package rushlink

import (
	"crypto/subtle"
	"encoding/base64"
	"fmt"
	"io"
	"log"
	"mime/multipart"
	"net/http"
	"net/url"
	"os"
	"time"

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

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

func uploadFileGetHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	id := vars["id"]

	var fu *fileUpload
	var badID bool
	if err := DB.View(func(tx *bolt.Tx) error {
		fuID, err := uuid.Parse(id)
		if err != nil {
			badID = true
			return err
		}
		fu, err = getFileUpload(tx, fuID)
		return err
	}); err != nil {
		if badID {
			renderError(w, r, http.StatusNotFound, "malformed file id")
			return
		} else {
			panic(err)
		}
	}

	filePath := fileStorePath(fu.ID, fu.FileName)
	file, err := os.Open(filePath)
	if err != nil {
		if os.IsNotExist(err) {
			log.Printf("error: %v should exist according to the database, but it doesn't", filePath)
			renderError(w, r, http.StatusNotFound, "file not found")
			return
		} else {
			panic(err)
		}
	}
	w.Header().Set("Content-Type", fu.ContentType)
	io.Copy(w, file)
}

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
	var fuID *uuid.UUID
	var fu *fileUpload
	if err := DB.View(func(tx *bolt.Tx) error {
		var err error
		p, err = getPaste(tx, key)
		if err != nil {
			return err
		}
		if p != nil && p.Type == pasteTypeFileUpload {
			var id uuid.UUID
			copy(id[:], p.Content)
			fuID = &id
			fu, err = getFileUpload(tx, id)
			if err != nil {
				return err
			}
		}
		return nil
	}); err != nil {
		panic(err)
	}

	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 pasteStatePresent:
		var location string
		switch p.Type {
		case pasteTypeFileUpload:
			if fu == nil {
				panic(fmt.Sprintf("file for id %v does not exist in database\n", fuID))
			}
			location = fu.url().String()
			break
		case pasteTypeRedirect:
			location = p.redirectURL().String()
			break
		default:
			panic("paste type unsupported")
		}
		if flags&viewNoRedirect == 0 {
			http.Redirect(w, r, location, http.StatusSeeOther)
		}
		fmt.Fprint(w, location)
	case pasteStateDeleted:
		renderError(w, r, http.StatusGone, "paste has been deleted\n")
	default:
		panic(errors.Errorf("invalid paste.State (%v) for key '%v'", p.State, p.Key))
	}
}

func newPasteHandler(w http.ResponseWriter, r *http.Request) {
	newPasteHandlerMultipart(w, r, func(w http.ResponseWriter, r *http.Request) {
		newPasteHandlerURLEncoded(w, r, func(w http.ResponseWriter, r *http.Request) {
			renderError(w, r, http.StatusBadRequest, "no form data in request\n")
		})
	})
}

// Try to parse the new-paste request as multi-part form.
//
// If there is no multi-part form in the request, this handler will call next.
func newPasteHandlerMultipart(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
	reader, err := r.MultipartReader()
	if err != nil {
		next(w, r)
		return
	}

	part, err := reader.NextPart()
	if err != nil {
		if err == io.EOF {
			renderError(w, r, http.StatusBadRequest, "multipart form is empty\n")
			return
		}
		panic(errors.Wrap(err, "multipart.Reader.NextPart"))
	}
	if part.FormName() != "file" {
		msg := fmt.Sprintf("invalid multipart form name: %v", part.FormName())
		renderError(w, r, http.StatusBadRequest, msg)
		return
	}

	newFileUploadPasteHandler(w, r, *part)
}

func newFileUploadPasteHandler(w http.ResponseWriter, r *http.Request, part multipart.Part) {
	var fu *fileUpload
	var paste *paste
	if err := DB.Update(func(tx *bolt.Tx) error {
		var err error
		// Create the fileUpload in the database
		fu, err = newFileUpload(tx, &part, part.FileName(), part.Header.Get("Content-Type"))
		if err != nil {
			panic(errors.Wrap(err, "creating fileUpload"))
		}

		paste, err = shortenFileUploadID(tx, fu.ID)
		return err
	}); err != nil {
		panic(err)
	}
	data := map[string]interface{}{"Paste": paste}
	render(w, r, "newFileUploadPasteSuccess", data)
}

func newPasteHandlerURLEncoded(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
	if err := r.ParseForm(); err != nil {
		next(w, r)
		return
	}
	shorten := r.PostFormValue("shorten")
	if shorten == "" {
		renderError(w, r, http.StatusBadRequest, "no 'shorten' param given\n")
		return
	}
	newRedirectPasteHandler(w, r, shorten)
}

func newRedirectPasteHandler(w http.ResponseWriter, r *http.Request, shorten string) {
	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)\n")
		return
	}
	if userURL.Host == "" {
		renderError(w, r, http.StatusBadRequest, "invalid url (unspecified host)\n")
		return
	}

	var paste *paste
	if err := 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\n")
		return
	}

	var errorCode int
	if err := 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\n", err))
		return
	}
}

// Add a new fileUpload redirect to the database
//
// Returns the new paste key if the fileUpload was successfully added to the
// database
func shortenFileUploadID(tx *bolt.Tx, id uuid.UUID) (*paste, error) {
	return shorten(tx, pasteTypeFileUpload, id[:])
}

// Add a new URL to the database
//
// Returns the new paste key if the url was successfully shortened
func shortenURL(tx *bolt.Tx, userURL *url.URL) (*paste, error) {
	return shorten(tx, pasteTypeRedirect, []byte(userURL.String()))
}

// Add a paste (of any kind) to the database with arbitrary content.
func shorten(tx *bolt.Tx, ty pasteType, content []byte) (*paste, error) {
	// Generate the paste key
	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:        ty,
		State:       pasteStatePresent,
		Content:     content,
		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")
}