def tag_reachable_scripts(cls, scratch):
"""Tag each script with attribute reachable.
The reachable attribute will be set false for any script that does not
begin with a hat block. Additionally, any script that begins with a
`when I receive` block whose event-name doesn't appear in a
corresponding broadcast block is marked as unreachable.
"""
scratch.kelp_prepared = True
reachable = set()
untriggered_events = {}
# Initial pass to find reachable and potentially reachable scripts
for script in cls.iter_scripts(scratch):
if not isinstance(script, kurt.Comment):
starting_type = HairballPlugin.script_start_type(script)
if starting_type == HairballPlugin.NO_HAT:
script.reachable = False
elif starting_type == HairballPlugin.HAT_WHEN_I_RECEIVE:
script.reachable = False # Value will be updated if reachable
message = script.blocks[0].args[0].lower()
untriggered_events.setdefault(message, set()).add(script)
else:
script.reachable = True
reachable.add(script)
# Expand reachable states based on broadcast events
while reachable:
for event in HairballPlugin.get_broadcast_events(reachable.pop()):
if event in untriggered_events:
for script in untriggered_events.pop(event):
script.reachable = True
reachable.add(script)
