package pagination

import (
	"math"
)

type Paginator interface {
	// Limit 数据条目数限制
	Limit() int32

	// Offset 数据偏移量
	Offset() int32
}

const (
	// DefaultPage 默认分页数
	DefaultPage = 1

	// DefaultPageSize 默认分页条目数
	DefaultPageSize = 20
)

var _ Paginator = (*Pagination)(nil)

type options struct {
	total int32
}

type Option func(*options)

type Pagination struct {
	page     int32
	pageSize int32
	total    int32
}

func WithTotal(b int32) Option {
	return func(c *options) {
		c.total = b
	}
}

func NewPagination(page, pageSize int32, opts ...Option) *Pagination {
	opt := options{
		total: 0,
	}

	for _, o := range opts {
		o(&opt)
	}

	return &Pagination{page: page, pageSize: pageSize, total: opt.total}
}

func (p Pagination) Page() int32 {
	if p.page < 1 {
		return DefaultPage
	}
	return p.page
}

func (p Pagination) PageSize() int32 {
	if p.pageSize < 1 {
		return DefaultPageSize
	}
	return p.pageSize
}

func (p Pagination) From() int32 {
	return (p.Page()-1)*p.PageSize() + 1
}

func (p Pagination) To() int32 {
	var to int32
	to = p.PageSize() * p.Page()
	if to > p.total {
		to = p.total
	}
	return to
}

func (p Pagination) LastPage() int32 {
	lastPage := math.Ceil(float64(p.total) / float64(p.PageSize()))
	if lastPage <= 0 {
		lastPage = 0
	}

	return int32(lastPage)
}

// Limit 实现 pagination.Paginator 方法
func (p Pagination) Limit() int32 {
	return p.PageSize()
}

func (p Pagination) Offset() int32 {
	return p.Limit() * (p.Page() - 1)
}