How to give different permission programmatically on Document Library for different group users?

Question

I have document library & 3 groups(AdminGroup,Reviewer,Distributor). I have already give a permission on groups, AdminGroup has Full Control, Reviewer has Reader & Distributor has None :

 roleDefinition = web.RoleDefinitions.GetByType(SPRoleType.Administrator); // Admin
 roleDefinition = web.RoleDefinitions.GetByType(SPRoleType.Reader); // Reviewer
 roleDefinition = web.RoleDefinitions.GetByType(SPRoleType.None); // Distributor

Now, I want to give permission on document library that :

• If anyone upload document it's Draft version should only visible to Reviewer,Admin & owner of the document. Distributor user can't see it if he is not owner.
• Reviewer Group's user can only view/edit the document & publish it but can't Approve/Reject it.
• Admin has full control. He can Add/Edit/View & Approve/reject the document.
• Distributor Group's user can only view his own documents & Approved documents.

Answer 1

Attach a event recevier and add item added / updated event to it for assigneing permission.

First break permission on item and then add required permission as per item status / metadata.

Answer 2

I have found the solution to assign permission to group:

 using (SPSite spSite = SPContext.Current.Site)
  {
     using (SPWeb web = spSite.OpenWeb())
     {
        web.AllowUnsafeUpdates = true;
        SPGroupCollection grpColl = SPContext.Current.Site.OpenWeb().SiteGroups;
        SPGroup spGroup =  grpColl.GetByName("myGroup");


    SPRoleAssignment roleAssignment = new SPRoleAssignment(spGroup);
    SPRoleDefinition roleDefinition = new SPRoleDefinition();

    roleDefinition = web.RoleDefinitions.GetByType(SPRoleType.Administrator); // for admin role

    SPRoleDefinitionBindingCollection roleDefinitionBindingCollection = new SPRoleDefinitionBindingCollection();
    roleDefinitionBindingCollection.Add(roleDefinition);
    roleAssignment.ImportRoleDefinitionBindings(roleDefinitionBindingCollection);
    web.AllowUnsafeUpdates = true;
    web.RoleAssignments.Add(roleAssignment);
    web.update();
    web.AllowUnsafeUpdates = false;
 }}

Then, Give same permission to Document Library.