package dm

import (
	"context"
	"errors"
	"fmt"

	gn "github.com/nbd-wtf/go-nostr"
	"github.com/nbd-wtf/go-nostr/keyer"
	"github.com/nbd-wtf/go-nostr/nip04"
	"github.com/nbd-wtf/go-nostr/nip59"
)

var ErrUnsupportedKind = errors.New("unsupported DM kind")

// BuildEvent builds the kind-4 or kind-1059 event(s) for a DM.
// For kind 1059 it returns the gift wrap addressed to the recipient.
// For kind 4 it returns a single signed event.
func BuildEvent(kind int, senderSk, recipientHex, content string) ([]gn.Event, error) {
	switch kind {
	case 4:
		return buildNip04(senderSk, recipientHex, content)
	case 1059:
		return buildNip17(senderSk, recipientHex, content)
	default:
		return nil, fmt.Errorf("%w: %d", ErrUnsupportedKind, kind)
	}
}

func buildNip04(sk, recipient, content string) ([]gn.Event, error) {
	shared, err := nip04.ComputeSharedSecret(recipient, sk)
	if err != nil {
		return nil, fmt.Errorf("nip04 shared: %w", err)
	}
	enc, err := nip04.Encrypt(content, shared)
	if err != nil {
		return nil, fmt.Errorf("nip04 encrypt: %w", err)
	}
	pk, err := gn.GetPublicKey(sk)
	if err != nil {
		return nil, err
	}
	ev := gn.Event{
		PubKey:    pk,
		CreatedAt: gn.Now(),
		Kind:      4,
		Tags:      gn.Tags{{"p", recipient}},
		Content:   enc,
	}
	if err := ev.Sign(sk); err != nil {
		return nil, fmt.Errorf("sign: %w", err)
	}
	return []gn.Event{ev}, nil
}

func buildNip17(sk, recipient, content string) ([]gn.Event, error) {
	ks, err := keyer.NewPlainKeySigner(sk)
	if err != nil {
		return nil, fmt.Errorf("keyer: %w", err)
	}
	ctx := context.Background()
	ourPubkey, err := ks.GetPublicKey(ctx)
	if err != nil {
		return nil, err
	}

	rumor := gn.Event{
		Kind:      gn.KindDirectMessage,
		Content:   content,
		Tags:      gn.Tags{{"p", recipient}},
		CreatedAt: gn.Now(),
		PubKey:    ourPubkey,
	}
	rumor.ID = rumor.GetID()

	wrap, err := nip59.GiftWrap(
		rumor,
		recipient,
		func(s string) (string, error) { return ks.Encrypt(ctx, s, recipient) },
		func(e *gn.Event) error { return ks.SignEvent(ctx, e) },
		nil,
	)
	if err != nil {
		return nil, fmt.Errorf("nip17 giftwrap: %w", err)
	}
	return []gn.Event{wrap}, nil
}