The first line of the file is specifically reserved to inform the compiler whether we are writing a contract, script, predicate, or library. To designate the file as a contract, use the contract keyword.
contract;
use std::{
auth::msg_sender,
call_frames::msg_asset_id,
constants::BASE_ASSET_ID,
context::{
msg_amount,
this_balance,
},
token::transfer,
hash::Hash
};
struct Item {
id: u64,
price: u64,
owner: Identity,
metadata: str[20],
total_bought: u64,
}
abi SwayStore {
// a function to list an item for sale
// takes the price and metadata as args
#[storage(read, write)]
fn list_item(price: u64, metadata: str[20]);
// a function to buy an item
// takes the item id as the arg
#[storage(read, write), payable]
fn buy_item(item_id: u64);
// a function to get a certain item
#[storage(read)]
fn get_item(item_id: u64) -> Item;
// a function to set the contract owner
#[storage(read, write)]
fn initialize_owner() -> Identity;
// a function to withdraw contract funds
#[storage(read)]
fn withdraw_funds();
// return the number of items listed
#[storage(read)]
fn get_count() -> u64;
}
storage {
// counter for total items listed
item_counter: u64 = 0,
// map of item IDs to Items
item_map: StorageMap<u64, Item> = StorageMap {},
// owner of the contract
owner: Option<Identity> = Option::None,
}
enum InvalidError {
IncorrectAssetId: AssetId,
NotEnoughTokens: u64,
OnlyOwner: Identity,
}
impl SwayStore for Contract {
#[storage(read, write)]
fn list_item(price: u64, metadata: str[20]) {
// increment the item counter
storage.item_counter.write(storage.item_counter.try_read().unwrap() + 1);
// get the message sender
let sender = msg_sender().unwrap();
// configure the item
let new_item: Item = Item {
id: storage.item_counter.try_read().unwrap(),
price: price,
owner: sender,
metadata: metadata,
total_bought: 0,
};
// save the new item to storage using the counter value
storage.item_map.insert(storage.item_counter.try_read().unwrap(), new_item);
}
#[storage(read, write), payable]
fn buy_item(item_id: u64) {
// get the asset id for the asset sent
let asset_id = msg_asset_id();
// require that the correct asset was sent
require(asset_id == BASE_ASSET_ID, InvalidError::IncorrectAssetId(asset_id));
// get the amount of coins sent
let amount = msg_amount();
// get the item to buy
let mut item = storage.item_map.get(item_id).try_read().unwrap();
// require that the amount is at least the price of the item
require(amount >= item.price, InvalidError::NotEnoughTokens(amount));
// update the total amount bought
item.total_bought += 1;
// update the item in the storage map
storage.item_map.insert(item_id, item);
// only charge commission if price is more than 0.1 ETH
if amount > 100_000_000 {
// keep a 5% commission
let commission = amount / 20;
let new_amount = amount - commission;
// send the payout minus commission to the seller
transfer(item.owner, asset_id, new_amount);
} else {
// send the full payout to the seller
transfer(item.owner, asset_id, amount);
}
}
#[storage(read)]
fn get_item(item_id: u64) -> Item {
// returns the item for the given item_id
storage.item_map.get(item_id).try_read().unwrap()
}
#[storage(read, write)]
fn initialize_owner() -> Identity {
let owner = storage.owner.try_read().unwrap();
// make sure the owner has NOT already been initialized
require(owner.is_none(), "owner already initialized");
// get the identity of the sender
let sender = msg_sender().unwrap();
// set the owner to the sender's identity
storage.owner.write(Option::Some(sender));
// return the owner
sender
}
#[storage(read)]
fn withdraw_funds() {
let owner = storage.owner.try_read().unwrap();
// make sure the owner has been initialized
require(owner.is_some(), "owner not initialized");
let sender = msg_sender().unwrap();
// require the sender to be the owner
require(sender == owner.unwrap(), InvalidError::OnlyOwner(sender));
// get the current balance of this contract for the base asset
let amount = this_balance(BASE_ASSET_ID);
// require the contract balance to be more than 0
require(amount > 0, InvalidError::NotEnoughTokens(amount));
// send the amount to the owner
transfer(owner.unwrap(), BASE_ASSET_ID, amount);
}
#[storage(read)]
fn get_count() -> u64 {
storage.item_counter.try_read().unwrap()
}
} The Sway standard library provides several utility types and methods we can use in our contract. To import a library, you can use the use keyword and ::, also called a namespace qualifier, to chain library names like this:
// imports the msg_sender function from the std library
use std::auth::msg_sender;You can also group together imports using curly brackets:
use std::{
auth::msg_sender,
storage::StorageVec,
}For this contract, here is what needs to be imported:
contract;
use std::{
auth::msg_sender,
call_frames::msg_asset_id,
constants::BASE_ASSET_ID,
context::{
msg_amount,
this_balance,
},
token::transfer,
hash::Hash
};
struct Item {
id: u64,
price: u64,
owner: Identity,
metadata: str[20],
total_bought: u64,
}
abi SwayStore {
// a function to list an item for sale
// takes the price and metadata as args
#[storage(read, write)]
fn list_item(price: u64, metadata: str[20]);
// a function to buy an item
// takes the item id as the arg
#[storage(read, write), payable]
fn buy_item(item_id: u64);
// a function to get a certain item
#[storage(read)]
fn get_item(item_id: u64) -> Item;
// a function to set the contract owner
#[storage(read, write)]
fn initialize_owner() -> Identity;
// a function to withdraw contract funds
#[storage(read)]
fn withdraw_funds();
// return the number of items listed
#[storage(read)]
fn get_count() -> u64;
}
storage {
// counter for total items listed
item_counter: u64 = 0,
// map of item IDs to Items
item_map: StorageMap<u64, Item> = StorageMap {},
// owner of the contract
owner: Option<Identity> = Option::None,
}
enum InvalidError {
IncorrectAssetId: AssetId,
NotEnoughTokens: u64,
OnlyOwner: Identity,
}
impl SwayStore for Contract {
#[storage(read, write)]
fn list_item(price: u64, metadata: str[20]) {
// increment the item counter
storage.item_counter.write(storage.item_counter.try_read().unwrap() + 1);
// get the message sender
let sender = msg_sender().unwrap();
// configure the item
let new_item: Item = Item {
id: storage.item_counter.try_read().unwrap(),
price: price,
owner: sender,
metadata: metadata,
total_bought: 0,
};
// save the new item to storage using the counter value
storage.item_map.insert(storage.item_counter.try_read().unwrap(), new_item);
}
#[storage(read, write), payable]
fn buy_item(item_id: u64) {
// get the asset id for the asset sent
let asset_id = msg_asset_id();
// require that the correct asset was sent
require(asset_id == BASE_ASSET_ID, InvalidError::IncorrectAssetId(asset_id));
// get the amount of coins sent
let amount = msg_amount();
// get the item to buy
let mut item = storage.item_map.get(item_id).try_read().unwrap();
// require that the amount is at least the price of the item
require(amount >= item.price, InvalidError::NotEnoughTokens(amount));
// update the total amount bought
item.total_bought += 1;
// update the item in the storage map
storage.item_map.insert(item_id, item);
// only charge commission if price is more than 0.1 ETH
if amount > 100_000_000 {
// keep a 5% commission
let commission = amount / 20;
let new_amount = amount - commission;
// send the payout minus commission to the seller
transfer(item.owner, asset_id, new_amount);
} else {
// send the full payout to the seller
transfer(item.owner, asset_id, amount);
}
}
#[storage(read)]
fn get_item(item_id: u64) -> Item {
// returns the item for the given item_id
storage.item_map.get(item_id).try_read().unwrap()
}
#[storage(read, write)]
fn initialize_owner() -> Identity {
let owner = storage.owner.try_read().unwrap();
// make sure the owner has NOT already been initialized
require(owner.is_none(), "owner already initialized");
// get the identity of the sender
let sender = msg_sender().unwrap();
// set the owner to the sender's identity
storage.owner.write(Option::Some(sender));
// return the owner
sender
}
#[storage(read)]
fn withdraw_funds() {
let owner = storage.owner.try_read().unwrap();
// make sure the owner has been initialized
require(owner.is_some(), "owner not initialized");
let sender = msg_sender().unwrap();
// require the sender to be the owner
require(sender == owner.unwrap(), InvalidError::OnlyOwner(sender));
// get the current balance of this contract for the base asset
let amount = this_balance(BASE_ASSET_ID);
// require the contract balance to be more than 0
require(amount > 0, InvalidError::NotEnoughTokens(amount));
// send the amount to the owner
transfer(owner.unwrap(), BASE_ASSET_ID, amount);
}
#[storage(read)]
fn get_count() -> u64 {
storage.item_counter.try_read().unwrap()
}
}We'll go through what each of these imports does as we use them in the next steps.
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