/*
** 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.
**
*/

#include "mu-indexer.hh"

#include <config.h>

#include <atomic>
#include <mutex>
#include <vector>
#include <thread>
#include <condition_variable>
#include <iostream>
#include <atomic>
#include <chrono>
using namespace std::chrono_literals;

#include "mu-scanner.hh"
#include "utils/mu-async-queue.hh"
#include "utils/mu-error.hh"
#include "../mu-store.hh"

using namespace Mu;

struct IndexState {
	enum State { Idle, Scanning, Cleaning };
	static const char* name(State s)
	{
		switch (s) {
		case Idle: return "idle";
		case Scanning: return "scanning";
		case Cleaning: return "cleaning";
		default: return "<error>";
		}
	}

	bool operator==(State rhs) const { return state_ == rhs; }

	void change_to(State new_state)
	{
		g_debug("changing indexer state %s->%s",
		        name((State)state_),
		        name((State)new_state));
		state_ = new_state;
	}

private:
	State state_{Idle};
};

struct Indexer::Private {
	Private(Mu::Store& store)
	    : store_{store}, scanner_{store_.metadata().root_maildir,
	                              [this](auto&& path, auto&& statbuf, auto&& info) {
					      return handler(path, statbuf, info);
				      }},
	      max_message_size_{store_.metadata().max_message_size},
	      batch_size_{store_.metadata().batch_size}
	{
		g_message("created indexer for %s -> %s (batch-size: %zu)",
		          store.metadata().root_maildir.c_str(),
		          store.metadata().database_path.c_str(),
		          batch_size_);
	}

	~Private() { stop(); }

	bool dir_predicate(const std::string& path, const struct dirent* dirent) const;
	bool handler(const std::string& fullpath, struct stat* statbuf, Scanner::HandleType htype);

	void maybe_start_worker();
	void worker();

	bool cleanup();

	bool start(const Indexer::Config& conf);
	bool stop();

	Indexer::Config conf_;
	Store&          store_;
	Scanner         scanner_;
	const size_t    max_message_size_;

	time_t                   dirstamp_{};
	std::size_t              max_workers_;
	std::vector<std::thread> workers_;
	std::thread              scanner_worker_;

	AsyncQueue<std::string> fq_;

	Progress     progress_;
	IndexState   state_;
	const size_t batch_size_; /**< Max number of messages added before
	                           * committing */

	std::mutex lock_, wlock_;
};

bool
Indexer::Private::handler(const std::string&  fullpath,
                          struct stat*        statbuf,
                          Scanner::HandleType htype)
{
	switch (htype) {
	case Scanner::HandleType::EnterDir:
	case Scanner::HandleType::EnterNewCur: {
		// in lazy-mode, we ignore this dir if its dirstamp suggest it
		// is up-to-date (this is _not_ always true; hence we call it
		// lazy-mode); only for actual message dirs, since the dir
		// tstamps may not bubble up.
		dirstamp_ = store_.dirstamp(fullpath);
		if (conf_.lazy_check && dirstamp_ >= statbuf->st_mtime &&
		    htype == Scanner::HandleType::EnterNewCur) {
			g_debug("skip %s (seems up-to-date)", fullpath.c_str());
			return false;
		}

		// don't index dirs with '.noindex'
		auto noindex = ::access((fullpath + "/.noindex").c_str(), F_OK) == 0;
		if (noindex) {
			g_debug("skip %s (has .noindex)", fullpath.c_str());
			return false; // don't descend into this dir.
		}

		// don't index dirs with '.noupdate', unless we do a full
		// (re)index.
		if (!conf_.ignore_noupdate) {
			auto noupdate = ::access((fullpath + "/.noupdate").c_str(), F_OK) == 0;
			if (noupdate) {
				g_debug("skip %s (has .noupdate)", fullpath.c_str());
				return false;
			}
		}

		g_debug("process %s", fullpath.c_str());
		return true;
	}
	case Scanner::HandleType::LeaveDir: {
		store_.set_dirstamp(fullpath, ::time(NULL));
		return true;
	}

	case Scanner::HandleType::File: {
		if ((size_t)statbuf->st_size > max_message_size_) {
			g_debug("skip %s (too big: %" G_GINT64_FORMAT " bytes)",
			        fullpath.c_str(),
			        (gint64)statbuf->st_size);
			return false;
		}

		// if the message is not in the db yet, or not up-to-date, queue
		// it for updating/inserting.
		if (statbuf->st_mtime <= dirstamp_ && store_.contains_message(fullpath)) {
			// g_debug ("skip %s: already up-to-date");
			return false;
		}

		fq_.push(std::string{fullpath});
		return true;
	}
	default: g_return_val_if_reached(false); return false;
	}
}

void
Indexer::Private::maybe_start_worker()
{
	std::lock_guard<std::mutex> wlock{wlock_};

	if (fq_.size() > workers_.size() && workers_.size() < max_workers_)
		workers_.emplace_back(std::thread([this] { worker(); }));
}

void
Indexer::Private::worker()
{
	std::string item;

	g_debug("started worker");

	/* note that transaction starting/committing is opportunistic,
	 * and are NOPs if we are already/not in a transaction */

	store_.begin_transaction();

	while (state_ == IndexState::Scanning || !fq_.empty()) {
		if (!fq_.pop(item, 250ms))
			continue;

		// g_debug ("popped (n=%zu) path %s", fq_.size(), item.c_str());
		++progress_.processed;

		try {
			std::unique_lock lock{lock_};

			store_.add_message(item);
			++progress_.updated;

			if (progress_.updated % batch_size_ == 0) {
				store_.commit_transaction();
				store_.begin_transaction();
			}

		} catch (const Mu::Error& er) {
			g_warning("error adding message @ %s: %s", item.c_str(), er.what());
		}

		maybe_start_worker();
	}

	store_.commit_transaction();
}

bool
Indexer::Private::cleanup()
{
	g_debug("starting cleanup");

	size_t                 n{};
	std::vector<Store::Id> orphans; // store messages without files.
	store_.for_each_message_path([&](Store::Id id, const std::string& path) {
		++n;
		if (::access(path.c_str(), R_OK) != 0) {
			g_debug("cannot read %s (id=%u); queueing for removal from store",
			        path.c_str(),
			        id);
			orphans.emplace_back(id);
		}

		return state_ == IndexState::Cleaning;
	});

	// No need for transactions here, remove_messages does that for us.
	if (orphans.empty())
		g_debug("nothing to clean up");
	else {
		g_debug("removing up %zu stale message(s) from store", orphans.size());
		store_.remove_messages(orphans);
		progress_.removed += orphans.size();
	}

	return true;
}

bool
Indexer::Private::start(const Indexer::Config& conf)
{
	stop();

	conf_ = conf;
	if (conf_.max_threads == 0)
		max_workers_ = std::thread::hardware_concurrency();
	else
		max_workers_ = conf.max_threads;

	g_debug("starting indexer with <= %zu worker thread(s)", max_workers_);
	g_debug("indexing: %s; clean-up: %s",
	        conf_.scan ? "yes" : "no",
	        conf_.cleanup ? "yes" : "no");

	workers_.emplace_back(std::thread([this] { worker(); }));

	state_.change_to(IndexState::Scanning);
	scanner_worker_ = std::thread([this] {
		progress_ = {};

		if (conf_.scan) {
			g_debug("starting scanner");
			if (!scanner_.start()) { // blocks.
				g_warning("failed to start scanner");
				goto leave;
			}
			g_debug("scanner finished with %zu file(s) in queue", fq_.size());
		}

		// now there may still be messages in the work queue...
		// finish those; this is a bit ugly; perhaps we should
		// handle SIGTERM etc.
		while (!fq_.empty())
			std::this_thread::sleep_for(100ms);

		if (conf_.cleanup) {
			g_debug("starting cleanup");
			state_.change_to(IndexState::Cleaning);
			cleanup();
			g_debug("cleanup finished");
		}
	leave:
		state_.change_to(IndexState::Idle);
	});

	g_debug("started indexer");
	return true;
}

bool
Indexer::Private::stop()
{
	scanner_.stop();
	state_.change_to(IndexState::Idle);

	const auto w_n = workers_.size();

	fq_.clear();
	if (scanner_worker_.joinable())
		scanner_worker_.join();

	for (auto&& w : workers_)
		if (w.joinable())
			w.join();
	workers_.clear();

	if (w_n > 0)
		g_debug("stopped indexer (joined %zu worker(s))", w_n);

	return true;
}

Indexer::Indexer(Store& store) : priv_{std::make_unique<Private>(store)} {}

Indexer::~Indexer() = default;

bool
Indexer::start(const Indexer::Config& conf)
{
	const auto mdir{priv_->store_.metadata().root_maildir};
	if (G_UNLIKELY(access(mdir.c_str(), R_OK) != 0)) {
		g_critical("'%s' is not readable: %s", mdir.c_str(), g_strerror(errno));
		return false;
	}

	std::lock_guard<std::mutex> l(priv_->lock_);
	if (is_running())
		return true;

	return priv_->start(conf);
}

bool
Indexer::stop()
{
	std::lock_guard<std::mutex> l(priv_->lock_);

	if (!is_running())
		return true;

	g_debug("stopping indexer");
	return priv_->stop();
}

bool
Indexer::is_running() const
{
	return !(priv_->state_ == IndexState::Idle) || !priv_->fq_.empty();
}

Indexer::Progress
Indexer::progress() const
{
	priv_->progress_.running = priv_->state_ == IndexState::Idle ? false : true;

	return priv_->progress_;
}