grader.js

#!/usr/bin/env node
/*
Automatically grade files for the presence of specified HTML tags/attributes.
Uses commander.js and cheerio. Teaches command line application development
and basic DOM parsing.

References:

 + cheerio
   - https://github.com/MatthewMueller/cheerio
   - http://encosia.com/cheerio-faster-windows-friendly-alternative-jsdom/
   - http://maxogden.com/scraping-with-node.html

 + commander.js
   - https://github.com/visionmedia/commander.js
   - http://tjholowaychuk.com/post/9103188408/commander-js-nodejs-command-line-interfaces-made-easy

 + JSON
   - http://en.wikipedia.org/wiki/JSON
   - https://developer.mozilla.org/en-US/docs/JSON
   - https://developer.mozilla.org/en-US/docs/JSON#JSON_in_Firefox_2
*/

var util = require('util');
var restler = require('restler');

var fs = require('fs');
var program = require('commander');
var cheerio = require('cheerio');
var HTMLFILE_DEFAULT = "index.html";
var CHECKSFILE_DEFAULT = "checks.json";

var assertFileExists = function(infile) {
    var instr = infile.toString();
    if(!fs.existsSync(instr)) {
        console.log("%s does not exist. Exiting.", instr);
        process.exit(1); // http://nodejs.org/api/process.html#process_process_exit_code
    }
    return instr;
};

var cheerioHtmlFile = function(htmlfile) {
    return cheerio.load(fs.readFileSync(htmlfile));
};

var loadChecks = function(checksfile) {
    return JSON.parse(fs.readFileSync(checksfile));
};

var checkHtmlFile = function(htmlfile, checksfile) {
    $ = cheerioHtmlFile(htmlfile);
    var checks = loadChecks(checksfile).sort();
    var out = {};
    for(var ii in checks) {
        var present = $(checks[ii]).length > 0;
        out[checks[ii]] = present;
    }
    return out;
};

var html2OutJson = function(htmlfile, checksfile){
    var checkJson = checkHtmlFile(program.file,program.checks);
    var outJson = JSON.stringify(checkJson, null, 4 );
    console.log(outJson);
};

var writeAndCheckHtmlFile = function(htmlfile, checksfile, url) {
    var writeAndCheck = function( result, response){
	if ( result instanceof Error ) {
	    console.error('Error! %s (%s)', util.format(result.message), url);
	 } else {
	     fs.writeFileSync(htmlfile, result);
	     html2OutJson(htmlfile, checksfile);
	 }
    };
    return writeAndCheck;
};
 


var url2OutJson = function(htmlfile, checksfile, url){
    var writeAndCheck = writeAndCheckHtmlFile(htmlfile, checksfile,url);
    restler.get(url).on('complete',writeAndCheck);
};

var clone = function(fn) {
    // Workaround for commander.js issue.
    // http://stackoverflow.com/a/6772648
    return fn.bind({});
};

if(require.main == module) {
    program
        .option('-c, --checks <check_file>', 'Path to checks.json', clone(assertFileExists), CHECKSFILE_DEFAULT)
        .option('-f, --file <html_file>', 'Path to index.html', clone(assertFileExists), HTMLFILE_DEFAULT)
    .option('-u, --url <url>' , 'URL')
        .parse(process.argv);
//    var checkJson = checkHtmlFile(program.file, program.checks);
//    var outJson = JSON.stringify(checkJson, null, 4);

    if ( program.url){
	url2OutJson(program.file, program.checks, program.url);
    } else {
	html2OutJson(program.file, program.checks);
    }
} else {
    exports.checkHtmlFile = checkHtmlFile;
}