package app

import (
	"fmt"
	"net/netip"
	"os"
	"sort"
	"strconv"
	"strings"
	"time"
)

const transportPolicyKernelEnvConntrackSticky = "SVPN_TRANSPORT_POLICY_CONNTRACK_STICKY"

var (
	transportPolicyKernelConntrackOutput = func(timeout time.Duration) (string, error) {
		stdout, stderr, code, err := transportPolicyKernelRunCommand(timeout, "conntrack", "-L", "-f", "ipv4")
		if err != nil || code != 0 {
			return "", fmt.Errorf("conntrack list failed: %v (stderr=%s code=%d)", err, strings.TrimSpace(stderr), code)
		}
		return stdout, nil
	}
	transportPolicyKernelSaveOwnerLocksState = saveTransportOwnerLocksState
)

type transportPolicyMarkOwner struct {
	ClientID   string
	ClientKind string
	IfaceID    string
	MarkHex    string
}

func transportPolicyKernelConntrackStickyEnabled() bool {
	switch strings.ToLower(strings.TrimSpace(os.Getenv(transportPolicyKernelEnvConntrackSticky))) {
	case "1", "true", "yes", "on":
		return true
	default:
		return false
	}
}

func refreshTransportPolicyOwnerLocksFromConntrack(staged transportPolicyRuntimeState) error {
	markOwner := collectTransportPolicyMarkOwners(staged.Interfaces)
	if len(markOwner) == 0 {
		_ = transportPolicyKernelSaveOwnerLocksState(TransportOwnerLockState{
			Version:        transportStateVersion,
			PolicyRevision: staged.PolicyRevision,
		})
		return nil
	}
	output, err := transportPolicyKernelConntrackOutput(8 * time.Second)
	if err != nil {
		return err
	}
	locks := parseTransportOwnerLocksFromConntrack(output, markOwner, staged.PolicyRevision)
	if err := transportPolicyKernelSaveOwnerLocksState(locks); err != nil {
		return fmt.Errorf("save owner locks failed: %w", err)
	}
	appendTraceLineRateLimited(
		"transport",
		fmt.Sprintf("policy conntrack sticky refresh: locks=%d revision=%d", len(locks.Items), staged.PolicyRevision),
		5*time.Second,
	)
	return nil
}

func collectTransportPolicyMarkOwners(interfaces []TransportPolicyCompileInterface) map[uint32]transportPolicyMarkOwner {
	out := map[uint32]transportPolicyMarkOwner{}
	for _, iface := range interfaces {
		ifaceID := normalizeTransportIfaceID(iface.IfaceID)
		for _, rule := range iface.Rules {
			markHex := strings.ToLower(strings.TrimSpace(rule.MarkHex))
			markRaw, ok := parseTransportMarkHex(markHex)
			if !ok {
				continue
			}
			if markRaw > uint64(^uint32(0)) {
				continue
			}
			mark := uint32(markRaw)
			if strings.TrimSpace(rule.ClientID) == "" {
				continue
			}
			if _, exists := out[mark]; exists {
				continue
			}
			out[mark] = transportPolicyMarkOwner{
				ClientID:   strings.TrimSpace(rule.ClientID),
				ClientKind: strings.TrimSpace(rule.ClientKind),
				IfaceID:    ifaceID,
				MarkHex:    markHex,
			}
		}
	}
	return out
}

func parseTransportOwnerLocksFromConntrack(raw string, markOwner map[uint32]transportPolicyMarkOwner, policyRevision int64) TransportOwnerLockState {
	now := time.Now().UTC().Format(time.RFC3339)
	byDst := map[string]TransportOwnerLockRecord{}
	lines := strings.Split(raw, "\n")
	for _, line := range lines {
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		dst, mark, proto, ok := parseTransportConntrackLockLine(line)
		if !ok {
			continue
		}
		owner, exists := markOwner[mark]
		if !exists {
			continue
		}
		key := dst.String()
		if _, exists := byDst[key]; exists {
			continue
		}
		byDst[key] = TransportOwnerLockRecord{
			DestinationIP: key,
			ClientID:      owner.ClientID,
			ClientKind:    owner.ClientKind,
			IfaceID:       owner.IfaceID,
			MarkHex:       owner.MarkHex,
			Proto:         proto,
			UpdatedAt:     now,
		}
	}

	items := make([]TransportOwnerLockRecord, 0, len(byDst))
	for _, item := range byDst {
		items = append(items, item)
	}
	sort.Slice(items, func(i, j int) bool {
		if items[i].DestinationIP != items[j].DestinationIP {
			return items[i].DestinationIP < items[j].DestinationIP
		}
		return items[i].ClientID < items[j].ClientID
	})
	return TransportOwnerLockState{
		Version:        transportStateVersion,
		UpdatedAt:      now,
		PolicyRevision: policyRevision,
		Count:          len(items),
		Items:          items,
	}
}

func parseTransportConntrackLockLine(line string) (dst netip.Addr, mark uint32, proto string, ok bool) {
	tokens := strings.Fields(strings.TrimSpace(line))
	if len(tokens) == 0 {
		return netip.Addr{}, 0, "", false
	}
	proto = strings.ToLower(strings.TrimSpace(tokens[0]))
	var gotDst bool
	var gotMark bool
	for _, tok := range tokens {
		if !gotDst && strings.HasPrefix(tok, "dst=") {
			val := strings.TrimPrefix(tok, "dst=")
			addr, err := netip.ParseAddr(strings.TrimSpace(val))
			if err == nil && addr.Is4() {
				dst = addr
				gotDst = true
			}
			continue
		}
		if !gotMark && strings.HasPrefix(tok, "mark=") {
			val := strings.TrimPrefix(tok, "mark=")
			parsed, ok := parseTransportConntrackMark(val)
			if ok {
				mark = parsed
				gotMark = true
			}
		}
	}
	if !gotDst || !gotMark {
		return netip.Addr{}, 0, "", false
	}
	return dst, mark, proto, true
}

func parseTransportConntrackMark(raw string) (uint32, bool) {
	v := strings.TrimSpace(raw)
	if v == "" {
		return 0, false
	}
	base := 10
	if strings.HasPrefix(strings.ToLower(v), "0x") {
		base = 16
		v = v[2:]
	}
	n, err := strconv.ParseUint(v, base, 32)
	if err != nil {
		return 0, false
	}
	return uint32(n), true
}