// Package beta gates features that are still being tried out.
//
// A beta feature works for a beta tester, in a server where beta features are
// on:
//
//   - A beta tester is a member of the beta server who has the Beta Tester
//     role. Both are chosen by the bot's owner on the dashboard.
//   - Beta features are on in the beta server itself, and in every other
//     server whose owner opted in on the dashboard. A feature that can act on
//     a whole server never reaches a server that didn't ask for it.
//
// Being a tester is about the person, so it is looked up in the beta server
// even when they use a feature somewhere else (see SetRolesLookup). Beta
// never replaces a feature's own permission checks: a beta command that needs
// Manage Server still needs it.
//
// Features that act without anyone running a command (an event handler, a
// background job) have no person to check, so they use ServerEnabled only.
//
// Everything fails closed. With no role configured, an ID that isn't a
// Discord ID, or a lookup that fails, nobody gets access.
package beta

import (
	"log"
	"regexp"
	"slices"
	"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
	servers         map[string]bool // opted-in servers, besides the beta server
}

var current atomic.Pointer[settings]

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

// idOrEmpty keeps a Discord ID and drops anything else, so a bad value 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; ignoring it", name, v)
		return ""
	}
	return v
}

// Configure sets the beta server, the Beta Tester role and the servers that
// opted in. It replaces everything set before, so call it with the full
// picture each time.
func Configure(guildID, roleID string, servers []string) {
	set := make(map[string]bool, len(servers))
	for _, id := range servers {
		if id = idOrEmpty("beta server", id); id != "" {
			set[id] = true
		}
	}
	current.Store(&settings{
		guildID: idOrEmpty("beta server", guildID),
		roleID:  idOrEmpty("beta role", roleID),
		servers: set,
	})
}

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

// RolesFunc returns a member's role IDs in a server, as Discord has them now,
// or an error (including "not in that server").
type RolesFunc func(guildID, userID string) ([]string, error)

var lookup atomic.Pointer[RolesFunc]

// SetRolesLookup tells the package how to find someone's roles in the beta
// server when they use a feature in another server. Without it, testers only
// qualify in the beta server itself.
func SetRolesLookup(f RolesFunc) { lookup.Store(&f) }

// GuildID is the beta server, or "" when it isn't set.
func GuildID() string { return get().guildID }

// Servers lists the servers that opted in, besides the beta server, in a
// stable order.
func Servers() []string {
	c := get()
	out := make([]string, 0, len(c.servers))
	for id := range c.servers {
		if id != c.guildID {
			out = append(out, id)
		}
	}
	slices.Sort(out)
	return out
}

// ServerEnabled reports whether beta features are on in a server: the beta
// server, or one whose owner opted in. Use it alone for anything no person
// triggers.
func ServerEnabled(guildID string) bool {
	c := get()
	return guildID != "" && (guildID == c.guildID || c.servers[guildID])
}

// Status describes where a member stands, for the /beta command.
type Status struct {
	ServerEnabled  bool // beta features are on in this server
	RoleConfigured bool // the owner has set a Beta Tester role
	HasRole        bool // the member is a tester
}

// StatusOf reports a member's standing in the server they're acting in.
func StatusOf(guildID string, member *discordgo.Member) Status {
	c := get()
	st := Status{
		ServerEnabled:  ServerEnabled(guildID),
		RoleConfigured: c.roleID != "",
	}
	if st.ServerEnabled && st.RoleConfigured && member != nil {
		st.HasRole = isTester(c, guildID, member)
	}
	return st
}

// isTester checks the Beta Tester role in the beta server. In the beta server
// the roles come with the interaction. Anywhere else they are looked up.
func isTester(c settings, guildID string, member *discordgo.Member) bool {
	if guildID == c.guildID {
		return slices.Contains(member.Roles, c.roleID)
	}
	f := lookup.Load()
	if f == nil || *f == nil || member.User == nil || member.User.ID == "" {
		return false
	}
	roles, err := (*f)(c.guildID, member.User.ID)
	if err != nil {
		return false
	}
	return slices.Contains(roles, c.roleID)
}

// Allowed reports whether a member may use beta features in guildID: beta
// features have to be on there, and the member has to be a tester. Use it for
// anything a person triggers that isn't a command, such as a button.
func Allowed(guildID string, member *discordgo.Member) bool {
	st := StatusOf(guildID, member)
	return st.ServerEnabled && st.RoleConfigured && st.HasRole
}

// AllowedInteraction is Allowed for an interaction. A DM has no member, so it
// never qualifies. The member comes 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 or this server 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)
	}
}