package handlers

import (
	"crypto/subtle"
	"encoding/base64"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"time"

	"github.com/gorilla/mux"
	"github.com/pkg/errors"
	bolt "go.etcd.io/bbolt"

	"gitea.hashru.nl/dsprenkels/rushlink/db"
)

type viewPaste uint

const (
	_ viewPaste = 1 << iota
	viewNoRedirect
	viewShowMeta
)

const CookieDeleteToken = "owner_token"

// These keys are designated reserved, and will not be randomly chosen
var ReservedPasteKeys = []string{"xd42", "example"}

// Base64 encoding and decoding
var base64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
var base64Encoder = base64.RawURLEncoding.WithPadding(base64.NoPadding)

func (t pasteType) String() string {
	switch t {
	case typeUndef:
		return "unknown"
	case typePaste:
		return "paste"
	case typeRedirect:
		return "redirect"
	default:
		return "invalid"
	}
}

func (t pasteState) String() string {
	switch t {
	case stateUndef:
		return "unknown"
	case statePresent:
		return "present"
	case stateDeleted:
		return "deleted"
	default:
		return "invalid"
	}
}

func indexGetHandler(w http.ResponseWriter, r *http.Request) {
	render(w, r, "index", map[string]interface{}{})
}

func viewPasteHandler(w http.ResponseWriter, r *http.Request) {
	viewPasteHandlerInner(w, r, 0)
}

func viewPasteHandlerNoRedirect(w http.ResponseWriter, r *http.Request) {
	viewPasteHandlerInner(w, r, viewNoRedirect)
}

func viewPasteHandlerMeta(w http.ResponseWriter, r *http.Request) {
	viewPasteHandlerInner(w, r, viewShowMeta)
}

func viewPasteHandlerInner(w http.ResponseWriter, r *http.Request, flags viewPaste) {
	vars := mux.Vars(r)
	key := vars["key"]
	var p *paste
	if err := db.DB.View(func(tx *bolt.Tx) error {
		var err error
		p, err = getPaste(tx, key)
		return err
	}); err != nil {
		panic(err)
		return
	}
	if p == nil {
		renderError(w, r, http.StatusNotFound, "url key not found in the database")
		return
	}

	if flags&viewShowMeta != 0 {
		canDelete := struct {
			Bool   bool
			String string
		}{Bool: false}
		deleteToken := getDeleteTokenFromRequest(r)
		if deleteToken == "" {
			canDelete.String = "undefined"
		} else {
			if subtle.ConstantTimeCompare([]byte(deleteToken), []byte(p.DeleteToken)) == 1 {
				canDelete.Bool = true
				canDelete.String = "correct"
			} else {
				canDelete.String = "invalid"
			}
		}

		data := map[string]interface{}{
			"Paste":     p,
			"CanDelete": canDelete,
		}
		render(w, r, "pasteMeta", data)
		return
	}

	switch p.State {
	case statePresent:
		if flags&viewNoRedirect == 0 {
			rawurl := string(p.Content)
			urlParse, err := url.Parse(rawurl)
			if err != nil {
				panic(errors.Wrapf(err, "invalid URL ('%v') in database for key '%v'", rawurl, p.Key))
			}
			http.Redirect(w, r, urlParse.String(), http.StatusSeeOther)
		}
		w.Write(p.Content)
	case stateDeleted:
		renderError(w, r, http.StatusGone, "paste has been deleted")
	default:
		panic(errors.Errorf("invalid paste.State (%v) for key '%v'", p.State, p.Key))
	}
}

func newPasteHandler(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseMultipartForm(50 * 1000 * 1000); err != nil {
		panic(err)
	}

	// Determine what kind of post this is, currently only `shorten=...`
	if len(r.PostForm) == 0 {
		renderError(w, r, http.StatusBadRequest, "empty body in POST request\n")
		return
	}
	shorten_values, prs := r.PostForm["shorten"]
	if !prs {
		renderError(w, r, http.StatusBadRequest, "no 'shorten' param given\n")
		return
	}
	if len(shorten_values) != 1 {
		renderError(w, r, http.StatusBadRequest, "only one 'shorten' param is allowed per request\n")
		return
	}

	newRedirectPasteHandler(w, r)
}

func newRedirectPasteHandler(w http.ResponseWriter, r *http.Request) {
	rawurl := r.PostForm.Get("shorten")
	userURL, err := url.ParseRequestURI(rawurl)
	if err != nil {
		msg := fmt.Sprintf("invalid url (%v): %v", err, rawurl)
		renderError(w, r, http.StatusBadRequest, msg)
		return
	}
	if userURL.Scheme == "" {
		renderError(w, r, http.StatusBadRequest, "invalid url (unspecified scheme)")
		return
	}
	if userURL.Host == "" {
		renderError(w, r, http.StatusBadRequest, "invalid url (unspecified host)")
		return
	}

	var paste *paste
	if err := db.DB.Update(func(tx *bolt.Tx) error {
		// Generate a new delete token for this paste
		var err error
		paste, err = shortenURL(tx, userURL)
		return err
	}); err != nil {
		panic(err)
	}
	data := map[string]interface{}{"Paste": paste}
	render(w, r, "newRedirectPasteSuccess", data)
}

// Delete a URL from the database
func deletePasteHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	key := vars["key"]

	deleteToken := getDeleteTokenFromRequest(r)
	if deleteToken == "" {
		renderError(w, r, http.StatusBadRequest, "no delete token provided")
		return
	}

	var errorCode int
	if err := db.DB.Update(func(tx *bolt.Tx) error {
		p, err := getPaste(tx, key)
		if err != nil {
			errorCode = http.StatusNotFound
			return err
		}
		if subtle.ConstantTimeCompare([]byte(deleteToken), []byte(p.DeleteToken)) == 1 {
			p.delete(tx)
		}
		errorCode = http.StatusForbidden
		return errors.New("invalid delete token")
	}); err != nil {
		log.Printf("error: %v\n", err)
		renderError(w, r, errorCode, fmt.Sprintf("error: %v", err))
		return
	}
}

// Add a new URL to the database
//
// Returns the new ID if the url was successfully shortened
func shortenURL(tx *bolt.Tx, userURL *url.URL) (*paste, error) {
	pasteKey, err := generatePasteKey(tx)
	if err != nil {
		return nil, errors.Wrap(err, "generating paste key")
	}

	// Also generate a deleteToken
	deleteToken, err := generateDeleteToken()
	if err != nil {
		return nil, errors.Wrap(err, "generating delete token")
	}

	// Store the new key
	p := paste{
		Type:        typeRedirect,
		State:       statePresent,
		Content:     []byte(userURL.String()),
		Key:         pasteKey,
		DeleteToken: deleteToken,
		TimeCreated: time.Now().UTC(),
	}
	if err := p.save(tx); err != nil {
		return nil, err
	}
	return &p, nil
}

func getDeleteTokenFromRequest(r *http.Request) string {
	return r.URL.Query().Get("deleteToken")
}