From 78e17cf1006063e53ef47ebc1c64bcaaff7d3466 Mon Sep 17 00:00:00 2001
From: SoXX <soxx@anthrove.art>
Date: Tue, 13 Aug 2024 10:29:47 +0200
Subject: [PATCH] feat(scopes): Add pagination support with Paginate and
 AdvancedPagination functions

- Introduce Paginate function for basic pagination
- Add AdvancedPagination for pagination, sorting, and counting
- Define Pagination struct to hold pagination data
- Set MaxPageSizeLimit and DefaultPageSize in models/constants
---
 pkg/database/scopes.go | 84 ++++++++++++++++++++++++++++++++++++++++++
 pkg/models/const.go    |  5 +++
 2 files changed, 89 insertions(+)
 create mode 100644 pkg/database/scopes.go

diff --git a/pkg/database/scopes.go b/pkg/database/scopes.go
new file mode 100644
index 0000000..0161872
--- /dev/null
+++ b/pkg/database/scopes.go
@@ -0,0 +1,84 @@
+package database
+
+import (
+	"math"
+
+	"git.anthrove.art/Anthrove/otter-space-sdk/v2/pkg/models"
+	"gorm.io/gorm"
+)
+
+type Pagination struct {
+	Limit      int    `json:"limit,omitempty;query:limit"`
+	Page       int    `json:"page,omitempty;query:page"`
+	Sort       string `json:"sort,omitempty;query:sort"`
+	TotalRows  int64  `json:"total_rows"`
+	TotalPages int    `json:"total_pages"`
+}
+
+// Paginate applies pagination to a GORM query.
+// It takes two parameters:
+//
+// - page: the current page number (1-based index). If the page is less than or equal to 0, it defaults to 1.
+//
+// - pageSize: the number of records per page. If the pageSize is greater than the MaxPageSizeLimit defined in models, it defaults to MaxPageSizeLimit. If the pageSize is less than or equal to 0, it defaults to DefaultPageSize defined in models.
+//
+// The function calculates the offset based on the page and pageSize, and applies the offset and limit to the GORM DB instance.
+func Paginate(page int, pageSize int) func(db *gorm.DB) *gorm.DB {
+	return func(db *gorm.DB) *gorm.DB {
+
+		if page <= 0 {
+			page = 1
+		}
+
+		switch {
+		case pageSize > models.MaxPageSizeLimit:
+			pageSize = models.MaxPageSizeLimit
+		case pageSize <= 0:
+			pageSize = models.DefaultPageSize
+		}
+
+		offset := (page - 1) * pageSize
+		return db.Offset(offset).Limit(pageSize)
+	}
+}
+
+// AdvancedPagination applies pagination, sorting, and counting to a GORM query.
+// Parameters:
+//
+// - value: The model or table to query.
+//
+// - pagination: A pointer to a Pagination struct containing page, limit, sort, total rows, and total pages information.
+//
+// - db: A pointer to the GORM database instance.
+//
+// The function calculates the offset based on the Page and Limit of the Pagination struct, and applies the offset and limit to the GORM DB instance.
+func AdvancedPagination(value any, pagination *Pagination, db *gorm.DB) func(db *gorm.DB) *gorm.DB {
+	var totalRows int64
+
+	if pagination.Page <= 0 {
+		pagination.Page = 1
+	}
+
+	if pagination.Sort == "" {
+		pagination.Sort = "Id desc"
+	}
+
+	switch {
+	case pagination.Limit > models.MaxPageSizeLimit:
+		pagination.Limit = models.MaxPageSizeLimit
+	case pagination.Limit <= 0:
+		pagination.Limit = models.DefaultPageSize
+	}
+
+	db.Model(value).Count(&totalRows)
+
+	pagination.TotalRows = totalRows
+	totalPages := int(math.Ceil(float64(totalRows) / float64(pagination.Limit)))
+	pagination.TotalPages = totalPages
+
+	offset := (pagination.Page - 1) * pagination.Limit
+
+	return func(db *gorm.DB) *gorm.DB {
+		return db.Offset(offset).Limit(pagination.Limit).Order(pagination.Sort)
+	}
+}
diff --git a/pkg/models/const.go b/pkg/models/const.go
index a6f25bc..092a803 100644
--- a/pkg/models/const.go
+++ b/pkg/models/const.go
@@ -24,6 +24,11 @@ type (
 	UserFavoriteID string
 )
 
+const (
+	MaxPageSizeLimit = 100
+	DefaultPageSize  = 50
+)
+
 const (
 	SFW          Rating = "safe"
 	NSFW         Rating = "explicit"