#include "Timer.h"

#include <windows.h>
#include <mmsystem.h>

#pragma comment(lib, "winmm.lib")

//-----------------------------------------------------------------------------
// Name: Timer()
// Desc: Performs timer opertations. Use the following commands:
//          TIMER_RESET           - to reset the timer
//          TIMER_START           - to start the timer
//          TIMER_STOP            - to stop (or pause) the timer
//          TIMER_ADVANCE         - to advance the timer by 0.1 seconds
//          TIMER_GETABSOLUTETIME - to get the absolute system time
//          TIMER_GETAPPTIME      - to get the current time
//          TIMER_GETELAPSEDTIME  - to get the time that elapsed between 
//                                  TIMER_GETELAPSEDTIME calls
//-----------------------------------------------------------------------------
float Timer(TIMER_COMMAND command)
{
    static BOOL     m_bTimerInitialized = FALSE;
    static BOOL     m_bUsingQPF         = FALSE;
    static LONGLONG m_llQPFTicksPerSec  = 0;

    // Initialize the timer
    if( FALSE == m_bTimerInitialized )
    {
        m_bTimerInitialized = TRUE;

        // Use QueryPerformanceFrequency() to get frequency of timer.  If QPF is
        // not supported, we will timeGetTime() which returns milliseconds.
        LARGE_INTEGER qwTicksPerSec;
        m_bUsingQPF = QueryPerformanceFrequency( &qwTicksPerSec );
        if( m_bUsingQPF )
            m_llQPFTicksPerSec = qwTicksPerSec.QuadPart;
    }

    if( m_bUsingQPF )
    {
        static LONGLONG m_llStopTime        = 0;
        static LONGLONG m_llLastElapsedTime = 0;
        static LONGLONG m_llBaseTime        = 0;
        double fTime;
        double fElapsedTime;
        LARGE_INTEGER qwTime;
        
        // Get either the current time or the stop time, depending
        // on whether we're stopped and what command was sent
        if( m_llStopTime != 0 && command != TIMER_START && command != TIMER_GETABSOLUTETIME)
            qwTime.QuadPart = m_llStopTime;
        else
            QueryPerformanceCounter( &qwTime );

        // Return the elapsed time
        if( command == TIMER_GETELAPSEDTIME )
        {
            fElapsedTime = (double) ( qwTime.QuadPart - m_llLastElapsedTime ) / (double) m_llQPFTicksPerSec;
            m_llLastElapsedTime = qwTime.QuadPart;
            return (FLOAT) fElapsedTime;
        }
    
        // Return the current time
        if( command == TIMER_GETAPPTIME )
        {
            double fAppTime = (double) ( qwTime.QuadPart - m_llBaseTime ) / (double) m_llQPFTicksPerSec;
            return (FLOAT) fAppTime;
        }
    
        // Reset the timer
        if( command == TIMER_RESET )
        {
            m_llBaseTime        = qwTime.QuadPart;
            m_llLastElapsedTime = qwTime.QuadPart;
            return 0.0f;
        }
    
        // Start the timer
        if( command == TIMER_START )
        {
            m_llBaseTime += qwTime.QuadPart - m_llStopTime;
            m_llStopTime = 0;
            m_llLastElapsedTime = qwTime.QuadPart;
            return 0.0f;
        }
    
        // Stop the timer
        if( command == TIMER_STOP )
        {
            m_llStopTime = qwTime.QuadPart;
            m_llLastElapsedTime = qwTime.QuadPart;
            return 0.0f;
        }
    
        // Advance the timer by 1/10th second
        if( command == TIMER_ADVANCE )
        {
            m_llStopTime += m_llQPFTicksPerSec/10;
            return 0.0f;
        }

        if( command == TIMER_GETABSOLUTETIME )
        {
            fTime = qwTime.QuadPart / (double) m_llQPFTicksPerSec;
            return (FLOAT) fTime;
        }

        return -1.0f; // Invalid command specified
    }
    else
    {
        // Get the time using timeGetTime()
        static double m_fLastElapsedTime  = 0.0;
        static double m_fBaseTime         = 0.0;
        static double m_fStopTime         = 0.0;
        double fTime;
        double fElapsedTime;
        
        // Get either the current time or the stop time, depending
        // on whether we're stopped and what command was sent
        if( m_fStopTime != 0.0 && command != TIMER_START && command != TIMER_GETABSOLUTETIME)
            fTime = m_fStopTime;
        else
            fTime = timeGetTime() * 0.001;
    
        // Return the elapsed time
        if( command == TIMER_GETELAPSEDTIME )
        {   
            fElapsedTime = (double) (fTime - m_fLastElapsedTime);
            m_fLastElapsedTime = fTime;
            return (FLOAT) fElapsedTime;
        }
    
        // Return the current time
        if( command == TIMER_GETAPPTIME )
        {
            return (FLOAT) (fTime - m_fBaseTime);
        }
    
        // Reset the timer
        if( command == TIMER_RESET )
        {
            m_fBaseTime         = fTime;
            m_fLastElapsedTime  = fTime;
            return 0.0f;
        }
    
        // Start the timer
        if( command == TIMER_START )
        {
            m_fBaseTime += fTime - m_fStopTime;
            m_fStopTime = 0.0f;
            m_fLastElapsedTime  = fTime;
            return 0.0f;
        }
    
        // Stop the timer
        if( command == TIMER_STOP )
        {
            m_fStopTime = fTime;
            return 0.0f;
        }
    
        // Advance the timer by 1/10th second
        if( command == TIMER_ADVANCE )
        {
            m_fStopTime += 0.1f;
            return 0.0f;
        }

        if( command == TIMER_GETABSOLUTETIME )
        {
            return (FLOAT) fTime;
        }

        return -1.0f; // Invalid command specified
    }
}
