mbtiles.cpp

#include "mbtiles.h"
#include "helpers.h"
#include <iostream>
#include <cmath>

using namespace sqlite;
using namespace std;

MBTiles::MBTiles():
  pendingStatements1(std::make_shared<std::vector<PendingStatement>>()),
  pendingStatements2(std::make_shared<std::vector<PendingStatement>>())
{}

MBTiles::~MBTiles() {
	if (db && inTransaction) db << "COMMIT;"; // commit all the changes if open
}

// ---- Write .mbtiles

void MBTiles::openForWriting(string &filename) {
	db.init(filename);

	db << "PRAGMA synchronous = OFF;";
	try {
		db << "PRAGMA application_id = 0x4d504258;";
	} catch(runtime_error &e) {
		cout << "Couldn't write SQLite application_id (not fatal): " << e.what() << endl;
	}
	try {
		db << "PRAGMA encoding = 'UTF-8';";
	} catch(runtime_error &e) {
		cout << "Couldn't set SQLite default encoding (not fatal): " << e.what() << endl;
	}
	try {
		db << "PRAGMA journal_mode=OFF;";
	} catch(runtime_error &e) {
		cout << "Couldn't turn journaling off (not fatal): " << e.what() << endl;
	}
	db << "PRAGMA page_size = 65536;";
	db << "VACUUM;"; // make sure page_size takes effect
	db << "CREATE TABLE IF NOT EXISTS metadata (name text, value text, UNIQUE (name));";
	db << "CREATE TABLE IF NOT EXISTS tiles (zoom_level integer, tile_column integer, tile_row integer, tile_data blob);";
	db << "CREATE UNIQUE INDEX IF NOT EXISTS tile_index on tiles (zoom_level, tile_column, tile_row);";
	preparedStatements.emplace_back(db << "INSERT INTO tiles (zoom_level, tile_column, tile_row, tile_data) VALUES (?,?,?,?);");
	preparedStatements.emplace_back(db << "REPLACE INTO tiles (zoom_level, tile_column, tile_row, tile_data) VALUES (?,?,?,?);");

	db << "BEGIN;"; // begin a transaction
	cout << "Creating mbtiles at " << filename << endl;
	inTransaction = true;
}
	
void MBTiles::writeMetadata(string key, string value) {
	m.lock();
	db << "REPLACE INTO metadata (name,value) VALUES (?,?);" << key << value;
	m.unlock();
}

void MBTiles::insertOrReplace(int zoom, int x, int y, const std::string& data, bool isMerge) {
	// NB: assumes we have the `m` mutex
	int tmsY = pow(2, zoom) - 1 - y;
	int s = isMerge ? 1 : 0;
	preparedStatements[s].reset();
	preparedStatements[s] << zoom << x << tmsY && data;
	preparedStatements[s].execute();
}

void MBTiles::flushPendingStatements() {
	// NB: assumes we have the `m` mutex

	for (int i = 0; i < 2; i++) {
		while(!pendingStatements2->empty()) {
			const PendingStatement& stmt = pendingStatements2->back();
			insertOrReplace(stmt.zoom, stmt.x, stmt.y, stmt.data, stmt.isMerge);
			pendingStatements2->pop_back();
		}

		std::lock_guard<std::mutex> lock(pendingStatementsMutex);
		pendingStatements1.swap(pendingStatements2);
	}
}
	
void MBTiles::saveTile(int zoom, int x, int y, string *data, bool isMerge) {
	// If the lock is available, write directly to SQLite.
	if (m.try_lock()) {
		insertOrReplace(zoom, x, y, *data, isMerge);
		flushPendingStatements();
		m.unlock();
	} else {
		// Else buffer the write for later, copying its binary blob.
		const std::lock_guard<std::mutex> lock(pendingStatementsMutex);
		pendingStatements1->push_back({zoom, x, y, *data, isMerge});
	}
}

void MBTiles::closeForWriting() {
	flushPendingStatements();
	preparedStatements[0].used(true);
	preparedStatements[1].used(true);
}

// ---- Read mbtiles

void MBTiles::openForReading(string &filename) {
	db.init(filename);
}

void MBTiles::readBoundingBox(double &minLon, double &maxLon, double &minLat, double &maxLat) {
	string boundsStr;
	db << "SELECT value FROM metadata WHERE name='bounds'" >> boundsStr;
	vector<string> b = split_string(boundsStr,',');
	minLon = stod(b[0]); minLat = stod(b[1]);
	maxLon = stod(b[2]); maxLat = stod(b[3]);
}

void MBTiles::readTileList(std::vector<std::tuple<int,int,int>> &tileList) {
	db << "SELECT zoom_level,tile_column,tile_row FROM tiles" >> [&](int z,int col, int row) {
		tileList.emplace_back(std::make_tuple(z,col,row));
	};
}

vector<char> MBTiles::readTile(int zoom, int col, int row) {
	vector<char> pbfBlob;
	db << "SELECT tile_data FROM tiles WHERE zoom_level=? AND tile_column=? AND tile_row=?" << zoom << col << row >> pbfBlob;
	return pbfBlob;
}

bool MBTiles::readTileAndUncompress(string &data, int zoom, int x, int y, bool isCompressed, bool asGzip) {
	m.lock();
	int tmsY = pow(2,zoom) - 1 - y;
	int exists=0;
	db << "SELECT COUNT(*) FROM tiles WHERE zoom_level=? AND tile_column=? AND tile_row=?" << zoom << x << tmsY >> exists;
	m.unlock();
	if (exists==0) return false;

	m.lock();
	std::vector<char> compressed;
	db << "SELECT tile_data FROM tiles WHERE zoom_level=? AND tile_column=? AND tile_row=?" << zoom << x << tmsY >> compressed;
	m.unlock();

	if (!isCompressed) {
		data = std::string(compressed.data(), compressed.size());
		return true;
	}

	try {
		decompress_string(data, compressed.data(), compressed.size(), asGzip);
		return true;
	} catch(std::runtime_error &e) {
		return false;
	}
}