/*
 * Copyright (C) 1996-2021 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */

/* DEBUG: section 71    Store Digest Manager */

/*
 * TODO: We probably do not track all the cases when
 *       storeDigestNoteStoreReady() must be called; this may prevent
 *       storeDigestRebuild/write schedule to be activated
 */

#include "squid.h"
#include "Debug.h"
#include "event.h"
#include "globals.h"
#include "mgr/Registration.h"
#include "store_digest.h"

#if USE_CACHE_DIGESTS
#include "CacheDigest.h"
#include "HttpReply.h"
#include "HttpRequest.h"
#include "internal.h"
#include "MemObject.h"
#include "PeerDigest.h"
#include "refresh.h"
#include "SquidConfig.h"
#include "SquidTime.h"
#include "Store.h"
#include "StoreSearch.h"
#include "util.h"

#include <cmath>

/*
 * local types
 */

class StoreDigestState
{
public:
    StoreDigestCBlock cblock;
    int rebuild_lock = 0;                 ///< bucket number
    StoreEntry * rewrite_lock = nullptr;  ///< points to store entry with the digest
    StoreEntry * publicEntry = nullptr;  ///< points to the previous store entry with the digest
    StoreSearchPointer theSearch;
    int rewrite_offset = 0;
    int rebuild_count = 0;
    int rewrite_count = 0;
};

class StoreDigestStats
{
public:
    int del_count = 0;          /* #store entries deleted from store_digest */
    int del_lost_count = 0;     /* #store entries not found in store_digest on delete */
    int add_count = 0;          /* #store entries accepted to store_digest */
    int add_coll_count = 0;     /* #accepted entries that collided with existing ones */
    int rej_count = 0;          /* #store entries not accepted to store_digest */
    int rej_coll_count = 0;     /* #not accepted entries that collided with existing ones */
};

/* local vars */
static StoreDigestState sd_state;
static StoreDigestStats sd_stats;

/* local prototypes */
static void storeDigestRebuildStart(void *datanotused);
static void storeDigestRebuildResume(void);
static void storeDigestRebuildFinish(void);
static void storeDigestRebuildStep(void *datanotused);
static void storeDigestRewriteStart(void *);
static void storeDigestRewriteResume(void);
static void storeDigestRewriteFinish(StoreEntry * e);
static EVH storeDigestSwapOutStep;
static void storeDigestCBlockSwapOut(StoreEntry * e);
static void storeDigestAdd(const StoreEntry *);

/// calculates digest capacity
static uint64_t
storeDigestCalcCap()
{
    /*
     * To-Do: Bloom proved that the optimal filter utilization is 50% (half of
     * the bits are off). However, we do not have a formula to calculate the
     * number of _entries_ we want to pre-allocate for.
     */
    const uint64_t hi_cap = Store::Root().maxSize() / Config.Store.avgObjectSize;
    const uint64_t lo_cap = 1 + Store::Root().currentSize() / Config.Store.avgObjectSize;
    const uint64_t e_count = StoreEntry::inUseCount();
    uint64_t cap = e_count ? e_count : hi_cap;
    debugs(71, 2, "have: " << e_count << ", want " << cap <<
           " entries; limits: [" << lo_cap << ", " << hi_cap << "]");

    if (cap < lo_cap)
        cap = lo_cap;

    /* do not enforce hi_cap limit, average-based estimation may be wrong
     *if (cap > hi_cap)
     *  cap = hi_cap;
     */

    // Bug 4534: we still have to set an upper-limit at some reasonable value though.
    // this matches cacheDigestCalcMaskSize doing (cap*bpe)+7 < INT_MAX
    const uint64_t absolute_max = (INT_MAX -8) / Config.digest.bits_per_entry;
    if (cap > absolute_max) {
        static time_t last_loud = 0;
        if (last_loud < squid_curtime - 86400) {
            debugs(71, DBG_IMPORTANT, "WARNING: Cache Digest cannot store " << cap << " entries. Limiting to " << absolute_max);
            last_loud = squid_curtime;
        } else {
            debugs(71, 3, "WARNING: Cache Digest cannot store " << cap << " entries. Limiting to " << absolute_max);
        }
        cap = absolute_max;
    }

    return cap;
}
#endif /* USE_CACHE_DIGESTS */

void
storeDigestInit(void)
{
    Mgr::RegisterAction("store_digest", "Store Digest", storeDigestReport, 0, 1);

#if USE_CACHE_DIGESTS
    if (!Config.onoff.digest_generation) {
        store_digest = NULL;
        debugs(71, 3, "Local cache digest generation disabled");
        return;
    }

    const uint64_t cap = storeDigestCalcCap();
    store_digest = new CacheDigest(cap, Config.digest.bits_per_entry);
    debugs(71, DBG_IMPORTANT, "Local cache digest enabled; rebuild/rewrite every " <<
           (int) Config.digest.rebuild_period << "/" <<
           (int) Config.digest.rewrite_period << " sec");

    sd_state = StoreDigestState();
#else
    store_digest = NULL;
    debugs(71, 3, "Local cache digest is 'off'");
#endif
}

/* called when store_rebuild completes */
void
storeDigestNoteStoreReady(void)
{
#if USE_CACHE_DIGESTS

    if (Config.onoff.digest_generation) {
        storeDigestRebuildStart(NULL);
        storeDigestRewriteStart(NULL);
    }

#endif
}

//TODO: this seems to be dead code. Is it needed?
void
storeDigestDel(const StoreEntry * entry)
{
#if USE_CACHE_DIGESTS

    if (!Config.onoff.digest_generation) {
        return;
    }

    assert(entry && store_digest);
    debugs(71, 6, "storeDigestDel: checking entry, key: " << entry->getMD5Text());

    if (!EBIT_TEST(entry->flags, KEY_PRIVATE)) {
        if (!store_digest->contains(static_cast<const cache_key *>(entry->key))) {
            ++sd_stats.del_lost_count;
            debugs(71, 6, "storeDigestDel: lost entry, key: " << entry->getMD5Text() << " url: " << entry->url()  );
        } else {
            ++sd_stats.del_count;
            store_digest->remove(static_cast<const cache_key *>(entry->key));
            debugs(71, 6, "storeDigestDel: deled entry, key: " << entry->getMD5Text());
        }
    }
#endif //USE_CACHE_DIGESTS
}

void
storeDigestReport(StoreEntry * e)
{
#if USE_CACHE_DIGESTS

    if (!Config.onoff.digest_generation) {
        return;
    }

    if (store_digest) {
        static const SBuf label("store");
        cacheDigestReport(store_digest, label, e);
        storeAppendPrintf(e, "\t added: %d rejected: %d ( %.2f %%) del-ed: %d\n",
                          sd_stats.add_count,
                          sd_stats.rej_count,
                          xpercent(sd_stats.rej_count, sd_stats.rej_count + sd_stats.add_count),
                          sd_stats.del_count);
        storeAppendPrintf(e, "\t collisions: on add: %.2f %% on rej: %.2f %%\n",
                          xpercent(sd_stats.add_coll_count, sd_stats.add_count),
                          xpercent(sd_stats.rej_coll_count, sd_stats.rej_count));
    } else {
        storeAppendPrintf(e, "store digest: disabled.\n");
    }

#endif //USE_CACHE_DIGESTS
}

/*
 * LOCAL FUNCTIONS
 */

#if USE_CACHE_DIGESTS

/* should we digest this entry? used by storeDigestAdd() */
static int
storeDigestAddable(const StoreEntry * e)
{
    /* add some stats! XXX */

    debugs(71, 6, "storeDigestAddable: checking entry, key: " << e->getMD5Text());

    /* check various entry flags (mimics StoreEntry::checkCachable XXX) */

    if (EBIT_TEST(e->flags, KEY_PRIVATE)) {
        debugs(71, 6, "storeDigestAddable: NO: private key");
        return 0;
    }

    if (EBIT_TEST(e->flags, ENTRY_NEGCACHED)) {
        debugs(71, 6, "storeDigestAddable: NO: negative cached");
        return 0;
    }

    if (EBIT_TEST(e->flags, RELEASE_REQUEST)) {
        debugs(71, 6, "storeDigestAddable: NO: release requested");
        return 0;
    }

    if (e->store_status == STORE_OK && EBIT_TEST(e->flags, ENTRY_BAD_LENGTH)) {
        debugs(71, 6, "storeDigestAddable: NO: wrong content-length");
        return 0;
    }

    /* do not digest huge objects */
    if (e->swap_file_sz > (uint64_t )Config.Store.maxObjectSize) {
        debugs(71, 6, "storeDigestAddable: NO: too big");
        return 0;
    }

    /* still here? check staleness */
    /* Note: We should use the time of the next rebuild, not (cur_time+period) */
    if (refreshCheckDigest(e, Config.digest.rebuild_period)) {
        debugs(71, 6, "storeDigestAdd: entry expires within " << Config.digest.rebuild_period << " secs, ignoring");
        return 0;
    }

    /*
     * idea: how about also skipping very fresh (thus, potentially
     * unstable) entries? Should be configurable through
     * cd_refresh_pattern, of course.
     */
    /*
     * idea: skip objects that are going to be purged before the next
     * update.
     */
    return 1;
}

static void
storeDigestAdd(const StoreEntry * entry)
{
    assert(entry && store_digest);

    if (storeDigestAddable(entry)) {
        ++sd_stats.add_count;

        if (store_digest->contains(static_cast<const cache_key *>(entry->key)))
            ++sd_stats.add_coll_count;

        store_digest->add(static_cast<const cache_key *>(entry->key));

        debugs(71, 6, "storeDigestAdd: added entry, key: " << entry->getMD5Text());
    } else {
        ++sd_stats.rej_count;

        if (store_digest->contains(static_cast<const cache_key *>(entry->key)))
            ++sd_stats.rej_coll_count;
    }
}

/* rebuilds digest from scratch */
static void
storeDigestRebuildStart(void *datanotused)
{
    assert(store_digest);
    /* prevent overlapping if rebuild schedule is too tight */

    if (sd_state.rebuild_lock) {
        debugs(71, DBG_IMPORTANT, "storeDigestRebuildStart: overlap detected, consider increasing rebuild period");
        return;
    }

    sd_state.rebuild_lock = 1;
    debugs(71, 2, "storeDigestRebuildStart: rebuild #" << sd_state.rebuild_count + 1);

    if (sd_state.rewrite_lock) {
        debugs(71, 2, "storeDigestRebuildStart: waiting for Rewrite to finish.");
        return;
    }

    storeDigestRebuildResume();
}

/// \returns true if we actually resized the digest
static bool
storeDigestResize()
{
    const uint64_t cap = storeDigestCalcCap();
    assert(store_digest);
    uint64_t diff;
    if (cap > store_digest->capacity)
        diff = cap - store_digest->capacity;
    else
        diff = store_digest->capacity - cap;
    debugs(71, 2, store_digest->capacity << " -> " << cap << "; change: " <<
           diff << " (" << xpercentInt(diff, store_digest->capacity) << "%)" );
    /* avoid minor adjustments */

    if (diff <= store_digest->capacity / 10) {
        debugs(71, 2, "small change, will not resize.");
        return false;
    } else {
        debugs(71, 2, "big change, resizing.");
        store_digest->updateCapacity(cap);
    }
    return true;
}

/* called be Rewrite to push Rebuild forward */
static void
storeDigestRebuildResume(void)
{
    assert(sd_state.rebuild_lock);
    assert(!sd_state.rewrite_lock);
    sd_state.theSearch = Store::Root().search();
    /* resize or clear */

    if (!storeDigestResize())
        store_digest->clear();     /* not clean()! */

    sd_stats = StoreDigestStats();

    eventAdd("storeDigestRebuildStep", storeDigestRebuildStep, NULL, 0.0, 1);
}

/* finishes swap out sequence for the digest; schedules next rebuild */
static void
storeDigestRebuildFinish(void)
{
    assert(sd_state.rebuild_lock);
    sd_state.rebuild_lock = 0;
    ++sd_state.rebuild_count;
    debugs(71, 2, "storeDigestRebuildFinish: done.");
    eventAdd("storeDigestRebuildStart", storeDigestRebuildStart, NULL, (double)
             Config.digest.rebuild_period, 1);
    /* resume pending Rewrite if any */

    if (sd_state.rewrite_lock)
        storeDigestRewriteResume();
}

/* recalculate a few hash buckets per invocation; schedules next step */
static void
storeDigestRebuildStep(void *datanotused)
{
    /* TODO: call Store::Root().size() to determine this.. */
    int count = Config.Store.objectsPerBucket * (int) ceil((double) store_hash_buckets *
                (double) Config.digest.rebuild_chunk_percentage / 100.0);
    assert(sd_state.rebuild_lock);

    debugs(71, 3, "storeDigestRebuildStep: buckets: " << store_hash_buckets << " entries to check: " << count);

    while (count-- && !sd_state.theSearch->isDone() && sd_state.theSearch->next())
        storeDigestAdd(sd_state.theSearch->currentItem());

    /* are we done ? */
    if (sd_state.theSearch->isDone())
        storeDigestRebuildFinish();
    else
        eventAdd("storeDigestRebuildStep", storeDigestRebuildStep, NULL, 0.0, 1);
}

/* starts swap out sequence for the digest */
static void
storeDigestRewriteStart(void *datanotused)
{
    assert(store_digest);
    /* prevent overlapping if rewrite schedule is too tight */

    if (sd_state.rewrite_lock) {
        debugs(71, DBG_IMPORTANT, "storeDigestRewrite: overlap detected, consider increasing rewrite period");
        return;
    }

    debugs(71, 2, "storeDigestRewrite: start rewrite #" << sd_state.rewrite_count + 1);

    const char *url = internalLocalUri("/squid-internal-periodic/", SBuf(StoreDigestFileName));
    const MasterXaction::Pointer mx = new MasterXaction(XactionInitiator::initCacheDigest);
    auto req = HttpRequest::FromUrlXXX(url, mx);

    RequestFlags flags;
    flags.cachable = true;

    StoreEntry *e = storeCreateEntry(url, url, flags, Http::METHOD_GET);
    assert(e);
    sd_state.rewrite_lock = e;
    debugs(71, 3, "storeDigestRewrite: url: " << url << " key: " << e->getMD5Text());
    e->mem_obj->request = req;

    /* wait for rebuild (if any) to finish */
    if (sd_state.rebuild_lock) {
        debugs(71, 2, "storeDigestRewriteStart: waiting for rebuild to finish.");
        return;
    }

    storeDigestRewriteResume();
}

static void
storeDigestRewriteResume(void)
{
    StoreEntry *e;

    assert(sd_state.rewrite_lock);
    assert(!sd_state.rebuild_lock);
    e = sd_state.rewrite_lock;
    sd_state.rewrite_offset = 0;
    EBIT_SET(e->flags, ENTRY_SPECIAL);
    /* setting public key will mark the old digest entry for removal once unlocked */
    e->setPublicKey();
    if (const auto oldEntry = sd_state.publicEntry) {
        oldEntry->release(true);
        sd_state.publicEntry = nullptr;
        oldEntry->unlock("storeDigestRewriteResume");
    }
    assert(e->locked());
    sd_state.publicEntry = e;
    /* fake reply */
    HttpReply *rep = new HttpReply;
    rep->setHeaders(Http::scOkay, "Cache Digest OK",
                    "application/cache-digest", (store_digest->mask_size + sizeof(sd_state.cblock)),
                    squid_curtime, (squid_curtime + Config.digest.rewrite_period) );
    debugs(71, 3, "storeDigestRewrite: entry expires on " << rep->expires <<
           " (" << std::showpos << (int) (rep->expires - squid_curtime) << ")");
    e->buffer();
    e->replaceHttpReply(rep);
    storeDigestCBlockSwapOut(e);
    e->flush();
    eventAdd("storeDigestSwapOutStep", storeDigestSwapOutStep, sd_state.rewrite_lock, 0.0, 1, false);
}

/* finishes swap out sequence for the digest; schedules next rewrite */
static void
storeDigestRewriteFinish(StoreEntry * e)
{
    assert(e == sd_state.rewrite_lock);
    e->complete();
    e->timestampsSet();
    debugs(71, 2, "storeDigestRewriteFinish: digest expires at " << e->expires <<
           " (" << std::showpos << (int) (e->expires - squid_curtime) << ")");
    /* is this the write order? @?@ */
    e->mem_obj->unlinkRequest();
    sd_state.rewrite_lock = NULL;
    ++sd_state.rewrite_count;
    eventAdd("storeDigestRewriteStart", storeDigestRewriteStart, NULL, (double)
             Config.digest.rewrite_period, 1);
    /* resume pending Rebuild if any */

    if (sd_state.rebuild_lock)
        storeDigestRebuildResume();
}

/* swaps out one digest "chunk" per invocation; schedules next swap out */
static void
storeDigestSwapOutStep(void *data)
{
    StoreEntry *e = static_cast<StoreEntry *>(data);
    int chunk_size = Config.digest.swapout_chunk_size;
    assert(e == sd_state.rewrite_lock);
    assert(e);
    /* _add_ check that nothing bad happened while we were waiting @?@ @?@ */

    if (static_cast<uint32_t>(sd_state.rewrite_offset + chunk_size) > store_digest->mask_size)
        chunk_size = store_digest->mask_size - sd_state.rewrite_offset;

    e->append(store_digest->mask + sd_state.rewrite_offset, chunk_size);

    debugs(71, 3, "storeDigestSwapOutStep: size: " << store_digest->mask_size <<
           " offset: " << sd_state.rewrite_offset << " chunk: " <<
           chunk_size << " bytes");

    sd_state.rewrite_offset += chunk_size;

    /* are we done ? */
    if (static_cast<uint32_t>(sd_state.rewrite_offset) >= store_digest->mask_size)
        storeDigestRewriteFinish(e);
    else
        eventAdd("storeDigestSwapOutStep", storeDigestSwapOutStep, data, 0.0, 1, false);
}

static void
storeDigestCBlockSwapOut(StoreEntry * e)
{
    memset(&sd_state.cblock, 0, sizeof(sd_state.cblock));
    sd_state.cblock.ver.current = htons(CacheDigestVer.current);
    sd_state.cblock.ver.required = htons(CacheDigestVer.required);
    sd_state.cblock.capacity = htonl(store_digest->capacity);
    sd_state.cblock.count = htonl(store_digest->count);
    sd_state.cblock.del_count = htonl(store_digest->del_count);
    sd_state.cblock.mask_size = htonl(store_digest->mask_size);
    sd_state.cblock.bits_per_entry = Config.digest.bits_per_entry;
    sd_state.cblock.hash_func_count = (unsigned char) CacheDigestHashFuncCount;
    e->append((char *) &sd_state.cblock, sizeof(sd_state.cblock));
}

#endif /* USE_CACHE_DIGESTS */

