A maternity house has admitted a primagravida complaining of irregular, intense labour pains that have been lasting for 36 hours. The woman is tired, failed to fall asleep at night. The fetus is in longitudinal lie, with cephalic presentation. The fetus heartbeat is clear and rhythmic, 145/min. Vaginal examination revealed that the uterine cervix was up to 3 cm long, dense, with retroflexion; the external orifice was closed; the discharges were of mucous nature. What is the most likely diagnosis?