// Copyright 2026 Arctel.net
// SPDX-License-Identifier: Apache-2.0

// Package nodeip detects the preferred public IP address for edge nodes.
package nodeip

import (
	"context"
	"net"
	"sync"
	"time"

	"github.com/Rain-kl/Wavelet/pkg/geoip"
	"github.com/Rain-kl/Wavelet/pkg/geoip/iputil"
)

const (
	outboundIPLookupTimeout = 5 * time.Second
	publicIPPriorityScore   = 2 // matches iputil.Score for public IPv4 addresses
	ipCacheTTL              = 10 * time.Minute
)

// LookupOutboundIP and LookupLocalIP are the provider functions used to detect the node's outbound/local IP.
// They are package-level variables so they can be overridden in tests.
var (
	LookupOutboundIP = geoip.GetOutboundIP
	LookupLocalIP    = DetectLocal

	cacheMu      sync.RWMutex
	cachedIP     string
	lastDetected time.Time
)

// Detect returns the best available outbound or local IPv4 address for this node.
func Detect() string {
	return DetectWithContext(context.Background())
}

// DetectWithContext returns the best available outbound or local IPv4 address, respecting ctx for cancellation.
func DetectWithContext(ctx context.Context) string {
	cacheMu.RLock()
	if cachedIP != "" && time.Since(lastDetected) < ipCacheTTL {
		ip := cachedIP
		cacheMu.RUnlock()
		return ip
	}
	cacheMu.RUnlock()

	var ip string
	if ip = detectOutbound(ctx); ip == "" {
		ip = LookupLocalIP()
	}

	if ip != "" {
		cacheMu.Lock()
		cachedIP = ip
		lastDetected = time.Now()
		cacheMu.Unlock()
	}
	return ip
}

func detectOutbound(ctx context.Context) string {
	ctx, cancel := context.WithTimeout(ctx, outboundIPLookupTimeout)
	defer cancel()
	ip, err := LookupOutboundIP(ctx)
	if err != nil || ip == nil {
		return ""
	}
	return ip.String()
}

// DetectLocal returns the highest-priority non-loopback local IPv4 address found on system interfaces.
func DetectLocal() string {
	interfaces, err := net.Interfaces()
	if err != nil {
		return ""
	}
	bestIP := ""
	bestPriority := -1
	for _, iface := range interfaces {
		if iface.Flags&net.FlagUp == 0 || iface.Flags&net.FlagLoopback != 0 {
			continue
		}
		addrs, err := iface.Addrs()
		if err != nil {
			continue
		}
		for _, addr := range addrs {
			ipNet, ok := addr.(*net.IPNet)
			if !ok || ipNet.IP == nil || ipNet.IP.IsLoopback() {
				continue
			}
			ipv4 := ipNet.IP.To4()
			if ipv4 == nil {
				continue
			}
			priority := iputil.Score(ipv4)
			if priority > bestPriority {
				bestIP = ipv4.String()
				bestPriority = priority
			}
			if bestPriority == publicIPPriorityScore {
				return bestIP
			}
		}
	}
	return bestIP
}

// ResetCacheForTest clears the cached IP.
func ResetCacheForTest() {
	cacheMu.Lock()
	cachedIP = ""
	lastDetected = time.Time{}
	cacheMu.Unlock()
}