package main

import (
	"bytes"
	"encoding/xml"
	"errors"
	"fmt"
	"log"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/gorilla/mux"
	"riedstra.dev/mitch/go-website/page"
)

type Author struct {
	Name  string `xml:"name"` // Required
	Uri   string `xml:"uri,omitempty"`
	Email string `xml:"email,omitempty"`
}

type Link struct {
	Href   string `xml:"href,attr,omitempty"`
	Rel    string `xml:"rel,attr,omitempty"`
	Type   string `xml:"type,attr,omitempty"`
	Title  string `xml:"Title,attr,omitempty"`
	Length string `xml:"Length,attr,omitempty"`
}

type Content struct {
	Type string `xml:"type,attr"`
	Data string `xml:",chardata"`
}

type Entry struct {
	// Spec requires this, autogenerated from Title and updated if otherwise
	// left empty
	Id string `xml:"id"`

	Title     string     `xml:"title"`   // Required
	Updated   *time.Time `xml:"updated"` // Required
	Author    *Author    `xml:"author,omitempty"`
	Published *time.Time `xml:"published,omitempty"`
	Links     []Link     `xml:"link,omitempty"`
	Content   *Content   `xml:"content,omitempty"`
}

func (i Entry) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
	type Alias Entry

	errs := []string{}
	if i.Title == "" {
		errs = append(errs, "Title Cannot be empty")
	}
	if i.Updated == nil {
		errs = append(errs, "Updated cannot be nil")
	}

	if len(errs) > 0 {
		return errors.New(strings.Join(errs, ","))
	}

	if i.Id == "" {
		i.Id = fmt.Sprintf("%s::%d", i.Title, i.Updated.Unix())
	}

	i2 := (*Alias)(&i)

	return e.EncodeElement(i2, start)
}

type Atom struct {
	Ns        string     `xml:"xmlns,attr"`
	Title     string     `xml:"title"`            // Required
	Id        string     `xml:"id"`               // Required
	Author    Author     `xml:"author,omitempty"` // Required
	Updated   *time.Time `xml:"updated"`          // Required
	Published *time.Time `xml:"published,omitempty"`
	Subtitle  string     `xml:"subtitle,omitempty"`
	Entries   []Entry    `xml:"entry"`
}

func (a Atom) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
	type Alias Atom

	a.Ns = "http://www.w3.org/2005/Atom"
	errs := []string{}
	if a.Id == "" {
		errs = append(errs, "ID Cannot be empty")
	}
	if a.Author.Name == "" {
		errs = append(errs, "Author Name cannot be empty")
	}
	if a.Updated == nil {
		errs = append(errs, "Updated cannot be empty")
	}

	if len(errs) > 0 {
		return errors.New(strings.Join(errs, ","))
	}

	start.Name = xml.Name{Local: "feed"}

	a2 := (*Alias)(&a)

	return e.EncodeElement(a2, start)
}

// FeedHandler takes care of pulling from the index all of the relevant posts
// and dumping them into an Atom feed.
//
// Relevant query parameters are:
//
// "content" if unset, or set to false content is omitted from the feed
// "limit=n" stop at "n" and return the feed
//
func (a *App) FeedHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	var addContent bool
	var limit int

	if _, ok := r.URL.Query()["content"]; ok {
		if r.URL.Query().Get("content") != "false" {
			addContent = true
		}
	}

	if l := r.URL.Query().Get("limit"); l != "" {
		i, err := strconv.Atoi(l)
		if err == nil {
			limit = i
		}
	}

	tag, ok := vars["tag"]
	if !ok {
		http.Error(w, "Tag not found or supplied", http.StatusNotFound)
		return
	}

	p := page.NewPage("index")
	index, err := p.Index()
	if err != nil {
		log.Println(err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}

	pages, ok := index[tag]
	if !ok {
		http.Error(w, "Invalid tag", http.StatusNotFound)
		return
	}

	pages, dateless := pages.RemoveDateless()
	for _, p := range dateless {
		log.Printf("Warning, page %s has no Date field. Skipping inclusion on feed", p)
	}
	pages.SortDate()

	feed := &Atom{
		Author:   a.Author,
		Title:    a.Title,
		Id:       a.FeedId,
		Updated:  &a.Updated.Time,
		Subtitle: a.Description,
	}

	entries := []Entry{}

	for n, p := range pages {
		if limit != 0 && n >= limit {
			break
		}

		content := &bytes.Buffer{}
		err := p.Render(content)
		if err != nil {
			log.Println(err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}

		entry := Entry{
			Title:   p.Title,
			Updated: &p.Date.Time,
			Links:   []Link{Link{Href: strings.Join([]string{a.SiteURL, p.Path()}, "/")}},
		}

		if p.AuthorName != "" {
			entry.Author = &Author{
				Name:  p.AuthorName,
			}
			if p.AuthorEmail != "" {
				entry.Author.Email = p.AuthorEmail
			}
		}

		if addContent {
			entry.Content = &Content{Type: "html", Data: content.String()}
		}

		entries = append(entries, entry)

	}

	feed.Entries = entries

	w.Header().Add("Content-type", "application/xml")
	w.Write([]byte(xml.Header))

	enc := xml.NewEncoder(w)
	enc.Indent("", "  ")

	err = enc.Encode(feed)
	if err != nil {
		log.Println(err)
		// Headers probably already sent, but we'll try anyway
		http.Error(w, "Internal server error", http.StatusInternalServerError)
	}

	return
}