Create discord package and connect/disconnect handlers

This change moves the discord session singleton to the internal/discord
package, and implements basic Connect/Disconnect handlers.

internal/discord/discord.go

@@ -0,0 +1,64 @@
+package discord
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/bwmarrin/discordgo"
+	"gitlab.com/whom/bingobot/internal/logging"
+)
+
+type Session struct {
+	connected bool
+	s         *discordgo.Session
+}
+
+var (
+	session *Session
+
+	ErrNotConnected = errors.New("session not connected")
+)
+
+func Connect(token string) error {
+	// throw away err because discordgo.New() actually can't return an error.
+	// https://github.com/bwmarrin/discordgo/blob/da9e191069d09e1b467145f5758d9b11cb9cca0d/discord.go#L32
+	s, _ := discordgo.New("Bot " + token)
+
+	session = &Session{
+		s: s,
+	}
+
+	addHandlers()
+
+	err := session.s.Open()
+
+	if err != nil {
+		return fmt.Errorf("failed to open discord session: %s", err)
+	}
+
+	return nil
+}
+
+func Close() {
+	err := session.s.Close()
+
+	if err != nil {
+		// don't bubble up this error because we can't do anything about it and
+		// the bot is exiting anyway.
+		logging.Error("could not close discord session gracefully", "type", "error", "error", err)
+	}
+
+	session.connected = false
+}
+
+func Connected() bool {
+	return session.connected
+}
+
+func User(uid string) (*discordgo.User, error) {
+	if !Connected() {
+		return nil, ErrNotConnected
+	}
+
+	return session.s.User(uid)
+}