Add rock, paper, scissors command

bot/bot.go

@@ -55,6 +55,11 @@ func (b *Bot) RegisterCommands() {
 		Func:  b.RollCommand(),
 		NArgs: 1,
 	})
+	AddCommand(&Command{
+		Name:  "rps",
+		Func:  b.RpsCommand(),
+		NArgs: 1,
+	})
 	AddCommand(&Command{
 		Name:  "time",
 		Func:  b.TimeCommand(),

bot/rps.go

@@ -0,0 +1,84 @@
+package bot
+
+import (
+	"fmt"
+	"math/rand"
+	"strings"
+
+	"github.com/bwmarrin/discordgo"
+)
+
+const (
+	Rock = iota
+	Paper
+	Scissors
+)
+
+var (
+	rpsVictoryMap map[int]int = map[int]int{
+		Rock:     Scissors,
+		Paper:    Rock,
+		Scissors: Paper,
+	}
+
+	rpsChoiceMap map[string]int = map[string]int{
+		"rock":     Rock,
+		"paper":    Paper,
+		"scissors": Scissors,
+	}
+
+	rpsEmojiMap map[int]string = map[int]string{
+		Rock:     "🪨️",
+		Paper:    "📝",
+		Scissors: "✂️",
+	}
+)
+
+func RpsRand() int {
+	n := rand.Intn(len(rpsVictoryMap))
+	i := 0
+	for _, v := range rpsChoiceMap {
+		if i == n {
+			return v
+		}
+		i++
+	}
+	panic("unreachable")
+}
+
+func (b *Bot) RpsCommand() CommandFunc {
+	return func(args []string, m *discordgo.MessageCreate) error {
+		var (
+			botChoice, playerChoice int
+			botEmoji, playerEmoji   string
+			c                       string
+		)
+
+		if len(args) != 1 {
+			b.Session.ChannelMessageSend(m.ChannelID, "help: `!rps (rock | paper | scissors)`")
+			return nil
+		}
+
+		c = strings.ToLower(args[0])
+
+		playerChoice, ok := rpsChoiceMap[c]
+		if !ok {
+			b.Session.ChannelMessageSend(m.ChannelID, "help: `!rps (rock | paper | scissors)`")
+		}
+
+		botChoice = RpsRand()
+		botEmoji = rpsEmojiMap[botChoice]
+		playerEmoji = rpsEmojiMap[playerChoice]
+
+		if botChoice == playerChoice {
+			b.Session.ChannelMessageSend(m.ChannelID, fmt.Sprintf("%s v %s: draw", botEmoji, playerEmoji))
+			return nil
+		} else if rpsVictoryMap[botChoice] == playerChoice {
+			b.Session.ChannelMessageSend(m.ChannelID, fmt.Sprintf("%s v %s: bot wins", botEmoji, playerEmoji))
+			return nil
+		}
+
+		b.Session.ChannelMessageSend(m.ChannelID, fmt.Sprintf("%s v %s: you win", botEmoji, playerEmoji))
+		return nil
+	}
+}