package agent

import (
	"bytes"
	"os"
	"regexp"
	"sync"
	"time"

	"github.com/mhsanaei/3x-ui/v3/internal/xray"
)

// ITEM6 B3: online users for the sing-box runtime (the §4.4 spike,
// concluded here).
//
// sing-box's v2ray_api has no online-user source. The access log
// does: for every authenticated connection sing-box logs
//
//	[<conn-id> <elapsed>] inbound/<type>[<tag>]: [<user>] inbound connection to <dest>
//
// with the same user name the stats counters use (verified against
// the real v1.13.21 binary for vless, shadowsocks and mixed;
// unauthenticated attempts only ever produce the preceding
// "inbound connection from" line, never this one). The tracker tails
// the managed process's log file from a cursor — NexusGate's
// observation discipline: a truncated/rotated file resets the cursor,
// reads are window-capped, only complete lines are consumed.
//
// Semantics versus the xray core's live-connection view: a user is
// online while an authenticated connection was observed within
// singboxOnlineGrace, OR while their counters moved in the latest
// snapshot (the traffic cycle merges that in — it covers long-lived
// connections that keep transferring). A connected-but-idle user
// ages out after the grace window: sing-box logs nothing per
// connection after setup, so idle-liveness is not observable without
// opening the clash_api connection table, which the §4.4 evidence
// base rules out. The wire contract is unchanged (onlines = [email]).

const singboxOnlineGrace = 150 * time.Second

// maxSingboxLogWindow caps one poll's read, NexusGate-style: when the
// cursor falls further behind (long downtime), only the tail is
// scanned for recent users.
const maxSingboxLogWindow = 2 * 1024 * 1024

var (
	// ANSI CSI sequences (sing-box colorizes the level and conn-id
	// even when redirected to a file) are stripped before matching.
	ansiCSIRegex = regexp.MustCompile("\x1b\\[[0-9;?]*[ -/]*[@-~]")
	// The authenticated-connection line. The user name is sing-box's
	// stats identity: email for most protocols, username for
	// mixed/socks/http.
	singboxAuthLineRegex = regexp.MustCompile(`\[([^\]\s]+)\] inbound connection to `)
)

// singboxOnlineTracker derives the online-user set from the managed
// process's access log. Safe for concurrent use.
type singboxOnlineTracker struct {
	path string

	mu       sync.Mutex
	offset   int64
	lastSeen map[string]int64 // user -> unix seconds of latest authenticated connection
}

func newSingboxOnlineTracker(path string) *singboxOnlineTracker {
	return &singboxOnlineTracker{path: path, lastSeen: make(map[string]int64)}
}

// stripANSI removes terminal color/control sequences from one log line.
func stripANSI(line string) string {
	if !bytes.ContainsRune([]byte(line), 0x1b) {
		return line
	}
	return ansiCSIRegex.ReplaceAllString(line, "")
}

// parseSingboxAuthLine extracts the user from one raw log line, or ""
// when the line is not an authenticated-connection record.
func parseSingboxAuthLine(line string) string {
	m := singboxAuthLineRegex.FindStringSubmatch(stripANSI(line))
	if m == nil {
		return ""
	}
	return m[1]
}

// Poll consumes the log written since the previous poll and records
// the users it proves active. Poll errors are swallowed by design:
// online data is best-effort and must never fail a traffic cycle.
func (t *singboxOnlineTracker) Poll(now time.Time) {
	t.mu.Lock()
	defer t.mu.Unlock()

	info, err := os.Stat(t.path)
	if err != nil {
		return
	}
	size := info.Size()
	if size < t.offset {
		t.offset = 0 // rotated/truncated: rescan from the top
	}
	start := t.offset
	if floor := size - maxSingboxLogWindow; floor > start {
		start = floor
	}
	if start >= size {
		t.offset = size
		return
	}
	f, err := os.Open(t.path)
	if err != nil {
		return
	}
	defer f.Close()
	buf := make([]byte, size-start)
	if _, err := f.ReadAt(buf, start); err != nil {
		return
	}
	end := bytes.LastIndex(buf, []byte("\n"))
	if end < 0 {
		return // no complete line yet; retry next poll
	}
	ts := now.Unix()
	for _, line := range bytes.Split(buf[:end], []byte("\n")) {
		if user := parseSingboxAuthLine(string(line)); user != "" {
			t.lastSeen[user] = ts
		}
	}
	t.offset = start + int64(end) + 1
	// Prune entries far beyond the grace window so the map stays
	// bounded on long-lived nodes.
	cutoff := ts - int64(singboxOnlineGrace/time.Second)*4
	for user, seen := range t.lastSeen {
		if seen < cutoff {
			delete(t.lastSeen, user)
		}
	}
}

// Online returns the users seen within the grace window.
func (t *singboxOnlineTracker) Online(now time.Time) []string {
	t.mu.Lock()
	defer t.mu.Unlock()
	cutoff := now.Unix() - int64(singboxOnlineGrace/time.Second)
	out := make([]string, 0, len(t.lastSeen))
	for user, seen := range t.lastSeen {
		if seen >= cutoff {
			out = append(out, user)
		}
	}
	return out
}

// mergeOnlineUsers unions the log tracker's view with the users whose
// counters moved in the latest snapshot (activity within the last
// poll interval), deduplicated, in xray.OnlineUser wire shape.
func mergeOnlineUsers(logUsers []string, snap *xray.TrafficSnapshot) []xray.OnlineUser {
	seen := make(map[string]struct{})
	out := make([]xray.OnlineUser, 0, len(logUsers))
	add := func(email string) {
		if email == "" {
			return
		}
		if _, dup := seen[email]; dup {
			return
		}
		seen[email] = struct{}{}
		out = append(out, xray.OnlineUser{Email: email})
	}
	for _, u := range logUsers {
		add(u)
	}
	if snap != nil {
		for _, ct := range snap.ClientTraffics {
			if ct != nil && ct.Up+ct.Down > 0 {
				add(ct.Email)
			}
		}
	}
	return out
}