dev day #65

internal/controllers/pagination_helper.go

@@ -0,0 +1,121 @@
+package controllers
+
+import (
+	"math"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+	"gorm.io/gorm"
+)
+
+// PaginationHelper provides pagination utilities
+type PaginationHelper struct{}
+
+// PaginationParams represents pagination parameters
+type PaginationParams struct {
+	Page     int `json:"page"`
+	PageSize int `json:"page_size"`
+	Offset   int `json:"-"`
+}
+
+// PaginationMeta represents pagination metadata
+type PaginationMeta struct {
+	Page       int   `json:"page"`
+	PageSize   int   `json:"page_size"`
+	Total      int64 `json:"total"`
+	TotalPages int   `json:"total_pages"`
+	HasNext    bool  `json:"has_next"`
+	HasPrev    bool  `json:"has_prev"`
+}
+
+// NewPaginationHelper creates a new PaginationHelper instance
+func NewPaginationHelper() *PaginationHelper {
+	return &PaginationHelper{}
+}
+
+// GetPaginationParams extracts pagination parameters from the request
+// Defaults: page=1, pageSize=20
+func (ph *PaginationHelper) GetPaginationParams(c *gin.Context) PaginationParams {
+	page, _ := strconv.Atoi(c.DefaultQuery("page", "1"))
+	pageSize, _ := strconv.Atoi(c.DefaultQuery("page_size", "20"))
+
+	// Validate and constrain values
+	if page < 1 {
+		page = 1
+	}
+	if pageSize < 1 {
+		pageSize = 20
+	}
+	if pageSize > 100 {
+		pageSize = 100 // Max page size to prevent abuse
+	}
+
+	offset := (page - 1) * pageSize
+
+	return PaginationParams{
+		Page:     page,
+		PageSize: pageSize,
+		Offset:   offset,
+	}
+}
+
+// BuildPaginationMeta creates pagination metadata
+func (ph *PaginationHelper) BuildPaginationMeta(params PaginationParams, total int64) PaginationMeta {
+	totalPages := int(math.Ceil(float64(total) / float64(params.PageSize)))
+	
+	return PaginationMeta{
+		Page:       params.Page,
+		PageSize:   params.PageSize,
+		Total:      total,
+		TotalPages: totalPages,
+		HasNext:    params.Page < totalPages,
+		HasPrev:    params.Page > 1,
+	}
+}
+
+// Paginate applies pagination to a GORM query and returns the paginated results with metadata
+func (ph *PaginationHelper) Paginate(c *gin.Context, db *gorm.DB, dest interface{}) (PaginationMeta, error) {
+	params := ph.GetPaginationParams(c)
+	
+	// Count total records
+	var total int64
+	if err := db.Count(&total).Error; err != nil {
+		return PaginationMeta{}, err
+	}
+	
+	// Apply pagination
+	if err := db.Offset(params.Offset).Limit(params.PageSize).Find(dest).Error; err != nil {
+		return PaginationMeta{}, err
+	}
+	
+	meta := ph.BuildPaginationMeta(params, total)
+	return meta, nil
+}
+
+// PaginateWithPreload applies pagination with preloading associations
+func (ph *PaginationHelper) PaginateWithPreload(c *gin.Context, db *gorm.DB, dest interface{}, preloads ...string) (PaginationMeta, error) {
+	params := ph.GetPaginationParams(c)
+	
+	// Count total records (without preload)
+	var total int64
+	if err := db.Count(&total).Error; err != nil {
+		return PaginationMeta{}, err
+	}
+	
+	// Apply preloads
+	query := db
+	for _, preload := range preloads {
+		query = query.Preload(preload)
+	}
+	
+	// Apply pagination
+	if err := query.Offset(params.Offset).Limit(params.PageSize).Find(dest).Error; err != nil {
+		return PaginationMeta{}, err
+	}
+	
+	meta := ph.BuildPaginationMeta(params, total)
+	return meta, nil
+}
+
+// Global PaginationHelper instance for convenience
+var Paginator = NewPaginationHelper()