HW18 Composer: Tea trade

Create a Business Network Archive (BNA) with the appropriate models, transactions, and access constraints that fulfill the requirements below. The BNA must have an initial transaction (setupHomework) that sets up a ledger state, where the fulfillment of each requirement can be demonstrated (assuming that the ledger is empty before the call of the initial transaction). Transactions that would dynamically add participants or assets are not needed, unless noted explicitly under the requirements, except the initializer transaction.

Please test your solution on Composer Playground before submission.

For every Participant and Asset type, the unique identifier must be a non-optional String field with the name id. The value of the field must conform to the following format: <TYPENAME>_<COUNTER>. For example, if we have a Participant type named User, then the id of the first created user must be USER_0, the id of the second user must be USER_1, etc.

Problem statement

Implement a BNA for tea sales.

• There are two participant types: Supplier and Consumer.
• Suppliers have names (non-unique), tea types associated with them as assets, and account balances.
• Tea assets contain the type name, the per unit price, and the amount available.
• Consumers have names (non-unique), and account balances.
• Suppliers can:
  • set the price of a given tea type associated with them (per unit price).
  • produce tea by supplying the tea type's name, and the amount produced:
    • if they already own the tea type specified, that asset's amount is increased,
    • if the tea type new to the supplier, a new tea asset is created with the appropriate name and amount, with a per unit price of 1.
• Consumers can:
  • buy a specified tea type and amount from a supplier, if the supplier has the required amount, which:
    • reduces the available amount of tea of that type, completely removing the asset from the supplier if the amount hits zero,
    • transfers the appropriate funds from the consumer's account to the supplier's account.

Additional requirements:

• The initializer transaction should set up at least one supplier, one consumer, and two tea types for the supplier.
• Transactions that create suppliers or consumers are not required.
• Negative balances are not possible, transactions that'd create such a state should be rejected.

Example scenario

Alice is a tea producer with an account balance of 0 units, and 2.5 units of black tea available (with an initial per unit price of 1). Bob is a consumer with an account of 10 units. Alice produces 1 unit of green tea and hopes for a sale. Bob buys 2 units of black tea, which increases Alice's account balance by 2, and leaves 0.5 units of black tea.

Transactions

• createTea
• setPriceForTea
• buyTea