def select_participant(event):
"""
Indicates selection of a participant by the wheel. This will cause updates to the weights for all participants
or removal of rigging if the wheel is rigged.
:param event: Lambda event containing the API Gateway request path parameters wheel_id and participant_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel to rig (DDB Hash Key)
"participant_id": string ID of the participant to rig (DDB Hash Key)
},
}
:return: response dictionary
"""
wheel_id = event['pathParameters']['wheel_id']
participant_id = event['pathParameters']['participant_id']
wheel = Wheel.get_existing_item(Key={'id': wheel_id})
participant = WheelParticipant.get_existing_item(Key={
'id': participant_id,
'wheel_id': wheel_id
})
choice_algorithm.select_participant(wheel, participant)
# Undo any rigging that has been set up
Wheel.update_item(Key={'id': wheel['id']},
UpdateExpression='remove rigging')
def rig_participant(event):
"""
Rig the specified wheel for the specified participant. Default behavior is comical rigging (hidden == False)
but hidden can be specified to indicate deceptive rigging (hidden == True)
:param event: Lambda event containing the API Gateway request path parameters wheel_id and participant_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel to rig (DDB Hash Key)
"participant_id": string ID of the participant to rig (DDB Hash Key)
},
"body":
{
"hidden": boolean indicates deceptive rigging if True, comical if False
}
}
:return: response dictionary
"""
# By default, rigging the wheel isn't hidden but they can be
wheel_id = event['pathParameters']['wheel_id']
participant_id = event['pathParameters']['participant_id']
hidden = bool(event['body'].get('hidden', False))
update = {'rigging': {'participant_id': participant_id, 'hidden': hidden}}
Wheel.update_item(Key={'id': wheel_id}, **to_update_kwargs(update))
def delete_wheel(event):
"""
Deletes the wheel and all of its participants
:param event: Lambda event containing the API Gateway request path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
}
}
:return: response dictionary
"""
wheel_id = event['pathParameters']['wheel_id']
# DynamoDB always succeeds for delete_item,
Wheel.delete_item(Key={'id': wheel_id})
# Clear out all participants of the wheel. Query will be empty if it was already deleted
with WheelParticipant.batch_writer() as batch:
query_params = {
'KeyConditionExpression': Key('wheel_id').eq(wheel_id),
'ProjectionExpression': 'id'
}
# We don't use the default generator here because we don't want the deletes to change the query results
for p in list(WheelParticipant.iter_query(**query_params)):
batch.delete_item(Key={'id': p['id'], 'wheel_id': wheel_id})
def list_participants(event):
"""
Gets the participants for the specified wheel_id
:param event: Lambda event containing the API Gateway request path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
},
}
:return: response dictionary containing a list of participants
{
"body":
[
participant1,
participant2,
...
participantn,
]
}
"""
wheel_id = event['pathParameters']['wheel_id']
# Make sure the wheel exists
Wheel.get_existing_item(Key={'id': wheel_id})
return list(
WheelParticipant.iter_query(
KeyConditionExpression=Key('wheel_id').eq(wheel_id)))
def wrap_participant_creation(wheel, participant):
participant['weight'] = 1
yield
Wheel.update_item(Key={'id': wheel['id']},
**to_update_kwargs({
'participant_count':
wheel['participant_count'] + 1
}))
def wrap_participant_creation(wheel, participant):
participant['weight'] = 1
yield
count = 0
with WheelParticipant.batch_writer() as batch:
for p in WheelParticipant.iter_query(
KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
count += 1
Wheel.update_item(Key={'id': wheel['id']},
**to_update_kwargs({'participant_count': count}))
def get_wheel(event):
"""
Returns the wheel object corresponding to the given wheel_id
:param event: Lambda event containing the API Gateway request path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
}
}
:return: response dictionary containing the requested wheel object if successful
{
"body":
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"participant_count": number of participants in the wheel,
"created_at": creation timestamp,
"updated_at": updated timestamp,
}
}
"""
return Wheel.get_existing_item(
Key={'id': event['pathParameters']['wheel_id']})
def delete_participant(event):
"""
Deletes the participant from the wheel and redistributes wheel weights
:param event: Lambda event containing the API Gateway request path parameters wheel_id and participant_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
"participant_id": string ID of the participant (DDB Hash Key)
},
}
:return: response dictionary
"""
wheel_id = event['pathParameters']['wheel_id']
participant_id = event['pathParameters']['participant_id']
# Make sure the wheel exists
wheel = Wheel.get_existing_item(Key={'id': wheel_id})
# REST-ful Deletes are idempotent and should not error if it's already been deleted
response = WheelParticipant.delete_item(Key={
'wheel_id': wheel_id,
'id': participant_id
},
ReturnValues='ALL_OLD')
if 'Attributes' in response:
choice_algorithm.on_participant_deletion(wheel, response['Attributes'])
def suggest_participant(event):
"""
Returns a suggested participant to be selected by the next wheel spin
:param event: Lambda event containing the API Gateway request path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
},
}
:return: response dictionary containing a selected participant_id
{
"body":
{
"participant_id": string ID of the suggested participant (DDB Hash Key),
"rigged": True (if rigged, otherwise this key is not present)
}
}
"""
wheel_id = event['pathParameters']['wheel_id']
wheel = Wheel.get_existing_item(Key={'id': wheel_id})
if 'rigging' in wheel:
participant_id = wheel['rigging']['participant_id']
# Use rigging only if the rigged participant is still available
if 'Item' in WheelParticipant.get_item(Key={
'wheel_id': wheel_id,
'id': participant_id
}):
return_value = {'participant_id': participant_id}
# Only return rigged: True if we're not using hidden rigging
if not wheel['rigging'].get('hidden', False):
return_value['rigged'] = True
return return_value
return {'participant_id': choice_algorithm.suggest_participant(wheel)}
def list_wheels(event):
"""
Get all available wheels
:param event: Lambda event containing query string parameters that are passed to Boto's scan() API for the wheel
table
{
"queryStringParameters":
{
...
}
}
:return: List of wheels
{
"body":
"Count": number of wheels,
"Items":
[
wheel1,
wheel2,
wheeln,
],
"ScannedCount": number of items before queryStringParameters were applied,
}
}
"""
parameters = event.get('queryStringParameters', None) or {}
return Wheel.scan(**parameters)
def on_participant_deletion(wheel, participant):
"""
Normalize the remaining participant weights to account for participant removal.
The ratio is based on the following:
1) The participant should be at weight=1 when it leaves the system (which is the same as it arrived)
2) That difference should be split by the remaining participants proportional by weight
This ensures that 'weight=0' participants are still at weight=0 and that the sum of all
weights is equal to the number of participants, so new additions are treated fairly
:param wheel: Wheel dictionary:
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"participant_count": number of participants in the wheel,
}
:param participant: Participant dictionary:
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"url": Participant's URL,
"wheel_id": string ID of the wheel the participant belongs to,
}
:return: None
"""
total_weight = participant['weight']
for p in WheelParticipant.iter_query(
KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
total_weight += p['weight']
weight = participant['weight']
remaining_weight = total_weight - weight # <-- no longer presumes existing weight balance via 'int(participant_count)'
ratio = (1 + ((weight - 1) / remaining_weight)) if (
remaining_weight != 0) else 1
num_participants = Decimal(0)
with WheelParticipant.batch_writer() as batch:
for p in WheelParticipant.iter_query(
KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
if p['id'] != participant['id']:
# This is cast to a string before turning into a decimal because of rounding/inexact guards in boto3
p['weight'] = Decimal(
str(float(p['weight']) *
float(ratio))) if (remaining_weight != 0) else 1
batch.put_item(Item=p)
num_participants = num_participants + 1
Wheel.update_item(Key={'id': wheel['id']},
**to_update_kwargs(
{'participant_count': num_participants}))
def select_participant(wheel, participant):
"""
Register the selection of a participant by updating the weights of all participants for a given wheel
:param wheel: Wheel dictionary:
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"participant_count": number of participants in the wheel,
}
:param participant: Participant dictionary:
{
"id": string ID of the participant (DDB Hash Key),
"name": string name of the participant,
"url": Participant's URL,
"wheel_id": string ID of the wheel the participant belongs to,
"weight": participant's weight in the selection algorithm
}
:return: None
"""
num_participants = 0
total_weight = Decimal(0)
for p in WheelParticipant.iter_query(
KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
num_participants = num_participants + 1
total_weight += p['weight']
# Factor is the number by which all weights must be multiplied
# so total weight will be equal to the number of participants.
factor = Decimal(num_participants) / total_weight
if num_participants > 1:
weight_share = participant['weight'] / Decimal(num_participants - 1)
with WheelParticipant.batch_writer() as batch:
# Redistribute and normalize the weights.
for p in WheelParticipant.iter_query(
KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
if p['id'] == participant['id']:
p['weight'] = 0
else:
p['weight'] += Decimal(weight_share)
p['weight'] *= factor
batch.put_item(Item=p)
Wheel.update_item(Key={'id': wheel['id']},
**to_update_kwargs(
{'participant_count': num_participants}))
def unrig_participant(event):
"""
Remove rigging for the specified wheel
:param event: Lambda event containing the API Gateway request path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
}
}
:return: response dictionary
"""
# By default, rigging the wheel isn't hidden but they can be
wheel_id = event['pathParameters']['wheel_id']
Wheel.update_item(Key={'id': wheel_id}, UpdateExpression='remove rigging')
def get_sub_wheel_size(wheel_name):
resp = Wheel.query(
IndexName='name_index',
KeyConditionExpression=Key('name').eq(wheel_name)
)
if len(resp['Items']): # if a matching wheel is found
return int(resp['Items'][0]['participant_count']) or 1 # if wheel size is 0, default to 1
return 1 # default to 1 if no matching wheel is found
def reset_wheel(wheel):
"""
Resets the weights of all participants in the wheel and updates the wheel's participant count
:param wheel: Wheel dictionary:
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"participant_count": number of participants in the wheel,
}
:return: None
"""
count = 0
with WheelParticipant.batch_writer() as batch:
for p in WheelParticipant.iter_query(KeyConditionExpression=Key('wheel_id').eq(wheel['id'])):
p['weight'] = get_sub_wheel_size(p['name'])
batch.put_item(Item=p)
count += 1
Wheel.update_item(Key={'id': wheel['id']}, **to_update_kwargs({'participant_count': count}))
def update_wheel(event):
"""
Update the name of the wheel and/or refresh its participant count
:param event: Lambda event containing the API Gateway request path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
},
"body":
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
}
}
:return: response dictionary containing the updated wheel object if successful
{
"body":
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"participant_count": number of participants in the wheel,
"created_at": creation timestamp,
"updated_at": updated timestamp,
}
}
"""
wheel_id = event['pathParameters']['wheel_id']
key = {'id': wheel_id}
# Make sure wheel exists
wheel = Wheel.get_existing_item(Key=key)
name = event['body'].get('name', None)
if not check_string(name):
raise base.BadRequestError(
"Updating a wheel requires a new name of at least 1 character in length"
)
update = {'name': name, 'updated_at': get_utc_timestamp()}
Wheel.update_item(Key=key, **to_update_kwargs(update))
# Represent the change locally for successful responses
wheel.update(update)
return wheel
def create_participant(event):
"""
Create a participant
:param event: Lambda event containing the API Gateway request body including a name and a url and the
path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
},
"body":
{
"name": participant name string,
"url: Valid URL for the participant,
}
}
:return: response dictionary containing new participant object if successful
{
"body":
{
"id": string ID of the participant (DDB Hash Key),
"wheel_id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"url: URL for the participant,
"created_at": creation timestamp,
"updated_at": updated timestamp,
}
}
"""
wheel_id = event['pathParameters']['wheel_id']
body = event['body']
if not check_string(body.get('name', None)) or not check_string(
body.get('url', None)):
raise base.BadRequestError(
"Participants require a name and url which must be at least 1 character in length"
)
wheel = Wheel.get_existing_item(Key={'id': wheel_id})
create_timestamp = get_utc_timestamp()
participant = {
'wheel_id': wheel_id,
'id': get_uuid(),
'name': body['name'],
'url': body['url'],
'created_at': create_timestamp,
'updated_at': create_timestamp,
}
with choice_algorithm.wrap_participant_creation(wheel, participant):
WheelParticipant.put_item(Item=participant)
return participant
def create_wheel(event):
"""
Create a wheel. Requires a name
:param event: Lambda event containing the API Gateway request body including a name
{
"body":
{
"name": string wheel name,
}
}
:return: response dictionary containing new wheel object if successful
{
"body":
{
"id": string ID of the wheel (DDB Hash Key),
"name": string name of the wheel,
"participant_count": number of participants in the wheel,
"created_at": creation timestamp,
"updated_at": updated timestamp,
}
}
"""
create_timestamp = get_utc_timestamp()
body = event['body']
if body is None or not check_string(body.get('name', None)):
raise base.BadRequestError(
f"New wheels require a name that must be a string with a length of at least 1. Got: {body}"
)
wheel = {
'id': get_uuid(),
'name': body['name'],
'created_at': create_timestamp,
'updated_at': create_timestamp,
}
with choice_algorithm.wrap_wheel_creation(wheel):
Wheel.put_item(Item=wheel)
return wheel
def reset_wheel(event):
"""
Resets the weights of all participants of the wheel
:param event: Lambda event containing the API Gateway request path parameter wheel_id
{
"pathParameters":
{
"wheel_id": string ID of the wheel (DDB Hash Key)
}
}
:return: response dictionary
"""
# Ensure that the wheel exists
wheel_id = event['pathParameters']['wheel_id']
wheel = Wheel.get_existing_item(Key={'id': wheel_id})
choice_algorithm.reset_wheel(wheel)
def test_fix_incorrect_participant_count(mock_dynamodb, setup_data,
mock_wheel_table):
out_of_whack = 999
wheel = setup_data['wheel']
wheel_id = wheel['id']
proper_participant_count = wheel['participant_count']
# # # # We will first test this on a select_participant operation.
# Throw the participant count way out of whack.
mock_wheel_table.update_item(Key={'id': wheel['id']},
**to_update_kwargs(
{'participant_count': out_of_whack}))
participant_count = mock_wheel_table.query(KeyConditionExpression=Key(
'id').eq(wheel['id']))['Items'][0].get('participant_count')
# # Ensure it's out of whack.
assert abs(out_of_whack - participant_count) < epsilon
# Select a participant to cause correction of participant count.
wheel = Wheel.get_existing_item(Key={'id': wheel_id})
choice_algorithm.select_participant(wheel, setup_data['participants'][0])
# ...and ensure it's back into whack.
participant_count = mock_wheel_table.query(KeyConditionExpression=Key(
'id').eq(wheel['id']))['Items'][0].get('participant_count')
assert abs(Decimal(proper_participant_count) - participant_count) < epsilon
# # # # We will next test this on a delete_participant operation.
# Throw the participant count way out of whack.
mock_wheel_table.update_item(Key={'id': wheel['id']},
**to_update_kwargs(
{'participant_count': out_of_whack}))
participant_count = mock_wheel_table.query(KeyConditionExpression=Key(
'id').eq(wheel['id']))['Items'][0].get('participant_count')
# # Ensure it's out of whack.
assert abs(out_of_whack - participant_count) < epsilon
# Delete a participant to cause correction of participant count.
event = {
'body': {},
'pathParameters': {
'wheel_id': wheel_id,
'participant_id': setup_data['participants'][0]['id']
}
}
wheel_participant.delete_participant(event)
# # ...and ensure it's back into whack.
participant_count = mock_wheel_table.query(KeyConditionExpression=Key(
'id').eq(wheel['id']))['Items'][0].get('participant_count')
assert abs((Decimal(proper_participant_count) - 1) -
participant_count) < epsilon
# # # # We will next test this on a create_participant operation.
# Throw the participant count way out of whack.
mock_wheel_table.update_item(Key={'id': wheel['id']},
**to_update_kwargs(
{'participant_count': out_of_whack}))
participant_count = mock_wheel_table.query(KeyConditionExpression=Key(
'id').eq(wheel['id']))['Items'][0].get('participant_count')
# # Ensure it's out of whack.
assert abs(out_of_whack - participant_count) < epsilon
# Add a participant to cause correction of participant count.
event = {
'pathParameters': {
'wheel_id': wheel_id
},
'body': {
'name': 'Ishmael-on-the-Sea',
'url': 'https://amazon.com'
}
}
wheel_participant.create_participant(event)
# # ...and ensure it's back into whack.
participant_count = mock_wheel_table.query(KeyConditionExpression=Key(
'id').eq(wheel['id']))['Items'][0].get('participant_count')
assert abs((Decimal(proper_participant_count)) -
participant_count) < epsilon
