func (*suite) TestNoEnv(c *gc.C) {
	envPath := gitjujutesting.HomePath(".juju", "environments.yaml")
	err := os.Remove(envPath)
	c.Assert(err, jc.ErrorIsNil)
	es, err := environs.ReadEnvirons("")
	c.Assert(es, gc.IsNil)
	c.Assert(err, jc.Satisfies, environs.IsNoEnv)
}

// There is simple ordering for the default environment.  Firstly check the
// JUJU_ENV environment variable.  If that is set, it gets used.  If it isn't
// set, look in the $JUJU_HOME/current-environment file.  If neither are
// available, read environments.yaml and use the default environment therein.
func getDefaultEnvironment() (string, error) {
	if defaultEnv := os.Getenv(osenv.JujuEnvEnvKey); defaultEnv != "" {
		return defaultEnv, nil
	}
	if currentEnv := ReadCurrentEnvironment(); currentEnv != "" {
		return currentEnv, nil
	}
	envs, err := environs.ReadEnvirons("")
	if err != nil {
		return "", err
	}
	if envs.Default == "" {
		return "", ErrNoEnvironmentSpecified
	}
	return envs.Default, nil
}

// GetDefaultEnvironment returns the name of the Juju default environment.
// There is simple ordering for the default environment.  Firstly check the
// JUJU_ENV environment variable.  If that is set, it gets used.  If it isn't
// set, look in the $JUJU_HOME/current-environment file.  If neither are
// available, read environments.yaml and use the default environment therein.
// If no default is specified in the environments file, an empty string is returned.
// Not having a default environment specified is not an error.
func GetDefaultEnvironment() (string, error) {
	if defaultEnv := os.Getenv(osenv.JujuEnvEnvKey); defaultEnv != "" {
		return defaultEnv, nil
	}
	if currentEnv := ReadCurrentEnvironment(); currentEnv != "" {
		return currentEnv, nil
	}
	envs, err := environs.ReadEnvirons("")
	if environs.IsNoEnv(err) {
		// That's fine, not an error here.
		return "", nil
	} else if err != nil {
		return "", errors.Trace(err)
	}
	return envs.Default, nil
}

func (*suite) TestDefaultConfigFile(c *gc.C) {
	env := `
environments:
    only:
        type: dummy
        state-server: false
        authorized-keys: i-am-a-key
`
	outfile, err := environs.WriteEnvirons("", env)
	c.Assert(err, jc.ErrorIsNil)
	path := gitjujutesting.HomePath(".juju", "environments.yaml")
	c.Assert(path, gc.Equals, outfile)

	envs, err := environs.ReadEnvirons("")
	c.Assert(err, jc.ErrorIsNil)
	cfg, err := envs.Config("")
	c.Assert(err, jc.ErrorIsNil)
	c.Assert(cfg.Name(), gc.Equals, "only")
}

func (*suite) TestNamedConfigFile(c *gc.C) {

	env := `
environments:
    only:
        type: dummy
        state-server: false
        authorized-keys: i-am-a-key
`
	path := filepath.Join(c.MkDir(), "a-file")
	outfile, err := environs.WriteEnvirons(path, env)
	c.Assert(err, jc.ErrorIsNil)
	c.Assert(path, gc.Equals, outfile)

	envs, err := environs.ReadEnvirons(path)
	c.Assert(err, jc.ErrorIsNil)
	cfg, err := envs.Config("")
	c.Assert(err, jc.ErrorIsNil)
	c.Assert(cfg.Name(), gc.Equals, "only")
}

// Run checks to see if there is already an environments.yaml file. In one does not exist already,
// a boilerplate version is created so that the user can edit it to get started.
func (c *initCommand) Run(context *cmd.Context) error {
	out := context.Stdout
	config := environs.BoilerplateConfig()
	if c.Show {
		fmt.Fprint(out, config)
		return nil
	}
	_, err := environs.ReadEnvirons("")
	if err == nil && !c.WriteFile {
		return errJujuEnvExists
	}
	if err != nil && !environs.IsNoEnv(err) {
		return err
	}
	filename, err := environs.WriteEnvirons("", config)
	if err != nil {
		return fmt.Errorf("A boilerplate environment configuration file could not be created: %s", err.Error())
	}
	fmt.Fprintf(out, "A boilerplate environment configuration file has been written to %s.\n", filename)
	fmt.Fprint(out, "Edit the file to configure your juju environment and run bootstrap.\n")
	return nil
}

// GetDefaultModel returns the name of the Juju default model.
// There is simple ordering for the default model.  Firstly check the
// JUJU_MODEL environment variable.  If that is set, it gets used.  If it isn't
// set, look in the $JUJU_DATA/current-model file.  If neither are
// available, read environments.yaml and use the default model therein.
// If no default is specified in the environments file, an empty string is returned.
// Not having a default model specified is not an error.
func GetDefaultModel() (string, error) {
	if defaultModel := os.Getenv(osenv.JujuModelEnvKey); defaultModel != "" {
		return defaultModel, nil
	}
	if currentModel, err := ReadCurrentModel(); err != nil {
		return "", errors.Trace(err)
	} else if currentModel != "" {
		return currentModel, nil
	}
	if currentController, err := ReadCurrentController(); err != nil {
		return "", errors.Trace(err)
	} else if currentController != "" {
		return "", errors.Errorf("not operating on an model, using controller %q", currentController)
	}
	models, err := environs.ReadEnvirons("")
	if environs.IsNoEnv(err) {
		// That's fine, not an error here.
		return "", nil
	} else if err != nil {
		return "", errors.Trace(err)
	}
	return models.Default, nil
}

// GetDefaultEnvironment returns the name of the Juju default environment.
// There is simple ordering for the default environment.  Firstly check the
// JUJU_ENV environment variable.  If that is set, it gets used.  If it isn't
// set, look in the $JUJU_HOME/current-environment file.  If neither are
// available, read environments.yaml and use the default environment therein.
// If no default is specified in the environments file, an empty string is returned.
// Not having a default environment specified is not an error.
func GetDefaultEnvironment() (string, error) {
	if defaultEnv := os.Getenv(osenv.JujuEnvEnvKey); defaultEnv != "" {
		return defaultEnv, nil
	}
	if currentEnv, err := ReadCurrentEnvironment(); err != nil {
		return "", errors.Trace(err)
	} else if currentEnv != "" {
		return currentEnv, nil
	}
	if currentSystem, err := ReadCurrentSystem(); err != nil {
		return "", errors.Trace(err)
	} else if currentSystem != "" {
		return "", errors.Errorf("not operating on an environment, using system %q", currentSystem)
	}
	envs, err := environs.ReadEnvirons("")
	if environs.IsNoEnv(err) {
		// That's fine, not an error here.
		return "", nil
	} else if err != nil {
		return "", errors.Trace(err)
	}
	return envs.Default, nil
}

func (c *SwitchCommand) Run(ctx *cmd.Context) error {
	// Switch is an alternative way of dealing with environments than using
	// the JUJU_ENV environment setting, and as such, doesn't play too well.
	// If JUJU_ENV is set we should report that as the current environment,
	// and not allow switching when it is set.

	// Passing through the empty string reads the default environments.yaml file.
	environments, err := environs.ReadEnvirons("")
	if err != nil {
		return errors.New("couldn't read the environment")
	}
	names := environments.Names()
	sort.Strings(names)

	if c.List {
		// List all environments.
		if c.EnvName != "" {
			return errors.New("cannot switch and list at the same time")
		}
		for _, name := range names {
			fmt.Fprintf(ctx.Stdout, "%s\n", name)
		}
		return nil
	}

	jujuEnv := os.Getenv("JUJU_ENV")
	if jujuEnv != "" {
		if c.EnvName == "" {
			fmt.Fprintf(ctx.Stdout, "%s\n", jujuEnv)
			return nil
		} else {
			return fmt.Errorf("cannot switch when JUJU_ENV is overriding the environment (set to %q)", jujuEnv)
		}
	}

	currentEnv := envcmd.ReadCurrentEnvironment()
	if currentEnv == "" {
		currentEnv = environments.Default
	}

	// Handle the different operation modes.
	switch {
	case c.EnvName == "" && currentEnv == "":
		// Nothing specified and nothing to switch to.
		return errors.New("no currently specified environment")
	case c.EnvName == "":
		// Simply print the current environment.
		fmt.Fprintf(ctx.Stdout, "%s\n", currentEnv)
	default:
		// Switch the environment.
		if !validEnvironmentName(c.EnvName, names) {
			return fmt.Errorf("%q is not a name of an existing defined environment", c.EnvName)
		}
		if err := envcmd.WriteCurrentEnvironment(c.EnvName); err != nil {
			return err
		}
		if currentEnv == "" {
			fmt.Fprintf(ctx.Stdout, "-> %s\n", c.EnvName)
		} else {
			fmt.Fprintf(ctx.Stdout, "%s -> %s\n", currentEnv, c.EnvName)
		}
	}
	return nil
}

// newAPIFromStore implements the bulk of NewAPIClientFromName
// but is separate for testing purposes.
func newAPIFromStore(envName string, store configstore.Storage, apiOpen apiOpenFunc) (apiState, error) {
	// Try to read the default environment configuration file.
	// If it doesn't exist, we carry on in case
	// there's some environment info for that environment.
	// This enables people to copy environment files
	// into their .juju/environments directory and have
	// them be directly useful with no further configuration changes.
	envs, err := environs.ReadEnvirons("")
	if err == nil {
		if envName == "" {
			envName = envs.Default
		}
		if envName == "" {
			return nil, fmt.Errorf("no default environment found")
		}
	} else if !environs.IsNoEnv(err) {
		return nil, err
	}

	// Try to connect to the API concurrently using two different
	// possible sources of truth for the API endpoint. Our
	// preference is for the API endpoint cached in the API info,
	// because we know that without needing to access any remote
	// provider. However, the addresses stored there may no longer
	// be current (and the network connection may take a very long
	// time to time out) so we also try to connect using information
	// found from the provider. We only start to make that
	// connection after some suitable delay, so that in the
	// hopefully usual case, we will make the connection to the API
	// and never hit the provider. By preference we use provider
	// attributes from the config store, but for backward
	// compatibility reasons, we fall back to information from
	// ReadEnvirons if that does not exist.
	chooseError := func(err0, err1 error) error {
		if err0 == nil {
			return err1
		}
		if errorImportance(err0) < errorImportance(err1) {
			err0, err1 = err1, err0
		}
		logger.Warningf("discarding API open error: %v", err1)
		return err0
	}
	try := parallel.NewTry(0, chooseError)

	info, err := store.ReadInfo(envName)
	if err != nil && !errors.IsNotFound(err) {
		return nil, err
	}
	var delay time.Duration
	if info != nil && len(info.APIEndpoint().Addresses) > 0 {
		logger.Debugf(
			"trying cached API connection settings - endpoints %v",
			info.APIEndpoint().Addresses,
		)
		try.Start(func(stop <-chan struct{}) (io.Closer, error) {
			return apiInfoConnect(info, apiOpen, stop)
		})
		// Delay the config connection until we've spent
		// some time trying to connect to the cached info.
		delay = providerConnectDelay
	} else {
		logger.Debugf("no cached API connection settings found")
	}
	try.Start(func(stop <-chan struct{}) (io.Closer, error) {
		cfg, err := getConfig(info, envs, envName)
		if err != nil {
			return nil, err
		}
		return apiConfigConnect(cfg, apiOpen, stop, delay, environInfoUserTag(info))
	})
	try.Close()
	val0, err := try.Result()
	if err != nil {
		if ierr, ok := err.(*infoConnectError); ok {
			// lose error encapsulation:
			err = ierr.error
		}
		return nil, err
	}

	st := val0.(apiState)
	addrConnectedTo, err := serverAddress(st.Addr())
	if err != nil {
		return nil, err
	}
	// Even though we are about to update API addresses based on
	// APIHostPorts in cacheChangedAPIInfo, we first cache the
	// addresses based on the provider lookup. This is because older API
	// servers didn't return their HostPort information on Login, and we
	// still want to cache our connection information to them.
	if cachedInfo, ok := st.(apiStateCachedInfo); ok {
		st = cachedInfo.apiState
		if cachedInfo.cachedInfo != nil && info != nil {
			// Cache the connection settings only if we used the
			// environment config, but any errors are just logged
			// as warnings, because they're not fatal.
			err = cacheAPIInfo(st, info, cachedInfo.cachedInfo)
//.........这里部分代码省略.........

func (c *switchCommand) Run(ctx *cmd.Context) error {
	// Switch is an alternative way of dealing with environments than using
	// the JUJU_ENV environment setting, and as such, doesn't play too well.
	// If JUJU_ENV is set we should report that as the current environment,
	// and not allow switching when it is set.

	// Passing through the empty string reads the default environments.yaml file.
	// If the environments.yaml file doesn't exist, just list environments in
	// the configstore.
	envFileExists := true
	names := set.NewStrings()
	environments, err := environs.ReadEnvirons("")
	if err != nil {
		if !environs.IsNoEnv(err) {
			return errors.Annotate(err, "couldn't read the environment")
		}
		envFileExists = false
	} else {
		for _, name := range environments.Names() {
			names.Add(name)
		}
	}

	configEnvirons, configControllers, err := getConfigstoreOptions()
	if err != nil {
		return err
	}
	names = names.Union(configEnvirons)
	names = names.Union(configControllers)

	if c.List {
		// List all environments and controllers.
		if c.EnvName != "" {
			return errors.New("cannot switch and list at the same time")
		}
		for _, name := range names.SortedValues() {
			if configControllers.Contains(name) && !configEnvirons.Contains(name) {
				name += controllerSuffix
			}
			fmt.Fprintf(ctx.Stdout, "%s\n", name)
		}
		return nil
	}

	jujuEnv := os.Getenv("JUJU_ENV")
	if jujuEnv != "" {
		if c.EnvName == "" {
			fmt.Fprintf(ctx.Stdout, "%s\n", jujuEnv)
			return nil
		} else {
			return errors.Errorf("cannot switch when JUJU_ENV is overriding the environment (set to %q)", jujuEnv)
		}
	}

	current, isController, err := envcmd.CurrentConnectionName()
	if err != nil {
		return errors.Trace(err)
	}
	if current == "" {
		if envFileExists {
			current = environments.Default
		}
	} else if isController {
		current += controllerSuffix
	}

	// Handle the different operation modes.
	switch {
	case c.EnvName == "" && current == "":
		// Nothing specified and nothing to switch to.
		return errors.New("no currently specified environment")
	case c.EnvName == "":
		// Simply print the current environment.
		fmt.Fprintf(ctx.Stdout, "%s\n", current)
		return nil
	default:
		// Switch the environment.
		if !names.Contains(c.EnvName) {
			return errors.Errorf("%q is not a name of an existing defined environment or controller", c.EnvName)
		}
		// If the name is not in the environment set, but is in the controller
		// set, then write the name into the current controller file.
		logger.Debugf("controllers: %v", configControllers)
		logger.Debugf("environs: %v", configEnvirons)
		newEnv := c.EnvName
		if configControllers.Contains(newEnv) && !configEnvirons.Contains(newEnv) {
			return envcmd.SetCurrentController(ctx, newEnv)
		}
		return envcmd.SetCurrentEnvironment(ctx, newEnv)
	}
}