package clientapi

import (
	"context"
	"errors"
	"net/http"

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

// The Client-Server half of the Application Service API: a service's
// as_token as an access token, acting as one of its users with
// ?user_id=, and the namespaces other users are kept out of.

// authenticateAppService turns a request carrying a service's as_token
// into an identity: the service's sender, or the user ?user_id= names.
//
// The user has to be the sender or in one of the service's user
// namespaces — exclusive or not, the spec does not distinguish — and has
// to exist: a service registers its users first, and acting as a user
// nobody created would hand out an identity with no account behind it.
func (c *ClientAPI) authenticateAppService(r *http.Request, svc *appservice.Service) (userapi.Authenticated, error) {
	userID := r.URL.Query().Get("user_id")
	if userID == "" {
		userID = svc.SenderUserID()
	}
	localpart, err := c.users.ParseLocalUserID(userID)
	switch {
	case errors.Is(err, userapi.ErrForeignServer):
		return userapi.Authenticated{}, httputil.Forbidden("An application service cannot act as a user of another server")
	case err != nil:
		return userapi.Authenticated{}, httputil.InvalidParam("%s is not a valid user ID", userID)
	}
	canonical := c.users.UserID(localpart)
	if !svc.OwnsUser(canonical) {
		return userapi.Authenticated{}, httputil.Forbidden("%s is not in the namespace of application service %s", canonical, svc.ID)
	}

	account, err := c.users.Account(r.Context(), localpart)
	switch {
	case errors.Is(err, userapi.ErrNoSuchUser):
		return userapi.Authenticated{}, httputil.Forbidden("Application service %s has not registered %s", svc.ID, canonical)
	case err != nil:
		return userapi.Authenticated{}, err
	case account.Deactivated:
		return userapi.Authenticated{}, httputil.UserDeactivated()
	}
	return userapi.Authenticated{
		UserID:     canonical,
		Localpart:  localpart,
		Admin:      account.Admin,
		AppService: svc.ID,
	}, nil
}

// rateLimitExempt lets an application service's own requests past the
// rate limiter, and the requests of the users it acts as when its
// registration says rate_limited: false.
//
// A bridge puppeting a thousand users from one address would otherwise
// share one bucket among all of them. The check is a map lookup on the
// token, so it is cheap enough to run ahead of the limiter.
func (c *ClientAPI) rateLimitExempt(r *http.Request) bool {
	svc := c.appservices.Registry().ByToken(accessTokenFrom(r))
	if svc == nil {
		return false
	}
	userID := r.URL.Query().Get("user_id")
	return userID == "" || userID == svc.SenderUserID() || !svc.RateLimitedUsers()
}

// checkExclusiveUser refuses a user ID in a namespace an application
// service has claimed, unless the request comes from that service.
func (c *ClientAPI) checkExclusiveUser(userID, asking string) error {
	if owner := c.appservices.Registry().ExclusiveUserOwner(userID); owner != nil && owner.ID != asking {
		return httputil.Exclusive("%s is reserved by an application service", userID)
	}
	return nil
}

// checkExclusiveAlias is checkExclusiveUser for a room alias.
func (c *ClientAPI) checkExclusiveAlias(alias string, auth userapi.Authenticated) error {
	if owner := c.appservices.Registry().ExclusiveAliasOwner(alias); owner != nil && owner.ID != auth.AppService {
		return httputil.Exclusive("%s is reserved by an application service", alias)
	}
	return nil
}

// resolveAlias resolves an alias, asking the application services whose
// namespace it is in when this server does not know it — which is how a
// bridge creates a portal room the first time somebody looks for it.
func (c *ClientAPI) resolveAlias(ctx context.Context, alias string) (roomserver.ResolvedAlias, error) {
	resolved, err := c.rooms.ResolveAlias(ctx, alias)
	if !errors.Is(err, roomserver.ErrNoSuchAlias) {
		return resolved, err
	}
	if !c.appservices.QueryAlias(ctx, alias) {
		return resolved, err
	}
	return c.rooms.ResolveAlias(ctx, alias)
}

// ensureAppServiceUser gives the application services a chance to create
// a local user that does not exist, before something that needs the user
// gives up on it. It reports whether the user exists afterwards.
func (c *ClientAPI) ensureAppServiceUser(ctx context.Context, localpart string) (bool, error) {
	exists, err := c.users.AccountExists(ctx, localpart)
	if err != nil || exists {
		return exists, err
	}
	if !c.appservices.QueryUser(ctx, c.users.UserID(localpart)) {
		return false, nil
	}
	return c.users.AccountExists(ctx, localpart)
}

// pingRequest is the body of the ping endpoint.
type pingRequest struct {
	TransactionID string `json:"transaction_id"`
}

// handleAppServicePing implements
// POST /_matrix/client/v1/appservice/{appserviceId}/ping: a service asking
// this server to ping it back, to check the two can reach each other.
func (c *ClientAPI) handleAppServicePing(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
	svc := c.appservices.Registry().ByID(r.PathValue("appserviceID"))
	if svc == nil || auth.AppService != svc.ID {
		return httputil.Forbidden("Only the application service itself may ask for its ping")
	}
	var req pingRequest
	if _, err := httputil.DecodeOptionalJSON(w, r, &req); err != nil {
		return err
	}

	took, err := c.appservices.Ping(r.Context(), svc, req.TransactionID)
	var status *appservice.BadStatusError
	switch {
	case err == nil:
	case errors.Is(err, appservice.ErrNoURL):
		return httputil.NewError(http.StatusBadRequest, httputil.ErrCodeURLNotSet,
			"Application service %s has no URL", svc.ID)
	case errors.As(err, &status):
		e := httputil.NewError(http.StatusBadGateway, httputil.ErrCodeBadStatus,
			"The application service answered the ping with %d", status.Status)
		e.RemoteStatus, e.RemoteBody = status.Status, status.Body
		return e
	case errors.Is(err, appservice.ErrConnectionTimeout):
		return httputil.NewError(http.StatusGatewayTimeout, httputil.ErrCodeConnectionTimeout,
			"The application service did not answer the ping in time")
	case errors.Is(err, appservice.ErrConnectionFailed):
		return httputil.NewError(http.StatusBadGateway, httputil.ErrCodeConnectionFailed,
			"Could not connect to the application service")
	default:
		return err
	}
	httputil.WriteJSON(w, http.StatusOK, map[string]int64{"duration_ms": took.Milliseconds()})
	return nil
}