// Package userapi owns accounts, passwords, devices, tokens and account
// data: everything that identifies a local user and their sessions.
//
// It is the component the Client-Server API handlers call for anything
// to do with who is making a request. The HTTP shapes live in clientapi;
// what is here is the part that would be the same behind any transport —
// which is also what makes `warp create-account` able to create an account
// without starting a server.
//
// Nothing in this package knows about rooms. A device's encryption keys
// are the keyserver's and its pushers the push server's, and both hear
// about a device going away through the DeviceObserver. Push rules are
// account data, but the push server is their only writer.
package userapi

import (
	"context"
	"errors"
	"log/slog"
	"sync"
	"time"

	"github.com/dariuszjaniak/warp/server/internal/storage"
)

// Errors callers have to tell apart. The storage sentinels are re-exported
// rather than translated: there is one error value with two names, so
// errors.Is works whichever package a caller reaches for.
var (
	ErrUserExists        = storage.ErrUserExists
	ErrNoSuchUser        = storage.ErrNoSuchUser
	ErrNoSuchDevice      = storage.ErrNoSuchDevice
	ErrNoSuchToken       = storage.ErrNoSuchToken
	ErrNoSuchAccountData = storage.ErrNoSuchAccountData

	// ErrTokenExpired is an access token that was valid and has timed out.
	// It is distinct from ErrNoSuchToken because the spec answers it with a
	// soft logout: the client may keep its encryption state and log in
	// again.
	ErrTokenExpired = errors.New("access token has expired")

	// ErrAccountDeactivated is a token belonging to an account that has
	// been deactivated.
	ErrAccountDeactivated = errors.New("account has been deactivated")

	// ErrWrongPassword is a failed password check. It is deliberately the
	// same error whether the account exists or not, so that callers cannot
	// turn it into a user-enumeration oracle by accident.
	ErrWrongPassword = errors.New("invalid password")

	// ErrNoPassword is an account that has no password set and so cannot
	// use m.login.password.
	ErrNoPassword = errors.New("account has no password")

	// ErrInvalidDeviceID is a client-supplied device ID that is empty, too
	// long or contains control characters.
	ErrInvalidDeviceID = errors.New("invalid device ID")
)

// API is the userapi component.
type API struct {
	serverName string
	store      storage.UserStore
	log        *slog.Logger
	now        func() time.Time

	accessTokenLifetime  time.Duration
	refreshTokenLifetime time.Duration

	// lastSeen throttles the last-seen bookkeeping; see RecordActivity.
	lastSeen sync.Map

	// observer hears about deleted and renamed devices; nil hears nothing.
	observer DeviceObserver
}

// DeviceObserver is told about changes to devices that something else
// keeps state for: the keyserver, whose keys for a deleted device have to
// go with it. *keyserver.API satisfies it.
//
// It is called after the change has been made, on the request path, and
// must not fail it: the device is already gone.
type DeviceObserver interface {
	// DevicesDeleted is called with the deleted device IDs, or with none
	// when every device of the user was deleted.
	DevicesDeleted(ctx context.Context, localpart string, deviceIDs []string)

	// DeviceRenamed is called when a device's display name changes.
	DeviceRenamed(ctx context.Context, localpart, deviceID string)
}

// SetDeviceObserver connects the observer. It is a setter because the
// keyserver is built after the userapi it reads devices from.
func (a *API) SetDeviceObserver(o DeviceObserver) { a.observer = o }

// Options configure the component.
type Options struct {
	// ServerName is the Matrix server name; it becomes the domain part of
	// every user ID this component hands out.
	ServerName string

	// Store is the persistence layer.
	Store storage.UserStore

	// AccessTokenLifetime expires issued access tokens. Zero issues tokens
	// that never expire.
	AccessTokenLifetime time.Duration

	// RefreshTokenLifetime bounds how long a refresh token stays usable.
	// Zero means no expiry.
	RefreshTokenLifetime time.Duration

	Logger *slog.Logger

	// Now is the clock, so tests can control token expiry. Nil means
	// time.Now.
	Now func() time.Time
}

// New builds the component.
func New(opts Options) (*API, error) {
	if opts.ServerName == "" {
		return nil, errors.New("userapi: ServerName must not be empty")
	}
	if opts.Store == nil {
		return nil, errors.New("userapi: Store must not be nil")
	}
	if opts.Logger == nil {
		opts.Logger = slog.Default()
	}
	if opts.Now == nil {
		opts.Now = time.Now
	}
	return &API{
		serverName:           opts.ServerName,
		store:                opts.Store,
		log:                  opts.Logger,
		now:                  opts.Now,
		accessTokenLifetime:  opts.AccessTokenLifetime,
		refreshTokenLifetime: opts.RefreshTokenLifetime,
	}, nil
}

// ServerName returns the server name user IDs are built with.
func (a *API) ServerName() string { return a.serverName }

// nowMS is the current time in the unit the store uses.
func (a *API) nowMS() int64 { return a.now().UnixMilli() }

// NewAccountRequest describes an account to create.
type NewAccountRequest struct {
	// Localpart is normalised and validated by CreateAccount.
	Localpart string

	// Password may be empty, which creates an account that cannot log in
	// with a password. `warp create-account` uses that for a placeholder
	// account; the admin API does not offer it.
	Password string

	DisplayName string
	Admin       bool
}

// CreateAccount validates the request, hashes the password and stores the
// account. It returns ErrUserExists if the name is taken and
// ErrInvalidLocalpart if the name is not usable.
func (a *API) CreateAccount(ctx context.Context, req NewAccountRequest) (storage.Account, error) {
	localpart := NormaliseLocalpart(req.Localpart)
	if err := ValidateLocalpart(localpart, a.serverName); err != nil {
		return storage.Account{}, err
	}

	var hash string
	if req.Password != "" {
		var err error
		if hash, err = HashPassword(req.Password); err != nil {
			return storage.Account{}, err
		}
	}

	acc, err := a.store.CreateAccount(ctx, storage.NewAccount{
		Localpart:    localpart,
		PasswordHash: hash,
		DisplayName:  req.DisplayName,
		Admin:        req.Admin,
		CreatedAtMS:  a.nowMS(),
	})
	if err != nil {
		return storage.Account{}, err
	}
	a.log.Info("created account", "user_id", a.UserID(localpart), "admin", req.Admin)
	return acc, nil
}

// Account reads an account by normalised localpart.
func (a *API) Account(ctx context.Context, localpart string) (storage.Account, error) {
	return a.store.Account(ctx, localpart)
}

// AccountExists reports whether a localpart is taken. It is the answer
// behind /register/available, and deliberately does not distinguish a
// deactivated account: the name stays reserved.
func (a *API) AccountExists(ctx context.Context, localpart string) (bool, error) {
	switch _, err := a.store.Account(ctx, localpart); {
	case err == nil:
		return true, nil
	case errors.Is(err, ErrNoSuchUser):
		return false, nil
	default:
		return false, err
	}
}

// SetAdmin grants or revokes the admin flag.
func (a *API) SetAdmin(ctx context.Context, localpart string, admin bool) error {
	return a.store.SetAdmin(ctx, localpart, admin)
}

// SetPassword replaces an account's password.
func (a *API) SetPassword(ctx context.Context, localpart, password string) error {
	hash, err := HashPassword(password)
	if err != nil {
		return err
	}
	return a.store.SetPasswordHash(ctx, localpart, hash)
}

// CheckPassword verifies a password against an account.
//
// Every failure path costs one argon2id hash, including an account that does
// not exist or has no password, so the time a rejection takes says nothing
// about which user names are real.
func (a *API) CheckPassword(ctx context.Context, localpart, password string) error {
	hash, err := a.store.PasswordHash(ctx, localpart)
	switch {
	case errors.Is(err, ErrNoSuchUser):
		_, _ = VerifyPassword(dummyPasswordHash, password)
		return ErrWrongPassword
	case err != nil:
		return err
	}
	if hash == "" {
		_, _ = VerifyPassword(dummyPasswordHash, password)
		return ErrNoPassword
	}

	ok, err := VerifyPassword(hash, password)
	switch {
	case errors.Is(err, ErrPasswordTooLong):
		return ErrWrongPassword
	case err != nil:
		// A malformed hash is an operational problem, not a wrong password.
		a.log.Error("stored password hash is unusable", "localpart", localpart, "error", err)
		return err
	case !ok:
		return ErrWrongPassword
	}
	return nil
}

// SessionRequest asks for a new device and its tokens.
type SessionRequest struct {
	// Localpart must already be normalised and must exist.
	Localpart string

	// DeviceID is the client's choice. Empty means generate one. Naming a
	// device that already exists re-uses it and revokes its old tokens.
	DeviceID string

	// DisplayName is initial_device_display_name: used only when the device
	// is created.
	DisplayName string

	// WithRefreshToken issues a refresh token alongside the access token.
	WithRefreshToken bool

	IP        string
	UserAgent string
}

// Session is the result of a login, a registration or a token refresh: what
// the client needs to start making requests.
type Session struct {
	UserID    string
	Localpart string
	DeviceID  string

	AccessToken string

	// RefreshToken is empty unless the client asked for one.
	RefreshToken string

	// ExpiresInMS is how long the access token is good for, or 0 when it
	// does not expire.
	ExpiresInMS int64
}

// CreateSession issues a device and tokens for an existing account.
func (a *API) CreateSession(ctx context.Context, req SessionRequest) (Session, error) {
	deviceID := req.DeviceID
	if deviceID == "" {
		var err error
		if deviceID, err = GenerateDeviceID(); err != nil {
			return Session{}, err
		}
	} else if err := ValidateDeviceID(deviceID); err != nil {
		return Session{}, err
	}

	accessToken, err := GenerateAccessToken()
	if err != nil {
		return Session{}, err
	}
	var refreshToken string
	if req.WithRefreshToken {
		if refreshToken, err = GenerateRefreshToken(); err != nil {
			return Session{}, err
		}
	}

	now := a.nowMS()
	session := storage.NewSession{
		Localpart:               req.Localpart,
		DeviceID:                deviceID,
		DisplayName:             req.DisplayName,
		CreatedAtMS:             now,
		AccessTokenHash:         HashToken(accessToken),
		AccessTokenExpiresAtMS:  expiryMS(now, a.accessTokenLifetime),
		RefreshTokenExpiresAtMS: expiryMS(now, a.refreshTokenLifetime),
		LastSeenIP:              req.IP,
		UserAgent:               req.UserAgent,
	}
	if refreshToken != "" {
		session.RefreshTokenHash = HashToken(refreshToken)
	}

	device, err := a.store.CreateSession(ctx, session)
	if err != nil {
		return Session{}, err
	}
	return Session{
		UserID:       a.UserID(req.Localpart),
		Localpart:    req.Localpart,
		DeviceID:     device.ID,
		AccessToken:  accessToken,
		RefreshToken: refreshToken,
		ExpiresInMS:  lifetimeMS(a.accessTokenLifetime),
	}, nil
}

// RefreshSession spends a refresh token and issues a new pair. It returns
// ErrNoSuchToken if the token is unknown or already spent.
func (a *API) RefreshSession(ctx context.Context, refreshToken string) (Session, error) {
	accessToken, err := GenerateAccessToken()
	if err != nil {
		return Session{}, err
	}
	newRefreshToken, err := GenerateRefreshToken()
	if err != nil {
		return Session{}, err
	}

	now := a.nowMS()
	info, err := a.store.RefreshSession(ctx, storage.RefreshedSession{
		RefreshTokenHash:        HashToken(refreshToken),
		NewAccessTokenHash:      HashToken(accessToken),
		AccessTokenExpiresAtMS:  expiryMS(now, a.accessTokenLifetime),
		NewRefreshTokenHash:     HashToken(newRefreshToken),
		RefreshTokenExpiresAtMS: expiryMS(now, a.refreshTokenLifetime),
		RefreshedAtMS:           now,
	})
	if err != nil {
		return Session{}, err
	}
	if info.Deactivated {
		return Session{}, ErrAccountDeactivated
	}
	return Session{
		UserID:       a.UserID(info.Localpart),
		Localpart:    info.Localpart,
		DeviceID:     info.DeviceID,
		AccessToken:  accessToken,
		RefreshToken: newRefreshToken,
		ExpiresInMS:  lifetimeMS(a.accessTokenLifetime),
	}, nil
}

// Authenticated is the identity behind a request: what the auth middleware
// resolves an access token into and what every authenticated handler is
// given.
type Authenticated struct {
	UserID    string
	Localpart string
	DeviceID  string
	Admin     bool
}

// Authenticate resolves an access token.
//
// It returns ErrNoSuchToken for an unknown token, ErrTokenExpired for one
// that has timed out, and ErrAccountDeactivated for a token whose account is
// gone. The caller turns those into M_UNKNOWN_TOKEN, a soft logout, and
// M_USER_DEACTIVATED respectively.
func (a *API) Authenticate(ctx context.Context, accessToken string) (Authenticated, error) {
	if accessToken == "" {
		return Authenticated{}, ErrNoSuchToken
	}
	info, err := a.store.TokenInfo(ctx, HashToken(accessToken))
	if err != nil {
		return Authenticated{}, err
	}
	if info.ExpiresAtMS != 0 && info.ExpiresAtMS <= a.nowMS() {
		return Authenticated{}, ErrTokenExpired
	}
	if info.Deactivated {
		return Authenticated{}, ErrAccountDeactivated
	}
	return Authenticated{
		UserID:    a.UserID(info.Localpart),
		Localpart: info.Localpart,
		DeviceID:  info.DeviceID,
		Admin:     info.Admin,
	}, nil
}

// lastSeenInterval is how stale the last-seen record of a device may get.
// Recording it on every request would double the write load of the whole C-S
// API to keep a field nothing reads more often than a user opens their
// device list.
const lastSeenInterval = time.Minute

// RecordActivity updates a device's last-seen timestamp, address and user
// agent, at most once per lastSeenInterval per device. A failure is logged
// and swallowed: the request it belongs to has already been authorised, and
// bookkeeping must not turn into a 500.
func (a *API) RecordActivity(ctx context.Context, auth Authenticated, ip, userAgent string) {
	key := auth.Localpart + "\x00" + auth.DeviceID
	now := a.now()

	if previous, ok := a.lastSeen.Load(key); ok {
		if at, ok := previous.(time.Time); ok && now.Sub(at) < lastSeenInterval {
			return
		}
	}
	a.lastSeen.Store(key, now)

	if err := a.store.TouchDevice(ctx, auth.Localpart, auth.DeviceID, ip, userAgent, now.UnixMilli()); err != nil {
		a.log.Warn("recording device activity failed",
			"user_id", auth.UserID, "device_id", auth.DeviceID, "error", err)
	}
}

// Device reads one of a user's devices.
func (a *API) Device(ctx context.Context, localpart, deviceID string) (storage.Device, error) {
	return a.store.Device(ctx, localpart, deviceID)
}

// Devices lists a user's devices.
func (a *API) Devices(ctx context.Context, localpart string) ([]storage.Device, error) {
	return a.store.Devices(ctx, localpart)
}

// SetDeviceDisplayName renames a device.
func (a *API) SetDeviceDisplayName(ctx context.Context, localpart, deviceID, displayName string) error {
	if err := a.store.SetDeviceDisplayName(ctx, localpart, deviceID, displayName); err != nil {
		return err
	}
	if a.observer != nil {
		a.observer.DeviceRenamed(ctx, localpart, deviceID)
	}
	return nil
}

// DeleteDevices revokes devices and their tokens. It is what /logout,
// /delete_devices and DELETE /devices/{id} all end up calling.
func (a *API) DeleteDevices(ctx context.Context, localpart string, deviceIDs []string) error {
	if len(deviceIDs) == 0 {
		return nil
	}
	if _, err := a.store.DeleteDevices(ctx, localpart, deviceIDs); err != nil {
		return err
	}
	a.forgetLastSeen(localpart, deviceIDs...)
	if a.observer != nil {
		a.observer.DevicesDeleted(ctx, localpart, deviceIDs)
	}
	return nil
}

// DeleteAllDevices revokes every device of a user: /logout/all.
func (a *API) DeleteAllDevices(ctx context.Context, localpart string) error {
	if _, err := a.store.DeleteAllDevices(ctx, localpart); err != nil {
		return err
	}
	a.forgetLastSeen(localpart)
	if a.observer != nil {
		a.observer.DevicesDeleted(ctx, localpart, nil)
	}
	return nil
}

// forgetLastSeen drops the throttle entries for devices that no longer
// exist, so the map does not grow with every logout. With no device IDs it
// clears every entry of the user.
func (a *API) forgetLastSeen(localpart string, deviceIDs ...string) {
	if len(deviceIDs) > 0 {
		for _, id := range deviceIDs {
			a.lastSeen.Delete(localpart + "\x00" + id)
		}
		return
	}
	prefix := localpart + "\x00"
	a.lastSeen.Range(func(key, _ any) bool {
		if s, ok := key.(string); ok && len(s) > len(prefix) && s[:len(prefix)] == prefix {
			a.lastSeen.Delete(key)
		}
		return true
	})
}

// SetDisplayName updates a user's profile display name.
func (a *API) SetDisplayName(ctx context.Context, localpart, displayName string) error {
	return a.store.SetDisplayName(ctx, localpart, displayName)
}

// SetAvatarURL updates a user's profile avatar.
func (a *API) SetAvatarURL(ctx context.Context, localpart, avatarURL string) error {
	return a.store.SetAvatarURL(ctx, localpart, avatarURL)
}

// AccountData reads one account data blob; roomID is empty for global data.
func (a *API) AccountData(ctx context.Context, localpart, roomID, dataType string) ([]byte, error) {
	return a.store.AccountData(ctx, localpart, roomID, dataType)
}

// SetAccountData writes one account data blob.
func (a *API) SetAccountData(ctx context.Context, localpart, roomID, dataType string, content []byte) error {
	return a.store.SetAccountData(ctx, localpart, roomID, dataType, content)
}

// ListAccounts returns a page of accounts for the admin API.
func (a *API) ListAccounts(ctx context.Context, filter storage.AccountFilter) ([]storage.Account, int, error) {
	return a.store.ListAccounts(ctx, filter)
}

// Stats returns the aggregate user counts for the admin API.
func (a *API) Stats(ctx context.Context) (storage.Stats, error) {
	return a.store.Stats(ctx)
}

// expiryMS turns a lifetime into an absolute deadline in the store's unit,
// or 0 for "never".
func expiryMS(nowMS int64, lifetime time.Duration) int64 {
	if lifetime <= 0 {
		return 0
	}
	return nowMS + lifetime.Milliseconds()
}

// lifetimeMS is the expires_in_ms a client is told, or 0 for "never".
func lifetimeMS(lifetime time.Duration) int64 {
	if lifetime <= 0 {
		return 0
	}
	return lifetime.Milliseconds()
}