// Copyright 2011 Google Inc.
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//
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//   notice, this list of conditions and the following disclaimer.
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//   may be used to endorse or promote products derived from this software
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#include "utils/logging/operations.hpp"

extern "C" {
#include <unistd.h>
}

#include <fstream>
#include <stdexcept>
#include <string>
#include <utility>
#include <vector>

#include "utils/datetime.hpp"
#include "utils/format/macros.hpp"
#include "utils/optional.ipp"
#include "utils/sanity.hpp"

namespace datetime = utils::datetime;
namespace fs = utils::fs;
namespace logging = utils::logging;

using utils::none;
using utils::optional;


/// The general idea for the application-wide logging goes like this:
///
/// 1. The application starts.  Logging is initialized to capture _all_ log
/// messages into memory regardless of their level by issuing a call to the
/// set_inmemory() function.
///
/// 2. The application offers the user a way to select the logging level and a
/// file into which to store the log.
///
/// 3. The application calls set_persistency providing a new log level and a log
/// file.  This must be done as early as possible, to minimize the chances of an
/// early crash not capturing any logs.
///
/// 4. At this point, any log messages stored into memory are flushed to disk
/// respecting the provided log level.
///
/// 5. The internal state of the logging module is updated to only capture
/// messages that are of the provided log level (or below) and is configured to
/// directly send messages to disk.
///
/// The call to set_inmemory() should only be performed by the user-facing
/// application.  Tests should skip this call so that the logging messages go to
/// stderr by default, thus generating a useful log to debug the tests.


namespace {


/// Current log level.
static logging::level log_level = logging::level_debug;


/// Indicates whether set_persistency() will be called automatically or not.
static bool auto_set_persistency = true;


/// First time recorded by the logging module.
static optional< datetime::timestamp > first_timestamp = none;


/// In-memory record of log entries before persistency is enabled.
static std::vector< std::pair< logging::level, std::string > > backlog;


/// Stream to the currently open log file.
static std::unique_ptr< std::ofstream > logfile;


/// Constant string to strftime to format timestamps.
static const char* timestamp_format = "%Y%m%d-%H%M%S";


/// Converts a level to a printable character.
///
/// \param level The level to convert.
///
/// \return The printable character, to be used in log messages.
static char
level_to_char(const logging::level level)
{
    switch (level) {
    case logging::level_error: return 'E';
    case logging::level_warning: return 'W';
    case logging::level_info: return 'I';
    case logging::level_debug: return 'D';
    default: UNREACHABLE;
    }
}


}  // anonymous namespace


/// Generates a standard log name.
///
/// This always adds the same timestamp to the log name for a particular run.
/// Also, the timestamp added to the file name corresponds to the first
/// timestamp recorded by the module; it does not necessarily contain the
/// current value of "now".
///
/// \param logdir The path to the directory in which to place the log.
/// \param progname The name of the program that is generating the log.
fs::path
logging::generate_log_name(const fs::path& logdir, const std::string& progname)
{
    if (!first_timestamp)
        first_timestamp = datetime::timestamp::now();
    // Update doc/troubleshooting.texi if you change the name format.
    return logdir / (F("%s.%s.log") % progname %
                     first_timestamp.get().strftime(timestamp_format));
}


/// Logs an entry to the log file.
///
/// If the log is not yet set to persistent mode, the entry is recorded in the
/// in-memory backlog.  Otherwise, it is just written to disk.
///
/// \param message_level The level of the entry.
/// \param file The file from which the log message is generated.
/// \param line The line from which the log message is generated.
/// \param user_message The raw message to store.
void
logging::log(const level message_level, const char* file, const int line,
             const std::string& user_message)
{
    const datetime::timestamp now = datetime::timestamp::now();
    if (!first_timestamp)
        first_timestamp = now;

    if (auto_set_persistency) {
        // These values are hardcoded here for testing purposes.  The
        // application should call set_inmemory() by itself during
        // initialization to avoid this, so that it has explicit control on how
        // the call to set_persistency() happens.
        set_persistency("debug", fs::path("/dev/stderr"));
        auto_set_persistency = false;
    }

    if (message_level > log_level)
        return;

    // Update doc/troubleshooting.texi if you change the log format.
    const std::string message = F("%s %s %s %s:%s: %s") %
        now.strftime(timestamp_format) % level_to_char(message_level) %
        ::getpid() % file % line % user_message;
    if (logfile.get() == NULL)
        backlog.push_back(std::make_pair(message_level, message));
    else {
        INV(backlog.empty());
        (*logfile) << message << '\n';
        (*logfile).flush();
    }
}


/// Sets the logging to record messages in memory for later flushing.
void
logging::set_inmemory(void)
{
    auto_set_persistency = false;
}


/// Makes the log persistent.
///
/// Calling this function flushes the in-memory log, if any, to disk and sets
/// the logging module to send log entries to disk from this point onwards.
/// There is no way back, and the caller program should execute this function as
/// early as possible to ensure that a crash at startup does not discard too
/// many useful log entries.
///
/// Any log entries above the provided new_level are discarded.
///
/// \param new_level The new log level.
/// \param path The file to write the logs to.
///
/// \throw std::range_error If the given log level is invalid.
/// \throw std::runtime_error If the given file cannot be created.
void
logging::set_persistency(const std::string& new_level, const fs::path& path)
{
    auto_set_persistency = false;

    PRE(logfile.get() == NULL);

    // Update doc/troubleshooting.info if you change the log levels.
    if (new_level == "debug")
        log_level = level_debug;
    else if (new_level == "error")
        log_level = level_error;
    else if (new_level == "info")
        log_level = level_info;
    else if (new_level == "warning")
        log_level = level_warning;
    else
        throw std::range_error(F("Unrecognized log level '%s'") % new_level);

    logfile.reset(new std::ofstream(path.c_str()));
    if (!(*logfile))
        throw std::runtime_error(F("Failed to create log file %s") % path);

    for (std::vector< std::pair< logging::level, std::string > >::const_iterator
         iter = backlog.begin(); iter != backlog.end(); iter++) {
        if ((*iter).first <= log_level)
            (*logfile) << (*iter).second << '\n';
    }
    (*logfile).flush();
    backlog.clear();
}