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

package usecase

import (
	"context"
	"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 {
			updatedChannel, err := uc.initializeChannel(ctx, c)
			if err != nil {
				return fmt.Errorf("uc.initializeChannel: %w", err)
			}

			c = updatedChannel
		}

		if c.Pts == 0 {
			log.Warn().Int64("telegram_id", c.TelegramID).Msg("Channel pts still empty, skipping diff")
			continue
		}

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

	return nil
}

func (uc *UseCase) processChannel(ctx context.Context, channel domain.Channel) error {
	diff, err := uc.telegram.GetChannelDiff(ctx, channel, 20)
	if err != nil {
		if isPrivateChannelError(err) {
			log.Warn().Err(err).Int64("telegram_id", channel.TelegramID).Msg("Private channel, attempting rejoin")
			if channel.InviteLink == "" {
				log.Warn().Int64("telegram_id", channel.TelegramID).Msg("No invite link stored, skipping channel")
				return nil
			}
			updatedChannel, joinErr := uc.telegram.ParseChannelMetaByInvite(ctx, channel.InviteLink)
			if joinErr != nil {
				log.Warn().Err(joinErr).Int64("telegram_id", channel.TelegramID).Msg("Invite rejoin failed")
				return nil
			}
			updatedChannel.ID = channel.ID
			updatedChannel.InviteLink = channel.InviteLink
			updatedChannel.Pts = 0
			if err := uc.database.UpdateChannel(ctx, updatedChannel); err != nil {
				return fmt.Errorf("database.UpdateChannel: %w", err)
			}
			return 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)
		}
	} else {
		channel.Pts = diff.NewPts
		err = uc.database.UpdateChannel(ctx, channel)
		if err != nil {
			return fmt.Errorf("database.UpdateChannel: %w", err)
		}
	}

	return nil
}

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

func (uc *UseCase) initializeChannel(ctx context.Context, channel domain.Channel) (domain.Channel, error) {
	c := channel
	if channel.Username != "" {
		updated, err := uc.telegram.ParseChannelMeta(ctx, channel.Username)
		if err != nil {
			return domain.Channel{}, fmt.Errorf("telegram.ParseChannelMeta: %w", err)
		}
		c = updated
	} else if channel.AccessHash == 0 {
		return domain.Channel{}, fmt.Errorf("channel %s missing access hash", channel.ID)
	} else {
		pts, err := uc.telegram.GetChannelPTS(ctx, channel)
		if err != nil {
			return domain.Channel{}, fmt.Errorf("telegram.GetChannelPTS: %w", err)
		}
		c.Pts = pts
	}

	// Preserve persistent channel ID from the database so foreign keys remain valid.
	c.ID = channel.ID

	posts, err := uc.telegram.GetChannelHistory(ctx, c, 20)
	if err != nil {
		return domain.Channel{}, fmt.Errorf("telegram.GetChannelHistory: %w", err)
	}

	err = transaction.Wrap(ctx, func(ctx context.Context) error {
		err = uc.database.UpdateChannel(ctx, c)
		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 {
		return domain.Channel{}, fmt.Errorf("transaction.Wrap: %w", err)
	}

	return c, nil
}