public class CourseHandler {
    private static Map<Id,Course__c> TriggeredCoursesNew {get;set;}
    private static Map<Id,Course__c> TriggeredCoursesOld {get;set;}

    private static List<Course__c>  Old_list {get;set;}
    private static List<Course__c>  New_list {get;set;}

    public CourseHandler(Map<Id,Course__c> courcesNew, Map<Id,Course__c> courcesOld, List<SObject> old_l, List<SObject> new_l ){
        TriggeredCoursesNew = courcesNew;
        TriggeredCoursesOld = courcesOld;
        Old_list = old_l;
        New_list = new_l;
    }


    public void beforeInsert(){
        List<Lesson__c> coursesLessons = new List<Lesson__c>();
        for(Course__c course :New_list){
            if(!(course.Final_Date__c >= Date.today())){
                course.Final_Date__c = Date.today().addMonths(1);
            }
        }
    }


    public void afterInsert(){
        List<Lesson__c> coursesLessons = new List<Lesson__c>();
        for(Course__c course : TriggeredCoursesNew.values()){
            Integer numDOfays = (course.Final_Date__c.daysBetween(Date.today())/5);
            Integer firstlessonAddition = Math.mod(numDOfays,5);
            Date lastLessonDate = course.Final_Date__c;

            for(integer i = 0; i<5; i++){
                if(i == 5){
                    coursesLessons.add(new Lesson__c(Name = course.Name+' Lesson '+ (5 - i), Course__c = course.Id, Date__c = lastLessonDate.addDays(firstlessonAddition)));
                }
                else{
                coursesLessons.add(new Lesson__c(Name = course.Name+' Lesson '+ (5 - i), Course__c = course.Id, Date__c = lastLessonDate));
                lastLessonDate = lastLessonDate.addDays(numDOfays);
                }
            }

        }
        insert coursesLessons;
    }

    public void afterUpdate(){
     if(CheckRecursive.run()){
        List<Lesson__c> lessonsToRecalc = new List<Lesson__c>();
        Map<Id, List<Lesson__c>> coursesToLessons = new Map<Id, List<Lesson__c>>();

        for(Lesson__c lesson : [SELECT Id, Date__c, Course__c  FROM Lesson__c WHERE Course__c IN :TriggeredCoursesOld.keySet()]){
            if(!coursesToLessons.containsKey(lesson.Course__c)){
                coursesToLessons.put(lesson.Course__c, new List<Lesson__c>{lesson});
            }
            else{
                coursesToLessons.get(lesson.Course__c).add(lesson);
            }
        }
        for(Course__c course :TriggeredCoursesNew.values()){
            if(TriggeredCoursesOld.get(course.Id).Final_Date__c <= course.Final_Date__c){

                Integer numDOfays = (course.Final_Date__c.daysBetween(Date.today())/coursesToLessons.get(course.Id).size());
                Integer firstlessonAddition = Math.mod(numDOfays,coursesToLessons.get(course.Id).size());
                Date lastLessonDate = course.Final_Date__c;
                integer i = 0;
                for(Lesson__c lesson :coursesToLessons.get(course.Id)){
                    if(i == 5){
                    lesson.Date__c = lastLessonDate.addDays(firstlessonAddition);
                    }
                    else{
                        lesson.Date__c = lastLessonDate;
                        lastLessonDate = lastLessonDate.addDays(numDOfays);
                        }
                    i++;
                    lessonsToRecalc.add(lesson);
                }

            }
            else {
                throw new DateException('Set date not erlier than privious!');
            }
        }
        update lessonsToRecalc;
        }
    }
    public class DateException extends Exception {}
}