package main

import (
	"bytes"
	"context"
	"fmt"
	"log"
	"time"

	"github.com/vmihailenco/msgpack/v5"

	"code.northwest.io/axon"
	"code.northwest.io/axon/relay/storage"
	"code.northwest.io/axon/relay/subscription"
	ws "code.northwest.io/axon/relay/websocket"
)

// Wire protocol message type constants.
const (
	// Client → Relay
	MsgTypeAuth        uint16 = 1
	MsgTypeSubscribe   uint16 = 2
	MsgTypeUnsubscribe uint16 = 3
	MsgTypePublish     uint16 = 4

	// Relay → Client
	MsgTypeChallenge uint16 = 10
	MsgTypeEvent     uint16 = 11
	MsgTypeEose      uint16 = 12
	MsgTypeOk        uint16 = 13
	MsgTypeError     uint16 = 14
)

// Payload types — Relay → Client

type ChallengePayload struct {
	Nonce []byte `msgpack:"nonce"`
}

type EventPayload struct {
	SubID string     `msgpack:"sub_id"`
	Event axon.Event `msgpack:"event"`
}

type EosePayload struct {
	SubID string `msgpack:"sub_id"`
}

type OkPayload struct {
	Message string `msgpack:"message"`
}

type ErrorPayload struct {
	Code    uint16 `msgpack:"code"`
	Message string `msgpack:"message"`
}

// Payload types — Client → Relay

type AuthPayload struct {
	PubKey []byte `msgpack:"pubkey"`
	Sig    []byte `msgpack:"sig"`
}

type SubscribePayload struct {
	SubID  string      `msgpack:"sub_id"`
	Filter axon.Filter `msgpack:"filter"`
}

type UnsubscribePayload struct {
	SubID string `msgpack:"sub_id"`
}

type PublishPayload struct {
	Event axon.Event `msgpack:"event"`
}

// conn holds per-connection state.
type conn struct {
	id        string // unique connection ID (hex nonce for logging)
	ws        *ws.Conn
	store     *storage.Storage
	global    *subscription.GlobalManager
	allowlist [][]byte
	relayURL  string

	authed bool
	pubkey []byte
	nonce  []byte

	mgr *subscription.Manager
}

// send encodes and writes a wire message to the client.
func (c *conn) send(msgType uint16, payload interface{}) error {
	b, err := msgpack.Marshal([]interface{}{msgType, payload})
	if err != nil {
		return fmt.Errorf("handler: marshal msg %d: %w", msgType, err)
	}
	return c.ws.Write(b)
}

// sendError sends an ErrorPayload. If fatal is true the connection is then closed.
func (c *conn) sendError(code uint16, message string, fatal bool) {
	_ = c.send(MsgTypeError, ErrorPayload{Code: code, Message: message})
	if fatal {
		c.ws.Close(1000, "")
	}
}

// serve is the main per-connection loop.
func (c *conn) serve(ctx context.Context) {
	defer func() {
		c.mgr.CloseAll()
		c.global.UnregisterConn(c.id)
	}()

	// Send challenge immediately on connect.
	if err := c.send(MsgTypeChallenge, ChallengePayload{Nonce: c.nonce}); err != nil {
		log.Printf("conn %s: send challenge: %v", c.id, err)
		return
	}

	// Start ping goroutine.
	pingStop := make(chan struct{})
	defer close(pingStop)
	go c.pingLoop(pingStop)

	for {
		raw, err := c.ws.Read(ctx)
		if err != nil {
			if ctx.Err() != nil {
				return
			}
			// Connection closed or read error.
			return
		}

		if err := c.dispatch(ctx, raw); err != nil {
			log.Printf("conn %s: dispatch: %v", c.id, err)
			return
		}
	}
}

// pingLoop sends a WebSocket ping every 30 seconds. If two consecutive pings
// go unanswered (no pong received within 30s each) the connection is closed.
func (c *conn) pingLoop(stop <-chan struct{}) {
	ticker := time.NewTicker(30 * time.Second)
	defer ticker.Stop()
	missed := 0
	for {
		select {
		case <-stop:
			return
		case <-ticker.C:
			if err := c.ws.Ping(); err != nil {
				return
			}
			missed++
			if missed >= 2 {
				log.Printf("conn %s: missed 2 pings, closing", c.id)
				c.ws.Close(1001, "ping timeout")
				return
			}
		}
	}
}

// dispatch parses a raw message and routes it to the appropriate handler.
func (c *conn) dispatch(ctx context.Context, raw []byte) error {
	// Decode as [uint16, rawPayload]
	var arr []msgpack.RawMessage
	if err := msgpack.Unmarshal(raw, &arr); err != nil {
		c.sendError(400, "malformed message", false)
		return nil
	}
	if len(arr) < 2 {
		c.sendError(400, "message too short", false)
		return nil
	}

	var msgType uint16
	if err := msgpack.Unmarshal(arr[0], &msgType); err != nil {
		c.sendError(400, "invalid message type", false)
		return nil
	}

	// Only MsgTypeAuth is allowed before authentication.
	if !c.authed && msgType != MsgTypeAuth {
		c.sendError(401, "not authenticated", true)
		return fmt.Errorf("unauthenticated message type %d", msgType)
	}

	switch msgType {
	case MsgTypeAuth:
		return c.handleAuth(arr[1])
	case MsgTypePublish:
		return c.handlePublish(ctx, arr[1])
	case MsgTypeSubscribe:
		return c.handleSubscribe(ctx, arr[1])
	case MsgTypeUnsubscribe:
		return c.handleUnsubscribe(arr[1])
	default:
		c.sendError(400, fmt.Sprintf("unknown message type %d", msgType), false)
	}
	return nil
}

// handleAuth processes an Auth message.
func (c *conn) handleAuth(raw msgpack.RawMessage) error {
	var p AuthPayload
	if err := msgpack.Unmarshal(raw, &p); err != nil {
		c.sendError(400, "malformed auth payload", true)
		return fmt.Errorf("unmarshal auth: %w", err)
	}

	if len(p.PubKey) != 32 {
		c.sendError(400, "pubkey must be 32 bytes", true)
		return fmt.Errorf("bad pubkey length %d", len(p.PubKey))
	}

	if !axon.VerifyChallenge(p.PubKey, c.nonce, c.relayURL, p.Sig) {
		c.sendError(401, "invalid signature", true)
		return fmt.Errorf("auth signature invalid")
	}

	// Check allowlist.
	if len(c.allowlist) > 0 {
		allowed := false
		for _, pk := range c.allowlist {
			if bytes.Equal(pk, p.PubKey) {
				allowed = true
				break
			}
		}
		if !allowed {
			c.sendError(403, "pubkey not in allowlist", true)
			return fmt.Errorf("pubkey not in allowlist")
		}
	}

	c.authed = true
	c.pubkey = p.PubKey
	return c.send(MsgTypeOk, OkPayload{Message: "authenticated"})
}

// handlePublish processes a Publish message.
func (c *conn) handlePublish(ctx context.Context, raw msgpack.RawMessage) error {
	var p PublishPayload
	if err := msgpack.Unmarshal(raw, &p); err != nil {
		c.sendError(400, "malformed publish payload", false)
		return nil
	}

	event := &p.Event

	// Content length check.
	if len(event.Content) > 65536 {
		c.sendError(413, "content exceeds 64KB limit", false)
		return nil
	}

	// Signature verification.
	if err := axon.Verify(event); err != nil {
		c.sendError(400, fmt.Sprintf("invalid event: %v", err), false)
		return nil
	}

	// Job request expiry check (kinds 5000–5999).
	if event.Kind >= 5000 && event.Kind < 6000 {
		if expired, err := isExpired(event); err != nil {
			c.sendError(400, fmt.Sprintf("bad expires_at tag: %v", err), false)
			return nil
		} else if expired {
			c.sendError(400, "job request has expired", false)
			return nil
		}
	}

	// Marshal envelope bytes for storage and fanout.
	envelopeBytes, err := axon.MarshalEvent(event)
	if err != nil {
		c.sendError(400, "could not marshal event", false)
		return nil
	}

	// Ephemeral events (3000–3999): fanout only, do not store.
	isEphemeral := event.Kind >= 3000 && event.Kind < 4000

	if !isEphemeral {
		// Duplicate check.
		exists, err := c.store.ExistsByID(ctx, event.ID)
		if err != nil {
			c.sendError(500, "internal error", false)
			return fmt.Errorf("exists check: %w", err)
		}
		if exists {
			c.sendError(409, "duplicate event", false)
			return nil
		}

		// Persist.
		if err := c.store.StoreEvent(ctx, event, envelopeBytes); err != nil {
			if err == storage.ErrDuplicate {
				c.sendError(409, "duplicate event", false)
				return nil
			}
			c.sendError(500, "internal error", false)
			return fmt.Errorf("store event: %w", err)
		}
	}

	// Fanout to all matching subscribers.
	c.global.Fanout(event, envelopeBytes)

	return c.send(MsgTypeOk, OkPayload{Message: "ok"})
}

// handleSubscribe processes a Subscribe message.
func (c *conn) handleSubscribe(ctx context.Context, raw msgpack.RawMessage) error {
	var p SubscribePayload
	if err := msgpack.Unmarshal(raw, &p); err != nil {
		c.sendError(400, "malformed subscribe payload", false)
		return nil
	}
	if p.SubID == "" {
		c.sendError(400, "sub_id required", false)
		return nil
	}

	// Query historical events.
	envelopes, err := c.store.QueryEvents(ctx, []axon.Filter{p.Filter})
	if err != nil {
		c.sendError(500, "internal error", false)
		return fmt.Errorf("query events: %w", err)
	}

	for _, envBytes := range envelopes {
		ev, err := axon.UnmarshalEvent(envBytes)
		if err != nil {
			log.Printf("conn %s: unmarshal stored event: %v", c.id, err)
			continue
		}
		if err := c.send(MsgTypeEvent, EventPayload{SubID: p.SubID, Event: *ev}); err != nil {
			return err
		}
	}

	// Send EOSE.
	if err := c.send(MsgTypeEose, EosePayload{SubID: p.SubID}); err != nil {
		return err
	}

	// Register for live fanout.
	sub := c.mgr.Add(p.SubID, []axon.Filter{p.Filter})
	c.global.Register(c.id, p.SubID, sub)

	// Start goroutine to stream live events to this client.
	go c.streamSub(sub)

	return nil
}

// streamSub reads from a subscription's Events channel and sends them to the
// client. Returns when the subscription or connection is closed.
func (c *conn) streamSub(sub *subscription.Subscription) {
	for envelopeBytes := range sub.Events {
		ev, err := axon.UnmarshalEvent(envelopeBytes)
		if err != nil {
			log.Printf("conn %s: sub %s: unmarshal live event: %v", c.id, sub.ID, err)
			continue
		}
		if err := c.send(MsgTypeEvent, EventPayload{SubID: sub.ID, Event: *ev}); err != nil {
			return
		}
	}
}

// handleUnsubscribe processes an Unsubscribe message.
func (c *conn) handleUnsubscribe(raw msgpack.RawMessage) error {
	var p UnsubscribePayload
	if err := msgpack.Unmarshal(raw, &p); err != nil {
		c.sendError(400, "malformed unsubscribe payload", false)
		return nil
	}
	c.mgr.Remove(p.SubID)
	c.global.Unregister(c.id, p.SubID)
	return nil
}

// isExpired checks the expires_at tag on a job request event.
// Returns (true, nil) if the event is expired, (false, nil) if not, or
// (false, err) if the tag is malformed.
func isExpired(event *axon.Event) (bool, error) {
	for _, tag := range event.Tags {
		if tag.Name != "expires_at" {
			continue
		}
		if len(tag.Values) == 0 {
			continue
		}
		var ts int64
		_, err := fmt.Sscanf(tag.Values[0], "%d", &ts)
		if err != nil {
			return false, fmt.Errorf("parse expires_at: %w", err)
		}
		return time.Now().Unix() > ts, nil
	}
	return false, nil
}