package netcheck

import (
	"context"
	"fmt"
	"net"
	"runtime"
	"sort"
	"strings"
	"sync"
	"time"

	"vpnclient/internal/config"
	"vpnclient/internal/linknorm"
	"vpnclient/internal/protocols/awg"
	"vpnclient/internal/protocols/hysteria2"
	"vpnclient/internal/protocols/xray"
)

// Result is a reachability measurement to a proxy host.
type Result struct {
	Name  string `json:"name"`
	Host  string `json:"host"`
	Port  string `json:"port"`
	Ms    int64  `json:"ms"`
	OK    bool   `json:"ok"`
	Soft  bool   `json:"soft,omitempty"` // UDP soft-up (timeout, no ICMP refuse)
	Error string `json:"error,omitempty"`
}

// Target describes one profile to ping.
type Target struct {
	Name     string
	Protocol config.Protocol
	Proxy    string
}

// PingProxyURI measures connect time to the host in a share/proxy URI.
func PingProxyURI(ctx context.Context, name, proxyURI string) Result {
	return PingProfile(ctx, name, "", proxyURI)
}

// PingAll pings targets in parallel (bounded concurrency) and sorts OK results by latency.
func PingAll(ctx context.Context, targets []Target) []Result {
	out := make([]Result, len(targets))
	if len(targets) == 0 {
		return out
	}
	// Scale with available OS threads (GOMAXPROCS); keep a useful floor/ceiling.
	workers := runtime.GOMAXPROCS(0) * 2
	if workers < 8 {
		workers = 8
	}
	if workers > 32 {
		workers = 32
	}
	if len(targets) < workers {
		workers = len(targets)
	}
	sem := make(chan struct{}, workers)
	var wg sync.WaitGroup
	for i, t := range targets {
		wg.Add(1)
		go func(i int, t Target) {
			defer wg.Done()
			sem <- struct{}{}
			defer func() { <-sem }()
			if strings.TrimSpace(t.Proxy) == "" {
				out[i] = Result{Name: t.Name, Error: "нет ссылки сервера"}
				return
			}
			out[i] = PingProfile(ctx, t.Name, t.Protocol, t.Proxy)
		}(i, t)
	}
	wg.Wait()

	sorted := append([]Result(nil), out...)
	sort.SliceStable(sorted, func(i, j int) bool {
		a, b := sorted[i], sorted[j]
		if a.OK != b.OK {
			return a.OK
		}
		if !a.OK {
			return a.Name < b.Name
		}
		if a.Ms != b.Ms {
			return a.Ms < b.Ms
		}
		return a.Name < b.Name
	})
	return sorted
}

// BestOK returns the lowest-latency hard OK result (excludes UDP soft-up).
// Soft-up nodes stay visible in the list but are not chosen as «Лучший».
func BestOK(results []Result) (Result, bool) {
	var best Result
	found := false
	for _, r := range results {
		if !r.OK || r.Soft {
			continue
		}
		if !found || r.Ms < best.Ms {
			best = r
			found = true
		}
	}
	return best, found
}

// PingProfile pings using protocol hints when available.
// Naive uses TCP; Hysteria 2 / AWG use UDP — TCP would always look "refused".
// When proto is set, Detect is skipped (trust stored protocol).
func PingProfile(ctx context.Context, name string, proto config.Protocol, proxyURI string) Result {
	res := Result{Name: name}
	if strings.TrimSpace(proxyURI) == "" {
		res.Error = "нет ссылки сервера"
		return res
	}

	var hy2, isAWG, isXray bool
	switch proto {
	case config.ProtocolHysteria2:
		hy2 = true
	case config.ProtocolAWG:
		isAWG = true
	case config.ProtocolVLESS, config.ProtocolVMess, config.ProtocolTrojan:
		isXray = true
	case config.ProtocolNaive:
		// TCP host parse below
	default:
		hy2 = hysteria2.Detect(proxyURI)
		isAWG = awg.Detect(proxyURI)
		isXray = xray.Detect(proxyURI)
	}

	var host, port string
	if isAWG {
		h, p, err := awg.HostPort(proxyURI)
		if err != nil {
			res.Error = err.Error()
			return res
		}
		host, port = h, p
	} else if isXray {
		h, p, err := xray.HostPort(proxyURI)
		if err != nil {
			res.Error = err.Error()
			return res
		}
		host, port = h, p
	} else if hy2 {
		h, p, err := hysteria2.HostPort(proxyURI)
		if err != nil {
			res.Error = err.Error()
			return res
		}
		host, port = h, p
	} else {
		normalized, _, _, err := linknorm.Normalize(proto, proxyURI)
		if err != nil {
			res.Error = err.Error()
			return res
		}
		rest := normalized
		if i := strings.Index(rest, "://"); i >= 0 {
			rest = rest[i+3:]
		}
		if at := strings.LastIndex(rest, "@"); at >= 0 {
			rest = rest[at+1:]
		}
		if i := strings.IndexAny(rest, "/?#"); i >= 0 {
			rest = rest[:i]
		}
		host = rest
		port = "443"
		if i := strings.LastIndex(rest, ":"); i >= 0 {
			host = rest[:i]
			port = rest[i+1:]
		}
	}

	res.Host = host
	res.Port = port
	if host == "" {
		res.Error = "нет хоста"
		return res
	}

	var (
		rtt  time.Duration
		soft bool
		err  error
	)
	if hy2 || isAWG {
		rtt, soft, err = probeUDP(ctx, host, port)
	} else {
		rtt, err = probeTCP(ctx, host, port)
	}
	if err != nil {
		res.Error = friendlyDialError(err, hy2 || isAWG)
		return res
	}
	ms := rtt.Milliseconds()
	if ms < 1 {
		ms = 1
	}
	res.Ms = ms
	res.OK = true
	res.Soft = soft
	return res
}

func probeTCP(ctx context.Context, host, port string) (time.Duration, error) {
	start := time.Now()
	d := net.Dialer{Timeout: 3 * time.Second}
	conn, err := d.DialContext(ctx, "tcp", net.JoinHostPort(host, port))
	if err != nil {
		return 0, err
	}
	_ = conn.Close()
	return time.Since(start), nil
}

// probeUDP checks Hy2/AWG endpoints.
//
// UDP VPN ports usually ignore a probe datagram (no reply). Treating read-timeout
// as failure marked live nodes as down. Semantics:
//   - ICMP / connection refused → down
//   - any reply → hard up (RTT to reply)
//   - short read-timeout after a successful write → soft-up (display only; not for Best)
func probeUDP(ctx context.Context, host, port string) (time.Duration, bool, error) {
	start := time.Now()
	d := net.Dialer{Timeout: 3 * time.Second}
	conn, err := d.DialContext(ctx, "udp", net.JoinHostPort(host, port))
	if err != nil {
		return 0, false, err
	}
	defer conn.Close()

	icmpWait := 350 * time.Millisecond
	deadline := time.Now().Add(icmpWait)
	if dl, ok := ctx.Deadline(); ok && dl.Before(deadline) {
		deadline = dl
	}
	_ = conn.SetDeadline(deadline)

	if _, err := conn.Write([]byte{0}); err != nil {
		return 0, false, err
	}
	afterWrite := time.Now()

	buf := make([]byte, 64)
	_, err = conn.Read(buf)
	if err == nil {
		return time.Since(start), false, nil
	}
	if ne, ok := err.(net.Error); ok && ne.Timeout() {
		return afterWrite.Sub(start), true, nil
	}
	return 0, false, err
}

func friendlyDialError(err error, udp bool) string {
	msg := err.Error()
	lower := strings.ToLower(msg)
	switch {
	case strings.Contains(lower, "refused"):
		if udp {
			return "UDP порт недоступен (connection refused)"
		}
		return "порт закрыт (connection refused)"
	case strings.Contains(lower, "timeout") || strings.Contains(lower, "timed out"):
		return "таймаут"
	case strings.Contains(lower, "no such host"):
		return "DNS: хост не найден"
	default:
		return fmt.Sprintf("недоступен: %v", err)
	}
}