package clientapi

import (
	"errors"
	"net/http"

	"github.com/dariuszjaniak/warp/server/internal/httputil"
	"github.com/dariuszjaniak/warp/server/internal/userapi"
)

// Login identifier types. Third-party identifiers (email, phone) need an
// identity server, which is a non-goal for now.
const (
	identifierUser = "m.id.user"
)

// loginIdentifier is the `identifier` object of a login or a password stage.
type loginIdentifier struct {
	Type string `json:"type"`
	User string `json:"user"`
}

// loginRequest is the body of POST /login.
type loginRequest struct {
	Type       string          `json:"type"`
	Identifier loginIdentifier `json:"identifier"`

	// User is the deprecated identifier form, still sent by older clients
	// and by some test harnesses.
	User string `json:"user"`

	Password string `json:"password"`

	DeviceID                 string `json:"device_id"`
	InitialDeviceDisplayName string `json:"initial_device_display_name"`
	RefreshToken             bool   `json:"refresh_token"`
}

// loginFlow is one entry of GET /login.
//
// The spec defines a flow as having `stages`, but for login every flow has
// exactly one, and clients have always read a flat `type`. Both are sent:
// `type` for the clients, `stages` for a strict reading of the spec.
type loginFlow struct {
	Type   string   `json:"type"`
	Stages []string `json:"stages,omitempty"`
}

type loginFlowsResponse struct {
	Flows []loginFlow `json:"flows"`
}

// loginResponse is the body of a successful login.
type loginResponse struct {
	UserID      string `json:"user_id"`
	AccessToken string `json:"access_token"`
	DeviceID    string `json:"device_id"`

	RefreshToken string `json:"refresh_token,omitempty"`
	ExpiresInMS  int64  `json:"expires_in_ms,omitempty"`

	// HomeServer is deprecated but still read by older clients.
	HomeServer string `json:"home_server,omitempty"`

	WellKnown *wellKnownDiscovery `json:"well_known,omitempty"`
}

// wellKnownDiscovery mirrors /.well-known/matrix/client, which the spec
// allows a login response to carry so a client does not have to fetch it.
type wellKnownDiscovery struct {
	Homeserver wellKnownBaseURL `json:"m.homeserver"`
}

type wellKnownBaseURL struct {
	BaseURL string `json:"base_url"`
}

// handleLoginFlows implements GET /_matrix/client/v3/login.
func (c *ClientAPI) handleLoginFlows(w http.ResponseWriter, _ *http.Request) error {
	flows := []loginFlow{{Type: stagePassword, Stages: []string{stagePassword}}}
	if !c.appservices.Registry().Empty() {
		flows = append(flows, loginFlow{Type: loginAppService, Stages: []string{loginAppService}})
	}
	httputil.WriteJSON(w, http.StatusOK, loginFlowsResponse{Flows: flows})
	return nil
}

// handleLogin implements POST /_matrix/client/v3/login.
//
// Every rejection is the same M_FORBIDDEN, whether the account does not
// exist, has no password or the password is wrong, and userapi spends the
// same work on each. A login endpoint that distinguishes them is a user
// directory for anyone who asks.
func (c *ClientAPI) handleLogin(w http.ResponseWriter, r *http.Request) error {
	var req loginRequest
	if err := httputil.DecodeJSON(w, r, &req); err != nil {
		return err
	}
	if req.Type != stagePassword && req.Type != loginAppService {
		return httputil.Unknown(http.StatusBadRequest, "Login type %q is not supported", req.Type)
	}

	identifier := req.Identifier.User
	switch {
	case identifier != "" && req.Identifier.Type != identifierUser:
		return httputil.InvalidParam("Login identifier type %q is not supported", req.Identifier.Type)
	case identifier == "":
		identifier = req.User
	}
	if identifier == "" {
		return httputil.MissingParam("A user identifier is required")
	}

	localpart, err := c.users.ParseLocalUserID(identifier)
	switch {
	case errors.Is(err, userapi.ErrForeignServer):
		// Not a federation matter: an account on another server has its
		// password there, and no amount of federation changes that.
		return httputil.Forbidden("Cannot log in as a user of another server")
	case err != nil:
		return httputil.Forbidden("Invalid username or password")
	}

	if req.Type == loginAppService {
		// The credential is the application service's token, and the
		// user has to be one of its own.
		svc := c.appservices.Registry().ByToken(accessTokenFrom(r))
		switch {
		case svc == nil && accessTokenFrom(r) == "":
			return httputil.MissingToken()
		case svc == nil:
			return httputil.UnknownToken(false)
		case !svc.OwnsUser(c.users.UserID(localpart)):
			return httputil.Forbidden("%s is not in the namespace of application service %s",
				c.users.UserID(localpart), svc.ID)
		}
	} else {
		switch err := c.users.CheckPassword(r.Context(), localpart, req.Password); {
		case err == nil:
		case errors.Is(err, userapi.ErrWrongPassword), errors.Is(err, userapi.ErrNoPassword):
			return httputil.Forbidden("Invalid username or password")
		default:
			return err
		}
	}

	account, err := c.users.Account(r.Context(), localpart)
	switch {
	case errors.Is(err, userapi.ErrNoSuchUser):
		// Only reachable for an application service login: a password
		// check has already failed for a user who does not exist.
		return httputil.Forbidden("%s does not exist", c.users.UserID(localpart))
	case err != nil:
		return err
	}
	if account.Deactivated {
		return httputil.UserDeactivated()
	}

	if req.DeviceID != "" {
		if err := userapi.ValidateDeviceID(req.DeviceID); err != nil {
			return httputil.InvalidParam("%s", err.Error())
		}
	}

	session, err := c.users.CreateSession(r.Context(), userapi.SessionRequest{
		Localpart:        localpart,
		DeviceID:         req.DeviceID,
		DisplayName:      req.InitialDeviceDisplayName,
		WithRefreshToken: req.RefreshToken,
		IP:               c.clientIP(r),
		UserAgent:        r.UserAgent(),
	})
	if err != nil {
		return err
	}

	resp := loginResponse{
		UserID:       session.UserID,
		AccessToken:  session.AccessToken,
		DeviceID:     session.DeviceID,
		RefreshToken: session.RefreshToken,
		ExpiresInMS:  session.ExpiresInMS,
		HomeServer:   c.serverName,
	}
	if c.clientBaseURL != "" {
		resp.WellKnown = &wellKnownDiscovery{
			Homeserver: wellKnownBaseURL{BaseURL: c.clientBaseURL},
		}
	}
	httputil.WriteJSON(w, http.StatusOK, resp)
	return nil
}

// refreshRequest is the body of POST /refresh.
type refreshRequest struct {
	RefreshToken string `json:"refresh_token"`
}

// refreshResponse is its answer.
type refreshResponse struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token"`
	ExpiresInMS  int64  `json:"expires_in_ms,omitempty"`
}

// handleRefresh implements POST /_matrix/client/v3/refresh.
//
// It is unauthenticated on purpose: the refresh token *is* the credential,
// and the access token it replaces has usually already expired.
func (c *ClientAPI) handleRefresh(w http.ResponseWriter, r *http.Request) error {
	var req refreshRequest
	if err := httputil.DecodeJSON(w, r, &req); err != nil {
		return err
	}
	if req.RefreshToken == "" {
		return httputil.MissingParam("refresh_token is required")
	}

	session, err := c.users.RefreshSession(r.Context(), req.RefreshToken)
	switch {
	case err == nil:
	case errors.Is(err, userapi.ErrNoSuchToken):
		// A soft logout: the device is probably still legitimate, it just
		// cannot prove it any more.
		return httputil.UnknownToken(true)
	case errors.Is(err, userapi.ErrAccountDeactivated):
		return httputil.UserDeactivated()
	default:
		return err
	}

	httputil.WriteJSON(w, http.StatusOK, refreshResponse{
		AccessToken:  session.AccessToken,
		RefreshToken: session.RefreshToken,
		ExpiresInMS:  session.ExpiresInMS,
	})
	return nil
}

// handleLogout implements POST /_matrix/client/v3/logout. Logging out
// deletes the device, not only the token: that is what the spec says, and it
// is what keeps a user's device list from filling up with dead entries.
func (c *ClientAPI) handleLogout(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
	if err := c.users.DeleteDevices(r.Context(), auth.Localpart, []string{auth.DeviceID}); err != nil {
		return err
	}
	httputil.WriteJSON(w, http.StatusOK, struct{}{})
	return nil
}

// handleLogoutAll implements POST /_matrix/client/v3/logout/all.
func (c *ClientAPI) handleLogoutAll(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
	if err := c.users.DeleteAllDevices(r.Context(), auth.Localpart); err != nil {
		return err
	}
	httputil.WriteJSON(w, http.StatusOK, struct{}{})
	return nil
}

// handleWhoami implements GET /_matrix/client/v3/account/whoami.
func (c *ClientAPI) handleWhoami(w http.ResponseWriter, _ *http.Request, auth userapi.Authenticated) error {
	httputil.WriteJSON(w, http.StatusOK, map[string]any{
		"user_id":   auth.UserID,
		"device_id": auth.DeviceID,
		// Guest accounts are not implemented, so this is always false
		// rather than omitted: clients branch on it.
		"is_guest": false,
	})
	return nil
}