/*
 * Apple // emulator for *nix 
 *
 * This software package is subject to the GNU General Public License
 * version 2 or later (your choice) as published by the Free Software
 * Foundation.
 *
 * THERE ARE NO WARRANTIES WHATSOEVER.
 *
 */

/*
 * 65c02 CPU Timing Support. Some source derived from AppleWin.
 *
 * Copyleft 2013 Aaron Culliney
 *
 */

#include "common.h"
#ifdef __APPLE__
#include "darwin-shim.h"
#endif

#define EXECUTION_PERIOD_NSECS 1000000  // AppleWin: nExecutionPeriodUsec

#define DEBUG_TIMING (!defined(NDEBUG) && 0) // enable to print timing stats
#if DEBUG_TIMING
#   define TIMING_LOG(...) LOG(__VA_ARGS__)
#else
#   define TIMING_LOG(...)
#endif

#define DISK_MOTOR_QUIET_NSECS 2000000

static const unsigned int uCyclesPerLine = 65; // 25 cycles of HBL & 40 cycles of HBL'
static const unsigned int uVisibleLinesPerFrame = 64*3; // 192
static const unsigned int uLinesPerFrame = 262; // 64 in each third of the screen & 70 in VBL
static const unsigned int dwClksPerFrame = uCyclesPerLine * uLinesPerFrame; // 17030

double g_fCurrentCLK6502 = CLK_6502;
bool g_bFullSpeed = false; // HACK TODO FIXME : prolly shouldn't be global anymore -- don't think it's necessary for speaker/soundcore/etc anymore ...
uint64_t g_nCumulativeCycles = 0;       // cumulative cycles since emulator (re)start
int g_nCpuCyclesFeedback = 0;
static unsigned int g_dwCyclesThisFrame = 0;

static bool alt_speed_enabled = false;

double cpu_scale_factor = 1.0;
double cpu_altscale_factor = 1.0;
bool auto_adjust_speed = true;

int gc_cycles_timer_0 = 0;
int gc_cycles_timer_1 = 0;

volatile uint8_t emul_reinitialize = 0;
pthread_t cpu_thread_id = 0;

static unsigned int g_nCyclesExecuted = 0; // # of cycles executed up to last IO access

// -----------------------------------------------------------------------------

struct timespec timespec_diff(struct timespec start, struct timespec end, bool *negative) {
    struct timespec t;

    if (negative)
    {
        *negative = false;
    }

    // if start > end, swizzle...
    if ( (start.tv_sec > end.tv_sec) || ((start.tv_sec == end.tv_sec) && (start.tv_nsec > end.tv_nsec)) )
    {
        t=start;
        start=end;
        end=t;
        if (negative)
        {
            *negative = true;
        }
    }

    // assuming time_t is signed ...
    if (end.tv_nsec < start.tv_nsec)
    {
        t.tv_sec  = end.tv_sec - start.tv_sec - 1;
        t.tv_nsec = 1000000000 + end.tv_nsec - start.tv_nsec;
    }
    else
    {
        t.tv_sec  = end.tv_sec  - start.tv_sec;
        t.tv_nsec = end.tv_nsec - start.tv_nsec;
    }

    return t;
}

static inline struct timespec timespec_add(struct timespec start, unsigned long nsecs) {

    start.tv_nsec += nsecs;
    if (start.tv_nsec > NANOSECONDS)
    {
        start.tv_sec += (start.tv_nsec / NANOSECONDS);
        start.tv_nsec %= NANOSECONDS;
    }

    return start;
}

static void _timing_initialize(double scale)
{
    if (g_bFullSpeed)
    {
        TIMING_LOG("timing_initialize() emulation at fullspeed ...");
        return;
    }

    g_fCurrentCLK6502 = CLK_6502 * scale;
    // this is extracted out of SetClksPerSpkrSample -- speaker.c
#ifdef AUDIO_ENABLED
    g_fClksPerSpkrSample = (double) (UINT) (g_fCurrentCLK6502 / (double)SPKR_SAMPLE_RATE);
    SpkrReinitialize();

    TIMING_LOG("timing_initialize() ... ClockRate:%0.2lf  ClockCyclesPerSpeakerSample:%0.2lf", g_fCurrentCLK6502, g_fClksPerSpkrSample);
#endif
}

static inline void _switch_to_fullspeed(void)
{
    g_bFullSpeed = true;
}

static inline void _switch_to_regular_speed(double scale)
{
    g_bFullSpeed = false;
    _timing_initialize(scale);
}

void timing_toggle_cpu_speed(void)
{
    alt_speed_enabled = !alt_speed_enabled;
    double scale_factor = alt_speed_enabled ? cpu_altscale_factor : cpu_scale_factor;
    if (scale_factor >= CPU_SCALE_FASTEST)
    {
        _switch_to_fullspeed();
    }
    else
    {
        _switch_to_regular_speed(scale_factor);
    }
}

void timing_initialize(void)
{
    _timing_initialize(cpu_scale_factor);
}

void *cpu_thread(void *dummyptr) {

    assert(pthread_self() == cpu_thread_id);

    struct timespec deltat;
    struct timespec t0;         // the target timer
    struct timespec ti, tj;     // actual time samples
    bool negative = false;
    long drift_adj_nsecs = 0;   // generic drift adjustment between target and actual

    int debugging_cycles0 = 0;
    int debugging_cycles = 0;

#if DEBUG_TIMING
    unsigned long dbg_ticks = 0;
    int speaker_neg_feedback = 0;
    int speaker_pos_feedback = 0;
    unsigned int dbg_cycles_executed = 0;
#endif

    do
    {
        g_nCumulativeCycles = 0;
        LOG("cpu_thread : begin main loop ...");

        clock_gettime(CLOCK_MONOTONIC, &t0);

        emul_reinitialize = 1;
        do {
            // -LOCK----------------------------------------------------------------------------------------- SAMPLE ti
            pthread_mutex_lock(&interface_mutex);
            clock_gettime(CLOCK_MONOTONIC, &ti);

            deltat = timespec_diff(t0, ti, &negative);
            if (deltat.tv_sec)
            {
                TIMING_LOG("NOTE : serious divergence from target time ...");
                t0 = ti;
                deltat = timespec_diff(t0, ti, &negative);
            }
            t0 = timespec_add(t0, EXECUTION_PERIOD_NSECS); // expected interval
            drift_adj_nsecs = negative ? ~deltat.tv_nsec : deltat.tv_nsec;

            // set up increment & decrement counters
            cpu65_cycles_to_execute = (g_fCurrentCLK6502 / 1000); // g_fCurrentCLK6502 * EXECUTION_PERIOD_NSECS / NANOSECONDS
            cpu65_cycles_to_execute += g_nCpuCyclesFeedback;
            if (cpu65_cycles_to_execute < 0)
            {
                cpu65_cycles_to_execute = 0;
            }

            g_nCyclesExecuted = 0;

#ifdef AUDIO_ENABLED
            MB_StartOfCpuExecute();
#endif
            if (is_debugging) {
                debugging_cycles0 = cpu65_cycles_to_execute;
                debugging_cycles  = cpu65_cycles_to_execute;
            }

            do {
                if (is_debugging) {
                    cpu65_cycles_to_execute = 1;
                }

                cpu65_cycle_count = 0;
                cpu65_run(); // run emulation for cpu65_cycles_to_execute cycles ...

                if (is_debugging) {
                    debugging_cycles -= cpu65_cycle_count;
                    if (c_debugger_should_break() || (debugging_cycles <= 0)) {
                        int err = 0;
                        if ((err = pthread_cond_signal(&ui_thread_cond))) {
                            ERRLOG("pthread_cond_signal : %d", err);
                        }
                        if ((err = pthread_cond_wait(&cpu_thread_cond, &interface_mutex))) {
                            ERRLOG("pthread_cond_wait : %d", err);
                        }
                        if (debugging_cycles <= 0) {
                            cpu65_cycle_count = debugging_cycles0 - debugging_cycles/*<=0*/;
                            break;
                        }
                    }
                }
                if (emul_reinitialize) {
                    reinitialize();
                }
            } while (is_debugging);
#if DEBUG_TIMING
            dbg_cycles_executed += cpu65_cycle_count;
#endif
            unsigned int uActualCyclesExecuted = cpu65_cycle_count;
            g_dwCyclesThisFrame += uActualCyclesExecuted;

#ifdef AUDIO_ENABLED
            MB_UpdateCycles(uActualCyclesExecuted);   // Update 6522s (NB. Do this before updating g_nCumulativeCycles below)
#endif

            // N.B.: IO calls that depend on accurate timing will update g_nCyclesExecuted
            const int nRemainingCycles = uActualCyclesExecuted - g_nCyclesExecuted;
            assert(nRemainingCycles >= 0);
            g_nCumulativeCycles += nRemainingCycles;

            if (!g_bFullSpeed)
            {
#ifdef AUDIO_ENABLED
                SpkrUpdate(uActualCyclesExecuted); // play audio
#endif
            }

            if (g_dwCyclesThisFrame >= dwClksPerFrame)
            {
                g_dwCyclesThisFrame -= dwClksPerFrame;
                //VideoEndOfVideoFrame();
#ifdef AUDIO_ENABLED
                MB_EndOfVideoFrame();
#endif
            }

            clock_gettime(CLOCK_MONOTONIC, &tj);
            pthread_mutex_unlock(&interface_mutex);
            // -UNLOCK--------------------------------------------------------------------------------------- SAMPLE tj

            if (auto_adjust_speed) {
                deltat = timespec_diff(disk6.motor_time, tj, &negative);
                assert(!negative);
                if (!g_bFullSpeed &&
#ifdef AUDIO_ENABLED
                        !Spkr_IsActive() &&
#endif
                        !video_dirty() && (!disk6.motor_off && (deltat.tv_sec || deltat.tv_nsec > DISK_MOTOR_QUIET_NSECS)) )
                {
                    TIMING_LOG("auto switching to full speed");
                    _switch_to_fullspeed();
                } else if (g_bFullSpeed && (
#ifdef AUDIO_ENABLED
                            Spkr_IsActive() ||
#endif
                            video_dirty() || (disk6.motor_off && (deltat.tv_sec || deltat.tv_nsec > DISK_MOTOR_QUIET_NSECS))) )
                {
                    TIMING_LOG("auto switching to regular speed");
                    _switch_to_regular_speed(alt_speed_enabled ? cpu_altscale_factor : cpu_scale_factor);
                }
            }

            if (!g_bFullSpeed) {
                deltat = timespec_diff(ti, tj, &negative);
                assert(!negative);
                long sleepfor = 0;
                if (!deltat.tv_sec)
                {
                    sleepfor = EXECUTION_PERIOD_NSECS - drift_adj_nsecs - deltat.tv_nsec;
                }

                if (sleepfor <= 0)
                {
                    // lagging ...
                    static time_t throttle_warning = 0;
                    if (t0.tv_sec - throttle_warning > 0)
                    {
                        TIMING_LOG("lagging... %ld . %ld", deltat.tv_sec, deltat.tv_nsec);
                        throttle_warning = t0.tv_sec;
                    }
                }
                else
                {
                    deltat.tv_sec = 0;
                    deltat.tv_nsec = sleepfor;
                    nanosleep(&deltat, NULL);
                }

#if DEBUG_TIMING
                // collect timing statistics
                if (speaker_neg_feedback > g_nCpuCyclesFeedback)
                {
                    speaker_neg_feedback = g_nCpuCyclesFeedback;
                }
                if (speaker_pos_feedback < g_nCpuCyclesFeedback)
                {
                    speaker_pos_feedback = g_nCpuCyclesFeedback;
                }

                dbg_ticks += EXECUTION_PERIOD_NSECS;
                if ((dbg_ticks % NANOSECONDS) == 0)
                {
                    LOG("tick:(%ld.%ld) real:(%ld.%ld) cycles exe: %d ... speaker feedback: %d/%d", t0.tv_sec, t0.tv_nsec, ti.tv_sec, ti.tv_nsec, dbg_cycles_executed, speaker_neg_feedback, speaker_pos_feedback);
                    dbg_cycles_executed = 0;
                    dbg_ticks = 0;
                    speaker_neg_feedback = 0;
                    speaker_pos_feedback = 0;
                }
#endif
            }
        } while (!emul_reinitialize);

        reinitialize();
    } while (1);

    return NULL;
}

// From AppleWin...

unsigned int CpuGetCyclesThisVideoFrame(const unsigned int nExecutedCycles) {
    CpuCalcCycles(nExecutedCycles);
    return g_dwCyclesThisFrame + g_nCyclesExecuted;
}

//      Called when an IO-reg is accessed & accurate cycle info is needed
void CpuCalcCycles(const unsigned long nExecutedCycles) {
    // Calc # of cycles executed since this func was last called
    const long nCycles = nExecutedCycles - g_nCyclesExecuted;
    assert(nCycles >= 0);
    g_nCumulativeCycles += nCycles;
    // HACK FIXME TODO
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wshorten-64-to-32"
    g_nCyclesExecuted = nExecutedCycles;
#pragma clang diagnostic pop
}