Salesforce APEX triggers to measure Account activities

Pear the object Account, the following fields have to be created: 1) number_of_next_activities__c 2) next_activity_date__c 3) number_of_past_activities__c 4) number_of_past_calls__c Behaviour 1) The field number_of_next_activities__c has to ALWAYS include a number that is the sum of: - the number of TASKS that are with status=NOT COMPLETED - the number of EVENTS that are with date=in the future 2) The field next_activity_date__c has to ALWAYS include the date/time of the next soonest activity which: - is a TASK and is NOT COMPLETED - OR is and EVENT and is in the FUTURE 3) The field number_of_past_activities__c has to ALWAYS include a number that is the sum of: - the number of TASKS that are with status=COMPLETED - the number of EVENTS that are with date=in the past 4) The field number_of_past_activities__c has to ALWAYS include a number that is the sum of: - the number of TASKS that are with status=COMPLETED and include the word "call" in the subject - the number of EVENTS that are with date=in the past and include the word "call" in the subject A trigger should be executed every time a change on a TASK happen (change of status, change of date, change of subject, change of related account/lead/object) A trigger should be executed every time a change on an EVENT happen (change of date, change of subject, change of related account/lead/object) OR when it moves from the future to the past as time passes (at the time of the event). bulk changes have to be supported. 100% coverage is required. TEST CASES: A) account TESTACCOUNT is created. It has no activity. The values must be: - number_of_next_activities__c 0 - next_activity_date__c BLANK - number_of_past_activities__c 0 - number_of_past_calls__c 0 B) an activity TASKA is created with date=tomorrow, subject=sendemail status=not started. - number_of_next_activities__c 1 - next_activity_date__c tomorrow - number_of_past_activities__c 0 - number_of_past_calls__c 0 C) the task TASKA is set as COMPLETED - number_of_next_activities__c 0 - next_activity_date__c BLANK - number_of_past_activities__c 1 - number_of_past_calls__c 0 D) the task TASKA is updated changing subject from sendemail to docall - number_of_next_activities__c 0 - next_activity_date__c BLANK - number_of_past_activities__c 1 - number_of_past_calls__c 1 E) an event EVENTA is create with date=tomorrow, subject=callmark - number_of_next_activities__c 1 - next_activity_date__c tomorrow - number_of_past_activities__c 1 - number_of_past_calls__c 1 F) a task TASKB is created with date=dayaftertomorrow, subject=calljohn - number_of_next_activities__c 2 - next_activity_date__c tomorrow - number_of_past_activities__c 1 - number_of_past_calls__c 1 G) EVENTA is moved from tomorrow to yesterday - number_of_next_activities__c 1 - next_activity_date__c dayaftertomorrow - number_of_past_activities__c 2 - number_of_past_calls__c 2