// Atom feed synthesizer
// Copyright (C) 2022  Nguyễn Gia Phong
//
// This file is part of Phylactery.
//
// Phylactery is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Phylactery is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with Phylactery.  If not, see <https://www.gnu.org/licenses/>.

package main

import (
	"archive/zip"
	"encoding/xml"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"time"
)

// Type Img represents an XHTML img tag.
type Img struct {
	Src string `xml:"src,attr"`
	Alt string `xml:"alt,attr"`
}

// Type Div represents an XHTML div tag.
type Div struct {
	NS  string `xml:"xmlns,attr"`
	Img []Img  `xml:"img"`
}

// Type AtomLink represents an atom:link element.
type AtomLink struct {
	Rel  string `xml:"rel,attr"`
	Href string `xml:"href,attr"`
}

// Type AtomContent represents an atom:content element.
type AtomContent struct {
	Type string `xml:"type,attr"`
	Div  Div    `xml:"div"`
}

// Type AtomEntry represents an Atom Entry Document.
type AtomEntry struct {
	Title   string      `xml:"title"`
	ID      string      `xml:"id"`
	Link    []AtomLink  `xml:"link"`
	Updated time.Time   `xml:"updated"`
	Content AtomContent `xml:"content"`
}

// Type AtomFeed represents an Atom Feed Document.
type AtomFeed struct {
	XMLName xml.Name    `xml:"http://www.w3.org/2005/Atom feed"`
	Title   string      `xml:"title"`
	ID      string      `xml:"id"`
	Link    []AtomLink  `xml:"link"`
	Updated time.Time   `xml:"updated"`
	Author  string      `xml:"author>name"`
	Entry   []AtomEntry `xml:"entry"`
}

// Function synthesizeAtom generates an Atom feed for given directory.
func synthesizeAtom(r *http.Request, dir string, updated time.Time) AtomFeed {
	baseURL := "http://" + r.Host
	if r.TLS != nil {
		baseURL = "https" + baseURL[4:]
	}
	var entries []AtomEntry
	filepath.WalkDir(dir, func(p string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() {
			return nil
		}
		name := strings.TrimPrefix(p, dir)[1:]
		u := escape(baseURL + path.Join(r.URL.Path, name))
		var images []Img
		cbz, err := zip.OpenReader(p)
		if err != nil {
			return nil
		}
		defer cbz.Close()
		for i, f := range cbz.File {
			if !isImageFile(f) {
				continue
			}
			images = append(images,
				Img{u + "?entry=" + strconv.Itoa(i), f.Name})
		}

		info, _ := d.Info()
		entries = append(entries, AtomEntry{
			Title:   name,
			ID:      name,
			Link:    []AtomLink{{"alternate", u}},
			Updated: info.ModTime(),
			Content: AtomContent{
				"xhtml",
				Div{"http://www.w3.org/1999/xhtml", images},
			},
		})
		return nil
	})

	id := escape(baseURL + r.URL.Path)
	return AtomFeed{
		Title: r.URL.Path[1 : len(r.URL.Path)-1],
		ID:    id,
		Link: []AtomLink{
			{"alternate", id},
			{"self", id + "?feed=atom"},
		},
		Updated: updated,
		Entry:   entries,
	}
}