go-web/framework/container.go

package framework

import (
	"fmt"
	"io"
	"sync"
)

type Container interface {
	// Bind binds a service provider to the container.
	//
	// If the service exists, the old one will be replaced by the new one.
	// No error is returned in this case.
	//
	// Return any Init() error.
	Bind(provider ServiceProvider) error

	// IsBound returns true the provider is bound to the container.
	IsBound(name string) bool

	// Make gets or creates a service by its name.
	//
	// Return error if the service cannot be initiated or doesn't exist.
	Make(name string) (interface{}, error)

	// MustMake makes a service, supposing that it is not instantiated before.
	// Return nil if error.
	MustMake(name string) interface{}

	// MakeNew creates a new instance of the service with different parameters.
	//
	// Used for non singleton services.
	MakeNew(name string, params []interface{}) (interface{}, error)
}

type GoWebContainer struct {
	// Must implement Container interfaces.
	Container

	// Service providers by name.
	providers map[string]ServiceProvider

	// Instantiated services by name.
	instances map[string]interface{}

	// RWMutex to protect the changes in container.
	mu sync.RWMutex
}

func errUnknownService(name string) error {
	return fmt.Errorf("service %q is not registered in the container", name)
}

func NewGoWebContainer() *GoWebContainer {
	return &GoWebContainer{
		providers: map[string]ServiceProvider{},
		instances: map[string]interface{}{},
		mu:        sync.RWMutex{},
	}
}

func (c *GoWebContainer) PrintProviders(w io.Writer) {
	ret := make([]string, len(c.providers))
	for _, provider := range c.providers {
		name := provider.Name()

		ret = append(ret, name)
	}
	fmt.Fprintf(w, "%v", ret)
}

func (c *GoWebContainer) Bind(provider ServiceProvider) error {
	c.bindProvider(provider)
	// Instantiate Later ?
	if provider.InstantiateLater() {
		return nil
	}

	// Instantiate now !
	_, err := c.instantiate(provider, nil)
	if err != nil {
		return err
	}

	return nil
}

func (c *GoWebContainer) bindProvider(provider ServiceProvider) {
	c.mu.Lock()
	defer c.mu.Unlock()
	name := provider.Name()
	c.providers[name] = provider
}

func (c *GoWebContainer) IsBound(name string) bool {
	return c.getServiceProvider(name) != nil
}

func (c *GoWebContainer) getServiceProvider(name string) ServiceProvider {
	c.mu.RLock()
	defer c.mu.RUnlock()

	provider, ok := c.providers[name]
	if ok {
		return provider
	}
	return nil
}

func (c *GoWebContainer) Make(name string) (interface{}, error) {
	return c.makeServiceInstance(name, nil, false)
}

func (c *GoWebContainer) MustMake(name string) interface{} {
	ins, err := c.makeServiceInstance(name, nil, false)
	if err != nil {
		return nil
	}
	return ins
}

func (c *GoWebContainer) MakeNew(name string, params []interface{}) (interface{}, error) {
	return c.makeServiceInstance(name, params, true)
}

func (c *GoWebContainer) getServiceInstance(name string) interface{} {
	c.mu.RLock()
	defer c.mu.RUnlock()

	instance, ok := c.instances[name]
	if ok {
		return instance
	}
	return nil
}

func (c *GoWebContainer) makeServiceInstance(
	name string,
	params []interface{},
	forceNew bool,
) (interface{}, error) {
	provider := c.getServiceProvider(name)
	if provider == nil {
		return nil, errUnknownService(name)
	}

	if forceNew {
		return c.instantiate(provider, params)
	}

	instance := c.getServiceInstance(name)

	if instance != nil {
		return instance, nil
	}

	// create a new instance
	return c.instantiate(provider, params)
}

// instantiate instantiates a new instance.
// If no params are provided, then default params are used.
func (c *GoWebContainer) instantiate(
	provider ServiceProvider,
	params []interface{},
) (interface{}, error) {
	c.mu.Lock()
	defer c.mu.Unlock()

	if err := provider.Init(c); err != nil {
		// TODO: Error should be wrapped.
		return nil, err
	}

	if params == nil {
		params = provider.Params(c)
	}

	construct := provider.Register(c)
	instance, err := construct(params...)
	if err != nil {
		// TODO: Error should be wrapped.
		return nil, err
	}

	c.instances[provider.Name()] = instance

	return instance, nil
}