package base

import (
	"context"
	"gorm.io/gorm"
	"gorm.io/gorm/schema"
	"sync"
)

const MaxPageSize = 10000

type Pagination[T schema.Tabler] struct {
	once  sync.Once
	Query *gorm.DB
	Error error
	Size  int
	Page  int
	total int64
	items []T
}

func (p *Pagination[T]) Total() int64 {
	return p.total
}

func (p *Pagination[T]) Items() []T {
	return p.items
}

func (p *Pagination[T]) Load() *Pagination[T] {
	p.once.Do(func() {
		if p.Size == 0 {
			p.Page = 1
			p.Size = MaxPageSize
		}

		query := p.Query
		if p.Query.Statement.Model == nil {
			var t T
			query = query.Model(t).Table(t.TableName() + " AS Main")
		} else {
			query = query.Table(query.Statement.Model.(schema.Tabler).TableName() + " AS Main")
		}

		p.Error = query.WithContext(context.Background()).Count(&p.total).Error

		if p.Error != nil {
			return
		}

		page := p.Page - 1

		if page < 0 {
			page = 0
		}

		offset := page * p.Size

		p.Error = query.WithContext(context.Background()).Offset(offset).Limit(p.Size).Find(&p.items).Error
	})
	return p
}