package pagination

import (
	"gorm.io/gorm"
)

type Paging struct {
	Page     uint `json:"page_number" example:"5"`
	Elements uint `json:"elements_per_page" example:"30"`
}

func (p Paging) Offset() int {
	return int(p.Elements) * int(p.Page-1)
}

func (p Paging) Limit() int {
	return int(p.Elements)
}

type Found[T any] struct {
	Items []T  `json:"items,omitempty"`
	Count uint `json:"items_count" example:"56"`
}

func Paginate[T any](paging Paging, stmt *gorm.DB) (Found[T], error) {
	var items []T
	var count int64

	base := stmt.Session(&gorm.Session{})

	countDB := stmt.Session(&gorm.Session{
		NewDB: true, // critical: do NOT reuse statement
	})

	if err := countDB.
		Table("(?) as sub", base).
		Count(&count).Error; err != nil {
		return Found[T]{}, err
	}

	err := base.
		Offset(paging.Offset()).
		Limit(paging.Limit()).
		Find(&items).
		Error
	if err != nil {
		return Found[T]{}, err
	}

	return Found[T]{
		Items: items,
		Count: uint(count),
	}, err
}