context.go

package toolbox

import (
	"fmt"
	"reflect"
	"sync"
)

// Context represents type safe map.
type Context interface {

	//GetRequired returns a value for a target type of error if it does not exist
	GetRequired(targetType interface{}) (interface{}, error)

	//GetOptional  returns a value for a target type
	GetOptional(targetType interface{}) interface{}

	//GetOptional into sets requested context value into target, returns true if value was found
	GetInto(targetType interface{}, target interface{}) bool

	//Put puts target type value to the context, or error if value exists,  is nil or incompatible with target type
	Put(targetType interface{}, value interface{}) error

	//Replace repaces value in the context
	Replace(targetType interface{}, value interface{}) error

	//Remove removes value from the context
	Remove(targetType interface{}) interface{}

	//Contains chekcs if a value of a terget type is in contet
	Contains(targetType interface{}) bool

	//Clone create a shallow copy of a context
	Clone() Context
}

type contextImpl struct {
	mux     sync.RWMutex
	context map[string]interface{}
}

func (c *contextImpl) getReflectType(targetType interface{}) reflect.Type {
	var reflectType reflect.Type
	var ok bool
	reflectType, ok = targetType.(reflect.Type)
	if !ok {
		reflectType = reflect.TypeOf(targetType)
	}
	return reflectType
}

func (c *contextImpl) getKey(targetType interface{}) string {
	var reflectType = c.getReflectType(targetType)
	return reflectType.String()
}

func (c *contextImpl) GetRequired(targetType interface{}) (interface{}, error) {
	if !c.Contains(targetType) {
		key := c.getKey(targetType)
		return nil, fmt.Errorf("failed to lookup key:" + key)
	}
	return c.GetOptional(targetType), nil
}

func (c *contextImpl) GetOptional(targetType interface{}) interface{} {
	key := c.getKey(targetType)
	c.mux.RLock()
	defer c.mux.RUnlock()
	if result, ok := c.context[key]; ok {
		return result
	}
	return nil
}

func (c *contextImpl) GetInto(targetType, target interface{}) bool {
	key := c.getKey(targetType)
	c.mux.RLock()
	defer c.mux.RUnlock()
	if result, ok := c.context[key]; ok {
		reflect.ValueOf(target).Elem().Set(reflect.ValueOf(result))
		return true
	}
	return false
}

func (c *contextImpl) Put(targetType interface{}, value interface{}) error {
	if c.Contains(targetType) {
		key := c.getKey(targetType)
		return fmt.Errorf("failed to put key - already exist: " + key)
	}
	return c.Replace(targetType, value)
}

func (c *contextImpl) Replace(targetType interface{}, value interface{}) error {
	key := c.getKey(targetType)
	targetReflectType := c.getReflectType(targetType)
	valueReflectType := reflect.TypeOf(value)
	if valueReflectType == targetReflectType {
		c.mux.Lock()
		c.context[key] = value
		c.mux.Unlock()
		return nil
	}

	if targetReflectType.Kind() == reflect.Ptr {
		converted := reflect.ValueOf(value).Elem().Convert(targetReflectType.Elem())
		convertedPointer := reflect.New(targetReflectType.Elem())
		convertedPointer.Elem().Set(converted)
		value = convertedPointer.Interface()

	} else {
		if !valueReflectType.AssignableTo(targetReflectType) {
			return fmt.Errorf("value of type %v is not assignable to %v", valueReflectType, targetReflectType)
		}
		value = reflect.ValueOf(value).Convert(targetReflectType).Interface()
	}
	c.mux.Lock()
	c.context[key] = value
	c.mux.Unlock()
	return nil
}

func (c *contextImpl) Remove(targetType interface{}) interface{} {
	key := c.getKey(targetType)
	result := c.GetOptional(targetType)
	c.mux.Lock()
	delete(c.context, key)
	c.mux.Unlock()
	return result
}

func (c *contextImpl) Contains(targetType interface{}) bool {
	key := c.getKey(targetType)
	c.mux.RLock()
	defer c.mux.RUnlock()
	if _, ok := c.context[key]; ok {
		return true
	}
	return false
}

func (c *contextImpl) Clone() Context {
	var result = &contextImpl{context: make(map[string]interface{})}
	c.mux.RLock()
	defer c.mux.RUnlock()
	for k, v := range c.context {
		result.context[k] = v
	}
	return result
}

// NewContext creates a new context
func NewContext() Context {
	var result Context = &contextImpl{context: make(map[string]interface{})}
	return result
}