// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

package ipnlocal

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"net/netip"
	"time"

	"tailscale.com/feature"
	"tailscale.com/feature/buildfeatures"
	"tailscale.com/ipn/ipnstate"
	"tailscale.com/tailcfg"
)

// Pinger is the [LocalBackend.Ping] method.
type Pinger interface {
	// Ping is a request to do a ping with the peer handling the given IP.
	Ping(ctx context.Context, ip netip.Addr, pingType tailcfg.PingType, size int) (*ipnstate.PingResult, error)
}

func (b *LocalBackend) Ping(ctx context.Context, ip netip.Addr, pingType tailcfg.PingType, size int) (*ipnstate.PingResult, error) {
	if pingType == tailcfg.PingPeerAPI {
		t0 := b.clock.Now()
		node, base, err := b.pingPeerAPI(ctx, ip)
		if err != nil && ctx.Err() != nil {
			return nil, ctx.Err()
		}
		d := b.clock.Since(t0)
		pr := &ipnstate.PingResult{
			IP:             ip.String(),
			NodeIP:         ip.String(),
			LatencySeconds: d.Seconds(),
			PeerAPIURL:     base,
		}
		if err != nil {
			pr.Err = err.Error()
		}
		if node.Valid() {
			pr.NodeName = node.Name()
		}
		return pr, nil
	}
	ch := make(chan *ipnstate.PingResult, 1)
	b.e.Ping(ip, pingType, size, func(pr *ipnstate.PingResult) {
		select {
		case ch <- pr:
		default:
		}
	})
	select {
	case pr := <-ch:
		return pr, nil
	case <-ctx.Done():
		return nil, ctx.Err()
	}
}

func (b *LocalBackend) pingPeerAPI(ctx context.Context, ip netip.Addr) (peer tailcfg.NodeView, peerBase string, err error) {
	if !buildfeatures.HasPeerAPIClient {
		return peer, peerBase, feature.ErrUnavailable
	}
	var zero tailcfg.NodeView
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()
	nm := b.NetMap()
	if nm == nil {
		return zero, "", errors.New("no netmap")
	}
	peer, ok := nm.PeerByTailscaleIP(ip)
	if !ok {
		return zero, "", fmt.Errorf("no peer found with Tailscale IP %v", ip)
	}
	if peer.Expired() {
		return zero, "", errors.New("peer's node key has expired")
	}
	base := peerAPIBase(nm, peer)
	if base == "" {
		return zero, "", fmt.Errorf("no PeerAPI base found for peer %v (%v)", peer.ID(), ip)
	}
	outReq, err := http.NewRequestWithContext(ctx, "HEAD", base, nil)
	if err != nil {
		return zero, "", err
	}
	tr := b.Dialer().PeerAPITransport()
	res, err := tr.RoundTrip(outReq)
	if err != nil {
		return zero, "", err
	}
	defer res.Body.Close() // but unnecessary on HEAD responses
	if res.StatusCode != http.StatusOK {
		return zero, "", fmt.Errorf("HTTP status %v", res.Status)
	}
	return peer, base, nil
}