Fix mood having drunk a barrel (4,4)
I believe the answer is:
make good
'fix' is the definition.
(thesaurus)
'mood having drunk a barrel' is the wordplay.
'having drunk' means one lot of letters goes inside another.
'barrel' becomes 'keg' (keg is a kind of barrel).
'a'+'keg'='akeg'
'mood' placed around 'akeg' is 'MAKE GOOD'.
(Other definitions for make good that I've seen before include "Succeed in life, do well" , "Replace (loss); fulfil (promise)" , "Repair; do well" , "Repair; be successful" , "Succeed, become prosperous" .)