ligo/gitlab-pages/docs/tutorials/get-started/tezos-taco-shop-payout.md

id	title
tezos-taco-shop-payout	Paying out profits from the Taco Shop

In the previous tutorial we've learned how to setup & interact with the LIGO CLI. Followed by implementation of a simple Taco Shop smart contract for our entepreneur Pedro. In this tutorial we'll make sure Pedro has access to tokens that people have spent at his shop when buying tacos.

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Analyzing the current contract

taco-shop.ligo

type taco_supply is record
    current_stock : nat;
    max_price : tez;
end
type taco_shop_storage is map(nat, taco_supply);

function buy_taco (const taco_kind_index: nat ; var taco_shop_storage : taco_shop_storage) : 
  (list(operation) * taco_shop_storage) is
  begin
    // Retrieve the taco_kind from the contract's storage
    const taco_kind : taco_supply = get_force(taco_kind_index, taco_shop_storage);
    
    const current_purchase_price : tez = taco_kind.max_price / taco_kind.current_stock;

    if amount =/= current_purchase_price then
      // we won't sell tacos if the amount isn't correct
      fail("Sorry, the taco you're trying to purchase has a different price");
    else
      // Decrease the stock by 1n, because we've just sold one
      taco_kind.current_stock := abs(taco_kind.current_stock - 1n);

    // Update the storage with the refreshed taco_kind
    taco_shop_storage[taco_kind_index] := taco_kind;
  end with ((nil : list(operation)), taco_shop_storage)

Purchase price formula

Pedro's Taco Shop contract currently enables customers to buy tacos, at a computed price based on a simple formula.

const current_purchase_price : tez = taco_kind.max_price / taco_kind.current_stock;

Replacing spendable smart contracts

However, due to the recent protocol upgrade of the Tezos mainnet, Pedro can't access the tokens stored in his Shop's contract directly. This was previously possible via spendable smart contracts, which are no longer available in the new protocol. We will have to implement a solution to access tokens from the contract programatically.

---

Designing a payout scheme

Pedro is a standalone bussines owner, and in our case, he doesn't have to split profits / earnings of the taco shop with anyone. So for the sake of simplicity, we'll payout all the earned XTZ directly to Pedro right after a succesful taco purchase.

This means that after all the purchase conditions of our contract are met - e.g. correct amount is sent to the contract - we'll not only decrease the supply of the individual purchased taco kind, but we'll also transfer this amount in a subsequent transaction to Pedro's personal address.

Forging a payout transaction

Defining the recipient

In order to send tokens, we will need a receiver address - which in our case will be Pedro's personal account. Additionally we'll wrap the given address as a contract(unit) - which represents either a contract with no parameters, or an implicit account.

const ownerAddress : address = "tz1TGu6TN5GSez2ndXXeDX6LgUDvLzPLqgYV";
const receiver : contract(unit) = get_contract(ownerAddress);

Would you like to learn more about addresses, contracts and operations in LIGO? Check out the LIGO cheat sheet

Adding the transaction to the list of output operations

Now we can transfer the amount received by buy_taco to Pedro's ownerAddress. We will do so by forging a transaction(unit, amount, receiver) within a list of operations returned at the end of our contract.

const payoutOperation : operation = transaction(unit, amount, receiver) ;
const operations : list(operation) = list
    payoutOperation
end;

---

Finalizing the contract

taco-shop.ligo

type taco_supply is record
    current_stock : nat;
    max_price : tez;
end
type taco_shop_storage is map(nat, taco_supply);

const ownerAddress: address = "tz1TGu6TN5GSez2ndXXeDX6LgUDvLzPLqgYV";

function buy_taco (const taco_kind_index: nat ; var taco_shop_storage : taco_shop_storage) : (list(operation) * taco_shop_storage) is
  begin
    // Retrieve the taco_kind from the contract's storage
    const taco_kind : taco_supply = get_force(taco_kind_index, taco_shop_storage);
    
    const current_purchase_price : tez = taco_kind.max_price / taco_kind.current_stock;

    if amount =/= current_purchase_price then
      // we won't sell tacos if the amount isn't correct
      fail("Sorry, the taco you're trying to purchase has a different price");
    else
      // Decrease the stock by 1n, because we've just sold one
      taco_kind.current_stock := abs(taco_kind.current_stock - 1n);

    // Update the storage with the refreshed taco_kind
    taco_shop_storage[taco_kind_index] := taco_kind;

    const receiver : contract(unit) = get_contract(ownerAddress);
    const payoutOperation : operation = transaction(unit, amount, receiver);
    const operations : list(operation) = list
      payoutOperation
    end;

  end with (operations, taco_shop_storage)

Dry-run the contract

To confirm that our contract is valid, we can dry run it. As a result we see a new operation in the list of returned operations to be executed subsequently.

ligo dry-run taco-shop.ligo --syntax pascaligo --amount 1 buy_taco 1n "map
    1n -> record
        current_stock = 50n;
        max_price = 50000000mtz;
    end;
    2n -> record
        current_stock = 20n;
        max_price = 75000000mtz;
    end;
end"

Operation(...bytes) included in the output

Done! Our tokens are no longer locked in the contract, and instead they are sent to Pedro's personal account/wallet.

---

👼 Bonus: donating part of the profits

Because Pedro is a member of the (STA) Specialty Taco Association, he has decided to donate 10% of the earnings to the STA. We'll just add a donationAddress to the contract, and compute a 10% donation sum from each taco purchase.

const ownerAddress: address = "tz1TGu6TN5GSez2ndXXeDX6LgUDvLzPLqgYV";
const donationAddress: address = "tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx";

const receiver : contract(unit) = get_contract(ownerAddress);
const donationReceiver : contract(unit) = get_contract(donationAddress);

const donationAmount: tez = amount / 10n;

const operations : list(operation) = list
  // Pedro will get 90% of the amount
  transaction(unit, amount - donationAmount, receiver);
  transaction(unit, donationAmount, donationReceiver);
end;

This will result into two operations being subsequently executed on the blockchain:

• Donation transfer (10%)
• Pedro's profits (90%)