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// This sample shows how to use Google Test listener API to implement
// a primitive leak checker.

#include <stdio.h>
#include <stdlib.h>

#include "gtest/gtest.h"
using ::testing::EmptyTestEventListener;
using ::testing::InitGoogleTest;
using ::testing::Test;
using ::testing::TestEventListeners;
using ::testing::TestInfo;
using ::testing::TestPartResult;
using ::testing::UnitTest;

namespace {
// We will track memory used by this class.
class Water
{
public:
    // Normal Water declarations go here.

    // operator new and operator delete help us control water allocation.
    void *operator new(size_t allocation_size)
    {
        allocated_++;
        return malloc(allocation_size);
    }

    void operator delete(void *block, size_t /* allocation_size */)
    {
        allocated_--;
        free(block);
    }

    static int allocated() { return allocated_; }

private:
    static int allocated_;
};

int Water::allocated_ = 0;

// This event listener monitors how many Water objects are created and
// destroyed by each test, and reports a failure if a test leaks some Water
// objects. It does this by comparing the number of live Water objects at
// the beginning of a test and at the end of a test.
class LeakChecker : public EmptyTestEventListener
{
private:
    // Called before a test starts.
    void OnTestStart(const TestInfo & /* test_info */) override
    {
        initially_allocated_ = Water::allocated();
    }

    // Called after a test ends.
    void OnTestEnd(const TestInfo & /* test_info */) override
    {
        int difference = Water::allocated() - initially_allocated_;

        // You can generate a failure in any event handler except
        // OnTestPartResult. Just use an appropriate Google Test assertion to do
        // it.
        EXPECT_LE(difference, 0) << "Leaked " << difference << " unit(s) of Water!";
    }

    int initially_allocated_;
};

TEST(ListenersTest, DoesNotLeak)
{
    Water *water = new Water;
    delete water;
}

// This should fail when the --check_for_leaks command line flag is
// specified.
TEST(ListenersTest, LeaksWater)
{
    Water *water = new Water;
    EXPECT_TRUE(water != nullptr);
}
} // namespace

int main(int argc, char **argv)
{
    InitGoogleTest(&argc, argv);

    bool check_for_leaks = false;
    if (argc > 1 && strcmp(argv[1], "--check_for_leaks") == 0)
        check_for_leaks = true;
    else
        printf("%s\n", "Run this program with --check_for_leaks to enable "
                       "custom leak checking in the tests.");

    // If we are given the --check_for_leaks command line flag, installs the
    // leak checker.
    if (check_for_leaks) {
        TestEventListeners &listeners = UnitTest::GetInstance()->listeners();

        // Adds the leak checker to the end of the test event listener list,
        // after the default text output printer and the default XML report
        // generator.
        //
        // The order is important - it ensures that failures generated in the
        // leak checker's OnTestEnd() method are processed by the text and XML
        // printers *before* their OnTestEnd() methods are called, such that
        // they are attributed to the right test. Remember that a listener
        // receives an OnXyzStart event *after* listeners preceding it in the
        // list received that event, and receives an OnXyzEnd event *before*
        // listeners preceding it.
        //
        // We don't need to worry about deleting the new listener later, as
        // Google Test will do it.
        listeners.Append(new LeakChecker);
    }
    return RUN_ALL_TESTS();
}
