discord/interaction.go

package discord

import (
	"bytes"
	"crypto/ed25519"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
)

type InteractionContextType int

const (
	InteractionContextTypeGuild InteractionContextType = iota
	InteractionContextTypeBotDM
	InteractionContextTypePrivateChannel
)

type InteractionType int

const (
	InteractionTypePing InteractionType = iota + 1
	InteractionTypeApplicationCommand
	InteractionTypeMessageComponent
	InteractionTypeApplicationCommandAutocomplete
	InteractionTypeModalSubmit
)

type Interaction[T any] struct {
	ID             string          `json:"id"`
	ApplicationID  string          `json:"application_id"`
	Type           InteractionType `json:"type"`
	Data           T               `json:"data"`
	Guild          any             `json:"guild"` // TODO: Partial guilds
	GuildID        string          `json:"guild_id"`
	Channel        any             `json:"channel"` // TODO: Partial channels
	ChannelID      string          `json:"channel_id"`
	Member         GuildMember     `json:"member"` // TODO: Guild member object
	User           User            `json:"user"`
	Token          string          `json:"token"`
	Version        int             `json:"version"`
	Message        any             `json:"message"` // TODO: Message object
	AppPermissions string          `json:"app_permissions"`
	GuildLocale    string          `json:"guild_locale"`
	Entitlements   []any           `json:"entitlements"` // TODO: Entitlements

	Context             InteractionContextType `json:"context"`
	AttachmentSizeLimit int                    `json:"attachment_size_limit"`

	AuthorizingIntegrationOwners map[string]any `json:"authorizing_integration_owners"` // TODO: Yeah maybe not?

	followupCount int
}

func (i *Interaction[T]) CallbackURL() string {
	return fmt.Sprintf(
		"https://discord.com/api/v10/interactions/%s/%s/callback",
		i.ID, i.Token,
	)
}

func (i *Interaction[T]) FollowupURL() string {
	return fmt.Sprintf(
		"https://discord.com/api/v10/webhooks/%s/%s", i.ApplicationID, i.Token,
	)
}

func (i *Interaction[T]) Reply(token string, message ComponentsV2Message) (*http.Response, error) {
	return requestWithToken(
		token, http.DefaultClient, "POST", i.CallbackURL(),
		InteractionResponse[ComponentsV2Message]{
			Type: InteractionResponseTypeChannelMessageWithSource,
			Data: message,
		},
	)
}

func (i *Interaction[T]) Defer(token string) (*http.Response, error) {
	return requestWithToken(
		token, http.DefaultClient, "POST", i.CallbackURL(),
		InteractionResponse[any]{
			Type: InteractionResponseTypeDeferredChannelMessageWithSource,
		},
	)
}

func (i *Interaction[T]) Followup(msg ComponentsV2Message) (*http.Response, error) {
	if i.followupCount >= 5 {
		return nil, errors.New("too many followups")
	}

	buf := &bytes.Buffer{}
	err := json.NewEncoder(buf).Encode(msg)
	if err != nil {
		return nil, err
	}

	url := "https://discord.com/api/v10/webhooks/" + i.ApplicationID + "/" + i.Token

	req, err := http.NewRequest("POST", url, buf)
	if err != nil {
		return nil, err
	}

	req.Header.Set("Content-Type", "application/json")

	resp, err := http.DefaultClient.Do(req)
	i.followupCount++

	return resp, err
}

type InteractionResponseType int

const (
	InteractionResponseTypePong InteractionResponseType = 1

	InteractionResponseTypeChannelMessageWithSource InteractionResponseType = iota + 3
	InteractionResponseTypeDeferredChannelMessageWithSource
	InteractionResponseTypeDeferredUpdateMessage
	InteractionResponseTypeUpdateMessage
	InteractionResponseTypeApplicationCommandAutocompleteResult
	InteractionResponseTypeModal

	InteractionResponseTypePremiumRequired // deprecated

	InteractionResponseTypeLaunchActivity InteractionResponseType = 12
)

type InteractionResponse[T any] struct {
	Type InteractionResponseType `json:"type"`
	Data T                       `json:"data,omitempty"`
}

func VerifyHTTPInteraction(publicKey ed25519.PublicKey, r *http.Request) (*Interaction[any], []byte, error) {
	sigHeader := r.Header.Get("X-Signature-Ed25519")
	signature, err := hex.DecodeString(sigHeader)
	if err != nil {
		return nil, nil, err
	}

	timestamp := []byte(r.Header.Get("X-Signature-Timestamp"))

	bs, err := io.ReadAll(r.Body)
	if err != nil {
		return nil, nil, err
	}

	ok := ed25519.Verify(publicKey, append(timestamp, bs...), signature)

	if !ok {
		return nil, nil, errors.New("unable to verify ed25519 signature")
	}

	req := Interaction[any]{}

	err = json.Unmarshal(bs, &req)
	return &req, bs, err
}