velox-bot/internal/beta/beta.go

// Package beta gates features that are still being tried out. A beta feature
// works only for members of the beta server who have the Beta Tester role:
// the server comes from BETA_GUILD_ID and the role from BETA_ROLE_ID, both set
// by the bot's owner in its environment, so nobody can change them from
// Discord.
//
// Everything fails closed. With no role configured, or an ID that isn't a
// Discord ID, nobody gets access.
package beta

import (
	"log"
	"regexp"
	"strings"
	"sync/atomic"

	"github.com/bwmarrin/discordgo"
)

// Handler is a slash command handler.
type Handler = func(s *discordgo.Session, i *discordgo.InteractionCreate)

type settings struct{ guildID, roleID string }

var current atomic.Pointer[settings]

var snowflake = regexp.MustCompile(`^[0-9]{1,20}$`)

// idOrEmpty keeps a Discord ID and drops anything else, so a typo in the
// environment turns beta features off instead of matching something odd.
func idOrEmpty(name, v string) string {
	v = strings.TrimSpace(v)
	if v == "" {
		return ""
	}
	if !snowflake.MatchString(v) {
		log.Printf("beta: %s %q isn't a Discord ID; beta features stay locked", name, v)
		return ""
	}
	return v
}

// Configure sets the beta server and the Beta Tester role. Call it once at
// startup.
func Configure(guildID, roleID string) {
	current.Store(&settings{
		guildID: idOrEmpty("BETA_GUILD_ID", guildID),
		roleID:  idOrEmpty("BETA_ROLE_ID", roleID),
	})
}

func get() settings {
	if s := current.Load(); s != nil {
		return *s
	}
	return settings{}
}

// GuildID is the beta server, or "" when beta features are off.
func GuildID() string { return get().guildID }

// Status describes where a member stands, for the /beta command.
type Status struct {
	InBetaGuild    bool // the interaction came from the beta server
	RoleConfigured bool // the owner has set a Beta Tester role
	HasRole        bool // the member has it
}

// StatusOf reports a member's standing in the guild they're acting in.
func StatusOf(guildID string, member *discordgo.Member) Status {
	c := get()
	st := Status{
		InBetaGuild:    c.guildID != "" && guildID == c.guildID,
		RoleConfigured: c.roleID != "",
	}
	if st.InBetaGuild && st.RoleConfigured && member != nil {
		for _, r := range member.Roles {
			if r == c.roleID {
				st.HasRole = true
				break
			}
		}
	}
	return st
}

// Allowed reports whether a member may use beta features in guildID: it has
// to be the beta server, and the member has to have the Beta Tester role.
// Use it for anything that isn't a command, such as an event handler.
func Allowed(guildID string, member *discordgo.Member) bool {
	st := StatusOf(guildID, member)
	return st.InBetaGuild && st.RoleConfigured && st.HasRole
}

// AllowedInteraction is Allowed for an interaction. A DM has no member, so it
// never qualifies. The member and their roles come from Discord with the
// interaction, not from anything the user typed.
func AllowedInteraction(i *discordgo.InteractionCreate) bool {
	return i != nil && i.Interaction != nil && Allowed(i.GuildID, i.Member)
}

// respond is how a refusal is sent; tests replace it.
var respond = func(s *discordgo.Session, i *discordgo.InteractionCreate, msg string) {
	if i.Type == discordgo.InteractionApplicationCommandAutocomplete {
		// Nothing to suggest, and a message isn't a valid reply here.
		_ = s.InteractionRespond(i.Interaction, &discordgo.InteractionResponse{
			Type: discordgo.InteractionApplicationCommandAutocompleteResult,
			Data: &discordgo.InteractionResponseData{Choices: []*discordgo.ApplicationCommandOptionChoice{}},
		})
		return
	}
	_ = s.InteractionRespond(i.Interaction, &discordgo.InteractionResponse{
		Type: discordgo.InteractionResponseChannelMessageWithSource,
		Data: &discordgo.InteractionResponseData{
			Content:         msg,
			Flags:           discordgo.MessageFlagsEphemeral,
			AllowedMentions: &discordgo.MessageAllowedMentions{},
		},
	})
}

const denied = "This feature is in beta and isn't available to you yet."

// Guard is for the start of a beta feature's handler, and for its component,
// modal and autocomplete handlers too (the command's gate doesn't cover
// those). It answers the user and returns false when they aren't allowed:
//
//	if !beta.Guard(s, i) { return }
func Guard(s *discordgo.Session, i *discordgo.InteractionCreate) bool {
	if AllowedInteraction(i) {
		return true
	}
	respond(s, i, denied)
	return false
}

// Gate wraps a command handler so it only runs for beta testers.
func Gate(h Handler) Handler {
	return func(s *discordgo.Session, i *discordgo.InteractionCreate) {
		if !Guard(s, i) {
			return
		}
		h(s, i)
	}
}