tgex-backend/tg_parser/internal/usecase/fetch_channels.go

package usecase

import (
	"context"
	"errors"
	"fmt"

	"github.com/TelegramExchange/pkg/transaction"
	"github.com/gotd/td/tgerr"
	"github.com/rs/zerolog/log"

	"github.com/TelegramExchange/tgex-backend/tg_parser/internal/domain"
)

func (uc *UseCase) FetchChannels(ctx context.Context) error {
	channels := uc.database.GetChannels(ctx)

	for _, c := range channels {
		if c.Pts == 0 {
			go uc.initializeChannel(ctx, c)
			continue
		}

		err := uc.processChannel(ctx, c)
		if err != nil {
			if isPrivateChannelError(err) {
				log.Warn().Int64("telegram_id", c.TelegramID).Msg("Private channel, attempting rejoin")
				go uc.rejoinChannel(ctx, c)

				return nil
			}
			return fmt.Errorf("uc.processChannel: %w", err)
		}
	}

	return nil
}

func isPrivateChannelError(err error) bool {
	return tgerr.Is(err, "CHANNEL_PRIVATE", "CHANNEL_INVALID", "CHANNEL_FORBIDDEN")
}

func (uc *UseCase) processChannel(ctx context.Context, channel domain.Channel) error {
	diff, err := uc.telegram.GetChannelDiff(ctx, channel, 20)
	if err != nil {
		return fmt.Errorf("telegram.GetChannelDiff: %w", err)
	}

	for _, p := range diff.NewPosts {
		log.Info().Msgf("New post: %s - Views: %d, Text: %.10s...", p.Link, p.Views, p.Text)

		err = uc.database.CreatePost(ctx, p)
		if err != nil {
			return fmt.Errorf("database.CreatePost: %w", err)
		}
	}

	for _, p := range diff.DeletedPosts {
		log.Info().Msgf("Deleted post: %s - Views: %d", p.Link, p.Views)

		err = uc.database.DeletePost(ctx, p)
		if err != nil {
			return fmt.Errorf("database.DeletePost: %w", err)
		}
	}

	// Update channel metadata if changed
	if diff.UpdatedChannel != nil {
		diff.UpdatedChannel.Pts = diff.NewPts
		err = uc.database.UpdateChannel(ctx, *diff.UpdatedChannel)
		if err != nil {
			return fmt.Errorf("database.UpdateChannel: %w", err)
		}

		return nil
	}

	channel.Pts = diff.NewPts
	err = uc.database.UpdateChannel(ctx, channel)
	if err != nil {
		return fmt.Errorf("database.UpdateChannel: %w", err)
	}

	return nil
}

func (uc *UseCase) rejoinChannel(ctx context.Context, channel domain.Channel) {
	defer func() {
		err := uc.database.UpdateChannel(ctx, channel)
		if err != nil {
			log.Err(err).Msg("database.UpdateChannel (rejoinChannel)")
		}
	}()

	if channel.InviteLink == "" {
		log.Warn().Int64("telegram_id", channel.TelegramID).Msg("No invite link stored, marking inaccessible")
		channel.IsAccessible = false

		return
	}

	updated, err := uc.telegram.ParseChannelMetaByInvite(ctx, channel.InviteLink)
	if err != nil {
		log.Warn().Err(err).Int64("telegram_id", channel.TelegramID).Msg("Invite rejoin failed, marking inaccessible")
		channel.IsAccessible = false

		return
	}

	channel.TelegramID = updated.TelegramID
	channel.Title = updated.Title
	channel.AccessHash = 0
	channel.Pts = 0
	channel.IsAccessible = true
}

func (uc *UseCase) initializeChannel(ctx context.Context, channel domain.Channel) {
	var (
		updated domain.Channel
		err     error
	)

	switch {
	case channel.Username != "":
		updated, err = uc.telegram.ParseChannelMeta(ctx, channel.Username)
	case channel.InviteLink != "":
		updated, err = uc.telegram.ParseChannelMetaByInvite(ctx, channel.InviteLink)
	default:
		err = errors.New("channel state invalid")
	}
	if err != nil {
		if isPrivateChannelError(err) {
			channel.IsAccessible = false

			err = uc.database.UpdateChannel(ctx, channel)
			if err != nil {
				log.Err(err).Msg("initializeChannel.uc.database.UpdateChannel")
			}
		}

		log.Error().Err(err).Msg("initializeChannel.ParseChannel")
		return
	}

	channel.Title = updated.Title
	channel.AccessHash = updated.AccessHash
	channel.Pts = updated.Pts

	const initPosts = 20
	posts, err := uc.telegram.GetChannelHistory(ctx, channel, initPosts)
	if err != nil {
		log.Error().Err(err).Msg("telegram.GetChannelHistory")
		return
	}

	err = transaction.Wrap(ctx, func(ctx context.Context) error {
		err = uc.database.UpdateChannel(ctx, channel)
		if err != nil {
			return fmt.Errorf("database.UpdateChannel: %w", err)
		}

		for _, p := range posts {
			log.Info().Msgf("New post (init): %s - Views: %d", p.Link, p.Views)

			err = uc.database.CreatePost(ctx, p)
			if err != nil {
				return fmt.Errorf("database.CreatePost: %w", err)
			}
		}
		return nil
	})
	if err != nil {
		log.Error().Err(err).Msg("transaction.Wrap")
	}
}