// 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"
	"log"
	"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/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"`

	// MasterKeyFile holds the key that wraps the vault keys the server keeps
	// in order to merge. It belongs outside DataDir: a copy of the data
	// directory alone must not be enough to open a vault.
	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 == "" {
		c.ExternalURL = "http://localhost" + c.Addr
	}
	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.MasterKeyFile == "" {
		c.MasterKeyFile = "/etc/keeporg/master.key"
	}
	if c.VaultKDF.MemoryKiB == 0 {
		c.VaultKDF = kdbx.DefaultKDF
	}
}

type Server struct {
	cfg     Config
	st      *store.Store
	blobs   *blob.Store
	hub     *Hub
	oidc    *oidcProvider
	keyring *secret.Keyring
	mux     *http.ServeMux
	log     *log.Logger
}

// New opens the server's data directory and wires up its routes.
func New(cfg Config, lg *log.Logger) (*Server, error) {
	cfg.Defaults()
	st, err := store.Open(filepath.Join(cfg.DataDir, "state.json"))
	if err != nil {
		return nil, err
	}
	blobs, err := blob.Open(filepath.Join(cfg.DataDir, "blobs"))
	if err != nil {
		return nil, err
	}
	s := &Server{cfg: cfg, st: st, blobs: blobs, hub: NewHub(), mux: http.NewServeMux(), log: lg}
	// Without a master key the server still serves every strategy that does
	// not need to read a vault; only merging and vault creation are refused.
	if kr, kerr := secret.LoadKeyring(cfg.MasterKeyFile); kerr != nil {
		lg.Printf("no master key, so this server cannot create or merge vaults: %v", kerr)
	} else {
		s.keyring = kr
	}
	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.
func (s *Server) Handler() http.Handler { return s.mux }

// 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("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("POST /web/password", s.webForm(s.handleWebChangePassword))
	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)

	// 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
	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 = &cp
		}
	})
	if out == nil {
		return nil, errUnauthorized
	}
	return out, nil
}

// bearer extracts a token from the Authorization header, or from the
// access_token query parameter, which EventSource clients need because they
// cannot set headers.
func bearer(r *http.Request) string {
	h := r.Header.Get("Authorization")
	if after, ok := strings.CutPrefix(h, "Bearer "); ok {
		return strings.TrimSpace(after)
	}
	return r.URL.Query().Get("access_token")
}

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