package sitemap

import (
	"bytes"
	"errors"
	"net/http"
	"time"

	"git.golem15.com/golem15/sm-sitemap-plugin/classes"
	"git.golem15.com/golem15/sm-sitemap-plugin/models"
	"git.golem15.com/golem15/summercms/modules/backpack"
	"git.golem15.com/golem15/summercms/modules/pact"
	"git.golem15.com/golem15/summercms/modules/surf"
	"gorm.io/gorm"
)

// The response headers of the sitemap routes.
const (
	contentTypeXML = "application/xml"
	cacheControl   = "no-cache, private"
)

// BucketSitemap is the throttle bucket of the sitemap routes.
const BucketSitemap = "sitemap-xml"

// FilesPath is the route of the per-group files. The index lists them at
// the site root (sitemap-<slug>-<n>.xml); the site's SEO layer or proxy
// maps the root names to this route.
const FilesPath = "/_sitemap/files/"

// Routes mounts GET /sitemap.xml (the index) and GET
// /_sitemap/files/{file} (one file) without the backend middleware: search
// engines fetch them anonymously. Both are served from the slot table, never
// generated per request, and throttled per client IP (BucketSitemap).
func (p *Plugin) Routes(r pact.Router) error {
	r.Get("/sitemap.xml", p.sitemapIndex, "throttle:"+BucketSitemap)
	r.Get("/_sitemap/files/{file}", p.sitemapFile, "throttle:"+BucketSitemap)
	r.Where("file", `sitemap-[a-z0-9-]+-[0-9]+\.xml`)
	return nil
}

// Buckets registers sitemap-xml: 60 requests a minute per client IP (behind
// the configured trusted proxies). 429 bodies are surf's
// {"message":"Too Many Attempts."}.
func (p *Plugin) Buckets() map[string]surf.Bucket {
	trusted := surf.TrustedProxies(nil)
	if p.app != nil {
		trusted = surf.TrustedProxies(p.app.Config)
	}
	return map[string]surf.Bucket{
		BucketSitemap: {
			Name:  BucketSitemap,
			Max:   60,
			Decay: time.Minute,
			Key: func(r *http.Request) string {
				return "sitemap-xml|" + surf.ClientIP(r, trusted)
			},
		},
	}
}

// indexRow is one file of the index query.
type indexRow struct {
	Grp     string     `gorm:"column:grp"`
	FileNo  int        `gorm:"column:file_no"`
	LastMod *time.Time `gorm:"column:lastmod"`
}

// sitemapIndex serves the sitemap index: one <sitemap> per file that lists
// at least one address, with the newest lastmod of its addresses. Without a
// site address (the setting, golem15.sitemap.site_url or app.url) it is a
// 404: a <loc> is never built from the request's Host.
func (p *Plugin) sitemapIndex(w http.ResponseWriter, r *http.Request) {
	db, err := database(p.app)
	if err != nil {
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	db = db.WithContext(r.Context())
	settings, err := classes.LoadSettings(db)
	if err != nil {
		pluginLog.Error("golem15.sitemap: load settings", "error", err)
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	site := classes.SiteURL(p.app, settings)
	if site == "" {
		pluginLog.Warn("golem15.sitemap: no site address; set the sitemap setting, golem15.sitemap.site_url or app.url")
		http.NotFound(w, r)
		return
	}
	var rows []indexRow
	if err := db.Raw(`SELECT grp, file_no, MAX(lastmod) AS lastmod FROM golem15_sitemap_urls
WHERE excluded_reason = '' AND file_no IS NOT NULL
GROUP BY grp, file_no ORDER BY grp, file_no`).Scan(&rows).Error; err != nil {
		pluginLog.Error("golem15.sitemap: index", "error", err)
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	files := make([]classes.IndexFile, 0, len(rows))
	for _, row := range rows {
		files = append(files, classes.IndexFile{Loc: site + "/" + classes.FileName(row.Grp, row.FileNo), LastMod: row.LastMod})
	}
	var buf bytes.Buffer
	if err := classes.WriteIndex(&buf, files); err != nil {
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	writeXML(w, buf.Bytes(), false)
}

// sitemapFile serves one file: its listed addresses in the order they were
// first seen. An unknown file, or one without a listed address, is a 404.
func (p *Plugin) sitemapFile(w http.ResponseWriter, r *http.Request) {
	grp, n, ok := classes.ParseFileName(r.PathValue("file"))
	if !ok {
		http.NotFound(w, r)
		return
	}
	db, err := database(p.app)
	if err != nil {
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	db = db.WithContext(r.Context())
	settings, err := classes.LoadSettings(db)
	if err != nil {
		pluginLog.Error("golem15.sitemap: load settings", "error", err)
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	site := classes.SiteURL(p.app, settings)
	var rows []models.URL
	if err := db.Where("grp = ? AND file_no = ? AND excluded_reason = ''", grp, n).Order("first_seen ASC, id ASC").Find(&rows).Error; err != nil {
		pluginLog.Error("golem15.sitemap: file", "file", r.PathValue("file"), "error", err)
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	entries := make([]classes.FileEntry, 0, len(rows))
	for _, row := range rows {
		loc := classes.Absolute(site, row.URL)
		if loc == "" {
			continue
		}
		entry := classes.FileEntry{Loc: loc, LastMod: row.LastMod}
		for _, a := range row.Alternates.Get() {
			if href := classes.Absolute(site, a.Href); href != "" {
				entry.Alternates = append(entry.Alternates, classes.FileAlternate{Hreflang: a.Hreflang, Href: href})
			}
		}
		entries = append(entries, entry)
	}
	if len(entries) == 0 {
		http.NotFound(w, r)
		return
	}
	var buf bytes.Buffer
	if err := classes.WriteURLSet(&buf, entries); err != nil {
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	writeXML(w, buf.Bytes(), true)
}

// writeXML answers 200 with an XML body. A file carries X-Robots-Tag
// noindex, so search engines read it without indexing it as a page.
func writeXML(w http.ResponseWriter, body []byte, noindex bool) {
	w.Header().Set("Content-Type", contentTypeXML)
	w.Header().Set("Cache-Control", cacheControl)
	if noindex {
		w.Header().Set("X-Robots-Tag", "noindex")
	}
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write(body)
}

// database returns the app's published *gorm.DB.
func database(app *backpack.App) (*gorm.DB, error) {
	if app == nil {
		return nil, errors.New("golem15.sitemap: app is not booted")
	}
	db, ok := app.Lookup[*gorm.DB]()
	if !ok || db == nil {
		return nil, errors.New("golem15.sitemap: database is not configured")
	}
	return db, nil
}