Blog/app/internal/logic/listpostslogic.go

package logic

import (
	"context"
	"database/sql"
	"time"

	"git.cialloo.com/CiallooWeb/Blog/app/internal/svc"
	"git.cialloo.com/CiallooWeb/Blog/app/internal/types"

	"github.com/aws/aws-sdk-go-v2/service/s3"
	"github.com/lib/pq"
	"github.com/zeromicro/go-zero/core/logx"
)

type ListPostsLogic struct {
	logx.Logger
	ctx    context.Context
	svcCtx *svc.ServiceContext
}

// Get a list of blog posts
func NewListPostsLogic(ctx context.Context, svcCtx *svc.ServiceContext) *ListPostsLogic {
	return &ListPostsLogic{
		Logger: logx.WithContext(ctx),
		ctx:    ctx,
		svcCtx: svcCtx,
	}
}

func (l *ListPostsLogic) ListPosts(req *types.ListPostsReq) (resp *types.ListPostsResp, err error) {
	// Determine pagination parameters with sane defaults.
	page := req.Page
	if page < 1 {
		page = 1
	}

	pageSize := req.PageSize
	if pageSize < 1 || pageSize > 100 {
		pageSize = 10
	}

	offset := (page - 1) * pageSize

	var (
		rows       *sql.Rows
		totalCount int
	)

	if len(req.TagIds) == 0 {
		countQuery := `SELECT COUNT(*) FROM posts`
		if err = l.svcCtx.DB.QueryRowContext(l.ctx, countQuery).Scan(&totalCount); err != nil {
			l.Errorf("Failed to get total count: %v", err)
			return nil, err
		}

		postsQuery := `
			SELECT p.id, p.title, p.created_at, p.updated_at, p.cover_id
			FROM posts p
			ORDER BY p.created_at DESC
			LIMIT $1 OFFSET $2
		`

		rows, err = l.svcCtx.DB.QueryContext(l.ctx, postsQuery, pageSize, offset)
		if err != nil {
			l.Errorf("Failed to get posts: %v", err)
			return nil, err
		}
	} else {
		tagArray := pq.Array(req.TagIds)

		countQuery := `
			SELECT COUNT(*)
			FROM (
				SELECT p.id
				FROM posts p
				INNER JOIN post_hashtags ph ON p.id = ph.post_id
				WHERE ph.hashtag_id = ANY($1)
				GROUP BY p.id
				HAVING COUNT(DISTINCT ph.hashtag_id) = $2
			) filtered_posts
		`

		if err = l.svcCtx.DB.QueryRowContext(l.ctx, countQuery, tagArray, len(req.TagIds)).Scan(&totalCount); err != nil {
			l.Errorf("Failed to get filtered total count: %v", err)
			return nil, err
		}

		postsQuery := `
			SELECT p.id, p.title, p.created_at, p.updated_at, p.cover_id
			FROM posts p
			INNER JOIN post_hashtags ph ON p.id = ph.post_id
			WHERE ph.hashtag_id = ANY($1)
			GROUP BY p.id, p.title, p.created_at, p.updated_at, p.cover_id
			HAVING COUNT(DISTINCT ph.hashtag_id) = $2
			ORDER BY p.created_at DESC
			LIMIT $3 OFFSET $4
		`

		rows, err = l.svcCtx.DB.QueryContext(l.ctx, postsQuery, tagArray, len(req.TagIds), pageSize, offset)
		if err != nil {
			l.Errorf("Failed to get filtered posts: %v", err)
			return nil, err
		}
	}

	defer rows.Close()

	posts := make([]types.ListPostsRespPosts, 0)
	for rows.Next() {
		var (
			post      types.ListPostsRespPosts
			coverID   sql.NullInt64
			createdAt time.Time
			updatedAt time.Time
		)

		if scanErr := rows.Scan(&post.PostId, &post.Title, &createdAt, &updatedAt, &coverID); scanErr != nil {
			l.Errorf("Failed to scan post: %v", scanErr)
			continue
		}

		post.CreatedAt = createdAt.UnixMilli()
		post.UpdatedAt = updatedAt.UnixMilli()

		if coverID.Valid {
			const coverQuery = `SELECT file_key FROM files WHERE id = $1`
			var fileKey string

			if queryErr := l.svcCtx.DB.QueryRowContext(l.ctx, coverQuery, coverID.Int64).Scan(&fileKey); queryErr == nil {
				expiration := time.Duration(l.svcCtx.Config.S3.PresignedURLExpiration) * time.Second
				presignClient := s3.NewPresignClient(l.svcCtx.S3Client)
				getObjectInput := &s3.GetObjectInput{
					Bucket: &l.svcCtx.Config.S3.Bucket,
					Key:    &fileKey,
				}

				if presignedReq, presignErr := presignClient.PresignGetObject(l.ctx, getObjectInput, func(opts *s3.PresignOptions) {
					opts.Expires = expiration
				}); presignErr == nil {
					post.CoverImageUrl = presignedReq.URL
				}
			}
		}

		posts = append(posts, post)
	}

	if rowsErr := rows.Err(); rowsErr != nil {
		l.Errorf("Error while iterating posts: %v", rowsErr)
		return nil, rowsErr
	}

	return &types.ListPostsResp{
		Posts:      posts,
		TotalCount: totalCount,
	}, nil
}