// Package ctcp provides TCP connect / port check functionality for RSMon.
//
// Semantics: the check opens a TCP connection to host:port using the
// dialer's timeout, and reports OK as soon as the kernel-level
// handshake completes (no banner read, no payload sent). Any dial
// failure (refused, timed out, network unreachable, no route, ...)
// is reported as ERR with the underlying error message so operators
// can distinguish configuration problems from real outages.
//
// Settings consumed from models.CheckSettings:
//   - port (string): TCP port to dial. Defaults to 80 when empty.
//   - timeout (int, seconds): per-dial budget. Clamped to at least 1s.
//   - host (string): optional override of the monitor host.
package ctcp

import (
	"fmt"
	"net"
	"time"

	"rocketgit.ru/rsmon/worker/app/models"
)

const (
	stateOK  = "OK"
	stateERR = "ERR"

	defaultTimeout = 5 * time.Second
	minTimeout     = 1 * time.Second
)

// Perform executes a single TCP connect check.
func Perform(c *models.Check) *Result {
	r := &Result{}
	settings := c.GetSettings()

	host := c.Monitor.Host
	if settings.Host != "" {
		host = settings.Host
	}
	if host == "" {
		r.State = stateERR
		r.Error = fmt.Errorf("tcp: empty host")
		return r
	}

	port := settings.Port
	if port == "" {
		port = "80"
	}

	timeout := time.Duration(settings.Timeout) * time.Second
	if timeout <= 0 {
		timeout = defaultTimeout
	}
	if timeout < minTimeout {
		timeout = minTimeout
	}

	addr := net.JoinHostPort(host, port)
	dialer := &net.Dialer{Timeout: timeout, DualStack: true}
	start := time.Now()
	conn, err := dialer.Dial("tcp", addr)
	r.Duration = time.Since(start)
	if err != nil {
		r.State = stateERR
		r.Error = err
		return r
	}
	r.RemoteAddr = conn.RemoteAddr().String()
	if closeErr := conn.Close(); closeErr != nil {
		r.Warnings = append(r.Warnings, fmt.Sprintf("close: %v", closeErr))
	}
	r.State = stateOK
	r.Infos = append(r.Infos, fmt.Sprintf("tcp %s in %.2fms", addr, float64(r.Duration.Microseconds())/1000.0))
	return r
}