rdbms.js

//require('../index');

// CONF.table_users = 'id:uid,name:string,dtcreated:date';
// TABLE('users').find().callback(console.log);
// TABLE('users').insert({ id: UID(), name: 'Peter', dtcreated: NOW });

const DELIMITER = '\0';
const Fs = require('fs');
const Path = require('path');

function RDBMS(filename, potemkin) {
	var t = this;
	t.headersize = 1024 * 5; // 5 kB
	t.filename = filename;
	t.version = 1;
	t.columns = {};
	t.commands = [];
	t.keys = [];
	t.ready = false;

	if (!potemkin) {
		t.next = function() {
			var item = t.commands.shift();
			if (item)
				t[item.name].apply(t, item.args);
		};
		t.refresh();
	}
}

RDBMS.prototype.insert = function(data, callback) {

	var self = this;

	if (!self.ready) {
		self.commands.push({ name: 'insert', args: arguments });
		return self;
	}

	var buffer = self.serialize(data);

	Fs.appendFile(self.filename, buffer, function() {
		callback && callback();
		self.next();
	});

	return self;
};

RDBMS.prototype.refresh = function() {
	var self = this;
	Fs.open(self.filename, 'r+', function(err, fd) {
		if (err) {
			Fs.writeFile(self.filename, Buffer.alloc(0), function() {
				self.refresh();
			});
		} else {
			self.fd = fd;
			self.load(self.next);
		}
	});
};

RDBMS.prototype.serializemeta = function(schema) {

	var self = this;
	var buffer = Buffer.alloc(self.headersize);
	var chunks = [];

	for (var key in schema) {
		var val = schema[key];
		chunks.push(key + ':' + val);
	}

	var columns = Buffer.from(chunks.join(DELIMITER), 'utf8');
	buffer.write('TableDB');
	buffer.writeInt8(1, 7); // version
	buffer.writeInt32BE(columns.length, 8); // size of columns
	columns.copy(buffer, 12);
	return buffer;
};

RDBMS.prototype.parsemeta = function(buffer) {

	var version = buffer.readInt8(7);
	if (!version)
		return;

	var length = buffer.readInt32BE(8);
	var arr = buffer.toString('utf8', 12, 12 + length).split(DELIMITER);
	var columns = {};

	for (var item of arr) {
		var kv = item.split(':');
		columns[kv[0]] = kv[1];
	}

	return { version: version, columns: columns };
};

RDBMS.prototype.serialize = function(row) {

	var self = this;
	var arr = [];

	for (var key in self.columns) {

		var val = row[key];
		if (val == null)
			val = '';
		else {
			if (val instanceof Date)
				val = val.getTime().toString(36);
			else if (typeof(val) === 'boolean')
				val = val ? 1 : 0;
			val = val.toString();
		}

		arr.push(val);
	}

	var data = arr.join(DELIMITER);
	var meta = Buffer.alloc(5);
	meta.writeInt8(1);
	meta.writeInt32BE(data.length, 1);
	return Buffer.concat([meta, Buffer.from(data, 'utf8')]);
};

RDBMS.prototype.parse = function(buffer, fields) {

	var self = this;
	var state = buffer.readInt8(0);
	if (state === 2)
		return;

	var size = buffer.readInt32BE(1);
	var offset = 5;
	var value = buffer.toString('utf8', offset, offset + size).split(DELIMITER);
	var doc = {};
	var indexer = -1;

	for (var key in self.meta) {

		indexer++;

		if (fields && !fields[key])
			continue;

		var col = self.meta[key];
		switch (col) {
			case 'date':
				doc[key] = value[indexer] ? new Date(parseInt(value[indexer], 36)) : null;
				break;
			case 'number':
				doc[key] = value[indexer] ? value[indexer] : null;
				break;
			case 'boolean':
				doc[key] = value[indexer] === '1' ? true : value[indexer] === '0' ? false : null;
				break;
			case 'string':
			default:
				doc[key] = value[indexer];
				break;
		}
	}

	return doc;
};

RDBMS.prototype.create = function(schema, callback) {
	var self = this;
	Fs.writeFile(self.filename, self.serializemeta(schema), function() {
		self.columns = schema;
		callback && callback();
	});
	return self;
};

RDBMS.prototype.load = function(callback) {

	var self = this;
	var buffer = Buffer.alloc(self.headersize);

	Fs.read(self.fd, buffer, 0, buffer.length, 0, function() {
		var meta = self.parsemeta(buffer);
		if (meta) {
			self.version = meta.version;
			self.columns = meta.columns;
			self.keys = Object.keys(self.columns);
			self.ready = true;
		}

		callback && callback();
		self.next();
	});

	return self;
};

RDBMS.create = function(filename, schema, callback) {
	var self = this;
	var db = new RDBMS(filename, true);
	Fs.writeFile(filename, db.serializemeta(schema), callback);
	return self;
};

(function() {

	// RDBMS.create(PATH.databases('users.tabledb'), { id: 'string', name: 'string', age: 'number', isremoved: 'boolean', date: 'date' }, console.log);

	var rdbms = new RDBMS(Path.join('databases', 'users.tabledb'));

	// rdbms.insert({ id: '123456', name: 'Peter', age: 33, isremoved: false, date: new Date() });

	// rdbms.create(rdbms.columns);
	// return;

	// var buf = rdbms.serialize({ id: UID(), name: 'Peter', isremoved: true, dtcreated: NOW });
	// console.log(rdbms.parse(buf));
	// var columns = rdbms.serializemeta(rdbms.columns);
	// console.log(rdbms.parsemeta(columns));
	// console.log(buf.toString('ascii'));
})();