// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_METRICS_PERSISTED_LOGS_H_
#define COMPONENTS_METRICS_PERSISTED_LOGS_H_

#include <string>
#include <vector>

#include "base/basictypes.h"
#include "base/logging.h"
#include "base/values.h"

class PrefService;

namespace metrics {

// Maintains a list of unsent logs that are written and restored from disk.
class PersistedLogs {
 public:
  // Used to produce a histogram that keeps track of the status of recalling
  // persisted per logs.
  enum LogReadStatus {
    RECALL_SUCCESS,         // We were able to correctly recall a persisted log.
    LIST_EMPTY,             // Attempting to recall from an empty list.
    LIST_SIZE_MISSING,      // Failed to recover list size using GetAsInteger().
    LIST_SIZE_TOO_SMALL,    // Too few elements in the list (less than 3).
    LIST_SIZE_CORRUPTION,   // List size is not as expected.
    LOG_STRING_CORRUPTION,  // Failed to recover log string using GetAsString().
    CHECKSUM_CORRUPTION,    // Failed to verify checksum.
    CHECKSUM_STRING_CORRUPTION,  // Failed to recover checksum string using
                                 // GetAsString().
    DECODE_FAIL,            // Failed to decode log.
    DEPRECATED_XML_PROTO_MISMATCH,  // The XML and protobuf logs have
                                    // inconsistent data.
    END_RECALL_STATUS       // Number of bins to use to create the histogram.
  };

  enum StoreType {
    NORMAL_STORE,       // A standard store operation.
    PROVISIONAL_STORE,  // A store operation that can be easily reverted later.
  };

  // Constructs a PersistedLogs that stores data in |local_state| under
  // the preference |pref_name|.  Calling code is responsible for ensuring that
  // the lifetime of |local_state| is longer than the lifetime of PersistedLogs.
  // When saving logs to disk, we will store either the first |min_log_count|
  // logs, or at least |min_log_bytes| bytes of logs, whichever is more.
  // If the optional max_log_size parameter is non-zero, all logs larger than
  // that limit will be dropped before logs are written to disk.
  PersistedLogs(PrefService* local_state,
                const char* pref_name,
                size_t min_log_count,
                size_t min_log_bytes,
                size_t max_log_size);
  ~PersistedLogs();

  // Write list to storage.
  void SerializeLogs();

  // Reads the list from the preference.
  LogReadStatus DeserializeLogs();

  // Adds a log to the list.  |input| will be swapped with an empty string.
  void StoreLog(std::string* input);

  // Stages the most recent log.  The staged_log will remain the same even if
  // additional logs are added.
  void StageLog();

  // Remove the staged log.
  void DiscardStagedLog();

  // Saves the staged log, then clears staged_log().
  // If |store_type| is PROVISIONAL_STORE, it can be dropped from storage with
  // a later call to DiscardLastProvisionalStore (if it hasn't already been
  // staged again).
  // This is intended to be used when logs are being saved while an upload is in
  // progress, in case the upload later succeeds.
  // This can only be called if has_staged_log() is true.
  void StoreStagedLogAsUnsent(StoreType store_type);

  // Discards the last log stored with StoreStagedLogAsUnsent with |store_type|
  // set to PROVISIONAL_STORE, as long as it hasn't already been re-staged. If
  // the log is no longer present, this is a no-op.
  void DiscardLastProvisionalStore();

  // True if a log has been staged.
  bool has_staged_log() const { return !staged_log_.log.empty(); };

  // Returns the element in the front of the list.
  const std::string& staged_log() const {
    DCHECK(has_staged_log());
    return staged_log_.log;
  }

  // Returns the element in the front of the list.
  const std::string& staged_log_hash() const {
    DCHECK(has_staged_log());
    return staged_log_.hash;
  }

  // The number of elements currently stored.
  size_t size() const { return list_.size(); }

  // True if there are no stored logs.
  bool empty() const { return list_.empty(); }

 private:
  // Writes the list to the ListValue.
  void WriteLogsToPrefList(base::ListValue* list);

  // Reads the list from the ListValue.
  LogReadStatus ReadLogsFromPrefList(const base::ListValue& list);

  // A weak pointer to the PrefService object to read and write the preference
  // from.  Calling code should ensure this object continues to exist for the
  // lifetime of the PersistedLogs object.
  PrefService* local_state_;

  // The name of the preference this object stores logs in.
  const char* pref_name_;

  // We will keep at least this |min_log_count_| logs or |min_log_bytes_| bytes
  // of logs, whichever is greater, when writing to disk.  These apply after
  // skipping logs greater than |max_log_size_|.
  const size_t min_log_count_;
  const size_t min_log_bytes_;

  // Logs greater than this size will not be written to disk.
  const size_t max_log_size_;

  struct LogHashPair {
    // Raw log text, typically a serialized protobuf.
    std::string log;
    // The SHA1 hash of log, stored to catch errors from memory corruption.
    std::string hash;
    // Swap the content of input into log and update the hash.
    void SwapLog(std::string* input);
    // Swap both log and hash from another LogHashPair.
    void Swap(LogHashPair* input);
  };
  // A list of all of the stored logs, stored with SHA1 hashes to check for
  // corruption while they are stored in memory.
  std::vector<LogHashPair> list_;

  // The log staged for upload.
  LogHashPair staged_log_;

  // The index and type of the last provisional store. If nothing has been
  // provisionally stored, or the last provisional store has already been
  // re-staged, the index will be -1;
  // This is necessary because during an upload there are two logs (staged
  // and current) and a client might store them in either order, so it's
  // not necessarily the case that the provisional store is the last store.
  int last_provisional_store_index_;

  DISALLOW_COPY_AND_ASSIGN(PersistedLogs);
};

}  // namespace metrics

#endif  // COMPONENTS_METRICS_PERSISTED_LOGS_H_