package context

import (
	"reflect"
	"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[interface{}]interface{})
	return c
}

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

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

	mtx sync.RWMutex
}

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

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

	if key == nil {
		panic("nil key")
	}
	if !reflect.TypeOf(key).Comparable() {
		panic("key is not comparable")
	}

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

	dc.attributes[key] = value
}

func (dc *defaultContext) GetAttribute(key interface{}) (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 interface{}) {
	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 interface{}) (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")
	}
}