package checkrunner

import (
	"context"
	"fmt"
	"net"
	"os"
	"time"

	"golang.org/x/net/icmp"
	"golang.org/x/net/ipv4"
)

// ICMPEcho sends up to `count` ICMP echo requests to host and reports
// success if at least one echo reply is received before timeout. Uses a
// raw ICMP socket (ip4:icmp), which requires either running as root or
// (on Linux, as deployed here) the CAP_NET_RAW capability — see the
// validator-agent and prober systemd units.
func ICMPEcho(host string, count int, timeout time.Duration) func(ctx context.Context) Result {
	return run("icmp", host, func(ctx context.Context) error {
		conn, err := icmp.ListenPacket("ip4:icmp", "0.0.0.0")
		if err != nil {
			return fmt.Errorf("open icmp socket (needs CAP_NET_RAW or root): %w", err)
		}
		defer conn.Close()

		dst, err := net.ResolveIPAddr("ip4", host)
		if err != nil {
			return fmt.Errorf("resolve %s: %w", host, err)
		}

		id := os.Getpid() & 0xffff
		var lastErr error
		for seq := 1; seq <= count; seq++ {
			if err := ctx.Err(); err != nil {
				return err
			}
			msg := icmp.Message{
				Type: ipv4.ICMPTypeEcho,
				Code: 0,
				Body: &icmp.Echo{
					ID:   id,
					Seq:  seq,
					Data: []byte("cloud-ip-validator"),
				},
			}
			wb, err := msg.Marshal(nil)
			if err != nil {
				return fmt.Errorf("marshal echo request: %w", err)
			}
			if _, err := conn.WriteTo(wb, dst); err != nil {
				lastErr = fmt.Errorf("write echo request: %w", err)
				continue
			}

			perAttempt := timeout / time.Duration(count)
			if perAttempt <= 0 {
				perAttempt = timeout
			}
			conn.SetReadDeadline(time.Now().Add(perAttempt))
			rb := make([]byte, 1500)
			n, _, err := conn.ReadFrom(rb)
			if err != nil {
				lastErr = fmt.Errorf("read echo reply: %w", err)
				continue
			}
			rm, err := icmp.ParseMessage(1 /* protocolICMP */, rb[:n])
			if err != nil {
				lastErr = fmt.Errorf("parse reply: %w", err)
				continue
			}
			if rm.Type == ipv4.ICMPTypeEchoReply {
				return nil
			}
			lastErr = fmt.Errorf("unexpected icmp type %v", rm.Type)
		}
		if lastErr == nil {
			lastErr = fmt.Errorf("no reply received")
		}
		return lastErr
	})
}