feat: replace HelloWorld with GuessTheNumber

- The HelloWorld contract is so simple as to be obtuse. It's confusing
  in its pointlessness. And it doesn't show off anything interesting
  about blockchain programming.

- GuessTheNumber represents a most-basic starting point for a contract
  that can show some interesting blockchain functionality. Already, it
  shows:

  - storing data
  - constructor
  - admin-guarded methods
  - forthcoming contracttrait composability pattern
    (stellar/rs-soroban-sdk#1522)
  - forthcoming admin SEP (https://github.com/AhaLabs/admin-sep)

- This represents the probable starting point for the contract. In its
  current state, it has many purposeful ommissions/shortcomings.

  - `unwrap` in `guess` causes error if admin did not yet call `reset`;
    need to extract number-setting logic to separate function and call
    it in both `reset` and `__constructor`
  - no XLM is currently owned by contract or awarded to winning guess;
    need to require XLM transfer from admin in `reset` as well as
    nominal fee to call `guess` (which gets added to pot)
  - can inspect contract storage to see stored number; need to obfuscate
    with fun crypto tricks

- These shortcomings would be addressed through an onboarding tutorial
  in the Stellar docs and maybe in the UI of the app itself, which so
  far has some very basic info about interacting with the contract

Author: chadoh

Cargo.lock

@@ -0,0 +1,23 @@
+[package]
+name = "guess-the-number"
+description = "Admin sets up the pot, anyone can guess to win it"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+publish = false
+version.workspace = true
+
+[package.metadata.stellar]
+# Set contract metadata for authors, homepage, and version based on the Cargo.toml package values
+cargo_inherit = true 
+
+[lib]
+crate-type = ["cdylib"]
+doctest = false
+
+[dependencies]
+soroban-sdk = { git = "https://github.com/AhaLabs/rs-soroban-sdk", rev = "5a99659f1483c926ff87ea45f8823b8c00dc4cbd" }
+admin-sep = { git = "https://github.com/AhaLabs/admin-sep", rev = "bf195f4d67cc96587974212f998680ccf9a61cd7" }
+
+[dev-dependencies]
+soroban-sdk = { git = "https://github.com/AhaLabs/rs-soroban-sdk", rev = "5a99659f1483c926ff87ea45f8823b8c00dc4cbd", features = ["testutils"] }

contracts/guess-the-number/Cargo.toml

@@ -0,0 +1,35 @@
+#![no_std]
+use admin_sep::{Administratable, Upgradable};
+use soroban_sdk::{contract, contractimpl, symbol_short, Address, Env, Symbol};
+
+#[contract]
+pub struct GuessTheNumber;
+
+#[contractimpl]
+impl Administratable for GuessTheNumber {}
+
+#[contractimpl]
+impl Upgradable for GuessTheNumber {}
+
+const THE_NUMBER: Symbol = symbol_short!("n");
+
+#[contractimpl]
+impl GuessTheNumber {
+    pub fn __constructor(env: &Env, admin: &Address) {
+        Self::set_admin(env, admin);
+    }
+
+    /// Update the number. Only callable by admin.
+    pub fn reset(env: &Env) {
+        Self::require_admin(env);
+        let new_number: u64 = env.prng().gen_range(1..=10);
+        env.storage().instance().set(&THE_NUMBER, &new_number);
+    }
+
+    /// Guess a number between 1 and 10
+    pub fn guess(env: &Env, a_number: u64) -> bool {
+        a_number == env.storage().instance().get::<_, u64>(&THE_NUMBER).unwrap()
+    }
+}
+
+mod test;

contracts/guess-the-number/src/lib.rs

@@ -0,0 +1,61 @@
+#![cfg(test)]
+extern crate std;
+
+use super::*;
+use soroban_sdk::{
+    testutils::{Address as _, MockAuth, MockAuthInvoke},
+    Address, Env, IntoVal,
+};
+
+#[test]
+fn only_admin_can_reset() {
+    let env = &Env::default();
+
+    let admin = Address::generate(env);
+    let user = Address::generate(env);
+
+    let client = generate_client(env, &admin);
+
+    set_caller(&client, "reset", &user);
+    assert!(client.try_reset().is_err());
+
+    set_caller(&client, "reset", &admin);
+    assert!(client.try_reset().is_ok());
+}
+
+#[test]
+fn one_guess_in_ten_returns_true() {
+    let env = &Env::default();
+
+    let admin = Address::generate(env);
+
+    let client = generate_client(env, &admin);
+
+    // set the number
+    set_caller(&client, "reset", &admin);
+    client.reset();
+
+    let trues: std::vec::Vec<_> = (1u64..=10).filter(|number| client.guess(number)).collect();
+    assert_eq!(trues.len(), 1);
+}
+
+fn generate_client<'a>(env: &Env, admin: &Address) -> GuessTheNumberClient<'a> {
+    let contract_id = env.register(GuessTheNumber, (admin,));
+    GuessTheNumberClient::new(env, &contract_id)
+}
+
+fn set_caller(client: &GuessTheNumberClient, method: &str, caller: &Address) {
+    // clear previous auth mocks
+    client.env.set_auths(&[]);
+
+    // mock auth as passed-in address
+    client.env.mock_auths(&[MockAuth {
+        address: caller,
+        invoke: &MockAuthInvoke {
+            contract: &client.address,
+            fn_name: method,
+            args: ().into_val(&client.env),
+            sub_invokes: &[],
+        },
+    }]);
+}

contracts/guess-the-number/src/test.rs

@@ -9,6 +9,11 @@ name = "me" # Required. Keys for this account will be saved to `./.stellar/ident
 default = true # Optional. Whether to use this account as the `--source` for commands that need one.
 
 [development.contracts]
+fungible_token_interface_example = { client = true, constructor_args = "--owner me --initial_supply 1000000000000000000000000" }
+nft_enumerable_example = { client = true, constructor_args = "--owner me" }
+
+# Rather than in one list, TOML allows specifying contracts in their own "sections"
+[development.contracts.guess_the_number]
 # Generate a contract client (NPM package) for this contract. This means:
 #   - compile (build) the contract source to Wasm
 #   - deploy the contract to the `network` specified above
@@ -20,27 +25,17 @@ default = true # Optional. Whether to use this account as the `--source` for com
 # You can only use `client = true` when:
 #   - the contract source must be part of the local Cargo workspace (in the
 #     PROJECT_ROOT/contracts folder)
-#   - The specified name here ("stellar_hello_world_contract") must match the
+#   - The specified name here ("guess_the_number") must match the
 #     underscored-version of the `name` in the contract's Cargo.toml.
 #   - The environment is `development` or `test`
-stellar_hello_world_contract = { client = true }
-
-# Rather than in one list, TOML allows specifying contracts in their own "sections"
-[development.contracts.fungible_token_interface_example]
 client = true
 
 # If your contract has a `__constructor`, specify your arguments to it here.
 # These are the same arguments you could pass after the `--` in a call to
 # `stellar contract deploy`
 # Only available in `development` and `test` environments
 constructor_args = """
---owner me --initial_supply "1000000000000000000000000"
-"""
-
-[development.contracts.nft_enumerable_example]
-client = true
-constructor_args = """
---owner me
+--admin me
 """
 
 # Calls to the contract to make after it's deployed and initialized with
@@ -59,9 +54,9 @@ constructor_args = """
 # `STELLAR_ACCOUNT=other-account`.
 #
 # Only supported in `development` and `test` environments.
-# after_deploy = """
-# mint --amount 2000000 --to me"
-# """
+after_deploy = """
+reset
+"""
 
 # Coming Soon: Specify live contracts to bind & import in this project using the given name.
 # During initialization, these contracts will also be "spooned" into the development network,