var pug = require('pug');
var nodemailer = require('nodemailer');
var crypto = require('crypto');
var fs = require('fs');
var settings = require('./settings');

// Translation
var locale = require('./locales/' + settings.language);
var lang = locale.server;

// Web server
var bodyParser = require('body-parser');
var cors = require('cors');
var express = require('express');
var app = express();

// Logging
var printit = require('printit');
var log = printit({
	prefix: 'SMAM',
	date: true
});


// nodemailer initial configuration
var transporter = nodemailer.createTransport(settings.mailserver);


// Verification tokens
var tokens = {};

// Default template
// JavaScript has no native way to handle multi-line strings, so we put our template
// in a comment inside a function fro which we generate a string.
// cf: https://tomasz.janczuk.org/2013/05/multi-line-strings-in-javascript-and.html
var defaultTemplate = (function() {/*
html
	body
		p.subj
			span(style="font-weight:bold") Subject: 
			span= subject
		p.from
			span(style="font-weight:bold") Sent from: 
			span= replyTo
		each field in custom
			p.custom
				span(style="font-weight:bold")= field.label + ': '
				span= field.value
		p.message
			span(style="font-weight:bold") Message: 
		
		p= html
*/}).toString().match(/[^]*\/\*([^]*)\*\/\}$/)[1];

// Serve static (JS + HTML) files
app.use(express.static('front'));
// Body parsing
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
// Allow cross-origin requests.
var corsOptions = {
  origin: settings.formOrigin,
  optionsSuccessStatus: 200 // some legacy browsers (IE11, various SmartTVs) choke on 204
};
app.use(cors(corsOptions));
// Taking care of preflight requests
app.options('*', cors(corsOptions));


// A request on /register generates a token and store it, along the user's
// address, on the tokens object
app.get('/register', function(req, res, next) {
	// Get IP from express
	let ip = req.headers['x-forwarded-for'] || req.connection.remoteAddress;
	if(tokens[ip] === undefined) {
		tokens[ip] = [];
	}
	// Generate token
	crypto.randomBytes(10, (err, buf) => { 
		let token = buf.toString('hex');
		// Store and send the token
		tokens[ip].push({
			token: token,
			// A token expires after 12h
			expire: new Date().getTime() + 12 * 3600 * 1000
		});
		res.status(200).send(token);
	});
});


// A request on /send with user input = mail to be sent
app.post('/send', function(req, res, next) {
	// Response will be JSON
	res.header('Access-Control-Allow-Headers', 'Content-Type');

	if(!checkBody(req.body)) {
		return res.status(400).send();
	}

	let ip = req.headers['x-forwarded-for'] || req.connection.remoteAddress;

	// Token verification
	if(!checkToken(ip, req.body.token)) {
		return res.status(403).send();
	}

	// Count the failures
	let status = {
		failed: 0,
		total: settings.recipients.length
	};

	// params will be used as:
	// - values for html generation from the pug template
	// - parameters for sending the mail(s)
	let params = {
		subject: req.body.subj,
		from: req.body.name + '<' + settings.mailserver.auth.user + '>',
		replyTo: req.body.name + ' <' + req.body.addr + '>',
		html: req.body.text
	};

	// Process custom fields to get data we can use in the HTML generation
	params.custom = processCustom(req.body.custom);

	// Replacing the mail's content with HTML from the pug template
	// Commenting the line below will bypass the generation and only user the
	// text entered by the user
	fs.access('template.pug', function(err) {
		// Checking if the template exists.
		// If not, fallback to the default template.
		// TODO: Parameterise the template file name.
		if(err) {
			params.html = pug.render(defaultTemplate, params);
		} else {
			params.html = pug.renderFile('template.pug', params);
		}

		log.info(lang.log_sending, params.replyTo);

		// Send the email to all users
		sendMails(params, function(err, infos) {
			if(err) {
				log.error(err);
			}
			logStatus(infos);
		}, function() {
			if(status.failed === status.total) {
				res.status(500).send();
			} else {
				res.status(200).send();
			}
		});
	});

});


// A request on /lang sends translated strings (according to the locale set in
// the app settings), alongside the boolean for the display of labels in the
// form block.
app.get('/lang', function(req, res, next) {
	// Response will be JSON
	res.header('Access-Control-Allow-Headers', 'Content-Type');

	// Preventing un-updated settings files
	let labels = true;
	if(settings.labels !== undefined) {
		labels = settings.labels;
	}

	// Send the infos
	res.status(200).send({
		'labels': labels,
		'translations': locale.client
	});
});


// A request on /fields sends data on custom fields.
app.get('/fields', function(req, res, next) {
	// Response will be JSON
	res.header('Access-Control-Allow-Headers', 'Content-Type');

	// Send an object anyway, its size will determine if we need to display any
	let customFields = settings.customFields || {};

	// Send custom fields data
	res.status(200).send(customFields);
});


// Use either the default port or the one chosen by the user (PORT env variable)
var port = process.env.PORT || 1970;
// Same for the host (using the HOST env variable)
var host = process.env.HOST || '0.0.0.0';
// Start the server
app.listen(port, host, function() {
	log.info(lang.log_server_start, host + ':' + port);
});


// Run the clean every hour
var tokensChecks = setTimeout(cleanTokens, 3600 * 1000);


// Send mails to the recipients specified in the JSON settings file
// content: object containing mail params
//  {
//	  subject: String
//	  from: String (following RFC 1036 (https://tools.ietf.org/html/rfc1036#section-2.1.1))
//	  html: String
//  }
// update(next, infos): Called each time a mail is sent with the infos provided
//					  by nodemailer
// done(): Called once each mail has been sent
function sendMails(params, update, done) {
	let mails = settings.recipients.map((recipient) => {
		// Promise for each recipient to send each mail asynchronously
		return new Promise((sent) => {
			params.to = recipient;
			// Send the email
			transporter.sendMail(params, (err, infos) => {
				sent();
				if(err) {
					return update(err, recipient);
				}
				update(null, infos);
				// Promise callback
			});
		});
	});
	// Run all the promises (= send all the mails)
	Promise.all(mails).then(done);
}


// Produces log from the infos provided by nodemailer
// infos: infos provided by nodemailer
// return: nothing
function logStatus(infos) {
	if(infos.accepted.length !== 0) {
		log.info(lang.log_send_success, infos.accepted[0]);
	}
	if(infos.rejected.length !== 0) {
		status.failed++;
		log.info(lang.log_send_failure, infos.rejected[0]);
	}
}


// Checks if the request's sender has been registered (and unregister it if not)
// ip: sender's IP address
// token: token used by the sender
// return: true if the user was registered, false else
function checkToken(ip, token) {
	let verified = false;

	// Check if there's at least one token for this IP
	if(tokens[ip] !== undefined) {
		if(tokens[ip].length !== 0) {
			// There's at least one element for this IP, let's check the tokens
			for(var i = 0; i < tokens[ip].length; i++) {
				if(!tokens[ip][i].token.localeCompare(token)) {
					// We found the right token
					verified = true;
					// Removing the token
					tokens[ip].pop(tokens[ip][i]);
					break;
				}
			}
		} 
	}

	if(!verified) {
		log.warn(ip, lang.log_invalid_token);
	}

	return verified;
}


// Checks if all the required fields are in the request body
// body: body taken from express's request object
// return: true if the body is valid, false else
function checkBody(body) {
	// Check default fields
	if(isInvalid(body.token) || isInvalid(body.subj) || isInvalid(body.name) 
		|| isInvalid(body.addr) || isInvalid(body.text)) {
		return false;
	}

	// Checking required custom fields
	for(let field in settings.customFields) {
		// No need to check the field if its not required in the settings
		if(settings.customFields[field].required) {
			if(isInvalid(body.custom[field])) {
				return false;
			}
		}
	}

	return true;
}


// Checks if the field is invalid. A field is considered as invalid if undefined
// or is an empty string
// field: user-input value of the field
// return: true if the field is valid, false if not
function isInvalid(field) {
	return (field === undefined || field.length == 0);
}

// Checks the tokens object to see if no token has expired
// return: nothing
function cleanTokens() {
	// Get current time for comparison
	let now = new Date().getTime();

	for(let ip in tokens) { // Check for each IP in the object
		for(let token of tokens[ip]) { // Check for each token of an IP
			if(token.expire < now) { // Token has expired
				tokens[ip].pop(token);
			}
		}
		if(tokens[ip].length === 0) { // No more element for this IP
			delete tokens[ip];
		}
	}

	log.info(lang.log_cleared_token);
}


// Process custom fields to something usable in the HTML generation
// For example, this function replaces indexes with answers in select fields
// custom: object describing data from custom fields
// return: an object with user-input data from each field:
// {
//	  field name: {
//		  value: String,
//		  label: String
//	  }
// }
function processCustom(custom) {
	let fields = {};

	// Process each field
	for(let field in custom) {
		let type = settings.customFields[field].type;
		// Match indexes with data when needed
		switch(type) {
			case 'select':  custom[field] = settings.customFields[field]
											.options[custom[field]];
							break;
		}

		// Insert data into the final object if the value is set
		if(!isInvalid(custom[field])) {
			fields[field] = {
				value: custom[field],
				label: settings.customFields[field].label
			}
		}
	}

	return fields;
}