package holepunch

import (
	"encoding/json"
	"fmt"
	"net"
	"strconv"
	"sync"
	"time"

	"github.com/fosrl/newt/bind"
	"github.com/fosrl/newt/logger"
	"github.com/fosrl/newt/util"
	"golang.org/x/crypto/chacha20poly1305"
	"golang.org/x/crypto/curve25519"
	mrand "golang.org/x/exp/rand"
	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
)

// ExitNode represents a WireGuard exit node for hole punching
type ExitNode struct {
	Endpoint  string `json:"endpoint"`
	RelayPort uint16 `json:"relayPort"`
	PublicKey string `json:"publicKey"`
}

// Manager handles UDP hole punching operations
type Manager struct {
	mu         sync.Mutex
	running    bool
	stopChan   chan struct{}
	sharedBind *bind.SharedBind
	ID         string
	token      string
	publicKey  string
	clientType string
	exitNodes  map[string]ExitNode // key is endpoint
	updateChan chan struct{}       // signals the goroutine to refresh exit nodes

	sendHolepunchInterval time.Duration
}

const sendHolepunchIntervalMax = 60 * time.Second
const sendHolepunchIntervalMin = 1 * time.Second

// NewManager creates a new hole punch manager
func NewManager(sharedBind *bind.SharedBind, ID string, clientType string, publicKey string) *Manager {
	return &Manager{
		sharedBind:            sharedBind,
		ID:                    ID,
		clientType:            clientType,
		publicKey:             publicKey,
		exitNodes:             make(map[string]ExitNode),
		sendHolepunchInterval: sendHolepunchIntervalMin,
	}
}

// SetToken updates the authentication token used for hole punching
func (m *Manager) SetToken(token string) {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.token = token
}

// IsRunning returns whether hole punching is currently active
func (m *Manager) IsRunning() bool {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.running
}

// Stop stops any ongoing hole punch operations
func (m *Manager) Stop() {
	m.mu.Lock()
	defer m.mu.Unlock()

	if !m.running {
		return
	}

	if m.stopChan != nil {
		close(m.stopChan)
		m.stopChan = nil
	}

	if m.updateChan != nil {
		close(m.updateChan)
		m.updateChan = nil
	}

	m.running = false
	logger.Info("Hole punch manager stopped")
}

// AddExitNode adds a new exit node to the rotation if it doesn't already exist
func (m *Manager) AddExitNode(exitNode ExitNode) bool {
	m.mu.Lock()
	defer m.mu.Unlock()

	if _, exists := m.exitNodes[exitNode.Endpoint]; exists {
		logger.Debug("Exit node %s already exists in rotation", exitNode.Endpoint)
		return false
	}

	m.exitNodes[exitNode.Endpoint] = exitNode
	logger.Info("Added exit node %s to hole punch rotation", exitNode.Endpoint)

	// Signal the goroutine to refresh if running
	if m.running && m.updateChan != nil {
		select {
		case m.updateChan <- struct{}{}:
		default:
			// Channel full or closed, skip
		}
	}

	return true
}

// RemoveExitNode removes an exit node from the rotation
func (m *Manager) RemoveExitNode(endpoint string) bool {
	m.mu.Lock()
	defer m.mu.Unlock()

	if _, exists := m.exitNodes[endpoint]; !exists {
		logger.Debug("Exit node %s not found in rotation", endpoint)
		return false
	}

	delete(m.exitNodes, endpoint)
	logger.Info("Removed exit node %s from hole punch rotation", endpoint)

	// Signal the goroutine to refresh if running
	if m.running && m.updateChan != nil {
		select {
		case m.updateChan <- struct{}{}:
		default:
			// Channel full or closed, skip
		}
	}

	return true
}

// GetExitNodes returns a copy of the current exit nodes
func (m *Manager) GetExitNodes() []ExitNode {
	m.mu.Lock()
	defer m.mu.Unlock()

	nodes := make([]ExitNode, 0, len(m.exitNodes))
	for _, node := range m.exitNodes {
		nodes = append(nodes, node)
	}
	return nodes
}

// ResetInterval resets the hole punch interval back to the minimum value,
// allowing it to climb back up through exponential backoff.
// This is useful when network conditions change or connectivity is restored.
func (m *Manager) ResetInterval() {
	m.mu.Lock()
	defer m.mu.Unlock()

	if m.sendHolepunchInterval != sendHolepunchIntervalMin {
		m.sendHolepunchInterval = sendHolepunchIntervalMin
		logger.Info("Reset hole punch interval to minimum (%v)", sendHolepunchIntervalMin)
	}

	// Signal the goroutine to apply the new interval if running
	if m.running && m.updateChan != nil {
		select {
		case m.updateChan <- struct{}{}:
		default:
			// Channel full or closed, skip
		}
	}
}

// TriggerHolePunch sends an immediate hole punch packet to all configured exit nodes
// This is useful for triggering hole punching on demand without waiting for the interval
func (m *Manager) TriggerHolePunch() error {
	m.mu.Lock()

	if len(m.exitNodes) == 0 {
		m.mu.Unlock()
		return fmt.Errorf("no exit nodes configured")
	}

	// Get a copy of exit nodes to work with
	currentExitNodes := make([]ExitNode, 0, len(m.exitNodes))
	for _, node := range m.exitNodes {
		currentExitNodes = append(currentExitNodes, node)
	}
	m.mu.Unlock()

	logger.Info("Triggering on-demand hole punch to %d exit nodes", len(currentExitNodes))

	// Send hole punch to all exit nodes
	successCount := 0
	for _, exitNode := range currentExitNodes {
		host, err := util.ResolveDomain(exitNode.Endpoint)
		if err != nil {
			logger.Warn("Failed to resolve endpoint %s: %v", exitNode.Endpoint, err)
			continue
		}

		serverAddr := net.JoinHostPort(host, strconv.Itoa(int(exitNode.RelayPort)))
		remoteAddr, err := net.ResolveUDPAddr("udp", serverAddr)
		if err != nil {
			logger.Error("Failed to resolve UDP address %s: %v", serverAddr, err)
			continue
		}

		if err := m.sendHolePunch(remoteAddr, exitNode.PublicKey); err != nil {
			logger.Warn("Failed to send on-demand hole punch to %s: %v", exitNode.Endpoint, err)
			continue
		}

		logger.Debug("Sent on-demand hole punch to %s", exitNode.Endpoint)
		successCount++
	}

	if successCount == 0 {
		return fmt.Errorf("failed to send hole punch to any exit node")
	}

	logger.Info("Successfully sent on-demand hole punch to %d/%d exit nodes", successCount, len(currentExitNodes))
	return nil
}

// StartMultipleExitNodes starts hole punching to multiple exit nodes
func (m *Manager) StartMultipleExitNodes(exitNodes []ExitNode) error {
	m.mu.Lock()

	if m.running {
		m.mu.Unlock()
		logger.Debug("UDP hole punch already running, skipping new request")
		return fmt.Errorf("hole punch already running")
	}

	// Populate exit nodes map
	m.exitNodes = make(map[string]ExitNode)
	for _, node := range exitNodes {
		m.exitNodes[node.Endpoint] = node
	}

	m.running = true
	m.stopChan = make(chan struct{})
	m.updateChan = make(chan struct{}, 1)
	m.mu.Unlock()

	logger.Info("Starting UDP hole punch to %d exit nodes with shared bind", len(exitNodes))

	go m.runMultipleExitNodes()

	return nil
}

// Start starts hole punching with the current set of exit nodes
func (m *Manager) Start() error {
	m.mu.Lock()

	if m.running {
		m.mu.Unlock()
		logger.Debug("UDP hole punch already running")
		return fmt.Errorf("hole punch already running")
	}

	m.running = true
	m.stopChan = make(chan struct{})
	m.updateChan = make(chan struct{}, 1)
	nodeCount := len(m.exitNodes)
	m.mu.Unlock()

	if nodeCount == 0 {
		logger.Info("Starting UDP hole punch manager (waiting for exit nodes to be added)")
	} else {
		logger.Info("Starting UDP hole punch with %d exit nodes", nodeCount)
	}

	go m.runMultipleExitNodes()

	return nil
}

// runMultipleExitNodes performs hole punching to multiple exit nodes
func (m *Manager) runMultipleExitNodes() {
	defer func() {
		m.mu.Lock()
		m.running = false
		m.mu.Unlock()
		logger.Info("UDP hole punch goroutine ended for all exit nodes")
	}()

	// Resolve all endpoints upfront
	type resolvedExitNode struct {
		remoteAddr   *net.UDPAddr
		publicKey    string
		endpointName string
	}

	resolveNodes := func() []resolvedExitNode {
		m.mu.Lock()
		currentExitNodes := make([]ExitNode, 0, len(m.exitNodes))
		for _, node := range m.exitNodes {
			currentExitNodes = append(currentExitNodes, node)
		}
		m.mu.Unlock()

		var resolvedNodes []resolvedExitNode
		for _, exitNode := range currentExitNodes {
			host, err := util.ResolveDomain(exitNode.Endpoint)
			if err != nil {
				logger.Warn("Failed to resolve endpoint %s: %v", exitNode.Endpoint, err)
				continue
			}

			serverAddr := net.JoinHostPort(host, strconv.Itoa(int(exitNode.RelayPort)))
			remoteAddr, err := net.ResolveUDPAddr("udp", serverAddr)
			if err != nil {
				logger.Error("Failed to resolve UDP address %s: %v", serverAddr, err)
				continue
			}

			resolvedNodes = append(resolvedNodes, resolvedExitNode{
				remoteAddr:   remoteAddr,
				publicKey:    exitNode.PublicKey,
				endpointName: exitNode.Endpoint,
			})
			logger.Info("Resolved exit node: %s -> %s", exitNode.Endpoint, remoteAddr.String())
		}
		return resolvedNodes
	}

	resolvedNodes := resolveNodes()

	if len(resolvedNodes) == 0 {
		logger.Info("No exit nodes available yet, waiting for nodes to be added")
	} else {
		// Send initial hole punch to all exit nodes
		for _, node := range resolvedNodes {
			if err := m.sendHolePunch(node.remoteAddr, node.publicKey); err != nil {
				logger.Warn("Failed to send initial hole punch to %s: %v", node.endpointName, err)
			}
		}
	}

	// Start with minimum interval
	m.mu.Lock()
	m.sendHolepunchInterval = sendHolepunchIntervalMin
	m.mu.Unlock()

	ticker := time.NewTicker(m.sendHolepunchInterval)
	defer ticker.Stop()

	for {
		select {
		case <-m.stopChan:
			logger.Debug("Hole punch stopped by signal")
			return
		case <-m.updateChan:
			// Re-resolve exit nodes when update is signaled
			logger.Info("Refreshing exit nodes for hole punching")
			resolvedNodes = resolveNodes()
			if len(resolvedNodes) == 0 {
				logger.Warn("No exit nodes available after refresh")
			} else {
				logger.Info("Updated resolved nodes count: %d", len(resolvedNodes))
			}
			// Reset interval to minimum on update
			m.mu.Lock()
			m.sendHolepunchInterval = sendHolepunchIntervalMin
			m.mu.Unlock()
			ticker.Reset(m.sendHolepunchInterval)
			// Send immediate hole punch to newly resolved nodes
			for _, node := range resolvedNodes {
				if err := m.sendHolePunch(node.remoteAddr, node.publicKey); err != nil {
					logger.Debug("Failed to send hole punch to %s: %v", node.endpointName, err)
				}
			}
		case <-ticker.C:
			// Send hole punch to all exit nodes (if any are available)
			if len(resolvedNodes) > 0 {
				for _, node := range resolvedNodes {
					if err := m.sendHolePunch(node.remoteAddr, node.publicKey); err != nil {
						logger.Debug("Failed to send hole punch to %s: %v", node.endpointName, err)
					}
				}
				// Exponential backoff: double the interval up to max
				m.mu.Lock()
				newInterval := m.sendHolepunchInterval * 2
				if newInterval > sendHolepunchIntervalMax {
					newInterval = sendHolepunchIntervalMax
				}
				if newInterval != m.sendHolepunchInterval {
					m.sendHolepunchInterval = newInterval
					ticker.Reset(m.sendHolepunchInterval)
					logger.Debug("Increased hole punch interval to %v", m.sendHolepunchInterval)
				}
				m.mu.Unlock()
			}
		}
	}
}

// sendHolePunch sends an encrypted hole punch packet using the shared bind
func (m *Manager) sendHolePunch(remoteAddr *net.UDPAddr, serverPubKey string) error {
	m.mu.Lock()
	token := m.token
	ID := m.ID
	m.mu.Unlock()

	if serverPubKey == "" || token == "" {
		return fmt.Errorf("server public key or OLM token is empty")
	}

	var payload interface{}
	if m.clientType == "newt" {
		payload = struct {
			ID        string `json:"newtId"`
			Token     string `json:"token"`
			PublicKey string `json:"publicKey"`
		}{
			ID:        ID,
			Token:     token,
			PublicKey: m.publicKey,
		}
	} else {
		payload = struct {
			ID        string `json:"olmId"`
			Token     string `json:"token"`
			PublicKey string `json:"publicKey"`
		}{
			ID:        ID,
			Token:     token,
			PublicKey: m.publicKey,
		}
	}

	// Convert payload to JSON
	payloadBytes, err := json.Marshal(payload)
	if err != nil {
		return fmt.Errorf("failed to marshal payload: %w", err)
	}

	// Encrypt the payload using the server's WireGuard public key
	encryptedPayload, err := encryptPayload(payloadBytes, serverPubKey)
	if err != nil {
		return fmt.Errorf("failed to encrypt payload: %w", err)
	}

	jsonData, err := json.Marshal(encryptedPayload)
	if err != nil {
		return fmt.Errorf("failed to marshal encrypted payload: %w", err)
	}

	_, err = m.sharedBind.WriteToUDP(jsonData, remoteAddr)
	if err != nil {
		return fmt.Errorf("failed to write to UDP: %w", err)
	}

	logger.Debug("Sent UDP hole punch to %s: %s", remoteAddr.String(), string(jsonData))

	return nil
}

// encryptPayload encrypts the payload using ChaCha20-Poly1305 AEAD with X25519 key exchange
func encryptPayload(payload []byte, serverPublicKey string) (interface{}, error) {
	// Generate an ephemeral keypair for this message
	ephemeralPrivateKey, err := wgtypes.GeneratePrivateKey()
	if err != nil {
		return nil, fmt.Errorf("failed to generate ephemeral private key: %v", err)
	}
	ephemeralPublicKey := ephemeralPrivateKey.PublicKey()

	// Parse the server's public key
	serverPubKey, err := wgtypes.ParseKey(serverPublicKey)
	if err != nil {
		return nil, fmt.Errorf("failed to parse server public key: %v", err)
	}

	// Use X25519 for key exchange
	var ephPrivKeyFixed [32]byte
	copy(ephPrivKeyFixed[:], ephemeralPrivateKey[:])

	// Perform X25519 key exchange
	sharedSecret, err := curve25519.X25519(ephPrivKeyFixed[:], serverPubKey[:])
	if err != nil {
		return nil, fmt.Errorf("failed to perform X25519 key exchange: %v", err)
	}

	// Create an AEAD cipher using the shared secret
	aead, err := chacha20poly1305.New(sharedSecret)
	if err != nil {
		return nil, fmt.Errorf("failed to create AEAD cipher: %v", err)
	}

	// Generate a random nonce
	nonce := make([]byte, aead.NonceSize())
	if _, err := mrand.Read(nonce); err != nil {
		return nil, fmt.Errorf("failed to generate nonce: %v", err)
	}

	// Encrypt the payload
	ciphertext := aead.Seal(nil, nonce, payload, nil)

	// Prepare the final encrypted message
	encryptedMsg := struct {
		EphemeralPublicKey string `json:"ephemeralPublicKey"`
		Nonce              []byte `json:"nonce"`
		Ciphertext         []byte `json:"ciphertext"`
	}{
		EphemeralPublicKey: ephemeralPublicKey.String(),
		Nonce:              nonce,
		Ciphertext:         ciphertext,
	}

	return encryptedMsg, nil
}