NFT Dutch Auction

This is the Cairo adaptation (with some modifications) of the Solidity by example NFT Dutch Auction.
Here's how it works:
The seller of the NFT deploys this contract with a startingPrice.
The auction lasts for a specified duration.
The price decreases over time.
Participants can purchase NFTs at any time as long as the totalSupply has not been reached.
The auction ends when either the totalSupply is reached or the duration has elapsed.
use starknet::ContractAddress;
 
#[starknet::interface]
pub trait IERC20<TContractState> {
    fn get_name(self: @TContractState) -> felt252;
    fn get_symbol(self: @TContractState) -> felt252;
    fn get_decimals(self: @TContractState) -> u8;
    fn get_total_supply(self: @TContractState) -> felt252;
    fn balance_of(self: @TContractState, account: ContractAddress) -> felt252;
    fn allowance(
        self: @TContractState, owner: ContractAddress, spender: ContractAddress,
    ) -> felt252;
    fn transfer(ref self: TContractState, recipient: ContractAddress, amount: felt252);
    fn transfer_from(
        ref self: TContractState,
        sender: ContractAddress,
        recipient: ContractAddress,
        amount: felt252,
    );
    fn approve(ref self: TContractState, spender: ContractAddress, amount: felt252);
    fn increase_allowance(ref self: TContractState, spender: ContractAddress, added_value: felt252);
    fn decrease_allowance(
        ref self: TContractState, spender: ContractAddress, subtracted_value: felt252,
    );
}
 
#[starknet::interface]
trait IERC721<TContractState> {
    fn get_name(self: @TContractState) -> felt252;
    fn get_symbol(self: @TContractState) -> felt252;
    fn get_token_uri(self: @TContractState, token_id: u256) -> felt252;
    fn balance_of(self: @TContractState, account: ContractAddress) -> u256;
    fn owner_of(self: @TContractState, token_id: u256) -> ContractAddress;
    fn get_approved(self: @TContractState, token_id: u256) -> ContractAddress;
    fn is_approved_for_all(
        self: @TContractState, owner: ContractAddress, operator: ContractAddress,
    ) -> bool;
    fn approve(ref self: TContractState, to: ContractAddress, token_id: u256);
    fn set_approval_for_all(ref self: TContractState, operator: ContractAddress, approved: bool);
    fn transfer_from(
        ref self: TContractState, from: ContractAddress, to: ContractAddress, token_id: u256,
    );
    fn mint(ref self: TContractState, to: ContractAddress, token_id: u256);
}
 
#[starknet::interface]
pub trait INFTDutchAuction<TContractState> {
    fn buy(ref self: TContractState, token_id: u256);
    fn get_price(self: @TContractState) -> u64;
}
 
#[starknet::contract]
pub mod NFTDutchAuction {
    use super::{IERC20Dispatcher, IERC20DispatcherTrait, IERC721Dispatcher, IERC721DispatcherTrait};
    use starknet::{ContractAddress, get_caller_address, get_block_timestamp};
    use starknet::storage::{StoragePointerReadAccess, StoragePointerWriteAccess};
 
    #[storage]
    struct Storage {
        erc20_token: ContractAddress,
        erc721_token: ContractAddress,
        starting_price: u64,
        seller: ContractAddress,
        duration: u64,
        discount_rate: u64,
        start_at: u64,
        expires_at: u64,
        purchase_count: u128,
        total_supply: u128,
    }
 
    mod Errors {
        pub const AUCTION_ENDED: felt252 = 'auction has ended';
        pub const LOW_STARTING_PRICE: felt252 = 'low starting price';
        pub const INSUFFICIENT_BALANCE: felt252 = 'insufficient balance';
    }
 
    #[constructor]
    fn constructor(
        ref self: ContractState,
        erc20_token: ContractAddress,
        erc721_token: ContractAddress,
        starting_price: u64,
        seller: ContractAddress,
        duration: u64,
        discount_rate: u64,
        total_supply: u128,
    ) {
        assert(starting_price >= discount_rate * duration, Errors::LOW_STARTING_PRICE);
 
        self.erc20_token.write(erc20_token);
        self.erc721_token.write(erc721_token);
        self.starting_price.write(starting_price);
        self.seller.write(seller);
        self.duration.write(duration);
        self.discount_rate.write(discount_rate);
        self.start_at.write(get_block_timestamp());
        self.expires_at.write(get_block_timestamp() + duration * 1000);
        self.total_supply.write(total_supply);
    }
 
    #[abi(embed_v0)]
    impl NFTDutchAuction of super::INFTDutchAuction<ContractState> {
        fn get_price(self: @ContractState) -> u64 {
            let time_elapsed = (get_block_timestamp() - self.start_at.read())
                / 1000; // Ignore milliseconds
            let discount = self.discount_rate.read() * time_elapsed;
            self.starting_price.read() - discount
        }
 
        fn buy(ref self: ContractState, token_id: u256) {
            // Check duration
            assert(get_block_timestamp() < self.expires_at.read(), Errors::AUCTION_ENDED);
            // Check total supply
            assert(self.purchase_count.read() < self.total_supply.read(), Errors::AUCTION_ENDED);
 
            let erc20_dispatcher = IERC20Dispatcher { contract_address: self.erc20_token.read() };
            let erc721_dispatcher = IERC721Dispatcher {
                contract_address: self.erc721_token.read(),
            };
 
            let caller = get_caller_address();
            // Get NFT price
            let price: u256 = self.get_price().into();
            let buyer_balance: u256 = erc20_dispatcher.balance_of(caller).into();
            // Ensure buyer has enough token for payment
            assert(buyer_balance >= price, Errors::INSUFFICIENT_BALANCE);
            // Transfer payment token from buyer to seller
            erc20_dispatcher.transfer_from(caller, self.seller.read(), price.try_into().unwrap());
            // Mint token to buyer's address
            erc721_dispatcher.mint(caller, token_id);
            // Increase purchase count
            self.purchase_count.write(self.purchase_count.read() + 1);
        }
    }
}