// Server entry point
// 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"
	"embed"
	"encoding/xml"
	"html/template"
	"io"
	"log"
	"net/http"
	"os"
	"path"
	"strconv"
	"strings"
)

//go:embed static/*
var static embed.FS

//go:embed templates/*.html
var templates embed.FS

// Type Page represents a comic page.
type Page struct {
	Index int
	Name  string
}

// Type Archive represents a comic book zip archive.
type Archive struct {
	Title string
	Prev  string
	Next  string
}

// Type Directory represents a library directory in file system.
type Directory struct {
	Title   string
	Entries []string
}

// Function main starts Phylactery serving comics from PHYLACTERY_LIBRARY
// and listening on PHYLACTERY_ADDRESS to serve at PHYLACTERY_BASE_URL.
func main() {
	http.Handle("/static/", http.FileServer(http.FS(static)))
	t, err := template.New("").Funcs(template.FuncMap{
		"escape": func(name string) template.URL {
			return template.URL(escape(name))
		},
	}).ParseFS(templates, "templates/*.html")
	if err != nil {
		log.Fatal(err)
	}
	lib := os.Getenv("PHYLACTERY_LIBRARY")
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		p := path.Join(lib, path.Clean(r.URL.Path))
		stat, err := os.Stat(p)
		if err != nil {
			http.NotFound(w, r)
			return
		}
		r.ParseForm()

		if stat.IsDir() {
			// Redirect URL without a trailing slash
			// pointing to a non-directory page
			if !strings.HasSuffix(r.URL.Path, "/") {
				http.Redirect(w, r, r.URL.Path+"/",
					http.StatusMovedPermanently)
				return
			}

			// Encode Atom feed
			if feedFormat, isFeed := r.Form["feed"]; isFeed {
				if r.URL.Path == "/" {
					http.Error(w, "no feed for /",
						http.StatusBadRequest)
					return
				}
				if feedFormat[0] != "atom" {
					http.Error(w, "unsupported feed format",
						http.StatusUnsupportedMediaType)
					return
				}
				w.Header().Set("Content-Type",
					"application/atom+xml")
				io.WriteString(w, xml.Header)
				enc := xml.NewEncoder(w)
				enc.Indent("", "  ")
				enc.Encode(synthesizeAtom(r, p, stat.ModTime()))
				return
			}

			// Render directory page
			entries, _ := os.ReadDir(p)
			var names []string
			for _, entry := range entries {
				if entry.IsDir() {
					names = append(names, entry.Name()+"/")
				} else {
					names = append(names, entry.Name())
				}
			}
			dir := Directory{stat.Name(), names}
			t.ExecuteTemplate(w, "directory.html", dir)
			return
		} else if strings.HasSuffix(r.URL.Path, "/") {
			// Redirect URL with a trailing slash
			// pointing to a non-directory page
			http.Redirect(w, r, r.URL.Path[:len(r.URL.Path)-1],
				http.StatusMovedPermanently)
			return
		}

		// Check if file is a valid ZIP archive
		cbz, err := zip.OpenReader(p)
		if err != nil {
			http.Error(w, "invalid cbz", http.StatusNotAcceptable)
			return
		}
		defer cbz.Close()

		// Respond with an image inside the CBZ
		if entry, isImage := r.Form["entry"]; isImage {
			i, err := strconv.Atoi(entry[0])
			if err != nil || i < 0 || i >= len(cbz.File) {
				http.NotFound(w, r)
				return
			}
			image, _ := cbz.File[i].Open()
			defer image.Close()
			io.Copy(w, image)
			return
		}

		// Render archive page
		entries, _ := os.ReadDir(path.Join(p, ".."))
		index := find(entries, stat.Name())
		prev := ""
		if index > 0 {
			prev = entries[index-1].Name()
		}
		next := ""
		if index < len(entries)-1 {
			next = entries[index+1].Name()
		}
		t.ExecuteTemplate(w, "archive-head.html",
			Archive{stat.Name(), prev, next})

		for i, f := range cbz.File {
			if isImageFile(f) {
				t.ExecuteTemplate(w, "archive-page.html",
					Page{i, f.Name})
			}
		}
		t.ExecuteTemplate(w, "archive-foot.html", nil)
	})

	addr := os.Getenv("PHYLACTERY_ADDRESS")
	log.Println("Listening on", addr)
	log.Fatal(http.ListenAndServe(addr, nil))
}