package gositemap

import (
	"encoding/xml"
	"fmt"
	"math"
	"path"
)

type ChangeFrequency string

const (
	Always  ChangeFrequency = "always"
	Hourly  ChangeFrequency = "hourly"
	Daily   ChangeFrequency = "daily"
	Weekly  ChangeFrequency = "weekly"
	Monthly ChangeFrequency = "monthly"
	Yearly  ChangeFrequency = "yearly"
	Never   ChangeFrequency = "never"
)

func (f ChangeFrequency) String() string {
	return string(f)
}

type urlSetXML struct {
	XMLName xml.Name  `xml:"http://www.sitemaps.org/schemas/sitemap/0.9 urlset"`
	URLs    []*urlXML `xml:"url"`
}

type urlXML struct {
	Loc        string           `xml:"loc"`
	LastMod    *string          `xml:"lastmod,omitempty"`
	ChangeFreq *ChangeFrequency `xml:"changefreq,omitempty"`
	Priority   *float64         `xml:"priority,omitempty"`
}

type siteMapIndexXML struct {
	XMLName  xml.Name      `xml:"http://www.sitemaps.org/schemas/sitemap/0.9 sitemapindex"`
	SiteMaps []*sitemapXML `xml:"sitemap"`
}

type sitemapXML struct {
	Loc     string  `xml:"loc"`
	LastMod *string `xml:"lastmod,omitempty"`
}

type SiteMap struct {
	urls             []*urlXML
	BaseURL          string
	MaxURLPerSiteMap int
}

func (m *SiteMap) AddURL(url string, lastMod *string, freq *ChangeFrequency, prio *float64) {
	m.urls = append(m.urls, &urlXML{
		Loc:        fmt.Sprintf("https://%s", path.Join(m.BaseURL, url)),
		LastMod:    lastMod,
		ChangeFreq: freq,
		Priority:   prio,
	})
}

func prefixXML(content []byte) []byte {
	return append([]byte(xml.Header), content...)
}

func (m *SiteMap) SiteMapIndex() ([]byte, error) {
	nSiteMaps := int(math.Floor(float64(len(m.urls))/float64(m.MaxURLPerSiteMap) + 1))
	index := &siteMapIndexXML{}

	for i := 0; i < nSiteMaps; i++ {
		index.SiteMaps = append(index.SiteMaps, &sitemapXML{
			Loc: fmt.Sprintf("https://%s/sitemap/%d", m.BaseURL, i),
		})
	}

	res, err := xml.Marshal(index)
	if err != nil {
		return nil, err
	}

	return prefixXML(res), nil
}

func (m *SiteMap) SiteMap(id int) ([]byte, error) {
	if m.MaxURLPerSiteMap*(id) >= len(m.urls) {
		return nil, nil
	}

	siteMap := &urlSetXML{}

	var urls []*urlXML
	if m.MaxURLPerSiteMap*(id+1) >= len(m.urls) {
		urls = m.urls[m.MaxURLPerSiteMap*id:]
	} else {
		urls = m.urls[m.MaxURLPerSiteMap*id : m.MaxURLPerSiteMap*(id+1)]
	}

	siteMap.URLs = append(siteMap.URLs, urls...)

	res, err := xml.Marshal(siteMap)
	if err != nil {
		return nil, err
	}

	return prefixXML(res), nil
}