// Package server implements the KeepOrg synchronization server: accounts,
// nested groups, per-database grants, and the versioned KDBX sync endpoints.
//
// The server never opens a KDBX file. It moves opaque bytes and arbitrates
// who wrote last, which keeps the master passwords entirely on the clients.
package server

import (
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"net"
	"net/http"
	"path/filepath"
	"strings"
	"time"

	"cc.tiredsysadmin.keeporg/internal/blob"
	"cc.tiredsysadmin.keeporg/internal/kdbx"
	"cc.tiredsysadmin.keeporg/internal/secret"
	"cc.tiredsysadmin.keeporg/internal/sqldb"
	"cc.tiredsysadmin.keeporg/internal/store"
)

// Config is the server's whole configuration surface.
type Config struct {
	Addr        string        `json:"addr"`
	DataDir     string        `json:"data_dir"`
	ExternalURL string        `json:"external_url"`
	SessionTTL  time.Duration `json:"session_ttl"`
	MaxDBSize   int64         `json:"max_db_size"`
	TLSCert     string        `json:"tls_cert,omitempty"`
	TLSKey      string        `json:"tls_key,omitempty"`
	OIDC        OIDCConfig    `json:"oidc"`

	// TrustedProxies are the reverse proxies whose X-Forwarded-For is
	// believed, as addresses or CIDR ranges. Rate limits count per client
	// address, and behind a proxy every request otherwise comes from it.
	TrustedProxies []string `json:"trusted_proxies,omitempty"`

	// Database is where the server keeps its data: postgres://… for
	// PostgreSQL, or sqlite:<path>. The default is a SQLite file in DataDir.
	Database string `json:"database"`

	// MasterKeyFile holds the key that encrypts everything in the database
	// and wraps the vault keys the server keeps in order to merge. It belongs
	// outside DataDir and outside the database's backups: either alone must
	// not be enough to read anything.
	MasterKeyFile string `json:"master_key_file"`
	// VaultKDF is the work factor of vaults this server creates. The server
	// pays it three times per merge, and so does every client on every open.
	VaultKDF kdbx.KDFParams `json:"vault_kdf"`
}

// Defaults fills in every value a deployment may leave unset.
func (c *Config) Defaults() {
	if c.Addr == "" {
		c.Addr = ":8765"
	}
	if c.DataDir == "" {
		c.DataDir = "/var/lib/keeporg"
	}
	if c.ExternalURL == "" {
		// ":8765" means every interface; "127.0.0.1:8765" names its host.
		host := c.Addr
		if strings.HasPrefix(host, ":") {
			host = "localhost" + host
		}
		c.ExternalURL = "http://" + host
	}
	c.ExternalURL = strings.TrimRight(c.ExternalURL, "/")
	if c.SessionTTL == 0 {
		c.SessionTTL = 90 * 24 * time.Hour
	}
	if c.MaxDBSize == 0 {
		c.MaxDBSize = 32 << 20
	}
	if c.Database == "" {
		c.Database = "sqlite:" + filepath.Join(c.DataDir, "keeporg.db")
	}
	if c.MasterKeyFile == "" {
		c.MasterKeyFile = "/etc/keeporg/master.key"
	}
	if c.VaultKDF.MemoryKiB == 0 {
		c.VaultKDF = kdbx.DefaultKDF
	}
}

type Server struct {
	cfg     Config
	db      *sqldb.DB
	st      *store.Store
	blobs   *blob.Store
	hub     *Hub
	oidc    *oidcProvider
	keyring *secret.Keyring
	limits  *limiter
	proxies []*net.IPNet
	merges  chan struct{} // a slot per merge allowed to run at once
	mux     *http.ServeMux
	log     *log.Logger
}

// New opens the server's database and wires up its routes.
func New(cfg Config, lg *log.Logger) (*Server, error) {
	cfg.Defaults()
	proxies, err := parseProxies(cfg.TrustedProxies)
	if err != nil {
		return nil, err
	}
	// Everything in the database is sealed under the master key, so there
	// is no serving without it.
	kr, err := secret.LoadKeyring(cfg.MasterKeyFile)
	if err != nil {
		return nil, fmt.Errorf("master key: %w", err)
	}
	st, db, err := OpenStore(cfg, kr)
	if err != nil {
		return nil, err
	}
	s := &Server{cfg: cfg, db: db, st: st, blobs: blob.Open(db, kr.Derive("blobs")),
		keyring: kr, limits: newLimiter(), proxies: proxies, merges: make(chan struct{}, 2),
		hub: NewHub(), mux: http.NewServeMux(), log: lg}
	if err := s.importLegacy(); err != nil {
		s.Close()
		return nil, fmt.Errorf("import %s: %w", cfg.DataDir, err)
	}
	if cfg.OIDC.Enabled() {
		s.oidc = newOIDCProvider(cfg.OIDC, cfg.ExternalURL+"/oidc/callback")
	}
	s.checkVaultKeys()
	s.routes()
	return s, nil
}

// checkVaultKeys reports at startup whether the master key still opens the
// vault keys in the state document. Getting this wrong is quiet and
// expensive: a container started without its master key mounted mints a new
// one, and every merge then fails one push at a time. Saying so once, at
// startup, is the difference between a puzzle and a fixable mistake.
func (s *Server) checkVaultKeys() {
	var total, broken int
	s.st.Read(func(st *store.State) {
		for id, d := range st.Databases {
			if d.WrappedKey == "" {
				continue
			}
			total++
			if s.keyring == nil {
				broken++
				continue
			}
			if _, err := s.keyring.Unwrap(id, d.WrappedKey); err != nil {
				broken++
			}
		}
	})
	switch {
	case broken == 0 && total > 0:
		s.log.Printf("%d vault keys available for merging", total)
	case broken > 0:
		s.log.Printf("WARNING: %d of %d stored vault keys do not open with this "+
			"master key. Those vaults cannot be merged until the original key is "+
			"restored ($%s, $%s, or %s). Nothing is lost: clients still open the "+
			"vaults with their own passwords.",
			broken, total, secret.MasterKeyEnv, secret.MasterKeyFileEnv,
			s.cfg.MasterKeyFile)
	}
}

// Store exposes the metadata store for bootstrap commands.
func (s *Server) Store() *store.Store { return s.st }

// Config returns the effective configuration.
func (s *Server) Config() Config { return s.cfg }

// Handler is the server's HTTP entry point.
// Handler is the server's HTTP surface, with the security headers every
// response carries.
func (s *Server) Handler() http.Handler {
	hsts := strings.HasPrefix(s.cfg.ExternalURL, "https://")
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("Referrer-Policy", "no-referrer")
		// The pages have no scripts, no images and no frames; their only
		// style is inline. Nothing may frame them, which is what stops a
		// sign-out or delete button being clicked through a disguise.
		h.Set("Content-Security-Policy", "default-src 'none'; style-src 'unsafe-inline'; "+
			"form-action 'self'; frame-ancestors 'none'; base-uri 'none'")
		h.Set("X-Frame-Options", "DENY")
		h.Set("Cross-Origin-Opener-Policy", "same-origin")
		// Pages carry CSRF tokens, invite links and, once, a TOTP secret;
		// API answers carry bearer tokens. None of it belongs in a cache.
		h.Set("Cache-Control", "no-store")
		if hsts {
			h.Set("Strict-Transport-Security", "max-age=63072000; includeSubDomains")
		}
		s.mux.ServeHTTP(w, r)
	})
}

// StartHousekeeping runs periodic expiry until done is closed.
func (s *Server) StartHousekeeping(done <-chan struct{}) {
	go func() {
		t := time.NewTicker(time.Hour)
		defer t.Stop()
		for {
			select {
			case <-done:
				return
			case <-t.C:
				if err := s.st.GC(time.Now()); err != nil {
					s.log.Printf("housekeeping: %v", err)
				}
			}
		}
	}()
}

func (s *Server) routes() {
	m := s.mux
	m.HandleFunc("GET /healthz", s.handleHealth)

	// Authentication.
	m.HandleFunc("POST /api/v1/auth/login", s.handleLogin)
	m.HandleFunc("POST /api/v1/auth/logout", s.authed(s.handleLogout))
	m.HandleFunc("GET /api/v1/auth/whoami", s.authed(s.handleWhoami))
	m.HandleFunc("POST /api/v1/auth/password", s.authed(s.handleChangePassword))
	m.HandleFunc("POST /api/v1/auth/totp/enroll", s.authed(s.handleTOTPEnroll))
	m.HandleFunc("POST /api/v1/auth/totp/confirm", s.authed(s.handleTOTPConfirm))
	m.HandleFunc("DELETE /api/v1/auth/totp", s.authed(s.handleTOTPDisable))
	m.HandleFunc("GET /api/v1/auth/sessions", s.authed(s.handleListSessions))
	m.HandleFunc("DELETE /api/v1/auth/sessions", s.authed(s.handleRevokeOtherSessions))
	m.HandleFunc("DELETE /api/v1/auth/sessions/{id}", s.authed(s.handleRevokeSession))
	m.HandleFunc("POST /api/v1/auth/device/start", s.handleDeviceStart)
	m.HandleFunc("POST /api/v1/auth/device/poll", s.handleDevicePoll)

	// The web interface: sign in, see your vaults, create one, and run the
	// server. Every page goes through webPage and every form through
	// webForm, which is where the session and the CSRF token are checked.
	m.HandleFunc("GET /{$}", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, "/web", http.StatusFound)
	})
	m.HandleFunc("GET /web", s.handleWebHome)
	m.HandleFunc("POST /web/signin", s.handleWebSignIn)
	m.HandleFunc("POST /web/signout", s.webForm(s.handleWebSignOut))
	m.HandleFunc("GET /web/vaults", s.webPage(s.handleWebVaults))
	m.HandleFunc("POST /web/vaults", s.webForm(s.handleWebCreateVault))
	m.HandleFunc("GET /web/account", s.webPage(s.handleWebAccount))
	m.HandleFunc("POST /web/account", s.webForm(s.handleWebAccountAction))
	m.HandleFunc("GET /web/vaults/{id}/delete", s.webPage(s.handleWebDeleteVaultPage))
	m.HandleFunc("POST /web/vaults/{id}/delete", s.webForm(s.handleWebDeleteVault))
	m.HandleFunc("GET /web/groups", s.webPage(s.handleWebGroups))
	m.HandleFunc("POST /web/groups", s.webForm(s.handleWebCreateGroup))
	m.HandleFunc("GET /web/groups/{id}", s.webPage(s.handleWebGroup))
	m.HandleFunc("POST /web/groups/{id}", s.webForm(s.handleWebGroupAction))
	m.HandleFunc("GET /web/users", s.webPage(s.handleWebUsers))
	m.HandleFunc("POST /web/users", s.webForm(s.handleWebUserAction))
	m.HandleFunc("GET /web/invites", s.webPage(s.handleWebInvites))
	m.HandleFunc("POST /web/invites", s.webForm(s.handleWebInviteAction))

	// Browser-facing pages: device approval, invite registration, OIDC.
	m.HandleFunc("GET /device", s.handleDevicePage)
	m.HandleFunc("POST /device", s.handleDeviceApprove)
	m.HandleFunc("GET /invite/{token}", s.handleInvitePage)
	m.HandleFunc("POST /invite/{token}", s.handleInviteRedeem)
	m.HandleFunc("GET /oidc/login", s.handleOIDCLogin)
	m.HandleFunc("GET /oidc/callback", s.handleOIDCCallback)
	m.HandleFunc("POST /oidc/approve", s.handleOIDCApprove)

	// Synchronization.
	m.HandleFunc("GET /api/v1/databases", s.authed(s.handleListDatabases))
	m.HandleFunc("GET /api/v1/databases/{id}/blob", s.authed(s.handleGetBlob))
	m.HandleFunc("PUT /api/v1/databases/{id}/blob", s.authed(s.handlePutBlob))
	m.HandleFunc("GET /api/v1/events", s.authed(s.handleEvents))

	// Vaults: a database the server created, and can merge.
	m.HandleFunc("POST /api/v1/vaults", s.authed(s.handleCreateVault))
	m.HandleFunc("POST /api/v1/databases/{id}/key", s.authed(s.handleSetVaultKey))

	// Administration.
	m.HandleFunc("POST /api/v1/databases", s.authed(s.handleCreateDatabase))
	m.HandleFunc("PATCH /api/v1/databases/{id}", s.authed(s.handlePatchDatabase))
	m.HandleFunc("DELETE /api/v1/databases/{id}", s.authed(s.handleDeleteDatabase))
	m.HandleFunc("GET /api/v1/groups", s.authed(s.handleListGroups))
	m.HandleFunc("POST /api/v1/groups", s.authed(s.handleCreateGroup))
	m.HandleFunc("DELETE /api/v1/groups/{id}", s.authed(s.handleDeleteGroup))
	m.HandleFunc("POST /api/v1/groups/{id}/members", s.authed(s.handleSetMember))
	m.HandleFunc("DELETE /api/v1/groups/{id}/members/{user}", s.authed(s.handleRemoveMember))
	m.HandleFunc("POST /api/v1/grants", s.authed(s.handleSetGrant))
	m.HandleFunc("DELETE /api/v1/grants", s.authed(s.handleDeleteGrant))
	m.HandleFunc("POST /api/v1/invites", s.authed(s.handleCreateInvite))
	m.HandleFunc("GET /api/v1/invites", s.authed(s.handleListInvites))
	m.HandleFunc("DELETE /api/v1/invites/{token}", s.authed(s.handleRevokeInvite))
	m.HandleFunc("GET /api/v1/users", s.authed(s.handleListUsers))
	m.HandleFunc("PATCH /api/v1/users/{id}", s.authed(s.handlePatchUser))
}

// ---- request plumbing ----

type apiError struct {
	Code    string `json:"code"`
	Message string `json:"error"`
}

var errUnauthorized = errors.New("unauthorized")

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	if v != nil {
		_ = json.NewEncoder(w).Encode(v)
	}
}

func fail(w http.ResponseWriter, status int, code, msg string) {
	writeJSON(w, status, apiError{Code: code, Message: msg})
}

func readJSON(w http.ResponseWriter, r *http.Request, v any) bool {
	dec := json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<20))
	dec.DisallowUnknownFields()
	if err := dec.Decode(v); err != nil {
		fail(w, http.StatusBadRequest, "bad_request", err.Error())
		return false
	}
	return true
}

// handler is an authenticated request handler.
type handler func(http.ResponseWriter, *http.Request, *store.User)

// authed resolves the bearer token to a live, enabled user before calling fn.
// Per-object permission is then checked inside the handler, where the object
// being acted on is known.
func (s *Server) authed(fn handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		u, err := s.userFromRequest(r)
		if err != nil {
			w.Header().Set("WWW-Authenticate", `Bearer realm="keeporg"`)
			fail(w, http.StatusUnauthorized, "unauthorized", "invalid or expired token")
			return
		}
		fn(w, r, u)
	}
}

func (s *Server) userFromRequest(r *http.Request) (*store.User, error) {
	tok := bearer(r)
	if tok == "" {
		return nil, errUnauthorized
	}
	var (
		out  *store.User
		seen time.Time
	)
	s.st.Read(func(st *store.State) {
		sess := st.Sessions[tok]
		if sess == nil || time.Now().After(sess.ExpiresAt) {
			return
		}
		if u := st.Users[sess.UserID]; u != nil && !u.Disabled {
			cp := *u
			out, seen = &cp, sess.LastSeenAt
		}
	})
	if out == nil {
		return nil, errUnauthorized
	}
	s.markSeen(tok, seen)
	return out, nil
}

// seenResolution is how stale a session's LastSeenAt may get before a
// request refreshes it. Each refresh rewrites the state document, so it is
// minutes, not seconds; the devices list only needs to tell today from last
// month.
const seenResolution = 5 * time.Minute

// markSeen records that a session was used, when its record is stale.
func (s *Server) markSeen(token string, last time.Time) {
	if time.Since(last) < seenResolution {
		return
	}
	_ = s.st.Update(func(st *store.State) error {
		if sess := st.Sessions[token]; sess != nil {
			sess.LastSeenAt = time.Now()
		}
		return nil
	})
}

// bearer extracts a token from the Authorization header. The event stream
// alone also takes ?access_token=, which clients before 0.12 sent; a token
// in a URL ends up in proxy logs, so nothing else accepts it, and current
// clients send the header there too.
func bearer(r *http.Request) string {
	h := r.Header.Get("Authorization")
	if after, ok := strings.CutPrefix(h, "Bearer "); ok {
		return strings.TrimSpace(after)
	}
	if r.URL.Path == "/api/v1/events" {
		return r.URL.Query().Get("access_token")
	}
	return ""
}

// sessionAlive reports whether a token still belongs to a live session of
// an enabled account, for long requests that outlast their authentication.
func (s *Server) sessionAlive(token string) bool {
	alive := false
	s.st.Read(func(st *store.State) {
		sess := st.Sessions[token]
		if sess == nil || time.Now().After(sess.ExpiresAt) {
			return
		}
		u := st.Users[sess.UserID]
		alive = u != nil && !u.Disabled
	})
	return alive
}

func (s *Server) newSession(st *store.State, userID, label string) *store.Session {
	now := time.Now()
	sess := &store.Session{
		Token:      secret.Token(),
		UserID:     userID,
		Label:      label,
		CSRF:       secret.Token(),
		CreatedAt:  now,
		ExpiresAt:  now.Add(s.cfg.SessionTTL),
		LastSeenAt: now,
	}
	st.Sessions[sess.Token] = sess
	return sess
}

// newBrowserSession is a session for a web cookie, named after the browser
// so that a list of them can be told apart.
func (s *Server) newBrowserSession(st *store.State, userID string, r *http.Request) *store.Session {
	sess := s.newSession(st, userID, browserLabel(r.UserAgent()))
	sess.Browser = true
	return sess
}

func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
	var users, dbs int
	s.st.Read(func(st *store.State) { users, dbs = len(st.Users), len(st.Databases) })
	writeJSON(w, http.StatusOK, map[string]any{
		"status": "ok", "users": users, "databases": dbs, "streams": s.hub.Count(),
	})
}