/* Copyright (c) 2002-2009 InMon Corp. Licensed under the terms of the InMon sFlow licence: */
/* http://www.inmon.com/technology/sflowlicense.txt */

#include "sflow_api.h"


/*_________________--------------------------__________________
  _________________   sfl_sampler_init       __________________
  -----------------__________________________------------------
*/

void sfl_sampler_init(SFLSampler *sampler, SFLAgent *agent, SFLDataSource_instance *pdsi)
{
    /* copy the dsi in case it points to sampler->dsi, which we are about to clear.
       (Thanks to Jagjit Choudray of Force 10 Networks for pointing out this bug) */
    SFLDataSource_instance dsi = *pdsi;

    /* preserve the *nxt pointer too, in case we are resetting this poller and it is
       already part of the agent's linked list (thanks to Matt Woodly for pointing this out) */
    SFLSampler *nxtPtr = sampler->nxt;
  
    /* clear everything */
    memset(sampler, 0, sizeof(*sampler));
  
    /* restore the linked list ptr */
    sampler->nxt = nxtPtr;
  
    /* now copy in the parameters */
    sampler->agent = agent;
    sampler->dsi = dsi;
  
    /* set defaults */
    sampler->sFlowFsMaximumHeaderSize = SFL_DEFAULT_HEADER_SIZE;
    sampler->sFlowFsPacketSamplingRate = SFL_DEFAULT_SAMPLING_RATE;
}

/*_________________--------------------------__________________
  _________________       reset              __________________
  -----------------__________________________------------------
*/

static void reset(SFLSampler *sampler)
{
    SFLDataSource_instance dsi = sampler->dsi;
    sfl_sampler_init(sampler, sampler->agent, &dsi);
}

/*_________________---------------------------__________________
  _________________      MIB access           __________________
  -----------------___________________________------------------
*/
u_int32_t sfl_sampler_get_sFlowFsReceiver(SFLSampler *sampler) {
    return sampler->sFlowFsReceiver;
}
void sfl_sampler_set_sFlowFsReceiver(SFLSampler *sampler, u_int32_t sFlowFsReceiver) {
    sampler->sFlowFsReceiver = sFlowFsReceiver;
    if(sFlowFsReceiver == 0) reset(sampler);
    else {
	/* retrieve and cache a direct pointer to my receiver */
	sampler->myReceiver = sfl_agent_getReceiver(sampler->agent, sampler->sFlowFsReceiver);
    }
}
u_int32_t sfl_sampler_get_sFlowFsPacketSamplingRate(SFLSampler *sampler) {
    return sampler->sFlowFsPacketSamplingRate;
}
void sfl_sampler_set_sFlowFsPacketSamplingRate(SFLSampler *sampler, u_int32_t sFlowFsPacketSamplingRate) {
    sampler->sFlowFsPacketSamplingRate = sFlowFsPacketSamplingRate;
}
u_int32_t sfl_sampler_get_sFlowFsMaximumHeaderSize(SFLSampler *sampler) {
    return sampler->sFlowFsMaximumHeaderSize;
}
void sfl_sampler_set_sFlowFsMaximumHeaderSize(SFLSampler *sampler, u_int32_t sFlowFsMaximumHeaderSize) {
    sampler->sFlowFsMaximumHeaderSize = sFlowFsMaximumHeaderSize;
}

/* call this to set a maximum samples-per-second threshold. If the sampler reaches this
   threshold it will automatically back off the sampling rate. A value of 0 disables the
   mechanism */
void sfl_sampler_set_backoffThreshold(SFLSampler *sampler, u_int32_t samplesPerSecond) {
    sampler->backoffThreshold = samplesPerSecond;
}
u_int32_t sfl_sampler_get_backoffThreshold(SFLSampler *sampler) {
    return sampler->backoffThreshold;
}
u_int32_t sfl_sampler_get_samplesLastTick(SFLSampler *sampler) {
    return sampler->samplesLastTick;
}

/*_________________---------------------------------__________________
  _________________   sequence number reset         __________________
  -----------------_________________________________------------------
  Used by the agent to indicate a samplePool discontinuity
  so that the sflow collector will know to ignore the next delta.
*/
void sfl_sampler_resetFlowSeqNo(SFLSampler *sampler) { sampler->flowSampleSeqNo = 0; }


/*_________________---------------------------__________________
  _________________    sfl_sampler_tick       __________________
  -----------------___________________________------------------
*/

void sfl_sampler_tick(SFLSampler *sampler, time_t now)
{
    if(sampler->backoffThreshold && sampler->samplesThisTick > sampler->backoffThreshold) {
	/* automatic backoff.  If using hardware sampling then this is where you have to
	 * call out to change the sampling rate and make sure that any other registers/variables
	 * that hold this value are updated.
	 */
	sampler->sFlowFsPacketSamplingRate *= 2;
    }
    sampler->samplesLastTick = sampler->samplesThisTick;
    sampler->samplesThisTick = 0;
}



/*_________________------------------------------__________________
  _________________ sfl_sampler_writeFlowSample  __________________
  -----------------______________________________------------------
*/

void sfl_sampler_writeFlowSample(SFLSampler *sampler, SFL_FLOW_SAMPLE_TYPE *fs)
{
    if(fs == NULL) return;
    sampler->samplesThisTick++;
    /* increment the sequence number */
    fs->sequence_number = ++sampler->flowSampleSeqNo;
    /* copy the other header fields in */
#ifdef SFL_USE_32BIT_INDEX
    fs->ds_class = SFL_DS_CLASS(sampler->dsi);
    fs->ds_index = SFL_DS_INDEX(sampler->dsi);
#else
    fs->source_id = SFL_DS_DATASOURCE(sampler->dsi);
#endif
    /* the sampling rate may have been set already. */
    if(fs->sampling_rate == 0) fs->sampling_rate = sampler->sFlowFsPacketSamplingRate;
    /* the samplePool may be maintained upstream too. */
    if( fs->sample_pool == 0) fs->sample_pool = sampler->samplePool;
    /* sent to my receiver */
    if(sampler->myReceiver) sfl_receiver_writeFlowSample(sampler->myReceiver, fs);
}

#ifdef SFLOW_SOFTWARE_SAMPLING

/* ================== software sampling ========================*/

/*_________________---------------------------__________________
  _________________     nextRandomSkip        __________________
  -----------------___________________________------------------
*/

inline static u_int32_t nextRandomSkip(u_int32_t mean)
{
    if(mean == 0 || mean == 1) return 1;
    return ((random() % ((2 * mean) - 1)) + 1);
} 

/*_________________---------------------------__________________
  _________________  sfl_sampler_takeSample   __________________
  -----------------___________________________------------------
*/

int sfl_sampler_takeSample(SFLSampler *sampler)
{
    if(sampler->skip == 0) {
	/* first time - seed the random number generator */
	srandom(SFL_DS_INDEX(sampler->dsi));
	sampler->skip = nextRandomSkip(sampler->sFlowFsPacketSamplingRate);
    }

    /* increment the samplePool */
    sampler->samplePool++;

    if(--sampler->skip == 0) {
	/* reached zero. Set the next skip and return true. */
	sampler->skip = nextRandomSkip(sampler->sFlowFsPacketSamplingRate);
	return 1;
    }
    return 0;
}

#endif /* SFLOW_SOFTWARE_SAMPLING */