package app

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// ---------------------------------------------------------------------
// smartdns runtime accelerator (nftset -> agvpn_dyn4)
// ---------------------------------------------------------------------

// EN: Runtime accelerator state is persisted separately from DNS mode.
// EN: This allows enabling/disabling SmartDNS nftset hook without changing
// EN: resolver primary behavior.
// RU: Состояние runtime-ускорителя хранится отдельно от DNS mode.
// RU: Это позволяет включать/выключать SmartDNS nftset-hook независимо от
// RU: основного пути через резолвер.

const (
	smartdnsRuntimeDomainSetLine = "domain-set -name agvpn_wild -file /etc/selective-vpn/smartdns.conf"
	smartdnsRuntimeNftsetLine    = "nftset /domain-set:agvpn_wild/#4:inet#agvpn#agvpn_dyn4"
	smartdnsRuntimeStateVersion  = 1
)

type smartDNSRuntimeState struct {
	Version   int    `json:"version"`
	Enabled   bool   `json:"enabled"`
	UpdatedAt string `json:"updated_at"`
}

func wildcardFillSource(runtimeEnabled bool) string {
	if runtimeEnabled {
		return "both"
	}
	return "resolver"
}

func normalizeSmartDNSRuntimeState(st smartDNSRuntimeState) smartDNSRuntimeState {
	if st.Version <= 0 {
		st.Version = smartdnsRuntimeStateVersion
	}
	return st
}

func smartDNSRuntimeEnabledFromConfig() (bool, error) {
	data, err := os.ReadFile(smartdnsMainConfig)
	if err != nil {
		return false, err
	}
	for _, raw := range strings.Split(string(data), "\n") {
		trimmed := strings.TrimSpace(raw)
		if trimmed == "" || strings.HasPrefix(trimmed, "#") {
			continue
		}
		if strings.Contains(trimmed, "nftset") &&
			strings.Contains(trimmed, "domain-set:agvpn_wild") &&
			strings.Contains(trimmed, "agvpn_dyn4") {
			return true, nil
		}
	}
	return false, nil
}

func inferSmartDNSRuntimeEnabled() bool {
	enabled, err := smartDNSRuntimeEnabledFromConfig()
	if err != nil {
		// Keep historical behavior on first run when config is unavailable.
		return true
	}
	return enabled
}

func loadSmartDNSRuntimeState(logf func(string, ...any)) smartDNSRuntimeState {
	if data, err := os.ReadFile(smartdnsRTPath); err == nil {
		var st smartDNSRuntimeState
		if json.Unmarshal(data, &st) == nil {
			return normalizeSmartDNSRuntimeState(st)
		}
		if logf != nil {
			logf("smartdns runtime: invalid state json at %s, rebuilding", smartdnsRTPath)
		}
	}

	st := smartDNSRuntimeState{
		Version:   smartdnsRuntimeStateVersion,
		Enabled:   inferSmartDNSRuntimeEnabled(),
		UpdatedAt: time.Now().UTC().Format(time.RFC3339),
	}
	_ = saveSmartDNSRuntimeState(st)
	return st
}

func saveSmartDNSRuntimeState(st smartDNSRuntimeState) error {
	st = normalizeSmartDNSRuntimeState(st)
	st.UpdatedAt = time.Now().UTC().Format(time.RFC3339)
	data, err := json.MarshalIndent(st, "", "  ")
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(smartdnsRTPath), 0o755); err != nil {
		return err
	}
	tmp := smartdnsRTPath + ".tmp"
	if err := os.WriteFile(tmp, data, 0o644); err != nil {
		return err
	}
	return os.Rename(tmp, smartdnsRTPath)
}

func smartDNSRuntimeEnabled() bool {
	return loadSmartDNSRuntimeState(nil).Enabled
}

func normalizeSmartDNSMainConfig(content string, enabled bool) string {
	normalized := strings.ReplaceAll(content, "\r\n", "\n")
	lines := strings.Split(normalized, "\n")
	out := make([]string, 0, len(lines)+4)

	seenDomain := false
	seenNftset := false

	isDomainLine := func(raw string) bool {
		t := strings.TrimSpace(raw)
		if strings.HasPrefix(t, "#") {
			t = strings.TrimSpace(strings.TrimPrefix(t, "#"))
		}
		return strings.HasPrefix(t, "domain-set ") &&
			strings.Contains(t, "-name agvpn_wild") &&
			strings.Contains(t, "/etc/selective-vpn/smartdns.conf")
	}
	isNftsetLine := func(raw string) bool {
		t := strings.TrimSpace(raw)
		if strings.HasPrefix(t, "#") {
			t = strings.TrimSpace(strings.TrimPrefix(t, "#"))
		}
		return strings.HasPrefix(t, "nftset ") &&
			strings.Contains(t, "domain-set:agvpn_wild") &&
			strings.Contains(t, "agvpn_dyn4")
	}

	for _, raw := range lines {
		switch {
		case isDomainLine(raw):
			if !seenDomain {
				if enabled {
					out = append(out, smartdnsRuntimeDomainSetLine)
				} else {
					out = append(out, "# "+smartdnsRuntimeDomainSetLine)
				}
				seenDomain = true
			}
		case isNftsetLine(raw):
			if !seenNftset {
				if enabled {
					out = append(out, smartdnsRuntimeNftsetLine)
				} else {
					out = append(out, "# "+smartdnsRuntimeNftsetLine)
				}
				seenNftset = true
			}
		default:
			out = append(out, raw)
		}
	}

	if enabled && (!seenDomain || !seenNftset) {
		if len(out) > 0 && strings.TrimSpace(out[len(out)-1]) != "" {
			out = append(out, "")
		}
		if !seenDomain {
			out = append(out, smartdnsRuntimeDomainSetLine)
		}
		if !seenNftset {
			out = append(out, smartdnsRuntimeNftsetLine)
		}
	}

	rendered := strings.Join(out, "\n")
	if !strings.HasSuffix(rendered, "\n") {
		rendered += "\n"
	}
	return rendered
}

func applySmartDNSRuntimeConfig(enabled bool) (bool, error) {
	data, err := os.ReadFile(smartdnsMainConfig)
	if err != nil {
		return false, err
	}
	current := strings.ReplaceAll(string(data), "\r\n", "\n")
	next := normalizeSmartDNSMainConfig(current, enabled)
	if next == current {
		return false, nil
	}
	tmp := smartdnsMainConfig + ".tmp"
	if err := os.WriteFile(tmp, []byte(next), 0o644); err != nil {
		return false, err
	}
	if err := os.Rename(tmp, smartdnsMainConfig); err != nil {
		return false, err
	}
	return true, nil
}

func smartDNSRuntimeSnapshot() SmartDNSRuntimeStatusResponse {
	st := loadSmartDNSRuntimeState(nil)
	appliedEnabled, err := smartDNSRuntimeEnabledFromConfig()
	msg := ""
	if err != nil {
		msg = fmt.Sprintf("config read error: %v", err)
	}
	return SmartDNSRuntimeStatusResponse{
		Enabled:        st.Enabled,
		AppliedEnable:  appliedEnabled,
		WildcardSource: wildcardFillSource(st.Enabled),
		UnitState:      smartdnsUnitState(),
		ConfigPath:     smartdnsMainConfig,
		Message:        msg,
	}
}