// Package pst sends commands to PstRotator over its UDP listener.
//
// PstRotator (Codrut Buda YO3DMU) exposes a simple text/XML protocol on
// a configurable UDP port (default 12000 on localhost). Each command is a
// single fire-and-forget datagram — no handshake, no response. This keeps
// us connectionless and means a misconfigured port silently no-ops rather
// than hanging the UI. Run the matching "Test" action to confirm the link.
package pst

import (
	"fmt"
	"net"
	"time"
)

// Client is a stateless UDP sender. Safe to construct cheaply per call —
// the underlying socket only lives for the length of one Write.
type Client struct {
	Host string // hostname or IP of the PstRotator host (usually "127.0.0.1")
	Port int    // UDP port (PstRotator default = 12000)
}

// New returns a Client with sane defaults applied for empty fields.
func New(host string, port int) *Client {
	if host == "" {
		host = "127.0.0.1"
	}
	if port <= 0 || port > 65535 {
		port = 12000
	}
	return &Client{Host: host, Port: port}
}

// GoTo points the antenna at azimuth (0-359°). If hasElevation is true
// and el >= 0 the elevation field is included too (VHF/satellite setups);
// otherwise PstRotator just turns in azimuth.
func (c *Client) GoTo(az int, hasElevation bool, el int) error {
	az = ((az % 360) + 360) % 360 // normalise to [0,360)
	if hasElevation && el >= 0 && el <= 180 {
		return c.send(fmt.Sprintf("<PST><AZIMUTH>%d</AZIMUTH><ELEVATION>%d</ELEVATION></PST>", az, el))
	}
	return c.send(fmt.Sprintf("<PST><AZIMUTH>%d</AZIMUTH></PST>", az))
}

// Stop interrupts any in-progress rotation.
func (c *Client) Stop() error {
	return c.send("<PST><STOP>1</STOP></PST>")
}

// Park sends the rotator to its parked position (configured inside
// PstRotator itself — we just trigger it).
func (c *Client) Park() error {
	return c.send("<PST><PARK>1</PARK></PST>")
}

func (c *Client) send(payload string) error {
	addr := fmt.Sprintf("%s:%d", c.Host, c.Port)
	conn, err := net.DialTimeout("udp", addr, 2*time.Second)
	if err != nil {
		return fmt.Errorf("dial PstRotator at %s: %w", addr, err)
	}
	defer conn.Close()
	_ = conn.SetWriteDeadline(time.Now().Add(2 * time.Second))
	if _, err := conn.Write([]byte(payload)); err != nil {
		return fmt.Errorf("send to PstRotator: %w", err)
	}
	return nil
}