/*
** Copyright (C) 2020 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
**
** This program is free software; you can redistribute it and/or modify it
** under the terms of the GNU General Public License as published by the
** Free Software Foundation; either version 3, or (at your option) any
** later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software Foundation,
** Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
**
*/

#define G_LOG_USE_STRUCTURED
#include <glib.h>
#include <glib/gstdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <iostream>
#include <fstream>
#include <cstring>

#include "mu-logger.hh"

using namespace Mu;

static bool           MuLogInitialized = false;
static Mu::LogOptions MuLogOptions;
static std::ofstream  MuStream;
static auto           MaxLogFileSize = 1000 * 1024;

static std::string MuLogPath;

static bool
maybe_open_logfile()
{
	if (MuStream.is_open())
		return true;

	MuStream.open(MuLogPath, std::ios::out | std::ios::app);
	if (!MuStream.is_open()) {
		std::cerr << "opening " << MuLogPath << " failed:" << g_strerror(errno)
			  << std::endl;
		return false;
	}

	MuStream.sync_with_stdio(false);
	return true;
}

static bool
maybe_rotate_logfile()
{
	static unsigned n = 0;

	if (n++ % 1000 != 0)
		return true;

	GStatBuf statbuf;
	if (g_stat(MuLogPath.c_str(), &statbuf) == -1 || statbuf.st_size <= MaxLogFileSize)
		return true;

	const auto old = MuLogPath + ".old";
	g_unlink(old.c_str()); // opportunistic

	if (MuStream.is_open())
		MuStream.close();

	if (g_rename(MuLogPath.c_str(), old.c_str()) != 0)
		std::cerr << "failed to rename " << MuLogPath << " -> " << old.c_str() << ": "
			  << g_strerror(errno) << std::endl;

	return maybe_open_logfile();
}

static GLogWriterOutput
log_file(GLogLevelFlags level, const GLogField* fields, gsize n_fields, gpointer user_data)
{
	if (!maybe_open_logfile())
		return G_LOG_WRITER_UNHANDLED;

	char   timebuf[22];
	time_t now{::time(NULL)};
	::strftime(timebuf, sizeof(timebuf), "%F %T", ::localtime(&now));

	char* msg = g_log_writer_format_fields(level, fields, n_fields, FALSE);
	if (msg && msg[0] == '\n') // hmm... seems lines start with '\n'r
		msg[0] = ' ';

	MuStream << timebuf << ' ' << msg << std::endl;

	g_free(msg);

	return maybe_rotate_logfile() ? G_LOG_WRITER_HANDLED : G_LOG_WRITER_UNHANDLED;
}

static GLogWriterOutput
log_stdouterr(GLogLevelFlags level, const GLogField* fields, gsize n_fields, gpointer user_data)
{
	return g_log_writer_standard_streams(level, fields, n_fields, user_data);
}

static GLogWriterOutput
log_journal(GLogLevelFlags level, const GLogField* fields, gsize n_fields, gpointer user_data)
{
	return g_log_writer_journald(level, fields, n_fields, user_data);
}

void
Mu::log_init(const std::string& path, Mu::LogOptions opts)
{
	if (MuLogInitialized) {
		g_error("logging is already initialized");
		return;
	}

	if (g_getenv("MU_LOG_STDOUTERR"))
		opts |= LogOptions::StdOutErr;

	MuLogOptions = opts;
	MuLogPath    = path;

	g_log_set_writer_func(
	    [](GLogLevelFlags level, const GLogField* fields, gsize n_fields, gpointer user_data) {
		    // filter out debug-level messages?
		    if (level == G_LOG_LEVEL_DEBUG &&
			(none_of(MuLogOptions & Mu::LogOptions::Debug)))
			    return G_LOG_WRITER_HANDLED;

		    // log criticals to stdout / err or if asked
		    if (level == G_LOG_LEVEL_CRITICAL ||
			any_of(MuLogOptions & Mu::LogOptions::StdOutErr)) {
			    log_stdouterr(level, fields, n_fields, user_data);
		    }

		    // log to the journal, or, if not available to a file.
		    if (log_journal(level, fields, n_fields, user_data) != G_LOG_WRITER_HANDLED)
			    return log_file(level, fields, n_fields, user_data);
		    else
			    return G_LOG_WRITER_HANDLED;
	    },
	    NULL,
	    NULL);

	g_message("logging initialized; debug: %s, stdout/stderr: %s",
		  any_of(log_get_options() & LogOptions::Debug) ? "yes" : "no",
		  any_of(log_get_options() & LogOptions::StdOutErr) ? "yes" : "no");

	MuLogInitialized = true;
}

void
Mu::log_uninit()
{
	if (!MuLogInitialized)
		return;

	if (MuStream.is_open())
		MuStream.close();

	MuLogInitialized = false;
}

void
Mu::log_set_options(Mu::LogOptions opts)
{
	MuLogOptions = opts;
}

Mu::LogOptions
Mu::log_get_options()
{
	return MuLogOptions;
}