CourseraCourseParser.php

<?php

/**
 * Takes in json text, and extracts relevant peices of info.
 * This code is specifically for coursera.org
 * 
 * @author Chris Rehfeld
 */

require_once 'AbstractCourseParser.php';



class CourseraCourseParser extends AbstractCourseParser
{
    protected $generalJsonText
            , $instructorJsonText;
    
    /**
     * Initializes the object, making it ready for the parse() method to be called.
     * 
     * @param string $generalJsonText the json text that contains the general info about the course
     * @param string $instructorJsonText the json text that contains info about the professors for the course
     * @throws IllegalArgumentException
     */
    public function __construct($homepageUrl, $generalJsonText, $instructorJsonText)
    {
        $this->homepageUrl = $homepageUrl;
        
        if (!is_string($generalJsonText) || !is_string($instructorJsonText))
        {
            throw new InvalidArgumentException("arg 1 and 2 must be string");
        }
        if (strlen($generalJsonText) < 20 || strlen($instructorJsonText) < 2)
        {
            throw new InvalidArgumentException("json text too short");
        }
        $this->generalJsonText = $generalJsonText;
        $this->instructorJsonText = $instructorJsonText;
    }
    
    
    /**
     * Trys to extract data. hopefully after this method is called, 
     * the getters should return valid info.
     * 
     * @throws CourseParsingException if something really bad happens
     */
    public function parse()
    {
        //marks that we attempted parsing
        $this->isParsed = true;
        
        $generalObj = json_decode($this->generalJsonText);
        if (!$generalObj)
        {
            throw new RuntimeException("json parsing failed for generalJsonText");
        }
        
        $instructorObj = json_decode($this->instructorJsonText);
        if (!$instructorObj)
        {
            throw new RuntimeException("json parsing failed for instructorJsonText");
        }
        
        //course description
        $this->courseDescription = strip_tags($generalObj->about_the_course);
        
        //university name
        $this->universityName = $generalObj->universities[0]->name;
        
        //course name
        $this->courseName = $generalObj->name;
        
        //workload
        if (preg_match('~(\d+)(\-(\d+)) hours?/week~', $generalObj->estimated_class_workload, $matches))
        {
            if (isset($matches[3]))
            {
                // case like: 5 hours/week
                $ave = ceil(($matches[1] + $matches[3] ) / 2);
            }
            else
            {
                // case like 5-6 hours/week
                $ave = (int) $matches[1];
            }
            if ($ave < 0 || $ave > 100)
            {
                throw new CourseParsingException("parsing of workload failed for $ave '{$generalObj->estimated_class_workload}'");
            }
            $this->workload = $ave;
        }
        
        
        
        //start date
        //we try to pick the "active" course, but, default to the first in the list
        //because sometimes there is no course marked as active
        $course = $generalObj->courses[0];
		foreach($generalObj->courses as $potentialActiveCourse) {
			if ($potentialActiveCourse->status)
            {
                $course = $potentialActiveCourse;
                break;
            }
		}

        if ($course->start_date_string)
        {
            // remove commas
            $dateStr = trim(str_replace(',', '', $course->start_date_string));
            if (preg_match('~^(\d{1,2} )?\w+ \d{2,4}$~', $dateStr))
            {
                $ts = '@' . strtotime($dateStr);
                $this->startDate = date_create($ts);
                // if we still failed...this is an unknown date format
                if (!$this->startDate)
                {
                    throw new CourseParsingException("Unknown date format. date_str='{$dateStr}'");
                }
            }
            elseif ($dateStr === 'Self-service')
            {
                $this->startDate = null;
            }
            else
            {
                throw new CourseParsingException("Unknown date format. date_str='{$dateStr}'");
            }
            
            
        }
        elseif ($course->start_year && $course->start_month)
        {
            //sometimes they omit the start day, assume first of the month
            $day = $course->start_day ? $course->start_day : 1;
            $this->startDate = date_create("{$course->start_year}-{$course->start_month}-$day 00:00:00");
            if (!$this->startDate)
            {
                throw new CourseParsingException("Unexpected date values. y:m:d = {$course->start_year}:{$course->start_month}:{$course->start_day}");
            }
        }
        else
        {
            //we assume this case is that the date is simply unspecified/"to be determined"
            $this->startDate = null;
        }

        
        //duration
        if (preg_match('~(\d+) weeks~', $course->duration_string, $matches))
        {
            //convert weeks to days
            $this->duration = $matches[1];
        }
        
        //calc end date, if possible
        if ($this->startDate && $this->duration)
        {
            //add the duration in seconds
            $endTimestamp = $this->startDate->format('U') + ($this->duration * 60 * 60 * 24 * 7);
            $this->endDate = new Datetime("@$endTimestamp");
        }
        
        
        //staff/professors
        $staff = array();
        foreach ($instructorObj as $prof) 
        {
            $name = strlen($prof->middle_name)
                  ? "{$prof->first_name} {$prof->middle_name} {$prof->last_name}"
                  : "{$prof->first_name} {$prof->last_name}";
            $image = $prof->photo;
            //sometimes theres blank entries where the name is just whitespace. skip.
            if (strlen(trim($name)))
            {
                $staff[] = compact('name', 'image');
            }
        }
        $this->otherProfessors = $staff;
        $this->primaryProfessor = $staff[0];
        
        
        //categories
        $categoryNames = array();
        foreach ($generalObj->categories as $category)
        {
            //trim names and make sure not empty, otherwise skip
            $name = trim($category->name);
            if (strlen($name))
            {
                $categoryNames[] = $name;
            }
        }
        $this->categoryNames = $categoryNames;
        
        //short description
        $this->shortCourseDescription = $generalObj->short_description;
        
        //long description
        $this->longCourseDescription = $generalObj->about_the_course;
        
        //video url
        if (strlen($generalObj->video) > 0)
        {
            if (!preg_match('~^[a-zA-Z0-9_-]{5,50}$~Di', $generalObj->video))
            {
                throw new CourseParsingException("Unexpected youtube url component format. val='{$generalObj->video}'");
            }
            else
            {
                $this->courseVideoUrl = 'http://www.youtube.com/watch?v=' . urlencode($generalObj->video);
            }
        }
        
        
        //photo url
        $photoUrl = $generalObj->photo;
        if (strlen($photoUrl) > 0)
        {
            $parts = parse_url($photoUrl);
            if (isset($parts['host']))
            {
                $this->coursePhotoUrl = $photoUrl;
            }
        }
       
        
        

    }
}