// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "db/log_reader.h"
#include "db/log_writer.h"
#include "include/env.h"
#include "util/coding.h"
#include "util/crc32c.h"
#include "util/random.h"
#include "util/testharness.h"

namespace leveldb {
namespace log {

// Construct a string of the specified length made out of the supplied
// partial string.
static std::string BigString(const std::string& partial_string, size_t n) {
  std::string result;
  while (result.size() < n) {
    result.append(partial_string);
  }
  result.resize(n);
  return result;
}

// Construct a string from a number
static std::string NumberString(int n) {
  char buf[50];
  snprintf(buf, sizeof(buf), "%d.", n);
  return std::string(buf);
}

// Return a skewed potentially long string
static std::string RandomSkewedString(int i, Random* rnd) {
  return BigString(NumberString(i), rnd->Skewed(17));
}

class LogTest {
 private:
  class StringDest : public WritableFile {
   public:
    std::string contents_;

    virtual Status Close() { return Status::OK(); }
    virtual Status Flush() { return Status::OK(); }
    virtual Status Sync() { return Status::OK(); }
    virtual Status Append(const Slice& slice) {
      contents_.append(slice.data(), slice.size());
      return Status::OK();
    }
  };

  class StringSource : public SequentialFile {
   public:
    Slice contents_;
    bool force_error_;
    bool returned_partial_;
    StringSource() : force_error_(false), returned_partial_(false) { }

    virtual Status Read(size_t n, Slice* result, char* scratch) {
      ASSERT_TRUE(!returned_partial_) << "must not Read() after eof/error";
      ASSERT_EQ(kBlockSize, n);

      if (force_error_) {
        force_error_ = false;
        returned_partial_ = true;
        return Status::Corruption("read error");
      }

      if (contents_.size() < n) {
        n = contents_.size();
        returned_partial_ = true;
      }
      *result = Slice(contents_.data(), n);
      contents_.remove_prefix(n);
      return Status::OK();
    }
  };

  class ReportCollector : public Reader::Reporter {
   public:
    size_t dropped_bytes_;
    std::string message_;

    ReportCollector() : dropped_bytes_(0) { }
    virtual void Corruption(size_t bytes, const Status& status) {
      dropped_bytes_ += bytes;
      message_.append(status.ToString());
    }
  };

  StringDest dest_;
  StringSource source_;
  ReportCollector report_;
  bool reading_;
  Writer writer_;
  Reader reader_;

 public:
  LogTest() : reading_(false),
              writer_(&dest_),
              reader_(&source_, &report_, true/*checksum*/) {
  }

  void Write(const std::string& msg) {
    ASSERT_TRUE(!reading_) << "Write() after starting to read";
    writer_.AddRecord(Slice(msg));
  }

  size_t WrittenBytes() const {
    return dest_.contents_.size();
  }

  std::string Read() {
    if (!reading_) {
      reading_ = true;
      source_.contents_ = Slice(dest_.contents_);
    }
    std::string scratch;
    Slice record;
    if (reader_.ReadRecord(&record, &scratch)) {
      return record.ToString();
    } else {
      return "EOF";
    }
  }

  void IncrementByte(int offset, int delta) {
    dest_.contents_[offset] += delta;
  }

  void SetByte(int offset, char new_byte) {
    dest_.contents_[offset] = new_byte;
  }

  void ShrinkSize(int bytes) {
    dest_.contents_.resize(dest_.contents_.size() - bytes);
  }

  void FixChecksum(int header_offset, int len) {
    // Compute crc of type/len/data
    uint32_t crc = crc32c::Value(&dest_.contents_[header_offset+6], 1 + len);
    crc = crc32c::Mask(crc);
    EncodeFixed32(&dest_.contents_[header_offset], crc);
  }

  void ForceError() {
    source_.force_error_ = true;
  }

  size_t DroppedBytes() const {
    return report_.dropped_bytes_;
  }

  // Returns OK iff recorded error message contains "msg"
  std::string MatchError(const std::string& msg) const {
    if (report_.message_.find(msg) == std::string::npos) {
      return report_.message_;
    } else {
      return "OK";
    }
  }
};

TEST(LogTest, Empty) {
  ASSERT_EQ("EOF", Read());
}

TEST(LogTest, ReadWrite) {
  Write("foo");
  Write("bar");
  Write("");
  Write("xxxx");
  ASSERT_EQ("foo", Read());
  ASSERT_EQ("bar", Read());
  ASSERT_EQ("", Read());
  ASSERT_EQ("xxxx", Read());
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ("EOF", Read());  // Make sure reads at eof work
}

TEST(LogTest, ManyBlocks) {
  for (int i = 0; i < 100000; i++) {
    Write(NumberString(i));
  }
  for (int i = 0; i < 100000; i++) {
    ASSERT_EQ(NumberString(i), Read());
  }
  ASSERT_EQ("EOF", Read());
}

TEST(LogTest, Fragmentation) {
  Write("small");
  Write(BigString("medium", 50000));
  Write(BigString("large", 100000));
  ASSERT_EQ("small", Read());
  ASSERT_EQ(BigString("medium", 50000), Read());
  ASSERT_EQ(BigString("large", 100000), Read());
  ASSERT_EQ("EOF", Read());
}

TEST(LogTest, MarginalTrailer) {
  // Make a trailer that is exactly the same length as an empty record.
  const int n = kBlockSize - 2*kHeaderSize;
  Write(BigString("foo", n));
  ASSERT_EQ(kBlockSize - kHeaderSize, WrittenBytes());
  Write("");
  Write("bar");
  ASSERT_EQ(BigString("foo", n), Read());
  ASSERT_EQ("", Read());
  ASSERT_EQ("bar", Read());
  ASSERT_EQ("EOF", Read());
}

TEST(LogTest, ShortTrailer) {
  const int n = kBlockSize - 2*kHeaderSize + 4;
  Write(BigString("foo", n));
  ASSERT_EQ(kBlockSize - kHeaderSize + 4, WrittenBytes());
  Write("");
  Write("bar");
  ASSERT_EQ(BigString("foo", n), Read());
  ASSERT_EQ("", Read());
  ASSERT_EQ("bar", Read());
  ASSERT_EQ("EOF", Read());
}

TEST(LogTest, AlignedEof) {
  const int n = kBlockSize - 2*kHeaderSize + 4;
  Write(BigString("foo", n));
  ASSERT_EQ(kBlockSize - kHeaderSize + 4, WrittenBytes());
  ASSERT_EQ(BigString("foo", n), Read());
  ASSERT_EQ("EOF", Read());
}

TEST(LogTest, RandomRead) {
  const int N = 500;
  Random write_rnd(301);
  for (int i = 0; i < N; i++) {
    Write(RandomSkewedString(i, &write_rnd));
  }
  Random read_rnd(301);
  for (int i = 0; i < N; i++) {
    ASSERT_EQ(RandomSkewedString(i, &read_rnd), Read());
  }
  ASSERT_EQ("EOF", Read());
}

// Tests of all the error paths in log_reader.cc follow:

TEST(LogTest, ReadError) {
  Write("foo");
  ForceError();
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(kBlockSize, DroppedBytes());
  ASSERT_EQ("OK", MatchError("read error"));
}

TEST(LogTest, BadRecordType) {
  Write("foo");
  // Type is stored in header[6]
  IncrementByte(6, 100);
  FixChecksum(0, 3);
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(3, DroppedBytes());
  ASSERT_EQ("OK", MatchError("unknown record type"));
}

TEST(LogTest, TruncatedTrailingRecord) {
  Write("foo");
  ShrinkSize(4);   // Drop all payload as well as a header byte
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(kHeaderSize - 1, DroppedBytes());
  ASSERT_EQ("OK", MatchError("truncated record at end of file"));
}

TEST(LogTest, BadLength) {
  Write("foo");
  ShrinkSize(1);
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(kHeaderSize + 2, DroppedBytes());
  ASSERT_EQ("OK", MatchError("bad record length"));
}

TEST(LogTest, ChecksumMismatch) {
  Write("foo");
  IncrementByte(0, 10);
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(3, DroppedBytes());
  ASSERT_EQ("OK", MatchError("checksum mismatch"));
}

TEST(LogTest, UnexpectedMiddleType) {
  Write("foo");
  SetByte(6, kMiddleType);
  FixChecksum(0, 3);
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(3, DroppedBytes());
  ASSERT_EQ("OK", MatchError("missing start"));
}

TEST(LogTest, UnexpectedLastType) {
  Write("foo");
  SetByte(6, kLastType);
  FixChecksum(0, 3);
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(3, DroppedBytes());
  ASSERT_EQ("OK", MatchError("missing start"));
}

TEST(LogTest, UnexpectedFullType) {
  Write("foo");
  Write("bar");
  SetByte(6, kFirstType);
  FixChecksum(0, 3);
  ASSERT_EQ("bar", Read());
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(3, DroppedBytes());
  ASSERT_EQ("OK", MatchError("partial record without end"));
}

TEST(LogTest, UnexpectedFirstType) {
  Write("foo");
  Write(BigString("bar", 100000));
  SetByte(6, kFirstType);
  FixChecksum(0, 3);
  ASSERT_EQ(BigString("bar", 100000), Read());
  ASSERT_EQ("EOF", Read());
  ASSERT_EQ(3, DroppedBytes());
  ASSERT_EQ("OK", MatchError("partial record without end"));
}

TEST(LogTest, ErrorJoinsRecords) {
  // Consider two fragmented records:
  //    first(R1) last(R1) first(R2) last(R2)
  // where the middle two fragments disappear.  We do not want
  // first(R1),last(R2) to get joined and returned as a valid record.

  // Write records that span two blocks
  Write(BigString("foo", kBlockSize));
  Write(BigString("bar", kBlockSize));
  Write("correct");

  // Wipe the middle block
  for (int offset = kBlockSize; offset < 2*kBlockSize; offset++) {
    SetByte(offset, 'x');
  }

  ASSERT_EQ("correct", Read());
  ASSERT_EQ("EOF", Read());
  const int dropped = DroppedBytes();
  ASSERT_LE(dropped, 2*kBlockSize + 100);
  ASSERT_GE(dropped, 2*kBlockSize);
}

}
}

int main(int argc, char** argv) {
  return leveldb::test::RunAllTests();
}