Shibboleth Developers

Hello, we are building an authentication&authority federation based on 
Shibboleth. For statisticing some data, we want to add some additional logs. 
now I have added some log sentences to the idp source codes and got the log 
data we want. 

But it comes to SP，I find myself completely lost. I failed to find documents 
about the SP sourcecode architecture. when analysing the SP sourcecodes, I 
found little comments and so many directories which really confused me. 
Would you mind provide me some documents which can help me analysis the 
sourcecodes or give me some advice? thanks a lot.