#include "stdafx.h"

typedef struct _MSG_ITEM{
  	SLIST_ENTRY ListEntry;
   	char * strText; 
} MSG_ITEM, *PMSG_ITEM;

HANDLE hEvent;
SLIST_HEADER ListHead;

void InitLogWriting(){
	InitializeSListHead(&ListHead);
    // manual reset must be turned off
    hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);  
}

void EndLogWriting(){
    char * ptr = new char[sizeof(MSG_ITEM)];

    PMSG_ITEM pListItem = (PMSG_ITEM) ptr;
    pListItem->strText = NULL;

	//insert new item into the list
    InterlockedPushEntrySList(&ListHead, &pListItem->ListEntry);

	//Signal emtpy message
    SetEvent(hEvent);
}

void WriteLogMessage(char * strMessage){

	//allocate memory for text and for list item
	//+1 is needed for zero at the end of the string
	UINT iBufferLength = sizeof(MSG_ITEM) + strlen(strMessage) + 1; 
    char * ptr = new char[iBufferLength];

    PMSG_ITEM pListItem = (PMSG_ITEM) ptr;
    pListItem->strText = ptr + sizeof(MSG_ITEM);
	strcpy(pListItem->strText, strMessage);


    //insert new item into the list
    InterlockedPushEntrySList(&ListHead, &pListItem->ListEntry);

    //signal to log writer thread
    SetEvent(hEvent);
}

void ReverseSList(PSLIST_ENTRY * pHead){
	SLIST_ENTRY * pPrev = NULL;
	SLIST_ENTRY * pThis = *pHead;
	SLIST_ENTRY * pNext = (*pHead)->Next;

   	while(pThis->Next){
		pNext = pThis->Next; 
		pThis->Next = pPrev;
		pPrev = pThis;
		pThis = pNext;
	}

	//list tail
	pThis->Next = pPrev;
	*pHead = pThis;
}

DWORD LogWritingThreadRoutine(LPVOID lpParam){
	PMSG_ITEM pListItem;
	PMSG_ITEM pPrevItem;
	char * pszText;

	while(WAIT_OBJECT_0==WaitForSingleObject(hEvent, INFINITE)){

		//fetch all items from the list
		pListItem = (PMSG_ITEM) InterlockedFlushSList(&ListHead);
                                          
                                           //reverse fetched sub list to get FIFO order
		if (pListItem) ReverseSList(&pListItem);

		//process all fetched items 
		while(pListItem){
			pszText = pListItem->strText;
			//exit thread if an empty message is received
			if (!pszText){
				//do not forget to call CloseHandle(hEvent) when 
				//the entire process is exiting
				return 0;
			}

			//process message text
			//contained in pszText
			// for example, AfxMessageBox(pszText, 0, 0);
			MessageBox(NULL, pszText, NULL, 0);
			
			pPrevItem = pListItem;
			
			pListItem = (PMSG_ITEM) pListItem->ListEntry.Next;
			
			//now we can delete the entire list item
			//including message text 
			delete [] (pPrevItem);

		}
	}
	return GetLastError();
}