login: relocate shared login finalization logic into embedded struct

All of the login methods need to do (effectively) the same thing once we
have a token, so refactor this out into something we can reuse.

pkg/connector/login_generic.go

@@ -0,0 +1,114 @@
+// mautrix-discord - A Matrix-Discord puppeting bridge.
+// Copyright (C) 2024 Tulir Asokan
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package connector
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/bwmarrin/discordgo"
+	"github.com/rs/zerolog"
+	"maunium.net/go/mautrix/bridgev2"
+	"maunium.net/go/mautrix/bridgev2/database"
+	"maunium.net/go/mautrix/bridgev2/networkid"
+)
+
+// DiscordGenericLogin is embedded within each struct that implements
+// bridgev2.LoginProcess in order to encapsulate the common behavior that needs
+// to occur after procuring a valid user token. Namely, creating a gateway
+// connection to Discord and an associated UserLogin to wrap things up.
+//
+// It also implements a baseline Cancel method that closes the gateway
+// connection.
+type DiscordGenericLogin struct {
+	User      *bridgev2.User
+	connector *DiscordConnector
+
+	Session *discordgo.Session
+
+	// The Discord user we've authenticated as. This is only non-nil if
+	// a call to FinalizeCreatingLogin has succeeded.
+	DiscordUser *discordgo.User
+}
+
+func (dl *DiscordGenericLogin) FinalizeCreatingLogin(ctx context.Context, token string) (*bridgev2.UserLogin, error) {
+	session, err := NewDiscordSession(ctx, token)
+	if err != nil {
+		return nil, fmt.Errorf("couldn't create discord session: %w", err)
+	}
+
+	client := DiscordClient{
+		connector: dl.connector,
+		Session:   session,
+	}
+	client.SetUp(ctx, nil)
+
+	err = client.connect(ctx)
+	if err != nil {
+		dl.Cancel()
+		return nil, err
+	}
+	// At this point we've opened a WebSocket connection to the gateway, received
+	// a READY packet, and know who we are.
+	user := session.State.User
+	dl.DiscordUser = user
+
+	dl.Session = session
+	ul, err := dl.User.NewLogin(ctx, &database.UserLogin{
+		ID: networkid.UserLoginID(user.ID),
+		Metadata: &UserLoginMetadata{
+			Token:            token,
+			HeartbeatSession: session.HeartbeatSession,
+		},
+	}, &bridgev2.NewLoginParams{
+		LoadUserLogin: func(ctx context.Context, login *bridgev2.UserLogin) error {
+			login.Client = &client
+			client.UserLogin = login
+
+			// Only now that we have a UserLogin can we begin syncing.
+			client.BeginSyncingIfUserLoginPresent(ctx)
+			return nil
+		},
+		DeleteOnConflict:  true,
+		DontReuseExisting: false,
+	})
+	if err != nil {
+		dl.Cancel()
+		return nil, fmt.Errorf("couldn't create login: %w", err)
+	}
+
+	zerolog.Ctx(ctx).Info().
+		Str("user_id", user.ID).
+		Str("user_username", user.Username).
+		Msg("Logged in to Discord")
+
+	return ul, nil
+}
+
+func (dl *DiscordGenericLogin) CompleteInstructions() string {
+	return fmt.Sprintf("Logged in as %s", dl.DiscordUser.Username)
+}
+
+func (dl *DiscordGenericLogin) Cancel() {
+	if dl.Session != nil {
+		dl.User.Log.Debug().Msg("Login cancelled, closing session")
+		err := dl.Session.Close()
+		if err != nil {
+			dl.User.Log.Err(err).Msg("Couldn't close Discord session in response to login cancellation")
+		}
+	}
+}