// Copyright 2017-2018 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! The Example: A simple example of a runtime module demonstrating
//! concepts, APIs and structures common to most runtime modules.

// Ensure we're `no_std` when compiling for Wasm.
#![cfg_attr(not(feature = "std"), no_std)]

// Assert macros used in tests.
extern crate sr_std;

// Needed for tests (`with_externalities`).
#[cfg(test)]
extern crate sr_io;

// Needed for the set of mock primitives used in our tests.
#[cfg(test)]
extern crate substrate_primitives;

// Needed for various traits. In our case, `OnFinalise`.
extern crate sr_primitives;

// Needed for deriving `Encode` and `Decode` for `RawEvent`.
#[macro_use]
extern crate parity_codec_derive;
extern crate parity_codec as codec;

// Needed for type-safe access to storage DB.
#[macro_use]
extern crate srml_support as support;
// `system` module provides us with all sorts of useful stuff and macros
// depend on it being around.
extern crate srml_system as system;
// `balances` module is needed for our little example. It's not required in
// general (though if you want your module to be able to work with tokens, then you
// might find it useful).
extern crate srml_balances as balances;

use support::{StorageValue, dispatch::Result};
use system::ensure_signed;

/// Our module's configuration trait. All our types and consts go in here. If the
/// module is dependent on specific other modules, then their configuration traits
/// should be added to our implied traits list.
///
/// `system::Trait` should always be included in our implied traits.
pub trait Trait: balances::Trait {
	/// The overarching event type.
	type Event: From<Event<Self>> + Into<<Self as system::Trait>::Event>;
}

// The module declaration. This states the entry points that we handle. The
// macro takes care of the marshalling of arguments and dispatch.
//
// Anyone can have these functions execute by signing and submitting
// an extrinsic. Ensure that calls into each of these execute in a time, memory and
// using storage space proportional to any costs paid for by the caller or otherwise the
// difficulty of forcing the call to happen.
//
// Generally you'll want to split these into three groups:
// - Public calls that are signed by an external account.
// - Root calls that are allowed to be made only by the governance system.
// - Inherent calls that are allowed to be made only by the block authors and validators.
//
// Information about where this dispatch initiated from is provided as the first argument
// "origin". As such functions must always look like:
//
// `fn foo(origin, bar: Bar, baz: Baz) -> Result;`
//
// The `Result` is required as part of the syntax (and expands to the conventional dispatch
// result of `Result<(), &'static str>`).
//
// When you come to `impl` them later in the module, you must specify the full type for `origin`:
//
// `fn foo(origin: T::Origin, bar: Bar, baz: Baz) { ... }`
//
// There are three entries in the `system::Origin` enum that correspond
// to the above bullets: `::Signed(AccountId)`, `::Root` and `::Inherent`. You should always match
// against them as the first thing you do in your function. There are three convenience calls
// in system that do the matching for you and return a convenient result: `ensure_signed`,
// `ensure_root` and `ensure_inherent`.
decl_module! {
	// Simple declaration of the `Module` type. Lets the macro know what its working on.
	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
		/// Deposit one of this module's events by using the default implementation.
		/// It is also possible to provide a custom implementation.
		fn deposit_event() = default;
		/// This is your public interface. Be extremely careful.
		/// This is just a simple example of how to interact with the module from the external
		/// world.
		// This just increases the value of `Dummy` by `increase_by`.
		//
		// Since this is a dispatched function there are two extremely important things to
		// remember:
		//
		// - MUST NOT PANIC: Under no circumstances (save, perhaps, storage getting into an
		// irreparably damaged state) must this function panic.
		// - NO SIDE-EFFECTS ON ERROR: This function must either complete totally (and return
		// `Ok(())` or it must have no side-effects on storage and return `Err('Some reason')`.
		//
		// The first is relatively easy to audit for - just ensure all panickers are removed from
		// logic that executes in production (which you do anyway, right?!). To ensure the second
		// is followed, you should do all tests for validity at the top of your function. This
		// is stuff like checking the sender (`origin`) or that state is such that the operation
		// makes sense.
		//
		// Once you've determined that it's all good, then enact the operation and change storage.
		// If you can't be certain that the operation will succeed without substantial computation
		// then you have a classic blockchain attack scenario. The normal way of managing this is
		// to attach a bond to the operation. As the first major alteration of storage, reserve
		// some value from the sender's account (`Balances` module has a `reserve` function for
		// exactly this scenario). This amount should be enough to cover any costs of the
		// substantial execution in case it turns out that you can't proceed with the operation.
		//
		// If it eventually transpires that the operation is fine and, therefore, that the
		// expense of the checks should be borne by the network, then you can refund the reserved
		// deposit. If, however, the operation turns out to be invalid and the computation is
		// wasted, then you can burn it or repatriate elsewhere.
		//
		// Security bonds ensure that attackers can't game it by ensuring that anyone interacting
		// with the system either progresses it or pays for the trouble of faffing around with
		// no progress.
		//
		// If you don't respect these rules, it is likely that your chain will be attackable.
		fn accumulate_dummy(origin, increase_by: T::Balance) -> Result {
			// This is a public call, so we ensure that the origin is some signed account.
			let _sender = ensure_signed(origin)?;

			// Read the value of dummy from storage.
			// let dummy = Self::dummy();
			// Will also work using the `::get` on the storage item type itself:
			// let dummy = <Dummy<T>>::get();

			// Calculate the new value.
			// let new_dummy = dummy.map_or(increase_by, |dummy| dummy + increase_by);

			// Put the new value into storage.
			// <Dummy<T>>::put(new_dummy);
			// Will also work with a reference:
			// <Dummy<T>>::put(&new_dummy);

			// Here's the new one of read and then modify the value.
			<Dummy<T>>::mutate(|dummy| {
				let new_dummy = dummy.map_or(increase_by, |dummy| dummy + increase_by);
				*dummy = Some(new_dummy);
			});

			// Let's deposit an event to let the outside world know this happened.
			Self::deposit_event(RawEvent::Dummy(increase_by));

			// All good.
			Ok(())
		}

		/// A privileged call; in this case it resets our dummy value to something new.
		// Implementation of a privileged call. This doesn't have an `origin` parameter because
		// it's not (directly) from an extrinsic, but rather the system as a whole has decided
		// to execute it. Different runtimes have different reasons for allow privileged
		// calls to be executed - we don't need to care why. Because it's privileged, we can
		// assume it's a one-off operation and substantial processing/storage/memory can be used
		// without worrying about gameability or attack scenarios.
		fn set_dummy(new_value: T::Balance) -> Result {
			// Put the new value into storage.
			<Dummy<T>>::put(new_value);

			// All good.
			Ok(())
		}

		// The signature could also look like: `fn on_finalise()`
		fn on_finalise(_n: T::BlockNumber) {
			// Anything that needs to be done at the end of the block.
			// We just kill our dummy storage item.
			<Dummy<T>>::kill();
		}
	}
}

/// An event in this module. Events are simple means of reporting specific conditions and
/// circumstances that have happened that users, Dapps and/or chain explorers would find
/// interesting and otherwise difficult to detect.
decl_event!(
	pub enum Event<T> where B = <T as balances::Trait>::Balance {
		// Just a normal `enum`, here's a dummy event to ensure it compiles.
		/// Dummy event, just here so there's a generic type that's used.
		Dummy(B),
	}
);

decl_storage! {
	// A macro for the Storage trait, and its implementation, for this module.
	// This allows for type-safe usage of the Substrate storage database, so you can
	// keep things around between blocks.
	trait Store for Module<T: Trait> as Example {
		// Any storage declarations of the form:
		//   `pub? Name get(getter_name)? [config()|config(myname)] [build(|_| {...})] : <type> (= <new_default_value>)?;`
		// where `<type>` is either:
		//   - `Type` (a basic value item); or
		//   - `map KeyType => ValueType` (a map item).
		//
		// Note that there are two optional modifiers for the storage type declaration.
		// - `Foo: Option<u32>`:
		//   - `Foo::put(1); Foo::get()` returns `Some(1)`;
		//   - `Foo::kill(); Foo::get()` returns `None`.
		// - `Foo: u32`:
		//   - `Foo::put(1); Foo::get()` returns `1`;
		//   - `Foo::kill(); Foo::get()` returns `0` (u32::default()).
		// e.g. Foo: u32;
		// e.g. pub Bar get(bar): map T::AccountId => Vec<(T::Balance, u64)>;
		//
		// For basic value items, you'll get a type which implements
		// `support::StorageValue`. For map items, you'll get a type which
		// implements `support::StorageMap`.
		//
		// If they have a getter (`get(getter_name)`), then your module will come
		// equipped with `fn getter_name() -> Type` for basic value items or
		// `fn getter_name(key: KeyType) -> ValueType` for map items.
		Dummy get(dummy) config(): Option<T::Balance>;

		// this one uses the default, we'll demonstrate the usage of 'mutate' API.
		Foo get(foo) config(): T::Balance;
	}
}

// The main implementation block for the module. Functions here fall into three broad
// categories:
// - Public interface. These are functions that are `pub` and generally fall into inspector
// functions that do not write to storage and operation functions that do.
// - Private functions. These are your usual private utilities unavailable to other modules.
impl<T: Trait> Module<T> {
	// Add public immutables and private mutables.
	#[allow(dead_code)]
	fn accumulate_foo(origin: T::Origin, increase_by: T::Balance) -> Result {
		let _sender = ensure_signed(origin)?;

		let prev = <Foo<T>>::get();
		// Because Foo has 'default', the type of 'foo' in closure is the raw type instead of an Option<> type.
		let result = <Foo<T>>::mutate(|foo| {
			*foo = *foo + increase_by;
			*foo
		});
		assert!(prev + increase_by == result);

		Ok(())
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	use sr_io::with_externalities;
	use substrate_primitives::{H256, Blake2Hasher};
	// The testing primitives are very useful for avoiding having to work with signatures
	// or public keys. `u64` is used as the `AccountId` and no `Signature`s are requried.
	use sr_primitives::{
		BuildStorage, traits::{BlakeTwo256, OnFinalise}, testing::{Digest, DigestItem, Header}
	};

	impl_outer_origin! {
		pub enum Origin for Test {}
	}

	// For testing the module, we construct most of a mock runtime. This means
	// first constructing a configuration type (`Test`) which `impl`s each of the
	// configuration traits of modules we want to use.
	#[derive(Clone, Eq, PartialEq)]
	pub struct Test;
	impl system::Trait for Test {
		type Origin = Origin;
		type Index = u64;
		type BlockNumber = u64;
		type Hash = H256;
		type Hashing = BlakeTwo256;
		type Digest = Digest;
		type AccountId = u64;
		type Header = Header;
		type Event = ();
		type Log = DigestItem;
	}
	impl balances::Trait for Test {
		type Balance = u64;
		type AccountIndex = u64;
		type OnFreeBalanceZero = ();
		type EnsureAccountLiquid = ();
		type Event = ();
	}
	impl Trait for Test {
		type Event = ();
	}
	type Example = Module<Test>;

	// This function basically just builds a genesis storage key/value store according to
	// our desired mockup.
	fn new_test_ext() -> sr_io::TestExternalities<Blake2Hasher> {
		let mut t = system::GenesisConfig::<Test>::default().build_storage().unwrap().0;
		// We use default for brevity, but you can configure as desired if needed.
		t.extend(balances::GenesisConfig::<Test>::default().build_storage().unwrap().0);
		t.extend(GenesisConfig::<Test>{
			dummy: 42,
			foo: 24,
		}.build_storage().unwrap().0);
		t.into()
	}

	#[test]
	fn it_works_for_optional_value() {
		with_externalities(&mut new_test_ext(), || {
			// Check that GenesisBuilder works properly.
			assert_eq!(Example::dummy(), Some(42));

			// Check that accumulate works when we have Some value in Dummy already.
			assert_ok!(Example::accumulate_dummy(Origin::signed(1), 27));
			assert_eq!(Example::dummy(), Some(69));

			// Check that finalising the block removes Dummy from storage.
			<Example as OnFinalise<u64>>::on_finalise(1);
			assert_eq!(Example::dummy(), None);

			// Check that accumulate works when we Dummy has None in it.
			assert_ok!(Example::accumulate_dummy(Origin::signed(1), 42));
			assert_eq!(Example::dummy(), Some(42));
		});
	}

	#[test]
	fn it_works_for_default_value() {
		with_externalities(&mut new_test_ext(), || {
			assert_eq!(Example::foo(), 24);
			assert_ok!(Example::accumulate_foo(Origin::signed(1), 1));
			assert_eq!(Example::foo(), 25);
		});
	}
}