// Package buzz implements a Channel for Buzz, a Nostr-based relay chat.
//
// Wire format: chat messages are kind:9 events scoped to a channel by an "h"
// tag. Mentions are "p" tags carrying the mentioned pubkey. The relay requires
// NIP-42 authentication (kind:22242) before it accepts a subscription.
package buzz

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"time"

	"github.com/nbd-wtf/go-nostr"
	"github.com/nbd-wtf/go-nostr/nip19"

	"github.com/sipeed/picoclaw/pkg/bus"
	"github.com/sipeed/picoclaw/pkg/channels"
	"github.com/sipeed/picoclaw/pkg/config"
	"github.com/sipeed/picoclaw/pkg/logger"
)

// kindStreamMessage is the Buzz chat message kind (NIP-29 style).
const kindStreamMessage = 9

// subscribeTimeout bounds how long Start waits for the relay to accept or
// reject a subscription before giving up.
const subscribeTimeout = 15 * time.Second

// BuzzChannel implements the Channel interface for a Buzz relay.
type BuzzChannel struct {
	*channels.BaseChannel
	bc     *config.Channel
	config *config.BuzzSettings

	secretKey string
	publicKey string

	relay  *nostr.Relay
	sub    *nostr.Subscription
	ctx    context.Context
	cancel context.CancelFunc
	wg     sync.WaitGroup
}

// NewBuzzChannel creates a new Buzz channel.
func NewBuzzChannel(
	bc *config.Channel,
	cfg *config.BuzzSettings,
	messageBus *bus.MessageBus,
) (*BuzzChannel, error) {
	if cfg.RelayURL == "" {
		return nil, fmt.Errorf("buzz relay_url is required")
	}
	if len(cfg.Channels) == 0 {
		return nil, fmt.Errorf("buzz channels is required: at least one channel ID to join")
	}

	sk, err := normalizeSecretKey(cfg.PrivateKey.String())
	if err != nil {
		return nil, err
	}
	pk, err := nostr.GetPublicKey(sk)
	if err != nil {
		return nil, fmt.Errorf("buzz private_key is not a valid secret key: %w", err)
	}

	base := channels.NewBaseChannel("buzz", cfg, messageBus, bc.AllowFrom,
		channels.WithGroupTrigger(bc.GroupTrigger),
		channels.WithReasoningChannelID(bc.ReasoningChannelID),
	)

	return &BuzzChannel{
		BaseChannel: base,
		bc:          bc,
		config:      cfg,
		secretKey:   sk,
		publicKey:   pk,
	}, nil
}

// normalizeSecretKey accepts either a 64-char hex secret key or an nsec1
// bech32 string and returns the hex form.
func normalizeSecretKey(key string) (string, error) {
	key = strings.TrimSpace(key)
	if key == "" {
		return "", fmt.Errorf("buzz private_key is required")
	}

	if strings.HasPrefix(key, "nsec1") {
		prefix, value, err := nip19.Decode(key)
		if err != nil {
			return "", fmt.Errorf("buzz private_key: invalid nsec: %w", err)
		}
		if prefix != "nsec" {
			return "", fmt.Errorf("buzz private_key: expected nsec, got %s", prefix)
		}
		sk, ok := value.(string)
		if !ok {
			return "", fmt.Errorf("buzz private_key: unexpected nsec payload")
		}
		return sk, nil
	}

	if len(key) != 64 {
		return "", fmt.Errorf("buzz private_key must be 64-char hex or an nsec1 string")
	}
	return key, nil
}

// Start connects to the relay, authenticates via NIP-42, and subscribes to the
// configured channels.
func (c *BuzzChannel) Start(ctx context.Context) error {
	logger.InfoC("buzz", "Starting Buzz channel")
	c.ctx, c.cancel = context.WithCancel(ctx)

	relay, err := nostr.RelayConnect(c.ctx, c.config.RelayURL)
	if err != nil {
		c.cancel()
		return fmt.Errorf("buzz relay connect failed: %w", err)
	}
	c.relay = relay

	channelIDs := []string(c.config.Channels)
	filters := nostr.Filters{{
		Kinds: []int{kindStreamMessage},
		Tags:  nostr.TagMap{"h": channelIDs},
	}}

	sub, err := c.subscribeAuthed(c.ctx, filters)
	if err != nil {
		_ = relay.Close()
		c.cancel()
		return err
	}
	c.sub = sub

	c.wg.Add(1)
	go func() {
		defer c.wg.Done()
		c.consume(sub)
	}()

	c.SetRunning(true)
	logger.InfoCF("buzz", "Buzz channel started", map[string]any{
		"relay":    c.config.RelayURL,
		"pubkey":   c.publicKey,
		"channels": len(channelIDs),
	})
	return nil
}

// subscribeAuthed subscribes, performing the NIP-42 handshake if the relay
// demands it.
//
// The handshake MUST be driven by the relay's rejection rather than attempted
// eagerly after connect. go-nostr stores the relay's challenge on an unexported
// field populated by its reader goroutine when the AUTH envelope arrives;
// calling Auth() straight after RelayConnect signs an auth event with an empty
// challenge tag, which every relay rejects. Waiting for "auth-required"
// guarantees the challenge has been read — the CLOSED envelope is processed
// after the AUTH envelope on that same goroutine, and receiving it over a
// channel establishes the happens-before edge that makes the read safe.
func (c *BuzzChannel) subscribeAuthed(
	ctx context.Context,
	filters nostr.Filters,
) (*nostr.Subscription, error) {
	sub, err := c.relay.Subscribe(ctx, filters)
	if err != nil {
		return nil, fmt.Errorf("buzz subscribe failed: %w", err)
	}

	select {
	case <-ctx.Done():
		return nil, ctx.Err()

	case <-sub.EndOfStoredEvents:
		// Relay accepted the subscription without requiring authentication.
		return sub, nil

	case reason := <-sub.ClosedReason:
		if !strings.HasPrefix(reason, "auth-required") {
			return nil, fmt.Errorf("buzz relay closed subscription: %s", reason)
		}
		sub.Unsub()

		if err := c.relay.Auth(ctx, func(evt *nostr.Event) error {
			return evt.Sign(c.secretKey)
		}); err != nil {
			return nil, fmt.Errorf("buzz NIP-42 auth failed: %w", err)
		}
		logger.InfoCF("buzz", "Authenticated to relay", map[string]any{
			"relay":  c.config.RelayURL,
			"pubkey": c.publicKey,
		})

		authed, err := c.relay.Subscribe(ctx, filters)
		if err != nil {
			return nil, fmt.Errorf("buzz subscribe after auth failed: %w", err)
		}
		select {
		case <-ctx.Done():
			return nil, ctx.Err()
		case <-authed.EndOfStoredEvents:
			return authed, nil
		case reason := <-authed.ClosedReason:
			// A second rejection means the identity is not permitted, not that
			// the handshake was mistimed — retrying would loop forever.
			return nil, fmt.Errorf("buzz relay rejected subscription after auth: %s", reason)
		case <-time.After(subscribeTimeout):
			return nil, fmt.Errorf("buzz timed out waiting for subscription after auth")
		}

	case <-time.After(subscribeTimeout):
		return nil, fmt.Errorf("buzz timed out waiting for relay to accept subscription")
	}
}

// Stop closes the subscription and disconnects from the relay.
func (c *BuzzChannel) Stop(ctx context.Context) error {
	logger.InfoC("buzz", "Stopping Buzz channel")
	c.SetRunning(false)

	if c.cancel != nil {
		c.cancel()
	}
	if c.sub != nil {
		c.sub.Unsub()
	}
	if c.relay != nil {
		if err := c.relay.Close(); err != nil {
			logger.WarnCF("buzz", "Relay close failed", map[string]any{"error": err.Error()})
		}
	}
	c.wg.Wait()

	logger.InfoC("buzz", "Buzz channel stopped")
	return nil
}

// Send publishes a kind:9 message scoped to the target channel.
func (c *BuzzChannel) Send(ctx context.Context, msg bus.OutboundMessage) ([]string, error) {
	if !c.IsRunning() {
		return nil, channels.ErrNotRunning
	}

	target := msg.ChatID
	if target == "" {
		return nil, fmt.Errorf("chat ID is empty: %w", channels.ErrSendFailed)
	}
	if strings.TrimSpace(msg.Content) == "" {
		return nil, nil
	}

	tags := nostr.Tags{nostr.Tag{"h", target}}
	if c.config.ReplyInThread && msg.ReplyToMessageID != "" {
		tags = append(tags, nostr.Tag{"e", msg.ReplyToMessageID, "", "reply"})
	}

	evt := nostr.Event{
		PubKey:    c.publicKey,
		CreatedAt: nostr.Now(),
		Kind:      kindStreamMessage,
		Tags:      tags,
		Content:   msg.Content,
	}
	if err := evt.Sign(c.secretKey); err != nil {
		return nil, fmt.Errorf("buzz sign failed: %w", errJoin(err, channels.ErrSendFailed))
	}

	if err := c.relay.Publish(ctx, evt); err != nil {
		return nil, fmt.Errorf("buzz publish failed: %w", errJoin(err, channels.ErrSendFailed))
	}

	logger.DebugCF("buzz", "Message sent", map[string]any{
		"channel":  target,
		"event_id": evt.ID,
	})
	return []string{evt.ID}, nil
}

// kindReaction is the NIP-25 reaction event kind.
const kindReaction = 7

// ReactToMessage implements channels.ReactionCapable.
// It publishes a NIP-25 kind:7 reaction event with content 👀 scoped to the
// same channel as the reacted message. The undo function is a no-op because
// NIP-25 does not define a standard way to remove a reaction.
func (c *BuzzChannel) ReactToMessage(ctx context.Context, chatID, messageID string) (func(), error) {
	if !c.IsRunning() {
		return func() {}, channels.ErrNotRunning
	}
	if messageID == "" {
		return func() {}, nil
	}

	evt := nostr.Event{
		PubKey:    c.publicKey,
		CreatedAt: nostr.Now(),
		Kind:      kindReaction,
		Tags: nostr.Tags{
			nostr.Tag{"e", messageID},
			nostr.Tag{"h", chatID},
		},
		Content: "👀",
	}
	if err := evt.Sign(c.secretKey); err != nil {
		return func() {}, fmt.Errorf("buzz reaction sign failed: %w", err)
	}

	if err := c.relay.Publish(ctx, evt); err != nil {
		return func() {}, fmt.Errorf("buzz reaction publish failed: %w", err)
	}

	logger.DebugCF("buzz", "Reaction sent", map[string]any{
		"channel":   chatID,
		"event_id":  evt.ID,
		"target_id": messageID,
	})
	return func() {}, nil
}

// errJoin wraps err so that errors.Is(result, sentinel) holds for the sentinel
// while preserving the underlying cause in the message.
func errJoin(err, sentinel error) error {
	return fmt.Errorf("%v: %w", err, sentinel)
}