package main

import (
	"bytes"
	"crypto/rand"
	"embed"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"html/template"
	"io"
	"log"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"

	"github.com/gabriel-vasile/mimetype"
	"github.com/robert-nix/ansihtml"
	flag "github.com/spf13/pflag"
)

const (
	MetadataExt     = ".metadata"
	DefaultMimeType = "application/octet-stream"
	DefaultMaxSize  = (10 << 23) // 83MB
)

type Server struct {
	data    string
	host    string
	maxSize int64
}

type Metadata struct {
	ContentType string `json:"contentType"`
}

//go:embed template.html
var static embed.FS

var tmpl = template.Must(template.ParseFS(static, "*.html"))

func detectMimetype(input io.Reader) (mimeType string, fileext string, recycled io.Reader, err error) {
	header := bytes.NewBuffer(nil)
	mtype, err := mimetype.DetectReader(io.TeeReader(input, header))
	recycled = io.MultiReader(header, input)
	return mtype.String(), mtype.Extension(), recycled, err
}

func serveAnsiHtml(w http.ResponseWriter, filename string) {
	f, err := os.Open(filename)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}
	w.Header().Add("content-type", "text/html")
	data, err := io.ReadAll(f)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}
	data = ansihtml.ConvertToHTML(data)
	data = fmt.Appendf(nil, "<pre>%s</pre>", strings.ReplaceAll(string(data), "\n", "<br>"))
	w.Write(data)
}

func writeMetadata(filename string, m *Metadata) error {
	f, err := os.OpenFile(filename, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	j := json.NewEncoder(f)
	return j.Encode(m)
}

func readMetadata(filename string) (*Metadata, error) {
	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	var m Metadata
	j := json.NewDecoder(f)
	if err := j.Decode(&m); err != nil {
		return nil, err
	}
	return &m, nil
}

func (s *Server) writeMetadata(name string, m *Metadata) error {
	filename := filepath.Join(s.data, name+MetadataExt)
	return writeMetadata(filename, m)
}

func (s *Server) randomFile(ext string) (*os.File, string, error) {
	var random [16]byte
	_, err := io.ReadFull(rand.Reader, random[:])
	if err != nil {
		return nil, "", err
	}
	name := base64.RawURLEncoding.EncodeToString(random[:]) + ext
	filename := filepath.Join(s.data, name)
	f, err := os.OpenFile(filename, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o644)
	if err != nil {
		return nil, "", err
	}
	return f, name, nil
}

func (s *Server) createPosting(rd io.Reader, mimeType string) (string, error) {
	var ext string
	if mimeType == "" || mimeType == "auto" {
		mimeType, ext, rd, _ = detectMimetype(rd)
	} else {
		mime := mimetype.Lookup(mimeType)
		if mime != nil {
			ext = mime.Extension()
		}
	}
	f, name, err := s.randomFile(ext)
	if err != nil {
		return "", fmt.Errorf("randomFile(): %w", err)
	}
	defer f.Close()
	if _, err := io.Copy(f, rd); err != nil {
		return "", fmt.Errorf("io.Copy(): %w", err)
	}
	f.Sync()
	m := Metadata{ContentType: mimeType}
	if err = s.writeMetadata(name, &m); err != nil {
		return "", fmt.Errorf("writeMetadata(): %w", err)
	}
	return name, nil
}

func (s *Server) postText(r *http.Request) (string, error) {
	text := r.Form.Get("text")
	if text == "" {
		return "", nil
	}
	mimeType := r.Form.Get("text_mimetype")
	return s.createPosting(strings.NewReader(text), mimeType)
}

func (s *Server) postFile(r *http.Request) (string, error) {
	mimeType := r.Form.Get("file_mimetype")
	file, _, err := r.FormFile("file")
	if err != nil {
		return "", err
	}
	defer file.Close()
	return s.createPosting(file, mimeType)
}

func (s *Server) servePosting(w http.ResponseWriter, r *http.Request, name string) {
	filename := filepath.Join(s.data, name)
	m, err := readMetadata(filename + MetadataExt)
	if err != nil {
		log.Print("readMetadata(): ", err)
		w.WriteHeader(http.StatusNotFound)
		return
	}
	h := w.Header()
	switch m.ContentType {
	case "text/x-ansi":
		serveAnsiHtml(w, filename)
		return
	case "text/x-url":
		location, err := os.ReadFile(filename)
		if err != nil {
			log.Print("read(): ", err)
			w.WriteHeader(http.StatusNotFound)
			return
		}
		w.Header().Add("location", string(location))
		w.WriteHeader(http.StatusFound)
		return
	case "":
		m.ContentType = "application/octet-stream"
	default:
	}
	h.Add("content-type", m.ContentType)
	http.ServeFile(w, r, filename)
}

func (s *Server) post(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		return
	}
	r.Body = http.MaxBytesReader(w, r.Body, s.maxSize) // impose maximum request size
	mimeType := r.Header.Get("content-type")
	if strings.HasPrefix(mimeType, "multipart/form-data;") {
		// max 8MB in RAM for multipart parsing
		if err := r.ParseMultipartForm(1 << 23); err != nil {
			log.Print("Error parse multipart form: ", err)
			w.WriteHeader(http.StatusInternalServerError)
			return
		}
		textName, err := s.postText(r)
		if err != nil {
			log.Print("Error text upload: ", err)
		}
		fileName, err := s.postFile(r)
		if err != nil {
			log.Print("Error file upload: ", err)
		}
		if fileName == "" && textName == "" {
			w.WriteHeader(http.StatusInternalServerError)
			return
		}
		log.Printf("Created posting: text=%s, file=%s", textName, fileName)
		location := fmt.Sprintf("/link?text=%s&file=%s", url.QueryEscape(textName), url.QueryEscape(fileName))
		w.Header().Add("location", location)
		w.WriteHeader(http.StatusFound)
	} else {
		if mimeType == "application/x-www-form-urlencoded" {
			mimeType = "auto"
		}
		name, err := s.createPosting(r.Body, mimeType)
		if err != nil {
			log.Print("failed to create file: ", err)
			w.WriteHeader(http.StatusInternalServerError)
			return
		}
		log.Printf("Created posting: %s", name)
		w.WriteHeader(http.StatusCreated)
		fmt.Fprintf(w, "%s/%s\n", s.host, name)
	}
}

func (s *Server) get(w http.ResponseWriter, r *http.Request) {
	path := r.URL.Path
	switch path {
	case "/":
		w.Header().Add("content-type", "text/html; charset=UTF-8")
		if err := tmpl.ExecuteTemplate(w, "template.html", map[string]any{"Form": true}); err != nil {
			w.WriteHeader(http.StatusInternalServerError)
		}
	case "/link":
		tmplData := map[string]string{
			"Host":     s.host,
			"TextLink": r.FormValue("text"),
			"FileLink": r.FormValue("file"),
		}
		if err := tmpl.ExecuteTemplate(w, "template.html", tmplData); err != nil {
			w.WriteHeader(http.StatusInternalServerError)
		}
	default:
		s.servePosting(w, r, filepath.Base(path))
	}
}

func (s *Server) Index(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet:
		s.get(w, r)
	case http.MethodPost:
		s.post(w, r)
	default:
		w.WriteHeader(http.StatusMethodNotAllowed)
	}
}

func main() {
	var (
		addr    string
		data    string
		host    string
		maxSize uint32
	)
	flag.StringVarP(&addr, "addr", "a", "0.0.0.0:9000", "The address to bind to")
	flag.StringVarP(&data, "data-path", "d", "./data", "The path to the data")
	flag.StringVarP(&host, "host", "h", "", "The host url, e.g. http://127.0.0.1")
	flag.Uint32VarP(&maxSize, "max-size", "", DefaultMaxSize, "The maximum file upload size")
	flag.Parse()

	datadir, err := filepath.Abs(data)
	if err != nil {
		log.Fatal(err)
	}
	s := &Server{
		data:    datadir,
		host:    host,
		maxSize: int64(maxSize),
	}
	mux := http.NewServeMux()
	mux.HandleFunc("/", s.Index)
	log.Printf("Listening at '%s'...", addr)
	if err := http.ListenAndServe(addr, mux); err != nil {
		log.Fatal(err)
	}
}