package context

import "sync"

type ContextKey string

func (c ContextKey) String() string {
	return string(c)
}

func NewContext(parent Context) Context {
	c := &defaultContext{
		Context: parent,
	}
	c.attributes = make(map[string]interface{})

	return c
}

type Context interface {
	Parent() Context
	SetAttribute(key string, value interface{})
	GetAttribute(key string) (value interface{})
	RemoveAttribute(key string)
	ContainsAttribute(key string) (exist bool)
}

type defaultContext struct {
	Context
	attributes map[string]interface{}

	mtx sync.RWMutex
}

func (dc *defaultContext) Parent() Context {
	return dc.Context
}

func (dc *defaultContext) SetAttribute(key string, value interface{}) {
	dc.checkInitialized()

	dc.mtx.Lock()
	defer dc.mtx.Unlock()

	dc.attributes[key] = value
}

func (dc *defaultContext) GetAttribute(key string) (value interface{}) {
	dc.checkInitialized()

	dc.mtx.RLock()
	defer dc.mtx.RUnlock()

	if _, ok := dc.attributes[key]; ok {
		return dc.attributes[key]
	}

	if nil == dc.Context {
		return nil
	}
	return dc.Context.GetAttribute(key)
}

func (dc *defaultContext) RemoveAttribute(key string) {
	dc.checkInitialized()

	dc.mtx.Lock()
	defer dc.mtx.Unlock()

	if _, ok := dc.attributes[key]; ok {
		delete(dc.attributes, key)
		return
	}

	if nil == dc.Context {
		return
	}

	dc.Context.RemoveAttribute(key)
}

func (dc *defaultContext) ContainsAttribute(key string) (exist bool) {
	dc.checkInitialized()

	dc.mtx.RLock()
	defer dc.mtx.RUnlock()

	if _, ok := dc.attributes[key]; ok {
		return true
	}

	if nil == dc.Context {
		return false
	}
	return dc.Context.ContainsAttribute(key)
}

func (dc *defaultContext) checkInitialized() {
	if nil == dc.attributes {
		panic("Attribute Manager: must be initialized")
	}
}