/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla code.
 *
 * The Initial Developer of the Original Code is
 * Mozilla Corporation.
 * Portions created by the Initial Developer are Copyright (C) 2011
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Taras Glek <tglek@mozilla.com>
 *   Vladan Djeric <vdjeric@mozilla.com>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

#include "base/histogram.h"
#include "nsIComponentManager.h"
#include "nsIServiceManager.h"
#include "nsCOMPtr.h"
#include "mozilla/ModuleUtils.h"
#include "nsIXPConnect.h"
#include "mozilla/Services.h"
#include "jsapi.h" 
#include "nsStringGlue.h"
#include "nsITelemetry.h"
#include "Telemetry.h" 
#include "nsTHashtable.h"
#include "nsHashKeys.h"
#include "nsBaseHashtable.h"
#include "nsXULAppAPI.h"
#include "nsThreadUtils.h"
#include "mozilla/Mutex.h"

namespace {

using namespace base;
using namespace mozilla;

class TelemetryImpl : public nsITelemetry
{
  NS_DECL_ISUPPORTS
  NS_DECL_NSITELEMETRY

public:
  TelemetryImpl();
  ~TelemetryImpl();
  
  static bool CanRecord();
  static already_AddRefed<nsITelemetry> CreateTelemetryInstance();
  static void ShutdownTelemetry();
  static void RecordSlowStatement(const nsACString &statement,
                                  const nsACString &dbName,
                                  PRUint32 delay);
  static nsresult GetHistogramEnumId(const char *name, Telemetry::ID *id);
  struct StmtStats {
    PRUint32 hitCount;
    PRUint32 totalTime;
  };
  typedef nsBaseHashtableET<nsCStringHashKey, StmtStats> SlowSQLEntryType;

private:
  bool AddSQLInfo(JSContext *cx, JSObject *rootObj, bool mainThread);

  // Like GetHistogramById, but returns the underlying C++ object, not the JS one.
  nsresult GetHistogramByName(const nsACString &name, Histogram **ret);
  bool ShouldReflectHistogram(Histogram *h);
  void IdentifyCorruptHistograms(StatisticsRecorder::Histograms &hs);
  typedef StatisticsRecorder::Histograms::iterator HistogramIterator;
  // This is used for speedy string->Telemetry::ID conversions
  typedef nsBaseHashtableET<nsCharPtrHashKey, Telemetry::ID> CharPtrEntryType;
  typedef nsTHashtable<CharPtrEntryType> HistogramMapType;
  HistogramMapType mHistogramMap;
  bool mCanRecord;
  static TelemetryImpl *sTelemetry;
  nsTHashtable<SlowSQLEntryType> mSlowSQLOnMainThread;
  nsTHashtable<SlowSQLEntryType> mSlowSQLOnOtherThread;
  nsTHashtable<nsCStringHashKey> mTrackedDBs;
  Mutex mHashMutex;
};

TelemetryImpl*  TelemetryImpl::sTelemetry = NULL;

// A initializer to initialize histogram collection
StatisticsRecorder gStatisticsRecorder;

// Hardcoded probes
struct TelemetryHistogram {
  const char *id;
  PRUint32 min;
  PRUint32 max;
  PRUint32 bucketCount;
  PRUint32 histogramType;
  const char *comment;
};

// Perform the checks at the beginning of HistogramGet at compile time, so
// that if people add incorrect histogram definitions, they get compiler
// errors.
#define HISTOGRAM(id, min, max, bucket_count, histogram_type, b) \
  PR_STATIC_ASSERT(nsITelemetry::HISTOGRAM_ ## histogram_type == nsITelemetry::HISTOGRAM_BOOLEAN || \
                   (min < max && bucket_count > 2 && min >= 1));

#include "TelemetryHistograms.h"

#undef HISTOGRAM

const TelemetryHistogram gHistograms[] = {
#define HISTOGRAM(id, min, max, bucket_count, histogram_type, comment) \
  { NS_STRINGIFY(id), min, max, bucket_count, \
    nsITelemetry::HISTOGRAM_ ## histogram_type, comment },

#include "TelemetryHistograms.h"

#undef HISTOGRAM
};
bool gCorruptHistograms[Telemetry::HistogramCount];

bool
TelemetryHistogramType(Histogram *h, PRUint32 *result)
{
  switch (h->histogram_type()) {
  case Histogram::HISTOGRAM:
    *result = nsITelemetry::HISTOGRAM_EXPONENTIAL;
    break;
  case Histogram::LINEAR_HISTOGRAM:
    *result = nsITelemetry::HISTOGRAM_LINEAR;
    break;
  case Histogram::BOOLEAN_HISTOGRAM:
    *result = nsITelemetry::HISTOGRAM_BOOLEAN;
    break;
  default:
    return false;
  }
  return true;
}

nsresult
HistogramGet(const char *name, PRUint32 min, PRUint32 max, PRUint32 bucketCount,
             PRUint32 histogramType, Histogram **result)
{
  if (histogramType != nsITelemetry::HISTOGRAM_BOOLEAN) {
    // Sanity checks for histogram parameters.
    if (min >= max)
      return NS_ERROR_ILLEGAL_VALUE;

    if (bucketCount <= 2)
      return NS_ERROR_ILLEGAL_VALUE;

    if (min < 1)
      return NS_ERROR_ILLEGAL_VALUE;
  }

  switch (histogramType) {
  case nsITelemetry::HISTOGRAM_EXPONENTIAL:
    *result = Histogram::FactoryGet(name, min, max, bucketCount, Histogram::kUmaTargetedHistogramFlag);
    break;
  case nsITelemetry::HISTOGRAM_LINEAR:
    *result = LinearHistogram::FactoryGet(name, min, max, bucketCount, Histogram::kUmaTargetedHistogramFlag);
    break;
  case nsITelemetry::HISTOGRAM_BOOLEAN:
    *result = BooleanHistogram::FactoryGet(name, Histogram::kUmaTargetedHistogramFlag);
    break;
  default:
    return NS_ERROR_INVALID_ARG;
  }
  return NS_OK;
}

// O(1) histogram lookup by numeric id
nsresult
GetHistogramByEnumId(Telemetry::ID id, Histogram **ret)
{
  static Histogram* knownHistograms[Telemetry::HistogramCount] = {0};
  Histogram *h = knownHistograms[id];
  if (h) {
    *ret = h;
    return NS_OK;
  }

  const TelemetryHistogram &p = gHistograms[id];
  nsresult rv = HistogramGet(p.id, p.min, p.max, p.bucketCount, p.histogramType, &h);
  if (NS_FAILED(rv))
    return rv;

  *ret = knownHistograms[id] = h;
  return NS_OK;
}

bool
FillRanges(JSContext *cx, JSObject *array, Histogram *h)
{
  for (size_t i = 0; i < h->bucket_count(); i++) {
    if (!JS_DefineElement(cx, array, i, INT_TO_JSVAL(h->ranges(i)), NULL, NULL, JSPROP_ENUMERATE))
      return false;
  }
  return true;
}

enum reflectStatus {
  REFLECT_OK,
  REFLECT_CORRUPT,
  REFLECT_FAILURE
};

enum reflectStatus
ReflectHistogramSnapshot(JSContext *cx, JSObject *obj, Histogram *h)
{
  Histogram::SampleSet ss;
  h->SnapshotSample(&ss);

  // We don't want to reflect corrupt histograms.
  if (h->FindCorruption(ss) != Histogram::NO_INCONSISTENCIES) {
    return REFLECT_CORRUPT;
  }

  JSObject *counts_array;
  JSObject *rarray;
  const size_t count = h->bucket_count();
  if (!(JS_DefineProperty(cx, obj, "min", INT_TO_JSVAL(h->declared_min()), NULL, NULL, JSPROP_ENUMERATE)
        && JS_DefineProperty(cx, obj, "max", INT_TO_JSVAL(h->declared_max()), NULL, NULL, JSPROP_ENUMERATE)
        && JS_DefineProperty(cx, obj, "histogram_type", INT_TO_JSVAL(h->histogram_type()), NULL, NULL, JSPROP_ENUMERATE)
        && JS_DefineProperty(cx, obj, "sum", DOUBLE_TO_JSVAL(ss.sum()), NULL, NULL, JSPROP_ENUMERATE)
        && (rarray = JS_NewArrayObject(cx, count, NULL))
        && JS_DefineProperty(cx, obj, "ranges", OBJECT_TO_JSVAL(rarray), NULL, NULL, JSPROP_ENUMERATE)
        && FillRanges(cx, rarray, h)
        && (counts_array = JS_NewArrayObject(cx, count, NULL))
        && JS_DefineProperty(cx, obj, "counts", OBJECT_TO_JSVAL(counts_array), NULL, NULL, JSPROP_ENUMERATE)
        )) {
    return REFLECT_FAILURE;
  }
  for (size_t i = 0; i < count; i++) {
    if (!JS_DefineElement(cx, counts_array, i, INT_TO_JSVAL(ss.counts(i)), NULL, NULL, JSPROP_ENUMERATE)) {
      return REFLECT_FAILURE;
    }
  }
  return REFLECT_OK;
}

JSBool
JSHistogram_Add(JSContext *cx, uintN argc, jsval *vp)
{
  if (!argc) {
    JS_ReportError(cx, "Expected one argument");
    return JS_FALSE;
  }

  jsval v = JS_ARGV(cx, vp)[0];
  int32 value;

  if (!(JSVAL_IS_NUMBER(v) || JSVAL_IS_BOOLEAN(v))) {
    JS_ReportError(cx, "Not a number");
    return JS_FALSE;
  }

  if (!JS_ValueToECMAInt32(cx, v, &value)) {
    return JS_FALSE;
  }

  if (TelemetryImpl::CanRecord()) {
    JSObject *obj = JS_THIS_OBJECT(cx, vp);
    if (!obj) {
      return JS_FALSE;
    }

    Histogram *h = static_cast<Histogram*>(JS_GetPrivate(cx, obj));
    if (h->histogram_type() == Histogram::BOOLEAN_HISTOGRAM)
      h->Add(!!value);
    else
      h->Add(value);
  }
  return JS_TRUE;
}

JSBool
JSHistogram_Snapshot(JSContext *cx, uintN argc, jsval *vp)
{
  JSObject *obj = JS_THIS_OBJECT(cx, vp);
  if (!obj) {
    return JS_FALSE;
  }

  Histogram *h = static_cast<Histogram*>(JS_GetPrivate(cx, obj));
  JSObject *snapshot = JS_NewObject(cx, NULL, NULL, NULL);
  if (!snapshot)
    return JS_FALSE;

  switch (ReflectHistogramSnapshot(cx, snapshot, h)) {
  case REFLECT_FAILURE:
    return JS_FALSE;
  case REFLECT_CORRUPT:
    JS_ReportError(cx, "Histogram is corrupt");
    return JS_FALSE;
  case REFLECT_OK:
    JS_SET_RVAL(cx, vp, OBJECT_TO_JSVAL(snapshot));
    return JS_TRUE;
  default:
    MOZ_NOT_REACHED("unhandled reflection status");
    return JS_FALSE;
  }
}

nsresult 
WrapAndReturnHistogram(Histogram *h, JSContext *cx, jsval *ret)
{
  static JSClass JSHistogram_class = {
    "JSHistogram",  /* name */
    JSCLASS_HAS_PRIVATE, /* flags */
    JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
    JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, JS_FinalizeStub,
    JSCLASS_NO_OPTIONAL_MEMBERS
  };

  JSObject *obj = JS_NewObject(cx, &JSHistogram_class, NULL, NULL);
  if (!obj)
    return NS_ERROR_FAILURE;
  *ret = OBJECT_TO_JSVAL(obj);
  return (JS_SetPrivate(cx, obj, h)
          && JS_DefineFunction (cx, obj, "add", JSHistogram_Add, 1, 0)
          && JS_DefineFunction (cx, obj, "snapshot", JSHistogram_Snapshot, 1, 0)) ? NS_OK : NS_ERROR_FAILURE;
}

TelemetryImpl::TelemetryImpl():
mCanRecord(XRE_GetProcessType() == GeckoProcessType_Default),
mHashMutex("Telemetry::mHashMutex")
{
  // A whitelist to prevent Telemetry reporting on Addon & Thunderbird DBs
  const char *trackedDBs[] = {
    "addons.sqlite", "chromeappsstore.sqlite", "content-prefs.sqlite",
    "cookies.sqlite", "downloads.sqlite", "extensions.sqlite",
    "formhistory.sqlite", "index.sqlite", "permissions.sqlite", "places.sqlite",
    "search.sqlite", "signons.sqlite", "urlclassifier3.sqlite",
    "webappsstore.sqlite"
  };

  mTrackedDBs.Init();
  for (size_t i = 0; i < ArrayLength(trackedDBs); i++)
    mTrackedDBs.PutEntry(nsDependentCString(trackedDBs[i]));

#ifdef DEBUG
  // Mark immutable to prevent asserts on simultaneous access from multiple threads
  mTrackedDBs.MarkImmutable();
#endif

  mSlowSQLOnMainThread.Init();
  mSlowSQLOnOtherThread.Init();
  mHistogramMap.Init(Telemetry::HistogramCount);
}

TelemetryImpl::~TelemetryImpl() {
  mSlowSQLOnMainThread.Clear();
  mSlowSQLOnOtherThread.Clear();
  mHistogramMap.Clear();
}

NS_IMETHODIMP
TelemetryImpl::NewHistogram(const nsACString &name, PRUint32 min, PRUint32 max, PRUint32 bucketCount, PRUint32 histogramType, JSContext *cx, jsval *ret)
{
  Histogram *h;
  nsresult rv = HistogramGet(PromiseFlatCString(name).get(), min, max, bucketCount, histogramType, &h);
  if (NS_FAILED(rv))
    return rv;
  h->ClearFlags(Histogram::kUmaTargetedHistogramFlag);
  return WrapAndReturnHistogram(h, cx, ret);
}

struct EnumeratorArgs {
  JSContext *cx;
  JSObject *statsObj;
};

PLDHashOperator
StatementEnumerator(TelemetryImpl::SlowSQLEntryType *entry, void *arg)
{
  EnumeratorArgs *args = static_cast<EnumeratorArgs *>(arg);
  const nsACString &sql = entry->GetKey();
  jsval hitCount = UINT_TO_JSVAL(entry->mData.hitCount);
  jsval totalTime = UINT_TO_JSVAL(entry->mData.totalTime);

  JSObject *arrayObj = JS_NewArrayObject(args->cx, 2, nsnull);
  if (!arrayObj ||
      !JS_SetElement(args->cx, arrayObj, 0, &hitCount) ||
      !JS_SetElement(args->cx, arrayObj, 1, &totalTime))
    return PL_DHASH_STOP;

  JSBool success = JS_DefineProperty(args->cx, args->statsObj,
                                     sql.BeginReading(),
                                     OBJECT_TO_JSVAL(arrayObj),
                                     NULL, NULL, JSPROP_ENUMERATE);
  if (!success)
    return PL_DHASH_STOP;

  return PL_DHASH_NEXT;
}

bool
TelemetryImpl::AddSQLInfo(JSContext *cx, JSObject *rootObj, bool mainThread)
{
  JSObject *statsObj = JS_NewObject(cx, NULL, NULL, NULL);
  if (!statsObj)
    return false;

  JSBool ok = JS_DefineProperty(cx, rootObj,
                                mainThread ? "mainThread" : "otherThreads",
                                OBJECT_TO_JSVAL(statsObj),
                                NULL, NULL, JSPROP_ENUMERATE);
  if (!ok)
    return false;

  EnumeratorArgs args = { cx, statsObj };
  nsTHashtable<SlowSQLEntryType> *sqlMap;
  sqlMap = (mainThread ? &mSlowSQLOnMainThread : &mSlowSQLOnOtherThread);
  PRUint32 num = sqlMap->EnumerateEntries(StatementEnumerator,
                                          static_cast<void*>(&args));
  if (num != sqlMap->Count())
    return false;

  return true;
}

nsresult
TelemetryImpl::GetHistogramEnumId(const char *name, Telemetry::ID *id)
{
  if (!sTelemetry) {
    return NS_ERROR_FAILURE;
  }

  // Cache names
  // Note the histogram names are statically allocated
  TelemetryImpl::HistogramMapType *map = &sTelemetry->mHistogramMap;
  if (!map->Count()) {
    for (PRUint32 i = 0; i < Telemetry::HistogramCount; i++) {
      CharPtrEntryType *entry = map->PutEntry(gHistograms[i].id);
      if (NS_UNLIKELY(!entry)) {
        map->Clear();
        return NS_ERROR_OUT_OF_MEMORY;
      }
      entry->mData = (Telemetry::ID) i;
    }
  }

  CharPtrEntryType *entry = map->GetEntry(name);
  if (!entry) {
    return NS_ERROR_INVALID_ARG;
  }
  *id = entry->mData;
  return NS_OK;
}

nsresult
TelemetryImpl::GetHistogramByName(const nsACString &name, Histogram **ret)
{
  Telemetry::ID id;
  nsresult rv = GetHistogramEnumId(PromiseFlatCString(name).get(), &id);
  if (NS_FAILED(rv)) {
    return rv;
  }

  rv = GetHistogramByEnumId(id, ret);
  if (NS_FAILED(rv))
    return rv;

  return NS_OK;
}

NS_IMETHODIMP
TelemetryImpl::HistogramFrom(const nsACString &name, const nsACString &existing_name,
                             JSContext *cx, jsval *ret)
{
  Histogram *existing;
  nsresult rv = GetHistogramByName(existing_name, &existing);
  if (NS_FAILED(rv))
    return rv;

  PRUint32 histogramType;
  bool success = TelemetryHistogramType(existing, &histogramType);
  if (!success)
    return NS_ERROR_INVALID_ARG;

  Histogram *clone;
  rv = HistogramGet(PromiseFlatCString(name).get(), existing->declared_min(),
                    existing->declared_max(), existing->bucket_count(),
                    histogramType, &clone);
  if (NS_FAILED(rv))
    return rv;

  Histogram::SampleSet ss;
  existing->SnapshotSample(&ss);
  clone->AddSampleSet(ss);
  return WrapAndReturnHistogram(clone, cx, ret);
}

void
TelemetryImpl::IdentifyCorruptHistograms(StatisticsRecorder::Histograms &hs)
{
  for (HistogramIterator it = hs.begin(); it != hs.end(); ++it) {
    Histogram *h = *it;

    Telemetry::ID id;
    nsresult rv = GetHistogramEnumId(h->histogram_name().c_str(), &id);
    // This histogram isn't a static histogram, just ignore it.
    if (NS_FAILED(rv)) {
      continue;
    }

    if (gCorruptHistograms[id]) {
      continue;
    }

    Histogram::SampleSet ss;
    h->SnapshotSample(&ss);
    Histogram::Inconsistencies check = h->FindCorruption(ss);
    bool corrupt = (check != Histogram::NO_INCONSISTENCIES);

    if (corrupt) {
      Telemetry::ID corruptID = Telemetry::HistogramCount;
      if (check & Histogram::RANGE_CHECKSUM_ERROR) {
        corruptID = Telemetry::RANGE_CHECKSUM_ERRORS;
      } else if (check & Histogram::BUCKET_ORDER_ERROR) {
        corruptID = Telemetry::BUCKET_ORDER_ERRORS;
      } else if (check & Histogram::COUNT_HIGH_ERROR) {
        corruptID = Telemetry::TOTAL_COUNT_HIGH_ERRORS;
      } else if (check & Histogram::COUNT_LOW_ERROR) {
        corruptID = Telemetry::TOTAL_COUNT_LOW_ERRORS;
      }
      Telemetry::Accumulate(corruptID, 1);
    }

    gCorruptHistograms[id] = corrupt;
  }
}

bool
TelemetryImpl::ShouldReflectHistogram(Histogram *h)
{
  const char *name = h->histogram_name().c_str();
  Telemetry::ID id;
  nsresult rv = GetHistogramEnumId(name, &id);
  if (NS_FAILED(rv)) {
    // GetHistogramEnumId generally should not fail.  But a lookup
    // failure shouldn't prevent us from reflecting histograms into JS.
    //
    // However, these two histograms are created by Histogram itself for
    // tracking corruption.  We have our own histograms for that, so
    // ignore these two.
    if (strcmp(name, "Histogram.InconsistentCountHigh") == 0
        || strcmp(name, "Histogram.InconsistentCountLow") == 0) {
      return false;
    }
    return true;
  } else {
    return !gCorruptHistograms[id];
  }
}

NS_IMETHODIMP
TelemetryImpl::GetHistogramSnapshots(JSContext *cx, jsval *ret)
{
  JSObject *root_obj = JS_NewObject(cx, NULL, NULL, NULL);
  if (!root_obj)
    return NS_ERROR_FAILURE;
  *ret = OBJECT_TO_JSVAL(root_obj);

  StatisticsRecorder::Histograms hs;
  StatisticsRecorder::GetHistograms(&hs);

  // We identify corrupt histograms first, rather than interspersing it
  // in the loop below, to ensure that our corruption statistics don't
  // depend on histogram enumeration order.
  //
  // Of course, we hope that all of these corruption-statistics
  // histograms are not themselves corrupt...
  IdentifyCorruptHistograms(hs);

  // OK, now we can actually reflect things.
  for (HistogramIterator it = hs.begin(); it != hs.end(); ++it) {
    Histogram *h = *it;
    if (!ShouldReflectHistogram(h)) {
      continue;
    }

    JSObject *hobj = JS_NewObject(cx, NULL, NULL, NULL);
    if (!hobj) {
      return NS_ERROR_FAILURE;
    }
    switch (ReflectHistogramSnapshot(cx, hobj, h)) {
    case REFLECT_CORRUPT:
      // We can still hit this case even if ShouldReflectHistograms
      // returns true.  The histogram lies outside of our control
      // somehow; just skip it.
      continue;
    case REFLECT_FAILURE:
      return NS_ERROR_FAILURE;
    case REFLECT_OK:
      if (!JS_DefineProperty(cx, root_obj, h->histogram_name().c_str(),
                             OBJECT_TO_JSVAL(hobj), NULL, NULL, JSPROP_ENUMERATE)) {
        return NS_ERROR_FAILURE;
      }
    }
  }
  return NS_OK;
}

NS_IMETHODIMP
TelemetryImpl::GetSlowSQL(JSContext *cx, jsval *ret)
{
  JSObject *root_obj = JS_NewObject(cx, NULL, NULL, NULL);
  if (!root_obj)
    return NS_ERROR_FAILURE;
  *ret = OBJECT_TO_JSVAL(root_obj);

  MutexAutoLock hashMutex(mHashMutex);
  // Add info about slow SQL queries on the main thread
  if (!AddSQLInfo(cx, root_obj, true))
    return NS_ERROR_FAILURE;
  // Add info about slow SQL queries on other threads
  if (!AddSQLInfo(cx, root_obj, false))
    return NS_ERROR_FAILURE;

  return NS_OK;
}

NS_IMETHODIMP
TelemetryImpl::GetRegisteredHistograms(JSContext *cx, jsval *ret)
{
  size_t count = ArrayLength(gHistograms);
  JSObject *info = JS_NewObject(cx, NULL, NULL, NULL);
  if (!info)
    return NS_ERROR_FAILURE;

  for (size_t i = 0; i < count; ++i) {
    JSString *comment = JS_InternString(cx, gHistograms[i].comment);
    
    if (!(comment
          && JS_DefineProperty(cx, info, gHistograms[i].id,
                               STRING_TO_JSVAL(comment), NULL, NULL,
                               JSPROP_ENUMERATE))) {
      return NS_ERROR_FAILURE;
    }
  }

  *ret = OBJECT_TO_JSVAL(info);
  return NS_OK;
}

NS_IMETHODIMP
TelemetryImpl::GetHistogramById(const nsACString &name, JSContext *cx, jsval *ret)
{
  Histogram *h;
  nsresult rv = GetHistogramByName(name, &h);
  if (NS_FAILED(rv))
    return rv;

  return WrapAndReturnHistogram(h, cx, ret);
}

NS_IMETHODIMP
TelemetryImpl::GetCanRecord(bool *ret) {
  *ret = mCanRecord;
  return NS_OK;
}

NS_IMETHODIMP
TelemetryImpl::SetCanRecord(bool canRecord) {
  mCanRecord = !!canRecord;
  return NS_OK;
}

bool
TelemetryImpl::CanRecord() {
  return !sTelemetry || sTelemetry->mCanRecord;
}

NS_IMETHODIMP
TelemetryImpl::GetCanSend(bool *ret) {
#if defined(MOZILLA_OFFICIAL) && defined(MOZ_TELEMETRY_REPORTING)
  *ret = true;
#else
  *ret = false;
#endif
  return NS_OK;
}

already_AddRefed<nsITelemetry>
TelemetryImpl::CreateTelemetryInstance()
{
  NS_ABORT_IF_FALSE(sTelemetry == NULL, "CreateTelemetryInstance may only be called once, via GetService()");
  sTelemetry = new TelemetryImpl(); 
  // AddRef for the local reference
  NS_ADDREF(sTelemetry);
  // AddRef for the caller
  NS_ADDREF(sTelemetry);
  return sTelemetry;
}

void
TelemetryImpl::ShutdownTelemetry()
{
  NS_IF_RELEASE(sTelemetry);
}

void
TelemetryImpl::RecordSlowStatement(const nsACString &statement,
                                   const nsACString &dbName,
                                   PRUint32 delay)
{
  MOZ_ASSERT(sTelemetry);
  if (!sTelemetry->mCanRecord || !sTelemetry->mTrackedDBs.GetEntry(dbName))
    return;

  nsTHashtable<SlowSQLEntryType> *slowSQLMap = NULL;
  if (NS_IsMainThread())
    slowSQLMap = &(sTelemetry->mSlowSQLOnMainThread);
  else
    slowSQLMap = &(sTelemetry->mSlowSQLOnOtherThread);

  MutexAutoLock hashMutex(sTelemetry->mHashMutex);
  SlowSQLEntryType *entry = slowSQLMap->GetEntry(statement);
  if (!entry) {
    entry = slowSQLMap->PutEntry(statement);
    if (NS_UNLIKELY(!entry))
      return;
    entry->mData.hitCount = 0;
    entry->mData.totalTime = 0;
  }
  entry->mData.hitCount++;
  entry->mData.totalTime += delay;
}

NS_IMPL_THREADSAFE_ISUPPORTS1(TelemetryImpl, nsITelemetry)
NS_GENERIC_FACTORY_SINGLETON_CONSTRUCTOR(nsITelemetry, TelemetryImpl::CreateTelemetryInstance)

#define NS_TELEMETRY_CID \
  {0xaea477f2, 0xb3a2, 0x469c, {0xaa, 0x29, 0x0a, 0x82, 0xd1, 0x32, 0xb8, 0x29}}
NS_DEFINE_NAMED_CID(NS_TELEMETRY_CID);

const Module::CIDEntry kTelemetryCIDs[] = {
  { &kNS_TELEMETRY_CID, false, NULL, nsITelemetryConstructor },
  { NULL }
};

const Module::ContractIDEntry kTelemetryContracts[] = {
  { "@mozilla.org/base/telemetry;1", &kNS_TELEMETRY_CID },
  { NULL }
};

const Module kTelemetryModule = {
  Module::kVersion,
  kTelemetryCIDs,
  kTelemetryContracts,
  NULL,
  NULL,
  NULL,
  TelemetryImpl::ShutdownTelemetry
};

} // anonymous namespace

namespace mozilla {
namespace Telemetry {

void
Accumulate(ID aHistogram, PRUint32 aSample)
{
  if (!TelemetryImpl::CanRecord()) {
    return;
  }
  Histogram *h;
  nsresult rv = GetHistogramByEnumId(aHistogram, &h);
  if (NS_SUCCEEDED(rv))
    h->Add(aSample);
}

void
AccumulateTimeDelta(ID aHistogram, TimeStamp start, TimeStamp end)
{
  Accumulate(aHistogram,
             static_cast<PRUint32>((end - start).ToMilliseconds()));
}

bool
CanRecord()
{
  return TelemetryImpl::CanRecord();
}

base::Histogram*
GetHistogramById(ID id)
{
  Histogram *h = NULL;
  GetHistogramByEnumId(id, &h);
  return h;
}

void
RecordSlowSQLStatement(const nsACString &statement,
                       const nsACString &dbName,
                       PRUint32 delay)
{
  TelemetryImpl::RecordSlowStatement(statement, dbName, delay);
}

void Init()
{
  // Make the service manager hold a long-lived reference to the service
  nsCOMPtr<nsITelemetry> telemetryService =
    do_GetService("@mozilla.org/base/telemetry;1");
  MOZ_ASSERT(telemetryService);
}

} // namespace Telemetry
} // namespace mozilla

NSMODULE_DEFN(nsTelemetryModule) = &kTelemetryModule;

/**
 * The XRE_TelemetryAdd function is to be used by embedding applications
 * that can't use mozilla::Telemetry::Accumulate() directly.
 */
void
XRE_TelemetryAccumulate(int aID, PRUint32 aSample)
{
  mozilla::Telemetry::Accumulate((mozilla::Telemetry::ID) aID, aSample);
}