website/pkg/models/pagination.go

package models

import (
	"fmt"
	"math"
	"math/rand"
	"net/http"
	"strconv"

	"code.nonshy.com/nonshy/website/pkg/config"
	"code.nonshy.com/nonshy/website/pkg/encryption"
)

// Pagination result object.
type Pagination struct {
	Page    int // provide <0 to mean "last page"
	PerPage int
	Total   int64
	Sort    string

	// privates
	lastPage bool
}

// Load the page from form or query parameters.
func (p *Pagination) ParsePage(r *http.Request) {
	raw := r.FormValue("page")
	a, err := strconv.Atoi(raw)
	if err == nil {
		if a <= 0 {
			p.lastPage = true
			a = 1
		}
		p.Page = a
	} else {
		p.Page = 1
	}
}

// Page for Iter.
type Page struct {
	Page      int  // label to show in the button
	IsCurrent bool // highlight the currently selected page button

	// this "button" is a drop-down menu of page numbers in the middle
	IsOverflow   bool
	overflowFrom int
	overflowTo   int
}

// Iter the pages, for templates.
//
// If there are fewer than 7 pages (configurable) this returns a simple slice of buttons
// for each of the 7 pages to be drawn. If there are a LOT of pages, the middle button of
// the pager should be a drop-down menu to pick from the pages within.
func (p *Pagination) Iter() []Page {
	var (
		pages = []Page{}
		total = p.Pages()
	)
	for i := 1; i <= total; i++ {
		pages = append(pages, Page{
			Page:      i,
			IsCurrent: i == p.Page,
		})
	}

	// Do we have A LOT of pages?
	if len(pages) > config.PagerButtonLimit+1 {
		// The left half of the buttons should be pages 1 thru N.
		// The right half are the final pages M thru Last.
		// In the middle will be the overflow drop-down of middle pages.
		var (
			endLength = config.PagerButtonLimit / 2
			start     = endLength + 1
			end       = len(pages) - endLength
			overflow  = Page{
				Page:         start,
				IsCurrent:    p.Page >= start && p.Page <= end,
				IsOverflow:   true,
				overflowFrom: start,
				overflowTo:   end,
			}
			result = []Page{}
		)

		// If we are currently selected on an overflow page, set the label to match.
		if overflow.IsCurrent {
			overflow.Page = p.Page
		}

		result = pages[:endLength]
		result = append(result, overflow)
		result = append(result, pages[end:]...)

		return result
	}
	return pages
}

// IterOverflow: if the Page represents an overflow drop-down menu, iterate the members of the menu
// for easy template integration.
func (p Page) IterOverflow() []Page {
	var result = []Page{}
	for i := p.overflowFrom; i <= p.overflowTo; i++ {
		result = append(result, Page{
			Page:      i,
			IsCurrent: p.Page == i,
		})
	}
	return result
}

// UniqueSerialID will return a unique JavaScript ID.
//
// It is used in front-end pages such as for Pagination drop-down menus, which may appear multiple times
// on a page and each use needs a unique ID attribute to connect the button to the dropdown.
func (p *Pagination) UniqueSerialID() string {
	return encryption.Hash([]byte(fmt.Sprintf("%d", rand.Intn(9000000))))
}

func (p Pagination) Pages() int {
	if p.PerPage == 0 {
		return 0
	}
	return int(math.Ceil(float64(p.Total) / float64(p.PerPage)))
}

func (p *Pagination) GetOffset() int {
	// Are we looking for the FINAL page?
	if p.lastPage && p.Pages() >= 1 {
		p.Page = p.Pages()
	}
	return (p.Page - 1) * p.PerPage
}

func (p *Pagination) HasNext() bool {
	return p.Page < p.Pages()
}

func (p *Pagination) HasPrevious() bool {
	return p.Page > 1
}

func (p *Pagination) Next() int {
	if p.Page >= p.Pages() {
		return p.Pages()
	}
	return p.Page + 1
}

func (p *Pagination) Previous() int {
	if p.Page > 1 {
		return p.Page - 1
	}
	return 1
}