, err error) {
	raw, err = c.roundTrip("B", true)
	if err != nil {
		return 0, raw, err
	}
	m := elRe.FindStringSubmatch(raw)
	if m == nil {
		return 0, raw, fmt.Errorf("unrecognised elevation reply %q", raw)
	}
	el, _ = strconv.Atoi(m[1])
	return el, raw, nil
}