package helpers

import (
	"gorm.io/gorm"
)

// Paginator 分页器
type Paginator[T any] struct {
	Page  int
	Limit int
	Count int64
	Total int
	Data  []T
}

// NewPaginator 创建一个新的分页器实例
func NewPaginator[T any](tx *gorm.DB, page, limit int) (*Paginator[T], error) {
	if page < 1 {
		page = 1
	}

	// get T
	beans := new([]T)

	count := int64(0)

	session := tx.Count(&count)

	if session.Error != nil {
		return nil, session.Error
	}

	paginator := &Paginator[T]{
		Page:  page,
		Limit: limit,
		Count: count,
		Total: int((count + int64(limit) - 1) / int64(limit)),
	}

	// find
	session = tx.Scopes(paginate(page, limit)).Find(&beans)

	paginator.Data = *beans

	return paginator, nil
}

func paginate(page int, limit int) func(db *gorm.DB) *gorm.DB {
	return func(db *gorm.DB) *gorm.DB {
		if page == 0 {
			page = 1
		}

		switch {
		case limit > 100:
			limit = 100
		case limit <= 0:
			limit = 10
		}
		offset := (page - 1) * limit
		return db.Offset(offset).Limit(limit)
	}
}