package web

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"encoding/json"
	"errors"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"time"

	"git.veillax.com/Veillax/mako/internal/config"
	"git.veillax.com/Veillax/mako/internal/oidc"
	"git.veillax.com/Veillax/mako/internal/store"
	"git.veillax.com/Veillax/mako/internal/vault"
)

// The vault is a second notebook that opens only with a passphrase. Its pages are encrypted with a key
// made from that passphrase together with the server's key, so the server cannot read them until you
// unlock it, and they are in no list, search or download of the ordinary notebook. Unlocked, it lives
// in memory only until you lock it, sign out, or leave it alone for a quarter of an hour.
const (
	vaultCookie  = "mako_vault"
	vaultIdle    = 15 * time.Minute
	vaultMinPass = 10
	vaultTries   = 5
	vaultWindow  = 10 * time.Minute
)

// vaultIterations is how slow it is to check one passphrase guess. Tests lower it.
var vaultIterations = 600_000

type vaultFile struct {
	Salt  string `json:"salt"`
	Iter  int    `json:"iter"`
	Check string `json:"check"` // a sealed word that only the right passphrase can open
}

// vaultState is an unlocked vault: one store shared by every browser holding a token for it.
type vaultState struct {
	st     *store.Store
	tokens map[string]time.Time // cookie value to when it lapses
}

func vaultDir(c config.Config, sub string) string {
	return filepath.Join(c.DataDir, "users", userKey(c, sub), "vault")
}

func readVaultFile(dir string) (vaultFile, bool) {
	var vf vaultFile
	b, err := os.ReadFile(filepath.Join(dir, "vault.json"))
	if err != nil || json.Unmarshal(b, &vf) != nil || vf.Salt == "" || vf.Iter < 1 {
		return vaultFile{}, false
	}
	return vf, true
}

func vaultBox(c config.Config, sub, pass string, vf vaultFile) (*vault.Cipher, error) {
	salt, err := base64.RawURLEncoding.DecodeString(vf.Salt)
	if err != nil {
		return nil, err
	}
	dk, err := vault.Passphrase(pass, salt, vf.Iter)
	if err != nil {
		return nil, err
	}
	return vault.New(c.Key+"|"+dk, c.OIDC.Issuer+"|vault", sub)
}

// sweepVaults forgets tokens that have lapsed, and vaults nobody holds a token for.
func (s *Server) sweepVaults(now time.Time) {
	for uk, vs := range s.vstate {
		for tok, exp := range vs.tokens {
			if now.After(exp) {
				delete(vs.tokens, tok)
				delete(s.vtoken, tok)
			}
		}
		if len(vs.tokens) == 0 {
			delete(s.vstate, uk)
		}
	}
}

// openVault returns the unlocked vault this browser holds the token for, and keeps it open a while longer.
func (s *Server) openVault(c config.Config, r *http.Request, sub string) (string, *store.Store, bool) {
	ck, err := r.Cookie(vaultCookie)
	if err != nil {
		return "", nil, false
	}
	now := time.Now()
	s.vmu.Lock()
	defer s.vmu.Unlock()
	s.sweepVaults(now)
	uk := s.vtoken[ck.Value]
	vs := s.vstate[uk]
	if vs == nil || uk != userKey(c, sub) {
		return "", nil, false
	}
	vs.tokens[ck.Value] = now.Add(vaultIdle)
	return ck.Value, vs.st, true
}

// startVault hands this browser a token for the vault, opening it if no one else has.
func (s *Server) startVault(w http.ResponseWriter, c config.Config, sub string, box *vault.Cipher) error {
	uk := userKey(c, sub)
	s.vmu.Lock()
	defer s.vmu.Unlock()
	s.sweepVaults(time.Now())
	vs := s.vstate[uk]
	if vs == nil {
		st, err := store.Open(vaultDir(c, sub), box)
		if err != nil {
			return err
		}
		vs = &vaultState{st: st, tokens: map[string]time.Time{}}
		s.vstate[uk] = vs
	}
	tok := oidc.Random(32)
	vs.tokens[tok] = time.Now().Add(vaultIdle)
	s.vtoken[tok] = uk
	setCookie(w, c, vaultCookie, tok, "/", vaultIdle)
	return nil
}

// lockVault drops this browser's token. The vault leaves memory once nobody holds one.
func (s *Server) lockVault(w http.ResponseWriter, r *http.Request) {
	c := s.cfg.Get()
	if ck, err := r.Cookie(vaultCookie); err == nil {
		s.vmu.Lock()
		if uk, ok := s.vtoken[ck.Value]; ok {
			delete(s.vtoken, ck.Value)
			if vs := s.vstate[uk]; vs != nil {
				delete(vs.tokens, ck.Value)
				if len(vs.tokens) == 0 {
					delete(s.vstate, uk)
				}
			}
		}
		s.vmu.Unlock()
	}
	setCookie(w, c, vaultCookie, "", "/", 0)
}

// vaultAPI is api for the pages in the vault: it needs the vault to be unlocked as well as a sign-in.
func (s *Server) vaultAPI(fn handlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		c := s.cfg.Get()
		ses, ok := s.session(c, r)
		if !ok {
			fail(w, http.StatusUnauthorized, "sign in required")
			return
		}
		if r.Method != http.MethodGet && r.Header.Get("X-Mako") != "1" {
			fail(w, http.StatusForbidden, "missing X-Mako header")
			return
		}
		tok, st, ok := s.openVault(c, r, ses.Sub)
		if !ok {
			failCode(w, http.StatusLocked, "the vault is locked", "locked")
			return
		}
		setCookie(w, c, vaultCookie, tok, "/", vaultIdle)
		r.Body = http.MaxBytesReader(w, r.Body, maxRequestBody)
		fn(w, r, principal{Sub: ses.Sub, Name: ses.Name, Email: ses.Email, st: st})
	}
}

func (s *Server) vaultInfo(w http.ResponseWriter, r *http.Request, p principal) {
	c := s.cfg.Get()
	_, exists := readVaultFile(vaultDir(c, p.Sub))
	_, _, unlocked := s.openVault(c, r, p.Sub)
	writeJSON(w, map[string]bool{"exists": exists, "unlocked": unlocked})
}

type passphraseBody struct {
	Passphrase string `json:"passphrase"`
}

func (s *Server) vaultCreate(w http.ResponseWriter, r *http.Request, p principal) {
	var in passphraseBody
	if !decode(w, r, &in) {
		return
	}
	c := s.cfg.Get()
	dir := vaultDir(c, p.Sub)
	if _, exists := readVaultFile(dir); exists {
		fail(w, http.StatusConflict, "you already have a vault; unlock it instead")
		return
	}
	if len([]rune(in.Passphrase)) < vaultMinPass {
		fail(w, http.StatusBadRequest, "pick a passphrase of at least 10 characters; a few words strung together is good")
		return
	}
	salt := make([]byte, 16)
	if _, err := rand.Read(salt); err != nil {
		fail(w, http.StatusInternalServerError, "could not make a vault")
		return
	}
	vf := vaultFile{Salt: base64.RawURLEncoding.EncodeToString(salt), Iter: vaultIterations}
	box, err := vaultBox(c, p.Sub, in.Passphrase, vf)
	if err != nil {
		fail(w, http.StatusInternalServerError, "could not make a vault")
		return
	}
	vf.Check = base64.RawURLEncoding.EncodeToString(box.Seal([]byte("mako vault"), "check"))
	b, _ := json.Marshal(vf)
	if err := os.MkdirAll(dir, 0o700); err != nil {
		log.Printf("vault: %v", err)
		fail(w, http.StatusInternalServerError, "could not make a vault")
		return
	}
	tmp := filepath.Join(dir, ".vault.json.tmp")
	err = os.WriteFile(tmp, b, 0o600)
	if err == nil {
		err = os.Rename(tmp, filepath.Join(dir, "vault.json"))
	}
	if err != nil {
		log.Printf("vault: %v", err)
		fail(w, http.StatusInternalServerError, "could not make a vault")
		return
	}
	if err := s.startVault(w, c, p.Sub, box); err != nil {
		log.Printf("vault: %v", err)
		fail(w, http.StatusInternalServerError, "could not open the vault; the server's log says why")
		return
	}
	writeJSON(w, map[string]bool{"exists": true, "unlocked": true})
}

func (s *Server) vaultUnlock(w http.ResponseWriter, r *http.Request, p principal) {
	var in passphraseBody
	if !decode(w, r, &in) {
		return
	}
	c := s.cfg.Get()
	vf, exists := readVaultFile(vaultDir(c, p.Sub))
	if !exists {
		fail(w, http.StatusNotFound, "you have no vault yet")
		return
	}
	uk, now := userKey(c, p.Sub), time.Now()
	s.vmu.Lock()
	recent := s.vfails[uk][:0]
	for _, t := range s.vfails[uk] {
		if now.Sub(t) < vaultWindow {
			recent = append(recent, t)
		}
	}
	s.vfails[uk] = recent
	tooMany := len(recent) >= vaultTries
	s.vmu.Unlock()
	if tooMany {
		failCode(w, http.StatusTooManyRequests, "too many wrong passphrases; try again in a few minutes", "too_many")
		return
	}
	box, err := vaultBox(c, p.Sub, in.Passphrase, vf)
	check, _ := base64.RawURLEncoding.DecodeString(vf.Check)
	var word []byte
	if err == nil {
		word, err = box.Open(check, "check")
	}
	if err != nil || subtle.ConstantTimeCompare(word, []byte("mako vault")) != 1 {
		s.vmu.Lock()
		s.vfails[uk] = append(s.vfails[uk], now)
		s.vmu.Unlock()
		failCode(w, http.StatusForbidden, "that is not the passphrase", "wrong_passphrase")
		return
	}
	s.vmu.Lock()
	delete(s.vfails, uk)
	s.vmu.Unlock()
	if err := s.startVault(w, c, p.Sub, box); err != nil {
		log.Printf("vault: %v", err)
		if errors.Is(err, vault.ErrWrongKey) {
			fail(w, http.StatusInternalServerError, "the vault's pages cannot be read with this key; the server's log says more")
		} else {
			fail(w, http.StatusInternalServerError, "could not open the vault; the server's log says why")
		}
		return
	}
	writeJSON(w, map[string]bool{"exists": true, "unlocked": true})
}

func (s *Server) vaultLock(w http.ResponseWriter, r *http.Request, p principal) {
	s.lockVault(w, r)
	writeJSON(w, map[string]bool{"exists": true, "unlocked": false})
}

// moveToVault takes a page out of the ordinary notebook and puts it in the vault, which must be unlocked.
// Links to it elsewhere become [[locked:id]], so the page's title stays in the vault only.
func (s *Server) moveToVault(w http.ResponseWriter, r *http.Request, p principal) {
	c := s.cfg.Get()
	_, vst, ok := s.openVault(c, r, p.Sub)
	if !ok {
		failCode(w, http.StatusLocked, "unlock the vault first", "locked")
		return
	}
	id := r.PathValue("id")
	n, err := p.st.Get(id)
	if err == nil && n.Trashed {
		err = store.ErrNotFound
	}
	if err != nil {
		storeFail(w, err)
		return
	}
	if _, err := vst.Import(n); err != nil {
		if errors.Is(err, store.ErrExists) {
			failCode(w, http.StatusConflict, existsMessage(n, "your vault"), "exists")
			return
		}
		storeFail(w, err)
		return
	}
	if _, err := p.st.Detach(id); err != nil {
		vst.Discard(id) // the page stays where it was
		storeFail(w, err)
		return
	}
	writeJSON(w, map[string]string{"id": id})
}

// moveFromVault brings a page back out of the vault into the ordinary notebook and points the
// [[locked:id]] links to it at its title again.
func (s *Server) moveFromVault(w http.ResponseWriter, r *http.Request, p principal) {
	main, err := s.notebook(s.cfg.Get(), p.Sub, p.Name, p.Email)
	if err != nil {
		fail(w, http.StatusInternalServerError, "could not open your notes; the server's log says why")
		return
	}
	id := r.PathValue("id")
	n, err := p.st.Get(id)
	if err == nil && n.Trashed {
		err = store.ErrNotFound
	}
	if err != nil {
		storeFail(w, err)
		return
	}
	in, err := main.Import(n)
	if err != nil {
		if errors.Is(err, store.ErrExists) {
			failCode(w, http.StatusConflict, existsMessage(n, "your notebook"), "exists")
			return
		}
		storeFail(w, err)
		return
	}
	if err := main.Reveal(id, in.Title); err != nil {
		main.Discard(id)
		storeFail(w, err)
		return
	}
	if err := p.st.Discard(id); err != nil {
		log.Printf("vault: moved %s out but could not remove it from the vault: %v", id, err)
		fail(w, http.StatusInternalServerError, "the page is back in your notebook, but a copy is still in the vault; the server's log says why")
		return
	}
	writeJSON(w, map[string]string{"id": id})
}

func existsMessage(n store.Note, where string) string {
	if n.Daily != "" {
		return where + " already has a journal page for that day"
	}
	return where + " already has this page"
}