package app

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

const (
	transportPolicyKernelEnvEnable  = "SVPN_TRANSPORT_POLICY_KERNEL_APPLY"
	transportPolicyKernelEnvIPRules = "SVPN_TRANSPORT_POLICY_KERNEL_IPRULES"
)

var (
	transportPolicyKernelRunCommand = runCommandTimeout
	transportPolicyKernelUpdateSet  = func(ctx context.Context, setName string, ips []string) error {
		return nftUpdateSetIPsSmart(ctx, setName, ips, nil)
	}
)

func applyTransportPolicyKernelStage(current, staged transportPolicyRuntimeState) error {
	if !transportPolicyKernelApplyEnabled() {
		return nil
	}
	if err := applyTransportPolicyKernelNftSets(current, staged); err != nil {
		return err
	}
	if transportPolicyKernelIPRulesEnabled() {
		if err := applyTransportPolicyKernelIPRules(staged); err != nil {
			return err
		}
	}
	if transportPolicyKernelConntrackStickyEnabled() {
		if err := refreshTransportPolicyOwnerLocksFromConntrack(staged); err != nil {
			appendTraceLineRateLimited(
				"transport",
				fmt.Sprintf("policy conntrack sticky refresh warning: %v", err),
				5*time.Second,
			)
		}
	}
	return nil
}

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

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

func applyTransportPolicyKernelNftSets(current, staged transportPolicyRuntimeState) error {
	desired := buildTransportPolicyCIDRSetElements(staged.Interfaces)
	currentSets := collectTransportPolicyCIDRSetNames(current.Interfaces)
	desiredSets := collectMapKeys(desired)

	_, _, _, _ = transportPolicyKernelRunCommand(5*time.Second, "nft", "add", "table", "inet", "agvpn")

	for _, setName := range desiredSets {
		if strings.TrimSpace(setName) == "" {
			continue
		}
		_, _, _, _ = transportPolicyKernelRunCommand(
			5*time.Second,
			"nft", "add", "set", "inet", "agvpn", setName,
			"{", "type", "ipv4_addr", ";", "flags", "interval", ";", "}",
		)
		ips := desired[setName]
		if len(ips) == 0 {
			_, stderr, _, err := transportPolicyKernelRunCommand(10*time.Second, "nft", "flush", "set", "inet", "agvpn", setName)
			if err != nil && !strings.Contains(strings.ToLower(stderr), "no such file") {
				return fmt.Errorf("nft flush %s failed: %v (%s)", setName, err, strings.TrimSpace(stderr))
			}
			continue
		}
		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		err := transportPolicyKernelUpdateSet(ctx, setName, ips)
		cancel()
		if err != nil {
			return fmt.Errorf("nft update set %s failed: %w", setName, err)
		}
	}

	for _, stale := range diffStringSet(currentSets, desiredSets) {
		if strings.TrimSpace(stale) == "" {
			continue
		}
		_, _, _, _ = transportPolicyKernelRunCommand(5*time.Second, "nft", "flush", "set", "inet", "agvpn", stale)
		_, _, _, _ = transportPolicyKernelRunCommand(5*time.Second, "nft", "delete", "set", "inet", "agvpn", stale)
	}

	appendTraceLineRateLimited(
		"transport",
		fmt.Sprintf("policy kernel nft stage: sets=%d stale=%d", len(desiredSets), len(diffStringSet(currentSets, desiredSets))),
		5*time.Second,
	)
	return nil
}

func applyTransportPolicyKernelIPRules(staged transportPolicyRuntimeState) error {
	type tuple struct {
		pref  int
		mark  string
		table string
	}
	seen := map[string]struct{}{}
	rules := make([]tuple, 0, 16)
	for _, iface := range staged.Interfaces {
		table := strings.TrimSpace(iface.RoutingTable)
		if normalizeTransportIfaceID(iface.IfaceID) == transportDefaultIfaceID {
			continue
		}
		if table == "" {
			continue
		}
		for _, r := range iface.Rules {
			mark := strings.ToLower(strings.TrimSpace(r.MarkHex))
			if _, ok := parseTransportMarkHex(mark); !ok {
				continue
			}
			if _, ok := parseTransportPref(r.PriorityBase); !ok {
				continue
			}
			key := strconv.Itoa(r.PriorityBase) + "|" + mark + "|" + table
			if _, ok := seen[key]; ok {
				continue
			}
			seen[key] = struct{}{}
			rules = append(rules, tuple{pref: r.PriorityBase, mark: mark, table: table})
		}
	}
	sort.Slice(rules, func(i, j int) bool { return rules[i].pref < rules[j].pref })
	for _, rule := range rules {
		_, _, _, _ = transportPolicyKernelRunCommand(4*time.Second, "ip", "-4", "rule", "del", "pref", strconv.Itoa(rule.pref))
		stdout, stderr, code, err := transportPolicyKernelRunCommand(
			5*time.Second,
			"ip", "-4", "rule", "add",
			"pref", strconv.Itoa(rule.pref),
			"fwmark", rule.mark,
			"lookup", rule.table,
		)
		if err != nil || code != 0 {
			return fmt.Errorf("ip rule add pref=%d mark=%s table=%s failed: %v (stdout=%s stderr=%s code=%d)",
				rule.pref, rule.mark, rule.table, err, strings.TrimSpace(stdout), strings.TrimSpace(stderr), code)
		}
	}
	appendTraceLineRateLimited(
		"transport",
		fmt.Sprintf("policy kernel iprule stage: rules=%d", len(rules)),
		5*time.Second,
	)
	return nil
}

func buildTransportPolicyCIDRSetElements(interfaces []TransportPolicyCompileInterface) map[string][]string {
	out := map[string][]string{}
	for _, iface := range interfaces {
		for _, rule := range iface.Rules {
			if strings.ToLower(strings.TrimSpace(rule.SelectorType)) != "cidr" {
				continue
			}
			setName := strings.TrimSpace(rule.NftSet)
			if setName == "" {
				continue
			}
			pfx, err := parseIntentCIDR(rule.SelectorValue)
			if err != nil {
				continue
			}
			ip := cidrToNftElement(pfx)
			if ip == "" {
				continue
			}
			out[setName] = appendUniqueString(out[setName], ip)
		}
	}
	for k := range out {
		sort.Strings(out[k])
	}
	return out
}

func cidrToNftElement(pfx netip.Prefix) string {
	if !pfx.IsValid() || !pfx.Addr().Is4() {
		return ""
	}
	if pfx.Bits() == 32 {
		return pfx.Addr().String()
	}
	return pfx.Masked().String()
}

func collectTransportPolicyCIDRSetNames(interfaces []TransportPolicyCompileInterface) []string {
	seen := map[string]struct{}{}
	for _, iface := range interfaces {
		for _, it := range iface.Sets {
			if strings.ToLower(strings.TrimSpace(it.SelectorType)) != "cidr" {
				continue
			}
			name := strings.TrimSpace(it.Name)
			if name == "" {
				continue
			}
			seen[name] = struct{}{}
		}
	}
	out := make([]string, 0, len(seen))
	for k := range seen {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

func collectMapKeys(m map[string][]string) []string {
	out := make([]string, 0, len(m))
	for k := range m {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

func diffStringSet(a, b []string) []string {
	if len(a) == 0 {
		return nil
	}
	inB := map[string]struct{}{}
	for _, it := range b {
		inB[it] = struct{}{}
	}
	out := make([]string, 0, len(a))
	for _, it := range a {
		if _, ok := inB[it]; ok {
			continue
		}
		out = append(out, it)
	}
	sort.Strings(out)
	return out
}

func appendUniqueString(in []string, v string) []string {
	val := strings.TrimSpace(v)
	if val == "" {
		return in
	}
	for _, it := range in {
		if it == val {
			return in
		}
	}
	return append(in, val)
}